Showing papers on "Pervious concrete published in 2008"

Hydrologic Comparison of Four Types of Permeable Pavement and Standard Asphalt in Eastern North Carolina

Abstract: A permeable pavement parking lot in eastern North Carolina consisting of four types of permeable pavement and standard asphalt was monitored from June 2006 to July 2007 for hydrologic differences in pavement surface runoff volumes, total outflow volumes, peak flow rates, and time to peak. The four permeable sections were pervious concrete (PC), two types of permeable interlocking concrete pavement (PICP) with small-sized aggregate in the joints and having 12.9% (PICP1) and 8.5% (PICP2) open surface area, and concrete grid pavers (CGP) filled with sand. The site was located in poorly drained soils, and all permeable sections were underlain by a crushed stone base layer with a perforated underdrain. All permeable pavements significantly and substantially reduced surface runoff volumes and peak flow rates from those of asphalt (p

Pervious Concrete Mixture Proportions for Improved Freeze-Thaw Durability

Abstract: Recent stormwater management regulations from the Environmental Protection Agency (EPA) and greater emphasis on sustainable development has increased interest in pervious pavement as a method for reducing stormwater runoff and improving stormwater quality. Pervious concrete is one of several pervious pavement systems that can be used to reduce stormwater runoff and treat stormwater on site. Pervious concrete systems have been used and are being proposed for all parts of the United States, including northern climates where severe freezing and thawing can occur. The purpose of the research is to develop pervious concrete mixtures that have sufficient porosity for stormwater infiltration along with desirable porosity, strength, and freeze-thaw durability. In this research, concrete mixtures were developed with single-sized river gravel aggregate (4.75 mm) and constant binder contents, together with high range water reducer. River sand was used as a replacement for up to 7 % coarse aggregate. Two different types of polypropylene fibers (a shorter fibrillated variable-length and a longer fibrillated single-length) were incorporated at several addition rates from 0 to 0.1 % by volume of concrete. The engineering properties of the aggregate were evaluated along with the porosity, permeability, strength, and freeze-thaw durability of selected concrete mixtures. The results indicate that the use of sand and fibers provided beneficial effects on pervious concrete properties, including increased strength, maintained or improved permeability, and enhanced freeze-thaw resistance.

Salt Weathering Distress on Concrete Exposed to Sodium Sulfate Environment

Abstract: Salt weathering or physical salt attack is known to be exhibited by rocks and stone monuments under certain environmental exposure conditions. Ordinary porous concrete exposed to sodium sulfate-containing soils has exhibited a similar phenomenon. Past researchers overlooked this type of physical attack on concrete, instead focusing on potentially far more harmful chemical sulfate attack. This paper's research investigation's primary focus is physical attack. A low C sub 3 A concrete mixture was made for physical attack promotion which contained ASTM Type II portland cement with a 0.65 water cement ratio. Cylindrical concrete specimens were, after curing, partially submerged for periods of up to 3.1 years in a 5% sodium sulfate solution. The humidity and temperature cycles the tests were conducted under simulated various ambient conditions, one of which promoted alternative mirabilite and thenardite conversion cycles. Overall, that significant scaling occurred when concrete was subjected to numerous thenardite-mirabilite conversion cycles and that concrete scaling occurred at directly above the solution level evaporation surfaces were indicated by the results.

Design and Calibration of a Large Open-Ended Coaxial Probe for the Measurement of the Dielectric Properties of Concrete

Abstract: The subject of this paper is the design and calibration of an open-ended coaxial probe for the nondestructive measurement of the dielectric properties of concrete. Measurements are made between 100-900 MHz, frequencies which are often used in geophysics and civil engineering for ground penetrating radar inspection. The probe is calibrated using measurements on saline solutions in conjunction with three different mathematical techniques for comparative study. Measurements of mortar and concrete specimens having different water/cement ratios were made in order to observe the standard deviations due to their heterogeneous nature. Similar to the case of relatively homogeneous rock specimens (limestone and granite), the standard deviation for heterogeneous concrete samples do not exceed 5%. In addition, the effect of the concrete's porosity on its dielectric properties was clearly observed: measured permittivity between 4-4.5 at 900 MHz for porous concrete, and between 6.5-7.5 at 900 MHz for dense concrete.

