Strength Properties and Shrinkage Behaviour of Roller Compacted Concrete

Abstract

Roller compacted concrete (RCC) is a dry concrete that exhibits zero slump. It gained popularity because of economy, strength and fast placement. Initially, the adoptability of RCC was limited to dam construction because of lower heat of hydration. RCC pavements have gained momentum in the last decade because of sustainability and initial cost benefits. Other benefits of RCC include higher structural capacity per unit thickness, higher sustainability rating and earlier opening to traffic. In order to attain sustainable development with RCC, some industrial waste products like fly-ash, ground granulated blast furnace slag (GBBS) can be used in high volumes as supplementary cementitious materials. In the present study, the effect of GGBS as partial replacement of Ordinary Portland cement (OPC) is explored in terms of strength properties and in service performance of RCC. The RCC mixes were prepared by using two types of coarse aggregates viz. crushed gravel (CG) and limestone (LS). The mix proportion of RCC was finalized based upon soil compaction approach. The RCC mixes were evaluated on the basis of compressive strength, split tensile strength, flexural strength, abrasion resistance and drying shrinkage strain. The effect of maximum ambient temperature i.e. 70 ± 2ºC on the shrinkage behaviour was also studied under two categories. Under the first category, specimens were subjected to a constant temperature of 70 ± 2ºC up to a period of 270 days; while in second category, temperature cycles of 12 hour heating at 70 ± 2ºC followed by a cooling at 10 ± 2ºC for a period of 12 hour were applied on the specimens for a period of one month. Further, all the strength properties, abrasion resistance and drying shrinkage of RCC were correlated to the compressive strength of RCC by performing different regression analysis. The strength properties results show that incorporation of GGBS into the RCC mix, leads to lower strength at early curing age, followed by strength higher than the control mix. The improvement in later age strength of mixes containing GGBS indicates that the glossy components in GGBS react slowly with water. RCC mix at 40% replacement level of cement vi with GGBS presents the highest strength values as compared to other replacement levels. The strength results were further supported by Scanning Electron Microscopy (SEM) and stoichiometric analysis. Depth of wear results also show that replacement of cement with GGBS leads to improvement in abrasion resistance after 28 days of curing period. The variation in aggregate type also had significant influence on the properties of resultant mix. RCC mix with limestone aggregates presents higher strength during the initial curing age, while mixes incorporating crushed gravel aggregates registered higher later age strength. Observed higher strength at early age with limestone aggregates can be attributed to the accelerated hydration occurring in mixes with limestone aggregates; while in mixes incorporating crushed gravel aggregates, hydration occurred at a steady rate. RCC mixes with limestone aggregates presents marginally better abrasion resistance as compared to crushed gravel aggregates, at all curing ages. Drying shrinkage strain results demonstrate that GGBS incorporation into the RCC mixes exhibited higher shrinkage strain than the control mix because of higher volume of paste and denser matrix produced by the GGBS particles. Mixes incorporating crushed gravel experienced 23% higher shrinkage strain than the mixes having limestone aggregates at end of drying duration which can be attributed to lower modulus of elasticity of crushed gravel as compared to limestone. The least shrinkage strain was observed in the mix having limestone aggregates and 20% GGBS incorporation level. Thermal shrinkage strain results show that heating the specimens at 70 ± 2ºC accelerated the shriankge at early duration of heating beacasue of acclearation in hydration reaction of cement. The variation in aggregate type and incorporation of GGBS effects the thermal shrinkage strain similar with the drying shrinkage strain. Heating and cooling cycles led to large initial variation in thermal strain, which reduced with the progressive increase in heating and cooling cycles irrespective of aggregate type and GGBS content. Further, the failure cycles predicted from the S-N curve shows that all prepared RCC mixes will sustain atleast one millions heating and cooling cycles.