| description abstract | In the quest to develop a green cement composite with the lowest possible carbon footprint and the highest possible use of industrial by-products, an experimental investigation was undertaken, replacing 1% of ordinary portland cement. This paper presents the results of an experimental program to develop a zero-cement composite, incorporating 2.5, 5, and 7.5% nanosilica, 72.5, 7, and 67.5% fly ash, 25% ground granulated blast furnace slag (GGBFS), and hydrated lime used as a cement additive at 1 and 15% of the total supplementary cementitious material. Compressive strength tests were undertaken to study the mechanical properties of mortar samples of various mix designs. In addition, scanning electron microscopy, thermogravimetry, and X-ray diffraction were undertaken in conjunction with quantitative phase analysis to investigate the various physicochemical changes taking place within the cement matrix and to formulate strategies for its further development. The results demonstrate that the addition of nanosilica and hydrated lime to low calcium/high-volume fly ash and GGBFS blend can help in achieving an environmentally friendly zero-cement composite without the need of any heat treatment. The optimum content of nanosilica was found to be 5%. With the further increase in nanosilica content, although the pozzolanic reaction and the resulting C─ S─ H/C─ A─ S─ H gel formation increases, it also increases the microcracking within the cement matrix, resulting in the reduction in compressive strength at both 7 and 28 days of curing. The siliceous hydrogarnet formed as a result of the pozzolanic reaction of amorphous silica (FA, GGBFS, NS), with the calcium aluminate present in GGBFS, shows very poor crystallinity with no visible peak reflection in X-ray diffraction data. The formation of siliceous hydrogarnet increases with the increase in amorphous nanosilica, but decreases with the increase in hydrated lime content. | |
