Calcined Clays for Sustainable Concrete

Table of Contents

1. Frontmatter

2. Exploration and Characterization of Various Types of Kaolinite Rich Clays, First-Ever Industrial Lab Trials, and Demonstration of LC3 in Pakistan

   Mubeen Ahmad Siddiqi, Tariq Jamil, Malik Mehboob Ahmed, Tehmina Ayub, Muhammad Danyal Sheikh, Chuanlin Hu, Faheem Lal

   Abstract

   Blended cements are very uncommon in Pakistan, and most of the supplementary cementitious materials (SCM) are used during the concrete production. With the increasing demand and scarcity of high-quality SCMs, cement industries are exploring new variants of blended cement for meeting the needs of the building and construction industry. Ongoing research on novel LC3 drew the attention of Fauji Cement Company Limited—a leading cement manufacturer in the country. We have explored many areas in the vicinity of the cement plant in search of potential clay reserves and found a vast range of naturally occurring clay containing 40 to 85 wt.% kaolinite mineral, suggesting its qualification for producing LC3 cement blend. During the exploration of kaolinite clay, it was observed that the region is enriched in white China clay and also has massive reserves of reddish clay which contains high kaolinite as well as iron contents. This typical reddish clay is not in the use of any industry, and its potential reserves are best suited to be used for manufacturing LC3. Different grades of fine calcined clay samples were mixed with ordinary Portland cement (CEM I 42,5 R) to prepare LC3-50 and LC3-65. Composition and performance of the resulting building materials were tested using XRF, PSD, standard consistency, setting times, compressive strengths, etc., as well as in an actual civil construction project for the first time in Pakistan by a cement manufacturer. Test results showed excellent compressive strength for up to 50% clinker replacement, indicating that clays of this region are suitable to be used for LC3 cement production.

3. Guatemalan LC3 Concrete vs Portland Pozzolanic Cement Concrete Review After 3 Years’ Trials

   Ricardo A. Posadas, B. Ariel Osorio, Roberto A. Díaz, P. Estuardo Herrera, Elvis G. García, Luis. A. Velásque

   Abstract

   The present work evaluates the performance of the first LC3 Limestone-Calcined Clay Cement in Guatemala, versus Portland pozzolanic cements after 3 years in concrete. C1 and C3, pozzolanic HE cement concretes, and C5, an LC3 concrete, present better compressive strength than C2 and C4 (C5 concrete has 20.96% more LC3 than C2 and C4). On durability tests, C2, C4, and C5 present more carbonation depth than C1 and C3, nevertheless C2, C4, and C5 have a superior performance on resistance to chloride ion penetration. With all the results obtained is recommended the use of an ordinary Portland cement concrete in an environmental condition of HR between 50 and 70% while the LC3 concretes are recommended in tidal zones.

4. Standardisation of LC3 in India: Lessons and Way Forward for Global Acceptance

   Shashank Bishnoi

   Abstract

   With cement standards on LC3 accepted widely around the world, the focus is now moving towards the commercialisation of the cement and increasing its acceptance by the market. The lessons that have been learnt during the process of standardisation in India can be applied for the further acceptance by the cement and construction industries. Further acceptance by the cement industry will require identification of suitable clay deposits and the best technologies for cement production. Use of the cement will require addition of the cement to concrete standards and building codes. Demand from users will require addition of the cement to relevant contracts of public infrastructure agencies. To overcome the inertia that is usual in conservative industries like construction will have to be overcome incentives for using sustainable materials. For this a proper system of certification of LC3 and the CO₂ emissions saved has to be established. This article discusses some of the lessons learnt while interacting with various stakeholders in the production and use of LC3 and the way forward to an accelerated global acceptance of the cement.

