Calcined Clay Research Articles

Thermal activation of kaolinite through potassium acetate intercalation: A structural and reactivity study

Calcined clays have emerged as a suitable alternative to partially replace conventional cement due to their high pozzolanic activity. This study explores a novel activation methodology for kaolinite, aiming to obtain metakaolin at lower temperatures than conventional thermal activation. This methodology involves a prior intercalation stage with potassium acetate (KAc) before thermal activation. The effectiveness of KAc intercalation was assessed through X-ray diffraction (XRD), indicating an intercalation ratio of approximately 90%. Several calcined temperatures were tested in accordance with the thermal behaviour analyzed through thermogravimetric analysis (TGA). Once calcined, the intercalated kaolinites exhibited enhanced reactivity compared to conventional calcined clays in the range between 400 °C to 550 °C, as demonstrated by modified Chapelle and Si/Al availability tests. A comprehensive structural characterization was conducted to facilitate a better understanding of the novel KAc-based metakaolin reactivity through various techniques (XRD, 27Al - 1H MAS NMR, and TGA). This focused on the crystalline changes in the kaolinite structure, the evolution of Al atoms conformation, and the OH behaviour at different thermal activation temperatures. Overall, this study highlights the potential of KAc intercalation as a strategy to obtain higher metakaolin content at lower temperatures than through conventional thermal treatments, offering insights into the development of its potential use as supplementary cementitious materials or alternative cementitious materials precursor.

Utilization of industrial waste sodium sulfate for calcined clay-based sustainable binder

This study explored the utilization of industrial waste Na2SO4 to develop a calcined clay-based sustainable cementitious composite inspired by ancient Roman concrete. Na2SO4 with or without the addition of NaCl was utilized, keeping the total Na2O quantity constant, and their performances at the macro and micro scale were compared. A separate set of samples was prepared using seawater. A medium-grade calcined clay, along with lime, was utilized as the binder. The salts were first dissolved in water and then used as the mixing water for sample preparation. A diverse array of characterization methods was utilized, encompassing thermogravimetric analysis, chemical extraction, X-ray diffraction (XRD), and Backscattered Scanning electron microscopy (SEM). It was observed that the salt-containing batches achieved compressive strength faster than the seawater samples. However, the strength remained in a comparable range (∼30 MPa) for all the samples after 28 days of curing. The initial strength of salt-containing samples was attributed to the formation of gypsum, ettringite, and hydrocalumite. Additionally, the geopolymer gel and calcium aluminum silicate hydrate (C-A-S-H) gel phases were present in all samples. Finally, this study also showed that lime-clay mortars can achieve a reduction in carbon footprint of up to 50 % compared to ordinary portland cement (OPC) mortars.

Feasibility of using calcined clays and reclaimed coal ashes in binary and ternary cementitious systems

This study evaluates the feasibility of using three different calcined clays (CCs) to partially replace ordinary Portland cement (OPC) in concretes. Furthermore, the best performing CC was investigated in conjunction with the addition of reclaimed fly ash (RFA) or reclaimed ground bottom ash (GBA) to partially replace OPC. OPC replacement levels by mass considered in the present study for both binary (i.e., OPC + CCs) and ternary (i.e., OPC + CC + GBA or RFA) cementitious systems were 10, 20, and 30 %. It was shown that, relative to the control mixture (CO), the utilization of CCs can significantly improve properties of the hardened concrete, at the cost of significantly reducing the workability of fresh concrete mixtures. Conversely, the incorporation of coal ashes to form ternary system produced concretes with superior hardened properties (relative to CO) while partially mitigating workability loss. Overall, both binary and ternary systems can produce concretes with significantly higher strength and surface resistivity. Additionally, characteristics of CCs that could be used as rapid indicators to predict their performance as supplementary cementitious materials (SCMs) in concrete were identified by coupling materials characterization techniques and concrete test results.

