Calcined Clay Research Articles

Long-term performance of MgO\u2013SiO2 binder

Magnesium silicate hydrate (M–S–H) formed on reaction of MgO and reactive SiO2 imparts binding characteristics similar to Portland cement (PC). Limited knowledge is available on the long-term mechanical and durability performance of M–S–H binder systems. In this study, the performance of MgO–SiO2 binder was assessed up to 365 days. In addition to silica fume (SF), the most widely used silica source with MgO, calcined clay (CC) with kaolinite content of ~ 40–50% and industrial grade metakaolin (MK) were also investigated. Mortar specimens were prepared with all the three silica sources at three different proportion levels of MgO and silica source. Thermodynamic modelling was carried out to further understand the changes occurring in the phase assemblage during hydration for the adopted proportions. Concrete mixes comprising of MgO and MK or SF in a ratio of 1:1 and PC as a control mix were cast a water to binder ratio of 0.4. The compressive strength and porosity were measured at 7, 28, 90 and 365 days on mortar and concrete specimens. In addition, elastic modulus and electrical resistivity was also measured on the concrete samples at all the above-mentioned ages. MgO mixes with CC and MK showed a continual increase in compressive strength until 365 days whereas strength retrogression was observed in MgO–SF mixes after 90 days. The durability indicators for MgO–MK concrete showed better or similar performance as compared to PC. The aluminum present in the CC and MK helps to improve the overall characteristics of the MgO–SiO2 binder.

A Study on Gel/Space Ratio Development in Binary Mixture Containing Portland Cement and Meta-Illite Calcined Clay/Rice Husk Ash.

Supplementary cementitious materials (SCMs) have been widely used to enhance both the microscopic and macroscopic properties of the Portland cement (PC)–SCM composite matrix. Few studies have been undertaken to establish the gel/space ratio of meta-illite calcined clay (MCC) and rice husk ash (RHA)-based high-performance concrete (HPC) mortar. This experimental paper describes a conventional degree of hydration (non-evaporable water) and porosity routes of establishing a link amid the gel/space ratio and compressive strength of a sieved mortar from Class 1 (50–75 MPa) HPC at an early age. Using the non-evaporable water method, this paper predicted the gel/space ratio of the hardened MCC/RHA-based HPC mortars and curved fitted into Powers’ exponent equation. The results from this study revealed that MCC or RHA additions (5–30% by weight of PC) to the PC-SCM matrix led to a moderate decline in the compressive strength of the low water-binder ratio (W/B) HPC mortar. The modification aimed at void volume (superabsorbent polymers, SAP, and air) applying Bolomey’s formula and Powers’ gel/space ratio developed a suitable fitting into the Powers’ model. This experimental procedure shows feasibility to predict the MCC and RHA outcome on the compressive strength of HPC.

Influence of processing parameters variation on the development of geopolymeric ceramic blocks with calcined kaolinite clay

The cement industry is responsible for a considerable part of the emission of gases that cause the greenhouse effect. In this context, geopolymer materials have been the subject of extensive studies, as they are an ecologically sustainable viable alternative to Portland cement. The geopolymer consists of a part rich in silica and alumina and another alkaline activating fraction, not having burning steps in its production chain, which consequently reduces the emission of CO2. Geopolymers also allow the incorporation of specific residues in its precursor part, such as calcined clays. The specimens for this study were produced by the molding process, using commercial metakaolin as the basis for the precursor fraction. After demolding, the test cups were subjected to ambient curing at 25 °C and thermal curing at 80 °C, for periods of 7, 14 and 28 days. The objective of this work was to analyze the behavior of geopolymers specimens against the variation of several parameters such as percentage of calcined clay (CC) incorporation into metakaolin in 10% and 20%, its granulometry in 100 and 200 Mesh, the molar ratio of SiO2/Al2O3, type and period of cure to evaluate technological properties such as resistance to bending, open porosity, water absorption, linear shrinkage and bulk density, aiming for future applications in the production of ceramic bricks. The results showed that an increase in the percentage of CC incorporation contributes to an improvement in the flexural strength, reaching 4.88 MPa to 20%. The molar SiO2/Al2O3 ratio of 3.0 was the most ideal. The importance of this study is linked to the evaluation of several parameters for the incorporation of calcined clay, in order to obtain properties required for future applications in ceramic bricks.

