Eco-friendly lightweight composite prepared with geopolymer and wheat straw

Agricultural waste is promising to be used for lightweight building materials. The combination of geopolymer and wheat straw (WS) is adopted to produce a kind of eco-friendly lightweight composite. Using the pretreated WS by NaOH and Na2SiO3 solutions, the influence of WS on the properties of geopolymer-wheat straw composite (GWSC) is investigated. The pretreated WS avoids the retarding effect of the untreated WS on the hydration of geopolymer and even presents an accelerating effect. Increasing the content of pretreated WS generally results in the reduction in apparent density and strength, the GWSC with the apparent density of 1000-1500 kg/m3 can be prepared, corresponding to the 28d compressive strength between 5 MPa and 25 MPa. The water absorption linearly increases with the increases of the pretreated WS content, while an appropriate amount of the pretreated WS can enhance the water resistance of GWSC. A WS/FA ratio lower than 8% can produce the GWSC with qualified thermal insulation performance. The alkaline treatment, especially NaOH treatment, significantly improves the bonding strength between fiber and geopolymer matrix. In addition, the pretreated WS saturated by NaOH and Na2SiO3 solutions is beneficial to the fluidity of geopolymer-WS mixture and could act as the internal curing agents to enhance the hydration of geopolymer.