The influence of ground granulated blastfurnace slag (GGBS) additions and time delay on the bleeding of concrete

Abstract Bleed tests were performed in accordance with ASTM C232-92 on concretes in which up to 85% of the cement was replaced with ground granulated blastfurnace slag (GGBS) obtained from a number of different sources. The time at which the bleed test was started was varied from 30 to 120 min to simulate site conditions. The addition of up to 55% slag increased the bleed capacity by 30% (compared to the plain Portland cement (OPC) mix) but had little effect on bleed rate. Increasing the slag content to 85% had no further significant effect on bleeding. The source of slag was also found to have little effect on the bleeding but comparisons made with results from 10 years ago suggest that now the present day slags have a much less marked effect on bleeding probably because they are ground finer. Delaying the start of the bleed test from 30 to 120 min reduced the bleed capacity of the OPC mix by more than 55% compared with 32% for the slag mixes. The reduction in bleed rate was similar for all mixes at about 45%.