Chemical and Microstructural Properties of Designed Cohesive M-S-H Pastes

Abstract

Concretes can be exposed to a magnesium attack in several environments leading to the formation of magnesium silicate hydrates (M-S-H) and brucite (MH). The formation of M-S-H is likely to alter the properties of the cement matrix because it is linked to the decalcification of C-S-H. However, relatively few data on M-S-H exist in the literature. In order to characterize, physically and mechanically, the M-S-H phase, pure M-S-H cohesive pastes are needed. This work studies the formation of cohesive M-S-H pastes made with MgO-to-SiO2 atomic ratios of 0.78, 1 and 1.3, from two types of silica (silica fume or colloidal silica) and under 20 °C and 50 °C thermal curing. X-ray diffraction and thermogravimetric analyses confirmed that the consumption of brucite and the formation of M-S-H were quicker with a 50 °C curing. Energy-dispersive X-ray spectroscopy and microtomography showed that colloidal silica enabled a better distribution of the particles than silica fume. Microstructural characterizations were conducted under the protocol with colloidal silica and 50 °C thermal curing. Porosity investigations allowed to describe the M-S-H pastes as highly porous materials with a low content of micropores in comparison with mesopores. The type of mixing influenced the mesopore size distribution.

Research progress on magnesium silicate hydrate phases and future opportunities

“…Similarly, Chiang et al [43] suggested a spherical structure for M-S-H with an average radius of 1.7±1 nm based on SAXS measurement. Finally, also N 2 -sorption measurements suggested a very small particle size with surface area calculated by BET above 200 m 2 /g on samples synthesised in suspension [41] and in pastes [44].…”

Effect of Curing Temperature on the Properties of a MgO-SiO2-H2O System Prepared Using Dead-Burned MgO

“…As a promising cementitious material, M-S-H gels have recently been studied with a focus on the characterization and properties of M-S-H prepared using reactive MgO [ 11 , 12 ]. The effect of foreign ions on the structure of M-S-H [ 13 , 14 ], the impact of MgO properties on reaction kinetics [ 15 ], the rehydration behavior of M-S-H from 200 to 800 °C [ 16 ], the interaction between M-S-H and C-S-H [ 17 ], pore structure [ 18 ], and shrinkage [ 19 , 20 , 21 ] were investigated. The water demand of MgO-SiO 2 -H 2 O systems with reactive MgO is higher than that of MgO-SiO 2 -H 2 O systems with dead-burned MgO [ 22 , 23 ].…”