UNIVERSITY OF WISCONSIN SYSTEM SOLID WASTE …

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Leaching Characteristics of Recycled Aggregate used as Road Base

May 2012

Student Investigators: Jiannan Chen, Brigitte Brown

Advisors: Tuncer B. Edil, James Tinjum

University of Wisconsin-Madison

UNIVERSITY OF WISCONSIN SYSTEM

SOLID WASTE RESEARCH PROGRAM Student Project Report

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Leaching Characteristics of Recycled Aggregate used as Road Base

Jiannan Chen

Graduate Research Assistant, Department of Geological Engineering, University of Wisconsin-Madison,

E-mail: [email protected]

Brigitte Brown

Undergraduate Research Assistant, Department of Geological Engineering, University of Wisconsin-

Madison, E-mail: [email protected]

Tuncer B. Edil

Professor and Research Director, Recycled Materials Resource Center, Department of Geological

Engineering, University of Wisconsin-Madison, E-mail: [email protected]

James M. Tinjum

Assistant Professor, Department of Geological Engineering, Civil and Environmental Engineering, and

Engineering Professional Development, University of Wisconsin-Madison, E-mail:

[email protected]

ABSTRACT:

The use of recycled concrete aggregate (RCA) as a road base has lowered costs of road

construction while preserving virgin aggregate resources. Laboratory column leach tests have shown that

leachate produced by RCA is persistently highly alkaline, potentially threatening groundwater quality.

However, field-monitoring studies of RCA road base have not produced similar alkaline leachates. Both

field and laboratory methods were employed to further study, compare, and predict leaching

characteristics of RCA as a road base. This study produced first flush field data to determine the initial

leaching characteristics of RCA. Congruent laboratory tests were also run to compare with field data.

This study will provide the data necessary to predict environmental impacts associated with the uses of

RCA as a road base in road construction.

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KEYWORDS: Recycled concrete aggregate, RCA, base course, leachate, pH, alkalinity, heavy metals.

INTRODUCTION

Ever-increasing road reconstruction due to aging infrastructure in the United States (U.S.) is causing

increased demand for virgin aggregate. The production of virgin aggregate constitutes one of the greatest

costs in highway construction. The demand for aggregate in the U.S. increased from 58 million tons in

1900 to 2.3 billion tons in 1996, and is estimated to reach 3.0 billion tons by 2020 (USGS 1997).

Additionally, nearly 123 million tons of waste is generated annually from building demolition (FHWA

2004), which adds to the societal cost of waste handling and disposal.

Currently, the construction industry is moving towards beneficial use of recycled waste materials

in construction in lieu of virgin aggregate. Specifically, recycled concrete aggregate (RCA) provides

excellent mechanical properties (e.g., lower specific gravity, higher resilient modulus, and freeze-thaw

durability) for use as base course aggregate in pavement structures (ACPA 2009). Moreover, use of RCA

has significant life-cycle benefits, such as reducing greenhouse gas emissions, energy and virgin

aggregate consumption, and costs of pavement construction. In the U.S., an average of 140 million tons

of RCA is produced annually (ACPA 2008), and at least 41 states recycle concrete pavement (FHWA

2004).

However, wise use of recycled materials also requires their safe use. Since RCA is a cement-

based material, there are concerns related to potentially elevated leaching patterns due to the inherent

high alkalinity of RCA. In practical applications using cement-based material, wide pH ranges (7.5 to 12)

due to both weathering of material and material alkalinity have been observed (Van der Sloot et al.

2008). High pH leachate from RCA will bring about the potential degradation of vegetation and

obstructed highway drainage through clogging, but more importantly in varying heavy metal leaching

characteristics (Engelsen et al. 2010, Dijkstra et al. 2004 and Dijkstra et al. 2006).

