CONTRIBUTION OF SI-29 HIGH-RESOLUTION NMR TO THE STUDY OF CONCRETE ALKALI-AGGREGATES REACTION

We report here a first Si-29 NMR investigation of the so-called alkali-aggregates reaction of concrete. In order to understand how a swelling gel can develop in concrete, we worked on a model system consisting in silica gel in interaction with a NaOH aqueous solution. The NMR techniques allowed us to identify three different precipitates which all can be the potentially swelling gel. Their precipitation takes place especially under the action of calcium compounds and their structure depends on the SiO2/Na2O ratio.