Study on impermeability of polymer modified repair mortar based on low field nuclear magnetic resonance technology
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摘要:
：1H低场核磁共振是通过氢原子能量变化分析水的分布和含量，一种快速、有效、无损的测试技术。通过三轴1H低场核磁共振获得了不同应力状态下可再分散乳胶粉(简称聚合物)改性修补砂浆中可蒸发水的横向弛豫时间(T2)和渗水量，据此分析了砂浆的抗渗性，并通过孔结构与微观形貌揭示了聚合物对砂浆可蒸发水横向弛豫特征的影响机制。研究表明：渗透压是修补砂浆横向弛豫时间和渗水量的主要影响因素，聚合物降低了不同渗透压下修补砂浆毛细孔和凝胶孔水的含量，6 MPa时渗水量降低57.3%，显著提升了修补砂浆的抗渗性能；聚合物提高了修补砂浆的韧性，三轴荷载作用下砂浆由交叉裂缝破坏变为压缩破坏，避免了砂浆在轴压作用下产生的抗渗性能突破。聚合物膜的阻隔和填充作用使砂浆孔隙率降低了3.28%，减弱了凝胶孔和毛细孔中的传输能力，从而降低了修补砂浆的横向弛豫强度和渗水量，提高了其抗渗性能。相较于传统的抗渗性检测方法，1H低场核磁共振可以表征水分的渗透过程，是一种切实可行的抗渗性检测方法。
Abstract:Low field 1H-nuclear magnetic resonance (NMR) is a quick, effective and nondestructive measuring technique to investigate the distribution and content of water by H-atom energy changes. Transverse relaxation time (T2) and seepage amount of redispersible polymer powder (polymer)-modified repair mortars were obtained by triaxial low field 1H-NMR, that was wont to analyze the permeability of the repair mortars. The mechanism of polymer influence on the transverse relaxation characteristics of repair mortars was explained by pore structure and micromorphology analysis. It’s shown that: Osmotic pressure is the main factor affecting the transverse relaxation time and seepage amount of mortar. Polymer reduces the water content in capillary and gel pores of repair mortar under different osmotic pressures, and the water seepage decreases by 57.3% at 6MPa, which significantly improves the impermeability of repair mortar. The polymer improves the toughness of the repair mortar, which makes the cross-cracking damage of mortar change into compression deterioration under three-axis loading conditions, thus avoiding the breakthrough of impermeability of the mortar under axial compression. The blocking and filling effect of polymer film reduces the porosity of mortar by 3.28%, and weakens the transmission ability in gel pores and capillary pores. Therefore, the transverse relaxation strength and water seepage of repair mortar are reduced, enhancing its impermeability. Compared with the traditional impermeability testing methods, low field 1H-NMR can characterize the water infiltration process and the seepage amount at different osmotic pressures, which is a practical impermeability testing method.
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Keywords:
- low field NMR /
- transverse relaxation time /
- seepage amount /
- polymer /
- repair mortar /
- impermeability
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图 3 聚合物和测试试样横向弛豫分布对比
Figure 3. Comparison of transverse relaxation distribution between polymer and test sample
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图 4 聚合物掺量对修补砂浆力学性能的影响
Figure 4. Influence of polymer content on mechanical properties of repairing mortar
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图 5 不同渗透时间修补砂浆横向弛豫时间分布
Figure 5. Transverse relaxation time distribution of repaired mortar at different penetration time
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图 6 不同渗透压修补砂浆横向弛豫时间分布
Figure 6. Transverse relaxation time distribution of repaired mortar at different penetration pressure
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图 7 不同轴压修补砂浆横向弛豫时间分布
Figure 7. Transverse relaxation time distribution of repaired mortar under different coaxial pressures
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图 8 三轴试验试样的破坏形貌(a)K0;(b)K9
