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South Dakota Department of Transportation
Project Synopsis
SD1992-04


Title: Reactivity & Durability of PCC Aggregates
Project Researcher: Dan Johnston, SDDOT
Project Manager: Dave Huft
Research Period: -
Status:
Cost: $0.00

Problem Statement:Several Portland Cement Concrete pavements in South Dakota exhibit distress caused by chemical reactions of concrete aggregates. The reactions are thought to be alkali-silica reactions in fine aggregate. Recent Department research evaluated the alkali-silica reactivity of twenty-one commonly used concrete sands. On the basis of this research, the Department decided to adopt a specification requiring concrete sands to exhibit no more than 0.2% expansion in the proposed ASTM P214 mortar bar expansion test. The specification allows substituting fly ash for cement to reduce expansion to 0.2% or less.

Because the specification has significant economic impact on aggregate producers and the Department, the P214 test must be repeatable and consistent. To be credible, the test should correlate with other recognized tests and, more importantly, with observed field performance. Although the Department has achieved a certain level of confidence with the test method and the specification, additional verification is desirable. The reasons for apparent discrepancies between results of different test methods must be understood. Correlation of test results with field performance and identification of other factors affecting field performance are also needed.

In the Departments last study, researchers recognized the possibility of pit variability, but limitations in study scope and duration prevented thorough investigation. It is not known whether the reactivity of sand sources varies significantly with depth or lateral location. Variability could frustrate attempts to maintain a consistently acceptable level of reactivity. Furthermore, it is not known whether certain reactive components could be mechanically separated from the sand to lessen its overall reactivity.

Finally, there is evidence that another chemical reaction, called alkali-carbonate reactivity, may be responsible for distress in some pavements. The extent and severity of alkali-carbonate reactions is unknown. Criteria for identification and verification are not established, nor are predictive tests determined. It is not known whether fine aggregates, coarse aggregates, or both contribute to this problem.

Findings:
Title: Reactivity & Durability of PCC Aggregates
Project Researcher: Dan Johnston, DOT
Project Manager: Dave Huft
Research Period: -
Status:
Cost: $0.00

Problem Statement:Several Portland Cement Concrete pavements in South Dakota exhibit distress caused by chemical reactions of concrete aggregates. The reactions are thought to be alkali-silica reactions in fine aggregate. Recent Department research evaluated the alkali-silica reactivity of twenty-one commonly used concrete sands. On the basis of this research, the Department decided to adopt a specification requiring concrete sands to exhibit no more than 0.2% expansion in the proposed ASTM P214 mortar bar expansion test. The specification allows substituting fly ash for cement to reduce expansion to 0.2% or less.

Because the specification has significant economic impact on aggregate producers and the Department, the P214 test must be repeatable and consistent. To be credible, the test should correlate with other recognized tests and, more importantly, with observed field performance. Although the Department has achieved a certain level of confidence with the test method and the specification, additional verification is desirable. The reasons for apparent discrepancies between results of different test methods must be understood. Correlation of test results with field performance and identification of other factors affecting field performance are also needed.

In the Departments last study, researchers recognized the possibility of pit variability, but limitations in study scope and duration prevented thorough investigation. It is not known whether the reactivity of sand sources varies significantly with depth or lateral location. Variability could frustrate attempts to maintain a consistently acceptable level of reactivity. Furthermore, it is not known whether certain reactive components could be mechanically separated from the sand to lessen its overall reactivity.

Finally, there is evidence that another chemical reaction, called alkali-carbonate reactivity, may be responsible for distress in some pavements. The extent and severity of alkali-carbonate reactions is unknown. Criteria for identification and verification are not established, nor are predictive tests determined. It is not known whether fine aggregates, coarse aggregates, or both contribute to this problem.

Findings:

Research Objectives:
1  To confirm ASTM P214 test results for South Dakota's primary fine aggregate sources.
2  To correlate the P214 test with other predictive tests and observed field performance.
3  To assess the variability of fine aggregate sources in terms of laboratory test results.
4  To explore the feasibility of separating reactive components from fine aggregates.
5  To determine the extent and severity of alkali-carbonate reactivity in South Dakota.
6  To develop recommendations concerning specifications for aggregate acceptance.

Research Tasks:
1  Review pertinent literature.
2  Acquire representative fine aggregate samples from sources historically used on South Dakota PCC paving projects and perform ASTM P214 tests on them.
3  Submit an interim report summarizing and ASTM P214 test results and recommendations concerning adoption of the proposed specification.
4  Compare P214 test results with prior test results and develop recommendations concerning adoption of a P214 based specification.
5  Test the fine aggregates using ASTM C289 and the South Dakota Autoclave Test procedures modified to include complete fine aggregate gradations.
6  Test selected reactive aggregates which have been washed or otherwise processed to determine whether reactivity levels are changed.
7  Conduct field surveys to evaluate the field performance of aggregates which have been used in pavements and structures.
8  Analyze field observations and laboratory test results to correlate test methods, to determine the effects of modifying the ASTM C289 and South Dakota Autoclave Test procedures, to evaluate the variability of aggregate sources, and to correlate test
9  Conduct field surveys and tests to determine the extent and severity of alkali-carbonate reactivity in South Dakota.
10  Develop recommendations concerning use of the proposed ASTM P214-based specification and use of alternative test methods.
11  Submit a final report summarizing relevant literature, research methodology, findings, and conclusions.
12  Present a summary of research, findings, and recommendations to the Department's Research Review Board.

Documents Available:

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