Drying shrinkage of mortar containing fly ash and chemical admixtures
- Mississippi State Univ., Mississippi State, MS (United States). Dept. of Civil Engineering
- American Buildings Co., Eufaula, AL (United States)
Portland cement concrete bridge deck slabs built in Mississippi, prior to the early 1980`s, did not typically show signs of non-structural cracks. Recently constructed deck slabs, however, have often suffered full-depth cracks which run transverse to the direction of traffic. The cracks may be attributed to structural design, material selection, and/or construction methods. The structural design and the construction methods for bridge deck slabs has not changed significantly in recent years, however the materials used in these slabs have changed. Slabs placed prior to the early 1980`s were constructed with plain Type I cement concrete. Within the past fifteen years, bridge deck slabs have typically included mineral and/or chemical admixtures. The pattern of the cracks and the fact that they form prior to traffic loads have led researchers to believe that drying shrinkage of concrete is, at least, a primary contributing factor. Researchers at Mississippi State University conducted a study concerning the effects of various admixtures on the drying shrinkage behavior of Type I cement mortar. Included in the study were a Class F fly ash, a water-reducing agent, and a water-reducing/set-retarding agent. The Class F fly ash replaced the Type I cement at a level of 20% by volume. The chemical admixtures were used to increase fresh mortar flow from 75--110%. Representative samples of each of the mixtures were moist-cured for each of 1, 3, and 7 days prior to exposure to drying conditions of 50% relative humidity. Results indicate that mixing water contents, water-reducing admixtures, and water-reducing/set-reducing admixtures all had significant effects on the drying shrinkage behavior of Type I cement mortar. Partial replacement of Type I cement with fly ash, however, did not have a significant influence on shrinkage. Also, the duration of moist cure prior to exposure to drying conditions did not significantly affect shrinkage.
- OSTI ID:
- 55400
- Report Number(s):
- CONF-9310328-; ISBN 1-56676-232-4; TRN: IM9525%%73
- Resource Relation:
- Conference: 1993 science and technology alliance materials conference, Greensboro, NC (United States), 27-29 Oct 1993; Other Information: PBD: 1995; Related Information: Is Part Of Science and technology alliance -- Materials conference `93; PB: 459 p.
- Country of Publication:
- United States
- Language:
- English
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