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Open Access 01.10.2023 | Technical Paper

Producing of alkali-activated artificial aggregates by pelletization of fly ash, slag, and seashell powder

verfasst von: Gopal Bharamappa Bekkeri, Kiran K. Shetty, Gopinatha Nayak

Erschienen in: Innovative Infrastructure Solutions | Ausgabe 10/2023

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Abstract

In the construction sector, the material supply chain of aggregates is frequently disturbed due to seasonal unavailability, quarrying issues, and environmental norms. The production of artificial aggregates has gained prominence to conserve natural resources and promote green construction practices. The current study encompasses the production of alkali-activated artificial aggregates through cold-bonding pelletization technique using three different raw materials, including fly ash, ground granulated blast furnace slag, and seashell powder in binary and ternary blending combinations. The cold bonding was achieved by alkali activation of binders with the aid of a sodium-based alkaline solution, which acts as an activator and hydrating liquid. The fresh artificial aggregates were subjected to surface treatment using the same alkaline solution to enhance their characteristics. The mechanical properties of artificial aggregates confirmed their potential as a substitute for conventional aggregates by exhibiting crushing and impact values of 18.19–27.53% and 12.06–18.85%, respectively. The microstructural and mineralogical characteristics depicted dense microstructure and compact matrix. The study concludes that artificial aggregates can effectively replace natural coarse aggregate in making structural concrete with many economic, environmental, and technical advantages.

Introduction

The building and construction sector is one of the most significant indicators of a country’s economic health. Since concrete is the primary and extensively used material in civil engineering, its manufacture can be seen as one of the significant contributors to excessive resource consumption and environmental degradation [1‐4]. This raises special attention over various industrial by-products and waste materials for substituting cement to subside the utilization of cement so that CO₂ emissions can be reduced [5‐13]. The total aggregate content accounts for 70–80% of the total volume of concrete, and the use of artificial aggregates produced from industrial waste and by-product materials as a partial or complete replacement for natural aggregate has received considerable scientific attention [14‐18]. This advancement has advantages, such as converting waste-to-value-added products, reducing quarry activities, and conserving natural resources [17, 19].

Pelletization is a widely used method in the metallurgical and pharmaceutical sectors; however, it has not been adopted much in the building sector. It is the process of agglomerating powdered waste materials into fresh pellets of the required size [17, 20‐22]. The fresh pellets are then strengthened to achieve the required strength for practical applications by sintering, cold-bonding, or autoclaving methods [23‐25]. The sintering method is used if the carbon content in a pelletizing material is high (2–6%) and is the process of fusing the waste particles together at a high temperature of over 1000 °C [21, 24, 26, 27]. In contrast, a cold-bonding or autoclaving method is employed when pelletizing material contains cementitious compounds (binders) regardless of carbon content, and it uses a temperature of less than 100 °C [21, 22, 27‐29]. Previous studies have demonstrated that pelletization is greatly influenced by pelletization parameters, including the angle and speed of the pelletizer and the pelletization duration [6, 21]. Further, it is also influenced by the characteristics of raw materials, such as specific surface area, size and shape of particles, moisture content, and wettability of particles [14, 15, 21, 30, 31].

FA is a waste material from thermal power stations that contributes to environmental damage and issues related to its disposal, as it frequently pollutes air and water [6, 32‐36]. Around 202 thermal power plants in India produce electricity and consume 686 million tonnes of coal annually. From data produced by the central electricity authority, it was reported that 232 million tonnes of FA in India was generated in 2020–2021 and is expected to generate further quantity in upcoming years due to increased infrastructure development activities [37]. Seashell is considered marine waste, and many coastal countries are facing problems of their vast quantity, and its management is becoming progressively challenging. Only a minimal amount of seashells is being used for various purposes such as handicrafts, fertilizers, and aggregates and additives in the construction sector. The unutilized seashell waste disposed of without proper treatment results in a foul odor due to rotting flesh in shells and the microbiological decomposition of salts into dangerous gases like ammonia and hydrogen sulfide [38, 39]. GGBFS is a by-product generated by steel industries [40, 41]. It is estimated that 0.45–0.50 tonnes of slag will be generated from each tonne of steel production. It will endanger the ecosystem if it is disposed of as waste, which contains the same constituents as cement but not in the same proportions [40].

The abundant material so generated as waste can be pelletized in a pelletizer by adding a trivial amount of binder, followed by spraying liquid to produce artificial aggregates. When moistened particles come in contact with each other, each grain’s surface forms a thin liquid layer, followed by bridges between the moistened particles at the place of their contact [42, 43]. The bonding forces gradually build up when the moistened particles are rotated into balls or pellets, and then formed pellets obtain strength through the mechanical forces built up when pellets collide with one another and to the sidewall of the pelletizer [20, 21, 44].

Most studies have developed artificial aggregates using cement as a binder. Smaller amounts of cement can only be added during the pelletization process; otherwise, emissions from the manufacture of cement would make this technique unfeasible and undesirable in terms of environmental issues [45]. To solve the emission issues with cement, researchers have identified cement-free binders by alkali activation of materials and geopolymerization. Their favorable mechanical and durability characteristics, with the advantage of waste utilization, have gained manufacturers’ attention [3, 7, 45, 46]. According to the literature, the alkali activator solution is a silica and alumina solvent that’s crucial for geopolymerization [3, 7, 46‐48]. The geopolymerization is greatly influenced by the alkali solution type, alkali activator concentration, binder-to-solution ratio, and curing regime [47, 48]. The best mechanical characteristics for artificial aggregate applications come from sodium hydroxide (NaOH) at concentrations between 8 molarity (M) and 12 M [47]. The optimal NaOH concentration for fly ash-based geopolymer, according to Gorhan et al., is 6 M [49]; however, Geetha et al. [50] discovered that 8 M is the minimal amount of NaOH required for synthesizing alkali-activated aggregates. The strength of artificial aggregates was found to rise with increasing NaOH molarity, and water absorption was reduced. Nevertheless, attempts have been undertaken to find the ideal NaOH concentration for producing artificial aggregates, and currently, there are no standards to determine the minimal NaOH concentration to form alkali-activated artificial aggregates [47]. It is also reported that the surface of the aggregates treated with water glass exhibited enhanced properties. This is attributed to the penetration of water glass into the surface pores of aggregates resulting in the healing of the microcracks and producing additional C–S–H by converting undesirable calcium hydroxide (Ca(OH)₂) [51].