BACKGROUND

Previous studies and reports from US DOT and University Wisconsin-Madison Geological Engineering

showed disconnect in the field and lab leaching tests results (MnDOT 2010). The leachate pH in a MN

DOT road section using RCA showed neutral pH (6.5 to 8.0) after 7 months, while leachate from column

tests using the same material showed a high pH (11.0 to 12.5) at the same pore volumes of flow (PVF)

(MnDOT, 2010). At the same time, the heavy metal leaching showed an obvious difference from field

and lab leachate. In September 2011, a new road section paved with RCA was installed at University

Wisconsin-Madison Lot 60, so that a direct look at the early leaching characteristics can be studied and

the disconnect of lab and field data could be evaluated. Moreover, both freshly crushed and stockpiled

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RCAs, which are widely used as backfill material, were used to identify the potential physical and

chemical difference between each material, respectively. Environmental impact evaluations and

recommendations will be given out as well as suggestions on recycled material use.

The primary objective of this study is to evaluate the environmental concern of leachate

alkalinity and hazardous element concentration from recycled concrete aggregate road base by

investigating the pH and heavy metal concentrations of leachate from field sites in the early flush and

long-term leaching scenario. A congruent lab batch test was conducted to better understand the leaching

mechanism. The two main outcomes were to develop a characterization of the elements’ leaching

behavior and to compare lab leaching methods to find the best way to simulate field conditions.

TEST MATERIALS

Two RCA samples and one natural lime stone sample were used in this study. Sample A, named freshly

crushed RCA (WR-F), came from a concrete pavement on Northport Drive, Madison, WI (Figure 1). The

service life of the concrete pavement was approximately 20 years. The RCA sample was taken three days

after demolition at Westport Quarry owned by Wingra Stone Company. Sample B, named stockpiled

RCA (WR-SP), was taken from Kampmeier Quarry of Wingra Stone Company located the Town of

Blooming Grove southeast of Madison, WI (Figure 2). The WR-SP RCA was stockpiled in the quarry for

5 to 10 years, and came from demolition of a building. Wingra Stone grinds the recycled concrete once

over and screens it through a 1.25 inch sieve for base course material. Visual inspection indicated that

RCA samples were free of impurities, e.g. wood chips or plastics.

To clarify the type of natural gravels in RCAs, a 2 kg specimen was taken from each RCA

sample, and natural gravels mixed in concrete were separated by hand and a 10% hydrochloride acid was

used to identify whether carbonate or non-carbonate content exist. A rough estimate showed the gravels

in concrete mixture were approximately 60 to 70% by weight to be limestone (Table 1). For this reason,

to compare the engineering properties and leaching behavior of RCA samples to natural aggregate base

course as a control, a natural limestone base course material was also used from Wingra Stone (Figure 3).

TEST METHODS

Physical Properties

The physical and hydraulic properties of materials were tested according to standards of the American

Society for Testing and Materials (ASTM) and the American Association of State Highway and

Transportation Officials (AASHTO). The material physical and hydraulic characterization tests including

grain size analysis, water content, dry unit weight, absorption, specific gravity, void ratio, compaction

characteristics and Unified Soil Classification System (USCS) class.

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Grain Size Analysis. The grain size distribution of stockpiled RCA, freshly crushed RCA, and natural

aggregate samples were determined according to ASTM D 422. The samples were first wet sieved

through sieve No. 200 to separate coarse and fine particles. The coarse portions were oven dried in 105

℃±2℃ for 24 hours prior to mechanical sieving.

Moisture Content. The moisture content was found for each sample following the ASTM D2216

Standard for soil and rock. A representative specimen was taken from each material, and oven dried in

105℃±2℃ for 24 hours. The mass loss was considered to be the moisture in the bulk specimen.

Absorption, Specific Gravity and Void Ratio. Absorption, bulk specific gravity SSD, and apparent

specific gravity were determined by AASHTO T85 - specific gravity and absorption of coarse aggregate.

The test procedure was exactly as the standard described.

Compaction. Modified Proctor compaction tests following ASTM D 698 (method B) were performed on

stockpiled RCA and freshly crushed RCA. From the compaction curves, the maximum dry unit weights

were determined along with their correlating moisture contents. Due to the uniform gradation and large

voids of natural limestone, the maximum dry unit weight of natural limestone was determined by shaking

table method following ASTM D4254.

