Durability and microstructure of eco-efficient ultra-high-performance concrete

Abstract

The sustainability of ultra-high-performance concrete (UHPC) could be enhanced by using by-product materials with high replacement percentages. This research aims to study the effect of using blast furnace cement (CEM III), fly ash (FA), and granulated blast furnace slag (GBFS) as partial replacements to cement in UHPC. CEM III with percentages of 30%, 50%, and 100%; FA and GBFS with percentages of 30% and 50% were used as replacements from ordinary Portland cement (OPC) weight. Compressive strength and modulus of elasticity tests were conducted to evaluate the results of UHPC specimens. The effect of sulfate attack was studied at concentrations of 5, 50, and 75 g/l, at 28, 90, and 180 days, for each concentration individually. Chloride penetration was also studied through the colorimetric method using the AgNO3 solution. The development of UHPC microstructural properties was studied via SEM and EDX analysis. Results showed that concrete with high cement replacement of FA up to 50% percentage had better results in compressive strength and modulus of elasticity reached to 160.9 MPa, and 51.64 GPa respectively. Concrete can still achieve ultra-high-performance of 157.4 MPa with FA replacement of up to 50% for a long period and a high concentration of sulfate attack. However, for CEM III or GBFS, attack period, sulfate concentration, or replacement percentage must be lowered to preserve the concrete still achieving ultra-high-performance. SEM images and EDX analysis for the enhanced UHPC structure show the high dense microstructure and so small ITZ thickness, and strengthened the results obtained from the conducted permeability and compressive strength tests.