Virtual Pervious Concrete: Microstructure, Percolation, and Permeability

Abstract: As the dramatic increase in pervious concrete usage continues, a better understanding of microstructure, durability, and transport property linkages will assist suppliers with mixture design and properties. Various virtual pervious concrete microstructural models are presented in this paper, and their computed transport properties and percolation characteristics are compared to real world pervious concretes. Of the various virtual pervious concretes the study explores, a correlation filter three-dimensional reconstruction algorithm-based one clearly provided a void structure closest to what is achieved in real pervious concretes. Durability issue extensions, such as clogging and freezing-and-thawing persistance, that use further virtual pervious concrete void structure analysis are introduced.

Water permeable concrete and pavement construction method

Abstract: The invention discloses permeable concrete and a pavement construction method. The permeable concrete comprises the following components: 1350 to 1800 parts of broken stones, 90 to 150 parts of water, 300 to 350 parts of cement, 10 to 70 parts of mineral powder, 10 to 70 parts of silicon ash and 0.3 to 7 parts of water reducing agent; if necessary, organic intensifying agent can be added. The construction method comprises the following steps: permeable concrete is mixed, poured and cured, an expansion joint is cut, and the filling and the other processes are performed. Concrete pavement prepared by the method has higher strength and water permeability, and the compression strength can reach or exceed 30 MPa; the flexural strength is above 4 MPa; the coefficient of water permeability is more than or equal to 1 mm/s; the requirements for the permeable concrete pavement can be fully satisfied. The permeable concrete is suitable for the construction of permeable concrete pavement, squares and parking lots; by adopting the method, the consumption of cement is small, the construction is simple, and the method is favorable for being popularized.

Healing effectiveness of cracks rehabilitation in reinforced concrete using electrodeposition method

Abstract: An electrodeposition method and its experimental device for rehabilitation of cracks in reinforced concrete were proposed. Porous concrete is proposed to simulate cracked concrete, and mass increment, permeation coefficient and sound velocity of ultrasonic wave were used to be evaluating indicators of healing effectiveness of crack rehabilitation in this method. Effect of currency density, concentration of electrolyte solution on healing effectiveness of porous reinforced concretes with different total void ratio was studied. The experimental results indicate that the simulation of porous concrete for cracks can reflect the healing effectiveness of electrodeposition method effectively. Total void ratio of porous concrete has little effect on healing effectiveness of electrodeposition at early ages. The higher the currency density or concentration of electrolyte solution is, the higher the electrodeposition rate and sound velocity in porous concrete are, and the lower the permeation coefficient of porous concrete will be. Mg(OH)2 crystals produced in high current density are large, thin sheet-shaped and arranged loosely.

Advancements in pervious concrete technology

Abstract: Pervious concrete has been used for many years in the southern United States but only recently have stormwater mandates implemented by the United States (U.S.) Environmental Protection Agency (EPA) created interest for more wide-spread installations, especially in freeze-thaw climates. Validation of the freeze-thaw durability of pervious concrete under the most extreme conditions created an opportunity to explore many additional aspects of pervious concrete and to improve durability through additional mixture characterization and new construction practices. While the material components are similar to conventional concrete, the idiosyncratic behavior of pervious concrete requires revaluating material effects and relationships. Many different factors influence the performance of conventional concrete and many different factors also affect pervious concrete, although limited data exist to support observed and expected responses. The most crucial factors include the specific effect on freeze-thaw durability caused by the coarse aggregate type. Since the volume of paste in a pervious concrete system is much less than traditional concrete and exposure conditions much more severe, aggregate durability criteria must be determined for this specific application. The more extreme exposure conditions also require investigating the effect of air entrainment on the concrete mortar. Air entrainment improves freeze-thaw durability in conventional concrete, but to date has yet to be evaluated in pervious concrete. In addition to mixture properties, construction practices must be modified to suit pervious concrete. While the workability of conventional concrete can be simply checked using a standard slump cone, no method currently exists to determine the workability of pervious concrete. However, workability of pervious concrete influences the ease of placement and density, which also controls the yield and ultimate durability. Determining pervious concrete workability will allow more consistency between placements and help quantify the effect various mixture components have on the fresh mixture behavior. Due to it’s very low water-to-cement ratio (~0.30) curing of pervious concrete is particularly important. Pervious concrete is currently cured under plastic instead of using a conventional curing compound. No research has previously been performed to evaluate the effect various common curing methods have on strength and durability. By

