Exploring microsilica’s role in ultra-high-strength ‎‎concrete: An ‎experimental study

The production of cement significantly contributes to global CO₂ emissions. Therefore, it is essential to ‎‎identify alternative supplementary cementitious materials (SCMs), such as fly ash, micro silica, and slag, ‎‎that enhance concrete performance while reducing environmental impact. Among these, micro silica (MS) ‎‎is considered one of the most effective SCMs. It is an ultrafine amorphous silica produced as a ‎byproduct ‎of electric arc furnace processes during the production of silicon or ferrosilicon alloys. Due to its high ‎‎pozzolanic reactivity and microfiller effect, MS contributes to matrix densification and reduced porosity, ‎‎thereby enhancing the strength and durability of concrete. This study investigated the effect of MS on ‎the ‎mechanical behavior of ultra-high-strength concrete (UHSC). Basalt aggregates are suitable for use ‎due to ‎their high strength, low reactivity, and excellent durability. For this purpose, based on both ‎technical and ‎economic considerations, a ۶۵: ۳۵ coarse and fine aggregate mixture was selected. To this ‎end, ۲۴ cubic ‎specimens (۱۰۰ mm) were prepared using four mix designs containing ۰ (control ‎scheme), ۵, ۱۰, and ۱۵% ‎MS by weight of cement. All mixes had a constant water-to-cement ratio (W/C) of ‎‎۰. ۰.۲ and identical ‎basalt aggregate grading. Compressive strength tests were conducted at curing ages of ۷, ‎‎۱۴, and ۲۸ days. ‎Specimens were prepared under standardized conditions and cured in a saturated lime-water tank at a ‎‎controlled temperature of ۲۳ ± ۱ °C until testing‎. The present study's findings showed ‎that the highest ‎compressive strength, recorded at ۱۳۳ MPa, was achieved at ۲۸ days for the specimen ‎containing ۱۵% MS, ‎representing a ۲۵% increase compared to the control scheme. The observed increase ‎in ‎compressive ‎strength is attributed to the pozzolanic reactions of MS, which reduce total porosity, limit ‎pore ‎connectivity, and promote matrix densification in the concrete microstructure.‎

کلیدواژه ها:

Ultra High Strength Concrete (UHCS) ، Supplementary ‎Cementitious Materials (SCMs) ، Microsilica Content ، Superplasticizer ، Pozzolanic materials ، Basalt