Nonlinear Mechanical Effect of Free Water on the Dynamic Compressive Strength and Fracture of High-Strength Concrete

• Published in: Materials 2021-07, Vol.14 (14), p.4011
• Main Authors: Shilko, Evgeny V., Konovalenko, Igor S., Konovalenko, Ivan S.
• Format: Article
• Language: English
• Subjects: Aqueous solutions; Compressive properties; Compressive strength; Computational fluid dynamics; Concrete; Cracks; Darcy number; Fluid flow; High strain rate; High strength concretes; Laboratories; Microporosity; Porous materials; Strain rate sensitivity; Stress state; Structural members; Subsystems
• ISSN: 1996-1944; 1996-1944
• DOI: 10.3390/ma14144011

It is well-known that the effect of interstitial fluid on the fracture pattern and strength of saturated high-strength concrete is determined by qualitatively different mechanisms at quasi-static and high strain rate loading. This paper shows that the intermediate range of strain rates (10−4 s−1 < ε˙ < 100 s−1) is also characterized by the presence of a peculiar mechanism of interstitial water effect on the concrete fracture and compressive strength. Using computer simulations, we have shown that such a mechanism is the competition of two oppositely directed processes: deformation of the pore space, which leads to an increase in pore pressure; and pore fluid flow. The balance of these processes can be effectively characterized by the Darcy number, which generalizes the notion of strain rate to fluid-saturated material. We have found that the dependence of the compressive strength of high-strength concrete on the Darcy number is a decreasing sigmoid function. The parameters of this function are determined by both low-scale (capillary) and large-scale (microscopic) pore subsystems in a concrete matrix. The capillary pore network determines the phenomenon of strain-rate sensitivity of fluid-saturated concrete and logistic form of the dependence of compressive strength on strain rate. Microporosity controls the actual boundary of the quasi-static loading regime for fluid-saturated samples and determines localized fracture patterns. The results of the study are relevant to the design of special-purpose concretes, as well as the assessment of the limits of safe impacts on concrete structural elements.