Comparison And Analysis Of Static Fracture Test With Different Notches

Static cracking technology is a development and supplement to traditional blasting technology.The cracking process has the advantages of no noise,no flying stones,no vibration,and no dust,and is widely used in the fields of rock cracking,tunnel excavation,and demolition of old buildings.The paper mainly through the indoor test method to study the effect of different notch methods on the static cracking effect of concrete test block.The main research contents and results are as follows:(1)The expansion properties of the static cracking agent were first tested.The effects of mixing water temperature and water agent ratio on the swelling properties of the breaker were discussed.The mixing water temperature was set to 20°C,30°C,and 40°C,and the ratio of water to solvent was 0.24,0.26,0.28,0.32.Tests have found that when the mixing water temperature is 20°C and the water agent ratio is 0.28,the maximum volume expansion rate is 3.484.(2)The first group of experiments mainly studied the effect of the number of notches on crack propagation.Through tests,it was found that during the static cracking process,4 to 5 cracks were generated in the round hole concrete test block,but the time for crack generation was late,and the position is relatively decentralized.Three cracks are generated in other test blocks.The cracks are generally diffused outward in the direction of the cut corners.The width of the first crack is the largest in all test pieces,and the width of the remaining cracks is relatively small.(3)The second group of experiments mainly studied the effect of notch angle on crack propagation.It is found by experiment that when the ratio of the slot depth a to the diameter of the reserved hole is kept constant,notch angle of 30° fracture orientation effect is good,when the notch angle is 60° crushing effect is better.(4)The third group of experiments mainly studied the effect of borehole spacing on crack propagation.Through experiments,it was found that 200 mm borehole spacing has better guided cracking effect in the three different borehole spacing cracking processes of 150 mm,200mm,and 250 mm.(5)By observing the strain time curve,it is found that the strain has already fluctuate within 1 hour before the macroscopic crack is seen,when pulled,the strain value increases,and when the pressure is applied,the strain value decreases.Observing the time curve of the wave speed,it was found that when a crack develops inside the concrete block,the ultrasonic wave velocity decays,and the decay speed of the wave velocity is positively correlated with the propagation speed of the crack.That is,the faster the crack propagation speed,the faster the decay speed.In the position where the wave velocity is first attenuated,cracks are generated first,and cracks diffuse from the bottom to the top.