Experimental Study On Salt-frozen Performance Of Pervious Recycled Aggregate Concrete

On December 31,2014,the country began to implement the sponge city pilot work.Sixteen cities,including Baicheng and Nanning,won the first batch of pilot cities."Sponge City" means that a city is like a sponge.When it rains,it absorbs water,stores water,seeps water and purifies water.When it uses water,it "releases" the stored water to make use of it.Pervious concrete is one of the main materials for the construction of pervious structure in sponge city.It is widely used in parks,squares,parking lots and pavements which do not require high strength.Therefore,recycled coarse aggregate pervious concrete can be prepared from abandoned building waste.Pervious concrete has poor frost resistance due to its structural characteristics,which limits its popularization and application in cold areas such as northeast China.It is of great significance to study the frost resistance durability of pervious concrete for speeding up the construction of sponge cities in cold regions.In this paper,the mechanical properties,pore structure,permeability and freeze-thaw times of recycled aggregate concrete in clear water and saline water are studied experimentally.A total of 161 concrete specimens were prepared in the laboratory.Material testing and mix ratio orthogonal test were carried out.The freeze-thaw characteristics of recycled aggregate pervious concrete in clear water and 3.5% NaCl brine medium were studied by fast freezing method.After every 10 freeze-thaw cycles,the compressive strength,relative dynamic modulus of elasticity and porosity of the specimens were tested,and the variation of the above parameters with freeze-thaw cycles was analyzed.A CT method for detecting the porosity of permeable concrete was established.The CT machine was used to detect the specimens after 20,40,60,80 and 100 freeze-thaw cycles.The image analysis program was programmed with MATLAB software to analyze the variation of micro-pore characteristics of recycled aggregate concrete with freeze-thaw cycles.Using MIMICS software,the CT image was reconstructed to generate a three-dimensional numerical model reflecting the real pore structure of concrete.The model was imported into ANSYS finite element for numerical simulation test.A new recycled aggregate pervious concrete was prepared from freeze-thaw damaged concrete,and its reusability was studied.