Volume Stability Of Permeable Concrete

With the continuous advancement of urbanization and the shortage of water resources caused by population accumulation,and the construction of a large number of high-rise buildings,the area of open space has been continuously reduced,resulting in nowhere to build pavement drainage facilities.Most of the current cities are dominated by cement,cement bricks or asphalt concrete pavements,which are impervious to water.When there is heavy rain,a large amount of rainwater is not discharged into the city.It is not uncommon for a large number of casualties and property losses due to internal defects.In addition,the comfort and safety of impervious roads will be significantly reduced due to road area water.Pervious concrete has been increasingly used in pavement due to its unique eco-environmental benefits and is gradually accepted by people.Although China has a large area and a vast area,a large part of it is in high latitudes.Due to the large seasonal temperature difference in the northern region,winter is not only cold but also has a long duration,which leads to the appearance of many buildings.Destruction occurred,and the performance was not as good as before.Especially for Ningxia,where the environment is dry and rainy,windy and sandy,with sufficient sunshine,strong evaporation,long winter duration,short summer,large annual temperature and daily temperature difference,the building is due to climate and the damage caused by the environment is even more numerous.Among them,the problem of concrete cracks is particularly prominent.According to statistics,in the cracks formed,the shrinkage cracks accounted for nearly 80%.In addition,the national survey results show that the severe cold problem has caused some damage to some large and medium-sized projects and individual small houses.In addition to the problem of frost heaving damage in concrete construction projects in the climate cold weather area,some mild climates in East China also have the same problems.If such problems can be solved,it will reduce a lot of economic losses.Therefore,the basic volume stability of drying,shrinkage,temperature deformation and frost resistance of permeable concrete applied to cold areas is studied and clarified,and corresponding characterization models are established to provide a research basis for the preparation and application of permeable concrete with good volume stability and theoretical support.In this paper,the coarse aggregate size,water-to-binder ratio and slurry set ratio are the controlling factors,and the shrinkage rate,deformation coefficient,mass loss rate and dynamic modulus decay rate are the main indicators.The orthogonal test is used to dry the shrinkage of the permeable concrete.The volume stability dominated by temperature deformation and frost resistance was studied and the corresponding model was established.The main conclusions are shown as follows:(1)The influence characteristics of each main factor on the volume stability of permeable concrete is clarified.In terms of drying shrinkage,the slurry set ratio has the greatest influence,the water-cement ratio is the second,and the stone gradation is the smallest;for temperature deformation and freeze-thaw The stone grading has the greatest influence,the water-to-gel ratio is the second,and the pulp collection ratio is the smallest.(2)It is determined through experiments that the optimum mixing ratio parameters of the permeable concrete that can be suitable for cold area are water-to-binder ratio 0.31,pulp set ratio 0.55,and stone grain size grading 4.75?9.50mm.(3)Compared with ordinary concrete,the overall strength of permeable concrete is low,and the 28d compressive strength is distributed between 15 and 25 MPa.The shrinkage rate of permeable concrete is less than that of ordinary concrete,and the smallest is 0.7 times that of ordinary concrete.After 70 times of freeze-thaw cycle of permeable concrete,the damage limit is basically reached,and the ordinary concrete with better frost resistance can resist 300 freeze-thaw cycles.The freeze-thaw damage of permeable concrete is mainly caused by hydrostatic pressure damage.The structure with large pores and high connectivity increases the destructive effect of hydrostatic pressure and is the root cause of low frost resistance of permeable concrete.