Recycled asphalt pavement - fly ash geopolymers as a sustainable pavement base material: Strength and toxic leaching investigations.

Ten-year chemical evolution of leachate and municipal solid waste incineration bottom ash used in a test road site

/pdf/life-cycle-assessment-model-for-road-construction-and-use-of-55fe1om10k.pdf

Life cycle assessment model for road construction and use of residues from waste incineration

The use of fly ash in highway applications as a stabilizing agent and soil amendment for embankments has become very common owing to its economical advantages. However, fly ash may contain toxic constituents that may pose environmental risk if they leach through the soil and reach groundwater. A series of water leach tests (WLTs), toxicity characteristic leaching procedure (TCLP) tests, and column leach tests (CLTs) were conducted to define the leaching of aluminum, arsenic, chromium, and zinc from a self-cementitious fly ash and four different off-spec high-carbon ashes. Laboratory results indicated that an increase in fly ash contents generally yields an increase in pH and leached metal concentrations regardless of the type of fly ash and metals. Furthermore, it was determined that there were significant differences in the leached metal concentrations measured in the three different laboratory tests, i.e., CCLT>CTCLP>CWLT. Analyses conducted using a numerical groundwater model indicated that pre...

Trace Metal Leaching from Embankment Soils Amended with High-Carbon Fly Ash

Reproducing ten years of road ageing--accelerated carbonation and leaching of EAF steel slag.

Significant amounts of recycled materials are being used in structural components of highways such as base, subbase, portland cement and asphalt concrete, and embankments. Past experience with recycled materials in highways has not shown a risk with respect to environmental impact and human health. However, environmental regulatory agencies frequently must assess risk to human health and the environment when conducting beneficial use determinations, particularly for new recycled materials. Contaminant leaching and advective transport are believed to be the primary transport pathways and both of them depend on in situ moisture conditions. The purpose of this study was to describe the state of the knowledge about water movement in the highway environment so that this knowledge may be incorporated into (1) practical leaching and preliminary impact assessments and (2) fate/transport models for use in risk assessment. Measurement techniques for moisture content, pore water pressure, and rainfall were discussed. For measuring in situ water content, time domain reflectometry (TDR) is a growing and promising technique. However, there is not a universal agreement on a TDR calibration equation. Laboratory techniques for measuring saturated hydraulic conductivity center on constant and falling head permeameter tests that should be conducted at low hydraulic gradients, and in addition, laminar and horizontal flow conditions. Hydraulic conductivity data for asphalt concrete, portland cement concrete (PCC), and base/subbase layers displayed wide scatter due to high variability in mixture designs and in measurement techniques. Factors affecting hydraulic conductivity are shape, size, and interconnectivity of air voids, and in PCC, the curing temperature and the type and extent of chemical reactions during hardening. Most of the evidence suggested that addition of recycled materials to PCC decreases the hydraulic conductivity after curing. Water enters pavements despite efforts to prevent it, but the extent of pavement deterioration can be reduced by proper drainage and maintenance. The major water ingress routes are infiltration through the pavement surfaces (through cracks and joints) and shoulders, melting of ice during the freezing/thawing cycles, capillary action, and seasonal changes in the water table. Most important water pathways that are discussed in greater detail in the literature are infiltration through cracks, joints and shoulders and drainage through edge drains. Groundwater level affects moisture conditions in the pavement and the subgrade if it is within approximately six meters from the surface. There is also literature on water pumping, temperature variations, geotechnical properties of base/subbase and subgrade layers as they relate to the water movement in the highway environment. Simplistic and more comprehensive approaches to modeling water movement in the highway environment were reviewed. Among all models presented, none closely matched the purpose of the present study.

A review of water movement in the highway environment: implications for recycled materials use

Modeling hydrology and reactive transport in roads: The effect of cracks, the edge, and contaminant properties

A review of roadway water movement for beneficial use of recycled materials

Reactive barriers are used to remediate contaminated sites where the potential for leaching of heavy metals exists. Permeable reactive barriers (PRB) could be used in highway applications below either embankments or base courses constructed with recycled materials where a possibility of contaminant leaching exists. The objective of this project is to develop technologies that use apatite minerals as PRB applied in highway construction that use recycled materials in alternative construction applications. Sorption of heavy metals and radionuclides onto apatite has been well demonstrated. Interest in apatite is primarily due to the high stability of the metal-phosphate minerals that result from the interaction between the contaminants and the apatite. However, the exact molecular scale mechanism of removal is not completely understood. This research sought to investigate the sorption mechanism using a combination of methods, including batch tests and surface analytical techniques, to study how Zn2+ is immobilized by apatite. Three different synthetic apatites were used in this investigation: hydroxyapatite (Ca5(PO4)3OH), fluoroapatite (Ca5(PO4)3F) and carbonate apatite (Ca5(PO4,CO3)3(OH)). BET isotherms indicate that at low Zn2+ concentrations sorption proceeds as surface complexation and at increased concentrations it is followed by the formation of a co-precipitate and in turn a pure precipitate. The zeta potential analysis is in agreement with the proposed complexation – co-precipitation/precipitation mechanism. In this study two distinct rates of change were observed in the surface charge (mV) of the apatite particle as a function of Zn2+ loading (mmol Zn/g Apatite). The spectroscopic analysis indicates that co-precipitation begins to occur even at concentrations well below the solubility limit of Zn – minerals. The XAS spectra of HAP and CAP at 0.0016 mM had very strong similarities to the mineral structure of scholzite, a naturally occurring Zn-phosphate mineral and to synthetic zinc phosphate, respectively. At 0.92 - 0.99 mmol Zn/g apatite XPS identified scholzite and hopeite as likely species present at the particle surface. It is proposed that dissolution-precipitation reactions account for the formation of a Zn-phosphate solid solution, this indicates that co-precipitation begins to occur well before the maximum sorption capacity, qmax, predicted by the Langmuir isotherm. At the elevated Zn2+ loadings of all three apatites, 8.22 mmol/g HAP, 4.48 mmol/g CAP and 2.74 mmol/g FAP, XAS evidenced similarities to hydrozincite, (Zn5(CO3)2(OH)6) and XPS identified the likely presence of zinc carbonate hydroxide, [ZnCO3]2·[Zn(OH)2]. The formation of a zinc carbonate hydroxide implies that dissolved CO3 plays an important role in the complexation of Zn2+, under the given experimental conditions. Results from this research suggest that surface complexation, surface precipitation, co-precipitation and precipitation all play an important role in the sorption mechanism of Zn2+ onto apatite. This identification of a Zn-phosphate co-precipitate and hydrozincite emphasize that although the formation of Zn-phosphates does occur, competing reactions also lead to the formation of other Zn complexes such as Zn carbonates and/or hydroxides.

https://rmrc.wisc.edu/wp-content/uploads/2012/10/Proj31FinalRpt.pdf

Permeable Reactive Barriers for Containment Control in Beneficial Use Applications in Highways

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A review of water movement in the highway environment: implications for recycled materials use

Modeling hydrology and reactive transport in roads: The effect of cracks, the edge, and contaminant properties

A review of roadway water movement for beneficial use of recycled materials

Permeable Reactive Barriers for Containment Control in Beneficial Use Applications in Highways