Analysis Of Fracture Characteristics Of Strain-Hardening Tailings Cementitious Composites

Currently,the application of strain-hardening cementitious composites for the building to be further developed in complex environment such as ocean,high-low temperature.It is a matter of great concern of engineering industry to study the stress intensity factor and energy factor of strain-hardening tailings cementitious composites(SHTCC)when it is broken,and then evaluate the life and safety of components with slit.Based on the theory of nonlinear fracture mechanics and the double-K fracture criterion,the three-point bending fracture test of SHTCC is carried out under normal circumstances,freeze-thaw cycle and sulfate corrosion.The main contents are as follows:(1)Based on the digital image correlation method,the displacement field and the strain field of the observation surface of the three-point bending beam were observed by non-contact video measuring instrument.By testing the results of cement mortar test,the rationality of using this method to determine the initial cracking load of the specimen was illustrated,and then,as a reference for follow-up study,SHTCC material initial cracking load and ultimate load ratio range was summarize based on the method.(2)The fracture characteristics of SHTCC under normal conditions were studied.The effects of specimen size,fly ash content,tailings content,fiber content and water-cement ratio on fracture parameters were studied.The results show that the size of the specimen has little effect on the fracture parameters.The fracture parameter is the largest when the fly ash content is 54.5%.As the fine aggregate,it is almost no effect on the fracture parameters that the replacement ratio of tailings is 50%.When the fiber content is 2% and water-cement ratio is 0.4,the initial fracture toughness of SHTCC is the highest.When the fiber content is 2% and water-cement ratio is 0.5,the unstable fracture toughness and fracture energy of SHTCC is the highest.(3)The fracture characteristics of SHTCC under freeze-thaw cycles were studied.The effects of freeze-thaw cycles,fiber content,water-cement ratio and other factors on fracture parameters were studied.The results show that the initial fracture toughness of SHTCC specimen is about 2 times of the value of cement mortar under the freeze-thaw cycles condition.The unstable fracture toughness is about 10 times of the value of cement mortar.The fracture energy is about 100 times of the value of cement mortar.(4)The fracture characteristics of SHTCC under the condition of sulfate corrosion in dry-wet cycles were studied.The effects of dry-wet cycles,fiber content,water-cement ratio and other factors on fracture parameters were studied.The results show that the initial fracture toughness of SHTCC specimen is about 2 times of the value of cement mortar under dry-wet cycles condition.The unstable fracture toughness is about 10 times of the value of cement mortar.The fracture energy is about 100 times of the value of cement mortar.SHTCC have excellent fracture characteristics under harsh environmental conditions such as conditionsfreeze-thaw cycles and sulfate corrosion comparing with cement mortar.