Question

How are mix proportions usually modified if concrete is to be pumped? Assume that the concrete was originally designed for conventional placement and the aggregate gradation has not be optimized.

Answer 1

Ans) The properties that affect the pump ability of concrete  are maximum size of aggregate , surface texture , porosity ,shape of aggregates and gradation Concrete made with angular and rough particle required to have an high amount of mortar to be pumped.So, originally designed concrete should be modified by increasing mortar content. For best pump ability , gradation should fall in the center of gradation specification. Porosity will affect pump ability of concrete because water is absorbed in great amount by porous aggregates in concrete .So, water content needed to increase by some amount if porous aggregates are used  Also, admixtures to be used in concrete to reduce friction between pipe and concrete.to make concrete more pump able