Concrete pressure on formwork: influence of cement combinations and superplasticising admixtures

This paper describes a study carried out to examine the effect of cement combinations and new superplasticising admixtures in concrete on lateral pressure development in column and wall formwork. The additions, used in structural grade concretes, included ground granulated blastfurnace slag (ggbs), fly ash (FA), silica fume (SF) and metakaolin (MK). Two superplasticising admixtures were also tested to examine water reduction/variable workability effects on concrete pressure. In addition to the constituent materials, the influence of rate of rise of concrete in formwork was also investigated. The tests involved instrumenting column and wall formwork with concrete and pore water pressure measuring devices (over their height) and recording pressure development, and the head of concrete rising vertically in the element during construction. Tests were mainly carried out under controlled conditions (20 elements of 3·0 and 8·0 m height) and supplemented with measurements at construction sites where the materials...