Pore structure and dynamic mechanical properties of geopolymer cement soil based on nuclear magnetic resonance technique
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摘要: 为研究养护龄期和偏高岭土（MK）掺量对地聚合物水泥土孔隙结构和动态力学特性的影响,借助分离式Hopkinson压杆（SHPB）试验系统开展了地聚合物水泥土动态单轴冲击压缩试验,并结合核磁共振（NMR）和扫描电镜（SEM）等分析手段研究了地聚合物水泥土的孔径分布和微观形貌变化特征。结果表明：地聚合物水泥土的动态抗压强度随MK掺量的增加呈现先增大后减小的变化趋势,在MK掺量为2%时出现峰值；其动态抗压强度在7～14 d内增长较缓；地聚合物水泥土的T2 分布曲线呈双峰型,以主峰所占面积为主,掺2%的MK能够有效改善孔隙分布,促进小孔隙向微孔隙转化；随着孔隙率的增加,地聚合物水泥土的动态抗压强度呈指数下降；MK掺量为2%时,地聚合物水泥土内部孔隙大幅度降低,水化产生的胶凝材料能够起到填充孔隙和连接土颗粒的作用。Abstract: To study the effects of curing age and metakaolin (MK) content on its pore structure and dynamic mechanical properties, the dynamic uniaxial impact compression tests on the geopolymer cement soil are carried out with the help of the split Hopkinson pressure bar (SHPB) system, in addition, its pore size distribution and microstructure characteristics are studied by combining the nuclear magnetic resonance (NMR) and scanning electron microscope (SEM) analytical methods. The results indicate that with the increase of MK content, the dynamic compressive strength of the geopolymer cement soil exhibits a trend of first increase and then decrease, and the peak value appeares at 2% MK content. Moreover, its dynamic compressive strength increases slowly in the period of 7~14 curing days. The T2 distribution curves of the geopolymer cement soil present bimodal characteristics, and the main peak accounts for large proportion. The incorporation of 2% MK can effectively improve the pore distribution and promote the conversion of small pores to micro pores. With the increase of porosity, the dynamic compressive strength of the geopolymer cement soil decreases exponentially. When the MK content is 2%, the internal pores of the geopolymer cement soil are greatly reduced, and the cementitious material produced by hydration can fill pores and connect soil particles.
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图 3 不同试验条件地聚合物水泥土动态应力-应变曲线
Figure 3. Dynamic stress-strain curves of geopolymer cement soil under different test conditions
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图 4 不同试验条件地聚合物水泥土动态抗压强度
Figure 4. Dynamic compressive strengths of geopolymer cement soil under different test conditions
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图 5 不同试验条件典型地聚合物水泥土T2曲线
Figure 5. Typical T2 curves of geopolymer cement soil under different test conditions
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图 7 不同试验条件典型地聚合物水泥土孔径分布
Figure 7. Typical distribution of poresize of geopolymer cement soil under different test conditions
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图 8 地聚合物水泥土孔隙率与动态抗压强度的关系
Figure 8. Relationship between porosity and dynamic compressive strength of geopolymer cement soil
表 1 重塑土颗粒级配
Table 1 Particle size distribution of remoulded soil
粒径/mm 0~0.075 0.075~0.425 0.425~0.63 0.63~1.25 1.25~2.00 占比/% 56.2 27.1 8.35 5.23 3.12 
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表 2 不同试验条件下地聚合物水泥土T2双峰面积
Table 2 Areas of T2 bimodal peaks of geopolymer cement soil under different test conditions
MK掺量 波峰类型 1 d 3 d 7 d 14 d 28 d 面积 占比/% 面积 占比/% 面积 占比/% 面积 占比/% 面积 占比/% 0% P1 3296 97.49 3175 97.78 3142 97.67 3117 98.01 2992 98.36 P2 85 2.51 72 2.22 75 2.33 63 1.99 50 1.64 2% P1 3056 98.04 3037 98.03 2989 98.14 2972 98.05 2744 98.98 P2 61 1.96 61 1.97 60 1.96 59 1.95 32 1.13 4% P1 3327 97.59 3237 97.59 3237 97.65 3222 98.02 3118 98.05 P2 82 2.41 80 2.41 78 2.35 65 1.98 62 1.95 6% P1 — — — — — — 3370 96.81 3443 97.05 P2 111 3.19 105 2.95
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