Title: Non-Air-Entrained High-Strength Concrete--Is it Frost Resistant?

Author(s): M. D. Cohen, Y. Zhou, and W. L. Dolch

Publication: Materials Journal

Volume: 89

Issue: 4

Appears on pages(s): 406-415

Keywords: air entrainment; compressive strength; frost resistance; high-strength concrete; non-air-entrained concrete; dynamic modulus; pulse velocity; resonant frequency; silica fume; Materials Research

DOI: 10.14359/2582

Date: 7/1/1992

Abstract:
Non-air-entrained high-strength concrete specimens with 0.35 water-cementitious materials ratio and 10 percent silica fume by mass of portland cement were cured for 7, 14, 21, and 56 days to evaluate the effects of the duration of curing in saturated limewater prior to the freezing and thawing cycles on their frost-resistant properties. The aggregates used in this investigation had a proven frost resistance. Therefore, the failure of the non-air-entrained concrete specimens could be attributed only to cracking of the paste. It was found that silica fume modified the frost-resistance mechanism of the paste in the concrete. All specimens failed when tested in accordance with the ASTM C 666 Standard Test, Procedure A, using 60 percent relative modulus as the failure criterion. The data suggested the possible existence of a 14 to 21-day pessium duration of curing in saturated limewater, which was associated with the largest gains in length and mass, the largest drops in bulk density and compressive strength, and the lowest number of cycles to failure (or lowest durability factor). ASTM C 666, Procedure A appeared to be a viable test for evaluating the frost resistance of the concrete, even though the required 14-day curing duration prior to the freezing and thawing cycles, lying within the premium curing range, yielded conservative results. There were some improvements to the frost-resistance properties when the duration of curing prior to the freezing and thawing cycles was reduced to 7 days or increased to 56 days, but the improvements were inadequate to enable the concrete to pass the standard test requirements. Thus, it is suggested that the failure of the specific non-air-entrained high-strength concrete tested in this investigation was due to inherent concrete properties, and not to the shortcoming of the ASTM C 666, Procedure A, standard test. An interesting observation was made when the dynamic moduli of the deteriorated specimens were compared to their compressive strengths. The damage induced in the mechanical property of the concrete after 300 cycles of freezing and thawing was mainly indicated by a significant drop in the moduli) i.e., down from 6.5 million psi at 0 cycles to 300,000 psi at 300 cycles). However, the compressive strengths did not show such a dramatic reduction. For instance, while the highest compressive strength was registered at about 11,000 psi at 0 cycles, the lowest was registered at about 8000 psi at 300 cycles. Even the lowest strength value still puts the concrete in the high-strength category. An explanation for this observation cannot be provided without further study of the microstructure, but it is clear that during the freezing and thawing cycles, a stage had been reached in the concrete deterioration process when the conventional relationship between the moduli and the compressive strengths no longer appeared to hold true.