Experimental Study On The Effect Of Basalt Fiber On Crack Propagation Of Cement Mortar At Early Age

Ordinary cement mortar contains a lot of initial cracks and micropores,which will affect its properties in the working environment and under load,adding high-performance fibers can effectively improve its mechanical properties.In order to study the effect of basalt fiber on the anti-cracking performance of cement mortar at the early age,two groups of specimens,basalt fiber reinforced cement mortar and ordinary cement mortar,were designed,and standard cement mortar specimens with artificial cracks were concreted.The influence of basalt fiber on the crack propagation of cement mortar at the early age was investigated from multiple angles and through different parameters through three-point bending strength test,combined with resistance strain gauges,digital speckle correlation method and infrared thermal imaging technology.The main study and conclusions of this work are as follows:(1)The load-displacement curves and basic mechanical performance parameters of these two groups of specimens were compared and analyzed;and further analysis of the impact of basalt fiber on the fracture properties of the specimen was carried out by calculating the fracture energy,critical stress intensity factor and elastic crack mouth opening width.It was found that the adding of basalt fiber can effectively improve the mechanical properties of cement mortar specimens at the early age,the flexural strength and compressive strength improved by 38.50% and 62.52%,and the magnitude of deformation corresponding to the maximum load increased by 47.2%.In terms of fracture performance parameters,the fracture energy,crack opening width and critical stress intensity factor of the basalt fiber reinforced cement mortar specimens were improved by 38.55%,32.00% and 38.56%,respectively,compared with ordinary cement mortar specimens.(2)Quantitative study of stress-strain characteristics and crack growth rate were performed through resistance strain gauges.It was found that the average crack growth rate of ordinary cement mortar and basalt fiber reinforced cement mortar specimens were 0.198 mm / s and 0.086 mm / s,respectively.With basalt fiber added,the crack growth rate of the specimen was reduced by 57.00%,and the fiber showed a significant retardation effect on the crack growth.(3)The speckle image was transformed into deformation information that could characterize the mechanical properties of the cement mortar specimen by the speckle correlation method.It was found that the digital speckle correlation method could present the full-field deformation of the specimen during the loading process intuitively.Information,localization strain zone appeared near the crack tip when the specimen failed;the crack resistance of the cement mortar specimen was improved effectively after the basalt fiber was added,and the initial cracking time of the specimen was retarded;The crack propagation slips along the fiber surface after encountering the fiber due to the properties of basalt fiber,and the crack propagation path is tortuous,which can be recongnized by the obvious crack bend path in the digital speckle cloud diagram.(4)The infrared radiation temperature on the surface of the tested specimen was detected by the infrared thermal camera during the loading test.It was found that the minimum,maximum and averaged infrared radiation temperature curves of the ordinary cement mortar specimens developed smoothly,while The infrared radiation temperature curves of the basalt fiber reinforced cement mortar test pieces showed an upward trend,which is related to the mechanical behaviors of debonding,slipping and the abruptment of the interface between the fiber and the cement matrix.