5. Suitability of Selected Tanzanian Kaolinite Clays for Producing LC3 Binders

   Emmanuel Safari Leo, Mark G. Alexander, Hans Beushausen

   Abstract

   One of the most promising current options for lowering the cost and environmental impact of cement is the use of blended cement. Well-established supplementary cementitious materials such as slag and fly ash are limited in most African countries. In Tanzania, a promising option lies in the production of LC3 binders. In this research, the suitability of kaolinite clays from two selected deposits in Tanzania for clinker replacement was assessed and compared with a reference sample from South Africa. Results indicate that both Tanzanian clays are suitable, based on the kaolinite content. However, factors such as the internal surface area of the clay also influence its performance.

6. Influence of Iron Impurities in Kaolinite Clay on Reactivity of Limestone Calcined Clay Cement upon Calcination

   Mehnaz Dhar, Aastha Singh, Shashank Bishnoi

   Abstract

   Calcined clays are widely used in blended cements to lower the carbon footprint associated with concrete industry. In the field, raw clays are often associated with iron impurities that may affect the properties of calcined clay. The present study investigates the influence of iron contaminated kaolinite clays on reactivity of limestone calcined clay cement. Natural and model clays with iron content varying from 5 to 22% were used. Clays were calcined in laboratory muffle furnace at two different temperatures of 750 and 850 °C. All iron rich clays satisfied the minimum reactivity benchmarks to be classified as a pozzolan according to lime reactivity test. The standard mortar compressive strength of LC3 prepared with each clay was evaluated at 3, 7, and 28 days. The strength values observed with blends made with natural clays remained in similar range. The behavior of model clays was found to be somewhat different as reactivity and strength values increased with the presence of iron impurity. The maximum strength gain was observed for kaolinitic clays with 12.5% iron content. It can be concluded from the study that low grade kaolinite clay with iron impurity up to 22% can be used for LC3 production based on their availability.

7. Insights on Admixtures Adsorption on Limestone Calcined Clay Cements

   Alberto Olivo, Alessandro Dalla Libera, Francesca Moratti, Sebastien Dhers, Kai Weldert, Peter Schwesig, Julien Bizzozero, Roberta Magarotto

   Abstract

   The substitution of ordinary Portland cement (OPC) with sustainable limestone calcined clay cements (LC3) has represented a major innovation in the building industry over the last 20 years, though some challenges require to be addressed still (Sharma et al. Limestone calcined clay cement and concrete: a state-of-the-art review. Cem. Concr. Res. 149, 2021). Most importantly, LC3’s lower calcination temperature than OPC (750–850 and 1450 °C, respectively), despite being environmentally benign, triggers a higher water and admixture demand. In this work, several superplasticizers were investigated to assess which are the most promising to be used with LC3 cements and the key physicochemical properties required for that purpose. The binder used for this investigation is based on a calcined clay from the Technical Research Center (TRC) for LC3 in India, a representative calcined clay that could be used in the construction sector in the near future. Kinetic profiles on LC3 proved to be similar to those on parent OPC material, indicating a similar interaction mechanism between admixture and binders. Nevertheless, the adsorption equilibrium value was considerably higher for LC3, which was correlated to its higher surface area. Adsorption on LC3’s individual components (i.e., calcined clay, OPC, limestone, gypsum) confirmed that differences in adsorption behaviour must be ascribed to calcined clay’s unique properties. Thanks to adsorption isotherms, a Langmuir–Hinshelwood adsorption mechanism was observed; most importantly, surface coverage at optimal dosage proved to be the lowest for the most dosage efficient admixtures, which are also characterized by the highest Langmuir equilibrium constant.

