research on permeable concrete
research on the function of permeable concrete refers to a kind of concrete material with high water permeability, which can form interconnected pores in its internal structure, and is also called discontinuous graded concrete and open pore 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 accumulation and waterlogging, which is of great significance to Jinan and other cities with huge traffic pressure and many vehicles; Improve the groundwater level, through the infiltration of permeable concrete, rainwater can penetrate into the grass-roots and soil through the concrete layer, and increase the groundwater recharge, especially for Jinan, the spring city, which can well maintain the groundwater level and ensure the normal gushing of springs; Part of the rainwater infiltrated into the grass roots can be partially evaporated in fine weather, thus playing a better role in alleviating the urban heat island effect; Permeable concrete pavement has the characteristics of low noise, which can reduce the noise of vehicles in narrow areas, reduce the impact of sound pollution on the environment and improve the quality of life of residents. The rainwater that penetrates into the ground can avoid contact with 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 side slip caused by local water accumulation in rainy weather. Finally, when driving at night, the sputtering and reflection caused by local water accumulation can be well alleviated. Classification of pervious concrete According to different materials, pervious concrete can be divided into the following two categories: cement pervious concrete. This type of concrete takes high-grade cement as cementing material, with the ratio of ashes to ashes of 3 ~ 4, water cement ratio of .2 ~ .35, porosity of 1% ~ 25%, compressive strength of 15 ~ 3～5MPa and flexural strength of 3 ~ 5 MPa. Polymer permeable concrete. This kind of concrete cementing material is rubber, asphalt and other cementing materials, which is famous for its high strength, and rubber, asphalt and other sources are extensive and cheap. Disadvantages are easy aging, poor durability and poor environmental friendliness. Under high temperature conditions, it is easy to block internal pores and reduce 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, etc. 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, while 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, leading to an increase in voids. 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 have a negative impact on 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 ranges from .25 to .4. 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 needed for filling, which will reduce the pore number and pore size 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 the relevant experimental data, the recommended values of aggregate particle size are as follows: gravel: 5 ~ 1 mm, ceramsite: 4.75 ~ 9.5 mm, 9.5 ~ 13.2～16mm and 13.2 ~ 16 mm. Target Porosity Porosity of pervious concrete is a key index affecting water permeability, and it 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 select 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%, 2% 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 a certain extent, prevent bleeding and segregation, and improve the compactness of concrete and the strength of finished products. Common mineral admixtures include fly ash and silica micropowder. 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 which can adjust the rheological characteristics of the mixture. Retarders and early strength agents with adjustable setting time; Waterproofing agent that can improve durability; Other additives with improved performance include expansion agent and antifreeze.
analysis of mixture ratio of rubber aggregate pervious concrete
Analysis of mixture ratio The construction of sponge city conforms to the requirements of a conservation-oriented and green society put forward by the state, and the use of rubber aggregate pervious concrete for urban road construction can, on the one hand, alleviate the urban heat island effect and improve the frost resistance, compression resistance, corrosion resistance and crack resistance of the pavement, on the other hand, reuse the waste tires that are eliminated every year in the city. In this paper, the optimal mixture ratio of rubber aggregate concrete will be studied. According to relevant experimental data, adding medium sand with sand ratio of 1% and 5kg/m3 rubber aggregate in the process of concrete preparation can obviously improve the compressive strength of concrete and obtain a water permeability coefficient of 1.47 mm/s. In this paper, referring to the Technical Specification for Permeable Concrete Pavement (CJJ/T135-29) and the existing design method of pervious concrete, the water-binder ratio of pervious concrete in rubber aggregate is selected as .3, and a comparative test is carried out. The blank control group is Group A in Table 1, without adding any aggregate, and the rest groups are shown in Table 1. As shown in Figure 1, the strength test results of the above five groups show that the average compressive strength of the five groups is 24.1MPa, the lowest is 21MPa and the highest is 27MPa, and the strength 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 water permeability coefficient is b < e < d < c < a, and the designed water permeability coefficient is 1mm/s, and all five groups of samples meet the requirements. Based on the comprehensive analysis of compressive strength test and permeability coefficient test results, the aggregate mixture ratio of Group D (1.5kg/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 pervious concrete Figure 3 shows the preparation process of pervious concrete. According to the rubber aggregate mixture ratio obtained in Section 2.1, the permeable 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 the project is to observe the collapse degree by hand, and it is qualified within 5mm to ensure that the porous structure can still be maintained after hardening. In the same way as the water-cement ratio analyzed in Section 1.3, the thinner or harder slurry can not guarantee the water permeability of the finished concrete.
study on failure forms of pervious concrete
in the application process of pervious concrete, there are several common failure forms, such as cracking, settlement, wear, freezing and thawing. The main reasons are as follows. Crack. The local traffic load is bad, and the overload can lead to cracking. In addition, improper selection of water permeability coefficient will lead to too fast water permeability, which will scour the soil at the grass-roots level, thus forming local pits at the grass-roots level, which will lead to the decline of the bearing capacity of the grass-roots level and lead to cracking. Temperature also has a great contribution to cracking. Because concrete is not an isotropic material, it is prone to uneven expansion and contraction under the influence of high and low temperatures, which leads to cracking. Settlement. In the process of drainage, the continuous scouring of pits on a large scale at the grass-roots level will lead to the continuous settlement of the pavement and affect the driving safety. Wear and tear 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 brakes suddenly, which will bring some wear to the pavement. Freezing and thawing Freeze-thaw damage is a special damage form of permeable concrete, which is mainly caused by 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, additives such as air entraining agent added in the preparation process can also prevent freeze-thaw damage.
in this paper, the application of permeable concrete in the construction of sponge city is studied, and the application function of permeable concrete is obtained. At the same time, the mixture ratio of rubber aggregate concrete is studied, and the best mixture ratio of 1.5kg/m3 in five groups is obtained, and the preparation process is analyzed. Finally, the main failure forms of permeable concrete in the application process are analyzed, which can provide some reference for the research of permeable concrete in the construction of sponge city.
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