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Donalson, Curtis, Najafi 1

Sustainable Assessment of Recycled Concrete Aggregate (RCA) Used in Highway Construction

Jeff Donalson (Corresponding Author)

Environmental Engineering Student Department of Environmental Engineering

University of Florida 365 Weil Hall, Post Office Box 116580

Gainesville, Florida 32611-6580 Phone: (863) 287-6873

Raymond Curtis District Manager

The LANE Construction Corporation 3995 Hwy 60 East

Mulberry, Florida 33860 Phone: (863) 425-8000, Fax: (863) 425-3995

Dr. Fazil T. Najafi Professor

Department of Civil and Coastal Engineering University of Florida

365 Weil Hall, Post Office Box 116580 Gainesville, Florida 32611-6580

Phone: (352) 392-9537 Ext. 1493, Fax: (352) 392-3394

Paper is submitted for publication and presentation for the 90th Annual Meeting of the Transportation Research Board in January 2011 in Washington, D.C.

Re-Submission Date: November 15, 2010

Word Count: 6,199 words + 2 figures + 3 tables = 7,449words

Keywords: Recycled Concrete Aggregate (RCA), highway construction, life cycle assessment,

cost-benefit analysis, lime rock

TRB 2011 Annual Meeting Paper revised from original submittal.


ABSTRACT 1

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Due to the increased volume of construction and demolition wastes deposited in landfills in recent years, the transformation of recycling waste materials into useful products for re-application in highway construction projects is recommended. Approximately 18% to 50% of construction and demolition waste could potentially be reclaimed and reused. Recycled concrete aggregate can be utilized in this fashion when substituted as a roadway base material in highway construction. The sustainability of recycled concrete aggregate used as a base material is currently unknown; therefore, this study determined the sustainability of recycled concrete aggregate when used in highway construction by comparing the environmental, social, and economic impacts of each product. The environmental impact was found to only demonstrate a reduced impact in favor of recycled concrete aggregate in process energy and disposal at -0.01 and 0.04 metric tons of carbon dioxide equivalents, respectively. It was determined that both recycled concrete aggregate and virgin lime rock aggregate are socially sustainable products; however, the leachability of recycled concrete aggregate was determined to be less than that of virgin lime rock aggregate. The life-cycle cost analysis, which was completed as if a project were located in Winter Haven, Florida, determined that recycled concrete aggregate was both economically sustainable and feasible for application as a base material in highway construction. As hypothesized, the use of recycled concrete aggregate not only demonstrates sustainable benefits, but also economic feasibility as long as the transportation distance is limited when compared to virgin lime rock aggregate.



INTRODUCTION 1 2 3 4 5 6 7 8 9

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The United States Department of Transportation (DOT) has noticed an increase in

construction and demolition (C&D) waste deposited in landfills in recent years. As a partial solution to this problem, the DOT recommends the recycling of waste materials into useful products for re-application in highway construction projects (1). In order to reduce the stress on the amount of natural resources used in the construction industry and disposed in landfills, recycling of construction and demolition (C&D) waste in the United States (U.S.) is becoming more common. Approximately 4 million miles (6.4 million km) of highways are currently being replaced every 20 to 40 years. Concrete is the most widely used of all construction material, as approximately 1 ton (0.91 Mg) of concrete is produced per person per year (2, 3). Also, aggregate is the largest component of concrete and its consumption is increasing each year. Approximately 1.3 billion tons (1.2 billion Mg) of natural aggregate is consumed each year in the U.S. construction industry. Further, 58% of the 1.3 billion tons of natural aggregate is used in highway construction as granular base material. Overall, it is becoming more difficult to permit new quarries due to the diminishing supply of virgin aggregate and the increasing cost of virgin aggregate and transportation (3). Recycled concrete aggregate is most frequently used in highway construction as a base material. When concrete aggregate is recycled for the purpose of reuse as a construction material, the product is then renamed recycled concrete aggregate (RCA). According to the Federal Highway Administration (FHWA), “RCA is a granular material manufactured by removing, crushing, and processing hydraulic-cement concrete pavement for reuse with a hydraulic cementing medium to produce fresh paving concrete (2).” RCA can be remanufactured as either coarse or fine aggregate. In 2002, the FHWA declared that the reuse of the materials used to construct the original highway structure is a decision that “… makes sound economic and environmental sense (4).”

The use of recycled materials are carefully tested and regulated to ensure that the structural integrity of the product is suitable for each project. Options for managing out-dated concrete pavement include the following possibilities: removal from the site and disposal into a C&D waste landfill; processing it into aggregate for later use in granular base, sub-base, or shoulder construction; processing the concrete pavement into a RCA suitable for use as backfill, granular embankment, or in low-performance asphalt or hydraulic-cement concrete; or processing the concrete pavement into a high quality RCA suitable for use in high-performance asphalt or hydraulic-cement concrete (1, 4). For highway construction, processing the RCA into a high-quality product is essential to uphold strength of material design standards (4).

