Discussion on Minimum Slump at Concrete Placement and on Quality Classification of Ready Mixed Concrete

Abstract

The addition of water to ready mixed concrete once turned into a social problem. One of the reasons was the fact that as the rebar density of structures increased, cases emerged where ready mixed concrete as specified in construction specifications failed to offer sufficient workability. Further, as the use of pumping increased construction speed, the need for a rational standard for slump selection according to construction conditions came to be needed. Against such backdrop, the Japan Society of Civil Engineers stipulated “minimum slump in casting” as one of the construction requirements in the Standard Specifications for Concrete Structures. Yet a common awareness with respect to specified slump values still cannot be said to exist to a sufficient degree among clients, builders, and ready-mixed concrete producers. Further, requirements for ready-mixed concrete quality and performance are growing increasingly diverse, but the Japanese Industrial Standards (JIS) provide only general specifications that fall far short of addressing the broad range of needs. There is also the view that a quality and performance classification system needs to be made part of the JIS standards. This paper presents the main findings of a survey and panel discussion to determine the direction of future studies with regard to these two issues.