Calcined Clays for Sustainable Concrete

This work extends the investigations on calcined clay-cement blends to soil stabilisation works as obtained for other pozzolans. Samples of calcined clay (CC) were prepared from a natural kaolinite clay source from south-west Nigeria and were blended with Portland cement (PC) in CC:PC ratios of 0:1 (control), 1:3, 1:1, 3:1 and 1:0 to stabilise samples of lateritic soils from two sources. For each blend, combined stabilisers’ percentages of 0, 2.5, 5, 7.5 and 10 of the soils’ dry weight were adopted. The physical properties of the soils placed them in the A-1-a and A-2-6 AASHTO classes with fineness moduli (FM) of 4.33 and 2.18 respectively, indicating that the A-2-6 soil is finer, while the corresponding exchangeable cations (ECs) were 1.678 meq/100 gms and 1.738 meq/100 gms; these indicating that the A-2-6 soil has higher capacity for pozzolanic reactions. The 28-day unconfined compressive strength (UCS) tests on the stabilised soils samples show that the 1:1 and 1:3 blends were better stabilisers; this translating to environmental friendly alternatives to cement. The effects of these blends were more pronounced for the A-2-6 soil being the finer and with higher EC of the two soils. The two blends showed enhanced performance on the A-2-6 soil up to 10% binder content with UCS being 120% and 160% of control for 1:1 and 1:3 blends respectively. For the A-1-a soil, the edge over control was limited to 5% and 7% binder contents for the 1:1 and 1:3 blends respectively. The FM and ECs of the parent soil were raised as factors with potentials of affecting the performance of CC:PC blends as soil stabilisers. The paper calls for further work on lateritic soils from other sources to clearly establish the impact of these factors on their strengths when stabilised with CC:PC blends.

Many of an extensive researches have been carried out by Libyan Industrial Research Center in natural row materials in south region of Libya [1] and the results found that there are many of material can be used as building material, one of these materials which widespread over large area is Kaolin clay. From that point of view civil Eng. Dep. at Sebha university-Libya start thinking of using Kaolin clay as a building material and a team work has been formed to carry out a deep research study work on possibility of using the local natural pozzolana in south of Libya as a partially replacement of Portland cement. Previous laboratory study [2] which carried out by the team work proved that there is a possibility to use south Libya natural Kaolin clay as partial replacement of OPC after calcination and milling to get active calcined clay (Metakaolin). Metakaolin being used very commonly as pozzolanic material or as supplementary cementing materials in mortar and concrete, and has exhibited considerable influence in enhancing the mechanical and durability properties of mortar and concrete as well as utilization of natural calcined clay has widely spread attention in the world to minimize the Portland cement consumption and manufacturing of which being environmentally damaging, in addition to its economic advantage.Metakaolin when mixed with cement the silica of the pozzolana combines with the free lime released during the hydration forms additional cementitious C-S-H gel. This paper investigates the effect of metakaolin (MK) cement replacement on the resistance of mortar to sulfate attack for two different metakaolin quarries. Four MK replacement levels were considered in the study: 0%, 10%, 15%, and 20% by weight of cement for two quarries. After the specified initial moist curing period, mortar specimens were immersed in 5% sodium sulfate solution for a total period of one year. The degree of sulfate attack was evaluated by measuring expansion of mortar prisms, compressive strength reduction and observation of appearance of deterioration that usually accompanying with sulfate attack. All metakaolins examined in this study led to increases in strength and resistance to sulfate attack in comparing with controls samples or according to standard limits.

The utilization of calcined clay as a pozzolanic material for concrete has received a lot of attention in recent years because of its sustainability and worldwide availability. The performance of concrete made using a locally sourced high kaolinite clay was examined to determine suitability for use in local transportation projects. For this work, the local clay was tested to determine optimal calcining temperature, limestone blend, and sulfate content using isothermal calorimetry (R3 method). The clay was calcined at 600 °C, 700 °C, 800 °C, and 850 °C. The effects of material reactivity as measured by calorimetry were compared to the chloride binding capacity.

Four new calcined kaolinitic clays as source of supplementary cementitious materials to production of cement with high level of clinker replacement were assessed in this research. Anhydrous cements were characterized by particle size distribution (PSD), specific surface (BET) and thermogravimetric analysis (TGA). The pastes were assessed by X ray diffraction (XRD), TGA and mercury intrusion porosimetry (MIP). The behavior of blends was too assessed by compressive strength in standard mortars. The specific surface of LC3 cement depends mainly on the specific surface of calcination product of clay, which depend as well on the mineralogical composition of the raw material and the calcination temperature. Results indicated an agreement with the kaolinite content in the original clay, pozzolanic reactivity and the performances of blended cements. The research showed the potentialities of cuban clay deposits from different geologic origin to be used in the production of ternary blended cements with similar performances to the Portland cement.

The growing interest in calcined clays as Supplementary Cementitious Materials (SCMs), from sources other than relatively pure industrial grade clay deposits, demands the development of new tools for the identification and evaluation of the potentialities of a given clay deposit as a source of raw materials for the production of SCMs. In this paper, a methodology for the preliminary assessment of kaolinitic clay deposits as a source of SCMs is presented and discussed. As a case study, the chemical and mineralogical composition of several non industrial grade kaolinitic clay deposits, identified and classified according to the proposed methodology, is related to the pozzolanic reactivity of their calcination products. The developed methodology allows to establish preliminary selection criteria based on the chemical composition of the raw material (% Al₂O₃ > 18,0; Al₂O₃/SiO₂ > 0,3; LOI > 7,0; % CaO < 3,0; % SO₃ < 3,0). Comparison of the potentialities between the different clay deposits is determined from its relative position in a plot that relates the content of Al₂O₃ and the weight loss within the range of temperatures that corresponds to the thermal decomposition of clay minerals, which are, in turn, the main parameters affecting the pozzolanic reactivity of calcination products. The presence of thermally active non clay minerals in the sample may also affects negatively the pozzolanic reactivity. Through the observed results, the developed methodology proves to be a practical and useful tool for the identification and evaluation of kaolinitic clay deposits as a source of pozzolans.

In this study, the influence of the calcined kaolinite content of calcined clay on the hydration of Limestone Calcined Clay Cement (LC3-50) is investigated. It is shown that with the increase of the calcined kaolinite content of the calcined clay, the clinker hydration degree decreases. The amount of reacted metakaolin increases with the calcined kaolinite content, leading to higher formation of C-A-S-H. However, for the LC3-50 with the highest-grade calcined clay, the formation of carboaluminate hydrates is limited. For this blend, the porosity is well refined at 3 days of hydration and does not significantly change later on.

The amount of reacted metakaolin is determined using two methods: mass balance and thermodynamic modeling. It is found that mass balance is the most promising method. Thermodynamic modeling gives slightly underestimated results at late ages.

In the present study, the durability properties of Earth of Datça-hydrated lime mortar (ED)M under steam curing conditions at atmospheric pressure was inspected and compared with relatively well-known “horasan” mortars consisting of hydrated lime and fired clay as artificial pozzolan. Resistance of the lime-pozzolan mortars to wetting and drying, salt crystallization, freeze-thaw cycling and ageing by SO₂ action tests was assessed. Tests results showed that both mortars produced under steam curing at atmospheric pressure can be used as load-bearing building bricks. The better behaviour of the ED(M) under ageing tests compared to Fired Clay-hydrated lime mortar (FC)M is in conformity with its efficient physical and mechanical characteristics.

This research work deals with the use of low-carbon cement SIG B45 (SIG B45 is LC3 cement produced at the Siguaney factory) in the manufacture of masonry mortars according to the dosage established by the NC175:2002 Cuban standard for both types II and III mortars. The experimental part focused on the use of SIG B45 cement, sand from “El Purio” and “Arimao” pit and PP-25 cement as a pattern sample. Tests carried out included flexural-compression strength, water absorption, water permeability, open porosity and bonding. Results attained from tests validate the use of LC3 cement in masonry mortars.

Hydraulic cement based composites in general and concrete in particular reveal different spatial heterogeneity at different scales. At macro engineering scale, e.g., meter or decimeter scale, the material is considered as isotropic and homogeneous, at a lower scale they are two phase material with aggregate particles dispersed in a matrix of the cement paste. One may also consider a third phase called interfacial transition zone (ITZ) at the interface of aggregate and paste. If one looks at cement paste itself at a finer level, it is heterogeneous at micro level, characterized by solid product of hydration reaction, un-hydrated cement, gel and capillary pores. At still finer atomistic level one may encounter further heterogeneity as well, in structure of the material.

Limestone Calcined Clay Cement (LC3) has been developed on a fast-track for induction in the Indian cement industry for the last four years. This paper presents the key challenges and opportunities, as identified by the Indian team, towards the induction of LC3 as a mainstream cement. As the development of the cement continues, the challenges towards its introduction continue to change and new opportunities that can be created by its introduction become apparent. While locating the correct raw materials and identifying the correct processing conditions were the challenges identified initially, as the technology become more clear, optimisation of cement characteristics and identification of performance parameters that would help in placing the product in the market remain important challenges for the industry. Development and acceptance of standards that would allow a suitable application of the technology will be important to ensure that the full potential of this cement is realised.

