Study On The Durability Of Magnesium Silicate Hydrate(M-S-H) Based Mortars

Magnesium silicate hydrate(M-S-H)cement,as a new type of eco-friendly buildingmateria,has low p H value,low hydration heat and excellent mechanical properties.It has potential application in the fields of encapsulation of nuclear waste,hazardous wastes,and wall insulation materials.In recent years,many scholars have conducted an extensive and in-depth research.The research mainly focuses on the mechanism of hydration reaction,mechanical properties.However,there are few reports on its durability performance.In this paper,the durability of magnesium silicate hydrate cement mortar is studied,including carbonation test,freeze-thaw resistance test,chloride permeability resistance test,drying shrinkage test and sulfate attack resistance test.At the same time,the mechanism of durability of magnesium silicate hydrate cement mortar is explored by means of various micro testing methods.The main research contents and results are as follows:(1)The carbonation test was performed on magnesium silicate hydrate cement mortars with different curing ages,and the compressive strength and microstructure of specimens after carbonation were tested.The results indicated that the compressive strength increased at first and then decreased during carbonation process.The carbonation products were tested and it was found that the carbonation products of M-S-H gel were the same as the carbonation products of Mg(OH)2,both of which were hydrated magnesium carbonates(HMCs),and Mg(OH)2 was easier carbonized than M-S-H gel.(2)The freeze-thaw resistance test of magnesium silicate hydrate cement mortars with different mixture proportions was carried out,and the mechanical properties,quality changes and pore structure of specimens were tested after freeze-thaw resistance test.The results showed that the mechanical properties of mortars decreased significantly with the increase of freeze-thaw cycles,and shedding and peeling occurred on the surface of the specimen.After freeze-thaw resistance test,the porosity of specimen increased and the pore size gradually developed from the small pore size to the large pore size.(3)The chloride permeability resistance test was carried out on magnesium silicate hydrate cement mortars with different mixture proportions,and chloride ion permeability coefficient and pore structure of specimens were tested.The results indicated that the chloride ion permeability coefficient increased gradually with the increase of water to cement ratio and sand content.The porosity of magnesium silicate hydrate cement mortar was 9.25%,mainlyconsisting of gel pores smaller than 10 nm.The structure was dense and had excellent resistance to penetration.(4)The drying shrinkage test was performed on magnesium silicate hydrate cement mortars with different mixture proportions,and the drying shrinkage rate and water loss rate of specimens were tested.The results showed that the drying shrinkage of magnesium silicate hydrate cement was serious.When sand content increased from 20% to 70%,the 28 d drying shrinkage rate decreased from 1.887% to 0.631% and the water loss rate also decreased from21.235% to 5.523%.When the water to cement ratio increased from 0.88% to 0.913% and the water loss rate also increased from 8.959% to 11.436%.(5)The sulfate attack resistance test was carried out on magnesium silicate hydrate cement mortars,and the compressive strength and microstructure of specimens were tested.The results indicated that the corrosion resistant coefficient of magnesium silicate hydrate cement mortars was about 1,and its ability of sulfate attack resistance was excellent.The hydration products of magnesium silicate hydrate cement were stable,and no new products were found in the microstructure test of samples after sulfate attack resistance test.In this paper,the durability of magnesium silicate hydrate cement mortars was tested,which provided a basis and reference for the research on the durability mechanism under environmental conditions.It was of great significance to guide the practical application of magnesium silicate hydrate cement...