Ultra-high-performance fiber-reinforced sustainable concrete modified with silica fume and wheat straw ash

Abstract

Developing ultra-high fiber-reinforced concrete (UHPFRC) demands an immense quantity of ordinary Portland cement (OPC). Using a high percentage of cement in UHPFRC leads to uneconomic concrete and significant release of CO2 into the atmosphere. Therefore, it is critical to address this issue by substituting the part of cement with a sustainable material. The current research has tried to tackle this issue by assessing the impact of adding wheat straw ash (WSA) and silica fume (SF) as a partial substitute of cement on the properties of UHPFRC on the static and dynamic compressive strength test, among other strength and durability characteristics. Two different batches of mixes were developed. The OPC was substituted for up to 40% in the first batch, with combined WSA plus SF at 10% intervals. In the second batch, OPC was replaced up to 40% with only WSA at an interval of 10%. Polypropylene fibers (PPFs) at 2% (by vol.) were added to modified samples to improve the ductility of concrete. The dynamic compression strength was evaluated utilizing a Split Hopkinson pressure bar, and quasi-static compression strength was determined using the compression machine. Moreover, splitting and flexural strength were also assessed, and water permeability and sorptivity tests were carried out for durability. The test outcome showed that the sample with 15% WSA plus 15% SF had higher compressive strength (174.8 MPa at 90 days) and improved durability than the sample with only 30% WSA (170.2 MPa at 90 days) and the control sample. The assessed properties tend to decline at 40% of WSA and 20% WSA with 20% SF. In dynamic compression strength, it was observed that the WSA and SF, and fibers samples performed similarly to the control sample, and these modified samples were not sensitive to strain rates. Adding 15% plus 15% SF had an optimal effect in improving the durability properties of UHPFRC. Also, the thermogravimetric analysis (TGA) confirms the role of WSA and SF in densifying the matrix of UHPFRC, decreasing the porous pores and amount of calcium-hydroxide and developing additional gels of calcium-silicate-hydrate, which enhances the strength and durability of UHPFRC. The current study revealed that the modified samples (with WSA and SF) had a low embedded CO2 for the sustainability features compared to the control sample.