Limestone Calcined Clay Cement (LC3) was produced on a pilot scale in a cement grinding unit. Raw clay was obtained from mines in Gujarat. Raw material that was otherwise unusable in applications like paint and paper was found to be suitable for the production. While most of the calcination of clay is being carried out using furnace oil and bio-mass, even petcoke was found to be suitable for application to LC2 to achieve cost reduction. Quality control was carried out using XRD, TGA and visual observation and the clay was carefully sorted into batches based on the test results. LC3 and LC2 were produced by inter-grinding the raw materials and a normal ball mill was found to be adequate for the production process. The test results showed that while Blaine’s fineness test may be a good initial measure to control the grinding process, due to differential grindability, laser diffractometry can provide a better assessment of grinding of all components of the cement. It was found that both LC3 and LC2 can be produced using widely available technologies with very little modifications. Physical tests on LC3 and LC2 were carried out and both were found suitable for general applications and some special applications.

The feasibility of the production of LC3 and LC2 in the North-Eastern states of Assam and Meghalaya were studied. Although there are many cement plants in the region, fly ash is not available. The easy availability of kaolinitic clays in the vicinity of the cement plants makes a strong case for the production of LC3 and LC2 in the region. Several clays in the area were assessed and suitable clays with more than 50% kaolin and up to 80% kaolin were found to be abundantly available. Trial production using locally available materials was carried out and the physical and chemical characterisation of LC2 and LC3 were carried out. The results from these studies are presented in this paper.

The use of High Performance Concrete (HPC) in specific applications, such as tall buildings or prestressed concrete, causes a creep of the concrete. The durability of the building could be reduced because of a too important deformation of the concrete.Most HPC are cast with silica fume, therefore data on creep properties exist. According to literature, the use of silica fume allows a decrease in the creep amplitude.Metakaolin is another cementitious addition which can be used in the case of HPC. However, to the authors’ knowledge the work on creep of concrete based on metakaolin is nearly nonexistent.The aim of this work was to improve the knowledge on creep of concrete based on metakaolin, especially when compared with concrete based on silica fume.This work allowed measuring the delayed deformation of concrete containing and comparing it with control concrete based on silica fume properties. In order to study the evolution of the materials induced by the creep, compressive strength and Young modulus tests were conducted. Finally, in order to improve the understanding of the creep deformation phenomena, a comparative study of drying kinetic.

Carbonates are primary minerals of the carbonatites and kamafugites sourced from Toro-Ankole geological region of the East African Rift system. Consequently, these materials are silica undersaturated. They are currently utilized as mineral additions in production of Portland pozzolana cements in Uganda. No published work exists to show how their unique composition might affect their pozzolanic performance and other concrete properties. This study investigated the effect of the carbonate minerals in the natural pozzolans and calcination on setting time, standard consistency, workability, soundness, early heat of hydration and strength development of blended cements. Two (2) samples, a carbonatite and a kamafugite sourced from deposits located in the Toro-Ankole geological region of the East African rift system were calcined in a furnace at 825 °C for one hour. The samples were then subjected to XRD analysis for mineralogical composition characterisation and to establish the effect of calcination at 825 °C on mineralogy. Setting time, standard consistency, workability, soundness and strength development were studied following standard procedures for testing blended Portland cements. Calcination led to a gain in compressive strength for both test pozzolans, the kamafugites showing a higher gain in strength than the carbonatite. The higher gain in pozzolanic performance for the kamafugites is likely due to kaolinite, a secondary mineral in the test pozzolan whose pozzolanic reactivity is activated by thermal destabilization. Calcination also led to pacification of the early age properties of cements blended with test carbonatites and kamafugites. The study reveals the carbonate minerals in the test pozzolans as a considered factor in accelerating early hydration of Portland cement. Hydration progression of Portland cement controls the important properties of fresh concrete (workability, setting and paste microstructure), which in turn directly impacts on the strength and durability properties of hardened concrete. Cements blended with carbonate bearing natural pozzolans therefore present interesting perspectives on how paste microstructure composition and durability performance properties might be impacted.

Given the availability of clay deposits in several geographical areas of the Cuban territory and the use of calcined clays as a source of Supplementary Cementitious Materials (SCM), it is necessary to evaluate the pozzolanic reactivity of its calcination products and because of the complexity in the chemical - mineralogical characteristics of the pozzolans. This work introduces a new rapid method to predict the potential character pozzolanic of these materials by alkaline solubility and presents the possible correlation with isothermal calorimetry in lime-pozzolan pastes following the R3 protocol. The raw materials were characterized by XRF, XRD and TGA.The clayey materials contain more than 70% of SiO2 + Al2O3 + Fe2O3, which guarantees its pozzolanic character after its thermal activation. The process of the dihydroxylation of the clay minerals happens between 350 °C and 650 °C, and for the deposit of Yaguajay the decomposition of the calcite is between 650 °C and 750 °C. Alkaline solubility test is a viable test to assess the pozzolanic reactivity of calcined kaolinitic clay due a good and directly correlation between the content of soluble aluminum and the total heat released (R = 0.995) and there is not a significant dispersion of the obtained data for each clay deposit (CV% between 0.01 and 2.80). The pozzolanic reactivity of its calcination products determined by isothermal calorimetric follows the sequence CG > LS > LL > YG and matches with Alkaline Solubility test.

This paper aims at assessing the implications of using Limestone Calcined Clay Cement (LC3) in the Cuban construction sector from a sustainability viewpoint. By means of combining Life Cycle Assessment (LCA), economic cost analysis and eco-efficiency approach, two construction techniques have been compared, taking as a functional unit one square meter of usable area. In spite of the inverse correlation between economic efficiency and ecological impact for all confronted techniques, complementary indicators showed some trade-offs at social level. The economic-ecological efficiency of LC3 potential use is linked to two different sources: the construction method and the cement type itself. Relevant decision-making considerations could support economic policy in the domain of construction industry in Cuba, if taking into consideration the eco-efficiency portfolio provided by this study. Authors conclude that no one construction method is superior per se from a sustainability viewpoint, but it rather requires major rethinking beyond economy and environment to embrace social indicators.

Calcined clay and limestone composite cementitious material system is a newly proposed low-carbon cement, which can effectively reduce energy consumption and carbon emissions of the traditional cement industry without changing the basic mechanical properties of cement-based materials. In this study, the degradation process of mortar samples of limestone and calcined clay cementitious material under sulfate attack was systematically studied by both macroscopic and microscopic analysis. The results show that compared with pure Portland cement, the addition of calcined clay and limestone can significantly reduce the expansion rate, loss of dynamic modulus and mass loss of mortar specimens under sulfate attack. The addition of calcined clay and limestone will refine the pore size distribution of mortar specimens, then inhibiting the diffusion of sulfate and formation of corrosive products, therefore leading to a significant improvement of the sulfate resistance.

Studies of illitic calcined clays are less developed than that corresponding to kaolinitic clays, but illite is one of the more abundant clayed minerals of the earth’s crust, as occurs in the Center of the Buenos Aires Province (Argentina) where the largest cement factories are located. Illite clays develop pozzolanic properties when they are thermally treated at 950 °C, causing dehydroxilation and collapse of structure to form a metastable or amorphous aluminosilicate. Illitic calcined clays don’t present a significant water demand and the compressive strength of blended cements attains to the corresponding to portland cement at 90 days. It is characterized as slow pozzolana. Illite incorporates certain proportion of reactive alumina and high proportion of alkalis, modifying the pore structure. From durability point of view, the incorporation of illite can affect the sulfate resistance of portland cements or the alkali-silica reaction (ASR). The aim of this paper is to study the behavior of two different illite calcined clay blended cements against chemical attack, like sulfate attack and harmful alkali silica reaction, using the test based on the ASTM C 1012 and ASTM C 441, respectively. For sulfate performance, illite calcined clays was blended with a low C₃A in 20% and 40% of weight replacement and a very high C₃A cement (white), using a 30% of weight replacement; while a low (Na₂O_eq < 0.5) and high alkali (Na₂O_eq = 1.03) cements were used in the ASR-test.After six months, the low and very high C₃A cements of both illitic clays shows low expansion in sulfate media (<0.05%) for blended cement without water demand. The ASR-expansion results show that illitic calcined clays reduce considerably the expansion of high alkali cements and it is not harmful to low alkali cement, but long test time results will be conclusive.

This work studies the real possibility of recycling ceramic waste from the manufacture of structural elements, in order to use it as pozzolanic addition on cement. The properties of the material where analyzed, the production process and the final product performance were studied to achieve an optimal use of this addition as a pozzolan and also as a fine aggregate in masonry production and waterproofing mortars for the roof cover finishing.Its technical and economical effectiveness is valued, and its social and ecological impact is also remarked.

