Search Results (14)

The cements industry is increasingly under pressure to reduce carbon emissions while maintaining performance standards. Limestone calcined clay cement (LC³) presents a promising low-carbon alternative; however, its performance depends significantly on the type and reactivity of clay used. This study investigates the effect of three common low-grade clay minerals—kaolinite, montmorillonite, and illite—on the behavior of LC³ blends. The clays were thermally activated and characterized using X-ray diffraction (XRD), thermogravimetric analysis (TGA), X-ray fluorescence spectroscopy (XRF), and Blaine air permeability testing to evaluate their mineralogical composition, thermal behavior, chemical content, and fineness. Pozzolanic reactivity was assessed using the modified Chapelle test. Microstructural development was examined through scanning electron microscopy (SEM) of the hydrated specimens at 28 days. The results confirmed a strong correlation between clay reactivity and hydration performance. Kaolinite showed the highest reactivity and fineness, contributing to a dense microstructure with reduced portlandite and enhanced formation of calcium silicate hydrate. Montmorillonite demonstrated comparable strength and favorable hydration characteristics, while illite, though less reactive initially, showed acceptable long-term behavior. Although kaolinite delivered the best overall performance, its limited availability and higher cost suggest that montmorillonite and illite represent viable and cost-effective alternatives, particularly in regions where kaolinite is scarce. This study highlights the suitability of regionally available, low-grade clays for use in LC³ systems, supporting sustainable and economically viable cement production. Full article

With the increasing demand for lithium resources and the enhancement of global environmental awareness, how to efficiently and environmentally develop clay-type lithium resources is of great strategic significance for future development. Clay-type lithium slag (LS) is a byproduct resulting from the extraction of lithium from clay-type lithium ores. Its primary chemical constituents include SiO₂ and Al₂O₃, and it exhibits potential pozzolanic properties. Clay-type lithium ore is of low grade, so a large amount of clay-type LS is produced during its production. In this study, calcined clay-type LS, limestone powder (LP), and cement clinker were used as the main raw materials to prepare low-carbon LC³ cementitious materials. The study focused on the effect of clay-type LS and LP on the new mixing properties, mechanical properties, hydration kinetics, and microstructure formation and transformation of the cementitious materials. The findings revealed that incorporating clay-type LS and LP significantly raised the standard consistency water demand of cement and reduced the setting time of the binding material. While clay-type LS and LP initially weakened the mechanical performance of the cement mortar, it enhanced these properties in the later stages. The compressive strength of LC-10 and LC-20 at 180 days exceeded that of the reference by 3.7% and 1.1%, respectively. In addition, the number of micropores between 3 and 20 nm in LC³ cement increased significantly. It showed that the addition of clay-type LS and LP could optimize the pore structure to some extent. According to research, the optimal content of clay-type LS and LP should not exceed 30%. This method not only consumes the solid waste of clay-type LS, but also facilitates the green and low-carbon transformation of the cement industry. Full article

Recent studies have shown the viability of low-grade calcined clays as a partial substitute for cement in construction applications. However, there is limited information about the performance of low-grade calcined clay in withstanding chloride-rich environments. This paper investigates the durability performance of mortar prepared by partially substituting cement with low-grade calcined clay. Naturally occurring clay having a kaolinite content of 17% was calcined at 900 °C, blended and used to prepare composite cement samples containing up to 40% by weight low-grade calcined clay. Durability studies were conducted using the rapid chloride penetration test (RCPT), freeze and thaw, sorptivity, permeable porosity, ultrasonic pulse velocity (UPV), and autogenous shrinkage. The incorporation of calcined clay resulted in significant improvements in durability properties, including reductions in sorptivity, permeable porosity, and chloride ion penetration. Additionally, enhanced freeze–thaw resistance was observed, indicating the ability of calcined clays to mitigate deterioration under harsh environmental conditions. These improvements in durability translate to extended service life and reduced maintenance requirements for concrete structures. Full article

