as a construction material that are easy for rainwater to penetrate, can not only absorb the rainwater runoff in the planned catchment area, but also filter and purify it, and then realize the intention of controlling external discharge flow and reducing pollutants.
However, in practice, after a period of use, the permeable bricks
will have different levels of water permeability decline or even disappear completely, and then lose the function of rainwater use and do not meet the requirements of green building reviews.
At present, the selection of permeable bricks
in the planning generally only considers its permeability coefficient. However, in practice, the duration of permeable bricks'
permeable function (ie, "permeability") is also an important evaluation factor that reflects its application performance. At present, there is no domestic discussion on this aspect and useful detection methods for permeation aging. In view of this situation, the author conducted relevant discussions with a view to providing reference and planning basis for the development of rainwater use and engineering planning.
1 Materials and methods
1. 1 Experimental equipment and sample experimental equipment: BT-9300H laser particle size spreader, drying box, water permeability test equipment, etc. The first choice of permeable brick
sample for experiment
See Table 1 for performance indicators.
1. 2-way stream imitating water sample equipment
1. 2. 1 particle size analysis of road dust sample
Collect the road dust samples of the pedestrian paths, residential paths and park paths in the second ring road to the fifth ring road in the urban area of Beijing. Select 3 to 5 points for each road section and mix them as the road section of the road section. The dust samples are sent to the laboratory for testing. The test results are shown in Table 2.
1. 2. 2 imitate water sample manufacturing
Based on the analysis results of the particle size of road dust samples, the annual average rainfall in Beijing and the mass concentration of suspended pollutants in rainwater runoff, Kaolin and pure water were used to simulate the flow of water samples in the road to make it.
1) Imitation of water sample volume calculation:
V = H × S. (1)
In the formula: V is the volume of the simulated water sample, L; H is the average rainfall in Beijing for many years, taking 571.9 mm; S is the water permeable area of the permeable brick sample, taking 200 mm × 200 mm.
2) Imitation of the mass of the solute in the water sample:
M = C × V. (2)
In the formula: M is the mass of the solute in the water sample, mg; C is the mass concentration of SS in the road flow in Beijing, taking 734 mg / L.
3) The quality of solutes with different particle sizes in water samples:
mi = α × M. (3)
In the formula: mi is the mass of solutes with different particle sizes in the water sample, mg; α is the share of solutes with different particle sizes,%. After calculation: V = 22.87 L; M = 16.79 mg; mi is shown in Table 3.
1. 3 experimental process
1) Put the sample in a drying box and blow dry it. The temperature is set to 80 ℃ for 24 hours.
2) Take out the dried sample and wait for the temperature to drop to room temperature, then use the water-permeability test equipment to test the water-permeability rate;
3) When the sample to be tested has no seepage water, put it in a drying box and blow dry it. The temperature is set to 80 ℃ for 24 hours.
4) Take out the re-dried sample and wait for the temperature to drop to room temperature, then filter it with water sample;
5) When there is no seepage water from the filtered sample, put it in a drying box and blow dry it. The temperature is set to 80 ℃ for 24 hours.
6) Take out the filtered and dried samples and wait for the temperature to drop to room temperature. Use the water permeability test equipment to test the water permeability.
2 Results and comments
2.1 Experimental data
The experimental data are shown in Tables 4 and 5.
Change the permeation rate of pervious brick
with time by collecting the experimental data
,see picture 1.
It can be seen from Figure 1 that the water permeability of samples 1 and 2 decreases with the addition of the application time, but the undulations decrease gradually; the water permeability of sample 2 is greater than that of sample 1. This is because the particulate matter has blocked the open space of the permeable brick
, and with the addition of the application time, the open space of the permeable brick
has become more severely blocked, affecting its ability to penetrate and causing its water permeability to decrease
. When the open space is blocked to a certain degree, it is difficult for particulate matter to enter the interior of the permeable brick
, and the undulations at which the permeable velocity decreases at this moment will become slower. Because the materials and structures of samples 1 and 2 are different, the water permeation speeds are also different.
Regression analysis of the changes in the water permeability of samples 1 and 2 in Fig. 1 with time, the results are: Y = 1.093 5X-0.509 3, R2 = 0.949 2; (4) Y = 1.615 9X-0.713 2, R2 = 0.969 3. (5)
In the formula: Y is the water permeability rate, m L / (min · cm2); X is the service life, year.
2. 3 instance verification
The above experimental data and analysis results are obtained in laboratory tests. In practical engineering, the rolling and trampling of vehicles and pedestrians, and road sweeping and other factors will affect the permeability of permeable bricks
. Therefore, the experimental and practical data are analyzed For comparison, the results are shown in Table 6.
It can be known from Table 6 that there is a certain deviation between the experimental data and the practical data. The actual water permeability is about 82% of the experimental water permeability. Therefore, considering the factors affecting the practice, the experimental data can be revised, that is: Vp = KVe . (6)
In the formula: Vp is the practical water permeability, m L / (min · cm2); Ve is the experimental water permeability, m L / (min · cm2); K is the correction coefficient.
3 Conclusions and opinions
1) It is a more scientific and useful method to test the permeation time of permeable bricks
based on data such as rainfall materials, mass concentration of pollutants in road flows, and particle size analysis results of dust particles on roads.
2) There are many factors that affect the permeation timeliness in practical engineering. There are differences between laboratory test results and practical conditions, and proofreading needs to be performed according to practical conditions.
3) In the project planning, it is advisable to use permeable bricks
with longer permeation time to optimize the planning based on the inspection results.
After analyzing the above content, the author aims to provide a more feasible method for detecting and commenting on the permeation time of pervious bricks
, but unfortunately, due to poor consideration, it only mimics the experiment of 5 years of use time limit, if it can mimic more applications Years of experiments will make the data more complete and more practical.