Influence of limestone powder content and size on transport properties of self-consolidating concrete.

摘要

Self-consolidating concrete (SCC) requires higher cementitious materials content than conventional vibratory-placed concrete. This requirement leads to higher time-dependent properties (i.e., shrinkage (drying and autogeneous) and creep), increases formwork pressure, and results in a higher production cost. One alternative to alleviate excess creep and shrinkage, and to reduce cost, is to replace a portion of cementitious materials with mineral additives. The objective of this study was to examine the role of limestone powder, as a partial replacement of cementitious materials, on transport properties of self-consolidating concrete (SCC). A total of 10 different SCCs, including a control concrete, was prepared and test specimens were cured for 28 and 90 days. A constant powder content of 475 kg/m3(800 lb/yd 3), constant coarse-to-fine aggregate ratio of 0.43, and uniform water-to-cementitious materials ratio of 0.45 were used. A high-range water reducing admixture was utilized and its dosage varied in order to achieve uniform target flow properties. The target flow properties were: slump flow of 625 mm +/- 25mm (25 inches +/- 1 inch), a visual stability index of 0 (highly stable) to 1 (stable), and J-Ring less than 50 mm (2 inches). The flow properties examined were slump flow, visual stability index (VSI), T50 flow time, and J-Ring. The evaluation of bulk properties included compressive strength and demolded unit weight. The transport properties of the studied SCCs consisted of absorption, capillary absorption, water penetration, rapid chloride penetration, rapid migration, and chloride diffusion.;For the first part of the study, limestone powder with an average size gradation of 8 microns, designated as L8, replaced a portion of cementitious materials (Portland cement and fly ash) at the levels of 5, 10, 15, 20, 25, and 30% by weight. It was found that the inclusion of L8 type limestone powder improved absorption, water penetration, capillary absorption, and rapid chloride penetration of the studied SCCs, in comparison with those of the control SCC, for both curing ages. While chloride diffusion and rapid migration coefficients did not improve at 28-day curing as compared to those obtained for the control SCC, a longer curing age (i.e. 90 days) provided for marginal (5%) to sizeable (30%) improvements in chloride diffusion and rapid migration coefficients, respectively. Improvements with each increasing 5% increment of limestone powder replacing a portion of cementitious materials were observed for rapid chloride penetration, capillary absorption, and absorption at 28- and 90-day curing. The 28-day cured limestone powder contained SCCs produced water penetration depths, rapid migration coefficients, and chloride diffusion coefficients which remained unaffected with increases in limestone powder content. All transport properties of the studied SCCs improved with increasing curing age from 28 to 90 days.;For the second part of the study, limestone powder, designated as L3, which had an average particle size of 3 microns, was used to substitute a portion of cementitious materials at the levels of 10, 15, and 20% by weight. It was observed that the finer limestone powder contained SCCs generally improved absorption, water penetration, rapid chloride penetration, and rapid migration as compared to those obtained for the coarser limestone powder contained SCCs. When higher limestone powder content (i.e., 20% by weight of cementitious materials) and longer curing age (i.e., 90 days) were used, the two limestone powder types had similar water penetration, rapid chloride penetration, and rapid migration results. Moreover, when 3 micron size limestone powder was used, with the exception of absorption test results, the remaining transport properties of the studied SCCs improved with an increase of curing age from 28 to 90 days.