RCA was not commonly used in high performance asphalt or hydraulic-cement concrete construction until many researched works published its effectiveness in recent years as a practical substitute for virgin aggregate. The main difference between RCA and virgin aggregates lies in the amount of cement paste remaining on the surface of the original natural aggregates after the manufacturing process. The accumulation of this cement paste leads to the lower particle density and higher porosity, variations in quality, and higher water absorption of the RCA. The most problematic difference is the accumulation of contaminants, including, but not limited to, glass, rubber, asphalt, bricks and other friable materials within RCA (5). In most highway construction projects, RCA replaces natural aggregates in the form of lime rock, soil-cement and shell.



Although the bulk of material in C&D waste is not hazardous, it has been historically misconceived as an inert waste. Misconceptions of C&D waste include minimal environmental impacts and a lack of contaminants such as those found in municipal solid wastes (MSW). However, C&D waste has been proven to undergo very active biological processes within landfills, elevating the degree of pollution within the leachate and landfill gas released. For instance, this biological activity can accelerate the quantity of metals (such as iron) released into the groundwater below a landfill and thus can contaminate the drinking water supply available to that community (6).

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Florida has a tremendous potential for groundwater pollution in the Floridan aquifer; however, bottom liners are not required in C&D landfills. Only twenty-three states in the United States actually require a C&D landfill bottom liner. In Florida, access to the aquifer is not only directly below the ground surface but also via surface water runoff. Thus, the EPA requires Florida’s C&D waste landfills to undergo mandatory groundwater monitoring to ensure that polluted contaminants are not reaching the aquifer via leaching or runoff (6).

Although constant advancements in technology limit the possibility for groundwater contamination to occur, it is imperative that the volume of waste entering landfills is reduced by preserving the limited amount of natural resources available. Of approximately 350 to 850 million tons (320 to 770 million Mg) of virgin lime rock and other remanufactured concrete materials used in highway construction each year in the U.S., 123 million tons (112 million Mg) of C&D waste is generated and disposed of in landfills. This means that with the implementation of recycled waste, approximately 18% to 50% of the waste could potentially be reclaimed and reused (6, 7).

Within this assessment, a cost-benefit analysis of the sustainable use of RCA in replacement of virgin lime rock aggregate (VLA) in Florida highway construction was determined. VLA is comprised of a combination of crushed limestone aggregate and natural sand. The three legs of sustainability (environmental, economic, and social impacts) were collectively analyzed using two separate methods. An economic life-cycle assessment was used to compare the cost effectiveness of RCA versus the virgin lime rock aggregate. Further, a literature review was completed to evaluate the potential environmental and social impacts of RCA. The economic life-cycle cost analysis was adopted from the national Recycled Materials Resource Center (RMRC), and the quantification of each environmental and economic benefit was based on one short ton of material (8). It was anticipated that upon conclusion of this assessment, the use of RCA in a Florida highway construction project would not only be a beneficial option, but also a sustainable option for the respective client only when the distance between the construction project and the crushing operation remains minimal and negligible to the cost of the total project.



METHODOLOGY 1 2 3 4 5 6 7 8 9

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Sustainability Review

Within this study, a collaborative review of environmental, social, and economic impacts of VLA versus RCA was used to identify and determine the sustainable potential of each product as a base material in highway construction. An extensive literature review of several peer-reviewed works was conducted to determine the overall environmental and social impacts of each product from cradle-to-grave. All data will be conservatively estimated to maintain the veracity of an actual highway construction project in Winter Haven, Florida. Further, studies evaluated for environmental impacts include a quantitative life-cycle assessment (LCA) comparison of the relative greenhouse gas (GHG) emissions as a metric ton of carbon dioxide equivalent per short tone of concrete (MTCO2E) adopted from the EPA’s Waste Reduction Model (WARM). Studies evaluated for social impacts include the following: a qualitative risk-based assessment of the potential groundwater contamination, which is based on (1) the National Primary and Secondary Drinking Water Standards regulated by the EPA and (2) the “Soil Cleanup Target Levels” (SCTL) published in Chapter 62-777, Table II of the Florida Administrative Code (F.A.C.) and regulated by the Florida Department of Environmental Protection (FDEP) (9-11). The economic impacts of VLA and RCA have been evaluated by collecting cost data on the processing, construction, labor, materials, supplies, and transportation costs from the LANE Construction Corporation, located in Mulberry, Florida. Further, the economic impact data will follow a life-cycle cost analysis (LCCA) approach adopted from the RMRC’s “User Guidelines for Byproducts and Secondary Use Materials in Pavement Construction (8).” RESULTS AND DISCUSSION Environmental Impact According to the FHWA, aggregate is the granular material used in concrete mixtures that compose approximately 90 to 95% of the mixture weight and provides a majority of the load bearing characteristics of the applied concrete (12). The aggregate retained on the No. 4 (4.75 mm) sieve is known as coarse aggregate, and the material passing the No. 4 (4.75 mm) sieve is called fine aggregate. Aggregate accounts for a majority of the environmental impacts associated with manufacturing and utilizing concrete and recycled concrete in highway construction. The production of recycled concrete includes an extensive, detailed process that requires precision. Figure 1, adopted from Chapter 5 of the ACI Committee Report, provides the typical production process for RCA (13, 15).

