Public Roads: A Journal of Highway Research and Development, Vol. 49 No. 2

Forster, Stephen W.; Harrigan, E.T.; Freedman, Mark; Staplin, L.K.; Decina, Lawrence E.; Sibley, Scott W. · 1985 · ROSA P / United States. Government Printing Office

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Summary

This paper, published in the September 1985 issue of *Public Roads*, reviews the technical viability and research status of using recycled Portland Cement Concrete (PCC) as aggregate in new PCC pavements. The research was motivated by economic pressures, including the rising cost of natural resources and energy, as well as environmental constraints such as zoning restrictions on new quarries and the high cost of landfill disposal. The article synthesizes findings from laboratory studies and field projects conducted by various state departments of transportation and the Federal Highway Administration (FHWA) to determine if recycled concrete meets performance standards. The review examines the physical properties of recycled aggregate, noting that crushed concrete particles have good shape but exhibit higher absorption and lower specific gravity than natural aggregates. Laboratory tests indicated that concrete mixes using recycled aggregate often had lower slumps and required higher cement contents to maintain workability, particularly when recycled material was used as fine aggregate. However, substituting 15 to 30 percent natural sand for recycled fines improved workability. Strength tests showed that recycled concrete had slightly lower compressive and flexural strengths than controls but still exceeded minimum pavement specifications. Durability testing revealed that recycled concrete often possessed higher frost resistance than the original concrete, and volume changes in response to temperature and moisture were similar to conventional mixes. Special concerns regarding recycled materials were also addressed. Studies on "D" cracked pavement showed that crushing the material and using fly ash as a cement replacement significantly reduced the potential for continued cracking. Chloride content analysis indicated that while surface layers of recycled pavement may contain high levels of sodium chloride from deicing, the overall concentration in the new mix is typically below critical thresholds for corrosion, provided the material is properly processed. The paper also highlights unresolved issues regarding alkali-aggregate reactivity, noting that further investigation is needed to determine if reactive minerals in old concrete can continue to cause expansion in new mixes. The authors conclude that recycling PCC is a viable alternative to using natural aggregate, provided that proper planning, testing, and construction techniques are employed. Key recommendations include separating coarse and fine recycled materials to prevent segregation, using natural sand to improve workability, and employing water-reducing admixtures. While current practices allow for high-quality concrete production, the paper identifies the need for further research into the long-term behavior of recycled materials derived from "D" cracked or alkali-reactive pavements and the establishment of critical chloride limits for various applications.

Key finding

Recycled concrete aggregate can produce high-quality concrete that meets strength and durability specifications, though it typically requires higher water and cement content or admixtures to achieve workability comparable to natural aggregate mixes.

Methodology

review

Provenance

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Summary generated by qwen3.6-27b-prismaquant on 2026-06-10; verification: verified.

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