Investigation of the use of Limestone Calcined Clay Cement (LC3) applied to Thailand

The replacement of clinker with supplementary cementitious materials (SCMs) is the most interesting solution to reduce the CO2 emissions from cement production. The abundant availability of clays, which have a sufficient amount of kaolinite content in Thailand, has led to the development of an alternative SCM. The raw materials in this study come from Thailand and are used to formulate limestone calcined clay cement (LC3). The objectives of this thesis are to investigate the influence of the substitution level, the cement composition and the calcination process of calcined clay on the hydration reaction, the mechanical, rheological and durability properties of LC3. The properties of LC3 were also investigated at 30°C simulating the climate conditions in Thailand for LC3 application. Limestone and calcined clay can replace clinker up to 45% with excellent results. LC3-80(2:1), LC3-65(2:1) and LC3-50(2:1) correspond to blended cements containing 80%, 65% and 50% of clinker, respectively, 5% of gypsum and 15%, 30% and 45% of calcined clay and limestone with a fixed ratio of 2:1. The replacement of clinker with calcined clay and limestone leads to a significant porosity refinement. This refinement results in the improvement of chloride ingress resistance. Concerning strength development, the gel-space ratio permits to correlate strength with the phase assemblage. The compressive strength of all LC3 blended systems meets the standard value of OPC type I (ASTM C150) or CEM I 42.5N (EN 197-1). Increasing temperature from 20°C to 30°C promotes the clinker hydration and the pozzolanic reaction resulting in the enhancement of strength development at the early ages. LC3-65(2:1) is commercially promising in Thailand in term of maximum substitution level coupled with satisfying results in terms of durability and strength. For the optimization of LC3 properties, the influence of the alkali content in cement is investigated. KOH or NaOH are used to adjust the alkali equivalent (%Na2Oeq = %Na2O + 0.658·%K2O) from 0.44% to 1.20%. Increasing alkalinity accelerates the clinker hydration and enhances the precipitation of hydration products at early ages but it shows the opposite at late ages. The lower gel-space ratio and the increase of porosity in high alkali condition cause the dramatical decrease of strength at later ages. NaOH is more harmful on the properties of LC3-65(2:1) than KOH. Therefore, the maximum alkali equivalent of LC3-65(2:1) is 0.77% Na2Oeq (or 0.99% Na2Oeq in PC) for KOH addition and 0.63% Na2Oeq (or 0.79% Na2Oeq in PC) for NaOH addition to prevent the negative effects at later ages. Concerning the influence of the calcination method, calcined clay produced by the rotary kiln process has a lower surface area compared to the clay calcined from the fluidized bed because of a coarser pore width of calcined clay particles. Accordingly, the calcined clay produced by fluidized bed has a slightly higher reactivity at the beginning but there is no significant difference in the reactivity of calcined clay between these two processes later on. In terms of fineness, no increase of reactivity is found for calcined clay finer than 10 µm, i.e. there is no need of overgrinding for calcined clay. The different calcination processes and the variation of kaolinite content (45-50%) do not impact the activation energy (Ea) of calcined clays.