The initial step illustrated in Figure 1 involves demolishing the concrete pavement and transporting the material to a processing plant. At the plant, the first initiative is to remove all steel (such as rebar), soil, and other contaminants from the demolished concrete. Next, the concrete is crushed and sized by screens that result in the aggregate product sized to meet the specific gradation requirements. The process of RCA production is identical to VLA production with the exception of the activities for the removal of steel, impurities and contaminants. The disposal tipping fees and demolition costs of the concrete aggregate and other unwanted constituents are typically included in the raw material costs (4).



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The extensive separation, crushing, and screening processes illustrated in Figure 1 represent the concern for removal of contaminants and foreign materials that exist in the virgin and recycled aggregate particles. The major contaminants found in RCA are plastics, wood, and paper; however, metals have also been found in RCA material. It is essential to reduce the amount of these contaminants in concrete aggregate before it is reused for highway construction or disposed of in a local C&D landfill (13). Thus, waste disposal is a vital environmental impact associated with the use of aggregates in highway construction.

FIGURE 1 Typical Crushing Plant Process & Procedure for Concrete Aggregate

FINAL TRANSPORTATION &

RE-APPLICATION

FRACTION OF CONCRETE DEMOLITION WASTE AND BRICK

RUBBLE < 40mm

WASHING, SCREENING, OR AIR-SIFTING

Removal of remaining contaminants such as plastics, paper, d d

SECONDARY

CRUSHING

MANUAL OR MECHANICAL REMOVAL OF REMAINING CONTAMINANTS

Removal of lightweight material such as plastics, paper, and wood

SECONDARY

SCREENING

DEMOLITION Selective demolition to reduce individual fragments of broken

concrete to a maximum of 40 to 70 mm

Separate storage of concrete, brick, rubble, and mixed demolition debris which is heavily contaminated with

wood, iron, plastics, and gypsum

MANUAL OR MECHANICAL PRE-SEPARATION

Removal of large pieces of wood, iron, paper, plastics, etc

PRIMARY SCREENING Removal of all minus 10mm fine material such as soil,

gypsum, etc

PRIMARY

CRUSHING

MAGNETIC SEPARATION

Removal of remaining ferrous matter

The typical concrete crushing procedure includes demolition, primary and secondary separation, primary and secondary crushing, primary and secondary screening, and washing. The process proceeds in order from demolition to secondary screening.

Figure 2 demonstrates the screening equipment used to separate the fine and coarse material in the recycling process of demolished concrete. In this step all fine material less than 0.39 inches (10 mm), such as soil or gypsum, is typically removed from the crushed concrete. Further, the final product for RCA contains a large amount of fine material.



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FIGURE 2 Primary Screening Equipment The screening equipment shown above is used at JVS Contracting in Bartow, Florida, in the primary screening process to remove foreign objects such as paper, plastics, wood and metal from the crushed concrete.

A quantitative comparison of the environmental impacts associated with the use of VLA versus RCA in highway construction is shown in Table 1 below. This quantitative analysis was compared by utilizing the EPA’s Waste Reduction Model (WARM). WARM estimates the carbon footprint as a GHG equivalent of recycling concrete aggregate as opposed to disposing it in a landfill. WARM also analyzes the GHG emission sources and sinks, including, but not limited to, the raw material and transportation stages of concrete’s life cycle. The net GHG emission is then calculated as MTCO2E. A positive MTCO2E value represents increased GHG emissions, while a negative MTCO2E represents reduced GHG emissions. Further, “GHG emissions associated with raw materials acquisition and manufacturing (RMAM) are (1) GHG emissions from energy used during the acquisition and manufacturing processes, (2) GHG emissions from energy used to transport raw materials, and (3) non-energy GHG emissions resulting from manufacturing processes. For the recycling emission factor, WARM compares the impact of producing aggregate from recycled concrete to the impact of producing virgin aggregate. (14)”

