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

Abstract

The hydration of M-S-H prepared using silica fume (SF) and dead-burned MgO cured at 20 °C, 50 °C, and 80 °C was investigated, and the properties and performance of this M-S-H were measured. The formation of M-S-H was characterized using XRD, FTIR, TGA, and 29Si MAS-NMR. Results show that the compressive strength of paste prepared using MgO calcined at 1450 °C for 2 h reached 25 MPa after 28 d. The shrinkage of mortar made with low reactivity MgO was lower than that made with high reactivity MgO. The pH value of MgO/SF paste mixed with dead-burned MgO did not exceed 10.4 at room temperature. The shrinkage of M-S-H prepared using dead-burned MgO was less than that prepared using more active MgO, and its strength did not decrease over time. No (or only a small amount of) Mg(OH)2 was formed, which is why the strength of M-S-H prepared with dead-burned MgO continually increased, without decreasing. The promotion of curing temperature favor process of MgO hydration and is beneficial for degree of silica polymerization. The sample cured in 50 °C water showed the highest relative degree of reaction.

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“…Another maximum exothermic peak at 417 °C is also observed in the DSC curve, with a mass loss in the temperature range of 380–500 °C in the TGA curve. This thermal event has been previously reported as the dehydroxylation of the hydroxide groups of the minerals present and the silanol of the silicates, the elimination of some of the exchange anions, such as CO 2 and OH- of the calcium carbonates M + (OH) n , M + CO 3 and from the M + –S–H gel, and from the loss of residual water in the pores resulting from the reaction [ [78] , [79] , [80] , [81] ]. The last thermal event is an exothermic peak at about 850 °C in the DSC and a slight mass loss recorded between 720 and 890 °C, which was associated with the decomposition of M + -S-H [ 82 ].…”

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“…This behavior is probably related to the amount of Mn present in MgO. The vibration frequency at 859 cm –1 is characteristic of the cubic phase of MgO. , The bands at 1428 and 1482 cm –1 are assigned to the stretching vibration of the carbonate anion (for example, CO), manifesting the presence of chemisorbed atmospheric CO 2 due to the acidic–basic properties of the surfaces of these materials. ,, The absorbance bands located at 1631 cm –1 and 3436 cm –1 indicate the existence of −OH stretching and bending vibrations from adsorbed H 2 O molecules from air. , The last band at 3693 cm –1 belongs to the −OH stretching vibration mode of hydroxyl groups. , …”

“…25,26 The last band at 3693 cm −1 belongs to the −OH stretching vibration mode of hydroxyl groups. 30,31 3.3. X-ray Photoelectron Spectroscopy (XPS) Analysis.…”