| As a new construction method, shotcrete has been widely used in many engineeringfields of underground tunnels, mining pit engineering, hydraulic engineering, thin-walledstructures, foundation pit support and so on. According to the survey, the projectenvironment of shotcrete are most extremely bad, during actual service they willinevitably suffer long-term effects of various environmental factors. How to ensure thesprayed concrete service with high durability in complex environments, and how toevaluate and predict its properties, are the major unsolved theoretical problems at homeand abroad. Thus, it is very important to carry out the durability study of concrete for theeconomic development and stability of China.This paper reports on conducting durability experiment of sulfate attack andcarbonation to investigate the durability properties of shotcrete using the method combingboth microscopic test and macroscopic properties, and its aim is to provide a theoreticalbasis to assess the durability of shotcrete. The main contents are as follows:Rapid carbonation tests are conducted to investigate the effects of constructiontechnology and steel fiber on anti-carbonation properties of shotcrete. The relationshipbetween carbonation depth and carbonation time, different carbonation rate on moldingsurfaces, and compressive strength and splitting tensile strength with increasingcarbonation time are studied to establish a quantitative relationship between mechanicalproperties and carbonation depth of shotcrete. Meanwhile, the carbonation mechanism ofshotcrete are deeply analyzed using microscopic testing methods of SEM and EDS. Theresults indicate that, compared with the normal concrete, shotcrete shows relatively small carbonation rate but larger dispersion degree of carbonation depth; the incorporation ofsteel fiber will reduce the carbonation depth and the discrete degree.In order to study the effects of construction technology and steel fiber on sulfateresistance performance of shotcrete, we carry out sulfate attack experiments on theshotcrete specimens. The degradation indicators of apparent condition, mass loss rate,corrosion resistance coefficient of compression strength, corrosion resistance coefficientof splitting tensile strength, and relative dynamic elastic modulus are also studied,respectively, to evaluate the deterioration process of shotcrete under the sulfate attackenvironment, and then establish the damage evolution model and the mechanicalproperties degradation model for shotcrete under sulfate attack environment. In addition,microscopic test methods SEM, XRD and thermal analysis are conducted to thoroughlystudy the microscopic degradation mechanism and damage laws of sulfate attack onshotcrete. The results indicate that, compared with normal concrete, shotcrete showsbetter resistance to sulfate erosion, and the incorporation of steel fiber can further enhancethe ability of anti-erosion. |