This study produced cold-bonded alkali-activated artificial aggregates using FA, GGBFS, and SSP by considering the binary and ternary mix approach through pelletization. The alkaline activator solution was used as a binder to agglomerate and strengthen the aggregates. The primary objective of this study was to assess the feasibility of raw materials in developing artificial aggregates of acceptable properties and to achieve their mass recycling. The present study emphasizes testing the aggregates for various physical and mechanical properties and comparing their results with the natural coarse aggregates to ensure suitability before they were used in concrete. Finally, scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis were performed to study the microstructure and analyze the mineralogical compounds formed in the aggregate mix.

Significance of the study

The demand for construction aggregates has escalated rapidly, resulting in excessive exploitation of nature. In parallel, waste management is challenging for industries. Manufacturing aggregates using industrial wastes such as FA and GGBFS would be a favorable solution. The utilization of SSP in the production of artificial aggregate is distinctive. Its flocculation characteristics promote nucleation or pelletization of the matrix. Artificial aggregates agonize to depict resistance to water absorption and satisfactory mechanical characteristics which are addressed in this research by providing surface treatment. The previous scientific studies do not espouse all the optimized parameters of pelletization and geopolymerization. The best-suited optimum values of these factors are identified and adopted in this research to continue the scope of previous research.

Raw materials and characterization

The FA, GGBFS, and SSP were utilized to produce alkali-activated artificial aggregates. FA was procured from the Padubidri thermal power plant in the Udupi district of Karnataka state. It was finer than 75 µm with minor breakable lumps. It was examined as per IS 3812 (part 1)—2003 [52]. The GGBFS was collected from Astra Chemicals, Tamil Nadu, India. The SSP of significantly finer size obtained by processing involves the collection of waste seashells, cleaning, crushing, and grinding. Figure 1 shows the overall process of obtaining SSP from waste seashells. The properties of FA, GGBFS, and SSP are presented in Table 1. The raw materials’ specific gravity and surface area were obtained using a Le Chatelier flask and surface area analyzer. The Le Chatelier flask has a long stem and bottom bulb made of thin glass. The bulb is 250 ml in capacity and has a mean diameter of 7.8 cm. On the flask’s stem, there are graduations in millimeters. A surface area analyzer uses gas adsorption analysis theory to determine a solid sample’s surface area. Where an inert gas, such as nitrogen, is continually blown over a solid sample. Due to weak van der Waals forces, small gas molecules adhere to the solid substrate and its porous structure, forming an adsorbed gas monolayer. Using this monomolecular layer and the rate of adsorption, a solid sample’s specific surface area can be determined. From obtained results, it can be observed that FA and SSP were lighter than GGBFS, and SSP had a higher surface area, which was followed by FA and GGBFS. In this study, alkali activators used were NaOH and sodium silicate (Na₂SiO₃). NaOH was 98% pure, and Na₂SiO₃ comprised 32.46% silica, 13.54% sodium oxide, and 54% water, collected from Kamath rice mills and industries in Mangalore, Karnataka, India. The NaOH solution of 10 M concentration was prepared by dissolving 400 g of NaOH flakes in 1 L of distilled water. Similarly, the NaOH solution of 8 M concentration was prepared by dissolving 320 g of NaOH flakes. Later, Na₂SiO₃ in liquid form was mixed with the prepared NaOH solution in a ratio of 2:1. Finally, the whole mixed solution was left at room temperature for one day before use.

Table 1

Properties of raw materials

Physical properties
Item	FA	GGBFS	SSP
Specific gravity	2.24	2.85	2.36
Specific surface area (m²/gm)	1.55	0.51	3.65
Z-average (d nm)	3089	3736	3043
PDI	0.573	0.497	0.412
Zeta potential (mV)	− 14.4	− 29.4	− 14
Chemical properties
Composition (%)	FA	GGBFS	SSP
SiO₂	51.67	35.370	0.85
Al₂O₃	21.62	18.03	0.21
CaO	3.90	33.05	74.00
Fe₂O₃	12.70	0.36	0.29
MgO	1.20	7.73	0.17
Na₂O	1.97	2.984	1.10
K₂O	1.81	0.232	0.075
P₂O₅	0.374	0.739	–
TiO₂	1.32	0.8	0.015
SO₃	0.66	0.012	–
MnO	0.081	0.12	–
Cl	0.024	0.009	–
Loss on ignition	2.15	0.26	–

The particle size distribution, polydispersity index (PDI), and Zeta-potential of the raw materials were analyzed using a Malvern particle size analyzer (zeta-sizer), which works on the concept of dynamic light scattering (DLS) [53]. The average particle size of FA, GGBFS, and SSP was obtained in terms of Z-average. As per test results, the SSP was finer than FA and GGBFS. Additionally, the PDI of raw materials was determined, which measures how unevenly the particles in a sample are distributed. The PDI, also referred to as the heterogeneity index, is a number obtained from the cumulants analysis of two parameters that were fitted to the correlation data. This dimensionless index is scaled such that a value greater than 0.7 indicates that the sample has an extremely wide particle size distribution, i.e., non-homogeneous distribution of particles [54, 55].

Further, one of the essential characteristics of raw materials, especially in the pelletization process, is the ability of particles to agglomerate or flocculate, which has been analyzed using the same instrument called zeta sizer in terms of zeta-potential. The zeta-potential value lies between + 30 and − 30 mv, considering that the particles in a sample can get agglomerate; the value nearer to zero indicates maximum agglomeration [56‐58]. According to obtained test results, the SSP was more capable of agglomerating, followed by FA and GGBFS. The values of the Z-average, PDI, and Zeta potential of all raw materials are reported in Table 1. The zeta-potential distribution of FA, GGBFS, and SSP is represented in Figs. 2 and 3.

The elemental composition of raw materials was determined using X-ray fluorescence spectroscopy (XRF) and is tabulated in Table 1. The main elemental composition of raw materials belongs to the Cao–SiO₂–Al₂O₃–Fe₂O₃ system. The morphological characteristics of FA, GGBFS, and SSP were studied by SEM. From Fig. 4, it can be observed that the particles of FA are spherical shaped with varied sizes and exhibit surfaces of smooth texture. In comparison, GGBFS particles are of angular shape with sharp edges and surfaces of smooth texture. The SSP particles exhibited a coral-reef-like or multi-layered hierarchical structure formed by stacking many similar flakes along parallel orientations.

