A Predictive Approach for Long-Term Performance of Recycled Materials Using Accelerated Aging - Volume 2: Appendices

Use of recycled materials in a proposed highway application frequently requires the assessment of physical and environmental performance. Future behavior is often difficult to predict. As an alternative to field demonstrations, there is a need to develop strategies to predict long-term physical and environmental performance. Accelerated aging is one means of exploring the long-term physical and environmental performance of recycled materials in a highway. Coal fly ash (CFA) use in portland cement concrete (PCC) was selected as a model system to develop an accelerated aging approach. Three types of accelerated aging were chosen for this project: Arrhenius aging (AA), cyclic loading (CL), and freeze-thaw exposure (FT). This approach, incorporated in an experimental design, allowed a systematic exploration of the separate effects and combined interactions of both developmental and degradative accelerated aging variables. A slab from U.S. Route 20 in northwest Iowa was used as both the basis for the concrete mixes and as a field verification site. The aging protocol impacted both physical and chemical properties of the prism monoliths. Generally speaking, the main effects were more important than the interactive effects, which was unexpected. It took about 9 months of elapsed time to age specimens to an equivalent age of up to 4 years. The equivalent ages matched well with the time frame seen in the field in Iowa for the onset of early distress and also matched well the chronological age of the field pavement. AA significantly reduced the compressive strength of the concrete, possibly indicating the onset of a deleterious reaction in the mix. CL affected the microcracking in the concrete. All aging variables affected the fine pore structure of the concrete. CL affected the Ca diffusional leaching from the monoliths. Logically, there appears to be a linkage between strength loss, microcracking, and leaching behavior of a major matrix constituent in the concrete (notably Ca). Most response variables from the aged laboratory prisms and the field samples were similar, suggesting that the method did a reasonable job of producing a laboratory pavement of similar age and distress to the field pavement. Certain field aging phenomena (microcracking from unknown sources, road salting, and carbonation) could not be recreated in the laboratory specimens.