Influence of blended powders on properties of Ultra-High Strength Fibre Reinforced Self Compacting Concrete subjected to elevated temperatures

Ultra-High Strength Fibre Reinforced Self Compacting Concrete (UHSFRSCC) is in great demand for use in construction projects around the globe. Unless fillers are utilized in this concrete, its production will come at an excessive environmental cost due to the high Carbon footprint of Portland cement. A gap in the published literature was identified, where quaternary mixes, containing Portland cement with three fillers, incorporating fibres, and achieving ultra high strength, were not cited. In this study ternary and quaternary mixes were designed and produced, satisfying the European Guidelines for SCC, with compressive strengths exceeding 115 MPa. Some mixes had compressive strengths between 125 – 150 MPa, which were not previously reported in the literature. The mixes contained Silica Fume (SF), Metakaolin (MK), Limestone powder (LS) as partial Portland cement replacement and quartz powder (QP) as partial sand replacement. Basalt Fibres were added to reinforce the matrix. Compressive & tensile strength of the mixes along with UPV, sorptivity, absorption and SEM Micro-structure features were studied at ambient temperature and after the samples were exposed to either 200 or 300 oC; since the behavior of HSC at elevated temperature is always a cause for concern. The active and inert fillers exhibited a synergic behavior at all temperature conditions. The mix containing: 15% SF, 5% MK, 20% LS and 34% QP achieved the best performance. Compressive and splitting tensile strength improve by 10% and 17% while sorptivity and absorption decline by 40% and 29% respectively at ambient temperature. Residual compressive strength improved by 10% and 19% while, residual splitting tensile strength significantly increases by 21% and 28% after exposure to elevated temperatures 200℃ and 300℃ respectively. Meanwhile, residual sorptivity decreases by 39% and 38% after exposure to these elevated temperatures. Microstructure properties supported and agreed with the mechanical and permeation characteristics results. The results will contribute to the development of UHSFRSCC in hot weather countries.