Study on pervious concrete
Study on the Function of Permeable Concrete Permeable concrete refers to a kind of concrete material with high permeability, which can form connected pores in its internal structure. Also known as discontinuous graded concrete and perforated concrete. High water permeability is its main functional feature. In addition, it has the following functions: reducing the pressure of urban drainage system, effectively distributing urban drainage load and avoiding local water logging, which is of great significance to cities with huge traffic pressure and many vehicles, such as Jinan; Increase the groundwater level, through the infiltration of permeable concrete, rainwater can penetrate into the grass-roots and soil through the concrete layer, and increase groundwater recharge, especially for Jinan, a spring city, which can maintain the groundwater level well and ensure the normal gushing of spring water; Part of the rainwater infiltrated into the grass-roots can be partially evaporated in fine weather, which plays a good role in alleviating the urban heat island effect; Permeable concrete pavement has the characteristics of low noise, which can reduce vehicle noise in narrow areas, reduce the impact of sound pollution on the environment and improve the quality of life of residents. The rainwater infiltrated into the ground can avoid contact with the sewage in the municipal pipe network, realize the purification of rainwater infiltration and avoid secondary pollution; It can improve urban driving safety. On the one hand, permeable concrete has large friction and small friction attenuation gradient. On the one hand, it can avoid vehicle sideslip caused by local water accumulation in rainy days. Finally, when driving at night, it can well alleviate the sputtering and reflection caused by local water accumulation. Classification of pervious concrete According to different materials, pervious concrete can be divided into the following two categories: cement pervious concrete. This kind of concrete takes high-grade cement as the cementing material, the cement-lime ratio is 3 ~ 4, the water-cement ratio is 0.2 ~ 0.35, the porosity is 10% ~ 25%, the compressive strength is 15 ~ 3~5MPa, and the flexural strength is 3~5MPa. Polymer permeable concrete. This kind of concrete cementing material is rubber, asphalt and other cementing materials, which is famous for its high strength. Rubber and asphalt are widely available and low in price. Disadvantages are easy aging, poor durability and poor environmental protection. Under the condition of high temperature, it is easy to block the internal pores and reduce the water seepage capacity. Parameter analysis of pervious concrete In the preparation process of pervious concrete, the main concerned parameters are water cement ratio, aggregate particle size, target porosity, mineral admixture and admixture. The strength and permeability of water-cement ratio permeable concrete are directly related to water-cement ratio. When the water-cement ratio is small, if a certain concrete porosity is ensured, the cement content in the finished test block will increase, but the water content will decrease, which will lead to the rapid hardening of the test block and greatly reduce the fluidity of the mixture in permeable concrete. At the same time, it will also lead to the coarse aggregate in concrete can not be completely wrapped, resulting in an increase in porosity. Although the water permeability has improved, the overall strength of concrete has decreased. On the contrary, when the water-cement ratio is large, it will not only adversely affect the water permeability of concrete, but also greatly affect the strength of concrete. According to relevant test data, the recommended water-cement ratio of permeable concrete is 0.25-0.40. Aggregate size coarse aggregate accumulation constitutes permeable concrete skeleton, and aggregate size has great influence on concrete strength and permeability. When the aggregate particle size is small, the specific surface area of the whole concrete increases, which leads to the increase of cement slurry required for filling, which will reduce the pore number and pore diameter of concrete, thus affecting the permeability of permeable concrete; However, the strength will increase with the decrease of concrete aggregate particle size. When the particle size of aggregate increases, permeable concrete shows high permeability and appropriate strength reduction. According to relevant test data, the recommended aggregate size is: crushed stone: 5 ~ 10 mm, ceramsite: 4.75 ~ 9.5 mm, 9.5 ~ 13.2 mm,16 mm. The target porosity of permeable concrete is a key index affecting water permeability and also has a great influence on concrete strength. According to different concrete requirements, when the strength requirement is weakened and the water permeability is emphasized, it is necessary to choose a larger porosity; On the contrary, when the strength is the main goal, the porosity should be controlled within a certain range. In addition, the target porosity is also directly related to the actual porosity of concrete. When designing the target porosity, it is necessary to select appropriate porosity, such as 15%, 20% and 25%. Mineral Admixtures and Admixtures The main function of mineral admixtures in concrete is to reduce the amount of cement in concrete, improve the fluidity of the mixture to some extent, prevent bleeding and segregation, and improve the compactness and finished product strength of concrete. Common mineral admixtures are fly ash and silica fume. There are many kinds of additives in the preparation of permeable concrete, which have different functions, mainly including water reducing agent and air entraining agent, and can adjust the rheological properties of the mixture. Retarder and early strength agent with adjustable setting time; Waterproofing agent capable of improving durability; Other additives with improved properties include expansion agents and antifreeze.
