Formation mechanism of early strength in geopolymer based on molar ratio of mineral components
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摘要: 通过调控地质聚合物内部的矿物组分SiO2/Al2O3、CaO/Al2O3与Na2O/Al2O3等的摩尔比,采用XRD与SEM观察地质聚合物反应程度与CaSiO3水化反应程度的复合变化规律,探究了地质聚合物反应与CaSiO3水化反应的复合协同作用效果。进一步揭示了地质聚合物的早期强度形成机制。研究表明:地质聚合物反应产物中含有一定量的石英组分,其物理性质和化学性质均十分稳定,强度较高。CaSiO3水化反应产物以水化CaSiO3为主,其内部结构疏松。随着SiO2/Al2O3和CaO/Al2O3摩尔比的增加,地质聚合物反应程度先增加后减少,CaSiO3水化反应程度先增加后趋于稳定且大于地质聚合物反应程度。当SiO2/Al2O3摩尔比为3.8、CaO/Al2O3摩尔比为2.750时,地质聚合物反应与CaSiO3水化反应的复合协同效果最佳,此时地质聚合物内石英质量分数约为66wt%,水化CaSiO3质量分数约为24wt%,力学性能良好。Abstract: X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to observe the compound change law of geopolymer reaction and the hydration reaction of calcium silicate by adjusting the molar ratio of SiO2/Al2O3, CaO/Al2O3 and Na2O/Al2O3 in the geopolymer. Then the compound synergistic effect of geopolymer reaction and the hydration reaction of CaSiO3 was explored. Furthermore, the formation mechanism of early strength in geopolymer was revealed. The results show that the geopolymer reaction products contain a certain amount of quartz component. The physical properties and chemical properties of quartz are very stable and the quartz strength is high. The products of hydration reaction of CaSiO3 are mainly CaSiO3 hydrate whose internal structure is loose. With the mole ratios of SiO2/Al2O3 and CaO/Al2O3 increasing, the degree of geopolymer reaction increases first and then decreases, and the degree of hydration reaction of CaSiO3 increases first and then stabilizes and is greater than the degree of geological polymer reaction. When the SiO2/Al2O3 molar ratio is 3.8 and the CaO/Al2O3 molar ratio is 2.750, the compound synergistic effect of geopolymer reaction and hydration reaction of CaSiO3 is the best. At this time, the proportion of quartz in geopolymer is about 66wt%, the proportion of CaSiO3 hydrate in geopolymer is about 24wt% and the mechanical properties are good.
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表 1 粉煤灰和高炉矿渣粉(GGBFS)的化学组成
Table 1. Chemical compositions of fly ash and ground granulated blast furnace slag(GGBFS)
wt% Material SiO2 Al2O3 Fe2O3 MgO CaO Na2O K2O MnO TiO2 Others Fly ash 42.34 25.84 5.46 1.17 6.66 1.13 1.05 0.11 1.07 15.17 GGBFS 29.73 13.58 1.01 6.56 36.39 0.28 0.55 0.09 0.6 11.21 表 2 水玻璃参数
Table 2. Properties of water glass
Color Modulus Baume degree/°Bé Na2O/wt% SiO2/wt% Transparent 3.24 39.5 9.25 29 表 3 地质聚合物净浆配合比设计
Table 3. Mix design of geopolymer paste
Mix Mole ratio Water-solid mass ratio Fly ash/g GGBFS/g Complex alkali activator/g SiO2/Al2O3 CaO/Al2O3 Na2O/Al2O3 SY1 3.4 0.866 0.442 0.3 369.7 69.4 135.8 SY2 3.5 1.337 0.442 0.3 302.6 140.9 126 SY3 3.6 1.808 0.442 0.3 244.6 202.7 117.4 SY4 3.7 2.279 0.442 0.3 194 256.7 110 SY5 3.8 2.750 0.442 0.3 149.4 304.2 103.4 SY6 3.9 3.221 0.442 0.3 109.8 346.4 97.6 SY7 4.0 3.693 0.442 0.3 74.4 384.1 92.4 表 4 不同矿物成分摩尔比地质聚合物抗压强度
Table 4. Compressive strengths of geopolymers under different mineral molar ratios
Mix Mole ratio Water-solid mass ratio Compressive strength/ MPa SiO2/Al2O3 CaO/Al2O3 3 d 7 d 28 d SY1 3.4 0.866 0.3 11.8 19.6 28.1 SY2 3.5 1.337 0.3 13.5 22.2 30.9 SY3 3.6 1.808 0.3 27 33.4 38.8 SY4 3.7 2.279 0.3 36.8 41.2 45.7 SY5 3.8 2.750 0.3 52.9 57.9 62.6 SY6 3.9 3.221 0.3 30.4 39 43.9 SY7 4.0 3.693 0.3 23.1 32.3 36.4 表 5 不同矿物组分摩尔比下地质聚合物抗折强度
Table 5. Flexural strengths of geopolymers under different mineral molar ratios
Mix Mole ratio Water-solid mass ratio Flexural strength/MPa SiO2/Al2O3 CaO/Al2O3 3 d 7 d 28 d SY1 3.4 0.866 0.3 6.1 7.2 8.9 SY2 3.5 1.337 0.3 6.4 7.6 9.1 SY3 3.6 1.808 0.3 7.2 8.3 9.6 SY4 3.7 2.279 0.3 7.9 8.9 10.3 SY5 3.8 2.750 0.3 9.6 10.2 11.2 SY6 3.9 3.221 0.3 4.2 5.8 6.9 SY7 4.0 3.693 0.3 3.1 4.5 5.6 表 6 地质聚合物主要反应产物定量分析
Table 6. Quantitative analysis of main reaction products of geopolymers
SY1 SY2 SY3 SY4 SY5 SY6 SY7 Mole ratio of SiO2/Al2O3 3.4 3.5 3.6 3.7 3.8 3.9 4 Mole ratio of CaO/Al2O3 0.866 1.337 1.808 2.279 2.75 3.221 3.693 Quartz/wt% 25 36 51 61 66 44 31 Mullite/wt% 30 24 18 10 6 4 3 CaSiO3 hydrate/wt% 6 13 18 22 24 44 59 -
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