Formwork Pressure of Self-Consolidating Concrete Made with Various Binder Types and Contents


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Title: Formwork Pressure of Self-Consolidating Concrete Made with Various Binder Types and Contents

Author(s): Joseph Assaad and Kamal H. Khayat

Publication: Materials Journal

Volume: 102

Issue: 4

Appears on pages(s): 215-223

Keywords: binder; concrete; formwork; thixotropy

Date: 7/1/2005

An experimental program was carried out to determine the effect of binder type and content on variations in lateral pressure of self-consolidating concrete (SCC). The mixtures were prepared with five binder types incorporated at various contents varying from 400 to 550 kg/m3. The influence of thixotropy, determined from concrete and concrete-equivalent-mortar (CEM) mixtures, on the variations of lateral pressure development was investigated. Test results show that, for a given binder content, the initial lateral pressure and rate of pressure drop with time are significantly affected by the binder type in use. Self-consolidating concrete made with 450 kg/m3 of Type 10 CSA cement (GU) and no supplementary cementitious materials exhibited the highest initial pressure corresponding to 98% of hydrostatic pressure. Mixtures made with quaternary, binary, and ternary cements of similar content developed lower initial relative pressures of 95, 94, and 90%, respectively. For a given binder type, the initial lateral pressure was found to increase with the binder content. This is attributed to the relatively lower coarse aggregate volume that reduces internal friction leading to greater lateral pressure. Test results also indicate that the rate of pressure drop following casting is dependent on the degree of increase in cohesion. Therefore, an increase in binder content resulted in a greater rate of gain in cohesiveness and a sharper drop in lateral pressure with time. Test results show that the increase in the degree of thixotropy of SCC and CEM can lead to lower initial pressure. For the monitoring of pressure drop with time, which is mainly dependent on the development of cohesion, thixotropy determined using CEM mixtures should be used to estimate the rate of variation in lateral pressure rather than those determined from SCC mixtures. This is because the increase in thixotropy determined from concrete mixtures is highly affected by internal friction resulting from the presence of coarse aggregate. This can overshadow the development of cohesion resulting from the binder phase that controls the rate of pressure drop with time.