The Development Of Mix Design Method For Self-compacting Concrete Based On The Rheological Characteristics Of Paste

Rock-filled concrete (RFC) is an innovative dam construction material that hasbeen widely used in hydraulic engineering in China. The RFC construction qualitymainly depends on the filling rate of the pouring self-compacting concrete (SCC),which is determined by the workability of SCC. The production of SCC with excellentworkability requires that appropriate mix proportions be devised. The purpose of thisthesis is to develop the mix design method for SCC based on the rheologicalcharacteristics of paste to simplify the mix design process and to save the amount oflaboratory work, testing time and materials required to produce SCC.The theoretical model suggested that the rheological characteristics of mortaraffected the flowability and segregation resistance of SCC by influencing the bearingforce and movement condition of gravel particles. The relation between the rheologicalcharacteristics of paste and the workability of SCC was then established by integratingthe existing analytical correlations between the rheological characteristics of paste andmortar. The workability of SCC and the mini-slump flow of the equivalent pasteswere tested to verify the model. The mix design method based on the rheologicalcharacteristics of paste was subsequently proposed and demonstrated to besimple and effective by the successful preparation of pure limestone powderSCC without cement. Using this method, we achieved the aim of predicting theworkability of SCC from the rheological characteristics of paste. A new conceptfor the mix design for SCC was provided.To better guide the adjustment of the parameters and modification the materialscharacteristics for the mix design, this thesis further studied the important factors of therheological characteristics of paste, i.e., polycarboxylate-type superplasticizer (sp),water, and cement hydration. Their mechanisms of action were analyzed. Asedimentation balance method was used to measure the size distribution of the flocs inthe limestone powder pastes. The water film thickness (WFT) of flocs was thencalculated and shown to be the determinant for the rheological characteristics of paste.Based on this WFT of flocs, the effects of sp and water on the powder flocculation andthe characteristics of paste were demonstrated and compared. While in the cement pastes, the rheological characteristics, adsorption of sp on powders and cementhydration products as a function of time were tested. The results indicated that theadsorption of sp on unit area of cement hydrates had strong positive correlation with therheological characteristics of paste. The study provided a theoretical basis for improvingboth the rheological characteristics of paste and their retention ability by means ofadjusting the parameters and modifying the materials characteristics.Lastly, this thesis has proposed and demonstrated a new mix design method forSCC based on the rheological characteristics of paste. The mechanisms of action of therelevant parameters were also investigated. A simple, efficient and rational solution forthe production and workability control of SCC under the RFC construction wasprovided.