The use of silica fume and replacement sand with Portland cement clinker to remove transition zone in concrete

Between the interface of cement paste and aggregate in concrete, there is a region with high porosity which is said to interfacial transition zone (ITZ). Transition zone causes the reduction of compressive strength and flexural strength, increased permeability and consequently increase the vulnerability of concrete against sulphates and chlorides penetration. Therefore, researchers have sought ways to improve the negative effects resulting from the ITZ. In this study, were used two techniques to removal ITZ. In the first technique was replaced 18% by weight of cement and silica fume and was produced reactive powder concrete (RPC). In the second technique, along with silica fume, Portland cement clinker was replaced completely with sand, which has led to production Reactive Powder-Aggregate Concrete (RPAC). Comparison of normal concrete (NC) compressive strength with RPAC and RPC showed that the 174 and 146% increase in compressive strength at the 7 days. Then, size of the ITZ were examined by using scanning electron microscopy. The depth of chloride penetration, water absorption and volume of open porosity of RPC and RPAC were compared with NC. The results showed reduced water absorption and chloride penetration depth.