In 2022, engineers mixed recycled textile fabric into cement; after accelerated aging, the silica-fume composite kept its flexural strength and retained post-crack performance

Engineers in 2022, tested a cement based composite reinforced with flax and recycled fabric waste, containing 30% silica fume, and found that it kept its pre-aging flexural performance after aging. The treated composite recorded between 14.3 and 15.4 MPa in flexural strength, while its toughness ranged from 8.1 to 8.7 kJ/m². The study, titled “Microstructural Properties of Hybrid Textile Waste-Flax Fabric-Reinforced Cement Composites,”explored whether the integration of recycled textile fibers into cement-based materials could solve durability issues found in natural fibers. The researchers produced a nonwoven fabric consisting of 65% recycled textile-waste fibers and 35% flax fibers.In its final composition, the fabric contained about 45% cotton and 20% polyester from the recycled portion, plus 35% flax. By using six layers of hybrid fabric, the researchers reinforced the cement-based composite. They substituted portions of the Portland cement matrix with silica fume at three distinct levels: 0%, to 15%, and 30%. Following production, the composites underwent testing for flexural and tensile performance under unaged conditions, as well as after accelerated wet-dry and freeze-thaw cycles.Silica fume reduced fibre degradation during accelerated aging The study found that wet-dry cycles had a greater effect on the textile-reinforced composites as opposed to freeze-thaw cycles. The flexural strength of the composite without silica fume fell from 16.5 MPa in the unaged condition to 10.0 MPa after wet-dry ageing, marking a reduction of 40%. Conversely, the composite containing 30% silica exhibited a different behaviour. Its strength measured 14.5 MPa before aging, after wet-dry cycles it was 14.3 MPa, and 15.4 MPa after freeze-thaw cycles. Consequently, the researchers determined that the 30% silica fume composite maintained similar performance across all tested conditions.In case of flexural toughness the results were almost the same: without silica fumes, toughness fell from 10.1 kJ/m² in the unaged condition to 6.5 kJ/m² after wet-dry cycles, indicating a loss of more than 35%. With 30% silica fume, toughness dipped only slightly, which limited the loss to about 5%. Researchers attributed this to the effect of silica fume on the matrix cement through their X-ray diffraction and thermogravimetric analysis, which revealed that the amount of calcium hydroxide in the matrix is reduced by increasing silica fume. Calcium hydroxide was reduced by almost 66% in the 30% silica fume sample when compared to the sample without silica fume. This minimized the alkaline conditions responsible for the degradation and embrittlement of the fibers during accelerated aging.Recycled textile fabric continued to contribute after cracking The main objective of the textile reinforcement was to improve the material’s behaviour after the cement matrix cracked. During flexural testing, the fibers transferred tensile stresses across cracks, which allowed the composite to sustain load and develop multiple instead of failing immediately after the first crack.After aging the material's post-cracking behavior became especially prominent. Under wet-dry cycles, the stiffness within the composite without silica fume degraded by more than 60%. Conversely, under the same conditions, for the composite with 30% silica fume the reduction was only 20%. Furthermore, when subjected to freeze-thaw cycles, the stiffness reduction for the 30% silica fume composite was limited to 7%.Tests for direct tensile showed the same effects, under the wet dry cycles the tensile strength of the composite without silica fume and the 30% silica fume composite was reduced by 50% and 15% respectively. Further microscopic examination confirmed that after wet-dry aging, fibers in the composite without silica fume suffered greater degradation whereas most fibers in the 30% silica fume composite retained their length after failure with degradation. The researchers concluded that when the cement matrix is modified with 30% silica fume, it prevents significant fiber embrittlement and retains flexural and post-cracking properties more effectively under wet-dry and freeze-thaw conditions, supporting its potential use in building components.You use AI every day. Now get your AI Quotient. Take the AIQ test.