In this paper, the difference in the microstructure development of limestone calcined clay cement (LC3) in comparison with the ordinary Portland cement (OPC) and Portland pozzolan cement (represented as FA30) at different water-binder ratios is shown. The results from the studies suggest that a mere adoption of a lower water binder ratio to reduce the capillary pore space for filling by hydrates, ensures only a marginal improvement in the kinetics of microstructural development, as seen from conductivity evolution in OPC and FA30. Highly reactive pozzolans ensure a more rapid drop in conductivity due to low-density hydrates resulting in lower capillary porosity and densification of the hydrate matrix. BSE micrographs also show a more densified binder matrix with LC3, mainly due to high pozzolanicity of calcined clay resulting in CSH with lower C/S ratio with a hybrid hydrated phase assemblage compared to OPC and FA30. The impact of improved kinetics of LC3 binder reflects in better durability parameters at an early age in the different concretes made with LC3 binder. It is seen that the fly ash based systems (FA30) show a marked increase in the concrete resistivity up to an age of 1-year curing. The resultant effect of such microstructural development on the chloride resistance of concretes is also discussed.

This investigation evaluates the behavior of processes of carbonation in the concrete made with cement low carbon LC3, under different environmental conditions. To determine the carbonated depth, the phenolphthalein technique is used. Generally the elements made from ternary cements are more sensitive to carbonation than those produced with Portland cements (PC), due to the effect of substitution of clinker with consequent reduction of the alkalinity, so it corresponds to test results conducted with elements manufactured at the Center for Research and Development of Construction (CIDC) in Havana (area of low aggressiveness) (Fig. 2) of 30 MPa characteristic strength, kept in a zone of relative humidity (HR) between 60 and 70%. On the other hand, when evaluating concrete characteristic design strength of 25 MPa produced in the company of Industrial Production (EPI) Villa Clara, located in Cayo Santa Maria (marine area of high environmental aggressiveness) (Fig. 1), items made with LC3 demonstrate a carbonated depth lower compared to concrete produced with PC, an atypical situation, which may be due to the high levels of porosity in conjunction with the effects of leaching more aggressively in concrete with a higher content of compounds soluble as CO₂.Fig. 1.Exposure site with high aggressivenessFig. 2.Exposure site with low aggressiveness

This paper shows the effect of metakaolin with different amorphous phase content on 2 and 7 day compressive strengths and microstructure of MK-blended cement pastes. The cement pastes that contained 0%, 10% and 50% MK were prepared at a constant water/binder ratio of 0.35 and cured at 22 °C for 2 days and 7 days. It was found that cement paste with high-quality MK (high amorphous phase content) resulted in a higher early age compressive strength than pastes with lower amorphous phase contents and this was attributed to high initial reactivity. The lowest amorphous phase content MK/cement blends achieved early age compressive strengths comparable to higher amorphous phase content MK/cement blends. The MK-blended pastes, prepared without a plasticizer, had higher degrees of agglomeration and lower strengths.

Hydration of cement is a long term chemical process which requires water. Construction industry often prefers cement with high early strength and short curing period. Limestone calcined clay cement (LC3), which can replace clinker up to 50%, has potential benefits in this regard due to its low clinker factor and rapid reaction kinetics. In this study, ordinary portland cement, fly ash based portland pozzolanic cement, limestone calcined clay cement and composite cement (OPC with slag and fly ash) were prepared in laboratory. Mortar cubes and paste specimens were cast at constant water to binder ratio. The samples then exposed to different curing regimes by changing it from water curing to air curing (R.H ≈ 10–20%) at selected intervals. The curing temperature was kept constant as 27 °C. Compressive strength of mortar cubes were taken at standard ages. Effect of curing conditions on phase assemblage were quantified using, quantitative x-ray diffraction.

Portand pozzolanic cement using fly ash (FA30), which replaces 30% of clinker, is the most produced cement in India. But, rules due to the fast depletion of natural resources and stricter on emissions, the industry is keen to reduce the clinker factor further. New ternary blended cement, limestone calcined clay cement (LC3) can be a good option due to its high clinker replacement and use of low grade raw materials. The cement is aimed for general purpose. India, having wide range of climatic conditions, producing general purpose cement for the entire country is always a hard task for cement companies. For a new cement, it is worthy to check the performance under different climatic conditions. In this regard, concrete columns were cast in both FA30 and LC3, and placed at 8 locations. NDT test was performed on columns to understand the performance concrete.

In this paper, two durability issues: Alkali Silica Reaction (ASR) and external sulfate attack were studied. The results of expansion were presented for a Normal Portland cement and a blended cement LC3 containing calcined clay and limestone as supplementary cementitious materials (SCMs). The systems containing SCMs did not expand after several years of exposure showing a high resistance to ASR and sulfate attack.

This project explores the influence of different particle size distributions of limestone on the workability and early-age strength development of LC3 materials. To quantify, and subsequently optimize, the packing, the modified Andreasen and Andersen model was used. Different systems were selected and studied using minicone tests and compressive strength (at 2, 7 and 28 days) to see which parameters govern workability and strength.

The present work focuses on key parameters which determine the best strength performance of two calcined clay mineral additions (1:1 and 2:1 type) and mixtures with limestone. Additionally, alternative options rather than increased admixture dosage have been investigated to mitigate the rheological problems typically found when calcined clays are incorporated to cement. Isothermal heat development measurements have shown that SO₃ content of blended cements can be effectively optimized based on early available alumina from clinker, but also from calcined clay. Flow measurements before mortar casting demonstrated that an adequate mixing procedure with a delayed addition of chemical admixtures can maximize their efficiency for particle dispersion. In order to reveal the influence of each main cement constituent on both workability and strength, multiple blended cements with different replacement levels, ratios of calcined clay to limestone, fineness of calcined clay and w/c ratios were tested. Results showed that the best strength development is achieved by calcined 1:1 clay for a lower ratio of calcined clay to limestone rather than calcined 2:1 clay for any given replacement level. On the other hand, workability is more strongly affected by the calcined 1:1 clay reducing the efficiency of superplasticizer (SP) required for achieving acceptable flow even at higher w/c ratio.The addition of fly ash on top of blended cements with 35% replacement of limestone and either calcined 1:1 or 2:1 clay certainly improves flow at high clinker replacements. However, strength performance of these new binders is only similar to corresponding calcined 2:1 blended cements with same replacement level, whist is significantly lowered in those containing calcined 1:1 clay. Therefore, w/c ratio may be potentially reduced to get even better strength performance with combinations of calcined 2:1 clay, limestone and fly ash.

The UK nuclear industry has a significant and challenging stockpile of nuclear wastes, and geopolymers produced from activation of the calcined clay metakaolin offer a valuable alternative to Portland cement-based systems. The characteristics of different formulations of metakaolin-based geopolymers, reacted with sodium and potassium silicate, are therefore of interest. As preliminary steps, the compressive strength and rheology of some metakaolin geopolymer grouts have been studied. This work showed that a potassium silicate-based geopolymer binder, with a sufficiently high water content can be produced to be highly workable. These grouts have a shear stress of approximately 80 Pa at a shear rate of 110 s−1 and can achieve compressive strengths of up to 40 MPa after 7 days of curing. This study is to be expanded in future and compared to the results produced from further analysis performed on the chemical structure of the geopolymer, as well as the overall physical characteristics achieved, to support the immobilisation, incorporation and retention of metal and oil based nuclear wastes.

Experimental results of pore size distribution and compressive strength on hardened cement-based pastes containing fine ground particles from the recycling of construction and demolition waste (CDW) are reported. Supplementary cementitious material (SCM) coming from the crushing of laboratory concrete beams and clay bricks were used at a replacement level of 10% by weight of Portland cement. A reference paste without any addition was designed with water-cement ratio of 0.4 and the pastes containing SCM kept the water-cementitious material ratio of 0.4 as well. Compressive strength tests were performed on water-cured samples for various ages from 24 h to 90 days and mercury intrusion porosimetry was performed at 28 days. The general results suggest pozzolanic activity by the clay material while the concrete waste appears to behave similar to an inert quartz inclusion.

Limestone calcined clay cement or LC3 is a ternary blend of clinker, calcined clay and limestone, usually with the clinker factor as low as between 0.4 to 0.5. Calcined clay acts as a source of reactive pozzolanic component of the ternary cement blend. The extent of reactivity of calcined clay depends on the kaolinite content of raw china clay. The present study explores the effect of kaolinite content of clay on the properties of the cement blend. The clays with different kaolinite content were collected from Bhuj area of Gujarat. The ranges of kaolinite content were broadly classified as 20–29%, 30–39%, 40–49%, 50–59%, 60–69% and 70–85%. LC3 blends were prepared using respective clays with addition of similar quality of clinker, limestone and gypsum. Identical conditions and process parameters for the production of the blend were maintained. Isothermal reactivity of calcined clays and LC3 blends were measured. Finally, the compressive strength of the LC3 mortar was tested. It was evident that the reactivity of calcined clay, LC3 blend and compressive strength varied almost linearly. However no definitive correlation of these properties could be established with kaolinite content of the respective clay. It was concluded that the quality and the performance of calcined clay in LC3 not only depends on kaolinite content of the clay but also on other properties like chemical composition, presence of various mineralogical phases and geology of the china clays.

