干湿循环下复合激发膏体充填材料宏-细-微观强化与损伤特性

Macro−meso−micro strengthening and damage characteristics of composite excitation paste filling material under dry-wet cycle

为探明盐-碱复合激发膏体充填材料的性能变化规律及干湿循环作用下充填体结构多尺度损伤机制,对以脱硫石膏和水泥熟料为复合激发剂的膏体充填材料进行多目标优化,并对最优配比下的充填体试块进行0~25次干湿循环,开展抗压强度、X射线衍射(XRD)、低场核磁共振(NMR)、扫描电镜(SEM)试验,揭示充填体宏观力学行为和微细观结构演化规律。研究结果表明:充填材料最优配比是矿渣掺量为50%,脱硫石膏与水泥熟料质量比为3:7,硅灰掺量为2.5%。随着干湿循环次数的增加,充填体宏观表现为抗压强度的折减及累积电导率升高,干湿循环10次时出现拐点,质量损失率和强度损失率分别达极小值-1.91%和-8.36%;在细观尺度上,T2谱反演良好,干湿循环作用10次后,横向弛豫时间逐渐右移且谱面积增大,表明膏体充填材料孔隙尺寸及数量随着干湿循环次数增加而增大;微观尺度上,钙矾石、石膏和方解石等侵蚀产物的膨胀结晶应力加速了微观孔隙结构的发育,反复干湿循环作用削减了C-S-H凝胶的黏聚力,由最初的堆叠蜂窝状劣化为小块状。综合宏、细、微观结构演变规律可知,孔隙结构的损伤演化与力学性能的劣化特征具有较好的同步性。

In order to explore the performance change law of salt-alkali composite excitation cemented paste backfill materials and the multi-scale damage mechanism of backfill structure under the action of dry-wet cycles,multi-objective optimization of paste filling materials with desulfurization gypsum and cement clinker as composite activators was carried out.The backfill specimens under optimal ratio was subjected to 0-25 dry-wet cycles,and tests on compressive strength,X-ray diffraction(XRD),low-field nuclear magnetic resonance(NMR),and scanning electron microscopy(SEM)were carried out to reveal the macroscopic mechanical behavior and microstructure evolution of the backfill.The results show that the optimal ratio of backfill material is slag content of 50%,mass ratio of desulfurization gypsum to cement clinker of 3꞉7,and silica fume content of 2.5%.With the increase of the number of dry-wet cycles,the macroscopic performance of the backfill is the reduction of compressive strength and the increase of cumulative conductivity.The inflection point occurs after 10 dry-wet cycles,the mass loss rate and strength loss rate reach the minimum value of-1.91%and-8.36%,respectively.On the mesoscopic scale,the T2 spectrum distribution form with good inversions.After 10 dry wet cycles,the transverse relaxation time constantly moves right and the spectral area increases,which indicates that the pore size and number of paste filling materials increase with the increase of dry-wet cycles.On the microscopic scale,the expansion and crystallization stress of erosion products such as ettringite,gypsum and calcite accelerates the development of microscopic pore structure,and the repeated dry-wet cycles reduce the cohesion of C-S-H gel,which deteriorates from the initial stacked honeycomb to small lumps.According to the evolution law of macroscopic,mesoscopic,and microscopic structures,the damage evolution of pore structures and the degradation characteristics of mechanical properties have good synchronization.