Performance Simulation of Permeable Concrete Materials Combined with Nanotechnology in Rainwater Management

Abstract

In recent years, China has entered a period of rapid urban development, but most of the cities with rapid development still have ground hardening, which makes it difficult for rainwater to penetrate and discharge. In order to achieve the rapid drainage of accumulated water in the city, nanotechnology was introduced, and permeable concrete based on NC and NS nanomaterials was proposed. Combined with finite element analysis, the permeable properties and mechanical properties of permeable concrete mixed with nanomaterials were analyzed. A comprehensive performance analysis of pervious concrete shows that the viscosity of permeable concrete mixed with nanomaterials is significantly higher than that of non-mixed pervious concrete, and the permeability coefficient of permeable concrete mixed with nanomaterials can reach 0.43 cm/s. A finite element analysis shows that the incorporation of nanomaterials can improve the compressive strength of permeable concrete. At the same time, under a rainwater environment simulation, the rainwater retention time of pervious concrete is only 2.35 s. The above results show that the incorporation of nanomaterials into pervious concrete can improve the water permeability of pervious concrete, improve the mechanical properties of pervious concrete, and increase its service life, which is of great significance to urban development and urban management.

1. Introduction

With the continuous development of cities, urban environmental problems have gradually become prominent, and the backwardness of the urban drainage pipe network facilities in cities has led to the problem of flooding on rainy days, which has attracted the attention of the public. In order to improve urban rainwater and flood management, the previous research proposed a new management concept of a sponge city, hoping to improve the water permeability of urban pavement and reduce the urban drainage pressure [1]. However, it is worth noting that the current rainwater and flood management in most sponge cities still finds it difficult to cope with the huge precipitation. Therefore, improving urban water permeability is an important direction of the current urban management development. In the current urban pavement construction, permeable concrete is generally used to drain pavement rainwater into the underground drainage pipeline. In order to reduce urban water accumulation more efficiently and effectively, a large number of studies are underway to explore the preparation plan for permeable concrete [2,3]. With the introduction of nanotechnology, some studies believe that, after adding nano-materials, the pore structure of cement concrete hydration is improved, the number of large pores is reduced, the number of small pores is increased, and the microstructure is more compact, meaning the effective porosity of the permeable concrete is increased, and its permeability coefficient is also increased [4]. According to some studies, compared with traditional concrete, the permeability coefficient of permeable concrete mixed with nanomaterials is improved, and the addition of nanomaterials changes the compressive strength of the permeable concrete, to a certain extent [5]. However, there are few studies on the performance of permeable concrete mixed with nano-materials in application, as well as few studies on the reasonable amount of nano-materials. In this study, taking urban storm flood management as the experimental background, the preparation scheme of permeable concrete based on nano-materials is proposed, and the most reasonable content of nano-materials is analyzed to provide theoretical support for urban storm flood management.

2. Related Work

In urban construction, with the development demand, the application of pervious concrete is gradually becoming widespread, and a large number of scholars have also begun to undertake corresponding research on pervious concrete. Marvin JT analyzes the performance of permeable interlocking concrete pavement from evaluation indicators, such as surface conditions and friction. The test analysis shows that, compared with traditional asphalt pavement, permeable interlocking concrete pavement will not cause any damage in a cold-weather environment. On black ice, pedestrians have a lower risk of slipping and a higher level of safety [6]. Mostafa Razzaghmanesh et al. took the permeable pavement of a parking lot as the research object, collected information such as road runoff and infiltration water quality in the parking lot, analyzed the content of harmful substances in the sample, and used statistical methods to determine that permeable concrete pavement can effectively remove the nitrogen-containing pollutants in rainwater and have a positive effect on urban pollution mitigation [7]. Cai J et al. proposed the use of waste recycling to prepare high-viscosity asphalt concrete and analyzed the water permeability of this asphalt concrete. The results show that the pervious concrete proposed in the study has a relatively significant water permeability, and the road test shows that the concrete has good stability at different temperatures and can be used in a variety of urban environments [8]. Yuan, X.L et al. discussed the application status of concrete permeable bricks in the development of sponge cities, and deeply analyzed the influencing factors of permeable concrete in the production process and the impact of permeable concrete on the urban environment and economic development. The results show that permeable concrete can effectively protect urban groundwater and save the construction cost of urban drainage systems [9]. Braswell AS et al. believe that the penetration effect of permeable concrete needs to be established on high-permeability soils. Therefore, in order to improve the permeable performance of pavement on low-permeability soils, permeable interlocking concrete is used to conduct a pavement drainage effect test. Permeable interlocking concrete can improve the water permeability of permeable concrete pavement on low-permeable soil, help reduce urban pavement pollutants, and effectively improve urban water quality [10].