In WARM, the benefits of recycling are calculated by comparing the difference between the emissions associated with producing one short ton of RCA and the emissions from producing one short ton of VLA. Non-energy emissions were considered negligent and, thus, are considered to be zero for both RCA and VLA. Three significant steps were used to calculate MTCO2E for both RCA and VLA. First, the MTCO2E of RCA is calculated from the combustion of fossil fuels for both process energy, which includes the energy required for extracting and processing the raw material, and transportation energy. Second, the MTCO2E is calculated for the production of recycled aggregate. Finally, the difference in MTCO2E between VLA and RCA production is calculated. The results for these environmental impacts of VLA



versus RCA are shown in Table 1a for process energy and transportation energy and Table 1b for the disposal of concrete (14).

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Table 1a demonstrates that the process energy and transportation energy stages demonstrate a beneficial environmental impact for RCA. Further, the total difference in RCA versus VLA (for one short ton of material) represents -0.01 MTCO2E in favor of RCA. The favorable environmental impact associated with RCA is wholly represented by the process energy stage of concrete’s life cycle (14).

Table 1b shows the environmental impacts associated with the disposal of concrete. According to WARM, approximately 0.04 MTCO2E is spent when concrete is disposed of in a landfill. Comparatively, no carbon is stored when demolished concrete is converted to RCA and diverted from disposal into a landfill. It is noteworthy to mention that the carbon storage when concrete is deposited in a landfill is difficult to quantify and considered to be beyond the scope of WARM. Therefore, WARM only counts the transportation of concrete to a landfill and operation of landfill equipment result in anthropogenic CO2 emissions due to the combustion of fossil fuels in the vehicles used to haul and move the wastes (14). TABLE 1 Comparison of Environmental Impacts of VLA versus RCA (Table 1a: Process Energy and Transportation Energy)

(a)

Material/Product

(b)

Process Energy

(c)

Transportation Energy

(d) Total

(d = b + c) RCA 0.00 0.01 0.01 VLA 0.01 0.01 0.02 TOTAL (RCA – VLA) -0.01 0.00 -0.01

19 20 (Table 1b: Landfill Emissions)

Material/Product RMAM (Current Mix of

Inputs)1

Transportation to Landfill

Landfill CH41 Avoided

Emissions from Energy

Recovery1

Landfill Carbon Sequestration1

Net Emissions (Post-

Consumer)

Concrete - 0.04 - - - 0.04 1 - = Zero Emissions 21

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Social Impact

Although the upper layers of highway pavement exposed to the atmosphere prevent most of the vertical, permeable flow to the base and sub-base layers unless failures in the structure occur, the base material in highway construction frequently is exposed to the saturated vadose zone beneath the roadway and within the upper portion of the groundwater table. In Florida, the vadose zone can be a partitioning agent transferring any chemical constituents that inhabit construction materials from its host material directly to the local groundwater (drinking water) supply. Further, the process of partitioning chemicals from a solid to an aqueous phase in the environment is often termed leaching, because the constituents are drawn out or “leached” from the host material into the surrounding environment (15, 16).

Therefore, in order to determine the social impacts of RCA used in highway construction, the release of these harmful chemical constituents through leaching was evaluated. This evaluation was performed by comparing multiple literature works which test the leaching ability (leachability) of natural and recycled concrete aggregate. Overall, the results indicate that RCA



is not only an environmentally sustainable product when compared to VLA, but is also a socially sustainable product (15, 16).

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The leachability of un-reactive ions observed by Sani et al concluded that the presence of RCA increases the leachability of un-reactive ions, such as sodium, potassium, and chloride (NA, K, Cl). However, the leachability of RCA for calcium (Ca) resulted in lower net leaching than VLA. In the study by Sani et al, the leachability of each product was “assessed by means of a dynamic leaching test, in which solidified cubes were immersed in aqueous solutions.” Further, it was also determined that the use of RCA as a structurally competent material in replacement of VLA causes an increase in the total porosity. This increased porosity may contribute to the lower ion leaching rate of calcium in RCA (15).

Engelsen et al evaluated the leaching characteristics of several types of RCA when dependent upon pH. This study represents the variability of exposure on a highway base material from vehicular pollutants and solid and liquid hazardous spills associated with routine traffic. In the case of a failure in the highway material structure, the sub-layers would be exposed to the petroleum, plastics, metallic, and wood-based contaminants available on the surface of the roadway. The variability of these factors could result in a significant variability in pH as local groundwater, surface water and storm water comprise of both acidic and basic pH levels. Therefore, the leachability of certain chemicals could possibly have a significant dependence on pH, especially in the presence of a strong alkaline material, such as concrete (16).

