John T. Kevern

Effect of Coarse Aggregate on the Freeze-Thaw Durability of Pervious Concrete

Pervious concrete is becoming more common as a storm-water management tool in freeze-thaw climates. One of the main concerns or obstacles preventing a more widespread application is the aspect of freeze-thaw durability, whether perceived or actual. This paper describes a series of tests designed to determine the specific role coarse aggregate has on the freeze-thaw durability of pervious concrete using the ASTM C666A procedure. 17 different coarse aggregate samples were obtained from locations across the United States and Canada. Pervious concrete mixtures were placed using a mixture proportion previously determined as freeze-thaw durable. The range of durable aggregate gradations clearly defined a gradation specification and suggestions are made for optimizing the gradation with a small portion of sand. Mixtures with excellent freeze-thaw performance contained either granite or highly durable river gravel. The impact of aggregate angularity on mixture proportions and ultimate yield is also discussed.

Cyclic Heat Island Impacts on Traditional Versus Pervious Concrete Pavement Systems

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.

Temperature Behavior of Pervious Concrete Systems

To achieve the permitted stormwater effluent limits required by the Clean Water Act, many best management practices (BMPs) are being utilized to reduce the overall stormwater volume and provide initial pretreatment and pollutant removal. One such BMP is use of portland cement pervious concrete (PCPC), which allows stormwater to pass through the pavement into an aggregate base below to infiltrate. Until now, the temperature response of the entire system (concrete, aggregate base, and natural soil) was not known. Since PCPC is an infiltration-based BMP, once a frost line forms under the base the infiltrating capacity is reduced or eliminated. PCPC also is recommended for use in warmer climates as a cooler pavement alternative to conventional concrete or asphalt. To quantify the temperature behavior of a pervious concrete system, a fully monitored parking lot—composed of half traditional concrete and half PCPC—was constructed at Iowa State University as part of the Iowa Pervious Concrete Stormwater Project. Sensors were installed through the profile of both pavements and into the underlying soil. The results show that insulation from the aggregate base underneath the pervious concrete substantially delays the formation of a frost layer and permeability is restored when meltwater is present. It was also observed that in direct sunlight, the pervious pavement became hotter than traditional concrete, whereas the daily low temperature of the two was similar, indicating less heat storage capacity in the pervious concrete.

The Effect of Curing Regime on Pervious Concrete Abrasion Resistance

The current method of curing pervious concrete is to cover with plastic for 7 days, although no studies have been performed to determine if that is sufficient or even required. This paper presents results of combinations of four different pervious concrete mixtures cured using six common curing methods. The surface abrasion of the concrete was tested using a rotary cutter device according to ASTM C944. The results show that the concrete abrasion resistance was improved with a majority surface-applied curing compounds; however the surfaces covered with plastic sheets produced the lowest abrasion levels. A majority of the curing regimes also produced higher flexural strength than the control concrete. There was no significant difference observed in the strength between curing under plastic sheets for 7 or 28 days. Of the surface-applied curing compounds, the best abrasion resistance and highest strength concrete was that applied with soybean oil. The best abrasion resistance and highest strength overall was the mixture containing fly ash and cured under plastic for 28 days.

Mixture Proportion Development and Performance Evaluation of Pervious Concrete for Overlay Applications

The results of studies to develop pervious concrete for use as an overlay material over traditional concrete to reduce noise, minimize splash and spray, and improve friction as a surface wearing course are described in this paper. Workability and compaction density testing methods were developed in order to ensure constructability and placement consistency. The mixture testing matrix consisted of evaluating aggregate type and gradation, cementitious material amounts and composition, and various admixtures. Selected mixtures were tested for permeability, strength, workability, overlay bond strength, and freezing-and-thawing durability. The selected mixture was self-consolidating and slip-formable and was placed at the MnROAD testing facility during late October 2008. The test results indicate that pervious concrete mixtures can be designed to be highly workable, sufficiently strong, permeable, and have excellent freezing-and-thawing durability, thus being suitable for pavement overlays.

