Title: Realistic Strength of Air-Entrained Concretes With and Without Fly Ash

Author(s): M. N. Hague, R. L. Day, and B. W. Langan

Publication: Materials Journal

Volume: 85

Issue: 4

Appears on pages(s): 241-247

Keywords: air entrained concretes; compressive strength; concretes; cores; curing; cylinders; fly ash; low temperature; Materials Research

DOI: 10.14359/2087

Date: 7/1/1988

Abstract:
Effects of various curing regimes on the strength development of both plain and fly ash concretes were studied. Three grades of air-entrained concretes with 28 day nominal strengths of 20, 30, and 40 MPa (2900, 4350, and 5800 psi) were cast. For each grade, 0, 20, 35, and 50 percent of the weight of cement was replaced by two subbituminous fly ashes. Cylinders were cured at 100 and 50 percent relative humidities and under outdoor ambient conditions--including a Canadian winter climate. Structural-size members were also exposed to the elements and strength was estimated by testing extracted cores. Results indicate exposure of test cylinders to site conditions does not adequately reflect strength development of the in situ concrete; this is particularly so if test cylinders are allowed to dry. Prediction of in situ strength from site-cured cylinders is particularly inaccurate for the fly ash concretes. For in situ concretes with a low total cementitious content, the inclusion of fly ash in appreciable quantities is likely to result in slower strength gain than plain concrete. However, for higher grade concretes (higher total cementitious content) even with high ash content, early exposure to the elements is no more detrimental than it is to plain concrete.