氧化物组成对无机矿物聚合物混凝土耐久性的影响
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摘要
无机矿物聚合物是近年来新发展起来的一类碱激发材料,多以天然铝硅酸盐矿物或工业固体废物为主要原料,在碱性激发剂作用下,原材料中的硅氧键和铝氧键发生断裂-重组反应,形成具有高强度、长期化学稳定性和耐久性的无机非金属材料。在课题组前期研究的基础上,本课题以矿渣和偏高岭土为主要原料,低模数水玻璃为激发剂制备无机矿物聚合物。通过改变原材料用量,使n(SiO_2)/n(Al_2O_3)=3.3~4.1、n(Na_2O)/n(Al_2O_3)=0.3~0.7及n(H_2O)/n(Na_2O)=18~22范围内变化,制备相应的胶砂和混凝土试件。分别研究氧化物组成n(SiO_2)/n(Al_2O_3)、n(Na_2O)/n(Al_2O_3)及n(H_2O)/n(Na_2O)对其胶砂试件和混凝土试件耐久性的影响。采用快速砂浆棒法研究无机矿物聚合物胶砂试件的碱集料反应和抗硫酸盐侵蚀性;采用饱盐混凝土电导率法(NEL法),研究其氯离子渗透性,并进行抗压强度测试;采用快冻法研究无机矿物聚合物混凝土试件的抗冻融循环能力;通过碳化深度考察无机矿物聚合物混凝土的抗碳化能力。同时,与普通硅酸盐水泥试件相应的耐久性能进行比较。
     碱集料反应(AAR)试验表明:随着氧化物摩尔比的增大,试件的线性膨胀率均先降低再升高,分别在n(SiO_2)/n(Al_2O_3)=3.9,n(Na_2O)/n(Al_2O_3)=0.4及n(H_2O)/n(Na_2O)=21时,线性膨胀率达最小,仅为0.087%,0.054%和0.065%;对n(SiO_2)/n(Al_2O_3)进行抑制试验中,粉煤灰掺量为20%,抑制效果最好。
     抗硫酸盐侵蚀性研究表明:胶砂试件5%Na2SO4和5%Na2SO4+5%MgSO4溶液中的线性膨胀率均先减小后增大,抗压抗蚀系数先增大后减小,分别在n(SiO_2)/n(Al_2O_3)=3.9,n(Na_2O)/n(Al_2O_3)=0.5及n(H_2O)/n(Na_2O)=19时抗硫酸盐侵蚀性能最好。在同强度等级条件下,无机矿物聚合物胶砂试件线性膨胀率仅是普通硅酸盐水泥胶砂试件的0.3倍,抗压抗蚀系数却是普通硅酸盐水泥胶砂的1.4倍。
     氯离子渗透性研究表明:随着氧化物摩尔比的增大,无机矿物聚合物混凝土试件的氯离子扩散系数均先减小后增大,分别当n(SiO_2)/n(Al_2O_3)=3.7,n(Na_2O)/n(Al_2O_3)=0.4及n(H_2O)/n(Na_2O)=21时,氯离子扩散系数最小,分别仅为2.4×10~(-8)cm~2/s,3.1×10~(-8)cm~2/s和2.1×10~(-8)cm~2/s;在同强度等级条件下,无机矿物聚合物混凝土28d氯离子扩散系数为普通混凝土的0.45倍,无机矿物聚合物抗压强度却是普通混凝土的1.5倍。抗冻性研究表明:经200次冻融循环后,随氧化物摩尔比在一定范围内递增,无机矿物聚合物混凝土抗冻性能先增强后降低,当n(SiO_2)/n(Al_2O_3)=3.7,n(Na_2O)/n(Al_2O_3)=0.4及n(H_2O)/n(Na_2O)=21时其抗冻性能最佳,其质量损失率分别为4.3%,4.4%和4.3%,相对动弹性模量分别下降到81.67%,85.86%和86.1%;与普通混凝土相比,在同强度等级的无机矿物聚合物混凝土的质量损失率为普通混凝土的0.68倍,相对动弹性模量仅是普通混凝土的0.93倍。
     碳化性能研究结果表明:随摩尔比增大,碳化深度均先减小后增大,并且随着龄期增长,后期碳化深度几乎为零,具有较强的抗碳化性能,n(SiO_2)/n(Al_2O_3)=3.9,n(Na_2O)/ n(Al_2O_3)=0.5及n(H_2O)/n(Na_2O)=21时,无机矿物聚合物混凝土56d碳化深度分别为4mm,2.3mm和2.6mm;同强度等级的普通水泥混凝土的碳化深度值是无机矿物聚合物的3.2倍。
     从IR分析可以得出,原材料生成由Si-O-Al、O-Si-O和Al-O组成的无机矿物聚合物骨架,共同构成三维网络结构,含有这些官能团的材料一般具有很好的耐久性能;XRD图谱中产物在20~38°呈馒头状弥散峰,表明无机矿物聚合物结构主要为无定形态,宽大的衍射峰包是硅铝酸盐特有的结构引起的;SEM中可以明显看出,无机矿物聚合物产物为连续空腔的网络状结构,连接紧密,致使无机矿物聚合物密实度较高,可以有效阻止外部水或侵蚀性离子进入,宏观上表现出很好的抗冻性、抗渗性和抗硫酸盐侵蚀等和密实性有关的耐久性能。
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(SiO_2)/n(Al_2O_3)=3.3~4.1, n(Na_2O)/n(Al_2O_3)=0.3~0.7 and n(H_2O)/n(Na_2O)=18~22.The effect on the durability properties of geopolymer was researched by oxide molar ratios n(SiO_2)/ n(Al_2O_3), n(Na_2O)/n(Al_2O_3) and n(H_2O)/n(Na_2O). 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(SiO_2)/n(Al_2O_3)=3.9, n(Na_2O)/n(Al_2O_3)=0.4 and n(H_2O)/n(Na_2O)=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(SiO_2)/n(Al_2O_3)=3.9, n(Na_2O)/n(Al_2O_3)=0.5 and n(H_2O)/n(Na_2O)=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(SiO_2)/n(Al_2O_3)=3.7, n(Na_2O)/n(Al_2O_3)=0.4 and n(H_2O)/n(Na_2O)=21, respectively 2.4×10~(-8)cm~2/s, 3.1×10~(-8)cm~2/s and 2.1×10~(-8)cm~2/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(SiO_2)/n(Al_2O_3)=3.7, n(SiO_2)/n(Na_2O)=0.4 and n(H_2O)/n(Na_2O)=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 decreases
     and then increases, and with the age growth, later period carbonation depth is almost zero, which have stronger carbonation resistance capacibility, when the n(SiO_2)/n(Al_2O_3)=3.9, n(Na_2O)/n(Al_2O_3)=0.5 and n(H_2O)/n(Na_2O)=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.
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