چكيده به لاتين
the rheological properties of fresh concrete with a w/b = 0.42 and incorporating two chemical admixtures, namely, polycarboxylate- (PC) and naphthalene sulfonate (NS)-based HRWRA were studied at three different ambient temperatures: 10, 20, and 30 °C. also viscosity-modifying admixture (VMA) and retarder were used to produce the selected matrices with slump flow of 700 ± 30 mm, visual stability index (VSI) of 0 or 1, and T50 of 2 to 5 s.
For short haul and casting times and a rapid construction site progress, a powder rich SCC with a high charge density can be considered as the best choice. If the casting process demands for enduring flowability retention and slow de-molding can be accepted, a high w/b mixture with low charge density should be preferred. The charge density and the mixture composition both can help finding the optimum adjustment for particular construction site conditions.
The results indicate that PC was found to be able to retain higher slump at relatively low dosage over prolonged mixing at high temperature than the other superplasticiser considered in this study. the highest compressive strength values were obtained when PC was used.
Besides temperature effects that can be related to PC, temperature effects on the VMA have to be considered for the VMA type SCC. The VMA type SCC requires a highly charged PC at low temperatures, whereas at high temperatures the effect of PC is less prominent.
Another important result show that retarders are important to enhance the workability of concrete at 10 and 20°C.