Experimental study on rainfall-runoff relation for porous pavements

Abstract: Impervious surfaces have long been implicated in the decline of watershed integrity in urban and urbanizing areas. Porous pavement is one solution to mitigating the problem of stormwater runoff problems. In this research, three available porous pavement systems were investigated to evaluate their infiltration capability of precipitation. Experiments were conducted to simulate different kinds of porous pavements having different sub-base materials in different cells. The discharge volumes were monitored from each cell, and the relationship between rainfall intensity, outflow and outflow duration was analyzed. Results show that these three porous pavements increased infiltration and decreased runoff. The optimum thickness of the porous pavement was 31 cm, which consisted of a 6 cm top layer of porous concrete and a 25 cm sub-base (10 cm concrete without sand and 15 cm aggregate base). Furthermore, under a rainfall rate of 59.36 mm/h, the runoff coefficient of the above porous pavement was zero, while the coefficient of the impervious pavement was 0.85. These results provide a clear indication of the value of porous pavement systems for broad expanses of the human engineered environment.

The aggregate gradation for the porous concrete pervious road base material

Abstract: The effects of the proportion of fine aggregate, the maximum size of the aggregate and the proportion of the 9.5 mm to 4.75 mm particle in the coarse aggregate on the properties of the porous concrete are investigated. Results indicate that the porous concrete with a cement dosage only 150 kg/m3 has high strength and satisfying permeability when the aggregate has a passing percentage of 4.75 mm around 10% to 15%, with the increase of the maximum size of the aggregate, the strength of the porous concrete decreases and the permeability increases. When the proportion of the 9.5 mm to 4.75 mm particle in the coarse aggregate is about 20%, there are no interference among the particles by Weymouth theory, the strength of the pervious porous concrete reaches the peak value. The optimum continues gradation limit of the aggregate for porous concrete pervious road base material is recommended according to the theoretical calculation and experimental results.

Winter performance assessment of permeable pavements: A comparative study of porous asphalt, pervious concrete, and conventional asphalt in a northern climate

Abstract: WINTER PERFORMANCE OF PERMEABLE PAVEMENTS by Kristopher M. Houle University of New Hampshire, September 2008 This study presents the findings from two active parking lots constructed of permeable pavements: porous asphalt and pervious concrete. Focus is given to the performance of these pavements in a cold-climate setting. Winter places great demands on pavements so it is of particular interest to evaluate how they compare to conventional designs. Analyses include measurements of frost penetration, surface infiltration rates, snow and ice cover, skid resistance, chloride retention, and effective salt loads. Infiltration rates were retained in winter conditions and with frost depths as high as 27inches. A 75% average reduction in annual salt use was observed for porous asphalt • based on low amounts of snow and ice cover and high skid resistance. 'Black-ice' did not form on pervious concrete, eliminating the need for salt during thawing-refreezing conditions. Pavement color and shading were found to be major factors influencing the amount and duration of snow/ice cover. A comparison of project costs is discussed.

A Novel Approach to Characterize Entrained Air Content in Pervious Concrete

Abstract: The current pervious concrete placed in cold climates generally contains air entrainment but, unlike traditional concrete, the evaluation of entrained air is not performed This paper presents results from a study that characterized the entrained air voids in pervious concrete using a RapidAir system The RapidAir system is an automatic device that determines the air void properties of hardened concrete according to ASTM C457, “Standard Test Method for Microscopical Determination of Parameters of the Air-Void System in Hardened Concrete” Two types of aggregates, ie, crushed limestone and rounded river gravel (pea gravel), and two types of air entraining agents, ie, natural and synthetic, were used The air entrainment dosage rates varied from zero to double the manufacturer’s recommended dosage Compressive strength, tensile strength, and freeze-thaw durability (ASTM C666A) of the pervious concrete were tested The results show that use of air entrainment improves workability of pervious concrete, thus reducing the overall porosity and increasing unit weight of the pervious concrete The strength and freeze-thaw durability also increases with the level of entrained air in pervious concrete

