Microstructural investigation of extrudable reactive powder concrete

Reactive Powder Concrete (RPC) is well known for having ultra-high mechanical performances and a very good durability. The goal of our study is to find an extrudable RPC for concrete pipes manufacturing. Five RPC concrete mixtures (W/C = 0.16) were synthesized with variable amounts of polycarboxylate superplasticizer, silica fume and crushed quartz. The first three compositions do not contain any crushed quartz and vary only by their increasing amount of superplasticizer. In the last two compositions, crushed quartz replaces a part of silica fume. Four of the formulations are extrudable. In this paper, we discuss the microstructure of the five samples before extrusion. A systematic study by scanning electron microscopy has been performed on polished sections and fractures. As expected for RPC, all the samples show a high amount of residual anhydrous clinker. The three compositions without crushed quartz are rather similar, whereas two effects of the addition of superplasticizer and quartz on hydration are observed for the two last compositions.