Future behavior of recycled materials in highway applications is often difficult to predict. Accelerated aging is one means of exploring the long-term physical and environmental performance. Coal fly ash (CFA), routinely used as a cementitious replacement in portland cement concrete pavement, was selected as a model system in an accelerated aging approach. US-20 near Fort Dodge, Iowa, was used as a source of field-aged pavement slab material and concrete mixture proportions. This pavement, constructed in 1987, experienced early failure and distress. The role of CFA, if any, in the failure is not known. Three types of accelerated aging treatments were chosen and applied on laboratory prisms made with the US-20 mixture proportions: arrhenius aging (AA), cyclic loading, and freeze-thaw exposure. Physical and environmental response variables were used to examine the pavement slab and the aged laboratory prisms. The aging protocol affected both physical and chemical properties of the monoliths. It took about 9 months of elapsed time to age specimens to an equivalent age of about 4 years. The equivalent ages matched well with the time frame seen in the field for the onset of early distress. Most response variables for the aged laboratory prisms and the field samples were similar, suggesting that the aging method reasonably produced a pavement of similar age and distress. The AA treatment produced an unexpected loss of strength, suggesting that the accelerated aging promoted the onset of a deleterious reaction. Distinguishing the source of trace metals in leachates was difficult, for all components (CFA, aggregates, cement) had similar elemental compositions and leachability. The use of both physical and environmental response variables showed linkages between compressive strength, microcracking, fine pore structure, Cl diffusive leaching (efflux related to road salting that increases the concentration of Cl in the monolith), and Ca diffusive leaching (related to change in matrix structure and loss of Ca).
A TCE-contaminated competent bedrock site in Portsmouth, NH was used to determine if a relation existed between microfracture surface geochemistry and the ecology and metabolic activity of attached microbes relative to terminal electron accepting processes (TEAPs) and TCE biodegradation. The bedrock is a metasandstone and metashale of the Silurian Kittery Formation. Eleven microfractures (MF 01-11) were extracted from cores of competent rock from 2 boreholes (BBC5 and BBC6) at depths >21.3 m below ground. The host rock had 3 nominal pore width sizes (131.1, 1.136, and 0.109 μm), a porosity of 0.8%, and a permeability of <1 μd. Microfracture surface precipitates were polycrystalline with grain sizes ranging from 10 to 100 μm. Petrography and XRD revealed that carbonates and quartz were the dominant microfracture surface precipitates. Mineral distribution was heterogeneous at the 10 μm scale. Oxidized and reduced iron species were identified with XPS on the microfracture precipitate surfaces. Carbon functional groups characteristic of NOM were also identified. SIMS mass fragment fingerprints suggested that TCE, PCE and/or VC were possibly adsorbed to NOM on the microfracture surfaces. Packer waters were alkaline (131-190 mg/L as CaCO 3 , pH 8.8 to 9.6), mildly reducing (Eh of −208 to 160 mV, DO of 0.4 to 2.5 mg/L), with low NPDOC values (0.8-1.7 mg/L), and measurable Fe (II) (0.1 mg/L) and Fe (III) (0.02 to 0.3 mg/L). Sulfate was the dominant anion in the packer sample water (110-120 mg/L). No sulfide was detected. H 2 was present in a number of the BBC wells at the site (2.2-7.3 nM). Amplification with specific primer sets of seven microfractures from BBC5 showed the presence of bacteria, Archaea, anaerobic dehalorespirers (Dehalococcoides sp.), sulfate reducing bacteria, and iron reducing bacteria (Geobacteraceae). Redox zonation may exist relative to spatial distance from within the microfracture network to the open fracture system. The microfracture surface precipitates, frequently spatially complex and comprised of a variety of C-, Fe-and S-containing minerals, may be another region for redox zonation. Fe was the dominant microfracture surface element and active Fe cycling is suspected. However, the primer data suggest that the microfracture network may have been more reducing than the open fracture system. In this case, the microfracture network may constitute a zone where more reductive metabolic processes occur, making this system similar to biogeochemical redox zones found in other environments.
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