On shrinkage and structure changes of pure and blended Portland concretes

Abstract

International audienceThis research investigates the long-term shrinkage and Relative Mass Loss (RML) of mature Portland concretes (pure CEMI and blended CEMV/A), at temperatures of 20°C and 80°C. When placed at 80°C and at relative humidities (RH) below 50-60%, concrete shrinkage increases with very slow stabilization kinetics by several hundreds of μm/m, while RML remains of about 0.2%. The origins of this continued shrinkage, simultaneously with limited RML, are investigated through the changes in (i) the pore structure of the concretes (by Mercury Intrusion Porosimetry and nitrogen adsorption) and in (ii) their solid phases (by TGA/DTA, FTIR spectroscopy coupled to DVS, quantitative X-Ray Diffraction by Rietveld analysis, and 29Si and 27Al MAS NMR). While the pore structure coarsens during continued shrinkage, several phase transformations occur, namely ettringite decomposition and changes in the silicate chain length of the C–A–S–H. While these structural changes are documented, their relationship with shrinkage/RML and to the pore structure is novel

Mesoscale pore structure of a high‐performance concrete by coupling focused ion beam/scanning electron microscopy and small angle X‐ray scattering

“…All mature concrete samples are taken from the same HPC as that studied in Refs . Its formulation is given in Table , with the calculation of the relative aggregate and paste volumes.…”

“…Its formulation is given in Table , with the calculation of the relative aggregate and paste volumes. After manufacturing and conditioning into pluricentimetric samples, the HPC is first matured for 6 months under water, and then dried either (a) at 20°C and stepwisely down to 30% relative humidity (RH), or (b) at 80°C and stepwisely down to 12% RH, for about 5 years, to study the effect of temperature on long‐term shrinkage . Sample mass is stable by <1% after this experiment.…”

Drying-induced atomic structural rearrangements in sodium-based calcium-alumino-silicate-hydrate gel and the mitigating effects of ZrO2 nanoparticles

“…A decrease in the MCL has also been observed in an OPC system with 22 wt% of slag and 22 wt% of silica fume as supplementary cementitious materials by 29 Si NMR spectroscopy when subjected to drying. 62 It is likely that as the interlayer water is being pulled out (which occurs after the evaporation of the water from the gel pores), the large drying-induced capillary stresses being exerted on the gel structure are high enough to cause bond breakage and subsequent rearrangement at the atomic length scale. Hence, these data show that the atomic structure of C-(N)-A-S-H gel likely undergoes disintegration to a certain degree as a result of exposure to extreme drying conditions.…”