Engelsen et al focused their study on six major elements: aluminum (Al), calcium (Ca), iron (Fe), magnesium (Mg), silicon (Si), and sulfur (S) as SO4

2-. Leachability was tested for each of the previously listed elements and molecules in the range of the entire pH spectrum. The leachability of each constituent was directly influenced by the acid neutralization of the host material (i.e., RCA or VLA). Thus, RCA had an overall higher tendency to retain the element and limit leachability when compared to VLA (15). Results for leachability of Ca in this study were also limited, which was also similar to the results in the study completed by Sani et al (15). However, trace amounts of leachate for all elements were recorded in both studies evaluated (16).

It is significant to note that although RCA leaches less harmful and less toxic amounts of chemicals than VLA, the actual amount of constituent reaching the groundwater is negligible when compared to the groundwater contamination limits of the EPA for potable drinking water (9-11, 16). For instance, Table 2 demonstrates threshold limits for the elements evaluated in this study from both (1) the National Primary and Secondary Drinking Water Standards regulated by the EPA and (2) the “Soil Cleanup Target Levels” (SCTL) published in Chapter 62-777, Table II of the Florida Administrative Code (F.A.C.) and regulated by the Florida Department of Environmental Protection (FDEP) (9-11). The listed regulations represent the maximum allowable and enforced Leachability limits for each contaminant as set by the EPA and FDEP. Each limit is based on the human health risk associated with exposure to the corresponding contaminant. Calcium, magnesium, and silicon are not enforced under these regulations because large quantities of either of these contaminants pose no water quality or human health risks to the surrounding environment (16).

As shown in Table 2, both aluminum and iron require either the Synthetic Precipitation Leaching Procedure (SPLP) test or the Toxicity Characteristic Leaching Procedure (TCLP) test to be performed to grade the degree of contaminated precipitation which will leach through the sampled soil and mobilize into the groundwater. For highway road base construction purposes, the SPLP Test is more applicable than the TCLP test (16-18).



The purpose of the TCLP test is to determine and identify “the mobility of both organic and inorganic analytes present in liquid, solid, and multiphasic wastes (17).” The TCLP test simulates landfill conditions and measures the percolation of liquids through a waste in the presence of an acidic solution. If a waste fails the TCLP test for any listed compound, the waste is considered a characteristic hazardous waste and may pose environmental and human health risks to the surrounding environment. A waste that fails the TCLP test is deemed a characteristic hazardous waste and is either listed in the code of federal regulations (40 CFR 261, Table 1) or will exhibit one of the following characteristics: ignitability, corrosivity, reactivity, or toxicity (17, 18).

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The purpose of the SPLP test is to determine and identify “the mobility of both organic and inorganic analytes present in liquids, soils, and wastes (17).” The SPLP is normally applied to soil samples in which leaching can cause contaminants to migrate into the groundwater supply. Similar to the TCLP test, a sample which fails the SPLP test is deemed a hazardous waste and the aggregate sample shall not be applied to the project area (17, 18). TABLE 2 Leachability Thresholds set by the EPA and FDEP on Leachable Elements within Concrete Aggregate

Contaminant SCTL Residential Direct Exposure

Threshold (mg/kg)

SCTL Leachability based on

Groundwater Criteria (mg/kg)

Secondary Drinking Water Standard

(mg/L)

Human Health Risk

Al 80,000 SPLP or TCLP** 0.05 to 0.2 mg/L Body Weight Ca NR* NR* NR* No Risk Mg NR* NR* NR* No Risk Si NR* NR* NR* No Risk Fe 53,000 SPLP or TCLP** 0.3 mg/L Gastrointestinal S as SO4

2- NR NR 250 mg/L Aesthetic, Odor NR: Not regulated under the listed regulation. 18

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** Leachability values may be derived using the SPLP test to calculate site-specific SCTLs or may be determined using TCLP in the event oily wastes are present.

Upon evaluating the ability of RCA and VLA to leach reactive and un-reactive chemicals

into the groundwater by comparing the studies of Sani et al and Engelsen et al and utilizing Table 2, the use of RCA in replacement of VLA in highway construction is sustainable to the social environment (15, 16). Economic Impact The economic analysis follows a life-cycle cost analysis adopted from the RMRC’s “User Guidelines for Byproducts and Secondary Use Materials in Pavement Construction.” This approach focuses on three specific costs of interest when evaluating the cost of using a recycled material in highway construction projects. The three cost categories include: (1) the cost of the material, (2) the cost of installation, and (3) the life-cycle cost of the pavement when using the material. Table 3 demonstrates the cost-benefit relationship between RCA and VLA within the defined cost categories (8).