The raw material sample’s mineral composition was identified using the XRD pattern. The diffraction peaks in the FA, GGBFS, and SSP samples are depicted in Fig. 5. The XRD was performed by focusing an X-ray beam on the material sample with a scanning rate of 0.02°/min from 5° to 80°. The XRD pattern of FA showed the same pattern reported in the literature [59‐61]. It was identified that the main crystalline phases in the FA were quartz and mullite. The XRD pattern of GGBFS shows an amorphous hump between the angel 2Ɵ = 20°–40°, and no such sharp diffraction peaks were detected; hence it contains an amorphous phase glass structure majorly identified as calcium silicate in accordance with the results of Bellum et al. [62], Coppola et al. [63], Divsholi et al. [64], Das et al. [65], and Zheng[66]. As seen by the peaks at various 2Ɵ angles in SSP confirms the presence of a chemical compound named calcium carbonate (CaCO₃), according to Vigneshwaran et al. [67] and Peng et al. [68] results and JCPDS 47-1743. The presence of CaCO₃ enhances the thermal and mechanical properties of the material.

Production of alkali-activated artificial aggregates

The artificial aggregates were produced using the pelletization technique, which mainly involves dry mixing, liquid spraying, agglomeration, collection of fresh pellets, and curing. The properties of artificial aggregates significantly depend upon the pelletization factors such as speed and angle of pelletizer, duration of pelletization, and curing regime in addition to raw material and binder properties. Hence, in a study, the pelletizer’s speed, angle, and pelletization duration were chosen based on previous research [20, 21, 29, 44, 51, 69, 70]. Figure 6 shows the disc-type pelletizer equipment, which has a 100 mm depth and 500 mm diameter pan with speed and angle variations from 1 to 65 rpm and 0–90°, respectively. In a study for the production of aggregate pellets, the angle and speed were maintained at 45° and 45 rpm, respectively, with a pelletization duration of 20 min.

Initially, the raw materials of around 3 kg were mixed in a rotating pelletizer disc for 2–3 min, followed by a sprinkling of alkali activator solution continuously until the moistened raw materials get agglomerated and formed pellets of the required size. After approximately 20 min, collected the fresh pellets carefully and kept them at an ambient temperature of 28 °C with a relative humidity of 85% for one day to attain the initial strength, then sealed and stored in the plastic bags until the testing period. At the end of the curing period, the aggregate pellets passing through a 20 mm IS sieve and retained on a 4.75 mm IS sieve were selected. The amount of alkali activator solution sprayed to the mixture was varied as the type of raw material used varied, which has been optimized based on the pelletization efficiency.

In a study, fourteen types of cold-bonded artificial aggregates were manufactured by employing the binary and ternary mix approach. A binary mix was made with FA, GGBFS, and an alkaline solution of molarity 8 and 10, while a ternary mix was made with FA, GGBFS, SSP, and an alkaline solution of molarity 10. In mixture nomenclatures, FA, GGBFS, and SSP are indicated by code letters F, G, and S. The number that comes after each code letter indicates the percentage of material used with respect to the total dry mixture mass. Additionally, the molarity of the alkaline solution is indicated by M. In the ternary mix, the dosages of SSP have been replaced with FA & GGBFS combination in the optimized binary mix (Base mix) at 5, 10, 15, and 20%. The optimization of the binary mix was done by considering the factors such as ease of handling the pellets in the pelletizer, pelletization efficiency, and physical and mechanical properties into account. The mix proportion of each type of aggregate is tabulated in Table 2. The overall production process of cold-bonded alkali-activated aggregates is illustrated in Fig. 7, and Fig. 8 presents pictures of all types of aggregates produced in the study.

Table 2

Mix proportions

Type No	Mix ID	Mix proportion (%)				Mix type
Type No	Mix ID	FA	GGBFS	SSP	Molarity (M)	Mix type
T1	F90G10M8	90	10	–	8	Binary
T2	F80G20M8	80	20	–	8
T3	F70G30M8	70	30	–	8
T4	F60G40M8	60	40	–	8
T5	F50G50M8	50	50	–	8
T6	F90G10M10	90	10	–	10
T7	F80G20M10	80	20	–	10
T8	F70G30M10	70	30	–	10
T9	F60G40M10	60	40	–	10
T10	F50G50M10	50	50	–	10
T11	F57.5G37.5S5M10	57.5	37.5	5	10	Ternary
T12	F55G35S10M10	55	35	10	10
T13	F52.5G32.5S15M10	52.5	32.5	15	10
T14	F50G30S20M10	50	30	20	10

Role of pelletization factors

The speed and the angle of inclination of the pelletizer disc and the duration of pelletization are considered pelletization factors [71]. These pelletization factors significantly influence the pelletization efficiency, water absorption, and strength of the aggregate pellets [71, 72]. The pelletization efficiency and strength of the aggregates depend more on the speed followed by the angle of the disc, and water absorption of aggregate depends more on the speed followed by the duration of pelletization [21, 72]. The improved pelletization efficiency, water absorption, and strength of pellets can be achieved with the increased speed of the pelletizer due to faster agglomeration of raw materials particles. However, this increased speed increases the collision between raw material particles and consolidation of nuclei until only a certain limit, after which centrifugal force prevents particles’ stratification, leading to particles stuck to the pelletizer’s side walls and hindering the agglomeration process [71, 73]. The angle of the pelletizer’s disc has a minor role in enhancing the properties mentioned above, but it influences the size and shape of the aggregate pellets. In the literature, researchers employed a pelletizer speed, angle of inclination of pelletizer disc, and duration of pelletization in the range 10–70 rpm, 20°–55°, and 10–20 min, respectively [1, 14‐16, 21, 47, 48, 74, 75]. Shivaprasad and Das reported that an increased speed from 30 to 50 rpm and an angle from 35° to 55° showed the least improvement in the properties of aggregate pellets [15]. Shi et al. revealed that reducing an angle (i.e., 30°) causes the formation of smaller size pellets (4–5 mm). In contrast, an increasing angle causes the breakdown of pellets due to gravitational force (i.e., 50°) [17, 76]. Baykal et al. [20] established the optimum range of speed, angle, and duration of pelletization as 35–55 rpm, 35°-55°, and 20 min, respectively, to obtain aggregate pellets of suitable properties. Gesoglue et al. and Ren et al. suggested the best speed and angle as 45 rpm and 45°, respectively [17, 19]. Hence, considering the above circumstances and suggested values, the pelletizer disc’s speed, angle, and pelletization duration were adopted as 45 rpm, 45°, and 20 min, respectively, to produce artificial aggregates in this study.

