Experimental research on dynamic mechanics of early age concrete

The single and double impact experiments were carried out on C20 and C40 concrete at five different ages using a 75 mm SHPB experimental device. The mechanical properties of early age concrete under impact loading were systematically studied from two aspects,namely curing age and strain rate. The results of
single impact test show that,on the one hand,the dynamic compressive strength of concrete under the same strain rate is logarithmically related to curing age,while the peak strain of concrete decreases with the increase of impact age. On the other hand,the uniaxial compressive strength at each curing age is in power relationship with the strain rate,and peak strain increases with the increase of strain rate. After the first impact,the concrete specimens are cured to the standard age,and then the second impact test in which the strain rates are the same is carried out to test the mechanical properties of concrete. The results of repeated impact tests show that when the first impact age is less than 3 days,the deformation ability of concrete decreases after reaching the stable age,but increases when impact age is more than 5 days. If the strain rate of the first impact test exceeds 25 s-1,the dynamic compressive strength will decrease with the increase of the first impact strain rate,and the later the age of the impact,the greater the reduction. Combined with the experimental results of C20 and C40 concrete,it is concluded that the lower the grade of concrete,the more its mechanical property is affected by strain rate and impact age.