Cost of Material 1 2 3 4 5 6 7 8 9

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In this case, the cost of material includes, but is not limited to, the cost that the purchaser would pay to have the concrete aggregate delivered to a project site. The cost of material can then be identified as the delivered price (DP). The delivered price (DP) is the accumulated sum of the following items: the price of the raw material (RM), cost of processing (PR), cost of stockpiling (ST), cost of loading (LD), cost of transporting (TR), and profit (P). Equation 1 below illustrates the collective ingredients involved with the cost of material (8).

DP = RM + PR + ST + LD + TR + P (1)

When performing an evaluation of Equation 1, it is important to clearly identify all parameters associated with the equation. The price of raw material (RM) simply includes the cost or value of the unprocessed material and is determined by the supplier. In this case, the disposal tipping fees and demolition costs of the concrete aggregate would be included in raw material costs. The cost of processing the material includes the costs associated with manufacturing the product. For instance, primary and secondary separation, crushing, screening and drying would be included in the processing costs for RCA. After processing occurs, the length of time in which the product is stored or stockpiled (ST) until it can be utilized in a construction project represents ST. The cost of loading (LD) is the cost to the purchaser for delivery of the product. The distance required for delivery and the type of haul vehicle involved makes up TR. Transportation costs (TR) can frequently represent a significant part of the overall DP. Profit (P) can be determined in two different ways. The seller can either add P to the cost of delivery or discount RM. In Table 3, P was in addition to the cost of delivery (8). It is important to note that for RCA, concrete products are delivered free of cost to the crushing source within the chosen project area. Therefore, the RM for RCA is negligible and is, thus, considered zero. Further, it is also important to notice that PR, ST, and LD for both RCA and VLA are equal in price. This is because the processing procedures for each product are very similar and demonstrate negligible variance. Although the margin of RCA to VLA for P is six to one, the most significant difference in DP is TR. Table 3 shows that because RCA is typically only used when the processing plant is in close proximity to the project site, TR for RCA is much less than for VLA. In this study, to have VLA delivered to the project site would require an extra 30 miles of transportation expenses over RCA. The total DP for RCA in Table 3 is $12.75 per ton compared with $13.20 per ton for VLA. Therefore, a slight benefit in RM is experienced when applying RCA instead of VLA in highway construction if the project is within close proximity to the crushing plant (8). Cost of Installation The cost of installation (CI), which includes the cost of design, construction and testing, is significant to the life-cycle cost when the cost of using the recycled material differs from the conventional material cost. Accordingly, the cost of installation is significant in this case. The cost associated for design of application (DR), cost for construction (CC), and cost of testing (RP) are equally summed to quantify CI. Therefore, CI was calculated as shown in Equation 2. In Table 3, the overall CI associated with the installation of aggregate material in highway construction revealed a benefit of $1.05 per ton of RCA used as a replacement to VLA (8).



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CI = DR + CC + RP (2)

The cost for design of application (DR) can be allotted to the specific amount of time and effort involved in the design. In this case, DR represents the specific amount of time and effort involved in designing the base of the structure. In this location, DR for both recycled and conventional materials is negligible assuming all materials are pre-approved for use (8).

The construction costs (CC) represent the procedures and activities that occur during the installation of either the recycled or conventional aggregate product. For instance, the recycled material could result in higher CC if special procedures, such as preparation or compaction, are required during installation. In this case, CC was $3.75 per ton of RCA compared with $4.50 per ton of VLA, inferring that the required installation of RCA is less complicated than VLA (8). The cost of testing (RP) involves any subsequent testing costs associated with the aggregate product. In Table 3, it is evident that RCA has less stringent requirements associated with RP over VLA prior to application. In this case, RP differed from $0.70 per ton of RCA to $1.00 per ton of VLA, for an overall benefit of $0.30 per ton of RCA used as a replacement to VLA (8). Life-Cycle Cost When either the annual maintenance costs or length of product life differs, a life-cycle cost analysis (LCCA) is necessary to determine an accurate cost-benefit comparison of recycled versus conventional aggregate used in highway construction. The approach derived from the RMRC is one of many different life-cycle cost approaches and focuses on the calculation of an annual effective cost (EC) resulting from the application of the respective aggregate. The EC calculation, shown in Equation 3, includes the annual maintenance cost (AM) plus an adjusted installation cost. The capital recovery factor (CRF) is determined as a function of a fixed interest rate (i) and product life (n) in years. The calculated CRF, demonstrated in Equation 4 below, used a fixed interest rate of 8% as i and a product life of 10 years as n, for both RCA and VLA. The CRF for RCA and VLA in Table 3 were calculated as $0.15 per ton of aggregate. The annual maintenance costs (AM) were considered $1.00 per ton of aggregate for both materials to maintain a conservative estimate. Although the value of n for RCA and VLA were not considered to be different, the LCCA was determined to complete the overall economic assessment (8).