Role of geopolymerization factors

Previous studies involved different activators; the most commonly used were NaOH and Na₂SiO₃ [2, 14‐16, 26, 31, 48, 77, 78]. As the raw material section mentioned, the activators used in this study were also NaOH and Na₂SiO₃. The concentration or molarity of NaOH solution, Na₂SiO₃/NaOH ratio, and SiO₂/Na₂O are considered the Geopolymerization factors. These geopolymerization factors influence the properties of aggregate pellets [6, 50, 77]. In the literature, for the production of aggregates associated with the alkali-activation, the researchers employed molarity of NaOH varies between 6 and 16 M, Na₂SiO₃/NaOH ratio between 1.5 and 3.0, and SiO₂/Na₂O ratio between 2.0 and 3.3 [14‐16, 30, 31, 50, 77]. Razak et al. [77] found that higher molarity of NaOH of 16 M causes efflorescence and voids in the pellets due to reduced workability caused by excessive alkali concentration. In contrast, the lower molarity of NaOH of 6 M forms pellets of weak properties [48, 77] and finally suggested to use 10 M concentration of NaOH to produce aggregate pellets of good properties [77]. Dewa et al. [16] reported that the pellets produced with the Na₂SiO₃/NaOH ratio of 2.0–2.5 for a given molarity of NaOH showed the best size and shape compared to the ratio of 1.5 and 3.0. Shivaprasad and Das reported that the increased SiO₂/Na₂O ratio improved the properties of aggregates and revealed that a ratio of more than 2.0 is the most suitable [15, 31]. Hence, from the above-discussed parameters, the molarity of NaOH, Na₂SiO₃/NaOH ratio, and SiO₂/Na₂O were considered as 8 M and 10 M, 2.0, and 2.40, respectively, to manufacture the aggregates in this study.

Surface treatment of aggregates

Surface treatment is one of the most effective ways to enhance the performance of artificial aggregates [79]. In previous research [17, 51, 80], the aggregate pellet surfaces treated with water glass (Na₂O + SiO₂) have exhibited positive results on water absorption, crushing, and impact strength. Also, Shivaprasad and Das [31] revealed that solution curing had improved the pellet’s physical and mechanical properties. Hence in this study, immediately after collecting fresh pellets from the pelletizer, the pellet surfaces were treated by sprinkling the alkaline solution made with a mixture of NaOH (10 M) and Na₂SiO₃. The sprinkled solution creates a layer over the surface, enters the surface pores of pellets, and helps improve the characteristics [17, 51, 80].

Testing of aggregates

The alkali-activated aggregates produced were tested for particle size distribution, specific gravity, bulk density, water absorption, crushing strength, and impact strength according to standard specifications specified in the IS (Indian standards) codes. The overview of tests conducted on the aggregates is explained as follows.

Pelletization efficiency

Pelletization efficiency is expressed in terms of the percentage weight of aggregates having a size greater than 4.75 mm (retained on a 4.75 mm IS sieve) among the total weight of aggregates produced [14, 15, 30, 31]. After sufficient days of curing, the aggregates pellets of known weight were placed on the 4.75 mm IS sieve and subjected to manual sieving. The aggregates pellets retained on the sieve were weighed, then pelletization efficiency was determined using Eq. (1).

$${\text{Pelletization}}\;{\text{efficiancy }}\left( {\text{\% }} \right){ } = \frac{{{\text{Weight}}\;{\text{of}}\;{\text{aggregates}}\;{\text{retained }}\;{\text{on }}\;4.75\;{\text{mm}}\;{\text{IS}}\;{\text{sieve}}}}{{{\text{Total}}\;{\text{weight}}\;{\text{of}}\;{\text{aggregates}}\;{\text{produced}}}} \times 100$$

(1)

Particle size distribution

The particle size distribution of aggregates was determined using the standard set of sieves as per—IS 383:2016 [81] and IS 2386 (part 1):1963 [82]. Additionally, each type of aggregate’s fineness modulus (FM) was determined by calculating the cumulative percentage weight retained on each sieve divided by 100. To find the FM of coarse aggregates, it is required to have sieve sizes of 80 mm, 40 mm, 20 mm, 10 mm, 4.75 mm, 2.36 mm, 1.18 mm, 0.6 mm, 0.3 mm, and 0.15 mm. A FM is an index number that is typically used to determine how coarse or fine the aggregate is. When the FM value is higher, the aggregate is coarser, and when it is lower, the aggregate is finer. The FM of coarse aggregates of 20 mm size ranges between 6 and 8. The FM of aggregates used in the study was determined using Eq. (2).

$${\text{Fineness }}\;{\text{modulus}} = \frac{{{\text{Cumulative}}\;{\text{percentage }}\;{\text{weight}}\;{\text{retained}}\;{\text{on }}\;{\text{each}}\;{\text{sieve}}}}{100}$$

(2)

Specific gravity, bulk density, and water absorption

The produced alkali-activated aggregates were tested for specific gravity, bulk density, and water absorption as per—IS 2386:1963 part 3 [83]. The specific gravity of aggregates was tested using the pycnometer method, wherein one kg of aggregates of sizes ranging between 4.75 to 10 mm was selected. The specific gravity of aggregates was calculated by measuring the weights of oven-dry samples in air, saturated surface-dry samples in air, and saturated samples in distilled water. The bulk density of aggregates was checked for both compacted and loose conditions. In the compacted condition, the aggregates were filled in three equal layers, and each layer was compacted with 25 blows. In contrast, the aggregates were not subjected to any tamping action in loose conditions. The bulk density of dried aggregates was calculated by measuring the weight of aggregates in a given volume of a cylindrical metal container. The water absorption of aggregates was determined by placing the oven-dried aggregate sample in water for 24 h and calculating the ratio of the weight of water absorbed by the aggregate sample to the weight of oven-dried aggregate. The study calculated values of aggregate properties mentioned above using Eqs. (3), (4), and (5).

$${\text{Specific gravity}} = \frac{{{\text{W}}_{1} }}{{{\text{W}}_{2} - {\text{W}}_{3} }}{ }$$

(3)

W₁—weight of oven-dry aggregates in air, W₂—weight of saturated surface-dry aggregates in air, W₃—weight of saturated aggregates in water

$${\text{Bulk density }}\left( {{\text{kg}}/{\text{m}}^{3} } \right) = \frac{{\text{W}}}{{\text{V}}}$$

(4)

W—weight of aggregates in a cylindrical metal container, V—volume of a cylindrical metal container

$${\text{Water absorption }}\left( {\text{\% }} \right) = \frac{{{\text{B}} - {\text{A}}}}{{\text{A}}} \times 100$$

(5)

A—weight of oven-dry aggregates, B—weight of saturated surface-dry aggregates after 24 h of water immersion.