Mitigating the ecological footprint of alkali-activated calcined clays by waste marble addition

Low-CO2, Portland-free cement binders can be produced by reaction of calcined clays in alkaline solutions, although the environmental footprint associated with alkaline activators may represent a point of concern. The amount of alkaline activator, and its embodied CO2, can be reduced by partial replacement of calcined clay with waste marble. Fresh and hardened state properties, as well as compositional and microstructural evolution of alkali-activated blends of calcined clay and waste marble, were investigated by combining experimental methods with thermodynamic modelling. It was shown that substitution of calcined clay with 30% waste marble was beneficial to the workability and mechanical properties of alkali-activated binders and can mitigate drying shrinkage. The physical and chemical role of calcium carbonate and the composition of the reaction products were discussed, along with the role of carbonation reactions occurring by uptake of atmospheric CO2. This approach can contribute to both reducing the CO2 footprint of cement and upcycling potentially hazardous waste from the dimension stone industry.

Effect of Bacillus Sphaericus Bacteria on the Calcined Clay Incorporated Cement Concrete

The partial substitution of Ordinary Portland Cement (OPC) with Supplementary Cementitious Materials is the most efficient way to reduce CO2 emissions in the worldwide cement production business (SCMs). Calcined clay can be considered one of the successful CO2 emission reduction techniques to achieve this. Calcined clay is used as an SCM in this study to replace cement to varied degrees in the pro-portions of 10%, 15%, and 20%. The self-healing capabilities of concrete are also investigated using calcined clay and Bacillus Sphaericus bacteria with a bacterial population of 108 cells/ml. Samples were evaluated for water absorption and compressive strength at 7, 14, and 28 days, respectively. When bacteria-embedded concrete is used in place of some calcined clay, the compressive strength of the concrete is raised by 21 percent, 24 percent, and 25 percent at 28 days. The bacteria in the calcined clay reduce the concrete's porosity and boost its compressive strength as a result, making concrete building more efficient and cost-effective.

Compressive strength, water absorption and pulse velocity tests of calcined clay- limestone cement mortars

The cement industry consumes a lot of energy and releases CO2 to the environment causing air pollution. The replacement of Portland cement is one way to reduce CO2. This research investigated the replacement of Portland cement (PC) by calcined clay (CC) and Limestone (LS). It was found that compressive strength reduced when using LS as PC replacement. On the other hand, using CC content from 10% to 30 wt% can improve the compressive strength in limestone mixes and reduce water absorption and void content. The mortar content of 30 wt% calcined clay gave the highest compressive strength, the lowest water absorption and void content. The pulse velocity test results were found to have a trend similar to that of the compressive strength results which showed a direct relationship between pulse velocity and compressive strength.[copyright information to be updated in production process]

Belite Limestone Calcined Clay Cements

Belite Limestone Calcined Clay Cements

Oxidation of pyrite (FeS2) and troilite (FeS) impurities in kaolinitic clays after calcination

Valorisation of locally available clays for producing blended cements is crucial for a widespread adoption of sustainable binders incorporating these materials. In some places, clays can be intermixed with small amounts of iron sulfides, which could eventually expand in the alkaline media of concrete and lead to cracking if clay particles are sufficiently fine. This study explored the stability of iron sulfides, namely troilite and pyrite, during calcination of clays and their influence in reactivity. It was found that both troilite and pyrite decompose and oxidize into hematite under typical calcination conditions for clays. Furthermore, there is no negative influence of the presence of iron sulfide phases on the reactivity of calcined clays. This shows that these clays are suitable for use in blended cements, provided that adequate quality control is conducted to ensure a complete decomposition of the iron sulfide phases.

