Study On The Impact Compressive Behavior Of Reactive Powder Concretes

Reactive powder concretes (RPCs) are a new kind of ultra-high-performance concretes. It has great potentials for application in the fields of civil engineering due to the advantages of ultra-high strength, low brittle, high durability and excellent characteristics of the economy and environmental protection. When concrete materials are applied in civil engineering, in addition to quasi-static loads, they often bear impact-, explosion-, and other dynamic loads, which are more destructive. Therefore, the dynamic properties are critical for their engineering applications.The reported studies of RPCs greatly focus on improving the synthesis technique, as well as their mechanical and physical properties under quasi-static loads. Few works ever involved into their dynamic mechanical properties. Moreover, it is known that the compressive strength of concrete-like materials is hydrostatic-stress-dependent, and the dynamic mechanical properties apart from the quasi-static properties should come from both the contributions of the hydrostatic-stress and strain-rate. Unfortunately, the available reports often misinterpreted the difference of the dynamic properties from the static properties as the pure strain-rate effect, which causes the strain-rate effect of materials to be over-estimated, and the developed theoretical models cannot exhibit the real dynamic properties of this kind of materials.The impact compressive properties of RPCs under different strain rates were tested in this study. Three types of RPCs with 0%, 1.5% and 2.0% steel contents were considered. The split Hopkinson pressure bar (SHPB) technique was used for dynamic loading. Some experimental results are received, which include the failure modes, dynamic stress-strain relations and the contribution of steel fibers for RPCs at different strain rates. In order to ensure the dynamic testing reliability, some effective measures were applied in experiments. For example, in order to decrease high-frequency-oscillation effect and achieve a nearly constant strain rate over a certain deformation range, different pulse shapers are experimentally compared, and the suitable shaping material and size are determined. In order to eliminate the testing error due to the non-parallel between the surfaces of the loading bar and the specimen, the technique of the adjustable loading jig was introduced in dynamic compressive experiment, which is commonly adopted in universal testing machines. RPCs are a kind of strain-rate- and hydrostatic-stress-dependent materials. The improvement of the apparent dynamic strength intensity factors (DSIFs) received in dynamic experiments comes from both the contributions of the hydrostatic-stress and the strain-rate. In order to differentiate the two components, quasi-static well-pressure experiments were carried out to determine the relationship of the hydrostatic-stress and the compressive strength of this kind of materials, and then the finite element (FE) method combined with linear Drucker-Prager model was used to simulate the SHPB impact loading and determine the improvement of the DSIF due to the transverse-inertia effect at different strain rates. The improvement of the DSIF due to the strain-rate effect is finally received by subtracting the transverse-inertia effect from the apparent DSIF. Moreover, the failure process of the specimens under impact loading was also numerically simulated and the wave dispersions for different types of input waves moving along the loading bar were also compared. The numerical results indicate that it is necessary and suitable to use the selected wave shaper in the dynamic expreiments.