The impact of alkali content on the properties of Limestone Calcined Clay Cement (LC3) was investigated in this study. KOH was added in order to increase the alkali content of the blended cements from 0.44% Na₂O_eq to 1.21% Na₂O_eq. The increase of alkali accelerates the degree of clinker hydration at 1 day but it slows down for later ages. Moreover, increasing alkalinity enhances the formation of carboaluminate phases at the early ages but the highest alkali content shows the smallest amount these phases at the later ages. The porosity decreases with increasing the percentage of alkali at 3 days but it is opposite at 28 days. The compressive strength can be boosted at early ages but there is loss gain strength at the later age for LC3-65 (2:1)-1.21% Na₂O_eq.

Metakaolin used as a SCM in concrete is obviously a very good tool to improve the resistance against acid and alkali attack too. Even if, finally, the mechanisms are not fully understood until now, lower mass loss (acid attack) or lower expansions (ASR) are showing their efficiency. Metakaolin, burnt by using relatively pure natural kaolin clays, contains Al₂O₃ and SiO₂ only with a ratio of approx. one. The question is: Are there any other clays maybe also in mixtures which are suitable for use as an admixture for concrete or even as a binder? This research work has a strong regional reference. Three clays from Lower Lusatia were selected. The clays and a wide range of mixtures too were burnt at different temperatures (between 600 to 700 °C) to find out the “best” results for such materials. The mixing process has also the background to eliminate fluctuations in the compositions of the clays. A continuous working rotary kiln with a continuous supply of clay materials was used for the production of calcined clay samples. Using this equipment, the rate of heating and the duration of stay of the material under almost practical conditions can be varied. Mineralogical compositions, measured before and after heating, confirm the formation of amorphous phases already under relatively low temperature conditions in dependence on the clay mineral species and the mixing relations. Reactivity (activity index and solubility in alkaline solutions) of each sample were determined and mortar bars were produced. In dependence on their reactivity parameters the so produced calcined clay samples influence mechanical and durability properties of concrete structures. The aim of this research project is to produce concrete bars with such calcined clay as a SCM and store them under extreme conditions in some of the Lusatian lakes.

Kaolin from a Serbian deposit, having a high content of mica and quartz, disordered kaolinite and a high specific surface area, was used to prepare metakaolin (MK). The calcination at temperatures of 700 °C or 750 °C for 30 to 180 min resulted in MK having high pozzolanic activity, but also significant aglomeration of particles. In order to disperse aglomerates, MK was milled, which resulted in increased pozzolanic activity and reduced particle size. The effects of MK and additionally milled metakaolin (MKmill) on the composite strengths and microstructure of the pastes were compared. We prepared and investigated composites in which ordinary Portland cement (OPC) was replaced with 10% to 50% of MK or MKmill, as well as the representative samples of paste for determination of microstructure.Compressive strengths higher than the control were obtained for composites having up to 30% of MK and up to 40% of MKmill, respectively. Increase of composite strengths with MKmill was more pronounced at lower cement replacement levels (10% and 20%).Compressive strength of composites containing agglomerated MK were satisfactory, which suggests that milling of MK, as well as purification of kaolin, may not be necessary.

Environmental concerns and sustainable development require increased replacement of cement. Most of previous studies have shown that the compressive strength of cement-based composites is maximized with a 20% content of metakaolin. We investigated composites prepared by replacing ordinary Portland Cement (OPC) with 30 to 50% of metakaolin (MK) and addition of appropriate amount of hydrated lime, which were ordinary cured for 2, 28 or 90 days. Hydration products and microstructure of the pastes were determined by X-ray diffraction (XRD), differential thermal analysis/thermal gravimetry (DTA/TG) and mercury intrusion porosimetry (MIP). MK was produced by calcination of kaolin from a Serbian deposit, which contained a high level of impurities.Replacement of OPC with 30% of MK achieved 28 days compressive strength equivalent to that of the control mix. Higher replacement levels, 40% and 50%, combined with the addition of hydrated lime, achieved satisfactory relative strengths of 94% and 87%, respectively. The positive contribution was particularly pronounced after 90 days for a composite containing 50% of MK. The results clearly showed a possibility of obtaining composites having acceptable compressive strength with reduced cement content in accordance with environmental and sustained development requirements.

Cements with calcined clays were tested for their performance in mortar, and compressive strength data was collected to quantify the reaction. References were run in all experiments to quantify relative performance differences.Calcined fineness becomes relevant for strength development at high Blaine values of calcined clay.20% calcined clay substitution shows the best resultsHigh substitution rates (35%) make the early strengths worse – compared to OPCDue to an increase of the clinker fineness the performance can be improvedWater demand of the blends is not critical for the strength developmentBM and VRM both show good results – considered in absolute terms, the VRM shows the highest strengths

This study evaluates the potential correlation between natural aging and hydrothermal curing (accelerated aging), related to the crystallisation of zeolites in potassium-based metakaolin geopolymer binders. 7-year old sealed-cured specimens, formulated with varying silicate contents, were evaluated. The effect of different accelerated aging durations on the mineralogy of these potassium-based geopolymers was also assessed. The results show that although zeolite formation is favoured under both natural and accelerated aging in potassium-based geopolymers, different types of zeolites are formed depending on the silicate content added to the mix, and the curing conditions of the specimens.

This study aims to investigate the carbonation resistance of limestone calcined clay (LC3) concrete. Ordinary Portland Cement (OPC) substitution rates considered were 15%, 30% and 45%. Low grade calcined clay was used with about 50% amorphous phase. Phenolphthalein indicator test was carried out in order to assess the carbonation depth of concrete exposed to natural and accelerated carbonation. Overall, results show that the carbonation front penetration is consistently increasing with the increase in OPC substitution rate Generally, LC3 concrete under performs compared to reference OPC concrete having similar 28 days compressive strength. At 30% OPC substitution rate, performance of LC3 concrete is close to that of OPC counterpart concrete, both having an average 28 days compressive strength of 36 MPa. Only a marginal increase in concrete cover would be enough to maintain the same service life. This is an important outcome showing that LC3 concrete with OPC substitution up to 30% is suitable for a large range of applications including outdoor exposure (assuming no other aggressive ions are involved). However, LC3 concrete with OPC substitution beyond 30% is not suitable in exposure condition where carbonation induced steel reinforcement corrosion can be an issue.

The production of cement with more than one main component plays a key role in prospective development in the cement industry.

Nearly 17 million tonnes of dimensional stones, such as marble, are produced in India annually. Around 7 million tonnes of stone dust waste is generated annually from the excavation and processing of these stones with an estimated wastage of 30–60% depending on the technology used. Stone dust waste generated, usually in the form of a slurry is dumped on open land, resulting in the wastage of productive land. The drying up of slurry leads to generation of fine air borne particles that can result in severe environmental pollution and health problems. The study shows that stone dust waste primarily consists of carbonate stones such as calcite, dolomite and magnetite. This study aims to understand the potential of utilizing stone dust waste in limestone calcined clay cement by replacing limestone with marble dust waste. Formation of carboaluminates was observed in the using marble dust as a replacement in LC3. It was found that stone dust waste can be used as a limestone substitute for the production of limestone calcined clay cement.

The reduction of the clinker content in concrete by replacing cement with supplementary cementitious materials (SCM) is widely used to lower the environmental impact of concrete. However, for some SCMs such as calcined clay this often leads to higher water requirements for the same concrete consistence. This severely limits the widespread implementation of green concrete technologies, both in practical terms, and in meeting the requirements of relevant concrete standards such as the national annexes to EN 206. In order to overcome this, a shift in mind-set from prescriptive to performance-based design criteria would be beneficial. Thus, we have proposed a performance-based design approach for the selection of binder systems, which we have successfully applied it to several combinations of SCMs. In this paper the procedure is described for a binder system consisting of calcined clay, limestone filler and fly ash. A parametric study was carried out on mortars, which included rheological properties, compressive strength and chloride migration. The requirements for each parameter was chosen based on the intended concrete application (highway bridge) and values obtained for a reference mix typically used for the application, i.e. a concrete that fulfils current Danish regulations. The proposed alternative binder system features a CO₂ footprint reduction of 30% compared to the reference concrete mix. However, the alternative concrete mix does not conform with current Danish regulation on the minimum w/c ratio.

Various clayey materials containing different clay minerals were calcined using muffle furnace and pilot scale flash calciner. While pure clay minerals can be easily calcined using soak calcination, mixed systems, especially Ca/Mg-rich materials, benefit from flash calcination. High process temperatures enable a complete calcination while the short retention time suppresses the formation of inert high-temperature phases.

Illite-chlorite clay from quarry located at Buenos Aires Province (Argentine) was characterized by XRD, FTIR and TG-DTA. Mineralogical transformations during clay firing under oxidizing conditions were studied from 100 to 1100 °C by XRD and FTIR. From select temperatures, calcined clay was ground (85% passing to 45 µm sieve) and the pozzolanic activity of blended cements (25% w/w) was evaluated by the Frattini test and the strength activity index (SAI). Finally, the hydration phase assemblage of blended cements was studied using XRD analysis. The solid-state phase transformations of clay during thermal treatment involves: water loss at low temperature; the partial dehydroxylation of chlorite resulting in the “modified chlorite structure” between 500 and 600 °C and its collapse at 800 °C; the dehydroxilation of illite is completed and its structure collapsed up to at 900 °C. Up to 1000 °C, the clay minerals are collapsed thoroughly, with formation of amorphous compounds.Results of Frattini tests indicate that materials present pozzolanic activity after 7 days when they are fired up to 900 °C, however the best SAI (~1.00) at 28 days occurs for clay calcined at 1100 °C. For blended cements, the hydration products assemblage is similar to plain Portland cement used at all ages.

