石膏质岩工程特性及其对混凝土劣化机制试验研究

Experimental Study on Engineering Characteristics of Gypsum Rock and its Degradation Mechanism for Concrete

石膏或者硬石膏与碳酸盐沉积共生的岩类一般称作石膏质岩,在整个地质沉积历史上分布广泛。一般情况下,石膏质岩遇水析出的SO4^2-会腐蚀混凝土,并产生体积膨胀,强度变差。当隧道穿越石膏质岩层时,这种工程性质会给隧道安全带来不利影响。该文从宜昌市至巴东县高速公路凉水井隧道围岩取样,通过X衍射试验、化学分析试验全面揭示了该地区石膏质岩化学及矿物组成。对石膏质岩粉末重塑样进行膨胀性试验,试验表明膨胀率的大小与重塑样的初始干密度有关,72 h膨胀力可达0. 18 k Pa^2. 19 k Pa,对工程结构物有一定危害。在静水与动水条件下分别对石膏质岩进行溶蚀溶出试验,试验表明,静态溶蚀存在溶解平衡,溶蚀量先增加后稳定;在动态溶蚀下试样质量一直降低直至整体结构被破坏;溶蚀速度受时间和流速影响。通过模拟试验,研究了石膏质岩析出离子对混凝土的劣化机制。上述研究结果对于工程实践有一定的指导意义。

Gypsum or anhydrite associated with carbonate deposits is generally called gypsum rocks,which are widely distributed throughout the geological and sedimentary history.Generally,SO4^2- precipitated from gypsum rock in water will corrode concrete and cause volume expansion and strength deterioration.When the tunnel passes through gypsum rock strata,this engineering property will bring adverse effects on tunnel safety.In this paper,the chemical and mineral composition of gypsum rocks in Liangshuijing Tunnel of Yichang-Badong Expressway are comprehensively revealed by X-ray diffraction and chemical analysis tests.Expansion test of gypsum powder remolded sample shows that the expansion rate is related to the initial dry density of the remolded sample.The expansion force can reach 0.18 kPa^2.19 kPa in 72 h,which is harmful to the engineering structure.The dissolution tests of gypsum rocks were carried out under hydrostatic and hydrodynamic conditions respectively.The results show that there exists dissolution equilibrium in static dissolution,and the dissolution amount increases first and then stabilizes;the quality of samples decreases until the whole structure is destroyed under dynamic dissolution;and the dissolution rate is affected by time and flow rate.The deterioration mechanism of gypsum ion on concrete was studied by simulation test.The above research results have certain guiding significance for engineering practice.