Effect Of Geopolymer Concrete's Durability By Oxide Composition

Geopolymer is a new type of alkali-activated binder which was developed in recent years,formed by aluminosilicate minerals or industrial solid waste in a highly alkaline environment,the silicon oxygen bond and aluminum oxygen bond fracture-reorganization to form a inorganic non-metallic materials which possess high compressive strength, long term chemical stability and durability.On the basis of earlier research, are used to in this paper. geopolymer was prepared by slag and metakaolin as major raw materials, with water glass of low modulus as alkali activator. Geopolymer mortar and concrete was prepared through the change of the raw materials content n(SiO₂)/n(Al₂O₃)=3.3⁴.1, n(Na₂O)/n(Al₂O₃)=0.3⁰.7 and n(H₂O)/n(Na₂O)=18²2.The effect on the durability properties of geopolymer was researched by oxide molar ratios n(SiO₂)/ n(Al₂O₃), n(Na₂O)/n(Al₂O₃) and n(H₂O)/n(Na₂O). The alkali-aggregate reaction and sulfate attack resistance of geopolymer is studied by accelerated mortar test of samples, Cl^- penetration and diffusion was studied by the NEL test and compressive strength was tested;the freeze-thaw resistance of geopolymer concrete was investigated by accelerated freez-thaw test,the carbonation resistance was investigated by the carbonation depth. meanwhile, the endurance quality was compared with Portland cement.Results of AAR test show that the linear expansion rate of samples firstly decreases and then increases with oxides increasing, the linear expansion rate minimum when geopolymer concrete oxidate in n(SiO₂)/n(Al₂O₃)=3.9, n(Na₂O)/n(Al₂O₃)=0.4 and n(H₂O)/n(Na₂O)=21, respectively 0.087%, 0.054% and 0.065%. The effect is the best when the content of fly ash is 20% in the restrain test.Test of sulfate attack resistance demonstrates that geopolymer has better sulfate attack resistance property. The linear expansion rate of geopolymer mortars is firstly decreases and then increases, and the compressive erosion resistance coefficient firstly increases and then decreases in 5%Na2SO4 and 5%Na2SO4+5%MgSO4 solution after 15 weeks of immersion, sulfate attack resistance is the best in n(SiO₂)/n(Al₂O₃)=3.9, n(Na₂O)/n(Al₂O₃)=0.5 and n(H₂O)/n(Na₂O)=19 geopolymer mortar specimens linear expansion rate for ordinary Portland cement specimens 0.3 times, the compressive erosion resistance coefficient is ordinary Portland cement 1.4 times.Cl^- penetration and diffusion show that geopolymer concrete firstly decreases and then increases with oxides increasing, the Cl^- diffusion coefficient minimum when geopolymer concrete oxidate in n(SiO₂)/n(Al₂O₃)=3.7, n(Na₂O)/n(Al₂O₃)=0.4 and n(H₂O)/n(Na₂O)=21, respectively 2.4×10^-8cm²/s, 3.1×10^-8cm²/s and 2.1×10^-8cm²/s. The conclusion the same strength grade conditions, 28d geopolymer concrete Cl^- diffusion coefficient for ordinary concrete 0.45 times, it compressive strength is ordinary concrete 1.5 times.The freeze-thaw resistance of geopolymer concrete firstly increases and then decreases with oxides increasing after 200 times of freeze-thaw cycle, The freeze-thaw resistance is the best when n(SiO₂)/n(Al₂O₃)=3.7, n(SiO₂)/n(Na₂O)=0.4 and n(H₂O)/n(Na₂O)=21, relative loss of quality rate is 4.3%, 4.4% and 4.3%, relative dynamic elastic modulus is 81.67%, 85.86% and 86.1%; Compared with Portland concrete, loss of quality rate for ordinary concrete 0.68 times, relative dynamic elastic modulus is only ordinary concrete 0.93 times. Carbonization result shows that with oxides increasing, carbonation depth first decreasesand then increases, and with the age growth, later period carbonation depth is almost zero, which have stronger carbonation resistance capacibility, when the n(SiO₂)/n(Al₂O₃)=3.9, n(Na₂O)/n(Al₂O₃)=0.5 and n(H₂O)/n(Na₂O)=21 which carbonation depth is within 5mm at the age of 56d separately for 4mm, 2.3 mm and 2.6 mm, the same strength grade conditions, Portland concrete carbonation resistance is geopolymer of 3.2 times.The IR analysis shows that raw materials by Si-O-Al, O-Si-O and Al-O composed of mineral polymer skeleton, together constitute the three-dimensional network structure, containing these functional materials are characterized by good durability. XRD of products in 20 38°is the bread shaped dispersion peak, show geopolymer structure is mainly for the amorphous, wide diffraction peak is silicon aluminium acid salt caused by the special structure. SEM can be obvious product for continuous cavity network structure, compact connection, cause geopolymer construetion higher, can effectively prevent external water or erosive ions into, macroscopic shows that with close-grained of durability, freeze-thaw resistance, penetration resistance and sulfate attack resistance are well.