This paper reviews the performance of low-grade calcined clay as a partial substitute for Portland cement in concrete, emphasizing its potential to enhance sustainability in construction. Thermal treatment of naturally occurring clays at optimal temperatures produces amorphous siliceous materials with pozzolanic properties. Clays with substantial kaolinite content exhibit significant pozzolanic reactivity when calcined at temperatures between 700 and 850 °C, with effective firing possible up to 1000 °C. Research shows that replacing Portland cement with calcined clays improves the mechanical and durability properties of concrete, with replacement levels ranging from 10% to 60%, depending on factors such as chemical composition, mineralogy, and reactivity. This paper synthesizes recent findings on low-grade calcined clays with 60–80% purity, which are more abundant, cost-effective, and easier to produce, particularly in developing regions lacking the resources and technology to process high-purity clays (>95% purity). Key aspects explored include calcination methods, optimal firing temperatures, and their effects on particle size distribution and pozzolanic activity. This study also examines the impact of low-grade calcined clay on fresh and hardened concrete and the durability properties of concrete and mortar. By providing a comprehensive analysis, this review highlights the potential of low-grade calcined clays to contribute to more sustainable and durable concrete production, emphasizing the need to optimize calcination processes and fully harness their pozzolanic properties. Full article

Limestone Calcined Clay Cement (LC³) has become a highlighted research topic over the past decade. Through various research, LC³ demonstrated the capability to supplement portions of cement, highlighting the possibility to decrease CO₂ emissions due to the low calcination temperatures and low levels of CO₂ released from the material during calcination. At this stage, there is no research into the feasibility of LC³ in any parts of Australia, limited research in finding clay, and incomplete research understanding how low calcination temperatures affect the compressive strength. The results show the feasibility of LC³, where we demonstrated the feasibility of a low calcination temperature of 650 °C and found that various overburden waste clays (clay in quarries and mines that are not needed) across the East Coast of Australia produced comparable compressive strength results to conventional Portland cement-based mixes. The results also indicate that optimising the particle size distribution of the calcined clay enhanced both the workability and compressive strength of the mortars. Full article

LC3 (limestone calcined clay cement) is poised to become the construction industry’s future as a so-called low-carbon-footprint cement. Research into this subject has determined the minimum kaolinite content in calcined clays to guarantee good mechanical performance. This study examines the use of clay from the Valencian Community (Spain), which has a lower kaolinite content than the recommended amount (around 30%) for use in LC3 and how its performance can be enhanced by replacing part of that clay with metakaolin. This study begins with a physico-chemical characterisation of the starting materials. This is followed by a microstructural analysis of cement pastes, which includes isothermal calorimetry, thermogravimetry, and X-ray diffraction tests at different curing ages. Finally, this study analyses the mechanical performance of standard mortars under compression to observe the evolution of the control mortars and the mortars with calcined clay and metakaolin over time. The results show that the LC3 mortars exhibited higher compressive strength in the mixtures with higher calcined kaolinite contents, achieved by adding metakaolin. Adding 6% metakaolin increased the compressive strength after 90 days, while 10% additions surpassed the control mortar’s compressive strength after 28 days. Mortars with 15% metakaolin exceeded the control mortar’s compressive strength after just 7 curing days. The hydration kinetics showed an acceleration of LC3 hydration with metakaolin additions due to the nucleation effect and the formation of monocarboaluminate and hemicarboaluminate (both AFm phases). The results suggest the potential for combining less reactive materials blended with highly reactive materials. Full article

The high kaolinite content of metakaolin makes it valuable to other industries, thereby affecting its availability and affordability for the production of limestone calcined clay cement (LC³). This work presents a study on the potential utilization of low-grade clay in place of pure metakaolin in the preparation of LC³ for mortar formulations. CEM I was partially substituted with calcined clay and limestone by 20, 30, 40, and 50 wt.%. The weight ratio of calcined clay and limestone was maintained at 2:1 for all mixes and the water-to-binder ratio was 0.48. X-ray diffraction (XRD), thermogravimetric analysis (TGA), and isothermal conduction calorimetry were used to study the hydration process and products after 28 days. Mechanical and durability assessments of the LC³ mortar specimens were conducted. LC³ specimens (marked LC20%, LC30%, LC40%, and LC50%) trailed the control sample by 1.2%, 4%, 9.8%, and 18%, respectively, at 28 days and 1.6%, 2.3%, 3.6%, and 5.5%, respectively, at 91 days. The optimum replacement of OPC clinker, calcined clay, and limestone was 20% (LC20%). Full article

