Recycled Materials and Byproducts in Highway Applications—Non-Coal Combustion Byproducts, Volume 3 (2013)

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

8 BOUND APPLICATIONS Asphalt Cement and Asphalt Concrete The only research published over the last decade on MSW byproducts in asphalt and asphalt concrete applications was based on studies conducted in Oman and Taiwan. In Oman, Hassan (2005) used MSW bottom ash as a partial replacement of fine aggregate (passing the 4.75 mm sieve) in asphalt con- crete mixes with 0%, 5%, 10%, 15%, 20%, 30%, and 40% by total weight of aggregate. Testing included characterization of physical properties for the MSW bottom ash (gradation and specific gravity) and leachate testing. Asphalt concrete mix testing included evaluations of optimum asphalt content by the Marshall method, moisture sensitivity (tensile strength ratio), and raveling (Cantabro method). Results showed that the Marshall flow number became insensitive to asphalt content at MSW bottom ash contents of 10% or higher. Increasing percentages of byproduct resulted in significant increases in air voids and voids in mineral aggre- gate, with corresponding decreases in bulk specific gravity of the compacted samples. Significant increases in raveling potential (Cantabro test) were seen once the percentage of MSW byproduct reached 30%. Moisture sensitivity began to increase for mixes with percentages of 20% and higher. Based on these results, the authors recommended limiting the use of MSW byproduct to 15% and 20% for surface and base course mixes, respectively. In Taiwan, Chen et al. (2008) evaluated the influence of MSW bottom ash as an aggregate substitute in asphalt con- crete mixes on physical properties and the leaching potential of mixtures. The physical property testing showed a higher resis- tance to rutting and increase sensitivity to moisture (low tensile strength ratios). The authors recommended limiting the use of MSW bottom ash to 20% in binder or base courses and to 10% in surface mixes (percent by weight of mix). The toxicity characteristic leaching tests showed, after mixing with asphalt cement, that the concentrations of heavy metals and toxicity levels were significantly reduced. It should be noted that no assessment of cracking potential was included in the study. Portland Cement Clinkers A Japanese laboratory study used two types of processed MSW prior to burning: raw MSW and washed MSW (Nabajyoti et al. 2007). Both byproducts were evaluated for volatile emissions from the MSW during the clinker production. Results showed the production process generated consid- erable amounts of sodium (Na), potassium (K), lead (Pb), zinc (Zn), and cadmium (Cd). Researchers noted toxic elements such as Pb and Cd remained captured in the clinker. The evaluation of the cement produced from the raw MSW ash was more reactive than the cement produced from the washed MSW ash. The use of MSW in clinker reduced the demand for CaCO3 from 70% (conventional clinker) to 50% when the byproduct was used. Research conducted in Greece by Sikalidis et al. (2002) investigated using MSW byproducts in the production of clinkers. First, the MSW was separated into two fractions. The heavy fraction consisted of mainly earthen materials, stones, broken ceramics, glass, and other similar materials. The light fraction consisted mainly of paper, wood, light plas- tics, leather and cloth pieces, various fibers, and other similar combustible materials. The dried and crushed heavy fraction was introduced into the rotary kiln at approximately 1100°C, which is about the location in the kiln where the other raw materials are added. The light fraction was used with a mix- ture of pet-coke to heat the rotary kiln (jets need to be designed especially for this fuel source blend). An economic analysis showed a modified kiln that could treat about 500 tons per day of MSW and that producing about 433 tons per day of mortar would be economically profitable for processing the lightweight MSW. Portland