Construction and Performance of Pervious Concrete Overlay at Minnesota Road Research Project

Portland cement pervious concrete (PCPC) has shown great potential to reduce roadway noise, improve splash and spray, and improve friction as a surface wearing course. A study is under way at Iowa State University and the National Concrete Pavement Technology Center to develop mix designs and procedures for PCPC overlays for highway applications. A report is produced on the construction and performance of a PCPC overlay constructed at the Minnesota Road Research Project low-volume roadway test facility to determine the effectiveness of pervious concrete as an overlay. Issues related to construction of the overlay are described, as are results of field tests to characterize the condition of the pavement 7 months following construction, to determine flow characteristics of the overlay, and to characterize the tire–pavement noise of the overlay. Results of these studies show that effective PCPC overlays can be designed for wearing course applications.

Resistance of Portland Cement Pervious Concrete to Deicing Chemicals

The damaging impact of deicing chemicals on portland cement pervious concrete materials was investigated. Two concrete mixes (with and without latex modification) were subjected to three deicing chemicals (sodium chloride, calcium chloride, and calcium-magnesium acetate) under a freezing–thawing or drying–wetting condition. Two deicing chemical application methods (saturated and drained) were employed. The impact of deicing chemicals on the concrete was evaluated based on concrete mass and strength losses. Of the deicing chemicals studied, the calcium chloride solution caused the most damage, while the calcium magnesium acetate caused the least. The saturated scaling test method, followed according to ASTM C672, provided much higher mass loss of tested concrete samples when compared with a modified, more realistic drained test method.

Evaluating Permeability and Infiltration Requirements for Pervious Concrete

This paper presents a unique combination of permeability, infiltration, and clogging testing results to provide background information for the specification and design of clog-resistant pervious concrete pavements. Pervious concrete cylindrical samples of various sizes and porosities were tested using a falling-head permeameter in the laboratory. The cylindrical wall effect on porosity and permeability was determined using image analysis along with testing variability. Infiltration was tested on a series of fixed void slab samples that were then clogged with compost, soil, and a compost–soil mixture. Cleaning effectiveness was measured and related to sample properties. The results show that cylinder permeability was highly variable, with 100-mm specimens producing the least variability of the two sizes tested (75 mm and 100 mm). Slab specimens with consistent cross-sectional infiltration were the most clog resistant and had the best infiltration remediation after cleaning. Samples with initial infiltration capacities greater than 750 cm/h were the most clog resistant. The best pavement performance resulted from uniform vertical permeability distribution and high initial infiltration capacity.

Using Drinking Water Treatment Waste as Low-Cost Internal Curing Agent for Concrete

Results from a preliminary study that investigated the potential of using drinking water treatment waste sludge as an internal curing agent for concrete are presented. The concept consists of using the high water content, primarily calcium carbonate material, as a concrete admixture. Two other commonly used internal curing agents - prewetted lightweight fine aggregate and a superabsorbent polymer - were investigated as a comparison. Cement mortars were tested for compressive strength, degree of hydration, and shrinkage. Micrographs of mortars containing the three different internal curing agents were compared visually to evaluate the distribution of internal curing agents and relative hydration. Results show that drinking water treatment waste is an effective internal curing agent, improving cement hydration, compressive strength, and mitigating autogenous shrinkage.

Heavy metal removal capacity of individual components of permeable reactive concrete

Permeable reactive barriers (PRBs) are a well-known technique for groundwater remediation using industrialized reactive media such as zero-valent iron and activated carbon. Permeable reactive concrete (PRC) is an alternative reactive medium composed of relatively inexpensive materials such as cement and aggregate. A variety of multimodal, simultaneous processes drive remediation of metals from contaminated groundwater within PRC systems due to the complex heterogeneous matrix formed during cement hydration. This research investigated the influence coarse aggregate, portland cement, fly ash, and various combinations had on the removal of lead, cadmium, and zinc in solution. Absorption, adsorption, precipitation, co-precipitation, and internal diffusion of the metals are common mechanisms of removal in the hydrated cement matrix and independent of the aggregate. Local aggregates can be used as the permeable structure also possessing high metal removal capabilities, however calcareous sources of aggregate are preferred due to improved removal with low leachability. Individual adsorption isotherms were linear or curvilinear up, indicating a preferred removal process. For PRC samples, metal saturation was not reached over the range of concentrations tested. Results were then used to compare removal against activated carbon and aggregate-based PRBs by estimating material costs for the remediation of an example heavy metal contaminated Superfund site located in the Midwestern United States, Joplin, Missouri.