EC = CI*(CRF) + AM (3)

CRF = (i (1 + i) n)/ ((1 + i) n – 1) (4)



TABLE 3 Comparisons of Economic Impacts of Virgin Limerock Aggregate versus RCA in Highway Construction

1 2

Recycled Concreted Aggregate

($USD per ton of aggregate)

Virgin Limerock Aggregate

($USD per ton of aggregate)

COST OF MATERIAL

Delivered Price (DP) 12.75 13.20 Price of Raw Material, F.O.B. (RM) 0.00 2.00 Cost of Processing the Material (PR) 3.00 3.00 Cost of Stockpiling the Material (ST) 0.50 0.50 Cost of Loading the Material (LD) 0.50 0.50 Cost of Transporting the Material (TR) 2.75 6.00

Profit (P) 6.00 1.20

COST OF INSTALLATION

Cost for Design of Application with Material (DR) 0.00 0.00

Cost for Construction with Material (CC) 3.75 4.50 Cost of Testing and Inspection for Proposed Application (RP) 0.70 1.00

Sub-Total Cost of Installation (CI) 4.45 5.50

LIFE-CYCLE COST

Annual Effective Cost (EC) 1.66 1.82 Cost of Installation (CI) 4.45 5.50 Capital Revovery Factor (CRF) 0.15 0.15

Annual Maintenance Cost (AM) 1.00 1.00

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As shown in Table 3, there is an economic incentive to use RCA as a replacement for VLA in highway base construction as DP, CI, and EC all exhibit a reduction in cost per ton of aggregate. Specifically, the cost of DP, CI, and EC is $0.45, $1.05, and $0.16 per ton of aggregate less expensive, respectively, when using RCA as a replacement for VLA in highway base construction. Therefore, the use of RCA in highway base construction in Winter Haven, Florida, is both economically sustainable and feasible (8). CONCLUSION The use of recycled concrete aggregate (RCA) as a replacement for virgin lime rock aggregate (VLA) in Florida highway base construction displayed limited impacts in the environmental, social, and economic categories. Thus, the use of RCA in Florida highway construction is deemed sustainable for the application of a base material. As hypothesized, the use of RCA not only demonstrates sustainable benefits, but is also economically feasible as long as the transportation distance is limited when compared to VLA (19).



The environmental impact of RCA versus VLA was found to be favorable in the extraction of raw materials, calculating -0.01 MTCO2E. Further, the environmental impact associated with transportation energy was found to be negligent, calculating 0.01 MTCO2E for both RCA and VLA when the same distance was traveled. The environmental impact associated with disposing concrete into a landfill was 0.04 MTCO2E, implying that recycling concrete is more beneficial when diverted from a landfill. Overall, the total environmental impact of RCA versus VLA demonstrates that RCA is a favorable option over VLA in the production of concrete aggregate (14).

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Upon reviewing the leachability of a selected array of elements contained in concrete aggregate, it was determined that both RCA and VLA are socially sustainable products; however, the leachability of RCA was determined to be less than that of VLA according to both Sani et al and Engelsen et al. Therefore, it was expected that both RCA and VLA would be deemed socially sustainable (15, 16).

The life-cycle cost analysis (LCCA) completed for a project located in Winter Haven, Florida, determined that RCA was both economically sustainable and feasible for application as a base material in highway construction. All three categories of the LCCA proved to be beneficial in favor of RCA over VLA. When calculating the cost of material, the cost of transporting the material was the determining factor of the calculation (8).

As markets differ through time, it is necessary to re-evaluate this assessment as frequently as possible. It is possible that the use of RCA over time could become the only viable option, as the amount of available natural resources continues to diminish. Further, cradle-to-grave qualitative and quantitative assessments on recycled road construction materials are essential factors in making intelligent decisions in sustainable highway construction applications (19, 20). ACKNOWLEDGEMENT

This work was supported by the fees paid to the University of Florida, Department of Civil and Coastal Engineering by the taxpayers of the State of Florida. Censtate Contractors, Inc. and JVS Contracting, Inc. provided information for this study. REFERENCES 1. Schroeder, R. A. The Use of Recycled Materials in Highway Construction. FHWA, Vol. 34

58, No. 2, U.S. Department of Transportation, 2004. 2. Marinkovix, S., V. Radonjanin, M. Malesev, I. Ignjatovic. Comparative Enivronmental 36

Assessment of Natural and Recycled Aggregate Concrete. Waste Management. 2010, pp 1-10.

3. Carpenter, A. C., K. H. Garner, J. Fopiano, C. H. Bensen, T.B. Edil. Life Cycle Based 39 Risk Assessment of Recycled Materials in Roadway Construction. Waste Management. Vol. 27, 2007, pp.1458-1464.

