Effect of High-Range Water-Reducing Admixture Type on Performance of Self-Consolidating Concrete


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Title: Effect of High-Range Water-Reducing Admixture Type on Performance of Self-Consolidating Concrete

Author(s): K.H. Khayat and S.-D. Hwang

Publication: Special Publication

Volume: 239


Appears on pages(s): 185-200

Keywords: concrete-equivalent mortar; high-range water-reducing admixture; PCP; PNS; restrained shrinkage; self-consolidating concrete; workability

Date: 10/1/2006

The workability characteristics of self-consolidating concrete (SCC) and performance of the hardened concrete depend on the type of high-range water reducing admixture (HRWRA) in use. An experimental investigation was undertaken to evaluate the effect of HRWRA type on key performance aspects of SCC, including workability, mechanical properties, transport properties, frost resistance, de-icing salt scaling resistance, and restrained shrinkage. The evaluated mixtures were proportioned with water-to-cementitious materials ratio of 0.42 using two types of blended cements. Two different types of polycarboxylate (PCP)-based HRWRAs, a polynaphthalene sulfonate (PNS)-based HRWRA, and three types of viscosity-enhancing admixtures (VEAs) that are compatible with the various HRWRAs were used in this investigation. The SCC mixtures had initial slump flow of 660 ± 20 mm and air volume of 6.5 ± 1.5%. As expected, the concrete made with PNS-based HRWRA had significantly higher HRWRA demand compared to similar concrete prepared with PCP-based HRWRA. For the selected binder type (B1 binder), the SCC proportioned with PNS-based HRWRA had higher maximum settlement values of 0.44% compared to 0.16% to 0.44% obtained in the case of similar SCC made with PCP-based HRWRA. Despite some spreads in mechanical properties, SCC mixtures made with either type of HRWRA exhibited excellent frost durability and chloride-ion impermeability. Higher resistance to shrinkage cracking was observed for the concrete made with PNS-based HRWRA than that with PCP-based HRWRA, despite the lower compressive strength and higher drying shrinkage of the former concrete. This can be due to relatively greater tensile creep coefficient and stress relaxation in tension for the B1-PNS mixture, thus reducing tensile stress by restrained shrinkage. In addition to the concrete investigation, concrete-equivalent mortars (CEMs) based on the tested SCC mixtures were prepared to evaluate the effect of HRWRA type on the minimum water content needed to initiate flow and the relative water demand required to increase fluidity. These parameters are closely related to packing density and robustness of the mixture, respectively. Flow characteristics of CEM made with different HRWRA types indicate that CEM made with PNS-based HRWRA exhibits higher relative water demand and greater robustness than CEM prepared with PCPbased HRWRA.