Chemical Properties

The total elemental compositions of all three materials were determined by acid digestion according to

EPA 3050B, and tests were conducted in triplicate. A 1:1 nitric acid digestion of 1 g of solid sample was

performed at 90 to 95°C for 2 h, and 30% H2O2 was added to start a peroxide reaction. The total carbon

(TC), total inorganic carbon (TIC), and total organic carbon (TOC) were determined with a SC144 DR

sulfur and carbon analyzer (LECO Inc., St. Joseph, MO, USA) by UW-Madison’s Soil and Plant

Analysis Lab.

Leaching Tests

Field leaching test and lab batch leaching tests were used in this study to characterize the RCA leaching

behavior.

Field Monitoring. Field monitoring of newly constructed gravity lysimeter collection well systems

located at Parking Lot 60 of the UW-Madison campus was conducted weekly starting September 23,

2012. A schematic view of the field lysimeter layout and design is shown in Figure 4. Six lysimeters

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were constructed, using stockpiled RCA, freshly crushed RCA, and natural aggregate each in two

lysimeters, one set being overlain by porous asphalt and one by regular asphalt (Figure 5 and 6).

Sampling of these wells was consistent with literature (O'Donnell 2007); Leachate was pumped out after

each sampling session to prevent the interference between rain flushes. A weather station was set up at

the Lot 60 site, to collect precipitation and air temprature data. The leachate samples were analyzed right

after delivery. pH, electrical conductivity (EC) and redox potential (Eh) were measured in the lab, and

all leachate samples were filter through 0.45 μm filter paper and preserved at pH < 2 under 4℃.

Batch Tests. The batch tests were performed with size reduced specimens at a liquid to solid ratio (L/S)

of 10:1 by weight. Batches were agitated in an end-over-end tumbler at a speed of 30±2 revolutions per

min (rpm). A wide pH range of 2 to 13 was used in the pH-dependent leaching tests, with target pH of 13,

12, 10.5, 9, 8, 7, 5.5, 4 and 2. A preliminary test was conducted to determine the contact time to

equilibrium and the acid/base addition required for each batch. Electrical conductivity (EC), pH and

oxidation-reduction potential (Eh) were determined after testing. A chemical model named LeachXS was

used to calculate the acid/base addition for each pH target.

Leachate Chemical Analysis

The leaching elements considered in this study were determined by inductively coupled plasma optical

emission spectrometry (ICP-OES). The USEPA detect limits and maximum contaminant level (MCL) for

drinking water of each element are listed in Table 2.

A Varian MPX ICP-OES with an axial torch was used to analyze elements in Table 2. Argon was

the fuel source. A Varian Autosampler SPS 3 was utilized for continuous analysis. Prior to analysis, the

ICP was calibrated by diluting certified concentrated standards supplied from High Purity Standards

(Charleston, North Carolina) and Fisher Scientific (Hanover Park, Illinois). The calibration standards

were prepared in a nitric acid. Calibration solutions had the same matrix as the samples to prevent

interferences.

The quality control guidelines outlined in USEPA procedure SW-846 were followed. Continuing

calibration verifications (CCV) and continuing calibration blanks (CCB) were analyzed every 10

samples, and a matrix-spike and sample duplicate were analyzed every 20 samples. Matrix-spiked

samples were spiked prior to digestion. Quality control requirements described in USEPA Method SW-

846 were met for all calibrated wavelengths. These criteria required CCVs within 10% of expected

values, CCBs below detection limits, concentrations of duplicate samples within 20% of the

concentration in the original sample, and spiked samples to have a recovery of 75-125% the non spiked

sample.

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TEST RESULTS

Material Properties

Physical Properties. A summary of physical properties of RCAs and natural lime aggregate with RCA

data from other studies is shown in Table 3. The grain size distribution curve of all three materials was

plotted along with data from Bozyurt (2011) in Figure 7. The seven RCA samples were similar with

optimum water content (Wopt) ranging from 8.7 to 11.2%, maximum dry unit weight (γd) from 18.9 to

20.8 kN/m3, absorption from 4.2 to 5.8, apparent specific gravity from 2.6 to 2.7, and void ratio from 0.3

to 0.4. No information was provided for the RCA source, concrete service life and age of stockpile.

