冻融循环对碱激发高炉矿渣微粉加固软土强度的影响

Influence of Freeze-thaw Cycle on Strength of Soft soil Solidified by Alkali-activated Ground Granulated Blast Furnace Slag

GGBS(高炉矿渣微粉)在适宜的碱激发剂的催化作用下能够生成良好的胶凝产物,可作为一种可持续发展材料替代水泥进行软土固化处理。为了研究冻融养护条件对其加固软土强度的影响,针对上海地区软土,以GGBS为原料、石灰为碱激发剂、石膏和硫酸钠为外掺剂进行加固处理,采用无侧限抗压强度试验、X射线衍射(XRD)试验和扫描电镜(SEM)试验对固化土的强度进行研究,并与标准养护条件下的试验结果进行对比,从宏观和微观两方面分析了冻融循环作用的影响。结果表明:两种养护条件下,固化土无侧限抗压强度均随龄期的增长而增大,但冻融养护条件下固化土的无侧限抗压强度均低于标准养护条件下的无侧限抗压强度,其原因为冻融循环抑制了水化反应,破坏了固化土的骨架结构,减弱了固化土抵抗变形的能力;标准养护条件下,石膏和硫酸钠的加入均能加快高炉矿渣的水化反应,且石膏能起到强度增强剂的作用,加入石膏和硫酸钠能降低冻融循环对固化土的影响,使其强度相对较大且硫酸钠的抵抗性更强;微观上,SEM和XRD试验表明冻融循环不改变固化土中物相种类,仅降低水化反应速率,导致未参与反应的高炉矿渣微粉量较大,水化产物的生成量减少,土颗粒间存在较多孔隙,相互之间黏结性减弱,无侧限抗压强度降低。

Ground granulated blast furnace slag(GGBS)can generate good cementitious products under the catalysis of appropriate alkali activator,which can be used as a sustainable material instead of cement to solidify soft soils.In order to study the influence of freeze-thaw curing conditions on the strength of reinforced soft soils,in view of the soft clay in Shanghai,using GGBS as raw material,lime as alkali-activator,gypsum and sodium sulfate as admixtures for reinforcement treatment,the strength of the solidified soil is studied by using unconfined compressive strength test,X-ray diffraction(XRD)test and scanning electron microscope(SEM)test,which is compared with the test result under standard curing conditions.The effect of freeze-thaw cycles is analyzed from both macroscopic and microscopic aspects.The result shows that(1)The unconfined compressive strength of the solidified soil increases with the increase of curing age under 2 curing conditions,but the unconfined compressive strength of the solidified soil under freeze-thaw cycle curing condition is lower than that under standard curing condition.The reason is that the freeze-thaw cycle inhibited the hydration reaction,destroyed the skeleton structure of the solidified soil,and weakened the ability of the solidified soil to resist deformation.(2)Under standard curing condition,the addition of gypsum and sodium sulfate can accelerate the hydration reaction of blast furnace slag,and gypsum can act as a strength enhancer,the addition of gypsum and sodium sulfate can reduce the influence of freeze-thaw cycles on the solidified soil,so that its strength is relatively large and the resistance of sodium sulfate is stronger.(3)On the microscopic level,SEM and XRD tests show that freeze-thaw cycles do not change the phase types in the solidified soil,but only reduce the hydration reaction rate,resulting in a larger amount of GGBS does not participate in the reaction,a reduction in the generation of hydration products,and more pores between soil particles,the adhesion between them is weakened,and the unconfined compressive strength is reduced.