Sand-Based Onsite Filter Pavement – Principles, Applications and Modeling Analysis
Abstract: According to the paving method, the permeable materials can be divided into two types: pre-cast / prefabricated, such as permeable bricks and permeable panels, and cast-in-place (such as pouring permeable concrete). If the laying site is regular and the scale is large, the on-site paving is preferred. The cost is low, the construction is fast and the degree of automation is high. In recent years, with the development of low-impact development, the development of sponge cities and the advancement of materials science, the types and performance of on-site pouring permeable materials have improved. In addition to traditional permeable concrete and asphalt, some new materials have emerged. For example, Elastopave and FilterPave of BASF in the United States are new permeable products that are laid on the site by polymer adhesives using fine stones and glass. However, the use of smaller diameter sand as the aggregated water-permeable material of the aggregate, due to the higher requirements for bonding, processing, and pore control, surface treatment and other technologies, there are few global commercial products.
This paper deals with a newly developed high-capacity, high-permeability, eco-friendly, cast-in-situ road, sand-based green ecological sponge greenway. Its paving structure mainly includes two parts: “elastic silica sand surface house” and “high-strength porous concrete fast drainage base layer”. The high-strength porous concrete rapid drainage base layer is made up of single-grain stone aggregate, cement, permeable concrete special hardener and water through special process. It is paved by professional mechanical equipment to ensure the high load-bearing capacity and high drainage performance of the road surface. The elastic silica sand surface layer is made of desert aeolian sand through a special process. The fluid sand is a new sand-based permeable composite material cast-in-water permeable paving material. It is hydrophilically modified by the interface to enhance the water permeability of the pavement. The micron-sized pores can effectively filter the rainwater while preventing the wall plugs. The cast-in-place pavement has the characteristics of low cost, fast construction, pattern paving, and landscape integration. This paper introduces the mechanism, application and model analysis of sand-based cast-in-place ecological sponge greenway. The fluid sand of the silica sand surface layer is the core building material of the sand-based cast-in-place ecological sponge greenway, which has good water retention and capillary action, is beneficial to promoting permeability and water evaporation, and is more ecologically similar to the apparent water cycle. In this study, the US EPA’s HELP model was used to simulate the long-term water balance of the pavement system, and the model’s “annual runoff total penetration rate” and “annual runoff total evaporation rate” were analyzed.
1.1 Permeable paving and sponge city construction
Permeable pavement refers to the application of a material with good water permeability and high porosity to the surface layer, the base layer or even the soil foundation. Under the premise of ensuring certain road strength and durability, the rainwater can smoothly enter the interior of the pavement structure. Through the base layer with temporary water storage capacity, it can be directly infiltrated into the soil foundation or enter the drainage pipe inside the pavement to eliminate the pavement, so as to achieve the pavement type of rainwater to reduce underground and eliminate surface runoff. Prefabricated permeable paving materials are produced and processed at the factory and transported to the construction site for artificial paving. The utility model has the advantages that the construction is convenient, the decoration can be matched with different blocks, and the cost is low, and the disadvantage is that the paving speed is slow and the construction process is complicated. Pervious concrete and permeable asphalt are common cast-in-place permeable paving materials. The construction method is for on-site personnel, materials, machinery, etc. The advantages are fast construction speed and simple process. The disadvantages are that there are curing period, poor decoration and high cost. In the permeable mode, the permeable pavement of the permeable paving material and the porous pavement and the pervious pavement of the material itself are generally permeable to the material itself. The material pore size, shape, porosity, and hydrophilic properties of the material are all critical.
Permeable pavement is an implementation way of the function of “seepage, stagnation, storage, purification, use and drainage” of sponge city. It is an indispensable component of “sponge city with natural accumulation, natural penetration and natural purification”. It is applied to urban roads, plazas, parking lots, etc.
1.2 Innovation of cast-in-place permeable pavement
Permeable materials are very important for the construction of sponge city. In the case of cast-in-place permeable paving materials, the above-mentioned permeable concrete and permeable asphalt have their own characteristics. The permeable concrete pavement has good water permeability, convenient construction, high durability and wide application range. The permeable asphalt pavement can effectively absorb the noise generated by the vehicle, and the paved surface is a flexible pavement, which can enhance the comfort of the vehicle. However, the permeable concrete pavement has high cost and long curing period; the permeable asphalt is semi-permeable material, and the formed pavement is easy to soften in summer and brittle in winter.