Strain-hardening magnesium-silicate-hydrate composites (SHMSHC) utilizing reactive magnesia cement (MgO) and calcined clay (metakaolin)

This study demonstrated the feasibility of utilizing calcined clay (metakaolin) as a silica source for the development of polyethylene (PE) fiber-reinforced strain-hardening magnesium-silicate-hydrate composite (SHMSHC). The study also discussed the effects of variation in the Mg/Si ratio of the mixture when pure silica source (silica fume with SiO2 content >90 %) is replaced with metakaolin (SiO2 content ⁓ 51 %) on the mechanical performance of SHMSHC. A comprehensive mechanical characterization of SHMSHC at composite scale and fiber-matrix interaction effects was conducted. The damage characterization was carried out using residual crack width and spacing analysis. The chemical characterization of the MSH matrix (SHMSHC without fibers) was performed using XRD, TGA, and FTIR, and the microstructural investigation was done using FE-SEM. The MgO-metakaolin paste based SHMSHC showed compressive strength of 51.9 MPa, tensile strength of 5.0 MPa, and tensile strain capacity of 4.7 %, demonstrating the feasibility of calcined clay utilization in SHMSHC. The tensile strain capacity was reduced after the addition of aggregates in SHMSHC. The study demonstrated that the variation in the Mg/Si ratio significantly affects the toughness of the MSH matrix and fiber-matrix interaction characteristics, influencing the strain-hardening potential of SHMSHC.

Low-carbon microwave curing of limestone calcined clay cement (LC3): Performance and mechanism

Limestone calcined clay cement (LC3) incorporates calcined clay and limestone as supplementary cementitious materials that can replace up to 50 % of conventional cement, significantly reducing the carbon emissions associated with cement production. However, challenges remain, including the inefficiencies of traditional curing methods and suboptimal early strength properties. Consequently, this study presents the low-carbon microwave curing approach for LC3 mortar. A comparative analysis of 15 different microwave curing systems was carried out. The results show that the optimum microwave curing efficiency is 300 W of heating power, 5 minutes of heating, 25 minutes of rest, and eight cycles. Three curing methods, including microwave curing, standard curing, and steam curing, were also compared. Microwave curing significantly increased the early strength of LC3 mortar, with 1-day compressive strength 1.78 times greater than standard curing and 1.26 times greater than steam curing. Microscopic studies show that the “thermal effect” of microwaving increases the internal Hc content of LC3, promotes the secondary hydration reaction of Ca(OH)2 within the LC3 material, and reduces the porosity of LC3, achieving reductions of 37.8 % and 8.9 % compared to standard and steam curing, respectively. This helps to improve the efficiency of the curing process. The results of this research will advance the use of low-carbon LC3 in building structures.

Alkali-activated calcined clay blended cement: Effect of NaOH activator on performance of HPEG PCEs and on early strength

The effect of NaOH on dispersing performance of HPEG PCE superplasticizers and early strength was studied in a calcined clay (CC) blended cement (OPC:CC = 70:30 wt./wt.). Activator impact on workability and mechanical properties was investigated on mortar via fluidity and strength tests. The results revealed a time-dependent impact. At early ages (16 h – 3 d), the strength of the NaOH-activated OPC/CC blend exceeds that of OPC, while at longer curing times (> 3 d) it is ∼ 30 % below that of OPC. Among the HPEG PCEs tested, the polymer possessing a medium long side chain (nEO = 50) performed best. Generally, NaOH addition prompted significantly increased PCE dosages. Heat flow calorimetry and in-situ XRD measurements suggest that NaOH promotes initial hydration of both OPC and CC, but later delays OPC reaction. Zeta potential measurements confirmed that NaOH significantly reduces the adsorbed amount of PCE on the binder, thus explaining higher dosage requirement.

Developing Geopolymer Composites with Structural Damage Control Potential: Utilization of Blast Furnace Slag, Calcined Clay, and MWCNT

Developing Geopolymer Composites with Structural Damage Control Potential: Utilization of Blast Furnace Slag, Calcined Clay, and MWCNT

3D Printing of Fiber-Reinforced Calcined Clay-Limestone-Based Cementitious Materials: From Mixture Design to Printability Evaluation

Sustainability and limitations in embedded reinforcement are the main obstacles in digital fabrication with concrete. This study proposed a 3D printable fiber-reinforced calcined clay-limestone-based cementitious material (FR-LC3). The binder systems incorporating calcined clay (CC) and limestone filler (LF) were optimized by determining the flow characteristics and water retention ability of the paste. The effect of fiber volume on the key fresh and mechanical properties of the fiber-reinforced mortars made with the optimized binder was evaluated. A combination of offline assessments and inline printing were employed to investigate the printability of the FR-LC3 with various binder systems and viscosity-modifying admixture (VMA) dosages. The results revealed that the binary system with 20% CC and the ternary system containing 30% CC and 15% LF were highly advantageous, with enhanced packing density, robustness, and water retention ability. Incorporating 2% 6-mm steel fiber contributed to the highest 28-day compressive and flexural strengths and toughness without significantly compromising the fluidity. Finally, the developed FR-LC3 mixtures were successfully printed using an extrusion-based 3D printer. The LF addition in the ternary system decreased the maximum buildable height of a single-wall printed object while reducing the SP/VMA ratio significantly increased the height due to enhanced yield stress and thixotropy.

