Guy Bastian

Effect of axial compressive damage on gas permeability of ordinary and high-performance concrete

Abstract Gas permeability is commonly used to evaluate durability characteristics of concrete. However, these values are often achieved using never stressed or damaged specimens. The objective of this study is to examine experimentally the effect of axial compressive loading on the permeability of three different types of concrete: ordinary concrete (OC), high-performance concrete (HPC), and high-performance steel fiber-reinforced concrete (HPFC). Monotonic and cyclic loads are applied on 220×110-mm diameter specimens. Stress levels vary between 60% and 90% of the ultimate strength. At the end of the loading phase, a disc is extracted from the middle part of the cylinders and is dried in a ventilated oven. Four different gas permeability tests are conducted during the drying procedure. The results show that, for each drying stage, the gas permeability of the discs increases with the load-induced strain. A correlation is worked out between the increase in permeability and the applied-strain/yield-strain ratio. Finally, a relationship between mechanical damage indicators and the increase in permeability is also discussed.

Etude du couplage thermochimique au sein de matrices cimentaires en cours d'hydratation

ABSTRACT At very early age, cementitious systems can undergo thermal variations due to the double exothermic and thermoactivated property of cement hydration. The parameters of this thermochemical coupling (thermal conductivity, specific heat capacity, apparent activation energy and chemical affinity) have been identified from the literature and measured on cement pastes during the first 24 hours of hydration. They are then used in a 2D numerical model for the computing of hydration degree and temperature field of hardening cement-based materials. The aim is to quantify the effect of the thermophysical parameter values on the prediction of the materials behaviour at very early age. The sensitivity study shows that the influence of thermal property values is particularly significant in the case of temperature field computation.

Perméabilité au gaz de bétons endommagés Interprétation de résultats expérimentaux

ABSTRACT Gas permeability is commonly used to evaluate durability characteristics of concrete. However, these values are often achieved using never stressed nor damaged specimens. The objective of this study is to examine experimentally the effect of axial compressive loading on the permeability of three different types of concrete: Ordinary Concrete, High Performance Concrete, and High Performance Steel Fiber Reinforced Concrete. Monotonic and cyclic loads are applied on 22 x 11-cm diameter specimens. Stress levels vary between 60% and 90% of the ultimate strength. After unloading, a disc is extracted from the middle part of the cylinders and is dried in a ventilated oven. The effects of both drying and maximum strain applied during loading are described and analyzed.

Séchage d'une dalle en béton : Etude expérimentale des gradients induits

ABSTRACT This work has been carried out as part of the LCPC research project OA9 « Transfers in concrete and durability of structures » on the basis of a very large experimentation achieved on a concrete slab and samples during their drying. For this purpose, we have implemented a very complete set of investigation methods. In addition to deformations, many parameters (microstructural, thermal, hydric ones…) have been measured and their evolution has been followed up since the early age and for several months. Important gradients of the properties have been made obvious and measured from the middle to the slab drying surface.