Formwork pressure and rheology of self consolidating concrete

Self consolidating concrete (SCC);Formwork dimensions;Lateral pressure;Rheology;Thixotropy;Structural buildup;Aggregate absorption;Static yield stress;Dynamic yield stress

Vallurupalli, Kavya ; Lange ; David A.

关键词: Self consolidating concrete (SCC);    Formwork dimensions;    Lateral pressure;    Rheology;    Thixotropy;    Structural buildup;    Aggregate absorption;    Static yield stress;    Dynamic yield stress;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/97509/VALLURUPALLI-THESIS-2017.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

The objective of this work was to understand the mechanisms responsible for formwork pressure drop over time in case of self consolidating concrete (SCC). The fresh state properties of SCC, mortar, and cement paste mixes like workability, static yield stress gain and temperature change over time were evaluated and correlated with the formwork pressure data. The mix parameters for the concrete, mortar mixes like water to cementitious ratio, the addition of fly ash, aggregate content, maximum aggregate size, aggregate moisture content, addition viscosity modifying agent, the addition of fibers were investigated. Emphasis was also placed on studying the influence of formwork dimensions on the formwork pressure. The results showed that the formwork pressure drop over time was highly dependent on the thixotropy which can be measured from static yield stress and dynamic yield stress gain over time. So a method for achieving the accurate yield stress values using the ICAR rheometer was developed. The accuracy of the pressure data obtained using the pressure sensors was also evaluated. Based on the results obtained, the accuracy of the Lange and Tejeda model in predicting the formwork pressure of self consolidating concrete was studied. The results showed that within first few hours of the pressure decay, the reversible changes in concrete dominate the pressure decay and slight variation in the mix proportions, mixing procedure alter the pressure decay significantly indicating the sensitivity of SCC mixes. The formwork dimensions also affect the pressure decay indicating the importance of including the formwork dimension parameter while developing the models for prediction of formwork pressure. Recommendations were made for reducing the variation in the mix properties, the importance of focussing on the particle to particle interaction within concrete for understanding its thixotropic properties that seem to be the primary cause of the pressure decay in the initial hours after casting before the hydration process becomes dominant.