Samples WR-F and WR-SP RCA fell into the gradation criteria of referenced RCA samples. However,

freshly crushed RCA showed a slightly higher absorption and void ratio, but lower maximum dry unit

weight, which could be explained by the cementing of un-reacted cement phase, e.g. lime, and

consolidation during the stockpile period. The crushed fines in RCA usually contain more cement phase,

and voids potentially fill up with fines during hydration in the stockpile (Chen et al. 2012). The natural

limestone aggregate was a uniformly graded material, and it was used as a conventional (control)

material.

Chemical Properties. Results from total elemental analysis by acid digestion and carbon content

analysis are shown in Table 4. Silicon was not tested in this study, and will be determined in follow up

X-ray diffraction analysis. Ca, Fe, Al, Mg, K, and Na were shown to be the major elements in the three

materials with more than 0.1% weight percentage. RCAs were most rich in Al and Fe, which are two

major elements in the cement phase. For trace elements, RCA showed higher concentrations of Ba, Cu,

Ni, Co, As and Cr than natural aggregate, which may be due to the cement additives, e.g. fly ash, slag.

Stockpiled RCA had higher total inorganic carbon (TIC) than freshly crushed RCA (6.7 to 6.5% wt) due

to the long period of carbon uptake during the stockpile period. The natural limestone was highly

carbonated with 10.7% wt. TIC. However, compared to TIC results from Chen et al. (2011), both WR-F

and WR-SP RCA had a relatively higher TIC than the reference range of 0.5 to 2.8% wt.. Follow up

mineralogy will provide a better understanding of the degree of carbonation in WR-F and WR-SP RCA

samples.

Field Leaching Test

Leachate pH. pH as a function of pore volumes of flow (PVF) for RCAs and natural aggregate in the Lot

60 field site is presented in Figure 8. No leachate was collected from RCA paved with regular asphalt

possibly due to lack of rain water penetration of the apshalt cap combined with high water absorbtion of

RCA. In contrast, leachate from lysimiters paved with porous asphalt was collected. The pH values of

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both the WR-F and WR-SP RCA exceeded the EPA’s drinking water standard, while the natural

aggregate fell within the standard range of 8.5 and 6.5 pH. The WR-SP and WR-F RCA samples follow

different pH trends. WR-F RCA leachate started with a high pH (12.6) and remained constant for the first

3 PVF, while WR-SP RCA started at a nuetral pH (7.3), gradually increased to a pH of 11.9 and then

decreased to a pH of 10.6 over 1.5 PVF. The pH of stockpiled RCA may have initially been low due to

the carbonation film around the particles. The carbonate would have first dissolved in the first flush of

rainwater, followed by cement hydration and resulting production of C-H-S, Ca(OH)2 or unreacted lime.

The lime when exposed to the water would result in increased pH. Long-term leachate monitoring will be

conducted until equllibrim pH is determined.

Heavy Metal Leaching. Concentrations of chromium (Cr), lead (Pb), selenium (Se), and antimony (Sb)

have exceeded the maximum contaminant level of USEPA drinking water standard, and figure 9 presents

the Se, Sb, Pb and Cr concentrations in leachate as a function of PVF. The leaching of Pb and Cr was

insignificant related to the total elmental quantity in solid phase at pH between 6.5 and 12.6 suggesting

that leaching is controlled by diffrent dissolution and desorption processes. The maximun leaching

occurred in the first 1 PVF for both Cr and Pb, and decreased to equillibrium level, but the values were

two times higher than the USEPA Maximum Contaminant Level. The leachate could have the potential

to contaminate groundwater and soil, but contaminant transport modeling should be utilized to consider

dilution and sorption processes that may occur between the RCA layer and adjacent water bodies.

Batch Tests

Figure 10 shows the acid neutralization capacity (ANC) curve of all three materials. Negative values in

Figure 10 represent base additions. The material pH (no acid or base added) of WR-F RCA was higher

than WR-SP (12.3 versus 11.8), which is as expected due to the consumption of more cement hydration

phase (e.g. portlandite). The ground natural limestone showed high alkalinity potential. However, field

leaching tests had neutral pH suggesting limestone needed more water residence time for dissolution and

reaction of alkaline species. A plateau around pH 4.0 to 6.0 was observed for all three materials.

