Influence of the Ms-modulus on the early-age volume change and heat release of slag and fly ash pastes activated by sodium hydroxide and sodium silicate

Blended pastes composed of slag and fly ash (ratio 50:50) are used with sodium hydroxide and sodium silicate as precursors. Each composition has the same solution to binder ratio (S/B) and the Ms-modulus varies between 1.04 and 1.58. All the experiments were conducted at a constant temperature of 20°C. The physical mechanisms related to the volume change in sealed condition are studied by means of repeated thermal variation using an adapted Autoshrink device, a new testing protocol and by means of isothermal calorimetry tests. From these tests, the autogenous strain, the coefficient of thermal expansion (CTE) and the heat release are determined. It is observed from the results, that an increase of the Ms-modulus causes a decrease of the autogenous shrinkage and the CTE. A linear relationship is observed between the autogenous shrinkage and the heat release by the binder. Thus, the development of the autogenous shrinkage seems to be mainly driven by one major mechanism in case of slag and fly ash paste activated by sodium hydroxide and sodium silicate

A conformal Petrov-Galerkin method for convection-dominated problems

In this paper, we present the 'conformal Petrov-Galerkin' (CPG) method in order to solve the 2D convection-diffusion equation on meshes composed of triangular elements. By 'conformal' it is meant that the discrete system is obtained front the continuous weak formulation by appropriately selecting different finite-dimensional subspaces for the shape and test functions without any additional stabilizing term. Our approach is based on searching continuous test functions that provide exact nodal values for a selected class Of Solutions. This method induces a stabilizing upwinding effect that removes the wiggles obtained with the Galerkin method. Copyright (C) 2008 John Wiley & Sons, Ltd

Further works on concrete at early age coordinated within COST TU1404 European Project

info:eu-repo/semantics/publishedVersio

Advanced techniques for the study of shrinkage-induced cracking of concrete with recycled aggregates at early age

The present work analyses the impact of the substitution of natural coarse gravel and sand by recycled gravel and sand on the concrete behavior under free and restrained condition since setting. The methodology presented in this paper associates a Temperature Stress Testing Machine (TSTM) with free shrinkage tests and other experimental advanced techniques, such as direct tensile testing and the monitoring of elastic properties using repeated loading testing. It is observed that the cracking sensitivity decreased with recycled concrete content in spite of lower tensile strength. This is due to the major influence of relaxation, but also damage and coupling effects. These phenomena contributed to a decrease of the stresses with different magnitude and kinetics. For concretes with recycled gravels, the major stress reduction was attributed to relaxation. The reduction of elastic modulus due to damage appeared from the first 24 h while creep seemed to develop later, as tensile stress to strength ratio became higher. Concrete with recycled sand had a different behavior with earlier creep development and lower damage.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Mechanical Properties

International audienc

Insights into bacterial cellulose biosynthesis by functional metagenomics on Antarctic soil samples.

In this study, the mining of an Antarctic soil sample by functional metagenomics allowed the isolation of a cold-adapted protein (RBcel1) that hydrolyzes only carboxymethyl cellulose. The new enzyme is related to family 5 of the glycosyl hydrolase (GH5) protein from Pseudomonas stutzeri (Pst_2494) and does not possess a carbohydrate-binding domain. The protein was produced and purified to homogeneity. RBcel1 displayed an endoglucanase activity, producing cellobiose and cellotriose, using carboxymethyl cellulose as a substrate. Moreover, the study of pH and the thermal dependence of the hydrolytic activity shows that RBcel1 was active from pH 6 to pH 9 and remained significantly active when temperature decreased (18% of activity at 10 degrees C). It is interesting that RBcel1 was able to synthetize non-reticulated cellulose using cellobiose as a substrate. Moreover, by a combination of bioinformatics and enzyme analysis, the physiological relevance of the RBcel1 protein and its mesophilic homologous Pst_2494 protein from P. stutzeri, A1501, was established as the key enzymes involved in the production of cellulose by bacteria. In addition, RBcel1 and Pst_2494 are the two primary enzymes belonging to the GH5 family involved in this process.The ISME Journal advance online publication, 21 May 2009; doi:10.1038/ismej.2009.48