Aggregate crushing and impact value

The crushing and impact strength tests of aggregates were conducted as per IS- 2386:1963 part 4 [84]. The crushing value is the resistance shown by the aggregates against the gradually applied compressive load. In contrast, the impact value is the resistance exhibited by the aggregates against the sudden loads. The aggregates of size 12.5 mm IS sieve passing and retained on the 10 mm IS sieve were used to find both the crushing and impact value. The crushing and impact value of aggregates was found by calculating the ratio of the weight of the crushed aggregates passed through a 2.36 mm IS sieve to the total weight of aggregates subjected to testing, which can be seen in Eq. (6).

$${\text{Crushing}}\;{\text{or}}\;{\text{Impact}}\;{\text{value}}\left( {\text{\% }} \right) = \frac{{{\text{Weight }}\;{\text{of}}\;{\text{crushed}}\;{\text{aggregates}}\;{\text{passed}}\;{\text{through}}\;{\text{a }}\;2.36\;{\text{mm }}\;{\text{IS}}\;{\text{sieve}}}}{{{\text{Total}}\;{\text{weight}}\;{\text{of}}\;{\text{aggregates}}\;{\text{subjected}}\;{\text{to}}\;{\text{testing}}}} \times 100$$

(6)

Microstructure analysis

The microstructure of produced aggregates after 28 days of curing was analyzed using SEM micrographs and XRD patterns, which help in studying the aggregate’s morphological and mineralogical composition characteristics, respectively. In SEM, the sample was first subjected to gold sputtering to satisfy the conductivity measurement and to get quality micrographs. During testing, the microscope was operated at a voltage of 10 kv. In XRD, an X-ray beam was focused on the material sample with a scanning rate of 0.02°/min from 5° to 80°.

Results and discussions

In this article, obtained results of both binary and ternary mix alkali-activated artificial aggregates were discussed simultaneously. The ternary mix aggregates were produced by replacing FA and GGBS combinations in the optimized binary mix (Base mix) with SSP. The optimization of the binary mix was done by considering the factors such as ease of handling the pellets in the pelletizer, pelletization efficiency, and physical and mechanical properties into account. Hence, based on these parameters, a binary mix F60G40M10 was considered a base mix to produce ternary mix artificial aggregates. The dosages of SSP were replaced with FA and GGBFS combination in the base mix at 5, 10, 15 and 20%.

Pelletization efficiency

The pelletization efficiency or production efficiency of the aggregates was determined by calculating the percentage weight of aggregates retained on the 4.75 mm IS sieve against the total weight of aggregates produced.

The pelletization efficiency of aggregates produced in this study varied between 86 and 100%, as illustrated in Fig. 9. First, by considering the binary mix approach, it was found that aggregates of type T1 to T3 under the 8 M group and T6, T7, and T10 under the 10 M group showed less production efficiency compared to remaining types. The production efficiency increased with the increased percentage of GGBFS in a mix which is attributed to enhanced agglomeration. It can also be observed that T1 and T6 aggregates produced using 8 M and 10 M alkaline solution, respectively, containing the same proportions of FA and GGBFS, needed much effort to maintain uniform shape and size during production. However, finally, they formed in an approximately oval shape compared to the remaining aggregate types of perfectly rounded shape produced with less effort due to lack of agglomeration of particles in a T1 and T6 mix containing a minimum quantity binder in the form of GGBFS. Besides, the aggregate of type T10 showed a sudden decrement in pelletization efficiency due to the higher content of GGBFS in the mix, making the nucleation process faster, resulting in pellets subjected to pelletization for more time and forming aggregates of irregular shape marginally. Therefore, it is worth noting that the binder content beyond a specific limit might inhibit the size and shape of pellets. A similar result was drawn by Gomathi et al. and Vali et al. [85, 86] stated that the duration of pelletization influences the size, shape, and efficiency of aggregates.

Furthermore, it can be noted that an increased concentration of alkaline solution also improved the pelletization efficiency. For instance, the 8 M alkaline solution aggregates produced exhibited lower pelletization efficiencies than 10 M group aggregates of the same mix proportions except for the T10 type. The sudden decrease in the pelletization efficiency of an aggregate of type T10 (under 10 M alkaline solution) when compared to an aggregate of type T5 (under 8 M alkaline solution) containing the same mix proportion might be caused by the rapid development of more cohesive mix led to an early formation of pellets followed by their prolonged pelletization results in pellets of irregular shape. Hence, it can be clear that the amount of binder content and the concentration of the alkaline solution used in the mix have an essential role in forming aggregate pellets of the required shape and size. The above-drawn hypothesis can also be seen in previous literature stating that the pelletization efficiency increases with increased molarity of NaOH and binder content in the mix [28, 50, 85]. In the case of ternary mix aggregates made of FA, GGBFS, and SSP, it was found that all types have shown 100% pelletization efficiency, which is attributed to added seashell powder of higher nucleation or agglomeration ability [87, 88] and higher specific area in addition to higher content of GGBFS.

Considering the duration of pelletization, in the binary mix group, it was noticed that the minimum time required to convert the mix into pellets was reduced as the GGBFS content in the mix increased. The minimum time taken by each type of mix to convert into pellets was between 15 to 11 min, while in the ternary group, the minimum time taken by each mix type to convert into pellets was significantly less, between 11 to 8 min. Hence, it can be revealed that seashell powder plays an essential role in nucleating the raw material particles into a pellet in a short duration [87, 88]. So, all formed pellets will get more time to undergo compaction by collision with one another, and to sidewalls of the pelletizer result in pellets of good strength.

Particle size distribution and fineness modulus

The size growth of the pellets depends on the pelletization duration, pelletizer angle, speed, and the type of binder used [21, 47, 48, 85, 89, 90]. Figure 10a–c depicts the gradation curves of the produced aggregates under binary and ternary mix groups, respectively. The aggregates of type T1, T2, and T6 are of slightly irregular shape, resulting in non-uniform distribution of particles compared to all remaining aggregates belonging to the well-graded category. The particle sizes of produced aggregates of all mixes range between 4.75 and 20 mm, with a maximum percentage of particle size ranging between 4.75 and 16 mm, satisfying the specified grading requirements for the 20 mm size of IS 383-2016 [81]. In addition, the average size of the aggregates indicated by the fineness modulus is represented in Fig. 11a and b. The FM of artificial aggregates produced under binary and ternary mix ranges between 6.57 and 6.96 and 6.53–6.76, and they correspondingly indicated average size ranges between 7.74 and 9.79 mm and 7.53–8.74 mm, respectively. Hence, from the visual notice and the above results, it can be concluded that the aggregates were spherical with a rough texture comprised of particles of all sizes, well-graded and comparable to natural aggregates. Lastly, the molarity of the NaOH solution has a negligible effect on the size of the aggregate pellets according to aggregates produced that have almost the same particle size distribution. This finding is quite comparable to previous work by Risdanareni et al. [47] in which an increased concentration of NaOH has not changed the particle size distribution of pellets.