8. Elucidating Interaction Mechanism Between Various Clay Minerals and Superplasticizers in Cementitious Binders

   Ojas Chaudhari, Gilles Plusquellec, Emilie L’Hôpital, Urs Mueller

   Abstract

   The replacement of Portland cement, with a combination of calcined clay (CC), limestone and gypsum provides a sustainable and cost-effective solution along with promising mechanical properties compared to ordinary Portland cement. However, the utilization of calcined clay has a negative impact on the workability of the blended cement, and superplasticizers are commonly added to the mix. Unfortunately, the interactions between superplasticizers and calcined clays are less known. Clays can be composed of various minerals (kaolinite, smectite, illite, etc.) which, in their dehydroxylated form, can all interact differently with polycarboxylate ether (PCE), altering the fresh concrete properties. Two types of CC with different mineral compositions (illitic and kaolinite clays) were investigated. The influence of CC replacement (0–30%) in Portland cement binder was studied with respect to the dispersing ability of available PCEs. The rheological properties of CC-cement blends in pastes with different PCEs were investigated using a rotational rheometer and mini-slump flow tests to understand the effect of the type of CC and the PCEs on the rheological properties of CC-cement paste. Adsorption measurements were made by total organic carbon (TOC). In addition, isothermal calorimetry was used to study the hydration reaction of cement when CC and PCEs are present. Overall data signify that PCEs are efficient to improve workability of OPC-CC blends, but that the use of kaolinite CC will negatively influence the required dosage of PCE, while illitic CC has less influence.

9. Investigating the Origin of the Impact of Iron Impurities on Performance of Calcined Clay Limestone Cement

   Tafadzwa Ronald Muzenda, Fabien Georget, Thomas Matschei

   Abstract

   The use of supplementary cementitious materials to replace clinker is one of the most powerful levers to cut down the carbon footprint of cementitious materials. This has led to an increased interest in research on calcined clay limestone cement (CCLC) over the last years. In this study, we first demonstrate the effect of iron secondary phases on the performance of calcined clays in CCLC then we focus on the interaction of iron secondary phases with kaolinite in kaolinitic clays. The results indicate that iron phases affect the physiochemical properties of calcined clays and this is shown by the high specific surface area. Further analysis shows that the iron is likely spread through the kaolinite structure which evidences the likelihood of substitution of Al³⁺ by iron. This reduces the crystallinity of kaolinite as supported by XRD and FTIR analysis. It is possible that the structural disturbance gives rise to more active sites that increase solubility. These findings help us to better understand how iron interacts with kaolinite in calcined clays and how that impacts performance.

10. Influence of Alkali Activators on the Properties of Quaternary Blended Limestone Calcined Clay Concrete Incorporating Pumice

    Shreenandan Sahoo, Subhajit Mondal

    Abstract

    The alkali-activated materials (AAM) are considered to be an alternative cementless binder to reduce the carbon footprint. In the hydration of binders, the alkali activators are essential and provide a high pH environment, which makes the hydration process faster. Desired alkali activators (molarity solution) can be prepared by mixing the sodium silicate and sodium hydroxide pellets in water under normal atmospheric pressure. In this study, natural pozzolans such as pumice and calcined clay are used as a replacement for the cement. In this paper, two types of natural pozzolan based alkali-activated concrete are tried to develop as a substitute cementitious material. The first one contains 40% pumice, 40% calcined clay, 15% limestone 5% gypsum, which is the 100% replacement of cement (i.e., lime pumice calcined clay concrete). The second one contains 50% cement of OPC 53 grade, 15% pumice, 15% calcined clay, 15% limestone, and 5% gypsum, which is the 50% replacement of cement (i.e., lime pumice calcined clay cement concrete). The influences of different molality of SH on the compressive strength and microstructural behavior of the two developed mixes are evaluated and reported.

11. Assessing the Workability of LC3 and OPC Concrete Using Rheometer

    Gopala Rao Dhoopadahalli, Ashirbad Satapathy, Manya Gupta, Shashank Bishnoi, Vanessa Kocaba, Pascal Boustingorry, Marie Teinturier, Caroline Autier

