透水混凝土是水泥、水和粗集料的混合物，几乎没有沙子. 它还经常含有化学外加剂. 透水混凝土创造了一个非常多孔的介质，允许水排到下面的土壤中. It is commonly produced to allow as much as five gal/ft²/min to pass through the body of the concrete.
通过允许降雨渗透路面到下层土壤, 铺好的地面的第一次平铺在现场. 该地区的自然渗透保持不变，因此水可以补充地下水位. This avoids surface runoff that must be held in detention ponds or added to the storm water surface runoff, 在它返回到本地流之前必须处理哪些. In many cases the pavement may also be designed with a layer of coarse granular material below the pavement to increase the storage potential of the system. This has proven to be an effective tool to increase the area of usable pavement on a project as well as satisfy local water management regulations.
透水混凝土在中国的一些地区已经使用了几十年. However recent interest in sustainable development and recognition of pervious pavements by the United States Environmental Protection Agency (EPA) as a best management practice for storm water management has heightened interest in its use. Its use supports national initiatives such as EPA’s Heat Island Reduction Initiative and Low Impact Development and provides a potential for credit in the 领导能源和环境设计 (LEED®) rating system for sustainable building construction.
透水混凝土可以通过吸收地表径流的“第一次冲刷”来改善水质, 降低接收水域的温升, increase base flow, and reduce flooding potential. 路面产生了降雨的短期储存滞留. 为了充分利用这些好处, 必须对透水混凝土系统的水文特性进行评估. The hydrological performance is usually a key parameter in decisions to use this material as a best management practice (BMP) for storm water management and is the characteristic of most interest to permit-granting agencies.
Passive and Active Mitigation Systems
In many situations, the using pervious concrete to replace an impervious surface may be considered a sufficient regulatory standard to manage runoff. In others , the regulations may require that runoff after development not exceed that or a percentage of of runoff prior to development. 这两个应用程序分别称为被动缓解和主动缓解. In the latter case, the pervious concrete pavement system must be designed specifically to handle much more rainfall than that which will fall on the pavement itself. For example, a parking lot can be used to capture excess runoff from rain falling both on itself and on surrounding areas, including, 雨水汇集并通过附近建筑物屋顶的排水沟排出.
A “passive” mitigation element is used only to reduce the quantity of impervious surface in a given area by replacing impervious surface with pervious surface. 一个被动的缓解因素可能也会得到很多好处, if not all, of the “first flush,提供额外的水文效益, 但不打算容纳来自相邻表面的多余径流.
An “active” mitigation system, on the other hand, is designed to maintain total runoff at some specified level for a particular site with several types of features. Pervious concrete used in an active mitigation system must capture a sizeable portion of the runoff from other areas on site as well as rain falling on its own “footprint.” Typically, such areas include buildings, 用传统路面铺筑的地区, and traffic islands and buffer zones. Active mitigation systems are particularly well suited to rehabilitating existing impervious areas for remedial control of urban runoff since they can be designed to capture runoff from adjacent areas. Depending on the size, geometry, 透水混凝土体系的孔隙率, 该场地的多余地表径流可以保持在或恢复到开发前的水平. Active pervious concrete pavement systems can also be designed as boundary features used in conjunction with conventional pavement to create a locally active, but site wide passive feature.
Figure 1. 在这个停车场的透水混凝土部分(芬利体育场, Chattanooga, Tennessee) help control runoff. (Photo courtesy of L. Tiefenthaler.)
For example, 一个透水混凝土系统可以被设计来捕捉和临时存储大量的数据, if not all, of the runoff from a conventionally paved parking area by placing a relatively narrow strip of pervious concrete over a deep, 清洁的石头基地沿停车场的边缘(见图. 1).
Pervious concrete borders used for tree wells or vegetated traffic islands can be designed as active elements, 帮助保持整个停车场的净径流在期望或限制的水平上. An important benefit of pervious concrete pavement systems with vegetated islands or tree wells is that adequate moisture may be available with minimal, if any, need for irrigation. This is particularly important when working with minimum tree density requirements or when protecting large, existing trees on the site. 主动缓解设计方法非常灵活，可以用于各种应用程序. Primary applications of pervious concrete in an active mitigation role therefore include commercial parking lots, 商业发展地盘的边界特征, and containment features designed to intercept at least a portion of overland surface runoff prior to entering drainage channels.
积极缓解应用的限制因素是排水不良的土壤(通常是那些土壤), 渗滤率显著小于0.1 inches per hour, because the pervious concrete system must be emptied and full storage capacity recovered in a reasonable amount of time (typically five days or less). Recovery time is typically not a major concern in passive mitigation applications with these types of soils since the infiltration is slow and runoff relatively high even with natural cover (see Fig. 2.)
Figure 2. Infiltration of rainfall into the soil increases the effective storage capacity of the pervious concrete pavement system.
Another important consideration in design of a pervious concrete system is the amount of storm water to be stored. 显然，更大的降雨会导致更多的径流. Different sizes of storms will result in different amounts of runoff and the selection of an appropriate design storm is important. Larger storms occur less often on average and storms are typically designated based on their return period. For example, a storm which occurs on average once in 20 years is designated a “20-year storm” and will be larger and produce more rainfall than a “10-year storm.“通常是地方当局选择设计风暴，如市或县的水委员会. Storms of interest in hydrologic design of small watersheds are typically the two-year storm and the 10-year storm. The two-year storm is often used as the “service load” storm for the watershed for water quality purposes. 在设计雨水收集系统时，传统上采用的是十年风暴. 许多地区的降雨量估计值可在网上查阅 NOAA's National Weather Service.
Tennis, P. D., Leming, M. L., and Akers, D. J., Pervious Concrete Pavements, EB302, Portland Cement Association, Skokie, Illinois, 以及全国预拌混凝土协会, Silver Spring, Maryland, 2004, 25 pages.