Pervious concrete is emerging as an alternative material for paving to help curtail nonpoint source pollution problems. The porosity of pervious concrete is an important variable needed for pavement system design and for material comparisons. This paper researches a method for measuring the porosity of pervious concrete from field-obtained cores by applying the Archimedes principle and using standard materials laboratory equipment. The error between different operators at different testing facilities was found to be around 2.2 % porosity.

A computerized falling head permeameter system was used to measure hydraulic conductivity of pervious concrete from samples taken from three different field-placed slabs with known porosities. Important differences between samples were found, and these follow the same trend as differences in porosity. The relationship between porosity and hydraulic conductivity is suggested as a tool for designing pervious concrete pavements as a stormwater pollution best management practice. A quantitative relationship between porosity and hydraulic conductivity was established based on the Carman-Kozeny equation for the samples tested. Samples with porosities less than 15% presented limited hydraulic conductivity. Important considerations on the measurement of hydraulic conductivity of pervious concrete samples are discussed, and the Ergun equation is used to explore the flow regime inside pervious concrete samples.

As the world becomes more urbanized, concerns over the urban heat island (UHI) are more pronounced. Increased urban temperatures have a negative affect on the natural and human environment by producing increased energy usage and smog formation. Pervious concrete pavement is one technology that may help mitigate increased urban temperatures. Temperature data from an instrumented site in Iowa and heat storage phenomena for various weather patterns are presented. The site contains both pervious concrete pavement with a solar reflectance index (SRI) of 14 and traditional concrete pavement with an SRI of 37. Leadership in Energy and Environmental Design (LEED) accepted a high SRI (>29) as one method to characterize a cool surface. Heat capacities of both systems were studied along with a sensitivity analysis of the inputs. The research supports the conclusion that even though pervious concrete may have a much lower SRI than traditional concrete made with similar materials, it can be considered a cool pavement option. In addition, daytime rainfalls combined with the internal high surface area result in significantly more removal of stored heat from the system, with a more rapid mitigation of UHI impacts and reduction in the potential for thermal shock from impervious surface runoff.