To investigate the reaction process of alkali-activated carbonatite, the dissolution behaviour of carbonatite in water glass solution was monitored by in-situ Polarizing Microscope (PM) and Digital Holographic Microscopy (DHM). Six types of carbonatites were mixed with water glass solution (M = 1.6), then observed constantly by PM and DHM. The polarizing microscope results showed that the size of all types of carbonate minerals was gradually reduced and the particles disappeared as the time prolonged, indicating that carbonatites reacted with water glass. The reaction rate of carbonatites with water glass was qualitatively characterized via the comparison of the dissolution time of carbonatite particles with the same size. The reaction rates between carbonatites and water glass solution followed the following order: calcium carbonate (chemical reagent) > carbonatite with 1.35% MgO > calcite > carbonatite with 11.37% MgO > carbonatite with 14.39% MgO > dolomite. DHM provides the quantitative results about the dissolution rate of carbonatite. However, the algorithm of three-dimensional reconstruction is still being improved, and the final results will be included in the full paper.

Given the growth of the construction industry in recent years, Portland cement production has been increasing, but the cement industry is adversely affected by sustainability, accounting for about 5% of the world’s CO₂ emissions. With the view to reduce these emissions, mitigating measures have been analyzed, and one of the most promising ones is the reduction of clinker/cement ratio, using as substitution mineral additions. This research aims to analyze the mechanical performance of mortars from the use of cement with addition of two types of metakaolin, one of these being more reactive, with the addition of limestone. From the characterization of these materials and the different substitution contents used from binary and ternary mixtures, it was verified that some of them have a good performance.

The goal of this study was to understand the behavior of clays from Iza, Boyaca, Colombia and their potential to be used in blended cement after calcination as pozzolan. The materials were characterized before and after thermal treatment by XRF, XRD, TGA and SEM. The performance in mortar was evaluated by compressive strength of mortar. The XRD analysis showed that the main minerals present in the raw materials were Kaolinite, Alunite, Quartz, Opal and Feldspars, each one with different behavior after activation. The performance of mortar was investigated by measuring the compressive strength according to ASTM C109. The produced blended cements were done with 30% of SCM and 70% of Ordinary Portland Cement (OPC). The optimization of the calcination temperature has been carried out using Thermal Gravimetric Analysis (TGA) as well as with X Ray Diffraction (XRD). After the calcination and depending on the temperature, both the Kaolinite as well as Alunite show structural changes with different effects on the performance. While kaolinite dehydroxylation significantly improves the performance, alunite decomposition into the new reactive phases KAl(SO₄)₂ and amorphous Al₂O₃ have strong effect on the early age of hydration, decreasing the workability, increasing the initial temperature of the mortar. This can nevertheless be controlled by optimizing the gypsum content.

The sustainability of the production of the Portland cement, among another factors, is directly related to the decrease of specific consumption of fuel and the decrease of the emissions of gases and contaminating particles. To decrease the clinker’s factor, an important alternative is to improve the environmental efficiency. It is demonstrated in this work that with the addition of thermally activated clays, a substantial decrease of the consumption of energy and CO₂ emissions occurs. In this sense, the Life Cycle Analysis (LCA) tool is used, and the methodology of baseline approved ACM0005: “Baseline consolidated methodology for increasing addition in cement production” (taken from IPCC, 2006) is used. The work is carried out in the Siguaney factory (Republic of Cuba), and proves to be innovative for the ternary system (clinker – activated clay – limestone), establishing the rate of emissions in 1191.15 kg CO₂/t.ck. Corresponding results are obtained for other important pollutants. It is demonstrated that in direct relationship with the decrease of the clinker consumption for ton of cement, the energy consumption decreases by 18%, which leads to obtaining ternary blended cement.

Low carbon cement is a ternary blended Portland cement with clinker factor as low as 0.50. It uses the synergetic hydration of clinker, calcined clay produced from mine waste and non-cement grade limestone to achieve properties comparable to commercial cements. In this limestone calcined clay cement (LC3) one of the most important raw material is the china clay. The present paper discusses the availability and occurrence spread of china clay in India. It has been shown through a GIS map that china clay is available almost throughout the entire country. The resource map is based on a GIS platform to have real time data on the raw material availability. To enable an informed decision making by cement companies, the occurrences and availability of fly ash used as pozzolana has also been shown in addition to location of integrated cement plants and grinding units. The map shows that there are quite some regions in India where the production of LC3 is feasible. This is contradictory to the view that almost the whole of India is feasible for fly ash pozzolana cement.

Corrosion of metal reinforcement is the most important durability concern of concrete infrastructures. In this research, chloride transport in mortars prepared using ternary blends of OPC-calcined clay-limestone (LC3) as the cementitious materials is assessed and compared to a reference OPC system. Three clays with varying kaolinite content (17%, 50% and 80%) were employed. Through XRD analysis, transformation of carboaluminate phases - the stable form of AFm in LC3 binders - to Friedels salt, as a consequence of exposure to NaCl solution was observed. In addition, porosity of LC3 binders, with kaolinite content of 50% and higher was found to be significantly refined, which helps reduction of the depth of chloride penetration. The findings support excellent behavior of LC3 cement, prepared using low-grade clays, in corrosive environments.

In this paper, the paste workability and hydration progress of blended cements containing different calcined illitic clays were studied. For blended cements with different replacement percentages, the particle packing, the water film thickness (WFT) and the flow spread was modelled and measured. Results indicate that blended cement with ground illitic calcined clays maintain or reduce the packing, so the flow spread of blended cement pastes decrease when the replacement percentage increases. For blended cements with 25% of calcined illitic clay, the early hydration was described by the calorimetric curve, and later the hydration products were analysed by XRD and TG analysis and the pore size distribution (MIP) at 2, 7, 28 and 91 days. Finally, the performance of blended cements was evaluated by the compressive strength. For blended cements, the hydration products are similar to that corresponding to ordinary Portland Cement (OPC) and it also produce a pore size refinement that improve the compressive strength at later age.

Through a collaborative work established between CIDEM and the Laboratory of Construction Materials at EPFL, a new cementitious system based on a synergetic combination of calcined clay and limestone as Portland’s clinker replacement was developed. The novelty of the system was that despite the low clinker content (50%) the resulting cement reached similar performance to pure Portland cement. The Cuban cement industry has collaborated with the introduction and take up of LC3 since early 2011, and it has gathered experiences, which could be useful for other cement makers around the globe. This paper discusses the roadmap followed by the technical team to introduce LC3as a mainstream product. The main areas of engagement were: (i) identification of reserves of suitable clay for the production of LC3, (ii) Realization of industrial trials for the manufacture of LC3, (iii) assessment of economic and environmental feasibility of the production, and (iv) formulation of new standards which cover the formulation of the new cement as well as its application in concrete. Results of the work of the multi-disciplinary team dealing with the introduction of LC3 shall be presented, including the formulation of the material with local raw materials, considerations about the process, and performance and durability of concrete.

The conventional use of binary cement is changing towards a composite cementitious system which allows two or more supplementary materials in combination. In this way, present study focuses on the preparation of limestone-calcined clay blend and introduction into cement system at variable replacement level to study their influence on the properties of resulting concrete. The hydration behaviour of the ternary blended cement was carried out using heat of hydration and XRD analysis. Similarly, compressive strength was performed on mortar cubes at different hydration ages (1, 3, 7 and 28 days). From this study, it was observed that, the limestone in the presence of calcined clay results in the formation of additional hydrates. Furthermore, it is found that this ternary combination can significantly improve the substitution level of clinker with good mechanical characteristics.

The study investigated the effects of selected potential chemical activators on thermal resistivity of calcined clay based cement mortars. 0.5 M Na₂SO₄ and 0.5 M NaOH were used as activator solutions. The chemical composition of sampled clays was determined by use of X-Ray Florescence (XRF) technique. Clays were incinerated at a temperature of 800 °C for 4 h. The calcined clays obtained were blended with OPC at replacement level of 35 percent by mass of the OPC to make the test cement labeled PCC35. The PCC35 mortar prisms measuring 40 mmx40mmx160mm were cast with activator solutions and cured in water. Compressive strength was determined at the 28th day of curing. As a control, OPC and PCC35 were similarly investigated without activator solutions. The 28 day cured mortars were exposed to a temperature of 700 °C for 2 h then cooled in water to room temperature and their compressive strengths determined. Chemically activated PCC35 and non-activated PCC35 exhibited lower loss in weight than OPC after exposure to the elevated temperatures. Chemically activated PCC35 and non-activated PCC35 exhibited higher residual compressive strength than OPC after exposure to the said temperatures. Na₂SO₄ activated mortars showed higher thermal resistance than NaOH activated mortars. Generally, chemically activated PCC35 exhibited the highest thermal resistance compared to non-activated PCC35 and commercial OPC mortars.

