Design and Application of Low Compaction Energy Concrete for Use in Slip-form Concrete Paving

摘要

Slipform self-consolidating concrete (SFSCC) requires sufficient fowability in order to consolidate without the use of internal vibration. However, this concrete must also gain sufficient green strength in order to keep its shape immediately after slipform paving; a process which involves consolidation and extrusion. It has been demonstrated for minimal compaction energy concrete used in SFSCC that small additions of clays (less than 1% by mass of cement) can make substantial improvements on the shape stability. Clays have also been shown to improve the cohesiveness of cement-based extruded materials at similarly low dosages. The purpose of this study is to quantify how both micro and nanoclay admixtures affect the strength of the cement paste microstructure from a rheological stand point and to compare this to the behavior of fresh concrete. Shear and compressive rheology techniques are used to measure how the solids volume fraction of cement suspensions with different admixtures evolves with stress. Based on these relationships, the effectiveness that different clays and other admixtures have on the balance between flowability and shape stability can be measured. A shear rheology method is used to investigate how the maximum packing fraction of flocs changes under increasing shear stress, while a compressive rheology method is used to determine changes in the local solids volume fraction (solids volume fraction of the sediment region, or sediment volume fraction) under increasing compressive stress. Results are compared to green strength tests performed on concrete mixes derived from the cement paste mixes investigated.