| Autor: |
Mousavinezhad, Seyedsaleh, Gonzales, Gregory J., Toledo, William K., Garcia, Judit M., Newtson, Craig M. |
| Předmět: |
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| Zdroj: |
AIP Conference Proceedings; 9/4/2023, Vol. 2928 Issue 1, p1-10, 10p |
| Abstrakt: |
Ultra high performance concrete (UHPC) is a remarkably durable concrete with high strength that contains a large amount of portland cement and supplementary cementitious materials (SCMs), particularly silica fume. Ultra fine particles of silica fume produce refined capillary pores and a dense microstructure; however, silica fume is considerably more expensive than cement and other SCMs so it is often replaced with class F fly ash that is substantially cheaper. Unfortunately, future availability of fly ash is uncertain because the energy industry has been investing in renewable energy production and removing coal burning generating stations from operation. Consequently, there is a growing need to find new, cost effective, and environmentally friendly alternatives for fly ash. This study assessed the effects of replacing fly ash and silica fume in UHPC mixtures with two alternative SCMs: metakaolin and a natural pozzolan (pumicite). To evaluate alternative SCMs, compression and flexural tests were conducted to identify acceptable UHPC mixtures (28-day compressive strength greater than 120 MPa). Then, shrinkage, frost resistance, and chloride ion permeability (rapid chloride permeability and surface resistivity tests) were assessed for acceptable UHPC mixtures. The results indicated that replacing up to 75% of the fly ash in the control mixture with natural pozzolan and replacing up to 100% of the fly ash and 25% of the silica fume in the control mixture with metakaolin led to mixtures with acceptable compressive strengths for UHPC (greater than 120 MPa). All UHPC mixtures produced in this study had shrinkage strains and relative dynamic modulus values after 300 cycles of freezing and thawing that were less than 371 µstrain and greater than 105, respectively. Additionally, both rapid chloride permeability and surface resistivity tests showed that all UHPC mixtures had "very low" susceptibility to chloride ion penetration. The results indicate that metakaolin and natural pozzolan are good candidates to partially or completely replace fly ash and to partially replace silica fume. [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
| Externí odkaz: |
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