Pore Structure And Surface Modification Research Of Straw-reinforced Geopolymer

In order to develop a new insulation building material with high strength and better corrosion resistance,straws were added into geopolymer to synthesis straw-reinforced geopolymer composites,which can save building energy consumption and broaden industrial utilization way of straw because of its good thermal insulation and light weight properties.The composites also overcome the defects of low strength in traditional straw building materials.In this study,durability of straw geopolymer was researched.Mercury intrusion porosimetery(MIP)and nitrogen adsorption-desorption(NAD)methods were employed to analyze pore structure of straw geopolymer.This study also explored the effect of alkali treatment modification,coupling agent modification and alkali and coupling agent joint modification of straw on compressive strength of straw geopolymer.Scanning electron microscopy(SEM),Fourier transform infrared spectroscopy(FT-IR)were used to observe the microstructure,analyze modification mechanism and the relationship between microsturcture and durability.The main results are as follows:(1)After the immersion in cellulose degradation bacteria liquid for28 days,the compressive strength of samples decreased to 33.68 MPa,but corrosion resistance coefficient of straw geopolymer all maintained above 0.921.Seawater erosion test shows after immersed in seawater for150 days,the compressive strength of samples declined to 32.36 MPa,still above 30 MPa,and corrosion resistance coefficient also maintained above 0.9.Straw geopolymer owned good bacteria and seawater corrosion resistance.(2)Mercury intrusion porosimetery(MIP)analyses show that mesopore volume accounts for 61.6% of total pore volume,followed by macropore volume accounting for 38.4%.The average pore diameter of straw geopolymer is 23.9 nm with total porosity of 25.66% and pores are mainly spherical shaped.Nitrogen adsorption-desorption analyses display that mesopores abound in straw geopolymer and pore structure is not regular.There are two pore size distribution(PSD)peaks in micropore size ranges of 1.0 nm and 1.6 nm.PSD peak in mesopore size occurs at about 30 nm,which is consistent with the conclusions from MIP.(3)Among all the modification methods,alkali treatment modification is the most effective method to enhance compressivestrength.Compressive strength of modified samples is up to 56.99 MPa at4wt% straw content;next in performance are the specimens with 1wt%KH550 modification have 11.5% strength increase.Compressive strength of samples which modified with other coupling agent basically has no enhancement.The worst performance is observed in samples with alkali and coupling agent joint modification.