Sébastien Remond

Influence of hardened cement paste content on the water absorption of fine recycled concrete aggregates

A linear relationship was found between the mean size of four granular classes (0/0.63, 0.63/1.25, 1.25/2.5, 2.5/5 mm) of different laboratory-made fine recycled concrete aggregates (FRCA) and their hardened cement paste content (CPC). A method based on salicylic acid dissolution was specifically developed for the measurement of CPC. Results showed that bound water and density of FRCA were strongly correlated with their CPC. Identically, the water absorption coefficient also followed a linear trend as a function of the CPC but only for the three coarser granular classes. Indeed, the water absorption coefficient of the finer fraction of FRCA (0/0.63 mm) cannot be correctly measured using European standard method EN 1097-6 or method no. 78 of IFSTTAR; but it can be obtained by extrapolation from the previous linear trend. As a consequence, the accurate total water absorption of FRCA (fraction 0/5 mm) can be estimated.

Influence of granular fraction and origin of recycled concrete aggregates on their properties

Abstract Large quantities of construction and demolition wastes are produced each year. In order to make good use of recycled concrete aggregates (RCA) in concrete, it is very important to study the influence of the granular fraction and the origin of RCA on their properties. In this study, RCA from industrial produced blocks (RCA_Blocks) and slabs (RCA_Slabs) were crushed and then separated into four granular fractions (0/2, 2/6.3, 6.3/14, 14/20 mm). Each granular fraction of RCA was physically characterised. Real RCA from recycling plant were also used for comparison. The results showed that recycled sands offered significantly higher cement paste content (higher bound water content) than coarse recycled aggregates. The fine RCA had therefore a higher water absorption coefficient compared to coarser fractions of RCA. The water absorption of finer fraction of RCA could be extrapolated precisely from the relationship between water absorption and cement paste content (or bound water content) of three coarse fractions of RCA. The values of hardened cement paste content obtained for the RCA_Blocks were lower than those measured on the RCA_Slabs, which was due to a smaller amount of initial cement paste content in blocks. The results showed that RCA_Slabs were more angular than RCA_Blocks.

Comportement au feu des bétons. Approche multiéchelle de l'endommagement thermique et identification expérimentale

ABSTRACT Within the framework of the study of concrete structures subjected to fire, a theoretical and experimental work has been achieved. The aim of this study is to investigate and to model the damage mechanisms of concrete after exposure to high temperature. The multiphase Numeral Concrete Model and the damage model, MODEV, implemented on finite element software SYMPHONIE, were used simultaneously to model the thermal damage of concrete exposed to high temperature. In order to validate the thermal damage model, an experimental investigation was carried out. The measurement of the mechanical characteristics of high performance cement paste and high performance mortar specimens were performed by 3 points bending tests after heating/cooling stage at 120, 250 and 400°C.

Microstructure et propriétés physico-chimiques de bétons autoplaçants chauffés de 20 à 600°C

ABSTRACT This paper presents an experimental study on the performance of self-compacting concrete (SCC), subjected to high temperatures. Three SCC mixtures and one vibrated concrete mixture were tested. Three concretes mixtures are coming from the French National Project B@P. The specimens of each concrete are heated at a rate of 1°C/min up to different temperatures (150, 300, 450 and 600°C). In order to ensure a uniform temperature throughout the specimen, the temperature is held constant at the temperature stage for one hour before cooling. Mechanical properties at ambient temperature and residual mechanical properties after heating have already been determined. We study the physico-chemical properties and the microstuctural characteristics. Thermogravimetric analysis, thermodifferential analysis, X-ray diffraction and microscopic observations with SEM are used. The aim of these studies is in particular to explain the observed residual compressive strength increase between 150 and 300°C.

Bétons autoplaçants à haute température: Propriétés mécaniques et physico-chimiques

ABSTRACT This paper presents an experimental study on the performance of self-compacting concrete (SCC), subjected to high temperature. Three SCC mixtures and one vibrated concrete are tested. Three concrete mixes come from the French National Project B@P. Mechanical and microstructural properties are studied at ambient temperature and after heating, namely the compressive strength, flexural strength, bulk modulus of elasticity, porosity and permeability. For each test, the specimens are heated at a rate of 1°C/min up to different temperatures (150, 300, 450 and 600°C). In order to ensure a uniform temperature throughout the specimen, the temperature is held constant at the target temperature for one hour before cooling. In addition, the specimen mass is measured before and after heating in order to determine the loss of water during the test.