The search for new supplementary cementing materials (SCM) creates opportunities to using new materials such as calcined clays and marl. However, such changes require a transition period, where introduction of new SCMs are most successful when they can be coupled and employed with the existing materials. For this purpose, a series of ternary mixes employing fly ash (F), calcined marl (C) and ordinary Portland cement (OPC) was evaluated against mono- and binary mixes of the components. It was found that due to the complementary water demand of fly ash and calcined marl, forming pastes made of ternary blends of FC-OPC leads to better rheology than pure OPC pastes, particularly when a F:C ratio of 1:1 was present, even up to 60% replacement of OPC. Any increase in C results in a decrease in flowability, while increasing the F proportion resulted in higher flow, with eventual bleeding. This was coupled with a synergetic improvement in the early age of hydration of the ternary mixes as compared to mono- or binary mixes.The results here indicate that ternary mix of fly ash-calcined marl-OPC can pave the way for future cementing systems, where it can be easily utilized even in the transition stage and allow the successful implementation of this material.

Limestone calcined clay cement (LC3) allows clinker replacement up to 50% but it can also be designed for other replacement levels based on the quality of raw materials and required properties. In this study, LC3 was prepared with different proportions using clinker replacement levels of 50%. Two different types of calcined clay and three different types of carbonates were used as supplementary cementitious materials (SCMs) for preparing LC3. The compressive strength of LC3 cement mortar cubes were checked for the age of 28 days. The pozzolanic strength potential of limestone and calcined clay (LC2) blends were tested with the lime reactivity test as per Indian Standard 1727. The lime reactivity test showed the highest reactivity for blends comprising clay and limestone in the proportion of 2:1. Similar result was observed in the case of LC3 mortar strength. The 28 days cement mortar strength results were correlated with the lime reactivity strength potential test and good correlation was observed. On the basis of results, it was concluded that the lime reactivity strength potential test could be directly applicable to the reactivity study of LC3 even at varying proportions of limestone and calcined clay.

The use of mass concrete for the construction of infrastructure has become more prevalent in recent history. However, the use of Portland cement as a binder material for massive concrete structures is both highly expensive and can come with durability issues such as delayed ettringite formation resulting from heat produced during hydration. The use of limestone calcined clay cement binder offers a low-cost alternative to mitigate potential problems borne from construction of mass concrete. This paper presents research in which limestone and calcined clay were used as partial replacement of Portland cement to create low heat, low cost binder for mass concrete members. The specimens were evaluated for the potential for delayed ettringite formation; results were confirmed with scanning electron microscopy. Isothermal conduction calorimetry was performed at temperatures of 23 °C, 70 °C, and 85 °C which showed a reduction in heat production in paste amended with limestone calcined clay cement (LC3). The results of this study indicate that the incorporation LC3 binder of calcined clay and limestone provides higher alumina and lower sulfate which contributes to the mitigation of deleterious ettringite formation. Several conclusions were drawn from this study: LC3 can be used to create more financially viable materials for developing areas to create massive concrete structures and the concrete produced with LC3 as the concrete has a lower potential for delayed ettringite formation due to both lowered heat and chemical composition.

The combination of a commercial calcium sulfoaluminate (CSA) cement with metakaolin (MK) and limestone (LS) as supplementary cementitious materials (SCMs) is investigated for a CSA replacement level of 20 wt%. In addition to a pure CSA cement, paste samples have been prepared for three blends with MK to LS ratios of MK/(MK + LS) = 0, 0.5 and 1. All blends used a molar gypsum/ye’elimite ratio of 0.5 and a water to binder ratio of w/b = 0.7. The hydration for the four series has been followed from 1 day to 182 days and the hydrate phase assemblages have been identified using XRD, TGA as well as 27Al and 29Si NMR and compared with predictions from thermodynamic modelling. The results show almost full degrees of reaction for ye’elimite in all blends and that the degrees of reaction for belite and MK have an important impact on the hydrate phases and their quantities formed in the ternary systems.

This paper looks at the study of intergrinding for the production of ternary cement based on clinker, calcined clay, limestone and gypsum with 50% of clinker substitution (LC3). The impact of grinding time on clinker, limestone and calcined clay PSD, and how this parameter influences the overall performance of the ternary cement is assessed. Laboratory cement blends were produced by grinding all components in a batch laboratory mill. Industrial cements produced through intergrinding in a continuous ball mill were used for comparison. Three fractions were identified: d<7 µm, 7 µm < d < 40 µm and d< 40 µm, for each of the cements studied and the amount of each component were assessed. Fresh and hardened state properties of blends were tested. Results indicate that in intergrinding most of clinker remains at the medium fraction, and further grinding cannot improve clinker fineness due to fine calcined clay muffle clinker fineness gaining. PSD of limestone and calcined clay is wider than clinker PSD, with a high amount of each material on fine fraction, having a strong impact on rheology. A change in calcined clay/limestone ratio from 2:1 to 1:1 improves clinker grinding and rheology but has a negative impact on strengths due to the less proportion of calcined clay that impact negatively on the pozzolanic reaction.

To prove the applicability of cement with calcined clays as main constituent in concrete the performance of such composite cements, especially with regard to durability, has to be demonstrated. Composite cements with different calcined clays were used in conventional concrete mixtures and tested for their resistance to carbonation, chloride migration, frost and frost-deicing salts. Attention had to be paid to the workability of the concretes which could be affected strongly by the increases in the water demand of cements with calcined clays. Adjustments with superplasticisers could become necessary. The results of the durability tests showed that the performance of such binder systems is comparable to cements with other substitution material like limestone, slag or fly ash.

The combination of a calcined clay with an alkali silicate or hydroxide solution has been identified since the 1920s to yield potentially useful materials. More recently these have become termed ‘geopolymers’, and have been popularised under that name. This paper briefly summarises some of the earlier history of alkali-calcined clay binders and related materials including synthetic zeolites, exploring some of the reasons underlying the more recent broadening of interest in this research field, and identifying some of the future opportunities that arise through the use of these materials. These cements may particularly be capable of offering very good technical performance and cost-effectiveness in a variety of applications, with an environmental emissions footprint lower than that of competing materials.

The influence of a calcined clay on the hydration of an oilwell cement was studied in slurries. The replacement grades of the cement (by weight of cement) were 5, 10 and 20% of the calcined clay. The slurries were prepared at a density of 1.80 g·cm−3 and hydrated in sealed containers at 30 and 60 °C during 24 h. A reference slurry was prepared where the cement was substituted by 5% of a zeolitic tuff. The water–to–solid ratio was 0.52 for each slurry. From the TGA and pozzolanic reactivity tests were shown that the calcined clay was more reactive than the zeolitic tuff. The isothermal calorimetry tests showed that the induction periods of the slurries were shorter when the cement was replaced by the calcined clay at both temperatures and they decreased with the increment of the temperature and the replacement level by the mineral addition, what could impact negatively the thickening time in real conditions. The MIP assays evidenced that the influence of the kind and the quantity of the mineral addition on the porosity of the hardened slurries is complex but in general it was observed a refinement of porosity and less total porosity when the slurries were hydrated at 60 °C. The XRD experiments showed that the phase assemblages when the slurries were cured at 60 °C were more complex and with more crystalline phases presents, which could have influences on the performance of the hardened slurries in real well conditions.

The influence of two pozzolanic additions, a calcined clay and a zeolitic tuff, on the hydration of a Portland cement was studied in pastes prepared with fresh water and substitute seawater. The pastes contained 0, 5, 10, 20 and 30% of each pozzolanic addition and were prepared with a water–to–solid ratio of 0.50. The hydration kinetic was evaluated by isothermal calorimetry at 30 °C and during 72 h. The bound chloride contents in the pastes were also quantified. The results of the experiments indicated that there was not a correlation between the kind of mixing water and the induction periods but these periods increased with the percent of substitution of the Portland cement and the increments were higher with the finest pozzolan and with the higher content of alumina containing phases (calcined clay). It was observed that during the acceleration periods the mineral additions increased the reaction rates and the release of heat during the principal peaks and the increments were higher in pastes with the calcined clay and in those prepared with artificial seawater. The total cumulative heats were higher in the systems where the Portland cement was substituted by the calcined clay (with higher content of alumina) and in the pastes that were prepared with substitute seawater. The capacity to bind chloride was related to the content of Al₂O₃ y Fe₂O₃ in the mineral addition and it was higher in pastes with calcined clay (with higher content of Fe₂O₃ and Al₂O₃ containing phases) but the zeolitic tuff was more effective to bind chlorides, in spite of having less quantity of phases providing Fe₂O₃ and Al₂O₃.

