•The concrete composition was suitable for the EPAC project, but it wouldn’t be suitable for every project. The overall full-strength curing time is increased for compositions with higher GGBS content.
• Typically, the 7-day strength of a 70% GGBS concrete will be 35% of the 28-day strength compared to 70-80% for a similar Portland cement CEM I concrete.
• The reduction in early strength will be more noticeable at high GGBS levels and low temperatures.
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• The concrete strength spec called for C30/40 which has been achieved without issue, the use of GGBS on EPAC had no effect on the strength required.
•Under normal circumstances, the striking times for concretes containing up to 50% GGBS do not increase to the point of significantly affecting the construction programme. However, concretes with higher levels of GGBS will not always achieve sufficient strength after one day to allow removal of vertical formwork, particularly at lower temperatures.
• The programme was not impacted at EPAC as we had allowed for sufficient shutters to be able to leave them in place for an extra couple of days. Once on site & following the pour of the first large wall section, it became evident that if we were able to stand the prefabricated rebar before moving the shutters in place, we could maintain the programme duration between each pour. We then designed the temporary works required to do this & flipped the sequence (rebar installation before standing the shutters). As a result, we improved the overall programme by ~6 weeks.