Керамика древнеберингоморской культуры со стоянки возле утеса Кожевникова (мыс Шмидта): особенности технологии

During the excavations of a dugout at the Kozhevnikov Cliff site (Cape Schmidt), N.N. Dikov obtained a collection of pottery vessels of the Old Bering Sea culture (fourteen specimens). The technology of ceramic production was analyzed using the methodology developed by A.A. Bobrinsky. It was determined that potters selected iron-rich clays of two subtypes, differing in the amount of natural sand content, for pottery production. Five recipes for the molding clay were identified, including three unmixed: 1) clay + sand (7 specimens); 2) clay + wool (3 specimens); 3) clay + organic solution (2 specimens); and two mixed – 4) clay + sand + organic solution (1 specimen); and 5) clay + sand + wool (1 specimen). The vessels were made in a base form, and the shape was additionally formed by paddling. On the outer surface of one artifact, a strap handle with an ear for threading a cord was made, and the remaining hole on the inside was patched with a cloth scrap. The surfaces of the vessels were treated by mechanical smoothing with a hard-smooth tool and/or fingers. Firing took place at temperatures above clay calcination and could be done in bonfires or hearths. The heterogeneity of pottery traditions was found among the population living in the dugout. The two identified two-component recipes for molding clay were formed as a result of mixing the adaptive pottery skills of bearers of different traditions of making unmixed recipes for molding clay. This indicates the beginning of cultural integration processes among bearers of different pottery skills that began to occur under the dominance of the tradition of using low-sanded clay of the first subtype and artificial sand addition in a 1 : 1 concentration.

Investigation on properties of Pervious Concrete incorporating Lime Calcined Clay Cement (LC3)

Investigation on properties of Pervious Concrete incorporating Lime Calcined Clay Cement (LC3)

Sustainable design of low-CO2 hybrid concrete incorporating calcined clay and limestone powder

Calcined clay and limestone powder are increasingly utilized to create sustainable concrete. This paper proposes a low-carbon design approach that involves the addition of calcined clay and limestone powder. The goal of optimized design is to minimize the carbon emissions, and the constraints of optimized design include strength and carbonation durability. Four different optimization design options were considered. Option 1 does not consider carbonation durability, only strength. The results of the optimized design show that the carbonation durability cannot be satisfactory for low-strength (30 MPa) and medium-strength (40 MPa) concrete. Option 2 considers strength and carbonation durability. The carbonation durability life is 50 years, and the CO2 concentration is 0.04 %. The results show that there is a cutoff point for strength (42.72 MPa). Below this cutoff point, the carbonation durability dominates the optimized design, and above this cutoff point, the strength dominates the optimized design. Option 3 also considers strength and carbonation durability. Compared with option 2, the CO2 concentration increases to 0.05 %. The results show that the strength cutoff also increased from 42.72 MPa to 46.45 MPa. Option 4 considers harsh carbonation conditions. The carbonation durability life is 100 years, and the CO2 concentration is 0.05 %. The results show that the actual strength (59.64 MPa) is the same for different design strength levels (30, 40, and 50 MPa). Considering the results of the optimized design, we discovered that as the strength increased, the CO2 emissions increased, and the water/binder ratio decreased. This finding illustrates the effectiveness of this method.

Performance of limestone calcined clay cement (LC3) incorporating low-grade marine clay

Clay is a globally abundant material and can potentially be used as a cement substitute after calcination. Though kaolinitic clay exhibits notable reactivity, the potential of low-grade clay with relatively low kaolinite content remains underexplored. This study comprehensively analyzed the chemical and mineralogical composition of marine clays at various locations and depths in Singapore, assessing their feasibility for preparing limestone calcined clay cement (LC3). The hydration kinetics and microstructure development of LC3 pastes, incorporating calcined marine clay, were investigated by XRD, isothermal calorimetry, SEM, and MIP. Additionally, a mini-migration test was employed to investigate chloride ion diffusion in LC3 pastes. The results revealed that Singapore marine clays contain relatively low kaolinite content (16–20% by QXRD). Despite a 25% reduction of 28 days compressive strength compared to reference OPC, LC3 samples exhibited outstanding resistance against chloride penetration regardless of kaolinite content (<40%) or replacement level (LC3-70 or LC3-50). The chloride diffusion coefficient (LC3-50) is one order of magnitude lower than the OPC system. Overall, our findings broaden the selection of raw materials for LC3 preparation and underscore the robustness of LC3 to resist chloride penetration, irrespective of variations in the clay's quality or source.