Specific gravity

Although the use of similar material for the manufacture of aggregates is associated with alkali activation, in most of the literature [14, 15, 25, 35, 51, 74, 78], it can be seen that the specific gravity of alkali-activated artificial aggregates showed an irregular or random pattern of results varied between 1.02 and 2.86. This incident demonstrated that pelletization factors and concentration of alkaline solution significantly impact aggregate performance [72, 91]. The test results of alkali-activated artificial aggregates produced in this study are presented and shown in Fig. 12a and b. It was found that the specific gravity of all produced artificial aggregates varied between 1.70 and 2.16, lying in a category of lightweight aggregates compared to natural aggregates exhibiting specific gravity of 2.58. In the binary mix group, the aggregates of type T1 produced with 8 M alkaline solution exhibited the lowest specific gravity (1.70), and the T10 type aggregate under the 10 M group recorded the highest specific gravity (2.16). The obtained results show that the specific gravity of aggregates increased with the increased percentage of GGBFS in a mix, which is attributed to the higher specific gravity of GGBFS than FA [2] and the use of calcium during the alkali-activation process [17, 19, 91‐93]. In addition, the improvement in the specific gravity of aggregates was observed with the increased concentration of an alkaline solution [72, 77, 85].

Considering the results of ternary mix aggregates, all aggregates showed an almost similar value of specific gravity around 2.05–2.09, close to the specific gravity of base mix aggregates. It can be observed that the addition of SSP to the mix by replacing FA and GGBFS in equal percentages shows no further effect by increasing specific gravity. This is attributed to SSP of lower specific gravity compared to GGBFS.

Bulk density

The bulk density measures an aggregate’s ability to occupy a given volume, and it depends mainly on the shape of the aggregates [74]. Furthermore, it is the key factor in deciding the density and self-weight or dead load of the structural components of concrete [2]. Similar to the case with specific gravity, the bulk density of alkali-activated artificial aggregates varied significantly with respect to the pelletization factors, geopolymerization factors, and processing methods [91]. The bulk densities of most materials described in previous research [1, 2] ranged between 700 and 1500 kg/m³, similar to the density of ordinary aggregates but more suitable for lightweight applications [2, 77]. The bulk density of all produced artificial aggregates tested for compacted and loose conditions is presented in Figs. 13a and b and 14a and b. The obtained results show that the loose and compacted bulk densities of artificial aggregates are between 1176.19 and 1298.43 kg/m³ and 1176.74 and 1314.88 kg/m³, respectively. In a binary mix group, both loose and compacted bulk densities were increased with the increased percentage of GGBFS (decreased percentage of FA) in a mix, which is attributed to GGBFS of higher specific gravity [2, 78, 85] and of unique role in making paste matrix denser due to enhanced alkali activation supported by the composition of GGBFS compared to FA [18, 26, 78, 94]. For instance, T6 type aggregates showed the loose and compacted bulk density of 1223.86 kg/m³ and 1275.25 kg/m³, respectively, for a 10% addition of GGBFS to the mix, while T10 type aggregates showed 1298.43 kg/m³ and 1314.88 kg/m³ for 50% addition of GGBFS. From the results, it was also observed that the increased concentration of the alkaline solution had increased aggregate density and a similar hypothesis can be seen in previous research work by Risdanareni et al. who found increased density with the increased concentration of NaOH solution [26, 47, 50, 85]. In a ternary mix, the aggregates were produced by adding SSP in different percentages to the base mix (F60G40M10) by removing FA and GGBFS in equal parts. The results show that the aggregates produced with 5% and 10% replacement of SSP have exhibited lower density than the density of base mix aggregates (T9), but it has crossed at 15% replacement. It is mainly due to the lower specific gravity of SSP than GGBFS, and it can be confirmed that the SSP has no such reactivity role and acts as filler material [38, 39, 87, 95].

From the results, it can be concluded that variation in density values between all mix group aggregates was relatively marginal due to the aggregate pellets’ rounded shape [2]. A comparison was also made between the natural and artificial aggregates, and it was observed that artificial aggregates had lesser densities than natural aggregates. The maximum and minimum densities observed for T10 and T1 type aggregates were 14.81% and 21.77% lighter than natural aggregates.

Water absorption

Water absorption of aggregate reveals the internal structure of it. Higher water absorption of aggregates shows more pores, which often adversely affects aggregates [91]. The precursors used in processing the aggregates had a substantial impact on this [6, 91]. Water absorption of artificial aggregates produced in this study was determined after 24 h of immersion in water, as shown in Fig. 15a and b, and it ranges between 4.95 and 0.7%, which can be considered the best results compared to previous literature [1, 2, 6, 15, 26‐28, 31, 45, 48, 74, 77, 78, 96‐102]. Among the produced artificial aggregates, aggregates of type T9, T10, and T13 showed water absorption ranging between 0.7 and 0.75%, comparable to natural granite aggregates of 0.5%. In addition to other influential factors, the surface treatment of artificial aggregates with the alkaline solution has contributed an essential role in achieving this low water absorption. The sprayed alkaline solution creates a layer on the aggregates’ surface; part of the solution penetrates the surface pores of aggregates, making them denser and also helping to enhance the alkali-activation process. A similar surface treatment effect was also observed in the research conducted by Ren et al. [17] and Shivaprasad et al. [31] From the findings, it can be observed that the aggregates having more density showed reduced water absorption and which can be supported by the literature stating that water absorption of artificial aggregates and density have an inverse relationship, i.e., water absorption decreased as the density of aggregates increased [19, 43, 90, 91, 101, 103]. In the binary mix group, the aggregates containing a combination of 90% FA and 10% GGBFS have shown more water absorption. This is mainly due to tiny pores and cracks, as shown by a microscopic image in Fig. 18c; it can be justified based on lower density, which implies that aggregates are permeable. The water absorption has gradually decreased with the increased addition of GGBFS in a mix. For instance, aggregates of type T1 to T5 under the 8 M group and T6 to T10 under the 10 M group containing an orderly decreased percentage of FA and increased percentage of GGBFS in the combination, showed water absorption of the order 4.95–1.05% and 4.15–0.7%, respectively. This is attributed to the formation of more geopolymer gel, close packing, higher density, and refined pore size of aggregates [19, 26, 78, 85, 104]. Further, it can be supported by the research conducted by Bui L et al. using the same raw materials and alkaline solution, found that the increased addition of GGBFS to FA had decreased the water absorption, especially the 50% addition had exhibited the lowest water absorption and revealed that the addition of GGBFS makes the microstructure denser by forming a greater amount of C–S–H gel results in the refinement of pores and porosity of aggregates [78]. It can also be observed that an increased concentration of alkaline solution has reduced the water absorption of aggregates due to enhanced geopolymer reaction. In a study, a 10 M concentration alkaline solution used to produce aggregates has decreased water absorption of aggregates in the 18–20% range compared to the 8 M alkaline solution. A similar hypothesis can be seen in most of the research stating that the increased molarity of NaOH positively affects water absorption.