Garrabrants et al. (2004) concluded that the plateau in the ANC could be explained by dissolution of

calcium carbonate (carbonation) in concrete, which is caused by a reaction between portlandite and

calcium silicate hydrate with carbon dioxide from the environment. Carbonation conditions may occur

during the concrete service life and in stockpile storage. A similar plateau width for WR-F and WR-SP

(11.0 and 10.0 mmol/g) coordinate with the TIC readings. The higher leachate pH could be due to the

dissolution of highly soluble alkaline species. During concrete service life, concrete will up take

carbonate to some degree. When demolished, the concrete will be crushed and thesurface area exposed to

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the environment will increase. If crushed RCA is stockpiled in the quarry for a long time, the freshly

crushed surface will take up carbon and a carbonation film with low solubility will wrap around the

particles.

CONCLUSION

In this study, recycled concrete aggregate (RCA) was evaluated for potential heavy metal leaching and

high alkalinity that has been historically observed surrounding its use as a road base coarse material. To

compare to a control, natural aggregate was also studied. Field observations as well as batch test results

have led to the following observations:

a. High alkaline was observed in the first few pore volumes of flow of leachate from both freshly

crushed and stockpiled RCA in field tests. However, pH had different leaching characteristics

from freshly crushed RCA and stockpiled RCA.

b. Heavy metal leaching from RCA exceeds the USEPA drinking water standard. However,

contaminant transport modeling to determine the effects due to soil absorption and dilution have

not been evaluated and thus the impact of heavy metal leaching on the environment is yet

unknown.

c. The carbon uptake during concrete service life and stockpiled age could change the alkaline

nature of RCA with consumption of concrete hydration phase, which will lower the leachate pH

of RCA.

Future studies include: additional mineralogical analysis to better understand the leaching mechanism

will include X-ray diffraction, serial batch tests, and Scanning Electron Microscopy (SEM). Additionally,

a WiscLeach model and Minteq model will be used to simulate the leaching process and further evaluate

contaminant transport and environmental impact.

ACKNOWLEDGEMENT

Support for this study was provided the University of Wisconsin System Solid Waste Research Program,

TPF-5 (129) Recycled Unbound Materials Pool Fund and Recycled Materials Resource Center. Any

opinions, findings, or conclusions expressed in this paper do not necessarily reflect the views of the

sponsors. Special thanks to Professor Craig H. Benson, James M. Tinjum, Tuncer B Edil and Sabrina L.

Bradshaw, lab managers Jackie B. Cooper and Xiaodong Wang, Geo-friends, University of Wisconsin-

Madison.

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REFERENCES

ACPA (2008). “Concrete - The Environment & Recycling.” http://www.acpa-southwest.org/environ.htm.

ACPA (2009). “Recycling Concrete Pavements.” American Concrete Pavement Association.

Bozyurt, O. (2011). “Behavior of recycled pavement and concrete aggregate as unbound road base.” MS

Thesis, Department of Geological Engineering, University of Wisconsin at Madison.

Chen, J., Bradshaw, S. L., Benson C. H., Tinjum, J. M., Edil, T. B. (2012). “pH-dependent Leaching of

Trace Elements from Recycled Concrete Aggregate.” Proceeding of GeoCongress 2012, March

25-29, Oakland, CA.

Cornelis, G., Johnson C. A., Gerven, T. V., Vandecasteele, C. (2008). “Leaching mechanisms of

Oxyanionic metalloid and metal species in alkaline solid wastes: a review.” Applied

Geochemistry. 23, 955–975.

Dijkstra, J. J., Meeussen, J. C. L., Comans, R. N. J. (2004). “Leaching of heavy metals from

contaminated soils: an experimental and modeling study.” Environmental Science & Technology,

38 (16), 4390–4395.

Dijkstra, J. J., Van der Sloot, H. A., Comans, R. N. J. (2006). “The leaching of major and trace

elements from MSWI bottom ash as a function of pH and time.” Applied Geochemistry, v 21, n 2,

335-351.

