Filler effect of inert mineral powder in concrete: Dissertation

Use of fine inert material powders to minimise water requirement in concrete was studied experimentally and theoretically based on particle packing. Superplasticiser was used through the experiments to allow small particles to fill spaces of their own size class. In lean mixes (cement content 140 - 200 kg/m3) with crushed aggregate use of inert mineral powder lowered water requirement up to 40 l/m3 compared to present technology. With more rounded gravel aggregate the reduction was clearly smaller. The experimental results were investigated with the Linear Packing Density Model (LPDM). Theoretically in densely packed mixes aggregates fill space as dense as possible and cement particles fill the remaining aggregate interspace leaving only minimum space for water. Such a mix has optimal composition, but in practice such mixes are not workable. The true water requirement is far greater than expected based solely on the particle system and more so the closer the particle composition is to the optimum composition. This is because in such mixes the interspaces between aggregate particles are not wide enough to allow cement paste movement. On the contrary, in lean mixes water is free to move in-between aggregate interspaces and in very rich ones the paste content is large enough for paste movement. Therefore in lean and rich mixes water requirement can be understood and calculated by the LPDM. To do this, both cement and aggregate packing must be taken into account by finding the proper value of monosize packing density for each component. The aggregate value was found to depend on mix consistency being approximately 0.50 for gravel and 0.42 for crushed aggregate while the value of cement, 0.36, did not appear to depend on consistency within the frame of the experiments. An empirical method is proposed for predicting water requirement near the optimal composition. Mechanical properties and long term behaviour of concretes with large amounts of inert quartz powder were experimentally studied.