活性MgO-粉煤灰固稳铅污染土冻融和温度效应研究

Freeze-thaw cycle and temperature effect of reactive MgO-fly ash stabilized Pb-contaminated soils

采用活性MgO和MgO-粉煤灰固稳不同初始Pb2+浓度污染土,通过冻融循环、恒温养护和毒性浸出试验,从无侧限抗压强度、浸出液pH值、Pb2+溶出浓度等角度评价了固稳铅污染土耐久性(冻融循环与温度效应),结果表明,活性MgO和MgO-粉煤灰可显著提高土体抗压强度、Pb2+稳定性及抵抗冻融循环能力。冻融循环次数增加,抗压强度与强度损失率表现为先上升至峰值后有所下降;冻结温度降低,固化土抗压强度减小;11次冻融后固化土残余强度高于75%,满足规范要求;冻融循环条件下,固化剂掺量从5%增至10%,使抗压强度提高2倍以上;固稳铅污染土最宜浓度为0.5%时具有较优的抵抗冻融循环性能;MgO和MgO-粉煤灰固化污染土Pb2+溶出量满足规范要求。初始Pb2+浓度与温度对MgO和MgO-粉煤灰固化体溶出特性有显著影响,温度升高可促进固稳铅污染土抗压强度;提高MgO和MgO-粉煤灰掺量对固化体具有明显增强作用。临界浓度与温度水平密切相关,温度升高可提高Pb2+临界浓度。

Reactive MgO and MgO-fly ash were selected to stabilize Pb2+-contaminated soils with different initial concentrations.The durability(freeze-thaw cycle and temperature effect) of stabilized Pb2+-contaminated soils was evaluated from unconfined compressive strength, pH value of leaching solution and Pb2+dissolution concentration by the freeze-thaw cycles,thermostatic curing and toxic leaching tests.The results show that the addition of reactive MgO and MgO-fly ash can improve the compressive strength, freeze-thaw resistance and Pb2+stability of soil.As the number of freeze-thaw cycle increases,the compressive strength and strength loss ratio rise up to the peak values,and then decrease. A decrease in freezing temperature induces correspondingly a decrease in strength of the solidified soil.The residual strength ratio of the solidified soil is higher than 75% after11 freeze-thaw cycles, which meets the specification requirements.An increase in curing agent content(5% to10%)increases the strength twice as high as the initial value under freeze-thaw cycles.The resistance of stabilized Pb2+-contaminated soil to freeze-thaw cycles is the optimum when the Pb2+concentration is about 0.5%.The dissolution amount of Pb2+from the contaminated soil solidified by MgO and MgO-fly ash meets the requirement of standards. The initial Pb2+concentration and temperature have significant effects on the dissolution characteristics of MgO and MgO-fly ash solidified soils,and an increase in temperature can promote the compressive strength of solidified lead-contaminated soils.Increase in the contents of MgO and MgO-fly ash can significantly improve the strength of solidified soils. The critical Pb2+concentration is closely related to temperature level,and raising the temperature can increase the critical Pb2+concentration.