Low-grade calcined clay, due to its low cost, availability and low temperature calcination, has been gaining attention in recent times as a supplementary cementitious material (SCM) in the manufacture of revolutionary building materials to improve the fresh and hardened properties of concrete. Silica fume, on the other hand, has been used, over the years, to improve the performance of concrete due to its reduced porosity and improved transition zone quality. In spite of the individual contribution of these two pozzolans to the strength and durability of concrete, there is a knowledge gap in the properties of ternary blended mixes utilizing calcined clay and silica fume. In this study, the synergistic effect of calcined clay and silica fume on the fresh and hardened properties of cementitious mortar have been investigated. The two pozzolans were used to partially substitute Portland cement to form a ternary blended composite binder having, at a maximum, a replacement of 30% by weight and a varying content of calcined clay and silica fume. The influence of the binary and ternary blended mixes on hydration, pozzolanic reactivity and the mechanical and durability properties of mortar was studied. From the results, partial replacement of cement with 30% calcined clay and silica fume caused significant reductions in the portlandite content of the two hydrated pastes at all curing ages. Drying shrinkage was found to be less severe in the control mortar than the blended cement mixes. Compared to the blended cement specimens, the control suffered the most weight (13.3%) and strength (10%) losses, as indicated by the sulphate resistance test. Full article

Availability of aluminosiliceous materials is essential for the production and promotion of geopolymer concrete. Unlike fly ash, which can only be found in industrial regions, clays are available almost everywhere but have not received sufficient attention to their potential use as a precursor for geopolymer synthesis. This study investigates the effectiveness of calcined clay as a sole and binary precursor (with fly ash) for the preparation of geopolymer mortar. Fly ash-based geopolymer containing between 0 and 100% low-grade calcined clay was prepared to investigate the effect of calcined clay replacement on the geopolymerization process and resultant mortar, using a constant liquid/solid ratio. Reagent-grade sodium hydroxide (NaOH) and sodium silicate (Na₂SiO₃) were mixed and used for the alkali solution preparation. Six different mortar mixes were formulated using sand and the geopolymer binder, comprising varying fly ash-to-calcined clay ratios. The combined effect of the two source materials on compressive strength, setting time, autogenous shrinkage, and porosity was studied. The source materials were characterized using XRD, SEM, FTIR, and XRF techniques. Isothermal calorimetry was used to characterize the effect of low-grade calcined clay on the geopolymerization process. The addition of calcined clay reduced the surface interaction between the dissolved particles in the alkali solution, leading to slow initial reactivity. Geopolymer mortar containing 20% calcined clay outperformed the reference geopolymer mortar by 5.6%, 17%, and 18.5% at 7, 28, and 91 days, respectively. The MIP analysis revealed that refinement of the pore structure of geopolymer specimens containing calcined clay resulted in the release of tensional forces within the pore fluid. Optimum replacement was found to be 20%. From this study, the mutual reliance on the physical and inherent properties of the two precursors to produce geopolymer mortar with desirable properties has been shown. The findings strongly suggest that clay containing low content of kaolinite can be calcined and added to fly ash, together with appropriate alkali activators, to produce a suitable geopolymer binder for construction applications. Full article

Results of experimental investigation on the mitigation of alkali–silica reaction (ASR) by low-grade calcined clay are presented. Domestic clay with an Al₂O₃ content equal to 26% and SiO₂—58% was used. The calcination temperatures were as follows: 650 °C, 750 °C, 850 °C and 950 °C, which were chosen much more widely than presented in previous studies. Pozzolanity of the raw and calcined clay was determined with the Fratini test. The performance of calcined clay to mitigate ASR was evaluated according to ASTM C1567 using reactive aggregates. A control mortar mixture was prepared with 100% Portland cement (Na₂O_eq = 1.12%) as a binder with reactive aggregate, and test mixtures were made with 10% and 20% of calcined clay as a cement replacement. The microstructure of the specimens was observed on the polished sections using scanning electron microscope (SEM) operated in backscattered mode (BSE). The results of expansion of mortar bars with reactive aggregate showed that replacing cement with calcined clay reduced the expansion of the mortar bars. The greater the cement replacement, the better results in terms of ASR mitigation. However, the influence of the calcination temperature was not as clear. The opposite trend was found with the use of 10% or 20% calcined clay. Full article

