Preparation Of Strain-hardening Geopolymer Composites By Hot-pressing Method And Their Properties

Strain-hardening cementitious composites（SHCCs）display a ductile feature with the development of numerous fine cracks under direct tension.Due to their high ductility and toughness,SHCCs are capable of increasing the impact resistance,anti-corrosion,and self-healing ability of concrete structures.However,Portland cement production is responsible for about 7%of global CO₂ emissions.As a type of low carbon binder with material properties comparable to ordinary Portland cement,geopolymers have recently been utilized to fabricate strain-hardening geopolymer composites（SHGCs）.Fly ash is a common precursor for producing geopolymer.Due to its low reactivity at room temperature,heat curing is generally applied in fabricating fly ash based geopolymer.In this study,a SHGC with high early strength and short production time was developed by using hot-press method.The parameters under investigation include liquid-solid ratio,age,temperature,pressure,fiber type and fiber content.The results of compressive strength tests and direct tensile tests have showed that the hot-pressing process and the addition of fibers increase the compressive strength by about 50%.The 1 and 7 d compressive strengths at are 53%and 73%of that of 28 d,respectively.The hot-pressed SHGC displayed prominent multiple-cracking and strain-hardening behavior,and the ultimate tensile strain is above 4%.With 1.5%the fiber content,hot-pressed SHGC presents optimum overall performance.Secondly,fly ash-based strain-hardening geopolymer composite（SHGC）plates were manufactured by hot-pressing method.The flexural behavior of SHGC was investigated by centrally loaded square plates.The parameters under investigation include liquid-solid ratio,age,temperature,pressure,fiber type and content.The influence of these parameters on load carrying capacity,deflection and toughness was studied.The results show that the load carrying capacity increases with age,temperature and pressure,while the ductility decreases slightly.The specimens gained66%and 89%load carrying capacity at 1 and 7 d,respectively,in the reference to that for 28 d.The maximum load and deflection under flexure for the plates with oiled polyvinyl alcohol（PVA）fibers are around 20%higher than that for those with non-oiled PVA fibers.Moreover,the interaction between fiber and matrix governs the stress transfer between them,and the interfacial bonding between hot-pressed geopolymer fiber and matrix was studied by single fiber pull-out test.The research parameters include liquid-solid ratio,age,temperature and pressure.The slip behavior,interface bonding strength and microstructures of interface transition zone were analyzed.The results show that hot-pressed can compact the matrix near the fiber,and the load-displacement curve shows a strong slip hardening behavior at 80℃and 3.2 MPa.Finally,the sustainability of hot-pressing SHGC was analyzed.The results show that hot-pressing process accounts for 27%～58%of total the energy consumption,and the energy consumption of hot-pressed SHGC is equivalent to that normal engineered cementitious composite（ECC）,and in terms of the CO₂ emission,the former is lower the latter.This has indicates that hot-pressed SHGC is associated with lower CO₂ emission.