The effect of mixture proportions on the properties of high strength concrete pavements

Abstract

Ultra-Thin Continuously Reinforced Concrete Pavement (UTCRCP) is an innovative pavement type that has the potential to fulfil South Africa’s pavement repair strategy requirements. It consists of a thin high strength concrete layer reinforced with steel mesh. Premature pavement failure occurs in UTCRCP and has been linked to the formation of cracks wide enough to allow water ingress into the supporting layers. Crack formation is influenced by environmental conditions and concrete mixture proportions of which the mixture proportions is the only factor that can be controlled by the manufacturers. To ensure that UTCRCP reaches its potential the effect of mixture proportions on the properties of High Strength Concrete (HSC) must be investigated with the aim of preventing excessive crack formation. A literature study had revealed that fly ash, silica fume, superplasticizers and high paste contents are commonly used in HSC. The influence of these mixture constituents was investigated in three sets of experiments. In the first set the effect of fly ash and silica fume was tested using mortars. A ternary cement blend was also selected to be used in the second set of experiments where the effect of paste content and superplasticizers on HSC was determined using multivariable analysis. The effect of a wider range of paste content on the properties of HSC was investigated in the third set of experiments. Results confirm that fly ash and silica fume are complimentary when used in ternary blends and these two supplementary cementitious materials may increase the total early-age deformation in mortars. The multivariable analysis revealed that within the parameter range tested paste content and superplasticizer dosage influenced the early-age properties but not the long-term properties of HSC. Through variation of the paste content over a wider range, from 25% to 60%, it was found that paste content does influence both the early-age and long-term properties of HSC. Overall it could be recognised that high paste contents have a detrimental effect on the properties of HSC with regards to early-age and long-term crack formation, and that caution should be exercised when selecting paste content during mix design.