Numerical Analysis Of Softening Relationship For Early-Age Concrete

Recently, with research approaches widened in the field of early-age concretes, some scholars began to adopt numerical simulation method in the fracture analysis of concretes at early stage. However, due to inaccurate constitutive relation, the numerical results are not always in accordance with laboratorial samples, which restricted the adoption of numerical simulation of fracture for early-age concretes.This paper proposes the numerical analysis of Class-I fracture for early-age concretes, in order to give a proper softening constitutional relation. The analysis is performed on the basis of related concrete mechanical and fracture-behavior experiments, and by the aid of common FEA software ABAQUS 6.5.Firstly, the typical 3-point bend-and-fracture experiment for early-age concrete beams is simulated and some mechanical behavior, e.g. load-crack mouth opening displacement (CMOD), are expressed.Secondly, some existing softening curves are compared and analyzed, including linear curves (e.g. linear, bilinear and trilinear), and nonlinear curves (e.g. exponential, hyperbolic). The results show that the softening curves for early-age concretes are somewhat similar with those of regular concretes. The initial slope of linear curves can ideally descript the peak value of LOAD—CMOD relation, but the softening part cannot properly simulated. On the other hand, the nonlinear curves are suitable for simulation of softening relation but lack accuracy at peak regions.As a result, the paper proposes a brand-new softening curve model which adopts linear relation to simulate the peak value, and uses nonlinear curves (e.g. exponential, hyperbolic) to express downgrading region. It is found that this model can precisely descript the fracture-softening behavior of early-age concretes.