Cement Replacement Italian researchers Polettini et al. (2001) investigated the mechanical behavior (setting time, unconfined compressive strength, shrinkage/expansion) of four different sources of Italian MSW fly ash byproducts (i.e., combustion ashes from air pollution control devices) used in portland cement mixes. Authors noted that MSW bottom ash, generally composed of aluminosilicate with small amounts of heavy metals, was not considered a hazardous material in the European Waste Catalogue. However, the MSW fly ash was considered haz- ardous because of concentrations of heavy metals, chlorinated organic compounds, and soluble salts. Researchers found that the high concentrations of heavy metals, chlorides, and sulfates significantly altered the hydra- tion behavior (setting time, strength gain over time) of the chapter three APPLICATIONS FOUND IN THE LITERATURE

9 portland cement. A suggestion for an upper limit on MSW fly ash was 20% by weight maximum allowable content. It was noted that even at low concentrations the inclusion of the MSW fly ash significantly delayed the strength gain of the composite cement. Filipponi et al. (2003) noted that MSW bottom ash is considered nonhazardous waste according to the European Waste Catalogue and would be acceptable material to use in concrete applications. These researchers evaluated different portland cement concrete (PCC) mixes that were prepared by blending MSW bottom ash with portland cement in vary- ing proportions and with different water to cement ratios. In general, the MSW bottom ash was not reactive (i.e., did not contribute to cementitious properties); authors suggested treatment of the byproduct to improve pozzolanic reactions. Italian researchers Bertolini et al. (2004) evaluated both MSW fly ash and MSW bottom ash in PCC. The MSW fly ash was subjected to a washing treatment to reduce the chloride content. The MSW bottom ash was ground with one of two methods: dry or wet grinding in a ball mill. MSW byprod- ucts were used as a cement substitute at 30% replacement by weight. The chemical composition of the byproducts, cement, and other additives were determined with inductively coupled plasma and x-ray defraction. The workability of the fresh con- crete was evaluated using both the standard slump test and the VeBe test. Hardened properties were determined for compres- sive strength (4-in. cubes), chloride by potentiometric titra- tion after grinding penetration (6-in. cubes, 1.18-in. diameter cores), and corrosion rate in solutions with pH from 11 to 13.5. Various compounds found in MSW ash are reviewed in Table 9. Although there was variation in the oxide percent- age between the sources of MSW bottom ash, there were significant differences between either of the bottom ashes and the MSW fly ash. The particle size distribution after dry ball mill grinding had a D50 size of approximately 0.015 mm, which reduced to 0.003 mm after wet ball mill grinding. Fresh concrete properties showed a significant reduction in slump (almost zero) with 30% MSW fly ash. After compaction on a vibratory table, the MSW fly ash 28-day compressive strength was only slightly lower compared with a control PCC with 30% coal combustion fly ash. Fresh concrete with the MSW dry grind bottom ash was similar to that of the control mix. During setting, the MSW bottom ash concrete showed significant expansion owing to the development of hydrogen gas. The authors attributed this to the presence of metallic traces of aluminum in the MSW bottom ashes, which, when in contact with the high pH in the solution, produces a high rate of corrosion. This reaction produces hydrogen gas, which was entrapped in the concrete before setting occurs. Experiments with just the MSW bottom ash in a solution of 14 pH water showed that 1 g of MSW bot- tom ash produced 0.15 liter of gas. Fresh mixes prepared with the wet ground MSW did not show this expansion reaction. The byproduct in this case was added to the mix in slurry form (1:1 for the MSW-water