This article presents the results of an experimental investigation into the mitigation of the alkali–silica reaction (ASR) resulting from using low-grade clay calcined at 850 °C. The clay used in the experiment was domestic clay with an Al₂O₃ content equal to 26% and a SiO₂ content of 58%. The performance of calcined clay in ASR mitigation was evaluated according to ASTM C1567 using reactive aggregates. The control mortar mixture consisted of 100% Portland cement (Na₂O_eq = 1.12%) binder and reactive aggregate. The test mixtures used the same reactive aggregate and binders, in which part of the cement was replaced with either 10%, 20% or 30% calcined clay. The microstructure of specimens was examined on the polished sections using a scanning electron microscope (SEM) operated in the backscattered mode (BSE). The results of expansion obtained from the mortar bars made with the reactive aggregate showed that replacing cement by calcined clay reduced their expansion, with the level of expansion decreasing with the increase in the level of cement replacement. Full article

The availability of some supplementary cementitious materials, especially fly ash, is of imminent concern in Europe due to the projected closure of several coal-fired power generation plants. Pure kaolinitic clays, which arguably have the potential to replace fly ash, are also scarce and expensive due to their use in other industrial applications. This paper examines the potential utilisation of low-grade kaolinitic clays for construction purposes. The clay sample was heat-treated at a temperature of 800 °C and evenly blended with Portland cement in substitutions of 10–30% by weight. The physical, chemical, mineralogical and mechanical characteristics of the blended calcined clay cement were determined. The Frattini test proved the pozzolanic potential of the calcined impure clay, as a plot of its CaO and OH⁻ was found below the lime solubility curve. The 28 days compressive strengths trailed the reference cement by 5.1%, 12.3% and 21.7%, respectively, at all replacement levels. The optimum replacement level between the three blends was found to be 20 wt.%. Full article

The potential application of alkali-activated material (AAM) as an alternative binder in concrete to reduce the environmental impact of cement production has now been established. However, as the production and availability of the primarily utilized waste materials, such as fly Ash and blast furnace slag, decrease, it is necessary to identify alternative materials. One such material is clay, which contains aluminosilicates and is abundantly available across the world. However, the reactivity of untreated low-grade clay can be low. Calcination can be used to activate clay, but this can consume significant energy. To address this issue, this paper reports the investigation of two calcination methodologies, utilizing low-temperature and high-temperature regimes of different durations, namely 24 h heating at 120 °C and 5 h at 750 °C and, and the results are compared with those of the mechanical performance of the AAM produced with untreated low-grade clay. The investigation used two alkali dosages, 10% and 15%, with an alkali modulus varying from 1.0 to 1.75. An increase in strength was observed with calcination of the clay at both 120 and 750 °C compared to untreated clay. Specimens with a dosage of 10% showed enhanced performance compared to those with 15%, with Alkali Modulus (AM) of 1.0 giving the optimal strength at 28 days for both dosages. The strengths achieved were in the range 10 to 20 MPa, suitable for use as concrete masonry brick. The conversion of Al (IV) is identified as the primary factor for the observed increase in strength. Full article

The goal of this study is to investigate the effects of different grades of calcined clay on the extrudability and early-age strength development under ambient conditions. Four mix designs were proposed. Three of them contained high, medium, and low grades of calcined clay, respectively, and one was the reference without calcined clay. In terms of extrudability, an extrusion test method based on the ram extruder was introduced to observe the quality of extruded material filaments, and to determine the extrusion pressure of tested materials at different ages. For evaluating the very early-age strength development, the penetration resistance test, the green strength test, and the ultrasonic pulse velocity test were applied. Furthermore, the mechanical properties of the developed mix designs were determined by the compressive strength test at 1, 7 and 28 days. Finally, the main finding of this study was that increasing the metakaolin content in calcined clay could significantly increase the extrusion pressures and green strength, shorten the initial setting time and enhance the compressive strength at 1, 7, and 28 days. Full article