George Wardeh

Analysis of concrete internal deterioration due to frost action

This study concerns the frost durability of an ordinary concrete without air-entraining agents. The water—cement ratio and the quantity of cement were chosen within the limitations imposed by the French standard. Physical and mechanical characteristics evolutions during freezing—thawing cycles have been followed. The obtained results show that the reduction in the mechanical resistance and the elastic modulus is accompanied by an increase in the intrinsic permeability. The damage is characterized by a scalar parameter, Df, due to frost action with which the resistance reduction as well as the permeability evolution may be described as a function of crack development. The pore liquid phase pressure, generated during ice formation, was also calculated by an inverse poroelastic analysis based on strains recorded during freezing—thawing cycles. A negative pore pressure of 25 MPa at a temperature of -15° C resulting in an effective stress representing 25% of the compressive strength was found.

Shear Behavior of Reinforced Recycled Aggregate Concrete Beams

The results from an experimental study on the shear behavior of concrete made with natural aggregates (NAC) and 100% recycled aggregates (RAC) are presented in this study. Full scale 200 × 250 × 1900 mm reinforced concrete beams without stirrups were manufactured from two mixtures with C35/45 target class of compressive strength and S4 class of workability. The beams were tested under 4 points bending for a shear span-to-depth ratio (a/d) equal to 1.5 and 3.0. The mechanical properties of two mixtures were characterized in terms of compressive strength, splitting tensile strength, and modulus of elasticity.

Bond and Cracking Behavior of Reinforced Concrete Members Incorporating Recycled Aggregates

The aim of the present work is to investigate the bond strength and cracking properties of recycled aggregate concretes (RAC). For this purpose, six recycled concrete aggregate mixtures and two conventional concrete mixtures with C25/30 and C35/45 target class of compressive strength and S4 class of workability were chosen. For both series, specimens were fabricated with different incorporation ratios of fine and coarse recycled aggregates and only coarse recycled aggregates.

Mechanical Behavior of Recycled Aggregate Concrete under Uniaxial Loading-Unloading Cycles

The paper presents the results of an experimental program related with the damage behavior of Recycled Aggregate Concrete (RAC) under uniaxial loading-unloading cycles. To this purpose, the effect of the percentage of recycled aggregates (RA) on the compressive mechanical properties of concrete was investigated. Eight mixes with C25/30 and C35/45 target class of compressive strength were prepared using normal or recycled coarse aggregates. For both series, a target S4 class of workability has been chosen. Cylindrical specimens were fabricated with different RCA replacement percentages of 0%, 30%, 100% fine and coarse RA and 100% of coarse RA. Uniaxial loading-unloading compression tests were performed using controlled displacement rate of 0.5 mm/min. From the obtained stress-strain curves, the scalar damage is quantified as the variation of the elastic modulus. Based on the experimental results, it was found that the damage depends on the replacement percentage of recycled aggregates and increases when the replacement ratio is high.

Physical and Mechanical Properties of Recycled Demolition Gravels Submitted to Freeze/Thaw in Comparison to Natural Ones

Nowadays, there is a significant increase in researches of concretes based on recycled aggregate. In this study, the recycled aggregates are provided from demolition waste. This work aims to characterize recycled gravels (RG) and to estimate their deterioration after their exposure to freezing and thawing cycles. The main objective is to determine the quality and suitability of RG by comparison to natural ones (NG) in manufacturing concretes dedicated to buildings, in particular when they are exposed to freeze/thaw. For each granular type, sieving, water absorption, porosity (n), Los Angeles (LA) and Micro-Deval (MDE) tests were conducted before and after their exposure to freezing/thawing in water according to European standards. The coefficient of water absorption, WA, was evaluated by three different methods. Results show that the law of mixtures can be used to predict all the studied properties of gravels mixes (natural and recycled gravels) except for MDE. Relationships are established between WA-density, LA-WA and LA-density on the basis on the results of this work and those of literature. Good correlation between the Micro-Deval (MDE) and the WA, as well as between MDE and LA was found. The analysis of the durability performance allowed concluding that, RGs are less resistant to freeze/thaw than NGs but their degradation, estimated through WA, n and MDE, is not significant.