STUDY OF PACKING EFFECTS ON SELF CONSOLIDATING CONCRETE (SCC) USING SECONDARY RAW MATERIALS (SRM)

Abstract

The classical idea of particle packing is based on Apollonian concept, in which the smaller sized particles fit into the voids left by larger particles. Well graded fine and coarse aggregates having greater range of particle size will reduce the voids in concrete and hence the paste required to fill those voids. Fine to coarse aggregate ratio can be adjusted by trials to have maximum packing density of granular mix with reduced voids between them. Crushed aggregate particles are very irregular in shape and pack more poorly together than naturally formed gravel. Aggregate voids increases the paste demand in the mix and this can be countered by use of very fine sized Secondary Raw Materials (SRM) to partially replace cement without adversely affecting the properties of concrete. Present study focuses on determination of optimum fine to coarse aggregate ratio to have a maximum packing density of granular phase of Self Consolidating Concrete (SCC). SRMs including Fly Ash (FA) and Limestone Powder (LSP) were also utilized to further improve the packing of mix. Flow, volume stability, heat of hydration and mechanical characteristics of Self Consolidating Concrete made with and without SRM were studied and compared to the mix formulation designed using EMMA based on Modified Andreasen and Andersen (MAA) approach. The ratio of fine to coarse aggregate was varied in 20-80% range, as a trial process, to see the effect in the degree of packing of aggregates in the SCC. The packing density and compressive strengths were found to be optimum when fine to coarse aggregate ratio was 50:50 in terms of weights in trial mixes while that based on MAA approach this ratio was around 51:49 with distribution modulus “q” equal to 0.25. Results showed that SCC prepared using SRMs (Modified Mixes) possesses higher packing density than that of SCC mixes in comparison to Control Mixes (CM) having no SRM. Modified Mixes (MM) show increased SP demand for target flow, higher flow times, better strengths, reduced total linear shrinkages and reduced heat peaks in calorimetry coupled with reduced air content. While MAA approach saves the time and materials needed in SCC mix design in trial process.