Predicting the Mix Proportions of Concrete Containing Calcined Clay Using Hybridized CNN and XGB and Employing the Shapley Method for Sensitivity Analysis

Predicting the Mix Proportions of Concrete Containing Calcined Clay Using Hybridized CNN and XGB and Employing the Shapley Method for Sensitivity Analysis

Initial Characteristics of Alkali-Silica Reaction Products in Mortar Containing Low-Purity Calcined Clay.

An alkali-silica reaction (ASR) is a chemical process that leads to the formation of an expansive gel, potentially causing durability issues in concrete structures. This article investigates the properties and behaviour of ASR products in mortar with the addition of low-purity calcined clay as an additional material. This study includes an evaluation of the expansion and microstructural characteristics of the mortar, as well as an analysis of the formation and behaviour of ASR products with different contents of calcined clay. Expansion tests of the mortar beam specimens were conducted according to ASTM C1567, and a detailed microscopic analysis of the reaction products was performed. Additionally, their mechanical properties were determined using nanoindentation. This study reveals that with an increasing calcined clay content, the amount of the crystalline form of the ASR gel decreases, while the nanohardness increases. The Young's modulus of the amorphous ASR products ranged from 5 to 12 GPa, while the nanohardness ranged from 0.41 to 0.67 GPa. The obtained results contribute to a better understanding of how the incorporation of low-purity calcined clay influences the ASR in mortar, providing valuable insights into developing sustainable and durable building materials for the construction industry.

Influences of metakaolin and calcined clay blended cement on chloride resistance and electrical resistivity of concrete

There are many different grades of kaolinite clays around the world. Low-grade kaolinite clay is more abundant than high-grade kaolinite clay in various regions. To aim toward the utilization of low-grade kaolinite clay having an original kaolinite content of about 40% to produce calcined clay, this paper investigated the durability properties of concrete incorporating calcined clay produced from high-grade kaolinite clay or high kaolinite content (commercially available metakaolin or CC1) and calcined clay produced from a low-grade kaolinite clay (CC2). Concrete mixtures were designed to have a water-to-binder ratio of 0.60. A fly ash-to-binder ratio of 0.20 and calcined kaolinite clay-to-binder ratios of 0.10 and 0.20 were studied. The chloride penetration resistance and the electrical resistivity of concrete were assessed, while the mercury intrusion porosimetry (MIP) was utilized in evaluating the pore structure of concrete. The test results revealed that concrete with CC1 and CC2 exhibited superior chloride penetration resistance and chloride binding capacity than OPC and FA20 concretes. Moreover, using a higher calcined clay-to-binder ratio resulted in a more refined pore structure, which significantly enhanced the chloride resistance of concrete. Although CC2 revealed less performance in improving chloride resistance than CC1, it had superior performance compared to fly ash.

Evaluation of the Durability of Concrete with the Use of Calcined Clays and Limestone in Salinas, Ecuador

This study aims at the evaluation of different formulations of concrete made with calcined clays and limestone (LC3 cement) exposed to aggressive environments. The study includes the evaluation of fresh and hardened properties and a comprehensive evaluation of durability over 24 months. The inclusion of calcined clays in cement increases the specific surface area of the cements, and thus the water demand. However, the high reactivity of calcined clays compared to any other pozzolan, and the synergy that occurs with limestones, enables the use of cements with very low clinker content that achieve strengths similar to those of Portland. Comparisons of LC3 formulations with Portland cement and with concrete containing silica fume prove the superiority of calcined clays in terms of strength and durability. The best results are obtained with LC3-50 cement with 50% clinker produced through co-grinding. Results of concrete made with a blend of 70% Portland cement with 30% LC2 (60% calcined clay, 35% limestone, 5% gypsum, separate ground) are also promising. All concretes made with LC3 show good durability in terms of the results of effective porosity, chloride permeability, and resistivity tests.