Water permeable concrete and manufacturing method thereof

Abstract: The invention discloses a pervious concrete and is characterized in that the pervious concrete is made by mixing cement, aggregate, water, water reducer agent and adhesive evenly; and the cement, the aggregate, the water, the water reducer agent and the adhesive are mixed in different weight proportions of 1-1.2 to 5.5-8.5 to 0.2-0.5 to 0.01-0.2 to 0.01-0.2. The invention can solve the natural ecology problems of hardened ground in cities, atmospheric circulation as well as soil and water moisture retention, thereby forming a high-quality natural ecology environment and maintaining urban ecological balance. The pervious concrete consists of two pervious surface courses and two macadam bases in different particles so as to provide a water storage structure which can store the water until the water penetrates into the soil; meanwhile, the invention can be made into building block, which can be provided with different decorative patterns and colors on the surface, and has the advantages of artistic quality, water permeability, good water retention, skid resistance, high strength, cold resistance and weather resistance, etc.

Evaluation and Optimization of Durable Pervious Concrete for Use in Urban Areas

Abstract: Although pervious concrete was first used in the nineteenth century, it has only recently begun to increase in popularity. As urban areas expand, the problems associated with runoff management have become more challenging. The focus on the negative environmental effects associated with pavement runoff has also increased. These two issues have spurred the recent interest in pervious concrete pavements; pervious concrete, however, has deficiencies which limit its application as pavements. These limitations include low compressive strength, flexural strength, clogging, and other durability issues. The overall purpose of this project was to provide tools to evaluate and improve the durability and strength of pervious concrete such that it may be more confidently employed in urban roadways. The specific objectives of this project were to (a) investigate the effect of mixture design on strength of pervious concrete (including the effect of fibers), (b) evaluate effect of clogging materials on coefficient of permeability, (c) and investigate the use of the dynamic pressurization test to evaluate the durability of pervious concrete. This report documents the results of the laboratory testing, and presents recommendations for mixture proportioning. In addition, recommendations are provided for optimizing the balance between compressive strength and permeability.

Colorful water permeable concrete pavement and construction technique

Abstract: The invention relates to a chromatic pervious concrete pavement material and a construction process thereof, which is characterized in that the formulation of a special concrete binding agent comprises 85 to 92 percents of cement (weight), 5 to 10 percents of silicon ash, and rubber powder, early strength admixture, water reducing agent and paint. The ash collection ratio is 4.0 to 6.0; the water cement ratio is 0.30 to 0.40; dry power shaped binding agent, aggregate and water are added in a concrete agitator according to the blending ratio so as to be churned into a mixture with uniform and proper dryness and humidity, which is then is used for paving and construction after being flattened; a low frequency flat oscillator is used for vibrating, compacting and leveling on the surface; the water is poured for maintenance; oily crylic acid resin is taken as mat coat agent to ensure that the color of the pavement is fresh. The chromatic pervious concrete pavement material and the construction process thereof have the advantages that steel-making industrial waste residue is adopted as the aggregate to change waste into valuables; the problem of low strength of the non-sand water permeability concrete material with a plurality of holes is solved by lower cost; compared with the high molecule permeable material, the cost is low, the strength is high, and the ageing resistance is good; compared with the sintering ceramics permeable material, the cost is low, the energy consumption is reduced, and the permeability effect is strong.

Pervious Concrete in Severe Exposures

Abstract: Porous pavement, especially portland cement pervious concrete (PCPC), helps control pollution discharge by allowing rainwater to rapidly infiltrate into an open-graded aggregate subbase and into the ground. Hydrocarbons become attached to the large surface area of the PCPC or the aggregate subbase and are reduced by natural attenuation, either through evaporation or biological degradation. PCPC also mechanically filters out larger pieces of metal or biological material for later collection during routine maintenance. Thus, the majority of first-flush pollutants are removed by the pervious concrete system, preventing the pollutants from entering stormwater collectors and being conveyed to local surface waters. By allowing stormwater to naturally percolate into the soil, PCPC can also reduce or eliminate the need for stormwater retention areas and the infrastructure required to convey the water. This article provides a summary of the authors' work in this area that focused on the durability of PCPC subjected to freeze/thaw cycles.