With the continuous development of nanotechnology, a large number of studies have begun to explore the practical application value of nanotechnology. Z Ding et al. applied nanotechnology to the diagnosis and treatment of oral cancer and believe that the use of nanotechnology to achieve drug delivery during the treatment of patients with oral cancer is of great significance, effectively avoiding fatal side effects during the treatment process; this is of great importance for the improvement of medical diagnosis and treatment [11]. Pa A et al. understood the current status of the application of nanotechnology in the repair of damaged organs and proposed that nanotechnology can show a more significant effect in the repair of hard tissues, such as cartilage and teeth, because the materials in nanotechnology have a multi-faceted structure, and natural tissues have a high similarity [12]. Arezki Y et al. studied the design of optical components and used innovative aspheric and freeform surfaces to design and, at the same time, improve the design accuracy to the nanometer level, to establish a traceable metrology chain for the optical surface of optical components [13]. In order to formulate a more ideal graphite thin film, Qh A et al. proposed a simple and effective method for the fabrication of nanoscale graphite thin films, which mainly reduced the influence of nickel GBs, thereby making the nanometer thickness of the graphite thin films more uniform [14]. Mei M et al. proposed a kind of photoluminescent display, which uses silicon dioxide for encapsulation to reduce the impact on the environment. The results show that the display proposed in the study has more stable color characteristics [15]. Nizina T A et al. proposed a concrete structure containing nanomaterials and set up physical and mechanical performance analysis experiments for the concrete. The results show that, after adding the nano-materials, the concrete has higher toughness and strength [16].

To sum up, in view of the current status of stormwater management in sponge cities, a large number of studies have proposed the effectiveness of permeable concrete, and have verified their conjectures through a large number of experiments. However, most of the experiments that with the acceleration of the urban development process., the permeable concrete material needs to further improve its water permeability. Some studies suggest that nanotechnology can be used to improve material performance, but nanotechnology has not been applied to the preparation of urban pavement concrete in a large number of examples. In this study, nanotechnology was combined to analyze the performance of different nanomaterials when mixed into permeable concrete to provide a reference for urban stormwater management. The research framework is shown in Figure 1.

As shown in Figure 1, the research first calculates the material demand for the permeable concrete, then calculates the mix proportion of each material in the concrete, and then develops the permeable concrete. Finally, the finite element software is selected for the finite element modeling of the permeable concrete, and the concrete performance is simulated based on the model.

There are two innovative points in the study. First, aiming at urban rainwater and flood management, the introduction of nanomaterials into permeable concrete is proposed, and the influence of different contents of nanomaterials on the concrete performance is analyzed. Secondly, in the performance analysis of the permeable concrete, finite element software is used to build the concrete model and evaluate its performance changes.

3. Preparation and Evaluation Method for Permeable Concrete Combined with Nano-Materials

3.1. Experimental Preparation and Preparation Method

Pervious concrete is a porous material, which is composed of aggregate and gel material. The porosity of pervious concrete used in urban pavement construction is between 15% and 25% [17]. In the research on the performance improvement of permeable concrete, it is generally believed that water permeability can be improved by changing the mix ratio of the aggregate and the gel material. However, a large number of studies have found that increasing the water absorption rate of the aggregate will lead to a volume expansion of the concrete at the same time. The cracking phenomenon occurs, and it is found that it is difficult to take into account the concrete quality and water permeability in the existing research [18,19]. Nanotechnology is a science and technology based on many modern advances. It is a technology concerning the properties and applications of materials with a structure size ranging from 1 nm to 100 nm. With the support of nanotechnology, nanomaterials have emerged as the times require. Nanomaterials are special materials at the nanometer level with high toughness and strength. At present, nanomaterials have been applied in many fields. To this end, starting from nanotechnology, it is expected that the small size effect, surface effect, quantum size effect, and macroscopic quantum tunnel effect of nanomaterials can be used to improve the water permeability of traditional permeable concrete.