Dynamical properties of environmental high-performance composites with calcined clay

Concrete structures may be exposed to dynamic loadings within short periods such as earthquakes and vehicles load, resulting in substantial damage to human life and property because of the collapse of concrete structures. The research achievements on dynamic properties of high-performance composites with LC3 (HPC-LC3) are limited, although dynamic loadings are commonly encountered in infrastructure. The study aims to develop a new-green concrete product (HPC-LC3) with high dynamical properties and promote its mass use in a vibration service environment by investigating dynamical properties of HPC-LC3. Dynamical properties of structure can be promoted at material level by means of enhancing the inherent ability of cement-matrix materials to passively absorb the vibrational energy. Dynamic properties of traditional HPC may be improved by incorporated LC3 because of excellent mechanical properties. The fiber pull-out, thermogravimetric analysis (TGA), (nuclear magnetic resonance) NMR, and microstructure test were used to reveal the enhanced mechanism of dynamic properties in the HPC with LC3 (HPC-LC3), and the economic efficiency of HPC is also evaluated to promote its mass application. The results indicate that the dynamic properties of HPC-LC3 increased by 47% in damping capacity, 102% in storage modulus, 16% in energy dissipation, in comparison with the reference (HPC-OPC). Meanwhile, compared with the reference, the compressive and flexural strengths of LC3-50 increased by 14% and 27%. TGA and NMR results indicate that LC3-50 shows better hydration characteristics, longer alumina-silicate chain length (from 3.9 to 8) than HPC-OPC. The proposed composites reduced embodied energy, embedded CO2 emissions, and costs of HPC by up to 33%, 45%, and 7%, respectively. Thus, the green product (HPC-LC3) with 30%–40% calcined clay, high dynamic properties and more sustainable, will be recommended to mass use in a vibration service environment.

Performance of sustainable mortar using calcined clay, fly ash, limestone powder and reinforced with hybrid fibers

Green mortar (GM) is a mortar that at least one of its components uses waste materials or materials that do not cause environmental destruction throughout their production. This research aims to design a mortar with the highest possible cement and sand substitutions with acceptable fresh and hardened properties. The experimental work was conduct in three phases. In phase one, calcined clay replaced cement by 20%, 25%, 30%, 35%, and 40% in mortar mixes. Then, the cement replacement raises to 50% by substituting cement with a combination of calcined clay (CC) and fly ash (FA) in different percentages in other mortar mixes. In phase two, limestone powder (LP) partially replaced sand by 20% and 30% (by weight) in two of the chosen mixes from phase one that contained high cement replacement and fairly good fresh and hardened properties. Then environmental impacts of GM mixes have been evaluated by estimating the reductions of CO2 emissions from producing such mixes. Phase three involved the effects of incorporating 0.5% fibers (by volume) on the properties of GM using two types of steel fibers with different aspect ratios. Ultra steel fibers (USF) with an aspect ratio of 65 and steel nail fibers (SNF) with an aspect ratio of 20. The inclusion of hybrid fibers was by combining USF and SNF in different percentages while maintaining the same volumetric fraction of 0.5%. The fresh and hardened properties have been determined in phase three also. The results show that replacing OPC with 25% CC provides the best increment on compressive strength by increasing the compressive strength by about 21% at 28 days. The use of 20% LD as sand replacement increases the flow and 28 days-compressive strength by about 55% and 13%, respectively, for the mortar that contains 35% CC+ 15% FA. The test results of reinforced mixes show that the hybridization of 0.175% USF and 0.325% SNF affords the best enhancements on the mechanical properties. The results obtained from the estimated reduction of CO2 emissions study reveal that incorporating 30% CC + 20% FA as cement replacements and 30% LP as a sand replacement reduces the CO2 emissions by approximately 41%. Therefore, adopting the concept of green mortar is a promising approach for mitigating CO2 emissions and preserving natural resources.

