| As a new-type pavement material,water permeable brick has a good performance of water permeability,which brings great benefits to the ecological environment.Generally,the natural aggregate and cement are mostly used as raw materials in the preparation of water permeable brick.Using recycled aggregate to prepare water permeable brick with the condition of low cement content,can not only reduces the consumption of natural aggregate resources,alleviates the environmental problems caused by construction waste,but also reduces the cement content and costs,which has a good social and economic double benefit.At present,due to the defects of water permeable brick prepared by recycled aggregate,including the low strength,utilization rate of recycled aggregate,high costs and complicated preparation technology,which further promotion and application are seriously hindered.In view of the above problems,this paper carries out the following researches:Firstly,four factors and four levels orthogonal test were adopted to preliminary study the effects of aggregate gradation,aggregate-binder ratio,content of fly ash,the forming pressure,water-binder ratio,curing method on compressive strength and permeability coefficient of water permeable brick along with multiple sets of single factor experiments.The reasonable mix proportion of water permeable brick was determined,and the preparation technology of water permeable brick was proposed.Secondly,based on the preliminary tests,the natural aggregate,particle-shaping recycled aggregate and simple-crushing recycled aggregate were selected as the aggregate of water permeable brick,respectively,hereafter undergoing autoclaved curing,steam curing and natural curing.The effects of aggregate gradation,aggregate-binder ratio,replacement ratio of fly ash,aggregate performance and curing methods on compressive strength,water permeability coefficient,frost resistance and water-retaining property of water permeable brick were systematically studied by three factors and three levels orthogonal test.The influence degree of different factors on the performance of water permeable brick was obtained through the range analysis,the optimum technological parameters of water permeable brick were determined,and theinfluence of porosity and pore structure on the frost resistance and water-retaining property was studied.Finally,on the basis of optimum mix proportion,the influence of the surface layer on the performance of water permeable brick was studied.The main conclusions of this paper are as follows:(1)The compressive strength,water permeability coefficient,frost resistance and water-retaining property of water permeable brick prepared by recycled aggregate can meet the requirements of "permeable brick"(JC/T 945-2005)and "recycled aggregate floor tile and permeable brick"(CJ/T 400-2012).The compressive strength is greater than 30 MPa,water permeability coefficient is greater than 1×10-2cm/s,the loss rate of compressive strength is less than 20%,and water-retaining ratio is greater than0.6g/cm2.(2)With the increase of the coarse aggregate amount and aggregate-binder ratio,the compressive strength of water permeable brick decreases,and the water permeability coefficient and the compressive strength loss rate increases.The optimum aggregate gradation,aggregate-binder ratio is 6:3:1 and 3.2.The compressive strength of brick increases with the forming pressure increases,but the compressive strength basically unchanged and the permeability coefficient decreases when the forming pressure exceeds 4.2MPa.Therefore,the optimum forming pressure is set to 4.2MPa.(3)With the increase of replacement ratio by fly ash,the water permeability coefficient decreases;the compressive strength of water permeable brick decreases with the increase of replacement ratio of fly ash through the natural curing and steam curing method;under the condition of autoclaved curing,the appropriate increment of fly ash content is conducive to the improvement of strength of water permeable brick,but the compressive strength began to decrease when the replacement ratio by fly ash is higher than 60%.Therefore,the optimum replacement ratio by fly ash is determined as 50%,the best curing condition is autoclave curing.(4)According to the results of range analysis,the influence degree of different factors on the compressive strength of water permeable brick in order is aggregate-binder ratio > aggregate gradation > forming pressure > replacement ratio by fly ash;the influence degree of different factors on the water permeability coefficient ofpermeable brick in order is aggregate gradation > aggregate-binder ratio > forming pressure > replacement ratio by fly ash.(5)Physical strengthening can effectively improve the performance of recycled aggregate,the water permeability coefficient of water permeable brick prepared by particle-shaping recycled aggregate is relatively smaller,but the compressive strength can reach more than 35 MPa,which is close to the strength of water permeable brick prepared by natural aggregate,and around 15% higher than that of water permeable brick prepared by simple-crushing recycled aggregate.(6)With the increase of water-binder ratio from 0.26 to 0.36,the compressive strength of water permeable brick prepared by recycled aggregate improves significantly,and the water permeable coefficient increases firstly and then decreases.When the water-binder ratio is 0.3,the water permeable coefficient of water permeable brick prepared by recycled aggregate is the largest,and the optimum range of water binder ratio is around 0.3.(7)The porosity,pore structure and performance and thickness of surface layer have great effects on the performance of water permeable brick.When the proportion of connected pores of water permeable brick is relatively high and the porosity ranges from 12% to 16%,the aggregate size is 2.36?4.75 mm,aggregate-binder ratio is 3.2,the replacement ratio by fly ash is 50%,and the thickness is 3mm,the best performance of water permeable brick can be achieved. |
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