In this study, nanomaterials are introduced to optimize permeable concrete in urban stormwater management. The nanomaterials include nano-silica and nano-calcium carbonate, of which the content of nano-silica is 98%, and the content of calcium carbonate is greater than 98.5%. In the formulation of pervious concrete, it is necessary to focus on calculating the mix ratio of concrete. In the study, the specific surface area method is used to determine the amount of aggregate and gel material. In the calculation process of the specific surface area method, the aggregate volume is first determined, as shown in Formula (1).

$$V=\frac{{\rho }_0\prime }{{\rho }_0}$$

(1)

In Formula (1), $V$ represents the aggregate volume in the unit volume of the pervious concrete in m³; ${\rho }_0\prime$ represents the close packing density of the pervious concrete in kg/m³; ${\rho }_0$ represents the apparent density in kg/m³. Next, the aggregate particles in the pervious concrete are calculated, as shown in Formula (2).

$$N=\frac{V}{\frac{4}{3}\pi R^3}$$

(2)

In Formula (2), $N$ represents the number of aggregate particles; and $R$ represents the average radius of aggregate particles. After this, the surface area of the pervious concrete aggregate is calculated; see Equation (3).

$$A=N\times 4\pi R^2$$

(3)

Finally, the theoretical porosity of the pervious concrete is determined, as shown in Formula (4).

$$P_t=1-V-V_j$$

(4)

In Formula (4), $V_j$ represents the total volume of the gel material, the thickness of the outer wrapping layer of the gel material. In the preparation process of the pervious concrete, the research determined the preparation and maintenance plan process, as shown in Figure 2.

Figure 2 shows that, in the preparation process of the pervious concrete, the pre-calculated ingredients are mixed according to the cement coating method. In the mixing process, the aggregate is first put in, and then a part of the water is added to pre-wet the coarse aggregate. A portion of the cement is then added, and mixing is continued after the cement is added until the first layer of grout is produced in the mixer. After the first layer of grout is produced, the remaining water and gel materials are poured into the mixer and mixed with the aggregate until the surface of the mixture appears shiny. In the addition of the nanomaterials, in order to avoid particle agglomeration caused by the larger particle-specific surface area of the nanomaterials, nano-calcium carbonate, and nano-silicon dioxide are ultrasonically dispersed. In the addition of nanomaterials to permeable concrete, it is necessary to fill the water and the water-reducing agent according to the ratio, then add the nanomaterials during the stirring process after adding the water-reducing agent, and continue to mix and stir. In the forming and curing of permeable concrete, in order to avoid the peeling of the gel material and aggregate, manual vibrating molding is used in the research to achieve the forming and curing of the permeable concrete combined with nanomaterials. It can be found from the maintenance process that manual vibrating molding requires layered vibrating. In order to avoid the evaporation of water after the layered vibrating, moisture curing was used to shape and cure the test block.

3.2. Finite Element Model of Pervious Concrete Based on Nanomaterials

In urban stormwater management, the permeable capacity of permeable pavement is the key to evaluating its comprehensive performance. For urban development, the mechanical properties of permeable pavement are the basis for its long-term application [20]. In order to understand the performance of nanomaterial-based pervious concrete in application, finite element analysis was used to simulate the overall permeable performance of the pervious concrete.

