Pervious concrete is an eco-friendly concrete with continuous pores, good air permeability and water permeability. Pavement can supplement groundwater, alleviate urban waterlogging, absorb sound and reduce noise, improve urban thermal environment, and have good environmental and social benefits. It is a green infrastructure in harmony with the natural environment, and has a very considerable prospect in the future urban road construction.

Application Trends and Market Demands of Pervious Concrete

1. Proposition of the concept of sponge city
In 2014, the Ministry of Construction issued a document to promote the application of permeable concrete, proposing that permeable pavement will cover 80% of the urban area by 2030, which will further promote the development of permeable concrete. The timetable set around this goal is that by 2020, 20% of the city's built-up areas will meet this requirement. If an urban built-up area has 100 square kilometers, at least 20 square kilometers will meet this requirement in 2020. By 2030, 80% of urban built-up areas will meet this requirement, so the market demand for pervious concrete paving is huge.

2. Construction of urban slow-moving system
The urban slow-moving system is slow-moving traffic, which is to take walking, bicycles, buses and other environmentally friendly travel methods as the main body of urban traffic, effectively solve the problems of fast and slow traffic conflicts, and difficulty in walking for slow-moving subjects, and guide residents to adopt "walking + public transportation", The "bicycle + bus" travel mode, in which permeable concrete, ceramic particle anti-skid trails, plastic runways and colored permeable asphalt are the dominant processes of the slow-moving system. According to the advantages of overall cost and ecological green performance, permeable concrete accounts for about 40% The share is increasing year by year.

3. National fitness trail construction
In order to thoroughly implement the spirit of the 19th National Congress of the Communist Party of China, further promote the widespread development of national fitness activities, and meet the diverse outdoor fitness needs of the people, on March 16 this year, 12 ministries and commissions, including the State Sports General Administration, the National Development and Reform Commission, and the Ministry of Finance, were organized. Jointly issued the "One Million Kilometers of Fitness Trails Project Implementation Plan", proposing that by 2020, we should strive to complete the construction of about 300 kilometers of fitness trails in every county (city, district) in the country. Economical and intensive use of resources, protection of the ecological environment, and emphasis on sustainable development. Then the proposal of this scheme is a great impetus to the market demand for permeable concrete.

4. Construction of beautiful villages and characteristic towns
The ecological problem of the land used for agricultural leisure projects has been paid more and more attention. The natural land itself is a natural cycle ecosystem. When designing the pavement, ecological green building materials should be used, and hardening paving that does not damage the ecological environment should be used as much as possible. practice to reduce the damage to the original ecological balance. As an environmentally friendly and ecological road material, permeable floor has good comprehensive benefits. It is a green infrastructure in harmony with the natural environment. Therefore, the construction of beautiful villages and characteristic towns has been vigorously promoted.

Common problems and solutions of pervious concrete
1. Insufficient strength of permeable floor
The strength of permeable concrete is affected by many factors, mainly including: the amount of cement added, the strength of the stone, the preparation process, the SiO2 content of the reinforcing agent, and whether the maintenance is standardized... Therefore, the strength of pervious concrete should be improved from the aspects of optimizing raw materials and reinforcing agents.
Solution:
(1) Reduce the particle size of coarse aggregate. The smaller the aggregate particle size, the greater the number of contact points between the aggregate particles in the unit volume of the formed structural skeleton, the greater the bonding area, and the higher the overall strength ratio of pervious concrete.
(2) The use of SR enhancer to increase the early strength of concrete, enhance the workability and viscosity of concrete, and improve the surface activity of cement, adding a concrete enhancer, the transformation increases the dispersibility of cement without changing the Basic performance, maintain the stability of the slurry wrapped on the surface of the slippery material, and can evenly adhere to the surface of the slippery material, enhance the connection rate of the concrete, and ensure that the permeable concrete has sufficient strength to meet the needs of water permeability.

2. The permeable floor swells or cracks
Due to changes in temperature and humidity, brittleness and unevenness of concrete, and unreasonable structure, cracks often appear in permeable concrete after a period of use, which has become a headache for many construction workers. So, how can we avoid this phenomenon?
Solution:
(1) Expansion joints of the structural layer are placed accurately, and the position of the construction joints on the day should be left at the position of the expansion joints, and should not be left at will.
(2) When the strength of the concrete reaches 70%, the seam should be cut in time, the depth of the seam should exceed the thickness of the surface layer, and the area of the single block should be kept at about 25 square meters.
(3) Strictly control the mixing ratio, accurate feeding, and the thickness of the surface layer left in the construction of the structural layer, which should meet the design requirements and control the flatness.
(4) The joint between the concrete and the surrounding objects shall be provided with a buffer belt to increase the air permeability.

3. Partial drop of stones on permeable floor
The main reasons for the partial shedding of permeable concrete are as follows: SR permeable concrete reinforcement (binder), insufficient cement delivery ratio or uneven mixing; excessive watering on the surface, loss of slurry on the stone surface; insufficient concrete strength; surrounding scrubbing When the water is eroded, the slurry is lost; the maintenance film is missing.

The main preventive measures to prevent permeable concrete from falling off are:
(1) Use qualified SR permeable concrete reinforcing agent materials; the reinforcing agent and cement are put in a sufficient amount as required and fully stirred.
(2) The pressure should not be too large during sprinkling maintenance, and it is strictly forbidden to spray directly with water pipes.
(3) Do a good job of shielding the permeable concrete part when washing the surrounding area.
(4) Carry out batching construction according to the designed concrete strength ratio.
(5) The maintenance film is tightly lapped and sealed, and the film covering maintenance must meet 7 days.

4. Pinholes or bubbles appear on the permeable floor
The root cause of pinholes in permeable floors is that the permeable floor finishes are rapidly volatilized after coating, making it too late for the paint to be replenished, resulting in the formation of many circular small circles, small holes or needle-shaped holes. These conditions are more likely to occur on permeable floors with varnishes and permeable floors with low pigment content.

Reason 1: The viscosity of the covering agent for the surface layer of the permeable floor is too large, and the temperature of the construction site is low. After the covering agent of the permeable floor surface layer is stirred, there are still residual air bubbles due to the short standing time.
Solution: The viscosity of the covering agent for the surface layer of the permeable floor should not be too large, and the temperature of the construction site should not be too low. After the permeable floor covering agent is stirred, it should be placed for a period of time until the air bubbles are cleared before construction.

Reason 2: There is moisture in the permeable floor covering material, and there is dust in the air at the construction site of the permeable floor.
Solution: Before construction, the moisture in the face covering agent and the dust in the air should be removed.

Reason 3: The permeable floor covering agent has poor leveling and poor release of air bubbles.
Solution: Adjust the formula of the permeable floor surface finish material.