Experiment And Research On Dynamic Compressive Properties Of Shrinkage-compensating Fly Ash Shotcrete With Magnetized Water

Fly ash has become an indispensable part of concrete raw materials, as the largest dosage mineral admixture with advantages of low engineering cost, energy conservation and environment protection. To prepare shrinkage-compensating fly ash shotcrete, mix with fly ash in shrinkage-compensating shotcrete, which has a good application prospect in the construction of mine and underground engineering, but fly ash will reduce the strength of concrete. Magnetized water can enhance the strength of concrete, especially the early-age strength. Therefore, this paper studies compressive and tensile properties, dynamic compressive properties and crack resistance of shrinkage-compensating fly ash shotcrete under the different fly ash contents and different types of magnetized water velocity through a large number of laboratory test and theoretical analysis, providing a reference for engineering application. The test results are as follows:When the magnetized induction intensity is 285 mT, the growth rate of 7-day compressive strength of shrinkage-compensating concrete and shrinkage-compensating shotcrete can respectively reach 6.4% and 14.2% compared with ordinary concrete when the water velocity is 0.9m/s and 2.1m/s. Magnetized water can make up for 7-day strength loss of concrete resulting from the accelerator. Compared with ordinary shrinkage-compensating concrete, the growth rate of 7-day compressive strength of shrinkage-compensating shotcrete is able to reach 11% when the water velocity is 2.1m/s. Magnetized water can reduce 7-day strength loss of concrete caused by fly ash. Compared with ordinary shrinkage-compensating shotcrete,7-day compressive strength of ordinary shrinkage-compensating fly ash shotcrete decreases by 10%, while 7-day compressive strength of shrinkage-compensating fly ash shotcrete with magnetized water only decreases by 3% when the water velocity is 2.1m/s.Conduct the orthogonal test between the magnetized water velocity of 1.2 m/s, 2.1m/s and the fly ash content of 0%,10%,15%,20%,25% and 30%, mix shrinkage-compensating fly ash shotcrete and analyze 28-day compressive and tensile strength, when the content of the accelerator and expansive agent is fixed at 2%,6% respectively. The result shows that magnetized water can effectively improve compressive and tensile properties of shrinkage-compensating fly ash shotcrete when water velocity is 2.1m/s, and fly ash content is 10%, and that its compressive and tensile strength can increase by 11.6% and 10.8% respectively compared with ordinary shrinkage-compensating fly ash shotcrete, obtaining best performance.Under the condition of the strain rate 22.5s-1, study the dynamic compressive properties of ordinary shrinkage-compensating fly ash shotcrete and magnetized water shrinkage-compensating fly ash shotcrete whose fly ash content are both 0%,10%, 15%,20%,25% and 30%, when the content of the accelerator and expansive agent is fixed at 2%,6% respectively. The result shows that magnetized water can effectively improve dynamic compressive properties of shrinkage-compensating fly ash shotcrete when water velocity is 2.1m/s, and fly ash content is 10%, and that its dynamic compressive strength can increase by 40% compared with ordinary shrinkage-compensating fly ash shotcrete, obtaining best performance.According to compressive and tensile mechanical test and dynamic compressive properties test, comparison tests of early-age crack resistance are conducted under the best match of magnetized water velocity and fly ash content, when the content of the accelerator and expansive agent is fixed at 2%,6% respectively. The coefficient of crack decrease of shrinkage-compensating fly ash shotcrete, magnetized water shrinkage-compensating shotcrete and magnetized water shrinkage-compensating fly ash shotcrete are 40.4%,94.2% and 95.0% respectively, and the early crack limiting grade are third one, first one and first one respectively. The best effect of anti-crack belongs to magnetized water shrinkage-compensating fly ash shotcrete.