In the ternary mix, it can be observed that the addition of SSP to the base mix up to 15% shows a positive effect on the water absorption, which is attributed to improved nucleation or agglomeration of powder mix leads to the formation of pellets of enhanced packing and denser structure. However, further addition of SSP by 20% has made the nucleation process faster, resulting in the formation of sticky pellets experiencing a lesser compaction pressure, resulting in raised water absorption. In addition, aggregates produced under a ternary group showed water absorption closer to base mix aggregates. However, they did not cross its value, possibly due to the reduced GGBFS content in the mix.

Aggregate impact value

Impact value is the ability of the aggregates to resist sudden load or sudden shock on it. For pelletized aggregates, it depends mainly on the pelletization factors, type and amount of binder used in the mix, and geopolymerization factors. The impact values of all types of artificial aggregates produced in this study are presented in Fig. 16a and b. In the binary mix group, it can be clear from the results that the increased addition of GGBFS has increased the impact strength of aggregates and achieved a higher strength compared to previous literature [2, 6, 15, 89, 91, 96, 99] and natural aggregates. For instance, under the 10 M group, the aggregates containing GGBFS of 20%, 30%, 40%, and 50% have improved impact strength by 17.19%, 17.56%, 18.19%, and 24.34% relative to aggregates containing 10% of GGBFS. It suggests that the GGBFS addition decreased the porosity of the matrix and improved the strength by forming a compact microstructure due to increased C–S–H and calcium-based geopolymer formation [2, 78, 91, 105]. Regarding the concentration of an alkaline solution, the molarity of NaOH plays a vital role in improving the impact strength of aggregates [17, 72]. This hypothesis is supported by aggregates of type T1–T5 under the 8 M group presented impact values in the range of 22.90–12.46%, and T6–T10 under the 10 M group in the range of 15.94–12.06%. In-depth, it might be attributed to the enhanced dissolution ability of raw materials at increased molarity, thus the availability of an adequate amount of Si⁴⁺ and Al³⁺ to involve in the geopolymerization process with high alkalinity medium [77].

Initially, adding 5% and 10% SSP in the ternary mix showed lower impact strength than the impact strength of base mix aggregates due to the reduced content of GGBFS in the mix. However, adding SSP by 15% exhibited aggregates of higher impact strength, which is more than the base mix aggregates and the highest among the remaining aggregates produced in a study. This can be due to the availability of a sufficient proportion of SSP to fill the voids. Moreover, the early agglomeration of powder particles into pellets and these pellets experiencing compaction pressure for a longer time by colliding with each other and to the pelletizer sidewalls results in a more densified and strengthened matrix. It can also be observed that the further addition of SSP of about 20% showed aggregates of declined strength, which is attributed to the restrained production process indicating faster nucleation of a mix, making aggregate pellets of sticky nature resulting in non-appearance of compaction pressure by the collision between the pellets required to form a densified matrix.

In addition to the influential factors discussed above, the surface treatment of aggregates with an alkaline solution also showed a significant part in achieving greater strength. Furthermore, the AIV has a direct relationship with bulk density and an inverse relationship with water absorption, i.e., aggregates with higher density presented higher impact strength, aggregates with higher water absorption presented lower impact strength, and vice versa [91]. Overall, the aggregates of all types produced in a study demonstrated the AIV within the acceptable limit given by IS:2386-1963 part 4 [84] after 28 days of curing age.

Aggregate crushing resistance value

The aggregate crushing value indicates the resistance to crushing under a gradually applied compressive load. The crushing value of all aggregates produced in a study ranged between 27.53 and 18.49%, as shown in Fig. 17a and b, and followed a similar result pattern as seen in the aggregate’s impact value. In the binary mix group, the aggregates of type T1 and T10 indicated the lowest and highest crushing strength. It can be observed that the increased binder content and concentration of NaOH solution improved the crushing strength by enhancing the agglomeration process and aggregate microstructure [2, 32, 77, 91, 106]. In the ternary mix, the addition of SSP of 15% exhibited higher crushing strength than the aggregates containing SSP of 5% and 10% and base mix aggregates. While aggregates made of 20% SSP declined the crushing strength abruptly due to the restrained production process caused by the faster nucleation given by the SSP, resulting in the formation of an adhesive or muddy mix.

Furthermore, the aggregates produced in this study exhibited higher crushing strength than the artificial aggregates in the literature [47, 48, 107], considering that the former had a lower density and greater water absorption than the latter. Compared to natural aggregates, the crushing strength of aggregates in this research was quite similar and within the acceptable limit given by IS:2386-1963 part 4 [84] after 28 days of curing age.

Microstructure

From the experimental data, it can be identified that an increase in GGBFS content will enhance the mechanical characteristics of the artificial aggregates. However, binder composition with GGBFS content beyond 40% would cause ill effects on artificial aggregates, such as increased size, crumbling, loss of uniform shape, and disturbed gradation of aggregates. Hence, the artificial aggregates exhibiting the best mechanical properties, morphology, and gradation were considered for microstructure studies.