Mix proportion analysis of rubber aggregate permeable concrete
Mixed analysis: building a sponge city conforms to the requirements of a conservation-oriented and green society proposed by the state. On the one hand, the use of rubber aggregate permeable concrete for urban road construction can alleviate the urban heat island effect and improve the frost resistance, compression resistance, corrosion resistance and crack resistance of pavement; On the other hand, we can reuse the waste tires eliminated every year in the city. In this paper, the optimum mixture ratio of rubber aggregate concrete will be studied. According to relevant test data, adding medium sand with sand ratio of 10% and rubber aggregate of 50kg/m3 in the process of concrete preparation can obviously improve the compressive strength of concrete and obtain the water permeability coefficient of1.47mm/s. In this paper, referring to "Technical Specification for Permeable Concrete Pavement" (CJJ/T 135-2009) and the existing mix design method of pervious concrete, the water-binder ratio of rubber aggregate in pervious concrete is selected as the blank control group, and there is no aggregate in table 1, and the other groups are shown in table 1. As shown in the figure 1, the above five groups of strength test results show that the average compressive strength of the five groups is 24. 1MPa, with the lowest being 2 1MPa and the highest being 27MPa, which meets the requirements. Figure 2 shows the test results of water permeability coefficient of five groups of data. The results show that the order of permeability coefficient is b < e < d < c < a, and the designed permeability coefficient is 1mm/s, and all five groups of samples meet the requirements. Based on the comprehensive analysis of the results of compressive strength test and permeability coefficient test, the aggregate ratio of Group D (10.5kg/m3) has both high compressive strength and high permeability coefficient, which is the best mixture ratio among the five groups in this test. Preparation process of permeable concrete Figure 3 shows the preparation process of permeable concrete. According to the rubber aggregate mixture ratio obtained in section 2. 1, the pervious concrete is prepared. In the preparation process, the cohesiveness of the slurry should be enough to ensure the shape of the wrapped aggregate. The judgment standard adopted in this project is to observe the degree of collapse by hand, and it is qualified within 50mm to ensure that the porous structure can still be maintained after hardening. Like the water-cement ratio analyzed in section 1.3, the thinner or harder the cement slurry is, the water permeability of the finished concrete cannot be guaranteed.
Study on failure form of permeable concrete
In the application of permeable concrete, there are several common failure forms, such as cracking, settlement, wear, freezing and thawing. The main reasons are as follows. Cracks. The local traffic load is not good, and overloading will lead to cracking. In addition, improper selection of water permeability coefficient will lead to too fast water permeability and scour the soil at the grass-roots level, thus forming local pits and grooves at the grass-roots level, leading to the decline of bearing capacity of the grass-roots level and cracking. Temperature also has a great contribution to cracking. Because concrete is not an isotropic material, it is easy to produce uneven expansion and contraction under the influence of high and low temperatures, which leads to cracking. Reconciliation. In the process of drainage, large-scale pit and groove erosion occurs at the grass-roots level, which will lead to continuous settlement of the road surface and affect the driving safety. Wear, whether it is permeable concrete or other forms of pavement, wear is a common failure form in the application process. The main reason is that the vehicle is overweight, the local friction is too large or the vehicle suddenly brakes, which will bring some wear to the road surface. Freeze-thaw freeze-thaw damage is a special damage form of permeable concrete, mainly due to the volume change caused by the phase change of water saturation in pores, which will lead to the destruction of concrete. For freeze-thaw damage, on the one hand, it is difficult for permeable concrete to reach water saturation, on the other hand, adding additives such as air entraining agent in the preparation process can also prevent freeze-thaw damage.
In this paper, the application of permeable concrete in sponge city construction is studied, and the application function of permeable concrete is obtained. At the same time, the mix proportion of rubber aggregate concrete is studied, and five groups of optimal mix proportion 10.5kg/m3 are obtained, and the preparation process is analyzed. Finally, the main failure forms of permeable concrete in the application process are analyzed, which provides some reference for the research of permeable concrete in sponge city construction.
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