The finite element analysis is to deconstruct the research object by solving the approximate solution of the boundary value of the partial differential equation, so as to carry out an in-depth calculation of each part of the research object. Pervious concrete pavement is a multi-layer structure, and each layer is composed of different materials [21]. The properties of concrete in different environments are different. With the change in load and external temperature, pervious concrete will show elastic changes. Under a long-term load, the cement in the pervious concrete is affected by carbonization and water loss, resulting in the phenomenon of volume deformation [22]. In the finite element analysis of permeable concrete nanomaterials, the pervious concrete is first identified as an elastic-plastic material, and its numerical analysis model is divided into two levels, according to the permeable concrete paving procedure, to analyze its permeable performance, wherein the surface layer is divided into the upper layer and the lower layer, and the base layer is divided into the base layer and the bottom layer. In the finite element analysis, the elastic and plastic models of the permeable concrete are constructed, and the linear elastic model is used as the material model for analyzing the performance of the pervious concrete. The simulated constitutive equation of the linear elastic model is shown in Equation (5).

$$\sigma =D^{e1}{\epsilon }^{e1}$$

(5)

In Formula (5), $\sigma$ represents the stress component vector; $\sigma$ represents the strain component variable; and ${\epsilon }^{e1}$ represents the elastic matrix. Taking the base layer of the pervious concrete as a linear elastic material, the shear modulus of the model can be calculated by Formula (6).

$$G=\frac{E}{2\times (1+\mu )}$$

(6)

In Formula (6), $E$ represents the elastic modulus of the model, $\mu$ represents the Poisson’s ratio of the model. In addition, the plastic model of the pervious concrete is calculated, and the constitutive equation of its plastic deformation is shown in Equation (7).

$$\sigma \prime =(1-d)E\epsilon$$

(7)

In Formula (7), $d$ represents the plastic deformation variable, and $\epsilon$ represents the plastic strain. The calculation method of the plastic deformation variable in the plastic deformation constitutive equation is shown in Formula (8).

$$d=\left\{\begin{array}{c}1-\frac{\rho n}{n-1+{(\frac{\epsilon }{\epsilon \prime })}^n}\begin{array}{cc}& x\le 1\end{array}\\ 1-\frac{\rho }{\alpha {(\frac{\epsilon }{\epsilon \prime }-1)}^2+\frac{\epsilon }{\epsilon \prime }}\begin{array}{cc}& x>1\end{array}\end{array}\right.$$

(8)

In Formula (8), $\rho$ represents the cement density; $\alpha$ represents the strain curve parameter; and $\epsilon \prime$ represents the compressive peak strain.

Using the finite element model to simulate the structure of permeable concrete pavement, it is necessary to analyze the seepage situation in the pavement. The analysis of the seepage situation in the pavement includes two fluids, liquid and gas, in the concrete pores. The simulation process is shown in Figure 3.

As shown in Figure 3, in the finite element simulation, the saturated infiltration model is first established. Secondly, the pore pressure dissipation is analyzed, and the impermeable layer is set, including the ground and the side. The permeability coefficient can be expressed by Formula (9).

$$K=\frac{\Delta H}{t_2-t_1}$$

(9)

In Formula (9), $\Delta H$ represents the water level difference; $t_1$ and $t_2$ indicate the recording time of the first and second time. The compression coefficient of the concrete is shown in Formula (10).

$$a=\frac{\Delta e}{p_2-p_1}$$

(10)

In Formula (10), $p_2$ represents the stress after compression; $p_1$ represents the stress before compression; and $\Delta e$ represents the void ratio.

4. Performance Test of Permeable Concrete Incorporating Nanomaterials

4.1. Comprehensive Performance Analysis of Pervious Concrete

Good cement has good slurry properties, including viscosity, fluidity, and so on. In the research, nanomaterials were introduced into the preparation of permeable concrete. Therefore, compared with traditional pervious concrete, the performance of the permeable concrete incorporating nanomaterials will change, to a certain extent, so its performance needs to be evaluated. First of all, the viscosity of permeable concrete mixed with nanomaterials is evaluated by using a distributed viscometer. The distributed viscometer is a rotational viscometer, which can evaluate viscosity by analyzing the resistance to the rotor in the cement slurry and evaluating the differences in the viscosity of the pervious concrete with different contents of materials with a change in the rotational speed. The materials included in the analysis included nano-silica, denoted by NS, nano-calcium carbonate, denoted by NC, and silica fume, denoted by SF; see Figure 4.