ratio). The water in the slurry was considered in overall volumetric mix design for the PCC. The authors suggested that a few days of rest after grinding may be sufficient to eliminate the expansive nature of the bottom ash. Hardened PCC properties of the control and wet ground MSW bottom ash had similar 28-day compressive strengths, with the byproduct mix having the potential for a higher long- term compressive strength than the control. In all cases there was a significant loss of compressive strength when using the MSW fly ash in the PCC (3190 psi and 8702 psi, respec- tively). Resistivity of wet ground MSW bottom ash had a higher electrical resistivity at 30 days than either the con- trol PCC or the control PCC with 30% coal fly ash (300, 80, and 160 mm, respectively). Chloride penetration was slightly lower for the wet ground MSW bottom ash than either the control or control with 30% coal fly ash at a depth of 10 mm (0.04%, 0.1%, and 0.15% by concrete mass, respectively, Compounds Oxides (%) Cement Fine Aggregate MSW Fly Ash MSW Bottom Ash (Source 1) MSW Bottom Ash (Source 2) Al 2 O 3 4 .71 6.15 1 0.72 10.29 6.36 Na 2 O 0.32 0 .19 11.34 2.46 1 .72 K 2 O 0.85 0 .19 6.94 0 .71 0.40 SO 3 3 .48 0.79 8 .49 1.21 3 .43 CaO 62.7 6 .53 37.32 13.25 15.89 Fe 2 O 2 1 .93 4.49 2 .6 1 4.17 6.53 MgO 1.99 1 .7 3 .3 2 .02 1.99 Mn O 2 1 .07 0.05 0 .05 0.06 0 .16 P 2 O 5 0 .15 1.07 1 .55 1.08 1 .77 Ti O 2 0 .19 0.39 — 0 .38 0.85 Si O 2 2 3.74 78.45 14.71 53.41 61.9 After Bertolini et al. (2004). — = date not reported. TABLE 9 PERCENT OF MAJOR ELEMENTS, NOT INCLUDING CHLORIDE, CALCULATED IN TERMS OF OXIDES

10 ate potential sulfate attack issues and problems if used with reinforcing steel. French researchers, Aubert et al. (2004) evaluated the development of a physio-chemical treatment for MSW fly ash, referred to as the REVASOLTM process. The process allowed for the reduction of the soluble fraction, fixes heavy metals, and eliminates dioxins. These researchers evaluated both engineer- ing properties (compressive strength, durability) and leaching potential of conventional concrete prepared with treated MSW fly ash. Mixes that were investigated in this study were a con- trol mix, two mixes with treated MSW fly ash (12% and 50%) substituted for cement, and two mixes with sand substituted for cement (12% and 50%) for comparison. Workability decreased with the increasing percentage of substitution of the treated MSW for cement. The workabil- ity of the 12% treated MSW and 12% sand fresh concrete were similar, with slumps of about 2.5 in. At the 50% levels, the treated MSW and sand mixes had slumps of 2 and 3 in., respectively; the control mix had a slump of 4.5 in. Porosity of the hardened concrete was measured using three methods: 1. Gas permeability: Hardened concrete (28 days, 68°F, 100% relative humidity) specimens are sawed to elimi- nate surface defects and skinning, then tested dry once steady-state conditions are established according to the French AFPC–AFREM recommendations using a Cembureau permeameter. 2. Water accessibility: Uses the difference between the mass of a specimen dry to the mass after saturation with water. 3. Total porosity: Uses the bulk and absolute densities of the concrete to determine the percentage of potentially permeable voids. The results are included in Table 10. At either 50% of sand or 50% MSW bottom ash, the permeability, porosity, and total porosity increased substantially. Leaching tests were conducted on monolithic PPC samples (Figure 2). When the MSW is encapsulated in hardened con- crete, only the chromium, copper, lead, and tin show a slight increase in the concentration in the leachate. As expected, the concentrations increased with the increasing percentage of MSW bottom ash in the mix. All concentrations were below the threshold values for the monolithic concrete samples. Aubert et al. (2004) also evaluated the potential environ- mental impact when the PCC is recycled. These researchers crushed concrete to simulate recycling PCC