Durability of Ternary Blended Concrete Incorporating Rice Husk Ash and Calcined Clay

Research on the combined substitution of supplementary cementitious materials (SCMs) has already demonstrated that it might be one of the few viable options to produce low-carbon concrete at scale. This paper presents an experimental investigation on the performance and durability of rice husk ash (RHA) and calcined clay (CC) in ternary blended concrete exposed to chloride attacks under wet/dry cycles. Portland cement (PC) was replaced by RHA and CC up to 50% by weight to produce low-carbon concrete. Samples were subjected to wet/dry cycles in 3.5% NaCl water, with mineralogical composition and microstructure development before and after exposure analysed by TGA-DSC, MIP, XRD, and SEM. The durability of the concrete against wet/dry cycles was investigated in terms of compressive strength, water absorption, open porosity, density, thermal conductivity, and electrical resistivity. The results showed that concrete mixes with CC and RHA up to 60% exhibited an increase of 33% in compressive strength, followed by minimal changes in water absorption. While a decrease in electrical resistivity was measured in all samples with RHA and CC, increasing the CC content to 50% resulted in improved resistance to chloride penetration. Increasing the CC content resulted in a more refined microstructure, with an overall decrease in porosity of up to 32% compared to the control series. While RHA alone did not contribute to significant improvements after wet/dry cycles, the combined substitution of RHA and CC at SCM replacement levels of 60% showed an overall improvement in hardened properties and durability. This investigation provides valuable insights into the long-term performance and strength of innovative low-carbon concrete.

COMPRESSIVE STRENGTH, FLOWABILITY, AND ULTRASONIC PULSE VELOCITY TESTS OF PORTLAND CEMENT-FLY ASH-CALCINED CLAY MORTARS

The cement production process significantly affects the environment and contributes to air pollution. Consequently, there is a growing emphasis on employing alternative materials or minimizing cement usage as a solution to address environmental issues and reduce air pollution. In this investigation, an examination was conducted by substituting Portland cement with a weight of 50% with both fly ash and calcined clay. The findings revealed that replacing Portland cement with fly ash resulted in a decrease in compression strength. However, concurrently incorporating calcined clay increased compressive strength. Higher compressive strength compared to the 50% Fly ash mix was achieved by adding 20 wt.% Metakaolin and 20 wt.% Calcined clay Lopburi due to their finer particle size. As a result, the pozzolanic reaction is better than Lampang calcine clay (30FA20CClam). Additionally, ultrasonic pulse velocity testing indicated that higher values in the specimen correlated with increased compressive strength.

Assessing the risk of ASR in LC3 binders based on low-grade calcined clay

The research investigates the impact of limestone calcined clay cement (LC3) on the mechanical properties and durability of cement-based materials in the context of alkali-silica reactions (ASR) for sustainable construction. Comparative experiments were conducted on binary and ternary blends of low-grade kaolinitic calcined clays and conventional supplementary cementitious materials (SCMs). Two distinct low-grade kaolinitic clays were calcined, and blends with Portland cement, ground-granulated blast-furnace slag (GGBFS), and silica fume (SF) were prepared for comparative analysis. Results reveal that replacing 30 wt% of Portland cement with these calcined clay blends substantially reduces expansion in mortar and concrete during accelerated and long-term tests, altering micropore structure. These blends demonstrate superior performance compared to other studied SCMs. Despite a slight decrease in compressive strength compared to the control mixture, there is a noteworthy improvement in permeability and resistance against expansion. Also, in the early stages of ASR, an improvement in concrete's mechanical properties and durability is observed, attributed to the ASR gel filling the pores.

Using ceramic demolition wastes for CO2-reduced cement production

This study focuses on assessing the pozzolanic potential of two types of ceramic demolition waste, namely terracotta roof tiles and sanitary porcelain, as substitutes for traditional calcined clays in blended and limestone calcined clay (LC3) cement production. Experimental methods employed include the modified Chapelle test and XRD for pozzolanic activity evaluation, flexural and compressive strength tests, capillary absorption measurements, and SEM for microstructure analysis. Mortars containing 10%, 20%, and 30% ceramic powders and 5%, 10%, or 15% limestone filler were tested. The findings showed that porcelain powders exhibited lower pozzolanic activity due to their lower surface area and higher firing temperature of the material. Up to 20% substitution of OPC with terracotta had minimal strength impact, with a 103% strength activity index (SAI) at 90 days. Ultrafine terracotta powder showed promise in LC3 production with up to 30% OPC substitution, achieving a 97% SAI after 90 days. The poor mechanical properties of porcelain-containing mortars were explained by surfactants present in sanitary porcelain. This research informs the cement and processing industries on the potential use of specific ceramic demolition waste materials in eco-cement production, offering insights into blended pozzolanic cements and LC3 formulations, with the goal of reducing the carbon footprint of cement manufacturing.