Age-dependent Size Effect and Fracture Characteristics of Ultra High Performance Concrete

TL;DR

This study investigates how aging influences the size effect and fracture properties of ultra high performance concrete using experiments, advanced simulations, and size effect analysis methods.

Contribution

It introduces a coupled hygro-thermo-chemical and discrete element modeling framework for predicting age-dependent fracture behavior of UHPC.

Findings

Age significantly affects the size effect and fracture energy of UHPC.

The combined experimental and simulation approach validates predictive modeling.

Analytical size effect methods are robust across different curing ages.

Abstract

This paper presents an investigation of the age-dependent size effect and fracture characteristics of an ultra high performance concrete (UHPC). The study is based on a unique set of experimental data connecting aging tests for two curing protocols of one size and scaled size effect tests of one age. Both aging and size effect studies are performed on notched three point bending tests. Experimental data is augmented by state of the art simulations employing a recently developed discrete element based early-age computational framework. The framework is constructed by coupling a hygro-thermo-chemical (HTC) model and the Lattice Discrete Particle Model (LDPM) through a set of aging functions. The HTC component allows taking into account variable curing conditions and predicts the maturity of concrete. The mechanical component, LDPM, simulates the failure behavior of concrete at the length scale of major heterogeneities. After careful calibration and validation the mesoscale HTC-LDPM model is uniquely posed to perform predictive simulations. The ultimate flexural strengths from experiments and simulations are analyzed by the cohesive size effect curve (CSEC) method, and the classical size effect law (SEL). The fracture energies obtained by LDPM, CSEC, SEL, and cohesive crack analyses are compared and an aging formulation for fracture properties is proposed. Based on experiments, simulations, and size effect analyses, the age-dependence of size effect and the robustness of analytical size effect methods are evaluated.