Stability Of Self-consolidating Concrete Research Articles

Effects of mix-design variables on the workability, rheology and stability of self-consolidating concrete

This study investigates the effects of basic mix design variables such as water/cement ratio (w/c), slump flow, coarse-to-total aggregate ratio (CA/TA), and maximum aggregate size (Dmax) on the main characteristics of self-consolidating concrete. The w/c of the mixtures was either 0.42 or 0.50. The CA/TA ranged between 0.45 and 0.53. Slump flow was adjusted to 550, 650 or 720 ±20 mm by varying the superplasticizer content. Dmax was varied as 10, 15 and 20 mm. V-funnel, L-box, rheometer, sieve segregation tests and a new test method, recently developed by the authors, for dynamic segregation resistance were performed. The effect of each variable on the test results were effectively summarized in a table. Increasing the w/c, CA/TA and Dmax decreased the superplasticizer demand and increased the flowability. When the slump flow, w/c and CA/TA were higher, viscosity was found to be lower. Higher values of CA/TA and Dmax were found to reduce the passing ability. Increasing the slump flow (or superplasticizer content), CA/TA and Dmax disturbed the stability. Generally, the effects of w/c and slump flow on the SCC characteristics were more pronounced when compared to those of CA/TA and Dmax. Good correlations were obtained between several test results.

Influence of recycled aggregates on dynamic/static stability of self-consolidating concrete

The effect of recycled concrete aggregate (RCA) on rheology and dynamic/static stability of highly flowable self-consolidating concrete (SCC) is not well quantified. Two series of SCC mixtures containing different RCA replacement levels and proportioned using the direct replacement and Equivalent Mortar Volume methods were considered in this study. Test results have shown that the increase in RCA replacement level leads to reduced rate of flow and passing ability, yet resulted in improved static stability given the greater relative water absorption that reduces the detrimental effects of free mixing water in fresh concrete. The use of four-bladed slotted vane rotating in infinite medium was found particularly useful to mitigate aggregate migration and enhance detection of internal friction resulting from RCA skeleton. Four “rheology boxes” enabling easier development and prediction of concrete stability for given application are proposed with respect to the European Guidelines for SCC.

Workability, Testing, and Performance of Self-Consolidating Concrete

Self-consolidating concrete (SCC) is a new category of high-performance concrete that exhibits a low resistance to flow to ensure high flowability and a moderate viscosity to maintain a homogeneous deformation through restricted sections, such as closely spaced reinforcement. This paper reviews the benefits of using SCC to facilitate the casting of densely reinforced sections and improve productivity and onsite working conditions. Workability requirements necessary to secure self-consolidation and the principles involved in proportioning such highly flowable concrete are discussed. Field-oriented tests useful in evaluating the deformability, filling capacity, and stability of SCC are presented. The performance of concrete mixes proportioned according to two main approaches needed to ensure high deformability, low risk of blockage during flow, and proper stability are compared. Such approaches involved the proportioning of concrete with a moderate water-to-cementitious material ratio (w/cm) of 0.41 and using a viscosity-enhancing admixture to increase stability, as well as mixes without any viscosity-enhancing admixture, but with lower w/cm of 0.35-0.38 to reduce free water content and provide stability. Mixes with both moderate and high contents of ternary cementitious materials were evaluated. The performance of each concrete was compared to that of a flowable concrete with 250-mm slump.