STUDY ON THE EFFECT OF ORGANIC CONTENT ON PROPERTIES OF MAGNESIUM PHOSPHATE CEMENT SOLIDIFIED SOIL
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摘要: 许多重要的软土工程譬如基坑、路基工程在破坏后需要快速修复,磷酸镁水泥的出现很好地满足了这一现代建设的要求,但不同地区软土的有机质含量不同,而有机质的含量对固化土的性质有着重要影响。为了研究磷酸镁水泥加固不同有机质含量软土的加固规律,本文通过向烘干后的软土中添加腐殖酸,人为制备不同有机质含量的土样,并取相同条件下PO水泥加固软土作对比,通过相关力学试验得到以下规律:两种水泥在加固不同含量有机质软土的过程中,加固效果都会随着有机质含量的升高而逐渐降低;磷酸镁水泥在快速修复和凝结方面明显优于PO水泥,但磷酸镁水泥中长期加固有机质软土的效果却不及PO水泥。同时利用SEM试验对得到的规律进行了解释并分析其微结构演化特征。该研究成果独到地分析了有机质含量变化对磷酸镁水泥加固效果的影响,证明了磷酸镁水泥可以应用于软土的抢修工程建设中,对加固软土工程具有指导和借鉴意义。Abstract: Many important soft soil projects need to be repaired quickly after failure, such as foundation pits and subgrade engineering. The appearance of magnesium phosphate cement satisfies the requirements of modern construction. However, the difference of the organic content of soft soil in different regions has an important influence on the properties of the solidified soil. We prepare soil samples with different organic contents by adding humic acid to the soft soil and study the reinforcement of soft soil with different organic contents by magnesium phosphate cement, contrast with the reinforced soft soil of PO cement under the same conditions. Finally, the following laws are obtained through the relevant mechanical tests: in the process of strengthening different organic contents of soft soil, the reinforcement effect can gradually decrease with the increase of organic content. Magnesium phosphate cement is obviously superior in rapid repair and condensation than PO cement. But long-term reinforcement effect of the magnesium phosphate cement in soft soil is not as good as that of PO cement. At the same time, SEM test is used to explain the obtained rules and analyze the microstructure evolution characteristics. Magnesium phosphate cement can be applied to the construction of soft soil repair projects. The research results uniquely analyze the influence of organic content change on the strengthening effect of magnesium phosphate cement, which has guiding and reference significance for reinforcing soft soil projects.
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Key words:
- Magnesium phosphate cement /
- PO cement /
- Soft soil /
- Mechanical strength /
- Microstructure
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表 1 软土的物理力学性质指标
Table 1. Physico-mechanical indices of soft soil samples
天然密度
/g·cm-3土粒
相对密度含水率
/%液限
/%塑限
/%塑性
指数液性
指数孔隙率 压缩模量
/MPa压缩系数
/MPa-1黏粒
/%有机质
/%1.81 2.70 39.7 45 22 23 0.68 0.63 1.702 0.826 41.3 0.3 表 2 磷酸镁水泥组成
Table 2. Composition of magnesium phosphate cement
组分 氧化镁(M) 磷酸二氢钾(P) 硼砂(B) 比例 20 5 1 表 3 PO水泥和磷酸镁水泥固化土无侧限抗压强度试验结果
Table 3. Test results of unconfined compressive strength of PO cement and magnesium phosphate cement solidified soil
编号 腐殖酸含量
/%无侧限抗压强度/kPa 7 d 14 d 28 d 磷酸镁水泥 PO水泥 磷酸镁水泥 PO水泥 磷酸镁水泥 PO水泥 1 0 497.48 253.96 635.31 995.28 787.73 1373.27 2 3 417.89 190.78 578.68 725.25 715.41 1131.86 3 6 371.28 162.85 423.85 611.23 555.22 1008.41 4 9 374.94 138.91 405.86 421.93 575.59 781.71 5 12 370.52 130.33 383.26 586.35 565.96 717.76 表 4 PO固化土和磷酸镁固化土黏聚力试验结果
Table 4. Test results of cohesion of PO-stabilized soils and magnesium phosphate-stabilized soils
编号 腐殖酸含量
/%黏聚力c/kPa 7 d 14 d 28 d 磷酸镁水泥 PO水泥 磷酸镁水泥 PO水泥 磷酸镁水泥 PO水泥 1 0 179.83 142.26 202.54 242.26 250.00 525.65 2 3 173.54 118.12 193.35 218.12 235.50 452.69 3 6 169.07 106.35 179.80 196.35 230.12 360.02 4 9 165.48 104.71 174.73 194.71 226.34 359.03 5 12 164.45 100.36 170.14 180.36 216.97 345.10 表 5 PO固化土和磷酸镁固化土内摩擦角试验结果
Table 5. Test results of internal friction angle of PO-stabilized soil and magnesium phosphate-stabilized soil
编号 腐殖酸含量
/%内摩擦角φ/(°) 7 d 14 d 28 d 磷酸镁水泥 PO水泥 磷酸镁水泥 PO水泥 磷酸镁水泥 PO水泥 1 0 29.69 27.18 31.53 35.94 32.06 40.10 2 3 27.27 24.16 29.00 33.50 30.75 35.11 3 6 23.12 20.67 25.96 30.50 27.06 33.98 4 9 21.96 19.45 23.37 28.00 24.00 32.23 5 12 17.20 15.41 19.00 24.50 20.31 24.98 表 6 物相统计及标记
Table 6. Phase statistics and markers
名称 化学式 标记 绿泥石 (Mg,Fe2+,Fe3+,Al)6((Si,Al)4O10)(OH)8 Chl 高岭石 Al2Si2O5(OH)4 K 水化磷酸镁 Mg3(PO4)2 MP 钾磷酸盐 MgKPO4·6H2O MKP 水滑石 Mg6Al2(CO3)(OH)16·4H2O HT 钙矾石 3CaO·Al2O3·3CaSO4·32H2O AFt 水化硅酸钙 CaO·Al2O3·10H2O CSH 方镁石 MgO M -
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