Concrete Mix Design By Packing Density Method

Abstract

Packing density is new kind of mix design method used to design different types of concrete. To optimize the particle packing density of concrete, the particles should be selected to fill up the voids between large particles with smaller particles and so on, in order to obtain a dense and stiff particle structure. Higher degree of particle packing leads to minimum voids, maximum density and requirement of cement and water will be less. In this work the co-relation curves are developed for packing density method between compression strength and water cement ratio, paste content to reduce the time involved in trial to decide water cement ratio and paste content for a particular grade of concrete. Results obtained by packing density method are compared with IS code method. The optimum bulk density was obtained at proportion of 42% coarse aggregates (20mm downsize), 18% coarse aggregates (12.5mm downsize) and 40% fine aggregates. Large number of trial casting were carried out for each grade of concrete (i.e., M20, M25, M30, M35 and M40) with different water cement ratio and three paste contents in excess of void content. To finalise mix proportions using packing density method flow table tests were carried out to decide water cement ratio and paste content in excess of void content for each grade of concrete. The finalised mix proportion for each grade of concrete was used to cast the cube specimens for 7 days and 28 days curing age. The cube compressive strength results obtained by packing density and IS code method are nearly same. The co-relation curves were plotted for packing density results alone and also combining the results of packing density and IS code methods. The co-relation curves were plotted between compressive strength vs water cement ratio at 7 and 28 days curing age and compressive strength vs paste content at 7 and 28 days curing age. Very good co-relation is obtained with a co-relation co- efficient of 0.953 (minimum) to 0.998 (maximum). These curves can be used to decide the water cement ratio and paste content for the specified grade of concrete incase of packing density method thus reducing the material and time involved in trial testing.