Absorption d'eau des granulats poreux : mesure et conséquences sur la formulation des mortiers et des bétons

Abstract : The environmental threat on non-renewable resources such as rounded natural aggregates strongly affects the materials available for the production of mortar or concrete. This leads to an increase in the relative contribution of alternative resources such as recycled or crushed aggregates. The interaction of water with these inclusions, especially the finest sand particles, is far more complex than in the case of the standard rounded natural aggregates. These alternative particles are indeed able to absorb far more water with very different kinetics than their previous counterparts. In order to take into account aggregates water content and correct the resulting water absorption with the aim of always producing the same material with the same properties, it is usual to correct the amount of mixing water added in the mix-design. However, the traditional standard used to measure rounded aggregates water absorption is not suitable for crushed aggregates. We propose, as a first step, to develop tests allowing for the assessment of water absorption and its kinetics in the case of crushed and recycled sands. To achieve this, we measure rheology losses of mortars by slump flow test and drying kinetics of saturated porous aggregates. We show that these methods are suitable to determine water absorption of crushed or recycled aggregates. In the second phase, we study the consequences of the use of porous aggregates in a new cementitious material. We observe water transfers between aggregates and fresh cement paste using nuclear magnetic resonance. We measure a lower final water absorption in the fresh cement paste than in pure water. We show that oven-drying of recycled aggregates in laboratory can impact cement paste microstructure by hydrates dehydration like calcium silicates or calcium aluminates. The rehydration of anhydrous by interstitial solution of fresh cement paste involves calcium precipitation in the pores and this precipitation can reduce water absorption by clogging aggregates porosity
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Jennifer Nael-Redolfi. Absorption d'eau des granulats poreux : mesure et conséquences sur la formulation des mortiers et des bétons. Mécanique des matériaux [physics.class-ph]. Université Paris-Est, 2016. Français. ⟨NNT : 2016PESC1008⟩. ⟨tel-01416393⟩

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