Long-term deflection of RC beams containing GGBFS

The results of experimental investigations into the long-term deflection of RC beams containing ground, granulated, blast-furnace slag (GGBFS) are presented. The creep deflection is determined under constant, sustained, four-point loading at the ages of 1, 3, 7, 14, 21, 28, 30, 56, 60, 90, 120 and 150 d. Elastic and creep deflection recovery is determined at the ages of 151, 153, 157, 164, 171, 178 and 180 d for reinforced concrete (RC) beams and RC beams containing GGBFS for all concrete mixes. The shrinkage deflection of RC beams and RC beams containing GGBFS for all concrete mixes is also measured at the corresponding ages of creep deflection measurement. The amount of cement replacement by GGBFS is varied from 20% to 60%. It is found that GGBFS concrete beams have much higher deflection than plain concrete beams. At 150 d, the average creep deflection of RC beams containing 20%, 40% and 60% GGBFS is 1·3, 1·7 and 2·0 times higher than for plain concrete beams. The experimental results of creep and shrinkage deflections of RC beams containing GGBFS are compared with available design codes. A new model for the prediction of long-term deflection of GGBFS concrete beams is proposed. For the Indian Standards code, modification factors for creep coefficient and shrinkage strain for GGBFS concrete are proposed.