| Water-retentive pavement is a kind of functional pavement,which can keep moisture inside the pavement structure and take away much latent heat by the evaporation of water,and suppress the temperature rise of the pavement surface and reduce the air temperature.This paper mainly deals with the materials composition design and performance evaluation etc.of waterretentive cement concrete.This study provides a technical solution and relevant technical support for the mitigation of urban heat island effect and the construction of "sponge city".In this paper,the effect of diatomite content on the performance of concrete was studied,at the same time,the optimum diatomite content is determined.By coMParing the economic and technical properties etc.of different water-retentive materials,the types and particle size of water retaining material were determined.The mix proportion of the maternal material was determined by the test and calculation.The maternal material combined with water retaining material by method of mixing,and the mixing process was determined by coMParing the different mixing methods.The frost resistance and strength of water-retaining specimens with different diatomite contents were analyzed.The water-absorbing test under different environmental conditions and the evaporation test of water-retaining specimens were designed.According to the test results,the performance of water absorption and evaporation of waterretaining specimens with different diatomite contents were analyzed.The temperature characteristics of the specimens was observed before and after sprinkling.According to the theory of surface energy balance,temperature and specimens parameters etc.,the temperature and energy behavior of concrete specimens with different water-retentive amount were calculated and analyzed.The specimens cooling performance was evaluated by using the temperature behavior and sensible heat and latent heat.The study found that the water absorption height and the water absorption rate of waterretaining specimen with 3.0% diatomite are maximum,which are 70.35% and 0.118g/cm~3 respectively.When the diatomite content is 3.0%,it is large and close to its maximum value for the frost resistance index,the compressive strength,the flexural strength,the amount of saturated water absorption and the amount of sprinkled water absorption of water-retentive specimen,the value are 99.1%,21.0MPa,2.64 MPa,0.140g/cm~3,0.140g/cm~3(40min)respectively.The evaporation rate of water-retaining specimen with 3.0% diatomite is 0.254 g/(m~2·s)at the beginning and 0.023 g/(m~2·s)at the 8.5th hour.Water-retentive cement concrete with diatomite can maintain a strong evaporation for 8.5 hours.CoMPared with Portland cement concrete,the maximum reduction value of the surface temperatures of water-retentive cement concrete with 3.0% diatomite is 5.1 °C on the first day after sprinkling,is 2.1 °C on the second day after sprinkling respectively.CoMPared with Portland cement concrete,waterretentive cement concrete with diatomite can significantly reduce the sensible heat release and increase the release of latent heat,especially the content is 3.0 % and above.When the content is 3.0 %,the reduction in sensible heat is 29.6 W/m~2 and 14.9 W/m~2 during the day and night respectively,and the increment in average latent heat is 57.2 W/m~2.Therefore,the optimum content of diatomite is 3.0 % finally.The cooling effect of water-retentive cement concrete pavement system with 3.0 % diatomite is remarkable,which have a certain mitigation effect on urban heat island. |
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