Nowadays, the Cement Cuban Industry has installed a productive capacity of 2.8 MMt of clinker per year, for a use of the 40% of this productive capacity for different reasons. The reported production in 2014 was 1.8 MMt. The current demand of cement exceeds the production, indicating the necessity of new investments in the cement sector to increase the productive capacity and the production but this is impossible in short-term. The projection of this demand in the period 2015–2020 will imply an annual increase of 18% due to the new age of the economic reorganization we are currently facing in our country and the increase of constructive activity. Today, the LC3 production constitutes a viable alternative to reduce this problem. The Cuban Cement Industry has shown a huge interest on the development and implementation of LC3. With that purpose, it is necessary to work on the introduction of this cement in the Cuban standard.Since 2015, CIDEM has representation in the CTN No. 22 “Cement” and the CTN No. 37 “Concrete and Mortars” portraying an active participation. At present, our research is based on three points:1.Development of a Technical Instructive about the determination clay potential to be use as pozzolan.2.Confection of the new standard about the specifications of ternary blended cement.3.Application of the NC 120:2014 “Hydraulic concrete — Specifications” for the development of concrete with LCC for the different levels of atmospheric and chemical aggressiveness.The main goal of this work is to develop an Implementation Strategy for LC3 in Cuba. This strategy links the standardization results to environmental and cost results including the clay deposit study, durability test and the experience acquired during several industrial trials. Siguaney Cement Factory has been selected to put into practice this strategy.

Geopolymer cement can be used as a ceramic matrix carrier for different applications such as antibacterial materials. In this work, an antibacterial geopolymer cement has been synthesized by loading the organic compound 5-chloro-2-(2, 4-Dichlorophenoxy) phenol also known as “Triclosan” into a geopolymer metakaolin and nano-silica based cement matrix. The antibacterial efficiency of Triclosan-geopolymer cement against Escherichia Coli (Gram-negative bacteria) and Staphylococcus Aureus (Gram-positive bacteria) was evaluated using the Halo method; results show that triclosan based Geopolymer cement are effective for preventing the reproduction of the E. coli and S. aureus bacteria. From results, a “room-temperature” antibacterial metakaolin based geopolymer cement for buildings with health and environmental protection can be obtained.

Kaolinite and montmorillonite have been examined at heating temperatures from 500–1100 °C. For each sample, the degrees of dissolution in acidic and basic media have been determined, using a 1.0 vol.% HF solution and an 8.0 M NaOH solution, respectively. The solid residues from these experiments are analyzed along with the calcined starting materials by 27Al and 29Si MAS NMR. A comparison of these spectra, before and after dissolution, enables a clear differentiation of the silicon and aluminium environments that are present in each sample, providing direct information about the aluminate and silicate species which are dissolved under basic and acidic conditions, i.e., identification of the active sites in calcined clays. Moreover, this procedure facilitates the structural assignment of the different silicon environments observed by 29Si NMR, shedding light on the dehydroxylation process and on the structural changes that occur for kaolinite and montmorillonite upon heat treatment.

The buildings of the Malecon, the historical section of Havana along the coastline, suffer accelerated degradation due to the aggressive environment. The primary damage mechanism at play is the crystallization of sodium chloride at repair mortar interfaces, as shown in petrographic and SEM analysis. This preferential precipitation leads to crystallization pressures that reduce the adherence of the lime based mortars from the substrate. Environmental monitoring shows that the daily relative humidity fluctuates around the deliquescence point of sodium chloride, exacerbating the problem through continual cycles of dissolution and recrystallization. The potential for an alternative repair material such as limestone calcined clay cement based mortar is discussed.

The main goal of the paper is to carry out the first implementation of a Life Cycle Sustainability Assessment (LCSA) in Cuba throughout a case of study related with the introduction of Low Carbon Cement in the country. First, an adapted model to assess economic, social and environmental impacts is developed according to cement sector conditions in the island. Secondly, the “adapted LCSA” is carried out comprising a life cycle assessment (LCA), an economic life cycle analysis (EcLCA) and a social-LCA (S-LCA). The environmental assessment includes impacts on climate change, particulate matter emission, fossil fuel depletion among others. The systems explored include all processes from cradle to industry ‘gate’. The cements assessed were Ordinary Portland Cement (OPC), Blended Cement (PPC) and Low Carbon Cement (LC3). For the EcLCA and S-LCA, indicators adjusted to Cuban conditions are proposed and assessed, using midpoint and endpoint levels to match with LCA methodology. Economically, conventional Portland cement presents the highest costs per ton, followed by PPC and LC3. In the S-LCA, LC3 introduction reduces sensitive social impacts in relation with different stakeholders: workers, local community and society. Environmentally, main impact, at global scale, is climate change and, at local level, particulate matter emission. Integrating the results from LCA, S-LCA and EcLCA shows a significant reduction on the climate and social impacts per cost when producing LC3. Finally, results show that LC3 introduction is the best option to meet sustainability goals of the cement industry in Cuba and LCSA can be considered a valuable tool to support decision-making processes oriented to sustainability.

The concept of using isothermal calorimetry for sulphate optimization of Portland cement was developed by Lerch more than 70 years ago. In this paper, we demonstrate a new calorimetry based approach for modern low clinker blended cements grounded in Lerch’s concept and that can be used for both periodic sulphate optimization and continuous process control to ensure optimum performance during daily cement production. More frequent sulphate optimization, coupled with daily process control, is especially important for binders that rely on optimum aluminate hydration, such as the novel LC3 cement that utilizes aluminate phases from both clinker aluminates and calcined clay. In the LC3 cement, the sulphate component is the major phase controlling the early hydration, strength development and admixture compatibility of the alumina bearing phases. Moreover, the calorimetry based approach described herein can be substantially automated and does not require a traditional laboratory setting, nor air conditioning, since the calorimetry itself provides a laboratory environment in its temperature control chamber. The only manual labour required for this concept is the weighing of binder, water, calcium sulphate and optional admixtures. The mixing, data collection, calibration, evaluation of the sulphate optimum and subsequent process control can all be automated, such as in Calmetrix Inc’s software suite for cement research and development.

The investigation reveals the reaction kinetics of three calcined phyllosilicates (metakaolin, metaillite and metamuscovite) in an alkaline solution which was prepared without the addition of clinker. The phyllosilicates were calcined at their individual optimal calcination temperature. Two test series without and with the addition of anhydrite were investigated. Calcite is present in all measurement series due to the impurity of portlandite. The reaction kinetics were investigated by means of isothermal calorimetry and in-situ x-ray diffraction (XRD). All measurement series show crystalline reaction products after 7 d in the absence of anhydrite. The addition of anhydrite leads to a first formation of ettringite within the first 13 h of reaction with all phyllosilicates tested. The water absorption capacity of phyllosilicates does not correlate with the specific surface area measure as BET-surface. Especially for metamuscovite, the high water absorption leads to a simultaneous formation of monosulfate and gypsum after 17 h. While metakaolin exhibits a significant concentration of dissolved alumina and silicon ions, the influences of metaillite and metamuscovite are less pronounced in that respect and exhibit reaction at a later stage. Nevertheless, it can be concluded that the reactivity of naturally occurring mixed layered clays cannot be reduced their metakaolin content but is due in addition to the contribution originating from other clays present in the mixtures. Metaillite and metamuscovite contribute even to the formation of hydrate phases at early ages of the reaction. Thus, the content and kind of phyllosilicates deserve more attention when used as supplementary cementitious material because of their high water absorption, their contribution to reactivity and their consumption of portlandite.

This study investigates the dispersing performance of three different polycarboxylate superplasticizers (PCEs) and a cationic polymer in the suspension of a calcined clay holding a mixture of different meta phases. It was found that the anionic PCEs as well as the cationic polymer can disperse this clay, thus suggesting that this calcined clay exhibits particles with positive as well as negative surface charges. Relative to PCEs, their dispersion ability is highest when their anionicity is particularly high. Adsorption and zeta potential measurements of the PCEs further elucidated this interaction.

The majority of cement available worldwide includes supplementary cementitious materials (SCMs) as a mineral additive to improve mechanical and durability properties of cement. The alkalinity of the concrete made using such cements is less as SCMs consume the calcium hydroxide produced on clinker hydration by the pozzolanic reaction. Quantity of calcium hydroxide available in the system is one of the major factors influencing carbonation resistance of the system. Numerous carbonation models are available which take the quantity of calcium hydroxide as input and predicts the carbonation depth. In blended systems, insignificant or very small amount of calcium hydroxide is present and hence prediction of carbonation depth using existing models becomes difficult. In this study, a new approach has been developed to predict carbonation depth in concrete made using blended cement based on total reserve alkalinity of the system along with other factors. The carbonation depth predicted by the above approach is in close relation with experimental data.

This study explored the delayed strains in limestone and calcined clay ternary blends. Autogenous shrinkage measurements are carried out over 2 months and compressive basic creep tests during 28 days after one month of curing. All tests are done using mixed with calcined clay at different metakaolin amounts or with variable mix designs. Results show that the presence of any type of clay, except pure metakaolin, has a similar impact on both autogenous shrinkage and basic creep. However, mix design seems to have an important contribution. Shrinkage rate is higher for blends than PC at 28 days, although reaching a similar amplitude at this age for most mixes. Creep amplitude and rate are reduced when using the blended systems.