Concrete perforated brick and manufacturing method thereof

Abstract: The invention discloses a porous concrete brick which is made from macadam with a particle size of 5-10 mm as coarse aggregate, sand with a modulus of 3.7-1.6 or stone dust and coal ash as fine aggregates, cement as binder, and silica sol and montmorillonite as modifiers. The weight percentages of the components are as follows: macadam 25-40%, sand or stone dust 15-25%, coal ash 15-25%, cement 15-20%, silica sol 2-5%, and montmorillonite 5-10%. The porous concrete brick is produced by mixing macadam, sand or stone dust, coal ash and montmorillonite at the given ratio to obtain a mixture A; mixing silica sol with water at the given ratio to obtain a liquid B; adding the liquid B into the mixture A and stirring; adding cement and water; stirring; extrusion molding; and curing to obtain the final product of porous concrete brick. With the above technical proposal, the strength and heat-insulating property of the porous concrete brick are improved and the shrinkage rate of the porous concrete brick is reduced.

A model for reactive porous transport during re-wetting of hardened concrete

Abstract: A mathematical model is developed that captures the transport of liquid water in hardened concrete, as well as the chemical reactions that occur between the imbibed water and the residual calcium silicate compounds residing in the porous concrete matrix. The main hypothesis in this model is that the reaction product -- calcium silicate hydrate gel -- clogs the pores within the concrete thereby hindering water transport. Numerical simulations are employed to determine the sensitivity of the model solution to changes in various physical parameters, and compare to experimental results available in the literature.

Portland Cement Pervious Concrete: A Field Experience from Sioux City

Abstract: Portland Cement Pervious Concrete (PCPC) is becoming more utilized across the U.S. due to increased re- quirements for stormwater management. This paper details the experience of the installation of a PCPC test sec- tion/parking area in Sioux City, Iowa. In order to evaluate a large number of mixture designs, the test section incorporated five different mixtures, each placed with and without air entraining agent, for a total of ten sections. Cylinder samples were prepared during construction and compared with core data. The samples were tested for void ratio, permeability, unit weight, compressive strength development with time, and spatial distribution of material properties across the pavement profile. The results show a high degree of variability in material properties between the top and bottom layers, especially in the bottom five cm (two in.). Strong relationships between unit weight, permeability, strength, and void ratio suggest that void ratio criteria determined from unit weight testing has the potential for use as QA/QC criteria for pervious con- crete field placement.

Preliminary Field Testing: Urban Heat Island Impacts and Pervious Concrete

Abstract: This paper will discuss how the Urban Heat Island (UHI) effect is a phenomenon where the air temperature surrounding an urban, or metropolitan area, is significantly higher than surrounding areas This negatively impacts energy use, human comfort, plant growth and water usage among other things There are many factors contributing to UHI, but the foci of this discussion are the differences in thermal properties of pavement construction materials Significant volumes of construction materials such as concrete, asphalt and steel have high thermal bulk properties, in addition to having different surface radiation properties Simply put, these materials can absorb, transfer and store more energy than rural landscapes Due to its open pore structure, pervious concrete may offer insulation benefits over normal paving materials in this regard Pervious concrete may help reduce the local effects of UHI in several ways, two of which are studied here First, pervious concrete has a relatively light color with a higher solar reflectance, or albedo, than darker pavements such as asphalt, although it may have a darker color or lower albedo due to mix characteristics and its uneven surface when compared to some other concretes Secondly, the open pore structure means pervious concrete may be less efficient at storing and transferring heat than other typical paving materials Therefore, pervious concrete may transfer less heat to the ground below than many paving materials This research focuses on preliminary, initial investigations into the albedo and thermal conductivity properties of pervious concrete relative to standard concrete and asphalt pavement It was found that the surface temperatures of pervious concrete as measured with a thermal gun were higher than similar traditional concrete pavement It was also found that pervious concrete with its open pore structure does indeed offer thermal insulation benefits with respect to heat transfer to the ground below

Permeable concrete, thin layer paving composition, and manufacturing method color concrete

