粗骨料粒径对混凝土动态压缩行为的影响研究

Effect of coarse aggregate size on the dynamic compression behavior of concrete

粗骨料作为混凝土材料组成最主要的部分,对混凝土力学性能和破坏模式有着很重要的影响。为了研究粗骨料平均粒径对混凝土动态力学性能的影响规律,针对不同平均粗骨料平均粒径(6、12、24 mm)的混凝土和砂浆材料进行了一系列SHPB试验,得到了不同应变率下各试件的应力-应变曲线,并对每种材料的动态增长因子(dynamic increase factor,DIF)与应变率的对数进行了线性拟合。结果表明:砂浆和混凝土材料的抗压强度具有明显的应变率效应,其动态抗压强度随着应变率的增加而逐渐增大,应力-应变曲线呈现相似的变化趋势;在相同的动态应变率条件下,平均粗骨料粒径为12 mm的混凝土的动态抗压强度最大,这与准静态条件下砂浆抗压强度最大截然不同;不同粗骨料粒径混凝土材料的应变率强化系数均大于砂浆材料,且随着粗骨料无量纲尺寸的增大,混凝土材料的应变率强化因子呈现先增大后减小的趋势。

As the most important part of concrete material,coarse aggregate has a very important influence on the mechanical properties and failure mode of concrete.In order to study the effect of the coarse aggregate average size on the dynamic mechanical properties of concrete,a series of SHPB experiments were carried out for concrete and mortar materials with different average particle sizes(6 mm,12 mm and 24 mm)of coarse aggregate.A dual-pulse shaper was used in the tests for dynamic stress equilibrium and constant strain rate loading.Moreover,the dynamic stress equilibrium in the test specimen was checked,and it is considered that the test data are valid when the dynamic imbalance factor is less than 5%.The stress-strain curves of the specimens under different strain rates were obtained,and the dynamic increase factor(DIF)of each material was linearly fitted with the logarithm of the strain rate.The results indicate that the compressive strength of the mortar and the concrete has an obvious strain rate effect,the dynamic compressive strength increases gradually with the strain rate,and the stress-strain curves show a similar trend.Under the same dynamic strain rate condition,the dynamic compressive strength of the concrete with an average coarse aggregate size of 12 mm is the highest,which is quite different from the maximum compressive strength of the mortar under quasi-static conditions.The CEB and other models are inapplicable to the relationship between the DIF and the strain rate because they do not consider the effect of the coarse aggregate size found in this study.Therefore,the specimen’s dynamic DIF and the logarithm of strain rate are fitted by Bischoff's model in the paper.The strain rate strengthening coefficient of concretes with different coarse aggregate sizes is larger than that of the mortar.With the increase of the coarse aggregate dimensionless size,the strain rate strengthening factor of the concrete increases at first and then decreases.