Mechanical behavior and microstructural mechanism of improved disintegrated carbonaceous mudstone

This study aims to improve the mechanical behavior of disintegrated carbonaceous mudstone, which is used as road embankment filler in southwestern China. Triaxial tests were performed on disintegrated carbonaceous mudstone modified by fly ash, cement, and red clay. Then the stress-strain relationships and shear strength parameters were analyzed. The microstructure and mineral composition of the materials were identified via scanning electron microscopy and X-ray diffraction. The results show that the stress-strain relationships changed from strain-hardening to strain-softening when disintegrated carbonaceous mudstone was modified with cement. By contrast, the addition of fly ash and red clay did not change the type of stress-strain relationships. The order of these three additives is cement, red clay and fly ash according to their influences on the cohesion. Disintegrated carbonaceous mudstone without cement all showed bulging failures, and that modified with cement exhibited shear failures or bulging-shear failures. The soil particles of the improved soil were well bonded by cementitious substances, so the microstructure was denser and more stable, which highly enhanced the mechanical behavior of disintegrated carbonaceous mudstone. The findings could offer references for the use of carbonaceous mudstone in embankment engineering.

红黏土裂隙湿化自愈行为及强度影响机制

许多黏性土在干缩开裂后受湿化作用会呈现裂隙自愈现象。为探究红黏土裂隙自愈行为及其对土体强度特性的影响机制,基于摄影识别与数字图像相关技术,分析湿化过程中红黏土试样顶面裂隙自愈与应变演化规律;并开展单轴拉伸试验与直剪试验,获取不同条件下红黏土的抗拉强度、抗剪强度及指标恢复率。最后采用扫描电镜观察裂隙自愈前后试样的微观形貌,阐明红黏土裂隙自愈及强度影响机制。结果表明:红黏土在湿化条件下表现出裂隙自愈行为,自愈过程中压应变区域不断向裂隙靠近,裂隙率快速减小并趋于稳定,裂隙自愈率可达90%以上;随饱水湿化时间增加,含裂隙红黏土的抗拉强度小幅提升,此时土表裂隙痕迹几乎消失;湿化条件下土颗粒膨胀程度有限,裂隙宽度越大其愈合难度越高,抗拉强度恢复程度也越低;裂隙深度增加后裂隙自愈率小幅提升,抗拉强度与黏聚力的恢复率增加,内摩擦角恢复率先减小后稳定;裂隙自愈主要源于土颗粒膨胀变形后引起裂隙两侧壁相互黏结,以及土颗粒崩解剥落后对裂隙的填充效应;由于细小颗粒与水混合后可能吸附在裂隙内形成假愈合现象,且土颗粒膨胀崩解将影响土体强度,故尽管表观上裂隙愈合程度良好,但抗拉强度与抗剪强度指标仅小幅恢复。

阿拉伯树胶改性预崩解炭质泥岩路用性能及改性机制

为提升预崩解炭质泥岩路用性能以用作路堤填料,采用阿拉伯树胶对预崩解炭质泥岩进行改性,分析改性后预崩解炭质泥岩的路用性能及改性机制。开展加州承载比(CBR)、回弹模量、无侧限抗压强度(UCS)及单轴抗拉强度试验,研究阿拉伯树胶掺量与养护龄期对改性预崩解炭质泥岩路用性能的影响,并通过崩解性、酸碱度(pH)、电导率、溶解性固体总量(TDS)及Zeta电位试验分析改性前后预崩解炭质泥岩理化特性的变化,结合扫描电镜(SEM)、X射线能谱分析(EDS)与傅里叶变换红外光谱分析(FTIR),探讨阿拉伯树胶对预崩解炭质泥岩的改性机制。研究结果表明:阿拉伯树胶能有效改善预崩解炭质泥岩的路用性能,且随掺量与养护龄期增加,路用性能改善程度逐渐增大;结合经济性考虑,阿拉伯树胶掺量为4%时路用性能改性效果最佳,CBR与回弹模量分别提升495%和427%,UCS与单轴抗拉强度均提升230%以上;掺入阿拉伯树胶可大幅降低预崩解炭质泥岩的崩解率、pH值、电导率、TDS及Zeta电位绝对值,改善预崩解炭质泥岩的水稳性;阿拉伯树胶通过降低预崩解炭质泥岩碱性、提供阳离子与颗粒表面离子发生离子交换并吸附在颗粒表面的方式,优化改性预崩解炭质泥岩内部结构性,通过胶结预崩解炭质泥岩颗粒、填充内部孔洞与孔隙的方式提升黏聚力与整体性,并包覆在颗粒与团聚体表层,阻隔外部环境直接作用。研究结果可为预崩解炭质泥岩再利用提供思路,并为阿拉伯树胶用作其他岩土材料的改性剂提供参考。