Abstract
Environmental concerns, stemming from high-energy demands and CO2 emission associated with cement manufacture, have brought about pressures to reduce cement consumption through the use of supplementary cementitious materials (SCMs). Besides addressing environmental concerns, the incorporation of SCMs in cement bound materials and concrete can modify and improve specific concrete properties. Metakaolin (MK) in an important SCM which can enhance the performance of cementitious composites through its high pozzolanic reactivity. This study was carried out to characterize the materials and to assess the effect of Libyan metakaolin (LMK) on the mechanical properties including the compressive strength of cement mortar. LMK was produced by calcining kaolinite clay at 700°C for 2 h. X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Differential Thermal Analysis / Thermo-Gravimetric analysis (DTA/TG) and Fourier Transform Infrared Spectroscopy (FTIR) s were performed on the raw and calcined kaolinite powders. Seven mixes were prepared with different LMK replacement percentages (0.0 to 30%), by weight of cement, and a constant water binder ratio (w/b) of 0.5. The specimens were cured for 3, 7, 28, 56 and 90 days. At the end of each curing period, the specimens were tested for compressive strength. The results confirm the transformation of kaolinite clay into metakaolin and the pozzolanic reactivity of the produced LMK and conforms to ASTM requirements in this respect. The study confirms that LMK could be effectively used in reducing cement content up to 30% by weight without compromising compressive strength of the cement mortar.
Highlights
The production of Portland cement is costly and energy intensive, but it requires large quantities of natural raw materials and produces large amount of carbon emission
The results showed that for the production of metakaolin to be used as pozzolanic material, the calcination temperature and the residence time are variables to be considered
It is worth mentioning that mixes with Libyan metakaolin (LMK) replacement level of 15% and higher were less workable than the mixes with lower replacement values
Summary
The production of Portland cement is costly and energy intensive, but it requires large quantities of natural raw materials and produces large amount of carbon emission. Et al [4], investigated the ability of the metakaolin to be used as a supplementary cementitious material and they reported that the metakaolin can be produced by thermal treatment (calcination) of the starting high-quality kaolin clay from Serbia. They stated that the optimal calcination parameters, for which nearly complete dehydroxylation of the material was achieved, are: temperature 650 °C and heating time of 90 min. The results showed that up to 30% replacement level, the blended mixes had higher compressive strengths than the control mix, at all testing ages, but for the 3 days strength
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