Study On Durability Of The Recycled Brick Powder ECC In The Salt Frozen Environment

Engineering Cementitious Composites?ECC?have strain hardening behavior and good crack-controlling capacity under tensile load.The ultimate tensile strain can be stabilized above 3%.It has multi-cracking characteristic,and the crack width is less than 0.1mm.This material has broad application prospects in improving the durability of reinforced concrete structures,improving the seismic performance of structures,and repairing and strengthening structures.At the same time,with the continuous advancement of the development of urbanization in China,a large number of old buildings have been demolished,which has brought a huge amount of construction waste.The waste clay bricks are crushed,ground,and used to prepare recycled brick powder ECC,which can not only absorb the construction waste,but also provide the new ways and ideas for the preparation and engineering application of ECC materials.There are a large number of salt lakes with the high and cold climate conditions in northwestern areas.The freeze-thaw cycles and the seawater erosion exist in buildings in the coastal areas of Northeast areas.The de-icing salts are widely used on roads and bridges in northern areas.The deicer-frost damage has become the main factors for the durability damage of buildings in these areas.Therefore,based on the fast freeze-thaw test,the appearance damage characteristics,mass loss rate,dynamic elastic modulus and compressive strength damage rate are used as durability index.Under the action of the clean water,3.5%Na Cl solution,5%Na₂SO₄ solution,and 3.5%Na Cl plus 5%Na₂SO₄ composite solution,the durability damage process and mechanism of the mid-strength concrete,primary ECC and recycled brick ECC were studied,and the freeze resistance mark is given.Based on the probability model and the damage mechanics theory,the evolution equations of freeze-thaw damage under different erosion solutions are established.The main research contents are as follows:?1?For the test of the basic mechanical properties of recycled brick ECC,the effects of different substitution rates of recycled brick on the compressive strength,flexural strength,bending and tensile properties were studied.The results show that the compressive and flexural strength decreases slightly with the increase of the replacement rate of recycled brick,and the effect of 100%replacement on the mid-span deflection of the four-point bending test and the ultimate tensile strain of the direct tension test is significant.?2?For the ECC durability of recycled brick in the different freeze-thaw environments,the different erosion solutions have the different effects on the durability.The influence degree of the mass loss rate is 3.5%Na Cl plus 5%Na₂SO₄,3.5%Na Cl,clear water,and 5%Na₂SO₄ from high level to low level.The influence degree of the dynamic elastic modulus is 3.5%Na Cl plus 5%Na₂SO₄,5%Na₂SO₄,3.5%Na Cl,and clear water from high level to low level.The influence degree of the compressive strength loss rate is 3.5%Na Cl plus 5%Na₂SO₄,5%Na₂SO₄,3.5%Na Cl,and clear water from high level to low level.?3?For the freeze-thaw damage model of the recycled brick ECC under the different freeze-thaw environments,the freeze-thaw damage model was established with the dynamic elastic modulus and the compressive strength as damage variables.The results show that the material has the advantages of good resistance to salt-frost,and longer service life than ordinary concrete.