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Materials 2017, 10(9), 1106; doi:10.3390/ma10091106

Microstructural Investigation of Heat-Treated Ultra-High Performance Concrete for Optimum Production

1
Department of Architecture & Architectural Engineering, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 08826, Korea
2
Department of Civil and Environmental Engineering, National University of Singapore, 1 Engineering Drive 2, Singapore 117576, Singapore
*
Authors to whom correspondence should be addressed.
Received: 26 August 2017 / Revised: 12 September 2017 / Accepted: 18 September 2017 / Published: 20 September 2017
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Abstract

For optimum production of ultra-high performance concrete (UHPC), the material and microstructural properties of UHPC cured under various heat treatment (HT) conditions are studied. The effects of HT temperature and duration on the hydration reaction, microstructure, and mechanical properties of UHPC are investigated. Increasing HT temperature accelerates both cement hydration and pozzolanic reaction, but the latter is more significantly affected. This accelerated pozzolanic reaction in UHPC clearly enhances compressive strength. However, strength after the HT becomes stable as most of the hydration finishes during the HT period. Particularly, it was concluded that the mechanical benefit of the increased temperature and duration on the 28 day-strength is not noticeable when the HT temperature is above 60 °C (with a 48 h duration) or the HT duration is longer than 12 h (with 90 °C temperature). On the other hand, even with a minimal HT condition such as 1 day at 60 °C or 12 h at 90 °C, outstanding compressive strength of 179 MPa and flexural tensile strength of 49 MPa are achieved at 28 days. Microstructural investigation conducted herein suggests that portlandite content can be a good indicator for the mechanical performance of UHPC regardless of its HT curing conditions. These findings can contribute to reducing manufacturing energy consumption, cost, and environmental impact in the production of UHPC and be helpful for practitioners to better understand the effect of HT on UHPC and optimize its production. View Full-Text
Keywords: ultra-high performance concrete; microstructure; pozzolanic reaction; heat-treatment; portlandite ultra-high performance concrete; microstructure; pozzolanic reaction; heat-treatment; portlandite
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Kang, S.-H.; Lee, J.-H.; Hong, S.-G.; Moon, J. Microstructural Investigation of Heat-Treated Ultra-High Performance Concrete for Optimum Production. Materials 2017, 10, 1106.

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