Research on durability and multi-index evaluation of carbon emissions for high-strength concrete with fly ash manufactured sand

To explore the influence of fly ash substitution rates (FASR) on the durability of high-strength manufactured sand concrete (MSC) and natural sand concrete (NSC), as well as the performance difference between MSC and NSC, workability tests, mechanical performance tests, and durability tests were conducted on MSC and NSC with different FASR, and carbon emissions estimation was carried out based on concrete mix proportion. The study shows that the workability of MSC is slightly lower than NSC, and an increase in FASR contributes to the improvement of concrete workability. The strength of MSC at all ages is superior to NSC, and an increase in FASR affects the early strength improvement of concrete, with more significant strength improvement at 10% and 15% FASR in the later stage. After sulfate attack, the wind sand erosion resistance of MSC is better than NSC, and a 15% FASR can significantly improve the wind sand erosion resistance of concrete. The frost resistance of MSC is better than that of NSC under 400 freeze-thaw cycles, and a 10% fly ash substitution can improve the frost resistance of concrete. The total carbon emissions from the production of raw materials to the transportation stage of MSC are slightly higher than NSC, an increase in FASR can effectively cut down the carbon emissions of concrete. To sum up, the performance of concrete is maximized at 10% and 15% FASR, with minimal environmental impact, indicating that manufactured sand (MS) instead of natural sand (NS) in high-strength concrete is completely feasible.