Autogenous shrinkage can be particularly high in mixtures made with relatively low w/cm, high content of cement, and supplementary cementitious materials exhibiting a high rate of pozzolanic reactivity at early age. Special attention should be given to protect the surface of SCC at early ages to minimize any desiccation. In very low w/cm mixtures, wet curing may be required. Drying shrinkage is related to the water and paste contents, as well as aggregate volume, size, and stiffness. The increased paste volume in SCC and reduction in aggregate content can lead to greater potential for drying shrinkage, which should be managed in the mixture proportioning process. The drying shrinkage increases with the increase in the content of powder materials, which can be particularly high in SCC mixtures. As in the case of drying shrinkage, creep of SCC is highly dependent on the mixture composition, paste volume, and aggregate content. For the same mixture proportions as that for conventional concrete, creep of SCC is expected to be similar to that of conventional concrete. When the SCC is proportioned with greater paste volume, however, it can exhibit higher creep than conventional concrete of similar compressive strength.
18.104.22.168 Bonding with aggregate or reinforcements
Several studies have reported that the interface between cement paste and aggregate or reinforcements is less porous and the bonding characteristics between them are better than conventional concrete. SCC flows easily around the reinforcement and bonds well. Up to 40% higher bonding strengths were measured for SCC compared to conventional concrete [156, 157 & 158]. This may be due to the lower water content and the higher powder volume in the SCC mixtures relative to the reference mixtures, which reduces the accumulation of bleed water under horizontally embedded reinforcement bars. In normal concrete, bleed water accumulation can increase the local w/cm under the bar and weaken the strength of the bond .