Influence of wet-dry cycles on vertical cutoff walls made of reactive magnesia-slag-bentonite-soil mixtures

Abstract

The strength and hydraulic conductivity of vertical cutoff walls consisting of reactive magnesia-activated ground granulated blast furnace slag (GGBS), bentonite, and soil (MSB) have been investigated in previous studies. However, there has been little comprehensive study of the influence of wet-dry cycles on the mechanical and microstructural properties of MSB backfills. In this paper, the durability of MSB backfills when exposed to wet-dry cycles is investigated. The variations in mass change, dry density, pH value, pore size distribution, and mineralogy are discussed. The results show that the mass change of ordinary Portland cement (OPC)-based and MSB backfills increases with respect to wet-dry cycles. The MSB backfills exhibit up to 8.2% higher mass change than OPC-based ones after 10 wet-dry cycles. The dry density, pH value, and unconfined compressive strength of MSB backfill decrease with the increasing number of wet-dry cycles. Increasing the GGBS-MgO content from 5% to 10% in MSB backfills results in 2.1–2.3 times higher strength, corresponding to a reduction of 2%–12% in cumulative pore volume; while increasing the bentonite content slightly reduces the strength of MSB mixtures, corresponding to an increase of cumulative pore volume by 4.6%–7.9%. The hydrotalcite-like phases and calcium silicate hydrate (C-S-H) are the primary hydration products in MSB backfills. Moreover, the continuous wet-dry cycles result in the precipitation of calcite and nesquehonite.

概要

目 的

• 1. 研究干湿循环作用下氧化镁激发矿渣-膨润土 (MSB) 竖向隔离墙的耐久特性.

• 2. 探讨干湿循环过程中循环级数对隔离墙的质量变化、干密度、pH 值、无侧限抗压强度、孔隙结构和微观产物等的影响, 并探究 MSB 的服役性能.

创新点

• 1. 通过干湿循环作用, 揭示新型 MSB 隔离墙与传统水泥基 (OPC) 隔离墙的耐久性差异;

• 2. 通过微观分析, 成功测定新型 MSB 隔离墙干湿循环后形成的水化产物.

方 法

• 1. 通过宏观实验分析, 在干湿循环作用下比较 MSB 隔离墙和 OPC 隔离墙的质量、干密度、 pH 值和无侧限抗压强度等参数的变化情况 (图 2 和 4~6);

• 2. 通过微观分析, 研究 MSB 隔离墙中氧化镁激发高炉矿渣 (GGBS-MgO) 和膨润土的掺量对空隙结构的影响 (图 8), 并探讨干湿循环作用如何影响碳酸钙和碳酸镁等水化产物的形成 (图9).

结 论

• 1. MSB 隔离墙的质量损失比 OPC 隔离墙高 1.1%~2.1%;

• 2. MSB 和 OPC 隔离墙的干密度和 pH 值均随干湿循环级数的增长而减小;

• 3. MSB 和 OPC 隔离墙的无侧限抗压强度随干湿循环级数的增长而降低;

• 4. 增加 GGBS-MgO 的掺量可减少 2%~12% 的累计进汞量, 而增加膨润土的掺量会增加 4.6%~7.9 %的进汞量;

• 5. 干湿循环可加速碳酸钙和碳酸镁等水化产物的形成.