Influence of Hycrete DSS on Virginia Department of Transportation Class A4 Concrete Mix Designs

About the report:

Virginia Department of Transportation (VDOT) Class A4 concrete mixtures containing Hycrete DSS were evaluated to determine the performance of the mixtures with respect to mechanical properties, alkali-silica reactivity, and corrosion of reinforcement. Class A4 concrete is mainly used in bridge decks and has a minimum 28-day compressive strength of 4,000 psi. The permeability of Class A4 concrete is expected to be below 2500 coulombs for resistance to corrosion and other aggressive solutions, and this is mainly achieved by the use of pozzolans or slag. The effects of admixing Hycrete DSS into a typical Class A4 concrete mixture at three dosage levels (0, 1, and 2 gal/yd3) and with two quantities of fly ash (0 and 159 lb/yd3) were determined. The study showed that Hycrete DSS with a defoaming agent achieves air contents that comply with VDOT specifications. In the severe test, some of the specimens had a high weight loss; this was not expected to be a problem because of their high durability factors. Long-term strengths in specimens with similar air contents (within specification) were comparable. The drying shrinkage values were acceptable in all mixtures, and the bond strength values for the mixtures were comparable. Thus, Hycrete DSS had no effect on the bond between fresh and hardened concrete. Resistance to alkali-silica reactivity was improved with the addition of fly ash, but the addition of Hycrete DSS had only a marginal effect. Although adding Hycrete DSS alone did not improve resistance to rapid chloride permeability, adding Class F fly ash did result in low permeability. Adding Hycrete DSS did lower sorptivity. Further evaluation indicated that adding Hycrete DSS at a sufficient concentration most likely restricts moisture intake and adding fly ash reduces the movement of moisture within the system. Therefore, when these two effects occur together in concrete, chloride movement into the concrete is considerably restricted. Based on the results of this study, the investigators recommend that VDOT's Structure & Bridge Division continue the use of pozzolans to reduce the influx of chloride ions and increase the life of structures. In addition, VDOT's Structure & Bridge Division should make a trial batch of the Class A4 concrete mixture with Hycrete DSS for placement in a bridge deck to evaluate the field performance of this product. If the field performance confirms the laboratory test results of this study, the use of Hycrete DSS is expected to lead to extended service life and to aid in minimizing maintenance costs. VDOT will spend approximately $15 million for new bridge decks this construction season. Based on a life cycle cost analysis, with a 10 percent increase in the service life of bridge decks or structures, VDOT would save $1.5 million dollars each year through the use of Hycrete DSS.

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