Papers by Author: Jean Pierre Bonnet

Abstract: Consolidation of cements and geopolymers can be explained by the formation of alkali silicate or alumino-silicate gels formed in situ during materials setting. To control such a system, a study concerning the use of sodium silicate gel as binder was initiated to manufacture consolidated materials with different size distribution of silica. The gels used as precursor of binder were synthesised by acidifying with hydrochloric acid, a concentrated sodium silicate. Consolidated materials were obtained by mixing the previous solution before gelation with granular materials (fine silica powder and sands). The existence domain of consolidated materials depends on the size distribution of sand. Consolidation of material is strong when the amount of silica is high. This result suggests a dissolution / precipitation reaction between gel and silica. Therefore, consolidation could be explained by the dissolution of small particles of silica and their precipitation into the grain boundary of sand. Mechanical properties are closed to those of cement materials.

Abstract: Consolidation of cementitious and geopolymeric materials involves silicate-based gel formation. This in situ mechanism is difficult to identify because it occurs in a complex and developing system representing only a minority phase. A study based on the behaviour of acidified sodium silicate solutions in alkaline medium, was therefore initiated in order to define the conditions of irreversible setting. A concentrated sodium silicate solution ([Si]=7 mol/l, pH=11.56, Si/Na=1.71) was used as starting solution. 29Si NMR spectroscopy, SAXS and elementary chemical analyses (ICP-AES) were used to characterize the various solutions. Acidification of initial solution, leads in a range of relatively low pH and silicon concentration to various gels formation: (i) reversible transparent gels made up of aggregates of particles (Si7O18H4Na4) and which do not change over time, (ii) soluble white gels that lead to gradual formation of a soluble solid consisting of colloid composition of NaSi1.87O4.24, (iii) “irreversible” gels which provide a syneresis phenomenon leading to formation of a strongly consolidated solid made up of soluble phase rich in sodium similar to white gels (NaSi1.87O4.24) and an insoluble phase type silica of composition NaSi12.66O25.82.