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Structural effects and real strain‑rate effects on compressive strength of sustainable concrete with crumb rubber in split Hopkinson pressure bar tests

100%

Feng W. , Chen B. , Tang Y. , Wei W. , He W. , Yang Y.

Archives of Civil and Mechanical Engineering

2022

tom Vol. 22, no. 3

art. no. e136

The dynamic increase factor (DIF) of the concrete material strength, obtained using a split Hopkinson pressure bar (SHPB), includes structural effects that do not precisely reflect the real strain-rate effect of concrete. To further clarify the real strain-rate effects of rubberised concrete (RC), an experimental investigation regarding the dynamic compressive response of ordinary concrete (NC) and RC with three rubber contents (10%, 20%, and 30%) was performed in this study. Additionally, based on a dynamic constitutive model, i.e., the Karagozian and Case (K&C) concrete model, numerical SHPB tests were conducted using the LS-DYNA software. According to the experimental results, all parameters of the K&C model were discussed, and the damage factors were modified to satisfy the mechanical properties of RC. After validating the numerical model, it was observed that the experimental DIF included the inertial enhancement and the real DIF. Moreover, because rubber particles effectively reduce the density and improve the deformation capacity of concrete, the real strain-rate effect of RC was found to be more rate-sensitive than that of NC by analysing the radial stress distribution. In addition to lateral inertia, another external source, namely, the interface friction between the specimen and bars, which can produce lateral confinement, was further studied. It was found that interface friction significantly contributes to lateral confinement; however, as the strain rate increased, the impact generally decreased. Finally, the mechanism of the strain-rate effect of RC was clarified.

Effect of rubber particles on impact resistance of concrete at a temperature of - 20 ℃

84%

Yu Y. , Jin Z. , Zhu H. , Song H.

tom Vol. 21, no. 3

383--396

Studies have shown that rubberised concrete is a potential pavement material. Pavement materials are generally expected to possess concrete with high impact resistance, especially in regions where winter temperatures remain lower than the freezing point for long periods. However, knowledge about the performance of rubberised concrete on impact under low temperatures is still limited. In this study, experiments were conducted to evaluate the compressive strength, elasticity modulus, bending strength, and impact resistance of rubberised concrete at room temperature (20 °C) and at a sub-zero temperature (− 20 °C). Meanwhile, a new U-shaped specimen drop-weight test was performed as an impact test. The results indicated that although the impact toughness of both rubberised and plain concrete types decreased at low temperatures, rubber particles also had positive effects on concrete impact resistance at − 20 °C. In addition to macroscopic tests, mercury injection and molecular dynamics simulations were performed to understand the mechanism through which rubber particles improve the impact resistance of concrete at low temperatures. The pores that could not freeze accounted for 1.55% of the total pores in plain concrete; this value was 2.36% in concrete with a rubber particle density of 50 kg/m3. From the results of this study, we can conclude that the addition of rubber can change the distribution of water or ice in concrete pores, which leads to an improvement in the toughness of concrete at a low temperature (- 20 °C).