With the continuous advancement of sponge city construction, in addition to permeable concrete and permeable asphalt, some new permeable paving materials have emerged. For example, the United States BASF company developed Elastopave and FilerPave. They are new water-permeable products that are laid on the spot by polymer adhesives using fine stones and glass debris as aggregates. However, the use of smaller diameter sand as the base and permeable material of the aggregate, due to the higher requirements for bonding technology, film coating technology, pore control, surface treatment and other technologies, there are few commercial products in the world.
1.3 Needs and deficiencies
In the past 30 years, developed countries such as the United States, Japan, Germany, and Italy have successively carried out research and practice on permeable pavement materials. China has also carried out targeted research and has made some progress. At present, the construction process of the sponge city is accelerating, and the scale and scope of the construction are continuously expanding. In addition to the performance requirements for the permeable pavement, the construction speed, the construction landscape effect, and the cost are also required. Especially when the laying site is regular and the scale is large, the cost is low, the construction is fast, and the automation is high, the advantages of the cast-in-place permeable paving are more prominent.
1.4 Long-term water balance model
HELP (Hydrologic Evaluation of Landfill Performance Model) is a classic water balance simulation software developed by the US Federal Environmental Protection Agency. Due to its classic model building method, mature hydro-hydraulic simulation, fast level measurement analysis, and decades of experience in all walks of life, HELP is the most common software for landfill water balance analysis, and many studies use HELP. The model is used to estimate evaporation and osmosis in other environments.
2 Research purposes
Rechsand has conducted research on cast-in-place permeable pavement on the basis of many years of sand industry. The purpose of this study is to: 1) Develop a new type of sand-based permeable composite material, the permeable pervious pavement material-flowing sand, by studying the comprehensive utilization development technology of desert aeolian sand, and reduce the cost while permeable water filtration. 2) Forming the flow process of fluid sand through experiments and formula optimization, laying the foundation for large-scale production of fluid sand, 3) Through engineering verification, continuously correcting and perfecting the technology, and finally forming a comprehensive application technology for fluid sand pavement molding– The sand-based cast-in-place ecological sponge greenway has high bearing capacity, good water permeability and environmental protection. 4) Through the model simulation, the long-term water semi-balance simulation of the pavement system is carried out, and the annual runoff total penetration rate analysis was carried out with “the annual runoff rate”.
3 Research methods, technical principles, technical solutions, models, etc.
The most critical component of the cast-in-place permeable pavement is the fluid sand of the surface layer. Fluid sand is a new type of sand-based permeable composite material with cast-in-place permeable pavement material. The elastic silica sand surface layer is made of fluid sand.
Research on the development and utilization of cast-in-place permeable pavement for desert aeolian sand. Using micro-particle interface modification technology, micro-particle all-package technology, experiment and optimization, determine the flow process of fluid sand formulation: performance analysis and optimization through model simulation, testing, comparative analysis, etc. Finally, demonstration and engineering methods to verify and improve processes and technologies.
In the paving, the fluid sand is the surface layer paving material, and the bottom layer of the road is high-strength porous cement. Rechsand combines the characteristics of fluid sand, permeable porous cement and the construction standards of permeable roads, etc., the pavement structure of the permeable road, the thickness and compaction degree of each structural layer, the formula and the suitable construction operation time, and the different specifications “texture”. The design and molding of the pattern have been innovated, forming a sand-based in-situ ecological sponge greenway technology.
Sand-based in-situ ecological sponge greenway pavement structure; including “elastic silica sand surface layer” and “high-strength porous cement rapid drainage base layer” two parts. The high-strength porous cement rapid drainage base layer is made up of single-grain stone aggregate, cement, permeable concrete special hardener and water through special process. It is paved by professional mechanical equipment to ensure the high load-bearing capacity and high drainage performance of the pavement. The elastic silica sand surface layer is made of fluid sand. The fluid sand enhances the water permeability of the road surface through hydrophilic modification of the interface. The unique micro-scale pores can effectively filter the rainwater while preventing clogging. The pavement has the characteristics of low cost, fast construction and landscape integration.