Figure 8. Failure morphology of triaxial test samples(a)K0;(b)K9
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图 9 聚合物掺量对修补砂浆孔结构的影响
Figure 9. Influence of polymer content on pore structure of repair mortar
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图 10 不同聚合物掺量修补砂浆的断面SEM图像
Figure 10. Cross-section SEM images of repair mortar with different polymer contents
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图 11 修补砂浆的断面EDS面扫图图谱和元素分布
Figure 11. Sectional EDS scan map and element distribution of the repair mortar
表 1 水泥的化学组成
Table 1 Chemical compositions of cement
SiO2 Al2O3 Fe2O3 CaO MgO SO3 Na2O f-CaO Loss 20.6 4.57 3.29 63.27 2.59 2.11 0.55 0.76 2.15 
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表 2 水泥物理力学性能
Table 2 Physical and mechanical properties of cement
Setting time/min Flexural strength/MPa Compressive strength/MPa Initial set Final set 3 d 7 d 28 d 3 d 7 d 28 d 128 196 5.3 6.4 8.5 26 35.9 45.6
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表 3 聚合物改性修补砂浆配合比
Table 3 Mix proportion of polymer modified repair mortar
Specimen No. Cement/g Sand/g Superplasticizer/g Defoamer/g Water/g Polymer/g K0 100 200 0.2 0.5 35 0 K3 100 200 0.2 0.5 35 3 K6 100 200 0.2 0.5 35 6 K9 100 200 0.2 0.5 35 9 K12 100 200 0.2 0.5 35 12 K15 100 200 0.2 0.5 35 15
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表 4 不同渗透时间修补砂浆渗水量
Table 4 Seepage amount of repaired mortar at different times
5 min 10 min 15 min 20 min 25 min 30 min K0 0.4% 0.71% 1.02% 1.29% 1.54% 1.72% K9 0.05% 0.13% 0.18% 0.22% 0.24% 0.27%
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表 5 不同渗透压修补砂浆渗水量
Table 5 Seepage amount of repaired mortar at different infiltration times
1 MPa 2 MPa 3 MPa 4 MPa 5 MPa 6 MPa K0 1.59% 3.1% 3.9% 4.26% 4.68% 5.34% K9 0.57% 0.97% 1.48% 1.79% 2.02% 2.28%
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表 6 不同轴压修补砂浆渗水量
Table 6 Seepage amount of repairing mortar under different coaxial pressure
20 MPa 30 MPa 40 MPa 50 MPa K0 0.03% −0.03% −0.11% −0.38% K9 −0.08% −0.13% −0.12% −0.03%
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表 7 聚合物掺量对修补砂浆孔隙率的影响
Table 7 Influence of polymer content on porosity of repair mortar
K0 K3 K6 K9 K12 K15 Porosity/% 10.73 9.25 8.53 7.45 8.49 9.84
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目的
水泥基材料渗透性和耐久性密切相关。目前，水泥基材料的抗渗测试有抗水渗透试验和抗氯离子渗透试验两种方法。这两种方法仅能测得水或离子的渗透结果，无法全面分析渗透过程，因此难以提供足够的数据分析水泥基材料抗渗性能。聚合物改性水泥基材料是一种有机-无机复合材料，具有高韧性、强粘结力和优异的抗渗性能。深入了解水在修补材料中的渗透过程，对揭示聚合物改性机理至关重要。H低场核磁共振是通过氢原子能量变化分析水的分布和含量，可快速、高效、无损的测试水在修补材料的渗透过程。相较于传统的抗渗性检测方法，H低场核磁共振可以表征水分的渗透过程和渗水量，是一种切实可行的抗渗性检测方法。
方法首先设计胶砂比为1:2，水灰比为0.35的修补砂浆，研究了0、3%、6%、9%、12%、15%水泥质量的聚合物对修补砂浆的抗折强度、抗压强度和粘结强度的影响。通过1H低场核磁共振技术测试了渗透压力、渗透时间和轴压对聚合物修补砂浆中可蒸发水的横向弛豫时间和渗水量的影响，并以此表征修补砂浆的抗渗性。最后，通过孔结构和微观形貌分析了聚合物对修补砂浆横向弛豫时间和渗水量的影响机理。
结果(1)聚合物提高了修补砂浆的力学性能，当掺量为9%时，砂浆的抗折强度和粘结强度分别增加了16.99%和57.45%，改善了修补砂浆的韧性和界面性能。(2)通过横向弛豫时间分布和渗水量可以有效的表征聚合物改性修补砂浆抗渗性能。随渗透压渗透时间的增加，水逐渐向修补砂浆凝胶孔隙和毛细孔隙中渗透，聚合物明显降低两者的增长趋势。(3)轴向压力作用下，修补砂浆中的孔隙被压缩，横向弛豫时间分布一个峰的峰值略有增加。当轴压增大到50MPa时，对照组试样横向弛豫时间分布突变，产生交叉裂缝破坏。聚合物改性修补砂浆产生明显的压缩变形未产生明显裂纹，试样的横向弛豫时间分布没有突变。(4)聚合物成膜后粘附在水化产物表面，分割、填充了水泥基材料的孔隙，孔隙率最大降低了3.28%，改善了修补砂浆的微观结构。
结论渗透压力是修补砂浆横向弛豫时间和渗水量的主要影响因素，聚合物降低了不同渗透压下修补砂浆毛细孔和凝胶孔水的含量，6MPa时渗水量降低57.3%，显著提升了修补砂浆的抗渗性能。聚合物提高了修补砂浆的韧性，三轴荷载作用下砂浆由交叉裂缝破坏变为压缩破坏，避免了砂浆在轴压作用下产生的抗渗性能突破。聚合物膜的阻隔和填充作用减弱了凝胶孔和毛细孔中的传输能力，从而降低了修补砂浆的横向弛豫强度和渗水量，提高了其抗渗性能。相较于传统的抗渗性检测方法，H低场核磁共振可以表征水分的渗透过程，是一种切实可行的抗渗性检测方法。
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