Early-age temperature rises in GGBS concrete - Part 2: T1 values for low heat and very low heat cements

To prevent early-age thermal cracking in massive and water-retaining concrete structures, crack control reinforcement is required. The amount of crack control reinforcement needed is proportional to the temperature fall from peak temperature to mean ambient temperature (T1). An important aspect of concrete design is therefore to estimate the T1 value. However, current technical documents that assist in this are not compatible with the design approach envisaged in BS EN 197-1 and BS EN 14216 based on cement classes rather than knowledge of the composition of the blend or combination. This paper describes tests carried out on a range of Portland cement (PC)/ggbs combinations to determine the proportions of ggbs that just met the requirements for the low heat and very low heat cement classes and determine T1 values appropriate to these combinations. Two sources of ggbs were selected; one regarded as a standard ggbs typical of most UK production, and the other specifically selected as a high fineness ggbs. Data for two formwork types, four section thicknesses and four cement contents were calculated. The resulting data may be used to at the design stage to calculate minimum crack control reinforcement, when the specifier will have only defined the cement class and cement content, and not the composition.