Experimental Research into the Cumulative Damage Effect and Strength Anisotropy of Fresh Concrete under Blast Vibration

To evaluate influence of blast vibrations on the long-term mechanical deterioration and damage anisotropy of fresh concrete, blast vibration tests were conducted by preparing concrete test blocks at different curing ages. On this basis, the internal relationships of factors including the curing age during vibrations, vibration blast velocity, and number of blast vibrations with the damage evolution were investigated. The results show that fresh concrete is more susceptible to blasting vibration in the initial setting stage, which changes the bonding performance between cementing materials and aggregates. Then irreversible damage is generated along the main direction of vibration, and cumulative damage occurs with the increasing number of blast vibrations. Fresh concrete was affected most by blasting vibration at an age of 1 day, and the compressive strength at 28 days was reduced by 44.17% under a single vibration event. The damage increased slowly in the concrete at curing ages from 1 to 7 day. Blast vibrations with a velocity of less than $96.2\mathrm{mm}/\mathrm{s}$ had a slight influence on changes in the compressive strength of concrete cured for 28 days. As the blast vibration velocity increased from 96.2 to $180.6\mathrm{mm}/\mathrm{s}$, the decrease rate of compressive strength in various directions accelerated and the strength decreased by as much as 40.59%. Therefore, it is suggested that the influence of the blast vibration velocity and the number of blast vibrations should be considered in alternating and parallel construction of blasting and concrete pouring work. Furthermore, blast vibration velocity, number of blast vibrations, and maximum attenuation coefficients of longitudinal wave velocities of vibrated concrete test blocks with the same curing age during vibrations differed along three directions, showing anisotropic characteristics. As the velocity and number of blast vibrations increased, the damage anisotropy became more significant. Therefore, the influence of anisotropy of cumulative damage evolution should be considered when establishing the safety criteria for fresh concrete subjected to blast vibrations.