and then re- assessed the leaching potential (Figure 3). Once the concrete was crushed, all elemental concentrations increased substan- tially in both the crushed control and crushed MSW PCC materials. The concentrations of chromium, lead, and arsenic after 6 months, 1-day cycles). The authors concluded that the wet ground MSW bottom ash could be expected to behave like a pozzolanic reaction. Research in Slovenia by Juricˇ et al. (2006) evaluated the influence of MSW bottom ash on the physical properties of the paste (i.e., binder) and PCC. The workability (slump) of the PCC was reduced by about 50% when 15% MSW bottom ash was included in the paste. The density (unit weight) of the fresh concrete increased when the byproduct was included in the PCC. The hardened concrete properties showed a decrease in the 28-day flexural and compressive strength of the mortar by 4.35 to 2.9 psi (0.03 to 0.02 MPa) per percent of MSW bottom ash used in the mix (percent by weight). The authors recommended that the amount of byproduct in the cement be limited to 15% for use in low-strength concrete mixtures. Mortars French researchers evaluated the mechanical strength of mor- tars with MSW fly ash, as well as the environmental impact of these mortars (Aubert et al. 2006). Two proprietary treat- ments of the MSW fly ash were used to minimize problems with swelling of the mortar when MSW fly ash is used. The first treatment, REVASOLTM, was based on a wash, phospha- tion, and calcinations of the MSW fly ash. The second treat- ment was a variation of the first and added sodium carbonate (Na2CO3) to the wash water to dissolve the metallic aluminum and sulfates. Both processes reduced swell; however, a poor stabilization of antimony and chromium is achieved. Portland Cement Concrete French researchers, Pera et al. (1997), evaluated the use of MSW bottom ash as an alternative aggregate in PCC. The MSW bottom ash material used passed the 20 mm sieve and was retained on the 4 mm sieve. The authors noted the MSW bottom ash properties showed lower, but still acceptable, density and strength characteristics. They also noted that the water absorption capacity was higher than typical con- struction aggregates. When used in PCC mixtures, the MSW bottom ash aggregate substitution resulted in swelling and cracking of the samples, which was attributed to a reaction between the cement and the metallic aluminum. A treatment with sodium hydroxide was proposed to avoid this problem. Experimentation with this approach showed that a substitu- tion of MSW bottom ash at up to 50% of the gravel content could be obtained while minimizing swelling. Berg and Neal (1998), U.S. researchers, found that MSW bottom ash could be considered a marginal aggregate for PCC applications. The MSW byproduct met most of the PCC-related ASTM standards such as aggregate gradation. However, the high angularity and brittle nature of the byproduct was thought to generate problems with use in PCC. They also found the sulfate and chloride concentrations to be high enough to cre-

11 Mix Gas Permeability (10-16m2) Water Porosity (%) Total Porosity (%) Control 3.3–4.6 14.2–15.1 14.2–16.7 Sand, 12% 1.9–5.1 12.7–14.2 14.5–16.2 MSW, 12% 1.6–4.6 13.4– 16.9 15.9–17.2 Sand, 50% 35.8–68.0 18.5–20.7 21.5–25.4 MSW, 50% 17.9–35.6 18.1–22.5 22.7–25.0 After Aubert et al. (2004). TABLE 10 PERMEABILITY OF PCC MIXES 69 58 251 11 3 1 1 3 90 64 161 13 5 0 2 3 182 63 289 26 10 1 5 2 0 500 1000 1500 2000 2500 Cr Ni Zn Cu Pb Cd Sn As Co nc en tra tio n, µ g/ kg Monolithic Concrete, Control 12% MSW Bottom Ash 50% MSW Bottom Ash Monolithic Concrete Materials FIGURE 2 Elements leached from monolithic concrete samples (after Aubert et al. 2004). 435 37 1 27 2 52 15 11 6 1 809 45 6 393 47 35 16 3 3 2,304 21 7 373 49 47 3 7 9 0 500 1000 1500 2000 2500 Cr Ni Zn Cu Pb Cd Sn As Co nc en tra tio n, µ g/ kg Crushed, Control 12% MSW Bottom Ash 50% MSW Bottom Ash Crushed Concrete Materials FIGURE 3 Elements leached from crushed concrete (after Aubert et al. 2004).