The effects of calcined kaolinitic clays as supplementary cementitious materials (SCMs) on the performance of pastes and mortars have been well studied. Less attention has been paid to the thermal transformation of halloysite than that of kaolinite and its possibility to be used as SCMs. Halloysite and kaolinite have identical chemical composition, except that halloysite may have two molecules of H₂O, as interlayer water. The content of additional water in the interlayers of halloysite has a decisive influence on the crystal morphology, which is generally curled rather than platy as in kaolinite. Common forms are elongated tubes and spheroids. The aim of this investigation is to study the hydration of blended cements with 25% of different calcined clays to evaluate the influence of the content and the morphology of halloysite in the development of the hydratation compounds, and compressive strength of mortars. Three clays with different halloysite/kaolinite content, and different morphology were analyzed. The hydrated phases present in pastes at 2, 7, and 28 days were identified by X-ray diffraction (XRD), and the content of CH by differential thermal analysis (DTA/TG). The compressive strength of mortars was tested at 2, 7, and 28 days. The pozzolanic reactivity of the calcined clays was influence by the kaolinite content and morphology of halloysite in natural clays. This results in different crystalline and amorphous aluminic phases obtained at different ages, and that the ensemble results differ, this affects the porosity and the compressive strength.

Waste materials from kaolinite processing was identified with a content of 46% of kaolinite and calcined and used for preparing Limestone Calcined Clay Cement (LC3). It has been found that thermal history of activation in the range of temperature from 750–800 °C does not change much the reactivity of the calcined kaolinitic clay based on strength test. R3 (rapid, relevant and reliable) calorimetry test method was also used for assessing the reactivity of calcined kaolinitic clay, which gives a result in good agreement with mortar strength test. The comparison test reveals that the reduction of flowability due to the addition of calcined clay can be compensated with the combination of limestone, and that the compressive strength of LC3-50 can have equivalent strength to the pure Portland cement, indicating the high reactivity of calcined clay and the synergy when combined with limestone. The design of a flash calciner with a capacity of 600t/d and thermal consumption of 620 kcal/kg in average is also introduced.

The aim of this work is focused to identify natural resources with industrial potential to be used as supplementary cementitious materials (SCMs) in Portland blended cements. Two clays obtained from the quarries near to Barker in Tandilia System (Buenos Aires- Argentina) were studied. The geneses of these rocks are by a hydrothermal alteration and include the presence of pyrophillite. Whole-rock were characterized by XRD and FTIR spectroscopy indicating that main clayed minerals are kaolinite (Si₂Al₂O₅(OH)₄), illite (K_0.66Si_3.33Al_2.66O₁₀(OH)₂) and pyrophillite (Si₄Al₂O₁₀(OH)₂) associated with feldspar. The thermal transformation was studied by differential thermal analysis and the phase changes were confirmed by XRD and FTIR. Samples of clays were calcined at different temperature (550 to 1050 °C), the electrical conductivity was measured and the dissolved silica in simulated pore water solution was quantified. The pozzolanic activity was measured by the compressive strength activity index, on blended cement mortars containing 25% by weight of calcined clays. Results showed pozzolanic activity after 7 days and the compressive strength values exceed the rate of replacement for both clays. The high water demand of sample containing pyrophillite can be attributed to the exfoliation that occurs during the water loss process.

One main obstacle impeding the implementation of calcined clays into the building material market is the insufficient experience with the long-term behaviour of the concerning concretes. To reduce this insecurity, a comprehensive study was performed which covered most of the relevant durability aspects of concrete made with calcined clay blended cements. For this purpose, different clays based on kaolinite, montmorillonite and illite were regarded which were fired at optimum temperatures according to the strength contribution in cement. After substituting 30% of Portland cement with the respective calcined clay, a number of investigations has been executed to show the performance under different environmental conditions.While the resistance against chemical working mechanisms like sulphate attack, alkali-silica reaction and chloride induced steel corrosion is improved, exposure to freeze-thaw changes and carbonation seem to limit the application of calcined clays in concrete. From the latter facts, it results the demand for a better understanding of the damaging processes and the material properties suppressing them. Therefore, new criterions appear to which the optimization of calcined clay manufacture has to be adjusted.

LC3 and LC2 produced in the plants of JK Lakshmi Cement were used in the construction of several pavements, AAC blocks and other practical applications like plaster and mortars. It was found that in most applications, OPC could be easily replaced by the same weight of LC3 without a negative impact on performance. Plain, reinforced and fibre-reinforced pavements were cast using the cement and the construction could be carried out using usual construction procedures. LC3 and LC2 could also be used in the production of autoclaved aerated concrete (AAC) blocks, without a significant change to the technology or performance. It was found that a better cohesion and flow could be obtained by the use of LC3 in place of OPC in mortars and plasters. For most applications, it was found that a direct replacement of OPC by LC3 was possible without negatively influencing the performance of the product.

Replacement of 30% of ordinary Portland cement (OPC) by metakaolin (MK) reduces the CO2 intensity but negatively impacts the workability. A critical challenge facing adoption of this next-generation infrastructure material is developing admixture systems that impart workability similar to unblended OPC while retaining the advantages in strength and environmental stability conferred by MK. Hierarchical machine learning is a highly-supervised methodology that integrates physical and statistical modelling to understand and optimize complex systems. Here it is applied to designing admixture formulations for OPC-MK blends, providing exceedingly rapid admixture development as well as formulations tailored to specific materials. Elucidating how MK impacts workability of these systems was addressed by screening the effects of superplasticizers, viscosity-modifying admixtures, and water-reducing admixtures on pore solution properties, OPC rheology and the colloidal properties of MK suspensions. Changes in slump spread of 70% OPC/30% MK blends as a function of admixture formulation were fit using regression methods. Increases in slump spread were found to be a strong function of pore solution viscosity, effects of superplasticizer on MK zeta potential and electrosteric interactions, and coupling between pore solution viscosity and osmolality with MK zeta potential and electrosteric interactions, respectively. Work toward designing new admixtures that optimize these interactions will also be pursued.

To address the sustainability concerns associated with Portland cement clinker production, the ternary blend of limestone, calcined clay and cement (which was named LC3) has recently been demonstrated to be an efficient solution. This work aims to contribute to the development of this promising material by applying latest techniques to characterize the chemo-mechanical properties of the complex heterogeneous microstructure of an LC3 paste by combining statistical nanoindentation and quantitative SEM-EDS techniques (SNI-QEDS). The results showed that the mechanical properties of LC3 come from a complex microstructure assemblage of C-A-S-H, Al-rich hydrates and anhydrous grains. Thus, the LC3 microstructure is composed by large anhydrous grains (clinker and calcined clay) embedded in a cementitious paste made of hydrates incorporating finely graded grains of anhydrous calcined clay, limestone and quartz. Moreover, the partial reaction of the calcined clay, limestone and Portlandite formed C-A-S-H and other Al-rich hydrates (likely including carboaluminates). Notably, the latter exhibited higher mechanical properties than those of C-A-S-H. Finally, the present work provides new knowledge for better understanding the complex LC3 microstructure towards advanced modelling and mix design optimization.

Toward broadening utilization of higher fractions (i.e., >10% by mass) of metakaolin (MK) in concrete construction, several key technical challenges remain. Among these are those associated with differences in early age properties deriving from greater MK additions; these include reduced workability, more rapid slump loss, and increased heat of hydration compared to traditional concrete. Due to competing dilution and acceleration effects associated with the introduction of finely divided limestone (and potentially more fine cement), these effects can be potentially exacerbated or ameliorated when MK is combined with Portland-limestone cement (PLC). This paper examines each of these challenges and offers solutions, in the form of recommended admixtures to improve workability and slump retention and refined heat of hydration models which consider the contributions of MK.

This study focused on understanding the influence of different amounts of calcite impurities (0 to 10% by mass) on the optimal parameters for clay dehydroxylation and the reactivity of the final calcined clay. A surface response experimental design was used to study the effect of maximum temperature, residence time and calcite content on different experimental responses. Specific surface and particle size distribution were used to characterize the physical properties of the calcined-clays. SEM coupled with EDS was selected to study the particle morphology and the composition of the amorphous phase formed, while XRD was used to assess the mineralogical composition after calcination. TGA analysis was used to measure the remaining amounts of kaolinite and calcite after calcination, while isothermal calorimetry was used to assess the reactivity of the different calcined-clays obtained. It was observed that specific surface area is the most sensitive parameter to variations in calcite content.

Limestone calcined-clay cements (LC3) take advantage of the synergetic effects of calcium carbonate reaction with the additional aluminium provided by the calcined clay. As temperature decreases, calcium carbonate solubility increase, therefore, the early-age hydration kinetics and the optimal proportioning of the ternary cement system are modified. This study explored the reactivity and mechanical performance of different LC3 systems cured at 10 and 20 ºC. Mixtures containing PC, PC-limestone and a LC3 blends with 50% clinker factors and 2:1 clay-to-limestone ratio were cast and compared. Hydration kinetics were assessed using isothermal calorimetry at each of the temperatures. The evolution of porosity was studied during hydration by MIP. Compressive strength was measured over time on cement paste cubes. Phase assemblage was monitored using XRD.