Belitic calcium sulfoaluminate as mineral admixture in limestone-calcined clay cement and low carbon dioxide binders

Cement manufacturing is one of the industries that has a significant impact on climate pollution, contributing approximately 6-8% to global CO₂ emissions and global warming. However, there has been a global shift towards more sustainable practices in various fields, including the cement industry. The aim of this study was to produce concrete binders based on calcined clays and limestone as a possible way to reduce the amount of clinker used in cement manufacturing. In order to produce limestone calcined clay cement, the study compared different concrete mixtures that included two different types of calcined clay (from the Egyptian deserts of Sinai and Zaafarana) in combination with limestone filler. The evaluation was based on compressive, indirect tensile and flexural strengths, and the degree of hydration. In this experiment, 9 cement-based concrete mixes, including a reference mix, were designed with fixed water content, sand, and basalt. Eight concrete mixes of limestone calcined clay cement (4 for each type of calcined clay) were produced, using 7.5%, 15%, 22.5%, and 30% of calcined clay, 10% of limestone filler, and 5% gypsum, with the remaining being clinker. The water consistency, setting times, Le Chatelier test, and compressive strengths of the concrete mixtures were evaluated. Furthermore, rapid chloride permeability test, XRD analysis and SEM study were conducted to investigate the kinetics of pore refinement and microstructure. The results showed that the binders exhibited a slight improvement in mechanical strengths compared to Ordinary Portland Cement, by 4.6%. Furthermore, the study revealed a significant pozzolanic activity and synergy between the calcined clay and limestone filler in the binder. Both limestone calcined clay cement concretes outperformed ordinary Portland cement, particularly in terms of workability and durability. The SEM images, processed using the MATLAB image processing toolbox, confirmed that the binder cement concretes have better pore refinement and microstructure compared to the Portland concrete, especially the Zaafarana mixture of 30% calcined clay at a curing age of 90 days. In conclusion, the development of limestone calcined clay cement concrete presents a promising approach for reducing the clinker content in cement production, thereby contributing to the global efforts towards more sustainable and environmentally-friendly construction materials.

The use of supplementary cementitious materials (SCMs); fly ash and granulated BF slag, by lowering clinker content in cement is a viable strategy to bring down CO2 emission during cement manufacture. Due to the large availability of clay and limestone all over the world, a new ternary cementitious cement system containing calcined clay and limestone could increase clinker substitution to about 50% without significantly influencing cement performance due to the synergy between aluminates from calcined clay and carbonates from limestone. In the present study, mechanical properties of different limestone calcined clay cement blends, prepared maintaining clinker substitution of 0.40, 0.45, 0.50, 0.55 and 0.60 was measured as per Indian standard IS:4031 and showed compressive strength comparable to the minimum strength requirements for blended cements as specified in Indian standard, in case of cement having clinker substitution rate of 0.50. Comparative evaluation of compressive strength of OPC and limestone calcined clay cement showed substantial increase in strength at later ages in case of limestone calcined clay cement as compared to OPC. The heat evolution of limestone calcined clay cement using isothermal calorimeter showed higher heat evolution with early attainment at all ages as compared to OPC. The limestone calcined clay cement showed its resistivity to different aggressive solutions such as seawater, sulfate and chloride solution salts along with lean water up to the period of 12 months.

The effects of replacing calcined clay with sewage sludge ash (SSA) treated under room temperature and high temperature ranging from 500 °C to 900 °C in limestone calcined clay cement (LC3) have been investigated in this paper. The optimal calcination temperature for SSA was found to be 800 °C based on the results of strength and microstructure observations. The main inorganic components of sludge ash are Fe2O3, SiO2, Al2O3, and CaO, which are very similar to the components of calcined clay in LC3, but with a very high content of Fe2O3 (55-61%) and P2O5 (9-10%). With different levels of the replacement of calcined clay with calcined SSA, setting time, compressive strength, XRD, TG/DSC, and SEM analyses of the modified LC3 pastes were conducted to identify the chemical compositions, physical properties, hydration products, microstructure, and the heavy metal contaminants within the pastes, which were compared to the results for normal LC3 paste. The incorporation of SSA significantly altered the morphologies of Ca(OH)2 and CaCO3, as well as modified the microstructure of the LC3 paste. In comparison to the pure OPC group, the LC3 pastes containing SSA exhibited a reduced Ca(OH)2 content and an increased CaCO3 content. Furthermore, the modified LC3 pastes with calcined SSA effectively facilitated the immobilization of heavy metal ions in SSA. The findings indicate the potential viability of utilizing calcined SSA as a replacement for calcined clay in LC3.

Use of spent fluid catalytic cracking catalyst (FCC) in Limestone Calcined Clay Cement (LC3) systems: Studies in pastes and mortars

LC³ Cement (Limestone Calcined Clay Cement) has established itself as an innovative and sustainable solution for the construction industry, offering a low-carbon alternative to conventional Portland cement (OPC). The formulation of this cement, as well as its applications, are frequently studied to enhance its efficiency. In this context, this study aims to contribute to the understanding of LC³ cement by incorporating regionally available raw materials into its formulation, providing a foundation for guiding future research on the subject. To achieve this, a systematic literature review was conducted, focusing on LC³ cement and cementitious materials incorporating various components, such as calcined clays and metakaolin, comparing the impact of these additions on the properties of the mix. Furthermore, based on the information gathered from the review, a preliminary study was carried out using calcined clay obtained from soil extracted in the city of Londrina, Paraná. Mortars with different levels of calcined clay and metakaolin additions were prepared, and their influence on compressive strength, as well as the impact of calcined clay addition on cement reactivity, was evaluated. The preliminary results indicate that the calcined clay from regional soil has potential for LC³ cement production. Thus, this study reinforces the role of research on alternative materials in the cement industry, highlighting the potential of using regional raw materials to produce more sustainable and efficient cements. Additionally, it underscores scientific advancements in LC³ cement and the possibility of its regional production.