12 increased significantly over those in the control crushed PCC materials. Only the chromium exceeded the legal thresholds in the case of the crushed concrete. As with the monolithic samples, the concentrations in the leachate increased with the increasing percentage of MSW in the PCC. Japanese researchers Horiguchi and Saeki (2004) evaluated the use of a MSW ash in the preparation of a special cement (Eco-cement) for use in controlled low strength materials (CLSM) mixes. The authors reported that acceptable leaching, strengths and flowability properties could be achieved with this specialty cement. Stabilized Base Danish researchers Cai et al. (2004) used MSW bottom ash and treated flue gas cleaning products and mixed each byproduct with 2.5% cement to determine the compressive strength and leaching potential over a 64-day period. The byproduct mixes had lower but acceptable strength charac- teristics. Heavy metal leaching results showed that the MSW bottom ash mixes had up to 100 times that of the reference (control) mixes. The results also showed Cl and Na were increased by a factor of from 20 to 100; from 2 to 10 times for K, calcium (Ca), and sulfate (SO4); and from 5 to 50 times for copper (Cu) (50 times), Cd, Pb, and Zn (5 times). The results from Cr and nickel (Ni) were similar to the control mix. UNBOUND APPLICATIONS For Florida Department of Transportation (FDOT) research for MSW use in highway applications the byproducts, in general, were classified as either a well-graded or poorly graded sand (SW or SP by Unified Soil Classification Sys- tem) (Cosentino et al. 1995a, b, c). Cosentino et al. (1995 a, b, c) noted that the MSW combined ash met FDOT criteria for use as highway subgrade materials. A demonstration proj- ect was constructed to evaluate engineering properties and leachate characteristics. Results for this project showed that moisture–density compaction properties, permeability, and unconfined compressive strength were a function of the com- paction energy and moisture content with similar behavior of conventional fill materials. The stress–strain characteristics were similar to those for sand. Leachate testing showed initial increases in concentra- tions of silver (Ag), arsenic (As), Ca, Cr, and Pb decreased over time. Although the concentrations were higher than in the control materials, none of the values exceeded the drink- ing water standards. Aggregates Researchers in Spain, Izquierdo et al. (2008) evaluated the use of MSW bottom ash as an aggregate substitute in unbound pavement layers under both laboratory and field conditions (Table 11). Although the mechanical properties of the MSW aggregates were found to be acceptable, the environmen- tal issues were considered the most important factor to be addressed. These researchers used two leaching tests that were the single-batch Dutch availability test, NEN 7341, and the two-batch European method EN 1247. The pH from the field evaluation of the MSW byproduct increased from 7.3 to 9.2 and was slightly lower than the laboratory values pre- dicted. The leachate also had high initial conductivity values indicating the release of elements occurring in salts. Trace Property Spanish Requirement for Bottom Ash for Various Applications Embankment and Landfill Base and Subbase Gravel–Cement Particle Size, 0.08 Tolerable: <25% passing Adequate: <35% passing Select: <25% passing 0.08 mm% (2/3)(0.4 mm%) 5.4% max Gradation Curve Shape — Granulometric curves ranging from S1 and S6 S3 Maximum Size Tolerable: at least 75% passing 15 cm Adequate: 100% passing 10 cm Select: 100% passing 8 cm Less than one-half of the compacted thickness 12.5 mm LA Abrasion — <50% 45% Proctor Values Tolerable: > 1.45 g/cm3 Adequate: > 1.75 g/cm3 Select: — No requirement Opt. moist. 12.3% at 1.8 g/cm3 CBR Tolerable: > 3 Adequate: > 5 with less than 2% swell Select: > 10 and no swell >20 90% 30 95% 56 100% 97 Sand Equivalent — >30% for medium and heavy traffic >25% for light traffic 52% Plasticity Tolerable: LL < 40 or LL < 65 and PI < 0.6 LL 9 Adequate: LL < 40 Select: LL < 30 and PI < 10 Non-plastic Non-plastic Organic Matter by Potassium Permanganate Method Tolerable: <2% Adequate: <1% Select: — — 1% After Forteza et al. (2004). — = data not reported; CBR = California bearing ratio. TABLE 11 SUMMARY OF SPANISH REQUIREMENTS AND MSW BOTTOM ASH PROPERTIES