Clay calcination technology: state-of-the-art review by the RILEM TC 282-CCL

The use of calcined clays as supplementary cementitious materials provides the opportunity to significantly reduce the cement industry’s carbon burden; however, use at a global scale requires a deep understanding of the extraction and processing of the clays to be used, which will uncover routes to optimise their reactivity. This will enable increased usage of calcined clays as cement replacements, further improving the sustainability of concretes produced with them. Existing technologies can be adopted to produce calcined clays at an industrial scale in many regions around the world. This paper, produced by RILEM TC 282-CCL on calcined clays as supplementary cementitious materials (working group 2), focuses on the production of calcined clays, presents an overview of clay mining, and assesses the current state of the art in clay calcination technology, covering the most relevant aspects from the clay deposit to the factory gate. The energetics and associated carbon footprint of the calcination process are also discussed, and an outlook on clay calcination is presented, discussing the technological advancements required to fulfil future global demand for this material in sustainable infrastructure development.

Recycled sand from sandstone waste: A new source of high-quality fine aggregate

The construction industry is facing a shortage issue of river sand, therefore broadening new sources of fine aggregate is imminent. This paper demonstrates the feasibility of a recycled sand from sandstone waste in mortar manufacturing by comprehensive assessment of workability, mechanical properties, water absorption, alkali silica reaction (ASR). The recycled sandstone sand (S-sand) has a smoother microscopic morphology and better particle size distribution than river sand (R-sand). Fine particles smaller than 150 µm in R-sand usually contain a large amount of impurities (such as clay) and are considered harmful. However, the S-sand containing ∼15.7% µm quartz grains <150 µm significantly improves the mortar performance in terms of compressive strength and ASR property. At the same water to binder ratio, the mortar using the S-sand shows worse workability than that using R-sand but a slight increase of water to binder ratio or adding water reducer improves not only the workability but also mechanical properties. For the ASR test, the S-sand shows potential uncertain risk as per ASTM C 1260. Using calcined clay or fly ash to replace 25% cement can effectively inhibit expansion risk. The compressive strength is reduced due to ASR, however, as the ASR progresses, it is somehow restored. This study also finds the good linear relationship between length change of mortar bar and mass change, which can be used to predict the sand ASR property. The results showed that S-sand produced by waste sandstone by-products can be used as high-quality fine aggregate.

High temperature impact on calcined clay-limestone cement concrete (LC3)

A lot of CO2 is released into the atmosphere during the manufacturing process of cement, which causes a global warming problem. Calcined clay-limestone cement concrete (LC3) can be used to partially solve this problem. Limestone cement concrete is produced from calcined clay-limestone cement which is an advanced ternary mixed cement formed by the combination of 30 percent low-grade calcined clay, 15 percent limestone powder, and 5 percent gypsum and 50 percent cement clinkers. That means 50 percent of cement clinkers are to be replaced by additional cementitious materials which are beneficial for reducing CO2 emission at the time of production of cement. In the present study, calcined clay-limestone cement is used to prepared concrete and compare it with concrete using ordinary portland cement (OPC) of grade 53. The physical and chemical characteristics of prepared cement samples were carried out and compared with OPC. M30 grade of concrete was prepared by calcined clay-limestone cement; mechanical properties such as compressive strength (CS) test are carried out on prepared concrete. After the age of 28 days, M30 grade of concrete was exposed to 100 °C, 200 °C, 400 °C, 600 °C, and 800 °C temperature, surface texture, weight loss, compressive strength test were carried on the cubes of size 150 × 150 × 150 mm3. The SEM analyses were carried out over 100 °C and 600 °C temperature on OPC and calcined clay-limestone cement concrete. The result shows that the compressive strength reduces with an increase in exposed temperature. The compressive strength decreases after 200 °C and significant losses occur after 400 °C. When the temperature reached 400 °C, noticeable minute cracks started to appear on the surface of the cube specimens.

Limestone Calcined Clay Cement for Three-Dimensional- Printed Engineered Cementitious Composites

Limestone Calcined Clay Cement for Three-Dimensional- Printed Engineered Cementitious Composites

Suitability of Blending Rice Husk Ash and Calcined Clay for the Production of Self-Compacting Concrete: A Review.

