Roller-compacted concrete pavement (RCCP) is increasingly considered a suitable alternative for road construction due to its lower overall construction cost, relatively high early-age strength, an‎d rapid execution. The main difference between RCCP an‎d conventional concrete lies in the mix design an‎d construction method. Nowadays, many researchers around the world are seeking to reduce the environmental impacts of the construction industry. Cement production releases a significant amount of carbon dioxide into the atmosphere. The most effective technique to reduce CO₂ emissions is to decrease the use of cement clinker by partially replacing it with supplementary materials. In addition, industrial by-products require effective utilization to prevent environmental damage. In this study, the use of fly ash, granulated blast furnace slag, an‎d their combination as cement substitutes in RCCP was investigated to reduce environmental impacts, while steel fibers were incorporated to improve mechanical properties. The specimens were prepared using a soil-based approach, an‎d compaction was carried out with a vibrating hammer. The experimental program was conducted in two phases. In the first phase, with a cement content equal to 15% of aggregate weight, three levels of steel fiber (0, 30, an‎d 45 kg/m³), three levels of fly ash (0, 20, an‎d 40% of binder weight), three levels of blast furnace slag (0, 20, an‎d 40% of binder weight), an‎d three moisture contents (4, 5, an‎d 6% of dry aggregate weight) were considered to determine the optimum moisture content for the main mix designs. In this stage, 189 cube specimens (100×100×100 mm) were tested to establish the optimum moisture content. In the second phase, 21 mix designs were obtained based on the determined optimum moisture content, an‎d the main specimens were cast. These specimens included compressive strength tests at 7, 28, an‎d 90 days (189 cube specimens of 100×100×100 mm), water absorption tests (42 cube specimens of 100×100×100 mm), an‎d flexural Toughness tests (42 prism specimens of 100×100×350 mm). Finally, using a genetic algorithm an‎d based on previous studies as well as the results of this research regarding the effects of fly ash, slag, an‎d steel fibers—both individually an‎d in combination—as well as other cement alternatives in RCCP, the optimal low-carbon mix design was obtained for each compressive strength level. The findings indicate that increasing steel fiber content in concrete mixes improves optimum moisture content, compressive strength, modulus of rupture, an‎d toughness index. The combined use of 20% fly ash an‎d blast furnace slag reduces strength at 7 days, but increases strength at 28 an‎d 90 days compared to mixes without cement replacement. Furthermore, incorporating 30 kg/m³ of steel fibers in mixes containing slag an‎d fly ash showed the best performance in terms of compressive strength an‎d water absorption. Replacing 20% of cement with a combination of fly ash an‎d blast furnace slag reduced water absorption an‎d enhanced long-term strength. The use of steel fibers an‎d cement replacement materials can have a positive effect on the properties of RCC while simultaneously reducing CO₂ emissions, although the use of steel fibers an‎d superplasticizers may lead to an increase in carbon emissions.

مرتضي مدح خوان

مهرداد حجازي , پيام اسدي