Engelsen, C. J., Van der Sloot, H. A., Wibetoe, G., Justnes, H., Lund, W., Stoltenberg - Hansson, E.

(2010). “Leaching characterization and geochemical modeling of minor and trace elements

released from recycled concrete aggregates.” Cement and Concrete Res., 40 (12), 1639-49.

FHWA (2004). “Recycled Concrete Aggregate – Federal Highway Administration National

Review.” Federal Highway Administration. Washington, D.C .

Garrabrants, A. C., Sanchez, F., Kosson, D. S. (2004). “Changes in constituent equilibrium leaching and

pore water characteristics of a Portland cement mortar as a result of Carbonation.” Waste

Manage. 24(1), 19–36.

MnDOT (2010). “Recycled Unbound Materials.” Report MN/ No.TPF-5(129), Minnesota DOT,

Maplewood.

O’Donnell, J. (2009). “Leaching of Trace Elements from Roadway Materials Stabilized with Fly Ash.”

MS Thesis, Department of Geological Engineering, University of Wisconsin at Madison.

USGS (1997). “Natural Aggregates – Foundation of America’s Future.” USGS Fact Sheet FS. United

States Geological Survey, U.S. Department of the Interior, Washington, D.C. 144-97.

Van der Sloot, H. A., Van Zomeren, A., Stenger, R., Schneider, M., Spanka, G., Stoltenberg-Hansson, E.,

Dath, P. (2008). “Environmental CRIteria for CEMent based products, Phase I: Ordinary

Portland Cements, Phase II: Blended Cement.” ECN-E--08-011, the Netherlands.

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TABLES

Table 1. Carbonate vs. Non-carbonate compositions of WR-F and WR-SP RCAs

WR-F RCA WR-SP RCA

Respect to Gravel % Non-Carbonates 21 16

% Carbonates 33 40

% Remainder 46 44

Respect to Agg. % Non-Carbonates 40 28

% Carbonates 60 72

Ratio Non-Carb : Carb.

(Carb : Non-Carb)

0.66:1 (1:1.5) 0.39:1 (1:2.5)

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Table 2. Elements considered in concrete leaching tests

Element Instrument MCL (ug/L) MDL (ug/L)

Aluminum ICP-OES 50-200** 2

Calcium ICP-OES - 31

Iron ICP-OES 0.3** 2

Magnesium ICP-OES - 1

Potassium ICP-OES - <1000

Silicon ICP-OES - <1000

Sodium ICP-OES - 3

Strontium ICP-OES 4000*** <1

Barium ICP-OES 2 0.08

Beryllium ICP-OES 4 0.11

Boron ICP-OES 6*** 2.2

Cadmium ICP-OES 5 0.53

Chromium ICP-OES 100 0.3

Cobalt ICP-OES - 0.8

Copper ICP-OES 1000** 2.7

Lead ICP-OES 15 3.8

Manganese ICP-OES 50 0.13

Molybdenum ICP-OES 40*** 3.3

Nickel ICP-OES 100*** 1.8

Vanadium ICP-OES - 0.8

Zinc ICP-OES 5000 0.5

Antimony ICP-OES 6 0.004

Arsenic ICP-OES 10 0.008

Mercury ICP-OES 2 0.03

Selenium ICP-OES 50 0.01

Thallium ICP-OES 2 0.006

*USEPA drinking water standard and Health Advisories

**Secondary drinking water regulation

***Health Advisories - Life time

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Table 3. Physical properties of RCAs and natural limestone with reference RCA samples

* From Bozyurt, O. (2011)

Material Source Wopt γd Absorption Specific gravity Void Ratio, q USCS

RCA

(kN/m3) % (Bulk) (Apparent) (Bulk) (Apparent) Classification

Michigan* 8.7 20.84 5.44 2.367 2.718 0.11 0.28 GP

Texas* 9.2 19.66 5.53 2.271 2.597 0.13 0.30 GP-GM

Colorado* 11.9 18.9 5.81 2.279 2.628 0.18 0.36 SM

Ohio* 11.8 19.36 6.50 2.243 2.627 0.14 0.33 SW-SM

California* 10.9 19.8 5.00 2.324 2.63 0.15 0.30 SP

New Jersey* 9.3 19.7 5.38 2.315 2.644 0.15 0.32 SP

WR(F) 10.8 19.4 4.23 2.521 2.694 0.27 0.36 GP

WR (SP) 9.9 19.9 4.21 2.480 2.645 0.22 0.30 SP

Limestone Lot 60 - 16.2 1.80 2.659 2.780 0.61 0.68 GW

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Table 4. Total elemental analysis and carbon content analysis results of WR-F RCA,

WR-SP RCA and natural aggregate

Sample Labels WR F WR SP Natural Aggr.

