Applied mixture optimization techniques for paste design of bonded roller-compacted fibre reinforced polymer modified concrete (BRCFRPMC) overlays

The overall composite performance of concrete is generally contingent on achieving the right proportion of blend. The use of mixture experiments provides a flexible, easy, and quick way of optimizing multi-component materials of this nature. This paper describes the use of optimization techniques within the concept of material mixture experiments for proportioning and designing the paste (P) component of a bonded roller compacted fibre reinforced polymer modified concrete. By constraining the range of variability of the paste constituents, a feasible design space was created with 13 experimental points treated based on the required structural and elastic properties of the overlay. The optimum consistency-time for full consolidation and composite behaviour with the substrate ordinary Portland cement concrete (OPCC) was established between 34.1 and 34.9 s, while the resulting apparent maximum density achieves between 97.1 and 98.0 % of the theoretical air-free density. The tensile and shear interfacial tests performed on the optimum mixture overlay also exhibited good bonding capability with the substrate OPCC. The combined effects of curing age and surface texture on bonding were also underlined

Flexural strength and elastic modulus of ambient-cured blended low-calcium fly ash geopolymer concrete

Fly ash geopolymer is an emerging alternative binder with low environmental impact and potential to enhance sustainability of concrete construction. Most previous works examined the properties of fly ash-based geopolymer concrete (GPC) subjected to curing at elevated temperature. To extend the use of GPC in cast-in-situ applications, this paper investigated the properties of blended low-calcium fly ash geopolymer concrete cured in ambient condition. Geopolymer concretes were produced using low-calcium fly ash with a small percentage of additive such as ground granulated blast furnace slag (GGBFS), ordinary Portland cement (OPC) or hydrated lime to enhance early age properties. Samples were cured in room environment (18–23 °C and 70 ± 10% relative humidity) until tested. The results show that, density of hardened GPC mixtures is similar to that of normal-weight OPC concrete. Inclusion of additives enhanced the mechanical strengths significantly as compared to control concrete. For similar compressive strength, flexural strength of ambient cured GPC was higher than that of OPC concrete. Modulus of elasticity of ambient cured GPC tend to be lower than that of OPC concrete of similar grade. Prediction of elastic modulus by Standards and empirical equations for OPC concrete were found not conservative for GPC. Thus, an equation for conservative prediction of elastic modulus of GPC is proposed