    Abstract

    This paper aims to investigate the workability of Limestone Calcined Clay Cement (LC3) concrete by rheometry which is a more reliable technique than conventional tests like slump test, etc. It is a well-known fact that the concrete made with LC3 is stiffer and has lower workability due to higher water demand, in comparison to other cements. Here the rheological properties of LC3 concrete are studied and then compared with the conventional Ordinary Portland Cement (OPC) concrete by using a concrete rheometer. An attritor-type impeller was attached to the central axis of the rheometer to simulate the mixing conditions present in concrete mixer. A total of five concrete mixes were designed at a constant water-cement ratio of 0.50: three of which were made with OPC and two with LC3. In OPC mixes, cement content and coarse aggregate-to-total aggregate ratio were varied from the control mix. While in LC3 mixes, two types of clays with different kaolinite content were selected to understand their effect on workability. The energy required for mixing the concrete is qualitatively analysed by measuring the torque at various rotation speeds for both OPC and LC3 concretes in presence of admixture. In OPC concrete, with increase in the fines, the concrete becomes stiffer and thus higher torque values were observed. In LC3 concrete higher torque values were observed when high kaolinitic clay was used. In practice, LC3 concrete requires more effort for mixing as compared to OPC. However, the torques values obtained for LC3 concrete was lower due to higher dosage of admixtures.

12. Amazon Kaolins as Raw Materials for News Blends of Limestone Calcined Clay Cement

    Marcio Barata, Euler Arruda Jr.

    Abstract

    The use of supplementary cementitious materials constitutes one of the main strategies by the global cement industry to limit the global warming. In the Amazon region, between 1990 and 2018, cements were produced with 14–30% calcined kaolin and 5–10% limestone. Posteriorly, use of calcined clays and limestone was replaced only by limestone up to 25%. A solution for the region to reduce costs and improve environmental indicators would be the large-scale use of limestone calcined clay cements (LC3) with other calcined kaolin/limestone ratios. The objective was to investigate the feasibility of new blends from the ratio of calcined kaolin to limestone below 2 and clinker replacement percentages above 50%. The results point to the possibility of using a greater amount of limestone in LC3 compositions while incorporating less clinker and calcined kaolin, bringing environmental benefits with reducing production costs. Changes in Brazilian standards are necessary to include new compositions of LC3.

13. Comparative Study of Fresh and Mechanical Properties on Low Clinker Cement Concrete

    Aastha Singh, Mehnaz Dhar, Abhilash Shukla, Shashank Bishnoi

    Abstract

    Demand for cement increases sharply with urbanisation and industrialization. Limestone calcined clay cement (LC3) offers similar strength, better durability and is environmentally friendly compared to OPC. However, this ternary cement presents a few concerns, such as early setting time and higher water requirement, which leads to higher admixture dosage. To determine the effects of low clinker cement in concrete, this study analyses the effects of water content, w/c ratio and coarse aggregate to total aggregate ratio (c/a) on LC3 and OPC concrete mixes. The mixes were prepared using crushed sand as the fine aggregate and a modified polycarboxylate polymer-based superplasticizer. Then, SP dosage was optimised for each mix to achieve a maximum slump of 120 mm without bleeding and segregation. A reference mix was selected for comparative analysis based on workability and compressive strength results after 28 days at different water contents and c/a ratios. It was found that a stiff mix was produced at a low c/a ratio in the reference mix as the fines content and water demand increased. The details of the reference mix are a w/c ratio of 0.4, a c/a ratio of 0.66 and cement and water contents of 450 kg/m³ and 180 kg/m³, respectively. Finally, the mechanical properties of the mixes were evaluated after 7 days and 28 days for different w/c ratios of OPC and LC3 concrete. The work carried out in this study will be useful for the development of concrete mixes with LC3.

14. Characterization of Calcined Clays

    Lucie Hallier, Youssef El Hafiane, Agnès Smith, David S. Smith, Amith Kalathingal, Rémi Barbarulo, Christophe Levy

    Abstract

    Calcined clays present a high water demand. Consequently, when used in mortars or concretes, calcined clays usually lead to a low workability. The origin of the increased water demand depends on the nature of the (calcined) clay. Hence, the aim of the present study is to determine the mineralogical and physical parameters of the calcined clays that affect the water demand. This paper presents some preliminary results on the characterization techniques implemented to characterize the mineralogy and physical parameters of calcined clays, and their rheological behavior when mixed with water.

