碱激发煤矸石粉对砒砂岩水泥复合土强度影响的试验研究

Experimental study on effect of alkali-activated gangue powder on strength of Pisha sandstone cement composite soil

为了降低砒砂岩区严重的水土流失,促进松散砒砂岩的有效利用,同时提高废弃煤矸石的利用率.借助X衍射、扫描电镜、热重和压汞等试验方法,从固化产物构成、微观形貌、孔隙结构演变等微观层面,揭示碱激发及煤矸石粉替代率对砒砂岩水泥复合土力学强度的影响机理.结果表明:碱的加入使得砒砂岩中的蒙脱石和煤矸石粉发生溶蚀,促进N-A-S-H和C-A-S-H凝胶的产生,使其强度增大;随着煤矸石粉替代量的增加和水泥掺量的相对降低,Ca含量降低,C-A-S-H凝胶含量下降,且N-A-S-H凝胶逐渐向无胶结性的钙(钠)菱沸石转化,导致其强度逐渐下降.当碱当量为4%,煤矸石粉替代率为7%时,煤矸石粉-砒砂岩水泥复合土孔隙率为29.20%,小孔占比为46.48%.且7 d强度可满足二级及二级以下公路底基层1.0~3.0 MPa的要求,该研究可为煤矸石粉-砒砂岩水泥复合土在道路铺设和渠道衬砌等应用中提供理论依据.

In order to reduce the serious soil erosion in the Pisha sandstone area,promote the effective utilization of loose Pisha sandstone,as well as improve the utilization rate of waste coal gangue,by use of X-ray diffraction,scanning electron microscopy,thermogravimetry,and mercury pressure test methods,the mechanism of alkali excitation and gangue powder substitution rate on the mechanical strength of Pisha sandstone-cement composite soil from the microscopic level of the composition of the curing product,microscopic morphology,and the evolution of the pore structure was revealed.The results show that the addition of alkali causes the dissolution of montmorillonite and coal gangue powder in Pisha sandstone,promotes the generation of N-A-S-H and C-A-S-H gel,which increases its strength.With the increase of gangue substitution and the relative reduction of cement dosage,the Ca content decreases,the C-A-S-H gel content decreases,and the N-A-S-H gel gradually transforms into non-cementitious Ca(Na)-lingite,resulting in a gradual decrease in its strength.When the alkali equivalent is 4%and the gangue substitution rate is 7%,the porosity of gangue powder-Pisha sandstone cement composite soil is 29.20%,and the proportion of small pores is 46.48%.Moreover,the 7d strength can meet the requirement of 1.0-3.0 MPa for the sub-base of secondary and sub-secondary highways.This study can provide a theoretical basis for the application of gangue powder-Pisha sandstone cement composite soil in road paving and channel lining.