Experimental Study On Influence Of Freeze-thaw Cycle On The Mechanics Behaviors Of Recycled Concrete Brick Masonry

In China, the masonry structure still has a large proportion of in-service structures.When masonry structures subjected to alternating positive and negative changes in theexternal temperature, the internal of masonry structure freeze-thaw damage occurs; innorthern China, especially in the Northeast area, the damage due to freeze has becomethe most important reason deducing the mechanical performance of masonry structure.A lot of research work of frost-resisting properties of mortar and block has been studied,but mortar and block work together in practice, so the research on the basic mechanicalproperties of masonry structure after freeze-thaw recycles has a very importantsignificance.However, due to the impact of test equipment and other reasons, there are norelevant reports on this area so far. Through theoretical analysis and experimental studyusing the advanced climate modeling system，the following jobs are done in this paper:A circulation system and damage evaluation for masonry was developedconsidering the equipment used and freeze-thaw codes of concrete. Through thefreeze-thaw cycle test of mixed mortar cubes and recycled concrete bricks, the effect offreeze-thaw environment on the performance of cubes and bricks were studied, and thedecay models of the compressive strength of mortar and brick with freeze-thaw cycleswere established.In order to study the effect of freeze-thaw environment on the shear behavior ofalong the seam section,32recycled concrete brick masonry specimens(the number ofsamples were expanded considering the discreteness of the masonry) were tested. The damage rule and the change of shear strength of specimens were compared andanalyzed with the increase of freeze-thaw cycles, and the decreasing relationshipbetween mean shear strength of masonry and the number of freeze-thaw cycle wasestablished; Combined with experimental phenomenon, the influence factors offreeze-thaw environment on shear properties of masonry were analyzed.In order to study the effects of Freeze-thaw environment on the compressionperformance,24recycled concrete brick masonry specimens were tested. Change ruleof compressive strength, elastic modulus and the constitutive relation curve wereanalyzed with the increase of the number of freeze-thaw cycle, the masonry stress-straincurve under different cycles and the degradation relationship between compressionstrength, elasticity modulus and the number of freeze-thaw cycle was established.The Damage Mechanics theory and Strain Equivalence Principle were applied tothe masonry structure, then the total damage of the masonry which withstand axial loadafter freeze-thaw cycles was equaled to the nonlinear coupling for both damage states:the damage due to freeze-thaw action and axial compression; the damage constitutivemodel of masonry under compression after freeze-thaw cycles, which was verified to berational by comparing with test data, was established based on the basic principle of theDamage Mechanics.