Mechanical and Durability Properties of High Volume Fly Ash Concrete

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Title: Mechanical and Durability Properties of High Volume Fly Ash Concrete

Author(s): V. Sirvivatnanon, H. T. Cao, and P. Nelson

Publication: Special Publication

Volume: 145

Issue:

Appears on pages(s): 967-984

Keywords: binders (materials); compressive strength; corrosion; creep properties; drying shrinkage; flexural strength; fly ash; low-heat cements; mechanical properties; modulus of elasticity; portland cement; sulfate resistance; sulfate-resisting cements; Materials

Date: 5/1/1994

Abstract:
In this study, structural-grade concretes with characteristic strength of 20 to 45 MPa were made with general purpose portland cement (ASTM Type I) and fly ash blends. High volumes of fly ash (ASTM Class F) in the range of 40 to 50 percent by weight of total binder were used. It was found that for an equivalent 28-day strength and slump, structural concretes with high-volume fly ash can provide a number of advantages over plain cement concretes, including lower drying shrinkage and better creep characteristics. Similar flexural strengths and elastic modulus were observed between equivalent plain cement and high-volume fly ash concretes. Experience obtained in field trials of high-volume fly ash concretes showed that they can be mixed, transported, placed, and finished using conventional concreting equipment and techniques. Laboratory studies of blended cements with high percentages of fly ash as cement replacement material indicated that steel passivation characteristics improved with age of hydration and that there was no negative effect caused by pozzolanic reaction. Electrochemical data using polarization resistance techniques on paste samples immersed in NaCl solution are given. The results indicated that, even with limited initial curing of 7 days, the corrosion rates of steel in 40 percent fly ash blend by weight were very similar to that of plain cement at high water-to-binder ratio (>0.6) and were lower than that of plain cement at low water-to-binder ratio ( 0.6). Data obtained from mortar samples subjected to sulfate environments suggested that the use of blended cements with high fly ash replacement could be beneficial in the case where the pH of the environment is low, such as that experienced by concrete structures in sewerage works.