Effect Of Viscosity-modifying Additive On The Lateral Pressure Of Self-compacting Concrete

Self-Compacting Concrete(SCC) could automatically fill the tiny gaps between the reinforcement without artificial vibration due to its high fluidity. However, the lateral pressure of the SCC on formwork is greater than ordinary concrete at the same height due to the high fluidity. At present, the factors influencing the lateral pressure, such as mineral admixture, viscosity-modifying agent, etc, have been studied in detail in some foreign countries, but few studies can be found in China. In this study, the sludge from sewage treatment plant containing flocculating constituents and a kind of polymer with low molecular weight were used as viscosity-modifying agents, as compared to a pasty welum gum. The influence of adding these agents on the lateral pressure of the formwork by the SCC was experimently investigated by using a simulated testing setup. The results showed that:(1) The addition of raw sludge presented a thickening effect on both the fresh cement paste and the self-compacting concrete, and the paste with the sludge addition showed an obvious thixotropical behavior. However, no thickening effect on the paste can be found when the dried ground sludge was added, and has little effect on the rheological behavior of the fresh paste. With the welan gum addition, the paste and concrete was also obviously thickened, but it seems that it does not make the paste show a more obvious thixotropy.(2) The initial lateral pressure on formwork by SCC can be reduced to a certain extent by adding the raw sludge, but not by incorporating the dry powder, probably because the former sludge showed a thickening effect, whereas the latter had not. However, the decay rate of the lateral pressure on formwork by SCC can be enhanced by adding both the raw sludge and the dry sludge, and the latter showed a more obvious decay rate in proper dosage. Though incorporation of the pasty welan gum can reduce the initial lateral pressure of SCC by thickening the paste, the decay rate of the lateral pressure showed nearly no promotion as compared to the control SCC.(3) While incorporating a kind of low, but with different, molecular weight polymer(P4 and P8) as the viscosity-modifying agent, the rheological behavior of the cement paste was apparently modified and the paste showed a typical thixotropy. The initial and the decay rate of the lateral pressure on formwork by SCC were also affected by adding VMA, but it depends on the molecular weight. While adding P4, the initial lateral pressure was hardly lowered, but the decay rate can be obviously promoted. However, while introducing P8, the initial lateral pressure was reduced, but the decay rate was less affected.