13 By Spanish standards, MSW bottom ash met all require- ments for soils classified as adequate. The Spanish embank- ment and landfill classification system had requirements for tolerable, adequate, and select soils. Table 3 provides the engi- neering properties of the bottom ash and the Spanish require- ments for embankments and landfills as well as for base and subbase materials. Swedish research by Åberg et al. (2006) evaluated the leaching potential trace metals and chlorides when MSW bottom ash is used as a base material under asphalt con- crete pavements. One full-scale field section was constructed using MSW bottom ash and another section using gravel (control section). The highest mobility metals and anions in the leachate were Cl, Cu, and Cr; the Cl and Cu concentra- tions decreased with time (over 12 months). The mobility of the Cr decreased over time. The concentrations of lead were very low over the 12-month monitoring period, and the authors attributed this to iron oxides. Prediction models (regression equations) were useful in predicting Ni, Pb, Zn, and Cu concentrations, but were less reliable for predicting Cd and Cr. The lack of accuracy was attributed to changes in pH and liquid to solid ratio values between the laboratory and field testing conditions. The regression equations used in the analysis were: Log Cd Log 10 4 2 0 22 0 04 0 004 0 03 2( ) = − − − −. . . . .x y xy x 10 7 7 1 9 0 11 10 10 8 1 9 2Cr Log Cu ( ) = − + ( ) = − − . . . . . x x x 0 02 0 11 10 11 0 2 3 0 12 1 2 2 . . . . . y x x x + ( ) = − +Log Pb Log 0 6 9 0 23 0 03 126 21 4 1 2 2 0 5 Zn Ni ( ) = − − = − − . . . . . . x x x y + +0 12 0 87 2. .xy x Where: x = pH y = liquid/solid ratio Another Swedish research project was conducted by Lidelow and Lagerkvist (2006) that evaluated full-scale field test sections; these were monitored for three years. The main elements in the leachate included Al (12.8–85.3 mg/l), Cr (2–125 mg/l), and Cu (0.15–1.9 mg/l) from the MSW bot- tom ash sections. The crushed rock sections showed concen- trations of Zn (1–780 mg/l). The initial release of compounds from the MSW bottom ash sections included Cl- (about 20 g/l). After three years, the Cu and Cl- were similar in con- centration to the crushed rock sections. However, the Al and Cr was still more than one order of magnitude higher in the MSW bottom ash sections compared with the crushed rock sections after three years. During rain events, diluted salt compound concentrations increased. Researchers noted that the laboratory results for evaluating the leachate from the metals showed very low release and the researchers con- cluded the trace metals in MSW were not a concern. Base and Subbase Cosentino et al. (1995 a, b, c) noted that the MSW com- bined ash met the FDOT criteria for use as highway sub- grade materials. A demonstration project was constructed to evaluate engineering properties and leachate charac- teristics. The project showed that MSW combination ash provided high strength and was relatively free draining. The environmental analysis showed concentrations of As, barium (Ba), Cd, Cr, Pb, mercury (Hg), selenium (Se), and Ag concentrations were below surface water and drinking water standards with the exception of Se. This was a con- cern for stockpiling or using the byproducts in unbound applications. Research in the Netherlands by Comans et al. (2000) studied the potential of a new technique to reduce the leaching poten- tial of Cu and molybdenum (Mo). The technique was designed to increase adsorption properties of the MSW bottom ash matrix by the inclusion of sorbent minerals added to the MSW byproduct. The most likely candidates for reducing leaching potential were found to be Fe(III) and Al(III) salts and in situ precipitation of the metal(hydr)oxides. A dura- ble reduction in the pH to near neutral of the MSW bottom ash was also found to be a major factor in controlling the leaching of Cu and Mo. A U.S. literature review by Chesner et al. (2000) noted that one or more of the following states were exploring the use of MSW byproducts as partial aggregate replacements in stabilized and granular bases as of 2000: Connecticut, Florida, Massachusetts, Minnesota, New Hampshire, New Jersey, and New York. International use of MSW combustion ash was limited to MSW bottom ash in these applications in the Netherlands, Denmark, Germany, and France. French research by Bruder-Hubscher et al. (2001) evalu- ated the environmental impact of MSW bottom ash in two field test sections. Results monitored over three years showed minimal impact when compared with test sections constructed with natural materials. In Spain, Forteza et al. (2004) evaluated the use of MSW byproducts in road base applications. These researchers eval- uated the physical and engineering properties of the MSW byproducts to determine if they could be substituted for aggre- gates in bases. The MSW bottom ash had acceptable aggre- gate and soil-related properties (see previous section). The environmental parameters evaluated were pH, conductivity, chloride content, sulfates, aluminum (Al), As, Ca, Cd, Cr, Cu, Fe, Hg, K, magnesium (Mg), manganese (Mn), Na, Ni, Pb, tin (Sn), and Zn. The authors concluded that trace metals did not pose an environmental problem.

