钾盐和磷酸盐对固化土早期强度的影响研究

Effects of potassium salt and phosphate on the early strength of stabilized soil

利用土壤板结原理,通过对硫铝酸盐水泥固化土无侧限抗压强度试验和水稳定性试验,探讨钾盐、磷酸盐对其早期强度的影响规律;通过X射线衍射(XRD)对固化土的物相成分进行了分析,探讨钾盐、磷酸盐影响固化土强度的变化内在机制。试验结果表明,钾盐、磷酸盐对固化土强度提高的阈值为0.6%,当盐掺入量低于该阈值时,固化土强度会随着盐掺量的增加而提高,当盐掺入量超过该阈值时,固化土强度会逐渐降低。盐掺入量不超过2%时,掺盐固化土水稳定性与未掺盐固化土差不多,7 d固化土软化系数基本保持在70%以上,但掺入K2SO4的固化土水稳定性较差,软化系数在60%左右。生成高强难溶具有膨胀性的矿物晶体是掺盐固化土早期强度提高的主要原因,但盐掺入量过高,固化土中矿物晶体过多膨胀作用,破坏固化土结构,而使固化土早期强度降低。

According to the features of soil solidification, a series of unconfined compression and water stability tests is conducted to investigate the effects of the variation of potassium salt and phosphate concentrations on the early strength of sulphoaluminate cement-stabilized soil. X-ray diffraction （XRD） analysis of phase composition of the stabilized soil is performed to reveal the mechanism for the changes of the early strength of the stabilized soil. The experimental results show that there is a threshold of about 0.6% in potassium salt and phosphate contents. If the mixing amount of the salts in the stabilized soil is lower than this threshold value, the strength of the stabilized soil increases with the increase of the salt concentration; while the amount exceeds the threshold, the strength of the stabilized soil will decrease. If the salt concentration is not more than 2%, the water stability of the stabilized soil with salt is similar to that without salt; the softening coefficient of the stabilized soils after 7-day curing is larger than 70%, whereas the water stability of the stabilized soil with K2SO4 is poorer, and the softening coefficient is about 60%. XRD analysis shows that the generation of insoluble mineral crystal with high strength and expansibility is the main reason that the early strength of the stabilized soil is improved after introducing potassium salt or phosphate. If the salt concentration is too high, the early strength of stabilized soil will be drastically reduced due to mineral crystal excessive expansion effect, which destroys the structure of stabilized soil.