Environmental Stability Of Straw-reinforced Geopolymer As Architectural Heat Preservation Composites

Recent years,a new type of high performance and environmentally friendly materials—Geopolymeric binder,have seen a great development across the world.Apart from the high compressive strength and excellent solidification properties,Geopolymeric binder also have good environmental durability and thermal insulation effect.On the other hand,straw has the characteristics of qualitative light,heat preservation,coupled with abundant resources in our country,it will be an practical significance to the building energy conservation and waste resource utilization in case of combining geopolymer and straw to produce a new type of lightweight architectural heat preservation composites.This experiment studies the heat preservation properties and environmental stability(high-temperature resistance,freeze-thaw properties,microorganisms erosion resistance,acid rain resistance)of straw-geopolymer.Scanning electron microscopy(SEM),X-ray diffraction(XRD),thermal gravimetric analysis(TGA),Fourier transform infrared spectroscopy(FT-IR)and other analyzes were used to explore the causes of heat preservation and environmental stability properties,and to provide theory basis for straw-geopolymer insulation building materials application.The main results were as follows:(1)The dense layered structure of geopolymer makes the material has a high compressive strength,meanwhile blocking the transfer of heat.When the straw content is 4%,the compressive strength of straw-geopolymer reaches 32.78 MPa and the thermal conductivity is 0.0946 W/m·K.They both meet the requirements of common building materials and the thermal insulation materials.(2)Results of thermal analysis show that the geopolymer composites can prevent the degradation of straw when elevated temperature<250 ℃.The remaining compressive strength is 35.94 MPa after calcination at 600 ℃ for 120 min.When calcined at<800 ℃,the composites own stable mineral structures and high temperature performance.(3)Freeze-thaw tests indicate that the compressive strength of composites can be maintained at>25 MPa,the mass loss are controlled within 1%in 20 freeze-thaw cycles.Moreover,no chemical structure changed in the process and therefore a preliminary determination can be made that straw-geopolymer has a certain resisting ability to freeze-thaw cycles.(4)Thiobacillus thiooxidans erosion tests show that the remaining compressive strength of blocks soaking for 21 d still have 26.30 MPa,the resist coefficient even reaches 0.93,exhibiting good bacteria corrosion resistant performance.FT-IR and SEM analysis showed that micro-cracks were found in the specimen surface after soaking for 28 d,which were caused by depolymerization reactions.However,only the surface was affected,there is no impact on the main structure of the geopolymer.(5)Acid rain leaching results show that the compressive strength can be maintained at more than 32 MPa after leaching for 1800 mL with the pH of 2.0,3.0,4.0,5.0 respectively,This value can meet the requirements of general building materials.Geopolymer is agreed to withstand long-term leaching of acid rain and remained stable.