It can be seen from Figure 4 that the viscosity of the concrete without the addition of the remaining materials showed a decreasing trend with the increase in the rotational speed of the viscometer, and finally decreased to 513 MPa s after the rotational speed reached 140 rad/min. When silica fume is added to the pervious concrete, the viscosity of the concrete is greater than that of the concrete without the material addition, and the viscosity of the concrete shows an increasing trend with the increase in the content of the silica fume material. When nano-silica is added to pervious concrete, the viscosity of the concrete is higher than that of the concrete without the material addition, and, when the silica content is 2.0% and the rotation speed reaches 180 rad/min, its viscosity is as high as 1238 MPa s. The viscosity of the permeable concrete after adding nano-calcium carbonate is also significantly higher than that of the concrete without the material addition, and, with 3.0% content of nano-calcium carbonate, the viscosity of the permeable concrete reaches 1192 when the speed reaches 180 rad/min MPa·s. The above results show that the incorporation of nanomaterials into permeable concrete can improve the viscosity of the concrete and maintain a high viscosity for a long time under an increasing rotational speed. Secondly, the fluidity of the cement paste of the permeable concrete is an important indicator for evaluating the workability of the concrete. Therefore, the change in the fluidity of the cement paste of the permeable concrete is analyzed in the study, as shown in Figure 5.

It can be seen from Figure 5 that, with the increase in the amount of different materials added, the fluidity of the cement paste in the permeable concrete shows a decreasing trend. Increasing the silica fume in the permeable concrete will cause the fluidity of the cement paste to show a decreasing trend with decreasing speed. When the content of silica fume reaches 20%, the fluidity of the cement paste decreases to 251.3 mm. Under the influence of the amount of nano-silica in the permeable concrete, the fluidity of the cement paste showed a decreasing trend, and, after the addition of nano-silica reached 20%, the fluidity of the cement paste decreased to 269.2 mm. When nano-calcium carbonate is added to the permeable concrete, the fluidity of the cement paste is reduced from 327.6 mm to 282.1 mm. The above results show that, with the continuous increase in the incorporation of nanomaterials, the fluidity of the cement will be significantly reduced. However, in the change in the fluidity of the cement slurry, after adding silica fume, the cement slurry keeps decreasing, while the fluidity of the cement slurry, after adding the nanomaterials, shows a certain amount of increase when the mixing amount is less than 1%, indicating that compared with silica fume, nanomaterials can improve the fluidity of cement paste, to a certain extent. Therefore, in the preparation of permeable concrete, adding appropriate nanomaterials helps to improve the fluidity of the concrete. In the performance analysis of the permeable concrete after incorporating the nanomaterials, X-ray diffraction (XRD) was used to analyze the cement paste, as shown in Figure 6.

It can be seen from Figure 6 that, in the cement slurry, the hardened powder includes calcium hydroxide, calcium carbonate, dicalcium silicate, and tricalcium silicate. From the curve changes in Figure 6, it can be seen that, when nano-silica is incorporated, the diffraction peaks of dicalcium silicate and tricalcium silicate in the cement show a decreasing trend compared with that of cement. At the same time, it can be seen that the diffraction peak intensity of the calcium hydroxide in the cement after adding nano-silica also decreases. The reason for the above phenomenon is that the incorporation of nano-silica can accelerate the hydration reaction of cement and increase the consumption rate of dicalcium silicate, tricalcium silicate, and calcium hydroxide. In addition, the diffraction intensity of the calcium hydroxide in the cement paste mixed with nano-calcium carbonate is stronger than that of the cement paste mixed without the material, indicating that nano-calcium carbonate cannot accelerate the consumption of calcium hydroxide, but it accelerates the hydration reaction and promotes the gradual increase in the crystallinity of the calcium hydroxide. When nano-silica and nano-calcium carbonate are mixed at the same time, the diffraction peak of the calcium hydroxide in the cement slurry decreases, indicating that the consumption rate of the calcium hydroxide increases at this time. The hydration reaction in the cement reduction is hindered, and the crystallinity of the cement paste after hydration is reduced. The water permeability of the pervious concrete in application is the key to ensure its effect in urban stormwater management. In this study, the permeability coefficient of permeable concrete under different nanomaterial dosages was analyzed, as shown in

Table 1. Difference of permeability coefficient of pervious concrete.

