Microstructural characteristics and carbonation resistance of coal bottom ash based concrete mixtures

The combined use of coal bottom ash (CBA) and ground CBA (GCBA) as partial replacement of fine natural aggregate (FNA) and Portland cement, respectively, was investigated for the production of concrete mixtures. Five concrete mixtures incorporating GCBA at 20 wt% replacement of binder and CBA at 0, 25, 50, 75 and 100 wt% replacement of FNA were produced and tested for strength, microstructural characteristics and carbonation resistance. A base concrete mixture made of conventional concrete was also produced as a reference concrete mixture. Test results showed that the combined use of GCBA and CBA in concrete mixtures results in enhancement of the microstructure, carbonation resistance and compressive strength of the resulting concrete mixtures. Scanning electron microscopy and X-ray diffraction analyses pointed at the occurrence of pozzolanic reaction and pore-filling effect of GCBA and CBA in the resulting concrete mixtures. It was observed that 25 wt% replacement of FNA with CBA is an optimum dosage considering its effects on the later age strength and durability characteristics of the resulting concrete mixtures.