Sensitivity of Rapid-Setting Self-Consolidating Concrete (RSSCC) to Mixture Production Variables

Abstract

When dealing with the issue of repair of the infrastructure, especially bridge deck and concrete pavements, the desire to minimize the traffic delays and inconvenience to the traveling public often leads to the use of rapid hardening repair materials. Frequently, the repairs need to be performed in confined spaces where repair materials are placed around the existing or newly installed reinforcement. As a result, it is very desirable for the repair material to have high fluidity that can ensure good compaction and facilitate flow to tight spaces, preferably without the use of a vibrator. Also, typically such repair concretes are prepared in small (~25-30 L) batches using low-capacity mortar mixers. The existing literature on self-consolidating concrete (SCC) clearly indicates that its stability, in terms of flowability and segregation resistance, can be significantly influenced by the quantities as well as by physical and chemical properties of the component materials. This paper presents the results of laboratory investigation on the sensitivity of rapid-setting self-consolidating concrete (RSSCC) to material and production variables that included: aggregate gradation, aggregate moisture content and the type of the mixer. The maximum size of the aggregate used in production of RSSCC in this study was 9mm and all mixtures were prepared using Type III Portland cement, silica fume, micro-fine fly ash, high-range water reducer, and an accelerator. Two types of mixers were used in this study: a 56 L-capacity rotary pan mixer and 26 L-capacity mortar paddle mixer. All mixtures were prepared using the same general proportions but the “as-mixed” aggregate moisture condition varied fiom dry (0% moisture) to twice the saturated surface dry (SSD) value. The aggregate gradation was also varied by using aggregates with different fineness modulus. It was observed that variation in aggregate moisture content and aggregate gradation resulted in noticeable changes in fresh concrete properties such as the slump flow, stability and V-funnel flow values. While changes in moisture content and gradation of aggregates had an impact on the early (6 h) compressive strength, the compressive strength at the end of 24 hours was not significantly affected.