SEM

From Fig. 18a, it can be observed that the aggregates’ surface contains many unreacted fly ash particles with micro-cracks on its surface. With the same binder composition, smooth and compact surfaces with fewer loose particles are observed in Fig. 18b. It is because of the increase in molarity, which provides more active hydroxyl ions for the geopolymerization, leading to better mechanical properties and compact microstructure. In Fig. 18c, it is noticed that in spite of using a 10 M activator solution, unreacted fly ash particles accumulated on the surface, and it does not appear to be smooth and intact. Micro pores confirm its pervious nature, which is also reinforced by higher water absorption values. Reduction in mechanical properties was observed when GGBFS content was reduced from 40 to 10% because of the lesser availability of active calcium ions to initiate polymerization at ambient temperature.

In Fig. 18d, the surface appears compact and impervious. However, the surface is not smooth and adheres to less quantity of unreacted loose particles on it. The increment in calcium ion due to the SSP will enhance nucleation, leading to aggregate formation at a lesser duration with the highest mechanical characteristics and dense matrix and better microstructural characteristics. These artificial aggregates with binder composition of 52.5% FA, 32.5% GGBFS, and 15% SSP with 10 M activator solution exhibited optimum mechanical behavior and enhanced microstructural characteristics.

XRD

The produced aggregate’s mineralogical compositions were determined by X-ray diffraction. Figure 19 shows the XRD pattern of aggregate types T4 (F60G40M8), T6 (F90G10M10), T9 (F60G40M10), T11 (F57.5G37.5S5M10), T12 (F55G35S10M10), and T13 (F52.5G32.5S15M10). Complex compounds are formed due to the chemical reaction between the binary and ternary blend mixes, which produces semi-crystalline peaks. As predicted, all binary and ternary alkaline-activated aggregate samples contain quartz, the main inorganic crystalline mineral constituent. Quartz is an unreacted particle in all aggregates, as seen at 2Ɵ = 21.64°, 27.12°, and 50.48°, respectively (PDF: 00-005-0490). This outcome is consistent with earlier studies by Sasui et al.[108], and Kamath et al. [109]. In the binary mix, the increased addition of GGBFS and molarity of alkaline solution results in decreased peak intensity of quartz mainly due to enhanced alkali-activation and formation of additional gel to the aggregate pellet. For instance, aggregates of type T9 produced with 40% GGBFS and 10 M alkaline solution has shown quartz of decreased peak intensity compared to aggregates containing GGBFS of 10% and 8 M alkaline solution. In the ternary mix, the aggregate samples containing SSP of 5%, 10%, and 15% exhibited orderly decreased peak intensity of quartz, revealing further enhanced alkali-activation of aggregate pellet results in improved properties compared to binary mix pellets.

The process of alkali-activation in the case of binary and ternary mix aggregate pellets, as shown in Fig. 19, results in the formation of gels that include calcium silicate hydrate (C–S–H), sodium aluminosilicate hydrate (N–A–S–H) and calcium aluminosilicate hydrate (C–A–S–H). The C–S–H can be seen at 2Ɵ = 29° and 64° (PDF: 00-003-0649), C–A–S–H and N–A–S–H present simultaneously in the form of sodium–calcium–alumina–silicate–hydrate (NCASH) at 2Ɵ = 33° and 36° (PDF: 00-025-0777). A similar XRD pattern can be seen in a study by Muralidhar Kamath et al. [109].

Conclusions

The following conclusions from the research study reported here that are relevant to the properties of the artificial aggregates and methods employed, as well as the variety of analyzed parameters, are outlined below:

The pelletization efficiency of artificial aggregate pellets ranged between 86 and 100%. With the addition of SSP, 100% pelletization efficiency can be achieved due to its high nucleation ability.

The increased content of SSP and GGBFS aids nucleation to form pellets in a lesser duration of 8–11 min.

The specific gravity of all artificial aggregates ranged from 1.70 to 2.16, lesser than natural coarse aggregates. The increased content of GGBFS and molarity of NaOH increased the specific gravity of artificial aggregates.

The difference in density among various combinations of artificial aggregates is marginal due to their rounded shape. The loose and compacted bulk density of artificial aggregates was in the range of 1176.19–1298.43 kg/m³ and 1176.74–1314.88 kg/m³, respectively, which are lighter by 14–21% compared to natural coarse aggregates.

The water absorption of artificial aggregates ranged between 4.95 and 0.7%. The aggregates containing 50% GGBFS achieved the lowest water absorption of 0.7%, comparable to natural coarse aggregates. The surface treatment of artificial aggregates with the alkaline solution contributed to achieving low water absorption.

The impact and crushing values ranged between 12.06 and 22.9% and 18.49–27.53%, respectively, lower than natural coarse aggregate and within the acceptable limit given by IS:2386-1963 part 4. The aggregates blended with SSP of 15%, FA of 52.5%, and GGBFS of 32.5% exhibited the highest strength by attaining the lowest impact and crushing values of 12.06% and 18.49%.

SEM micrographs revealed that the aggregates blended with 52.5% of FA, 32.5% of GGBFS, and 15% of SSP with 10 M activator solution showed better microstructural characteristics by forming a compact and dense matrix with lesser unreacted particles. XRD results confirmed the alkali activation process in the aggregate pellets by forming hydrated products, including, C–S–H, C–A–S–H, and N–A–S–H, which have a more significant role in enhancing the properties of aggregates.

Declarations

Conflict of interest

The authors have no relevant financial or non-financial interests to disclose.

Ethical approval

This paper neither was published nor is under review elsewhere.

All the authors are aware of this paper.

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Titel: Producing of alkali-activated artificial aggregates by pelletization of fly ash, slag, and seashell powder
verfasst von: Gopal Bharamappa Bekkeri
Kiran K. Shetty
Gopinatha Nayak
Publikationsdatum: 01.10.2023
Verlag: Springer International Publishing
Erschienen in: Innovative Infrastructure Solutions / Ausgabe 10/2023
Print ISSN: 2364-4176
Elektronische ISSN: 2364-4184
DOI: https://doi.org/10.1007/s41062-023-01227-1

Springer Professional

Abstract

Introduction

Significance of the study

Raw materials and characterization

Production of alkali-activated artificial aggregates

Role of pelletization factors

Role of geopolymerization factors

Surface treatment of aggregates

Testing of aggregates

Pelletization efficiency

Particle size distribution

Specific gravity, bulk density, and water absorption

Aggregate crushing and impact value

Microstructure analysis

Results and discussions

Pelletization efficiency

Particle size distribution and fineness modulus

Specific gravity

Bulk density

Water absorption

Aggregate impact value

Aggregate crushing resistance value

Microstructure

SEM

XRD

Conclusions

Declarations

Conflict of interest

Ethical approval

Informed consent

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