The development of sustainable, high-performance cementitious materials for infrastructure rehabilitation presents not only technical but also institutional and regulatory challenges. Belitic calcium sulfoaluminate (BCSA) cement—first developed in the United States in the 1970s—has emerged as a promising low-carbon alternative, especially in applications requiring rapid strength gain. This presentation reviews recent progress in BCSA cement technology, examines some of its performance characteristics and environmental benefits, and explores its synergistic potential as an early-strength enhancer in widely adopted low-carbon cements such as Portland-limestone cement (PLC) and limestone-calcined clay cement (LC3.

Comparative study of limestone calcined clay cement produced with mechanically activated kaolin and calcined kaolin

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.

Limestone calcined clay cement (LC3): A sustainable solution for mitigating environmental impact in the construction sector

Effect of calcined clay and marble dust powder as cementitious material on the mechanical properties and embodied carbon of high strength concrete by using RSM-based modelling

Shrinkage and creep of high-performance concrete based on calcium sulfoaluminate cement

Limestone calcined clay cement (LC3) holds promise as a new type of sustainable cement-based material, but the mechanisms underpinning its engineering performance are still poorly understood. Here, a metal intrusion-enhanced imaging approach was employed to quantitatively analyze and link the pore structure development of LC3 to its hydration process, i.e. solid-phase development, and mechanical performance. We found that the early age microstructural development in LC3 is inhomogeneous, with the perimeter of limestone particles displaying higher porosity relative to that surrounding calcined clay and clinker. At later ages, the formation of carboaluminates and calcium-aluminate-silicate-hydrates homogenized the overall microstructure of LC3, thereby delivering improved mechanical performance. Overall, our analysis suggested a more efficient particle packing in LC3 mixes, which decreases the volume/connectivity of micro-pores and can account for LC3’s notable flexural strength. These findings can assist the development of improved LC3 binder formulations alongside other ternary binders with possibly higher limestone additions.

The combination of calcined kaolinitic clays and limestone in Limestone Calcined Clay Cement (LC3) is a promising approach to reduce the cost and the CO2 emissions of cement production by reducing the clinker content of cement. This thesis investigates the feasibility of using various grades of calcined clays in LC3. LC3-50 blends with a clinker content reduced to 50% are studied. The factors controlling the reactivity of LC3-50 blends containing various grades of calcined kaolinitic clays were first studied. A benchmark test of mortar strength was developed. Similar strength to plain Portland cement (PC) can be obtained even for clays with 40% of calcined kaolinite only. Moreover, strengths are strongly dependent on the calcined kaolinite content of the calcined clay. The development of the new Rapid, Relevant and Reliable (R3) pozzolanic test allows the evaluation of the reactivity of calcined clays after only 24 h by isothermal calorimetry and 3 days simply using an oven, and it allows the prediction of the strength development of LC3-50 mortars. To explain strength results, a phase assemblage study was carried out. In order to determine the amount of reacted metakaolin, three methods were tested and mass balance was found to be the most reliable one. The phase assemblage study showed that a critical refinement of pore connectivity is reached already at 3 days for LC3-50 blends with high calcined kaolinite content. From this point on, clinker hydration is slowed down, and the formation of crystalline hydration products is limited. The on-going reaction of metakaolin leads to the higher incorporation of aluminium in the calcium alumino silicate hydrate (C-A-S-H). The C-A-S-H was fully characterized in terms of composition, morphology and density. No change in morphology was observed by Transmission Electron Microscopy. The C-A-S-H density determined by 1H-Nuclear Magnetic Resonance was also found to be similar between PC and LC3-50 with different calcined kaolinite content. Combining all this information, a good relationship is obtained between strength and gel space ratio for PC and for the LC3-50 blends. Finally, the chloride resistance was tested through ponding and chloride binding isotherm tests. The results also support previous findings for the use of calcined clays with a calcined kaolinite content of at least 40% to get a better chloride resistance than PC. These results are mainly explained by the pore connectivity refinement of LC3-50 blends compared with PC. The chloride binding is the highest for clays with 40-50% of calcined kaolinite.

The substitution of Ordinary Portland Cement (OPC) with Supplementary Cementitious Materials (SCMs) is a key strategy for reducing the carbon footprint of construction materials. In this study, LC 3 (Limestone Calcined Clay Cement) binders were developed using a calcined clay rich in kaolinite and illite, sourced from a naturally occurring deposit, offering an alternative to conventional high-purity kaolinite clays. The primary objective was to investigate the impact of this clay composition on the hydration behaviour, phase composition and mechanical properties of LC 3 systems. The performance of the designed composite (with the clay dosage from 20% to 40%) was assessed through isothermal calorimetry, simultaneous thermal analysis, and basic physical and mechanical properties determination. The binders exhibited relatively high hydration heat over 200 J.g −1 at 7 days, but a modified course of hydration. Consequently, they showed noticeably lower bulk density (by 7 to 16%), slightly improved flexural strength (by 3 to 27%) and varying compressive strength (ranging from -26% to 13% depending on composition). These findings demonstrate the potential of kaolinite-illite clays as viable SCM sources in LC 3 formulations, broadening the raw material base and promoting regional material utilisation in sustainable cement production.

Harnessing iron tailings as supplementary cementitious materials in Limestone Calcined Clay Cement (LC3): An innovative approach towards sustainable construction