14 crushed rock materials did not agree with the field results. However, the results agreed fairly well for the MSW bottom ash materials. French researchers Bouvet et al. (2007) specifically evalu- ated the leaching of Pb from MSW bottom ash when used in roadway base applications. Findings from this study indicated that the release of lead when water conditions have a neu- tral pH (about 7) was very low (<2%). The release percentage increased with a water pH of 4 and ranged from 4% to 47%. In Denmark, Hjelmar et al. (2007) placed and evaluated six large-scale field test sections placed in October 2002. Three of the sections used different MSW bottom ashes as sub-base materials under asphalt concrete test sections. Com- parisons between the water quality from the field sections and laboratory studies showed good agreement in results for salts but less agreement for some trace elements. The differ- ences between the laboratory and field results were attributed to differences in the pH of the water between laboratory and field experiments. In Spain, Vegas et al. (2008) conducted a detailed char- acterization of material properties for three byproducts: con- struction and demolition waste, slag, and MSW bottom ash. The findings indicated that fresh MSW bottom ash could be suitable for roadway base material as long as it does not con- tain high concentrations of soluble salts. The authors noted fresh MSW bottom ash had higher concentrations of soluble salts than weathered MSW bottom ash. Other Spanish researchers, Izquierdo et al. (2008), also compared the results of leaching evaluations (NEN 7341, EN 12457) and found reasonable agreement between the lab and field. In addition, these researchers developed estimates of depletion periods of extractable fractions for a number of elements in field conditions. Compounds that were read- ily depleted included Na, K, or Cl- salts with more than 50% of the compounds leaching out in the early stages of testing. The elements lead and vanadium (V) also followed this trend. Other elements that showed delayed depletion (i.e., needing additional extractions) including Al, titanium (Ti), Cu, cobalt (Co), Ni, Zn, Cr, As, and Se. The authors related this delayed leaching to the ionic strength of the initial leachate. Slightly soluble salts of Ca, Mg, and rubidium (Rb) were found to have progressive depletion. Other elements with progressive deple- tion behavior included tungsten (W) and antimony (Sb). Slow (delayed) depletion behavior was noted for SO42–, strontium (Sr), Ba, bromine (B), Mo, and silicon (Si). Embankments and Flowable Fill The RMRC website (2008) indicated that European expe- rience in MSW use in embankments encompassed more than 20 years, whereas the United States has only evalu- ated use in fills as demonstration projects. Internationally, the Netherlands, Denmark, France, and Sweden have used MSW bottom ash in a limited number of embankment appli- cations. Only Denmark was identified as having some expe- rience with this byproduct in either backfills or flowable fills (Chesner et al. 2000). Life-Cycle Cost Assessment Life-cycle cost assessment programs differ from life-cycle cost analysis programs in that they consider both financial costs as well as resource, energy consumption, environmental impact, construction, operation, and maintenance (including the use of roadway salts) over the life of the pavement. Birgisdottir et al. (2005, 2006) used the ROAD-RES (Denmark) program for life-cycle cost assessment, developed at the Technical Uni- versity of Denmark, to evaluate two different scenarios. The first scenario was the control with only natural materials and the second scenario used MSW bottom ash as a replacement for gravel in the sub-base layers. This evaluation showed only marginal differences in the environmental impacts (primarily emissions from fuel consumption) and resource consumption. Ground-water contamination leaching potential was linked to the use of road salt rather than the MSW bottom ash.