Laboratory investigation on the strength and freezing-thawing resistance of fly ash based geopolymer stabilized soil
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摘要:
粉煤灰基地聚物作为一种低碳胶凝材料，在地基处理中的应用越来越受到关注。但是目前关于碱激发胶凝材料加固土在冻融极端气候条件下的工程特性尚不清楚，有必要进一步开展冻融循环条件下加固土的强度、变形特征及其影响因素研究。通过室内试验研究了原材料硅铝比、碱激发剂模数及碱溶液浓度对粉煤灰基地聚物固化土的强度与抗冻融性能的影响及微观机理。结果表明：地聚物加固土的无侧限抗压强度在碱激发剂模数增大及碱溶液浓度减小条件下，表现出降低趋势，而与原材料硅铝比之间在1.15~1.35范围内呈现出正相关变化趋势，28 d地聚物加固土的无侧限抗压强度最高可达8.98 MPa；当硅铝比在1.25~1.35范围、碱溶液浓度为5.42~22.78 mol/L时，28 d地聚物加固土能够抵御1次以上冻融循环，最高可达6次；地聚物加固土表现出最佳的抗冻融性能与聚合反应生成的凝胶数量多且以富硅相为主相关，而表现出抗压强度高则与聚合反应生成的凝胶数量多且以富铝相为主相关。研究成果将为粉煤灰地基地聚物加固土配合比设计提供技术参考，促进碱激发胶凝材料在地基处理中的应用。
Abstract:As a low-carbon cementitious material, the application of fly ash based geopolymer in ground improvement has attracted more and more attention. However, the engineering characteristics of the soil stabilized by alkali activated cementitious material under the freezing-thawing extreme climate conditions are not clear. It is necessary to further study the strength, deformation characteristics and their influencing factors of the improved soil under the freezing-thawing cycle. Several laboratory tests are carried out to investigate the effects of the ratio of silicon to aluminum in raw material (Si/Al), modulus of alkali-activator and alkali solution concentration on the unconfined compressive strength (UCS) and the freezing-thawing resistance of fly ash based geopolymer stabilized soil, and the corresponding micro mechanism. The results show that (1) the UCS of geopolymer stabilized soil decreases with the increasing alkali-activator modulus and the decreasing alkali solution concentration, while increases with the Si/Al value in the range of 1.15 to 1.35, and the unconfined compressive strength of 28 d geopolymer stabilized soil can reach 8.98 MPa. (2) When the Si/Al value changes from 1.25 to 1.35 and the alkali solution concentration is within the range of 5.42 to 22.78 mol/L, the 28 d geopolymer stabilized soil can resist more than one (up to 6) freezing-thawing cycle. (3) The best performance of the freezing-thawing resistance of fly ash based geopolymer stabilized soil is mainly related to large number of Si-rich aluminosilicate gel generated by polymerization, while the highest compressive strength is related to the amount of Al-rich aluminosilicate gel generated by polymerization. The research results will provide technical reference for the mix design of soil stabilization with fly ash based geopolymer, and promote the application of alkali activated cementitious material in ground improvement.
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表 1 试验用土的主要物理性质指标
Table 1. Main physical properties of the test soil
天然含水率w/% 液限wL/% 塑限wP/% 液性指数IL 塑性指数IP 43.0 45.0 22.5 0.91 22.5 
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表 2 试验分组
Table 2. Test groups
组号 Si/Al M L/S C/（mol·L−1） A B A1 1.15 1.0 0.3 4.66 2.17 0.67 A2 1.15 1.2 0.3 3.25 2.25 0.71 A3 1.15 1.4 0.3 2.20 2.32 0.75 A4 1.15 1.6 0.3 1.40 2.38 0.78 A5 1.15 1.8 0.3 0.76 2.42 0.80 B1 1.20 1.0 0.3 7.42 1.90 0.97 B2 1.20 1.2 0.3 5.09 1.97 1.05 B3 1.20 1.4 0.3 3.57 2.07 1.15 B4 1.20 1.6 0.3 2.27 2.12 1.23 B5 1.20 1.8 0.3 1.25 2.18 1.29 C1 1.25 1.0 0.3 11.00 1.69 1.29 C2 1.25 1.2 0.3 8.10 1.78 1.46 C3 1.25 1.4 0.3 5.42 1.86 1.65 C4 1.25 1.6 0.3 3.50 1.93 1.80 C5 1.25 1.8 0.3 1.92 1.98 1.94 D1 1.30 1.0 0.3 15.89 1.52 1.64 D2 1.30 1.2 0.3 11.53 1.62 1.95 D3 1.30 1.4 0.3 8.09 1.70 2.26 D4 1.30 1.6 0.3 5.28 1.76 2.56 D5 1.30 1.8 0.3 2.94 1.81 2.86 E1 1.35 1.0 0.3 22.78 1.38 2.02 E2 1.35 1.2 0.3 17.05 1.48 2.51 E3 1.35 1.4 0.3 12.23 1.56 3.04 E4 1.35 1.6 0.3 8.13 1.62 3.61 E5 1.35 1.8 0.3 4.61 1.67 4.23
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表 3 地聚物加固土的冻融循环次数
Table 3. Freezing-thawing cycles of different groups
组号 C1 C2 C3 D1 D2 D3 E1 E2 E3 冻融循环次数 2 2 2 3 3 2 6 4 3 注：其余试验组的冻融循环次数均小于2次。
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