Impacting factors and properties of limestone calcined clay cements (LC³)

Abstract

This paper details the main factors influencing the performance of limestone calcined clay cements (LC3). The kaolinite content plays a major role in the rheological properties as well as strength development. Even in the presence of secondary phases, kaolinite can be accurately quantified by thermogravimetric analysis. The performance of LC3 is slightly influenced by the calcination process of clay, but it can be optimized by using the correct calcination temperature and applying a specific mix design with adjusted sulfate and alkali content. The hydration reactions of LC3 are fully characterized. They vary slightly from plain cement. There is no significant change in terms of phase assemblage. The main properties of LC3 are also described. LC3 blends show a lower creep compliance and a delay in shrinkage strains compared with plain cement. Concerning durability, LC3 blends show outstanding performance with respect to resisting chloride ingress and expansion from the alkali–silica reaction.

Recent Progress in Green Cement Technology Utilizing Low-Carbon Emission Fuels and Raw Materials: A Review

“…Clays are abundant materials worldwide and made up of silicon and aluminum oxides, which constitutes three quarters of the earth's crust [65]. The most suitable clays are kaolinite, which are widely available in equatorial to subtropical environments, which is where rapidly developing countries are located and where most of cement demand is likely to increase in the coming decades [64,66]. The pozzolanic activity of kaolinite is achieved when calcined at temperatures between 600 and 800 • C [55].…”

Suitability of Remediated PFAS-Affected Soil in Cement Pastes and Mortars

“…It appeared that the reference sand had no peak or shoulder within this range, but the dry received soil showed a very minor shoulder and the calcined soil a more pronounced shoulder. When kaolinite transforms to metakaolin during calcination, the following chemical reaction (Equation (1)) takes place [36,59]:…”

“…Although the dry received sample had pozzolanic activity, samples prepared with it provided 6% lower compressive strength compared with the paste with calcined soil. The lower measured compressive strength compared to the calcined soil likely originated from the lower temperature used for the heat treatment at the pyrolysis plant (~550-650 • C vs. T calcination = 750 • C), which was insufficient to achieve a high level of activation of the clays in the heat-treated soils [36,67,68]. The compositional differences, namely the lower kaolinite but greater metakaolin content of the calcined soil compared to that of the dry received soil, have been shown in the previous section and support the findings on the mechanical performance of the two different samples.…”

“…Arguably, the most important is a reduction of the considerable carbon footprint of cement manufacture: clinker is kilned at~1500 • C vs. soil pyrolytic treatment, at~550-650 • C. Any cement clinker offset by calcined soils necessarily leads to an increased energy efficiency of cement manufacture. SCM-clinker blends have been shown to provide comparable strengths at lower ordinary Portland cement (OPC) contents and also result in superior concrete durability, reduced heat of hydration and hence reduced risk of early age thermal cracking [36][37][38][39]. By considering calcined soils as a source of fine aggregates, the currently experienced shortage of aggregates can be eased, particularly where the fine aggregate replacement (FAR) is sourced near, or indeed from, major projects.…”

More sustainable constructions using limestone calcined clay cement (LC³)

“…Another durability advantage, is the ability to suppress expansive alkali silica reaction with reactive aggregates. We now have materials under test in alkaline solutions at 38°C for over 4 years with no sign of expansion, even with known highly reactive aggregates, whereas plain cement is highly-expansing [17].…”