Over the past twenty years high strength concrete and reactive powder concrete (RPC) have been investigated by many researchers. At present, preliminary experiments to produce RPC are in progress in Croatia. The preliminary investigation described in this paper involved testing of concrete mixtures having different concrete components. Sand and superplasticizer samples used in the tests were varied as for their respective origins, while steel fibers, cement and silica fume were obtained from the same sources. The compressive and flexural strengths were measured after 7 and 28 days. The selection of the right sand was done based on the strength results obtained. The results of testing will serve as guidelines for further investigations.