Study On The Influence Of Simulated Service Environment On The Strength And Bonding Properties Of Magnesium Phosphate Mortar

Cement concrete roads built in the early stage are damaged in different degrees as the service life increases,and rapid repair and reinforcement of them is of significance in terms of social and economic benefits.As a new type of green cementitious material,magnesium phosphate cement is rather advantageous in rapid repair,which is benefited from its early strength,short setting time and good volume stability.Many achievements have been made with regard to material composition,hydration mechanism,workability and early strength of magnesium phosphate cement,but influence of service environment on the strength and bonding properties of magnesium phosphate cement is rarely reported.By employing magnesium phosphate cement mortar as the raw material in this paper,the effects of service environment on the strength and bonding properties of magnesium phosphate cement are studied exhaustively under different simulating environments(drying,soaking,sulfate attack,dry-wet cycles and freeze-thaw cycles),different matrix conditions(matrix strength grade,matrix interface roughness state and interface dry and wet state),as well as various simulating service age,cycle times and drying curing time,on which the observation of micro-morphology of hydration products and the failure morphology of bonding interface is based.The main conclusions are as follows:(1)Compared with dry environment,the strength of magnesium phosphate cement mortar in the immersion and sulfate attack environment for 7 days is improved,followed by significant deterioration from 28 days to 180 days;initially,the strength of magnesium phosphate cement mortar increases with the increase of dry-wet cycles and freeze-thaw cycles increase,and then decreasing,and it is worth noting that this influence could be mitigated by increasing of drying curing time;the crystal morphology and distribution state of the hydrated product of magnesium phosphate cement would change as the environment changes,which may further lead to the changes in microstructure and density.(2)The bonding properties of magnesium phosphate cement mortar decreased with the increase of matrix strength grade at or before 7d,and increased with the increase of matrix strength grade after 7d;at different ages,the bonding properties of magnesium phosphate cement mortar with dry and rough interface are higher than those with wet and smooth interface,respectively.(3)Compared with the dry environment,water immersion and sulfate attack environment will have a significant adverse effect on the bonding properties of magnesium phosphate cement mortar;both the wet-dry cycles and the freeze-thaw cycles will have an adverse effect on the bonding properties of the magnesium phosphate cement mortar,especially for the freeze-thaw cycles,while the increase of dry curing time can reduce the extent of the adverse effect;the failure of the magnesium phosphate cement mortar bonding specimen does not always occur at the bonding interface,and its failure morphology is affected by the strength of the magnesium phosphate cement mortar itself,the strength of the matrix and the bonding strength at the interface,and the part with lower strength will be damaged first and then destroyed.