Abstract: Permeable asphalt concrete is provided to allow vehicles and people passing through within 1~2 hours after pavement and to have excellent strength and durability, a thin layer paving composition is provided to be water soluble, to put in various colors easily, to have excellent adhesive property with a road surface and to shorten the curing hour by hardening rapidly, and a construction method of pavement with colored patterns using the permeable asphalt concrete and the thin layer paving composition is provided to maintain the water permeability of the permeable asphalt concrete and permeable concrete surface to the maximum and to heighten aesthetic effects by having various colors and patterns. A water soluble thin layer paving composition comprises 20~50 weight percent urethane acryl aqueous emulsion, 5~15 weight percent water, 30~60 weight percent calcium carbonate, 5~20 weight percent inorganic pigments, and 1~10 weight percent filler selected from fumed silica, dolomite, silica, calcium carbonate, glass bead and ceramic aggregate. Permeable asphalt concrete having excellent bond strength in comparison with asphalt concrete comprises 3~6 weight percent asphalt, 0.1~1.0 weight percent styrene resins, 0.1~1.0 weight percent rheology modifiers including one or more thermoplastic resins selected from linear low density polyethylene, low density polyethylene, high density polyethylene, ethylene vinyl acetate copolymer resins and poly acrylate, 0.1~0.5 weight percent fiber reinforcement and 0.1~10 weight percent additives including one or more materials selected from calcium chloride, bentonite, sodium gluconate, lignin and resin, per 100 weight percent aggregate composed of 50~80 weight percent coarse aggregate, 15~40 weight percent fine aggregate and 5~10 weight percent filler. A construction method of pavement with colored patterns using permeable asphalt concrete and a thin layer paving composition comprises the steps of: spreading permeable concrete or permeable asphalt concrete; covering stencil paper having various patterns on the upper part of the permeable concrete or permeable asphalt concrete; applying a water soluble thin layer paving composition on the stencil paper; and removing the stencil paper.

Filter Element for Water Loaded with Solid Particles and Dissolved Toxic Substances and Purification System Equipped with Said Filter Element Test System for Portable Analyzer

Abstract: The invention relates to a filter element consisting of a molded body of porous concrete, which element is arranged in the water stream of a purification system. In particular, the filter element ( 10 ) is a molded pervious concrete layer arranged as a partition between a lower compartment ( 9 ) and an upper compartment ( 11 ) of a treatment chamber ( 8 ), wherein the water inlet ( 12 ) opens into the lower compartment ( 9 ) and a water outlet ( 17 ) issues from the upper compartment ( 11 ). The pervious concrete filter layer may contain one or more additives to enhance adsorption of pollutants, such as heavy metal ions, phosphorous, hydrocarbons or other target soluble pollutants.

Method for preparing vegetation form cellular concrete

Abstract: The invention provides a method for preparing vegetation form porous concrete, adopting the 'pre-coating' technology, a slurry body with specific compositions coats coarse aggregates to form a sphere with a relatively uniform particle diameter, based on the physical coacervation of the sphere and the agglutination of the surface slurry body of the sphere; and the porous and macroporous structure, the cementation between solid phases of which is good and gas phases of which are communicated, is formed. The method comprises the concrete preparation steps that: (1) the fluidity and the viscosity range of the slurry body used to coat the aggregates are determined, and the mixing ratio is worked out by an absolute volume method; (2) the four-step stirring working procedure and the shaping model of the combination of the vibration and the pressuring are adopted; and (3) hole spaces are subjected to alkali-sealing treatment. The invention solves the difficult problems existing in the prior method that because of the downflow of the slurry body, the distribution of the pore spaces is not uniform and the discontinuous pore spaces increase, and the alkalinity in concrete pore spaces is relatively high, which are adverse to the growth of plants. When the vegetation form porous concrete prepared by the method of the invention is applied to road shoulder separator inserts, construction roofs, protection banks and protection slopes and parking lots of a highway, and good landscape effects and ecological environmental protection significance are achieved.

Experimental Study on Pervious Concrete

Abstract: Due to its excellent air and water permeability, pervious concrete has become an environmental friendly material in paving application, providing its benefits in reducing the runoff water, enhancing pavement skid resistance by rapid drainage of water, and reducing pavement noise. However, its high porosity and low strength limit its popularity. Based on the concept of pervious concrete, a mix design approach especially for pervious concrete was proposed and an experimental study was undertaken to produce high performance pervious concrete by using gap-graded coarse aggregates and adjusting cement content. The results indicated that pervious concrete with compressive strength up to 33.5 MPa and permeability coefficient of 6 ml/min can be obtained by using this mix design approach. The results also showed that for pervious concrete made with gap-graded aggregates, the strength increases, and the permeability coefficient decreases with the decrease of the aggregate size. There is an optimum content of cement used to coat the coarse aggregates, enhancing the cement-aggregate interface bonding and overall performance of pervious concrete.