One principal approach to achieve self-compacting properties is the increased amount of finer constituents of the mixture. This, in turn, increases cement consumption leading to higher greenhouse gas emissions. Pozzolanic materials, like rice husk ash or calcined highly kaolinitic clays, have gained increased attention as supplementary cementitious materials in self-compacting concrete production. These materials could be viable alternative supplementary cementitious materials for sub-Saharan Africa which already lacks fly ash, slag and silica fume. This current effort reviews the impact of rice husk ash and calcined clays for the production of self-compacting concrete. Special focus is on their impact on rheological, mechanical and durability properties of self-compacting concrete. Rice husk ash and, in particular, calcined highly kaolinitic clays are introduced as technical and cost-effective supplementary materials for use in self-compacting. The review disclosed a lack of knowledge when it comes to the use of low-kaolinitic calcined clays as sole SCM or together with rice husk ash, which could be a very promising combination for e.g., several countries in Africa. Further studies are needed on the rheological properties, shrinkage, creep, and durability of self-compacting concrete produced with other calcined common clays and their blend with rice husk ash.

Environmental and technical assessment to support sustainable strategies for limestone calcined clay cement production in Brazil

This study analyzed the mechanical and environmental performance of an alternative low-carbon cement (Limestone Calcined Clay Cement, LC3) made from different Brazilian natural and waste clay-based materials. Data from an extensive laboratory program to characterize the alternative materials have been utilized. A Life Cycle Assessment (LCA) based on a cradle-to-gate approach was also performed. The results give decision-makers and the cement industry a better understanding of environmental impact at regional, national, and local levels. Moreover, this study opens a new perspective on the natural and waste clay-based materials to further the production of eco-efficient cements in Brazil and other countries.

Random Forest Modeling for Fly Ash-Calcined Clay Geopolymer Composite Strength Detection

Geopolymer is an eco-friendly material used in civil engineering works. For geopolymer concrete (GPC) preparation, waste fly ash (FA) and calcined clay (CC) together were used with percentage variation from 5, 10, and 15. In the mix design for geopolymers, there is no systematic methodology developed. In this study, the random forest regression method was used to forecast compressive strength and split tensile strength. The input content involved were caustic soda with 12 M, 14 M, and 16 M; sodium silicate; coarse aggregate passing 20 mm and 10 mm sieve; crushed stone dust; superplasticizer; curing temperature; curing time; added water; and retention time. The standard age of 28 days was used, and a total of 35 samples with a target-specified compressive strength of 30 MPa were prepared. In all, 20% of total data were trained, and 80% of data testing was performed. Efficacy in terms of mean absolute error (MAE), root mean square error (RMSE), coefficient of determination (R2), and MSE (mean squared error) is suggested in the model. The results demonstrated that the RFR model is likely to predict GPC compressive strength (MAE = 1.85 MPa, MSE = 0.05 MPa, RMSE = 2.61 MPa, and R2 = 0.93) and split tensile strength (MAE = 0.20 MPa, MSE = 6.83 MPa, RMSE = 0.24 MPa, and R2 = 0.90) during training.

A Mass Balance Approach for Thermogravimetric Analysis in Pozzolanic Reactivity R3 Test and Effect of Drying Methods.

The reactivity of supplementary cementitious materials (SCMs) is a key issue in the sustainability of cement-based materials. In this study, the effect of drying with isopropanol and acetone as well as the interpretation of thermogravimetric data on the results of an R3 test for evaluation of the SCM pozzolanic reaction were investigated. R3 samples consisting of calcium hydroxide, potassium hydroxide, potassium sulphate, water, and SCM were prepared. Besides silica fume, three different types of calcined clays were investigated as SCMs. These were a relatively pure metakaolin, a quartz-rich metakaolin, and a mixed calcined clay, where the amount of other types of clays was two times higher than the kaolinite content. Thermogravimetric analysis (TGA) was carried out on seven-day-old samples dried with isopropanol and acetone to stop the reaction processes. Additional calorimetric measurement of the R3 samples was carried out for evaluation of the reaction kinetics. Results show that drying with isopropanol is more suitable for analysis of R3 samples compared to acetone. The use of acetone results in increased carbonation and TGA mass losses until 40 (isothermal drying for 30 min) and 105 °C (ramp heating), indicating that parts of the acetone remain in the sample, causing problems in the interpretation of TGA data. A mass balance approach was proposed to calculate calcium hydroxide consumption from TGA data, while also considering the amount of carbonates in the sample and TGA data corrections of original SCMs. With this approach, an improvement of the linear correlation of TGA results and heat release from calorimetric measurement was achieved.

