چكيده به لاتين
Abstract:
Self-consolidating concrete (SCC) is a new class of high-performance concrete that can flow readily under its own weight and consolidate without mechanical vibrations. SCC has been successfully used in North America in the precast industry; however, the use of SCC in cast-in-place applications has been hindered by some technical issues, including formwork pressure exerted by SCC. One of the most important properties of concrete that can affect this issue is Thixotropy.
In this study, thixotropy is rather used to assess the effect of various mixture parameters on formwork pressure. Thixotropy is determined by the evaluation of the structural buildup at rest using a concrete rheometer and based on 3 most common test methods; including Breakdown Structure Aria (by Khayat), Hysressis aria (by Ferron) & Static yield stress growing rate (by Roussel). Pressure device is employed to evaluate the formwork pressure characteristics. These characteristics include the initial maximum pressure after casting and pressure decay. In total, 15 SCC batches were prepared with various w/c ratios, cement contents, and some mineral admixtures to evaluation of workability, thixotropy level and formwork pressure. The results showed that concrete of greater level of thixotropy can develop greater structural build-up when left in rest and displays lower lateral pressure during placement and rapid decay of pressure thereafter.
The first part of examination was study on Correlations between thixotropy test methods’s results. Coefficient of correlations (R2) were good between all methods. The second was evaluation of correlations between 3 main methods and 6 suggested thixotropic indices and formwork pressure characteristics. All of thixotropic indices show good correlations
with the relative initial maximum lateral pressure (K0) and pressure decay [ΔK(0 − tc)] but Khayat method and Hystressis method have greater R2 with initial maximum lateral pressure and pressure decay,respectively.
Keywords: Self-Consolidating Concrete, Workability, Mineral admixture, Formwork pressure