4. Gee, KK. W. Use of Recycled Concrete Pavement as Aggregate in Hydraulic-Cement 42 Concrete Pavement. FHWA Publication-T 5040.37. U.S. Department of Transportation, 2007.

5. Paranavithana, S., A. Mohajerani. Effects of Recycled Concrete Aggregates on Properties 45 of Asphalt Concrete. Resource Conservation and Recycling, Vol. 48, 2006, pp.1-12.



6. Jambeck, J. R., T. G. Townsend, H. M. Solo-Gabriele. Landfill Disposal of CCA-Treated 1 Wood with Construction and Demolition (C&D) Debris; Arsenic, Chromium, and Copper Concentrations in Leachate. Environmental Science and Technology, Vol.42, 2008, pp. 5740-5745.

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7. Mongon, A. Paving the Way to Recycled Roads. Dartmouth Engineer: Thayer School of 5 Engineering at Dartmouth, 2007. www.dartmouthengineer.com/2007/05/paving-the-way-6 to-recycled-roads/. Accessed May 26, 2010. 7

9 8. User Guidelines for Byproducts and Secondary Use Materials in Pavement Construction: 8

Evaluation Guidance, Cost Issues. Recycled Material Resource Center. www.recycledmaterials.org/tools/uguidelines/cost.asp. Accessed May 26, 2010. 10

9. National Primary Drinking Water Standards. United States Environmental Protection 11 Agency. http://ecfr.gpoaccess.gov/cgi/t/text/text-12 idx?c=ecfr&sid=2f9f06e36cc38f40750d79229123704c&rgn=div5&view=text&node=40:13 22.0.1.1.3&idno=40. Accessed June 4, 2010. 14

10. National Secondary Drinking Water Standards. United States Environmental Protection 15 Agency. http://ecfr.gpoaccess.gov/cgi/t/text/text-16 idx?c=ecfr&sid=2f9f06e36cc38f40750d79229123704c&rgn=div5&view=text&node=40:17 22.0.1.1.5&idno=40. Accessed June 4, 2010. 18

11. Soil Cleanup Target Levels. Florida Department of Environmental Protection. 19 www.dep.state.fl.us/waste/quick_topics/rules/documents/62-777/TableIISoilCTLs4-17-20 05.pdf. Accessed May 26, 2010. 21

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12. Heinz, R. E. Asphalt Concrete Mix Design and Field Control. FHWA Publication-T 22 5040.27. U.S. Department of Transportation, 1988.

13. Lamond, J. F. Removal and Reuse of Hardened Concrete. American Concrete Institute 24 (ACI) Committee 555. ACI 555R-01, Chapter 5, 2001, pp. 18-24.

14. EPA. Waste Reduction Model Documentation: Concrete Chapter. 26 http://www.epa.gov/cgi-bin/epalink?logname=allsearch&referrer=recycled concrete 27 aggregate|2|All&target=http://www.epa.gov/climate/climatechange/wycd/waste/downloa28 ds/concrete-chapter10-28-10.pdf. 29

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15. Sani, D., G. Moriconi, G. Fava, V. Corinaldesi. Leaching and Mechanical Behavior of 30 Concrete Manufactured with Recycled Aggregates. Waste Management. Vol. 25, 2005, pp. 177-182.

16. Engelsen, C. J., H. A. Van der Sloot, G. Wibetoe, G. Petkovic, E. Stoltenberg-Hansson, 33 W. Lund. Release of Major Elements from Recycled Concrete Aggregates and Geochemical Modelling. Cement and Concrete Research. Vol. 39, 2009, pp.446-459.

17. TCLP: Toxicity Characteristic Leaching Procedure and Characteristic Hazardous 36 Wastes. EHSO: Hazardous Waste Fact Sheet. www.EHSO.com. Accessed July 3, 2010. 37

18. Synthetic Precipitation Leaching Procedure. United States Environmental Protection 38 Agency: Method 1312, 1994. http://www.caslab.com/EPA-Methods/PDF/EPA-Method-39 1312.pdf. Accessed July 3, 2010. 40

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19. Lee, J. C., T. B. Edil, J. M. Tinjum, C. H. Bensen. Qualitative Assessment of 41 Environmental and Economic Benefits of Using Recycled Construction Materials in Highway Construction. In Transportation Research Record: Journal of the Transportation Research Board, No. 2505, Transportation Research Board of the National Academies, Washington, D.C. 2009, pp. 1-11.



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20. Chowdhury, R., D. Apul, T. Fry. A Life Cycle Based Environmental Impacts Assessment 1 of Construction Materials Used in Road Construction. Resources, Conservation and Recycling. Vol. 54, 2010, pp.250-255.


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