The sand-based cast-in-place ecological sponge greenway process is as follows; Foundation treatment – vertical mold – laying graded gravel (if any) – laying permeable concrete – formwork – brushing adhesive – laying silica sand surface layer – roll compaction – Cutting expansion joints – curing, cleaning.
3.4 Model research
This study first tested some of the basic performance parameters associated with evaporation of the two products. The test results are used for some of the inputs required for the HELP model. Based on the historical average climate, this study uses the climate data generation function of the HELP model to approximate the climate scenarios of domestic cities. Then, through the HELP model, a 30-year, daily-based continuous water balance simulation and statistical analysis was carried out for possible future projects in Jinan, Shandong and Shaanxi.
4 Discussion of results
4.1 Research results
Through research and experiment, the fluid sand with silica sand as the main aggregate and organic binder as the main bonding material is selected as a new type of green building material, which has good fluidity and water permeability, and has certain elasticity. It is sand. The most critical materials for the construction of the ecological sponge greenway can be widely used in pavement construction such as park trails, fitness trails, bicycle lanes, urban greenways and fitness plazas.
The development of sand-based cast-in-place ecological sponge greenway technology, special paving structure and construction technology will give full play to the superior performance of fluid sand. Since the fluid sand surface layer is made of 20-100 mesh colored silica sand, the aggregate has good fluidity, easy compaction and flatness, so the laying efficiency is high. At the same time, the fluid sand construction does not need to be like a large particle permeable concrete. The roller compactor is needed, and the construction is convenient. Compared with the paving of the permeable brick, the fluid sand construction does not need to lay the leveling layer, and the on-site construction efficiency is high and the cost is low; the cast-in-place technology realizes the customizable landscape fusion effect of the fluid sand surface layer, and humane.
4.2 Parameter test results
Through the detection of the State Key Laboratory of Silica Sand Resources, the indicators of the flow rate of water permeability, water filtration rate and water permeability rate decrease rate all showed high levels.
4.3 Water balance model simulation results
Because sand-based materials have better water permeability and water retention properties. Through the water balance simulation, it is found that in addition to effectively reducing runoff, the ecological sponge greenway has good evaporation and penetration enhancement effects. It has made a good contribution to a series of goals such as reducing inward delivery, heat island mitigation, replenishing groundwater, and restoring the pre-development water cycle to sponge cities.
4.4 Use Case Introduction
During May of 2018 , the above-mentioned ecological sponge greenway technology was adopted in the municipal industrial construction of tourism infrastructure in the tourist area of Yuanshangdu. The project has a construction volume of about 40,000 square meters and is used for the pavilion of the leisure plaza in the scenic spot of the Shanglan Banner and the roads in the scenic area. Figure 3 shows some photos of the paving process. The project is located in the Zhengqi Banner of Inner Mongolia Autonomous Region. The effect after paving and the reflection of the people from all walks of life.
Figure 3 Construction of cast-in-place sand foundation cast-in-place ecological sponge greenway
The new fluid sand material obtained by surface modification and coating treatment of sand has good water permeability, water retention and other properties, and has good strength. It is a sand-based cast-on ecological sponge greenway. The key part, when applying sand-based in-situ ecological sponge greenway technology, it is easy to transport and low in cost. Compared with traditional permeable concrete and permeable asphalt, fluid sand is more in line with road construction construction standards and sponge city green environmental protection construction requirements, and has a good application prospect and market potential. Through the continuous water balance simulation of the HELP model, the calculation of the evaporation and the reductive replenishment of the ecological sponge greenway shows that the pavement has good evaporation to alleviate the urban heat island effect, and can significantly enhance the infiltration of groundwater. .
6 Future work recommendations
The production and construction of sand-based cast-in-place ecological sponge permeable paving materials need to be adapted to local conditions, according to construction requirements and site conditions, with certain technical difficulties, high requirements for technicians, and need to summarize the formulation process plan to form a fixed preparation. And construction parameters, easy to apply and promote, improve its effect on water use. In addition, although the HELP software used in the research uses the mature hydraulic model and the water balance analysis method, many weather parameters of the model need to be further optimized to better adapt to Chinese conditions.