15. Study on Applicability of Low-Clinker Cement-LC3 in Concrete Repair Work

    Bharati, Lupesh, Shashank Bishnoi

    Abstract

    Demand for repair mortar is quite high in the Asian market owing to the deteriorating concrete structures. Hence, this study endeavors to examine the applicability of limestone calcined clay cement (LC3) as a repair material for concrete that involves reinforcement. For this LC3, ordinary Portland cement (OPC) and Pozzolanic Portland Cement (PPC) repair mortars were developed. The effect of admixture dosage on strength development of different blends was studied, which shows admixture dosage plays a significant role in strength gain for repair mortar, especially in case of LC3. Besides strength, repair mortar must exhibit compatibility and bond with substrate concrete. Hence, in this study bonding behavior between existing substrate concrete and repair mortar was compared using slant shear and split tensile tests. It has been observed that LC3 repair mortar creates a good bond with existing OPC and PPC substrates. In addition, transport properties tests performed on the repair mortars exhibited that LC3 will be best in hindering the ingress of moisture and oxygen which are essential to cause corrosion in reinforced concrete structures.

16. Combustion Pyrometamorphites as a Natural Resource for Calcined Clays

    Klaus-Juergen Huenger

    Abstract

    What happens, when coal seams burn? Not only in history but also in present times the coal fires had and have devastating effects on the environment undoubtedly. However, such processes led to a thermal influence of the rock surrounding the coal seams. The heat of the fire roasts the overlying sedimentary rocks. Most of them consist of clay minerals, which are thermal changed. Clay minerals were formed in dependence on the heat, the duration of fire, and by changing the composition of the sedimentary rock metamorphically. This process is called pyrometamorphism and the formed rocks are combustion pyrometamorphites. Different pyrometamorphites from a coal-mining region in Germany were characterized by chemical, physical, and mineralogical methods. The solubilities in alkaline solutions were also a main part of the investigations. Finally, the reaction behavior as supplementary cementing material was measured in comparison to other common substances. The results are exciting because some of the investigated materials have excellent properties regarding color, solubility, and reactivity. They can be characterized as a naturally formed metakaolin. However, there are limitations on its use. Not the complete material has such excellent properties; it depends on different factors. Additionally, it must be stated that the locations, where such rocks can be found, cannot be described as a normal quarry. On the other hand, this paper should be an incentive to search systematically for such rocks worldwide. The CO₂ release in the past by coal seams burning can contribute to a CO₂ reduction in the present and future.

17. Influence and Addition of Nano-SiO2 on LC3

    Vishwaajith Pemmasani, Vinuthna Ambatipudi, Visalakshi Talakokula, Aditya Abburi, Sri Kalyana Rama Josyula

    Abstract

    Limestone calcined clay cement is a new type of cementitious material that is composed of limestone powder, calcined clay, and clinker. The main advantage of using this material as a standard and mainstream cement is because it is cost efficient and reduces CO2 emissions by 40%. Nano-silica contains a very high amount of SiO2 (over 99%) and can be used to produce a filling effect. The effect of the addition of nano-silica on concrete and cement is very desirous. Nano-silica helps in accelerating the cement hydration process, increasing the durability and compressive strength. Considering these desirable properties of LC3 and nano-SiO2, a series of experiments were conducted. The aim of this paper is to evaluate the effects of nano-SiO2 on LC3 and study the possible applications in practical implementations.

18. Effect of Fineness and Addition Levels of Low-Grade Czech Clay on the Microstructure and Compressive Strength of Calcined Clay-Limestone Cement

    Lenka Scheinherrová, Vojtěch Pommer, Meenakshi Sharma

    Abstract

    This study explores the feasibility of utilizing local Czech clay from the Kadaň area, with a yield of ~ 35% kaolin from the clay matrix, to produce limestone calcined clay cement (LC3). The raw clay was first ground using a laboratory-scale disk mill to achieve different fineness and then calcined at 800 °C. Pozzolanic activity of calcined clay was assessed using an accelerated R³ pozzolanic test. The effect of the fineness of raw clay on the microstructure development and the compressive strength of LC3 with 20, 35, and 50% cement replacement was studied at 28 days of hydration.