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35 Summary of Findings Based on the results of the research in this project, the fol- lowing findings are made: 1. Concrete materials, concrete production procedures, con- struction practices, and field conditions affect, to varying degrees, the air-void system of concrete. 2. The type of air-entraining admixture has a statistically sig- nificant effect on the concrete air-void system (spacing factor). Also, cement alkali level and coarse aggregate shape were found to have a significant effect on the spac- ing factor. 3. The air-void spacing factor decreases with increases in mixing duration, decreases as crushed aggregate are used instead of rounded aggregate, and increases with increased cement alkali level. The two-factor interaction analysis indicated that the spacing factor increases when the com- bined mixing duration and alkali level increases. 4. Compressive strength decreases with increasing tempera- ture, using rounded aggregate instead of crushed aggre- gate, increasing w/c, and increasing cement alkali level. 5. The highest compressive strength (average of six different air-entraining admixtures) was measured for mixes made with crushed coarse aggregate, low water-cement ratio, and low-alkali cement and mixed at low temperature. 6. Compressive and flexural strengths with non-Vinsol resin air-entraining admixtures were generally lower than those for mixtures with Vinsol resin admixtures. In addition to these findings, procedures are proposed to eval- uate and qualify air-entraining admixtures for use in concrete for highway applications,using the laboratory test methods that are expected to yield comparable field performance. Also, per- formance (acceptance) requirements are proposed for paving concrete and structural concrete, such that an air-entraining admixture can be qualified for either or both applications. Suggested Research Suitability of the proposed procedures was confirmed based on a limited laboratory evaluation. Further evaluation using concrete mixtures prepared for use in highway pave- ments or bridge decks is recommended. C H A P T E R 5 Summary of Findings and Suggested Research
