Interfacial interaction of aggregate-cement paste in concrete

Abstract

The chemical and physical interactions in the interfacial transition zone (ITZ) between three different types of coarse aggregates (limestone, granite and basalt) and cement paste were investigated. The results show that all the aggregates are chemically active. Significant amounts of Ca²⁺, K⁺, and Na⁺ are absorbed by all the aggregates from the cement solution, granite and basalt also absorb significant amounts of OH⁻ and release significant amounts of Si⁴⁺ into cement solution. The XRD, EDXA and pore structure results of the ITZ also show that more clinkers participate in the cement hydration in the ITZ of granite and basalt, and more hydrates are generated, hence resulting in a denser ITZ structure with a lower content of macropores. Although the limestone has the least activity, the connection between it and cement paste is tight, due to its rough surface and higher water absorption. Whereas the granite with smooth surface and lower water absorption has a loose connection with cement paste, many pores and cracks are visible, which is very detrimental to the concrete durability.

Keywords

aggregate / cement paste / chemical interaction / pore structure

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