Experiment No	Nano-Silica	Nano-Calcium Carbonate	Silica Fume	Permeability Coefficient (cm/s)
1	1%	/	/	0.33
2	1.5%	/	/	0.39
3	/	1%	/	0.38
4	/	1.5%	/	0.42
5	/	/	5%	0.29
6	/	/	8%	0.34
7	/	/	10%	0.31
8	1.5%	1.5%	8%	0.43

.

It can be seen from Table 1 that the permeability coefficient of the pervious concrete without any material is 0.36 cm/s, and the permeability coefficient of the pervious concrete after only adding 1.5% of nano-silica is 0.39 cm/s. The permeability coefficient of the pervious concrete is 0.42 cm/s when 1.5% of nano-calcium carbonate is added, and the permeability coefficient of the pervious concrete when only 10% silica fume is added is 0.31 cm/s. When 1.5% nano-silica, 1.5% nano-calcium carbonate, and 8% silica fume are added at the same time, the permeability coefficient of pervious concrete is the highest, reaching 0.43 cm/s. These results show that adding appropriate nanomaterials can improve the permeability coefficient of pervious concrete.

4.2. Finite Element Analysis of Permeable Concrete Mixed with Nanomaterials

In the study, finite element analysis was introduced to analyze the structure of permeable concrete mixed with nanomaterials. ABAQUS 6.14 finite element software was selected to build the material model. During the calculation of soil volume, the mesh of the finite element is fixed on the skeleton of the soil structure. The gas and liquid phases can flow freely through the mesh. The flow of the gas and liquid phases must meet the continuous equation. The saturated infiltration model is established, and the same step size and asymmetric matrix storage are used. During the whole consolidation process, the permeability coefficient and compression coefficient of the soil are constant, and the compression and consolidation of the soil only occur in the vertical direction. First, the compressive strength changes in concrete mixed with nanomaterials and silica fume were analyzed, as shown in Figure 7.

It can be seen from Figure 7 that, with the increase in the content of the added material, the compressive strength of the pervious concrete shows a trend of first increasing, and then decreasing. In the blank group, the pervious concrete was not mixed with any material, and its compressive strength remained at 16.3 MPa. When silica fume is added to permeable concrete, its compressive strength shows an increasing trend in the early stage. When the content of silica fume exceeds 4%, the compressive strength of the concrete shows a decreasing trend, and finally decreases to below 15.0 MPa. After adding nanomaterials silica fume, the compressive strength of the concrete was evaluated. The results showed that the compressive strength of permeable concrete reached the maximum value when the content of nanomaterials was 2% and the content of silica fume was 4%. The compressive strength value at this time was 19.6 MPa. The above results show that the incorporation of nanomaterials can improve the compressive strength of pervious concrete under specific content conditions. In order to gain an in-depth understanding of the specific effects of the addition amount of nanomaterials on the compressive strength of permeable concrete, differential multiple comparisons were used, as shown in

Table 2. Difference multiple comparison.

Content (%)	Nano-Silica/Nano-Calcium Carbonate	Average Difference	Standard Error	Sig.	95% CI
1	2	0.189	0.283	0.504	[−0.405, 0.783]
	3	1.726	0.283	0	[1.135, 2.323]
2	1	−0.189	0.283	0.504	[−0.783, 0.405]
	3	1.529	0.283	0	[0.929, 2.131]
3	1	−1.726	0.283	0	[−2.323, −1.135]
	2	−1.529	0.283	0	[−2.131, 0.929]

.

