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Many durability related problems in concrete structures are caused due to early-age cracking. Though early-age cracking is not detrimental to the structure, this will open up the way for the long-term durability issues, hence, needs to be mitigated. Cracking of such types in concrete is commonly prevented by adding fibres. Present work aims at studying the potential use of basalt fibres in controlling the shrinkage cracks at early age, otherwise this fibre is considered not suitable for use in concrete as it would degrade under alkaline environment. Further, to sustain the long-term durability, an attempt has been made to reduce the alkalinity of the concrete by replacing the cement with fly ash up to 50%. Concrete specimens made with two water to binder ratios (w/b), six replacement levels of fly ash, and one type of fibre are used for this study. Crack width and crack area generally used for evaluating the extent of shrinkage cracks are measured and analyzed. As the shrinkage cracks are very thin to measure manually, image analysis technique has been employed to measure the crack widths. Results indicate that to a greater extent cracks developed during early age has been effectively mitigated with the incorporation of fly ash. Further, it is found that basalt fibres are effective in arresting the shrinkage cracks. Furthermore, it is concluded that manual measurement will under or overestimate the crack width, hence, image analysis technique can be successfully used for measuring the crack widths.

To achieve sustainability in construction, research is currently geared up to utilise more fly ash (FA) in cement. The low early-age strength development of FA–cement composite prevents its broader acceptance and usage in the construction sector. Many attempts have been made by various researchers, including through the use of chemical accelerators, to eliminate this well-known disadvantage of FA–cement composites. This study aims to investigate the influence of various non-chloride chemical accelerators such as calcium formate, calcium nitrate and calcium carbonate in altering the hydration products formed at various replacement levels of FA. The influence of chemical accelerators on two major compounds – tricalcium silicate (C3S) and tricalcium aluminate (C3A) – that are mainly responsible for early-age strength development are discussed in this study. It is found that all the chemical accelerators can be safely used to improve the early-age strength of FA–cement composites at least to the level of 35% of FA replacement prescribed by the existing codes without compromising the long-term strength.

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Thermal behavior, surface area, oxide, mineralogical composition, and structural functional groups of raw and thermally treated five local kaolin clays [Ijero-Ekiti (IJ), Ikere-Ekiti (IK), Isan-Ekiti (IS), Abusoro (AB) and Odigbo (OD)] from two states in SouthWest Nigeria were studied in order to determine their potential uses. These properties were measured using thermogravimetric analysis coupled with differential thermal analysis (TGA/DTA), surface area and porosity analysis, X-ray fluorescence (XRF), X-Ray Diffractometry (XRD) and Fourier Transform infra-red spectroscopy (FTIR) respectively. The TGA/ DTA showed major mass losses and broad endothermic bands at temperatures 390-700 °C, which were associated with dehydroxylation of kaolinite and other clay minerals. Thermal treatment increased the surface area of the raw clays. The XRF results showed oxides of kaolinite, illite, quartz, feldspar, hematite, anatase and the phases were confirmed by XRD. The FTIR spectra displayed the characteristic absorption bands of the minerals. Combining the obtained results, Ijero-Ekiti clay was identified as feldspar (albite)-quartz containing clay, Ikere-Ekiti and Isan-Ekiti clays as kaolinite-dominated clays, Abusoro clay as kaolinite-illite-montmorillonite-containing clay and Odigbo clay as kaolinite-illite-containing clay. The TGA/DTA, XRD and FTIR indicated that crystalline kaolinite in the clays were converted into amorphous metakaolinite after thermal treatment. Based on the properties displayed, clays from IK, IS, AB and OD deposits can be thermally treated to form useful supplementary cementitious and geopolymer materials to make binders in building and construction while clay from IJ deposit can be a potential raw material for ceramic production.

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