Evaluation of concrete structures by combining non-destructive testing methods (SENSO project)

The management and maintenance of the built heritage is one of the main interests of the owners of concrete structures. The engineers wish to obtain quantitative information about concrete properties and their variability. Non-destructive testing (NDT) is very popular in this context as it quickly provides relevant information on the integrity and evolution of the material, but several kinds of indicators representative of the concrete condition need to be evaluated. A French Project, named SENSO, aims to develop methods for the non-destructive evaluation of concrete based on a multi-techniques approach. Several families of techniques are concerned (ultrasonic, electromagnetic, electrical, etc.). The main objective is to define the sensitivity of the techniques and the variability of the evaluation for each indicator concerned. To achieve this, a large experimental programme, involving a representative range of concretes and several indicators, has been carried out. A large database, linking the NDT observables and the indicators, allows the different observables to be distinguished in terms of quality (linked to the variability) and in terms of relevance for the characterisation of each indicator. The improvement of the indicator evaluation by means of technique combinatio

Porous structure of the ITZ around galvanized and ordinary steel reinforcements

International audienceThe use of galvanized bars is one of the solutions recommended to avoid corrosion of reinforced concrete structures. The reaction between the galvanized coating and the wet concrete produces zinc hydroxide, and subsequently calcium hydroxyzincate, accompanied often by the evolution of hydrogen. The tests carried in this study show, 19 h after casting, a modification of the pore size distribution and an increase in porosity of the interfacial transition zone (ITZ) between the cement paste and the galvanized steel, in comparison with the ITZ of cement paste–steel contact surface. However, the characteristics of the ITZ change over time: at the test period of 28 days, the porous structure of the ITZ around galvanized and ordinary steel is not significantly different. This difference decrease is due to the formation of calcium hydroxyzincate. Calcium hydroxyzincate favors the hydration at the ITZ. This compound, as well as cement hydration products can fill the porous structure in this zone

Analysis of progressive damage to reinforced ordinary and high performance concrete in relation to loading

International audienceThis paper deals with the effect of loading on the microstructure of reinforced high performance and normal concrete. In the case of reinforced concrete structures, cracking is the only visible sign of mechanical degradation and is accompanied by microscopic damage to the concrete.To account for this damage, experiments on three different concretes with compressive strengths (f c28) of 45 MPa, 80 MPa and 100 MPa were carried out. The loadless initial state of concrete and the damage state after loading were described using the single replica technique observed on SEM. The way in which the microcracks extended was revealed, with predominantly aggregated bond failure and crack branching occurring with cracks spreading out around the coarse aggregate under stable progressive fracture conditions. An increase in the specific area of microcracks was seen to result from an increase in load. This phenomenon could have an influence on the durability properties of reinforced concrete structures

Mechanical behaviour of corroded reinforced concrete beams—Part 1: Experimental study of corroded beams

International audienceSteel corrosion in reinforced concrete leads to crack occurrence along the reinforcement (secondary cracks), to a reduction in bond strength and a reduction in steel cross section. The purpose of this study is to determine the effect of these deteriorations on the global behaviour of reinforced concrete structural elements in their service and ultimate states. Mechanical experimentation was carried out on fourteen-year-old reinforced concrete beams, on two control elements and two corroded beams. A comparative analysis of the results obtained on the beams showed that concrete cracking in the compressive area had no significant influence on the behaviour in service of the corroded elements. However, significant modifications of service behaviour were observed, due to the degradations in the tensile zone, namely: loss of bending stiffness, dissymmetrical behaviour. Finally, the measure of the residual steel cross-section of the corroded re-bars showed that the loss of bending stiffnes due to steel corrosion cannot be merely explained in terms of steel cross-section reduction. Concerning the ultimate behaviour, the loss of steel cross-section is the main parameter which leads to a reduction of bearing capacity and ductility. Another part will explain the separate and coupling effects of bond strength and steel cross-section loss on the mechanical behaviour of corroded beams

Effect of loading on carbonation penetration in reinforced concrete elements

International audienceConcrete tensile microcracking due to a mechanical loading enhances the diffusion of aggressive agents from concrete cover to the reinforcements, which leads to the beginning of the propagation period of steel corrosion. The purpose of this work is to quantify the effect of concrete microcracking on CO2 penetration. Concrete carbonation was studied on two 13-year-old reinforced concrete beams subjected to atmospheric carbonation. Indeed, these beams were exposed to the climate of the south-west of France but in a covered place and were always stored in a loaded state. Because the microcracking network is quite impossible to characterise, the tensile stress in the reinforcements was chosen as the main parameter of the microcracking state. This investigation results on a proposed model whose accuracy predicts the increase of the carbonation depth of the concrete in relation to the tensile stress in rebar

Electrochemical chloride extraction (ECE) from steel-reinforced concrete specimens contaminated by “artificial” sea-water

International audienc