Analysis of the behavior of ultra high performance concrete at early age

Abstract

Abstract:Ultra high performance concretes (UHPCs) are cementitious composite materials with high level of performance characterized by high compressive strength, high tensile strength and superior durability, reached by low water-to-binder ratio, optimized aggregate size distribution, thermal activation, and fiber reinforcement. In the past couple of decades, more and more UHPCs have been developed and found their ways into practice. Thus, the demand for computational models capable of describing and predicting relevant aging phenomena to assist design and planning is increasing. This paper presents the early age experimental characterization as well as the results of subsequent simulations of a typical UHPC matrix. Performed and simulated tests include unconfined compression, splitting (Brazilian), and three-point-bending tests. The computational framework is formulated by coupling a hygro-thermo-chemical (HTC) theory and a comprehensive mesoscale discrete model with formulated aging functions. The HTC component allows taking into account various types of curing conditions with varying temperature and relative humidity and predicting the level of concrete aging. The mechanical component, the Lattice Discrete Particle Model (LDPM), permits the simulation of the failure behavior of concrete at the length scale of major heterogeneities. The aging functions relate the mesoscale LDPM mechanical properties in terms of aging degree, defined in this work as the ratio between the quasi-static elastic modulus at a certain age and its asymptotic value. The obtained results provide insights in both UHPC early age mechanisms and a computational model for the analysis of aging UHPC structures.

Age-dependent size effect and fracture characteristics of ultra-high performance concrete

“…The proposed computational framework can accurately simulate the development of the internal structure of concrete (C-S-H reactions) and the corresponding effects on the mechanical properties. The details of the computational framework can be found in Wan et al [1] and are summarized in Appendix A.…”

“…In an earlier paper the authors developed a computational framework for the analysis of aging UHPC structures [1]. Such a framework is also quintessential for the scientific investigation of time-dependent processes such as creep, shrinkage [11,6,7], and ASR [8] which are affected by spatial gradients in material properties.…”

“…A review of relevant research is given in [1] and summarized below. Ulm and Coussy [44] studied the thermochemo-mechanical coupling of concrete at early age with a formulation based upon thermodynamics of open porous media composed of a skeleton and several fluid phases saturating the porous space.…”

“…The HTC model and LDPM are selected as basis for the early age mechanical model formulated in the authors' previous work [1]. The hygro-thermo-chemical (HTC) model is coupled with the Lattice Discrete Particle Model (LDPM) by aging functions formulated in terms of aging degree.…”

“…Although size effect has long been known in the civil engineering community, its age dependence has not been studied in the available literature. With the recently developed aging framework HTC-LDPM [1], it becomes now possible to investigate the age-dependence of size effect through calibrated simulations and validated predictions. During the formulation of the framework, namely the aging functions to compute tensile strength, tensile characteristic length, and fracture energy, major insights regarding the evolution of fracture characteristics were gained, which are extensively discussed in the following sections.…”