Role of an Amorphous Silica in Portland Cement Concrete

Abstract

An amorphous silica (AS) replacing up to 10% of the portland cement by mass in concrete behaved partly as a traditional pozzolan, partly crystallized to quartz and the rest underwent some (crystal) structural reorganization without morphological changes. The pozzolanic behavior was evident from a reduction in the calcium hydroxide content of AS-cement paste with time. A new crystalline phase was observed in the scanning electron microscope only when AS was present, and energy dispersive X-ray microanalysis coupled with X-ray absorption near edge structure spectroscopy confirmed that it was the most stable form of silica, quartz. The presence of AS changed the concrete’s microstructure, aggregate–paste interface, and pore size distribution.