As can be seen in Table 2, when the dosage of nanomaterials is 1% and 2%, the significance test shows that the ratio of nano-silica and nano-calcium carbonate has different effects on the pervious concrete. It can be seen that the ratio of nano-silica and nano-calcium carbonate in the nanomaterials will affect the compressive strength of the permeable concrete. When the content of the nanomaterials is 3%, nanomaterials will lead to changes in the compressive strength of the permeable concrete; that is, the content of 3% of nanomaterials will have a very significant impact on the compressive strength of the pervious concrete. After the compressive strength of the pervious concrete was analyzed, the correlation between the compressive strength of the pervious concrete and its mass loss rate was evaluated, as shown in Figure 8.

It can be seen from Figure 8 that, with the continuous increase of the compressive strength of concrete, its mass loss rate shows a decreasing trend, showing that the wear rate of the permeable concrete gradually decreases. From the correlation analysis in Figure 8 it can be found that, when the compressive strength of pervious concrete is 19.6 MPa, the mass loss rate of the pervious concrete is 2.1%. Therefore, it can be seen that when the nanomaterial content is 2% and the silica fume content is 4%, the concrete mass loss rate is 2.1%. Finally, the pore water pressure of the permeable concrete incorporating nanomaterials was analyzed, as shown in Figure 9.

It can be seen from Figure 9 that the pore pressure of the permeable concrete mixed with nanomaterials shows, first a trend of increasing, then decreasing, and then increasing again, and it can be seen that the pore water pressure of the concrete surface layer is higher than the pore water pressure of the concrete base layer. From the change in the pore water pressure of the pervious concrete, it can be seen that the pore water pressure of the concrete in the simulation begins to drop to a negative value after 1.95 s, indicating that the retention time of rainwater on the surface of permeable concrete mixed with nanomaterials is 1.97 s. After that, with the increase in time, the pore water pressure of the concrete gradually, and, at 2.35 s, the pore water pressure approached 0. Therefore, the above results show that, in a rainfall environment, the retention time of rainwater on the surface of the permeable concrete mixed with nanomaterials is only 1.95 s, and the total retention time of rainwater in the pervious concrete is only 2.35 s. Finally, the cubic meter consumption of a material according to the mix ratios in concrete is shown in

Table 3. Cubic meter consumption of materials.

Material Science	Coarse Aggregate	Cement	Fly Ash	Water	Water-Reducing Agent	NC	NS
Consumption (kg/m3)	1548.4	366.3	29.6	111.2	5.5	11.1	11.1

.

The internal structure of the permeable concrete obtained after consolidation is shown in Figure 10.

5. Conclusions

Stormwater management in urban development is an important evaluation index that reflects the comprehensive strength of a city, and it is also the key to the healthy development of a city. In order to improve the ability of urban stormwater management, the research takes urban permeable concrete pavement as the research object, proposes a preparation scheme of urban permeable concrete combined with nanotechnology, and uses finite element analysis and simulation to determine its performance. The results show that, in the preparation of permeable concrete, there are significant differences in the viscosity and fluidity of the permeable concrete mixed with different contents of nanomaterials, and the hydration reaction of the permeable concrete differs in an XRD analysis of the effect of the addition of different nanomaterials. When adding nano-calcium carbonate, the crystallinity of the concrete is higher. Finally, through experiments, it was found that, when the contents of nano-silica, nano-calcium carbonate, and silica fume were 1.5%, 1.5%, and 8%, respectively, the water permeability of the concrete was the highest, reaching 0.43 cm/s. The finite element analysis shows that the compressive strength of the permeable concrete when the nanomaterial content is 2% and the silica fume content is 4% reaches 19.6 MPa. Under the compressive strength of MPa, the mass loss rate of the pervious concrete is reduced to 2.1%. Finally, the rainwater infiltration simulation of the pervious concrete shows that, as the simulation progresses, the water accumulation time on the concrete is only 2.35 s. The above results show that, in the preparation of urban permeable concrete, adding appropriate nanomaterials can improve the comprehensive performance of the concrete, improve the permeability coefficient of the pervious concrete, increase its infiltration effect on rainwater, and, at the same time, improve the mechanical properties of pervious concrete and increase its service life. This is of great value in the development of urban stormwater management.