Comparison of limestone calcined clay cement and ordinary Portland cement for stabilization/solidification of Pb-Zn smelter residue.

Decreasing carbon emissions by replacing Portland cement (PC) with supplementary cementitious materials (SCMs), such as low-grade limestone (LS) and calcined clays (CC), has tremendous potential for stabilization/solidification (S/S) of industrial hazardous waste primarily with heavy metals. Recently, a low-carbon-based cementitious binder, namely, limestone calcined clay cement (LC), has emerged as an alternative for S/S treatment of wastes. However, comprehensive comparison between LC and PC application in solidifying/stabilizing wastes has not been conducted. This study aims to investigate the S/S efficiency of Pb-Zn smelter residue (LZSR) comprising heavy metals lead (Pb), zinc (Zn), and cadmium (Cd) at higher concentrations. LZSR is treated with LC and PC for capturing strength and leaching toxicity. The test results indicate that low-grade CC and LS in the LC binder can promote the alkaline environment, and act as fillers in solidifying heavy metals. The toxicity characteristic leaching procedure leaching concentrations of untreated (UT) LZSR were 503 mg/kg, 1266 mg/kg, and 251 mg/kg for Pb, Zn, and Cd, respectively. After a 28-day curing, the leaching concentrations in LC-treated LZSR reduced to 4.33 mg/kg, 189.68 mg/kg, and 0.46 mg/kg, while the leaching concentrations of PC-treated LZSR reduced to 29 mg/kg, 338 mg/kg, and 6 mg/kg for Pb, Zn, and Cd, respectively. The maximum immobilization efficiencies for Pb, Zn, and Cd reached 85%, 99%, and 99%, respectively. Moreover, the insoluble phases for Pb, Zn, and Cd obtained from the sequential extraction test results were 63.5%, 72.1%, and 42.4% for LC-treated LZSR and 35.7%, 38%, and 43% for PC-treated LZSR with binder content of 8% binder and curing time of 28 days. Increasing curing time and binder content reduced leaching concentrations, and the underneath mechanisms were interpreted by XRD, SEM-EDS, and FTIR analyses. Overall, the results indicate that Pb, Zn, and Cd can be successfully immobilized using 8% LC binder by transforming soluble heavy metals to insoluble hydroxides and their complexes.

In Situ Measurements of the Chemical Stability of a Cast Aluminum Alloy Embedded in a Cement Paste with a High Amount of Supplementary Cementitious Material

In traditional reinforced concrete, the alkaline pore solution which passivates the steel rebars will get neutralized with time in an exposed environment. Therefore, to prevent corrosion initiation, the permeability of the concrete is reduced and extra-thick concrete covers the steel rebars. Aluminum is passive in the neutralized environment, but the calcium hydroxide formed during the cement hydration will dissolve the aluminum. By substituting 55% of the cement in traditional cement paste with fast reactive supplementary cementitious material (SCM), aluminum will be compatible over time. In the initial state however, before the SCM consumes the hydroxide formed during the rapid cement hydration by the pozzolanic reaction, aluminum may corrode. Hydrogen gas then develops, resulting in a porous cement region enclosing the rebars with potentially reduced bond strength. In the present work, the chemical stability of a sand-cast aluminum lattice embedded in a paste where cement is replaced by 55% calcined kaolinitic clay is investigated by gas chromatography and open-circuit potential during the cement hydration. The hydrogen gas development stagnated for all measurements, indicating that aluminum is compatible with the novel cement paste. Two stable potentials were observed for the non-heat-treated samples, indicating the formation of a metastable complex. Being able to use aluminum-reinforced concrete constructions would result in an extraordinary long service life with low cement consumption, which will potentially result in a substantial reduction in the third-largest CO2 emitting industry.