Experimental Study On The Mechanism Of Durability Deterioration Of Repair Mortar-Concrete Interface For Water Release Structures In Cold Regions

In the course of service,hydraulic buildings could be affected by environmental factors and produce various kinds of diseases,which seriously affect the life of the project.In cold northern regions,water drainage buildings are often damaged by the coupling effect of freeze-thaw cycles and water abrasion,which seriously affects the safe operation of the project.Therefore,damaged hydraulic concrete structures must be repaired and reinforced in a timely manner,and the durability of the repair material and its bonding interface with the substrate concrete determines the quality of the repair and reinforcement.In this paper,EVA modified cementitious mortar(EVA mortar)and metal aggregate abrasion resistant mortar(metal mortar)were selected as repair materials.The durability deterioration of the repair mortar and its bonded interface with the substrate concrete under three test conditions(freeze-thaw,abrasion,alternating freeze-thaw and abrasion)were investigated by freeze-thaw and abrasion tests,respectively.The microstructural changes of the interface between the repair mortar and the substrate concrete were investigated by scanning electron microscopy(SEM),and the macroscopic and microscopic aspects were combined to reveal the durability deterioration mechanism of the repair mortar-concrete interface.The main findings of the study are as follows:(1)The alternating effects of freeze-thaw and abrasion caused more severe damage to the repair mortar than either a single freeze-thaw or single abrasion effect.After freeze-thawing,the repair mortar exhibits lower resistance to abrasion,in the form of greater depth of abrasion and lower resistance to abrasion.The loss of compressive strength of the mortar first decreases and then increases under a single abrasion;the rate of loss of compressive stren gth increases under a single freeze-thaw or alternating action;the rate of loss of compressive strength of the mortar under the three test conditions in descending order is:alternating>freeze-thaw>abrasion.The resistance of the repair mortar to abrasion is positively correlated with the compressive strength of the mortar,but freeze-thaw action weakens this relationship.Compared to EVA mortars,metal mortars exhibit higher resistance to abrasion and freezing.(2)The alternating effects of freeze-thaw and abrasion not only resulted in deeper pits and larger holes in the repair mortar-concrete combination specimens than the single action,but also led to an increase in the width of the interfacial transition zone between the aggregate and the mortar matrix in the substrate concrete.As the number of freeze-thaw cycles or abrasion time increased,the mass loss of the repair mortar-concrete specimens showed a gradual acceleration.The resistance to abrasion tends to decrease with increasing abrasion time,and specimens subjected to alternating freeze-thaw and abrasion exhibit lower resistance to abrasion.(3)As the number of freeze-thaw cycles or abrasion time increases,the rate of loss of interfacial splitting tensile strength and shear strength of the specimens increases.The rate of deterioration of interfacial splitting tensile strength and shear strength under different test conditions in descending order is:alternation>freeze-thaw>abrasion.Under the alternating effect of freeze-thaw and abrasion,the damage pattern of the interface of the specimen mainly showed a trend of decreasing and then increasing damage of the substrate concrete and increasing and then decreasing damage of the interface slip.(4)Under the influence of freeze-thaw and abrasion,the structure of the interface between the repair mortar and the concrete substrate is damaged and the width of the interface increases,with the alternating effects of freeze-thaw and abrasion causing the greatest damage to the interface.Under the alternating action of freeze-thaw and abrasion,cracks are created and expanded at the interface,and with the increase in the number of freeze-thaw and abrasion times,the mortar and concrete matrix become loose and the width of the interface increases,resulting in the debonding of the repair mortar from the substrate concrete.Compared to the EVA mortarconcrete specimens,the metal mortar-concrete specimens are more susceptible to debonding by freeze-thaw and abrasion.