Ca (%) >20 >20 >20

Fe (%) 0.83 0.65 0.33

Al (%) 0.52 0.41 0.10

Mg (%) 8.47 8.69 >10

Na (%) 0.84 0.37 0.45

K (%) 0.15 0.11 0.08

Mn (%) 0.04 0.04 0.03

Ba (mg/kg) 2 2.3 0.4

Cu (mg/kg) 1.4 1.1 0.3

Ni (mg/kg) 0.6 0.5 0.1

Co (mg/kg) 0.3 0.2 n.d.

Mo (mg/kg) 0.1 0.1 n.d.

Tl (mg/kg) n.d. n.d. 0.1

Pb (mg/kg) 0.4 0.3 0.4

Se (mg/kg) 1.7 1.7 1.6

As (mg/kg) 1.1 1.1 0.6

Cr (mg/kg) 0.7 0.6 0.2

Total Carbon (%) 6.8 7.4 11.7

Total Inorganic Carbon (%) 6.5 6.9 10.7

Total Organic Carbon (%) 0.27 0.54 0.95

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FIGURES

(A) Freshly crushed (WR-F) RCA

(B) Stockpiled (WR-SP) RCA

Figure 2. Photographs of recycled concrete aggreagates in this study

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Figure 3. Photograph of natural limestone aggregate used in this study

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Figure 4. Schematic view of lysimeter layout and design (A) Lysimeter layout (B) Cross section view of

lysimeter collection system.

(A)

(B)

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Figure 5. HDPE geomembrane lysimeters usd in this study

Figure 6. Asphalt paving around flushmount

19

0

20

40

60

80

100

0.010.1110100

PSD

MnRoad (Class 5)

CA RCA

CO RCA

MI RCA

TX RCA

Natural Aggr. Lot 60

WG(F) RCA

WG(SP) RCA

Particle Diameter (mm)

Figure 7. Grain size distribution (GSD) curves, for stockpiled RCA, freshly crushed RCA, and natural

aggregate with reference RCA data.

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4

6

8

10

12

14

0 0.5 1 1.5 2 2.5 3 3.5

Fresh RCA (R)Fresh RCA (P)Stockpiled RCA (P)Natural Aggr. (R)Natural Aggr. (P)

PVF

Figure 8. pH as a function of pore volumes of flow (PVF) for RCAs and natural aggregate in the Lot 60

field site

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10-1

100

101

102

103

0 0.5 1 1.5 2 2.5 3

Se

WR(SP) RCAWR(F) RCANatural Aggr.

PVF

USEPA

(A)

10-1

100

101

102

0 0.5 1 1.5 2 2.5 3

Pb

WR(SP) RCAWR(F) RCANatural Aggr.

PVF

USEPA

(B)

10-1

100

101

102

103

0 0.5 1 1.5 2 2.5 3

Cr

WR(SP) RCAWR(F) RCANatural Aggr.

PVF

USEPA

(C)

10-1

100

101

102

0 0.5 1 1.5 2 2.5 3

Sb

WR(SP) RCAWR(F) RCANatural Aggr.

PVF

USEPA

(D)

Figure 9. Heavy metal concentrations in leachate from field sites as a function of PVF

(a) Selenium (b) Lead (c) Chromium (d) Antimony

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0

2

4

6

8

10

12

14

-5 0 5 10 15 20

WR-FWR-SPNatural Aggregate

Acid/Base Addition (mmol/g)

Base Acid

Figure 10. Acid neutralization capacity (ANC) curve of all three materials from batch leaching tests