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Open AccessArticle

Does a High Amount of Unhydrated Portland Cement Ensure an Effective Autogenous Self-Healing of Mortar?

1
Department of Civil, Environmental and Natural Resources Engineering, Division of Structural and Fire Engineering, Luleå Tekniska Universitet, 97187 Luleå, Sweden
2
Skanska, Warfvinges väg 25, 112 74 Stockholm, Sweden
*
Author to whom correspondence should be addressed.
Materials 2019, 12(20), 3298; https://doi.org/10.3390/ma12203298
Received: 16 September 2019 / Revised: 7 October 2019 / Accepted: 9 October 2019 / Published: 11 October 2019
(This article belongs to the Special Issue High and Ultra-High Performance Concrete for Sustainable Construction)
It is commonly accepted that the autogenous self-healing of concrete is mainly controlled by the hydration of Portland cement and its extent depends on the availability of anhydrous particles. High-performance (HPCs) and ultra-high performance concretes (UHPCs) incorporating very high amounts of cement and having a low water-to-cement ratio reach the hydration degree of only 70–50%. Consequently, the presence of a large amount of unhydrated cement should result in excellent autogenous self-healing. The main aim of this study was to examine whether this commonly accepted hypothesis was correct. The study included tests performed on UHPC and mortars with a low water-to-cement ratio and high cement content. Additionally, aging effects were verified on 12-month-old UHPC samples. Analysis was conducted on the crack surfaces and inside of the cracks. The results strongly indicated that the formation of a dense microstructure and rapidly hydrating, freshly exposed anhydrous cement particles could significantly limit or even hinder the self-healing process. The availability of anhydrous cement appeared not to guarantee development of a highly effective healing process. View Full-Text
Keywords: continued hydration; ultra-high performance concrete; cracking; microstructure; calcite continued hydration; ultra-high performance concrete; cracking; microstructure; calcite
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Rajczakowska, M.; Nilsson, L.; Habermehl-Cwirzen, K.; Hedlund, H.; Cwirzen, A. Does a High Amount of Unhydrated Portland Cement Ensure an Effective Autogenous Self-Healing of Mortar? Materials 2019, 12, 3298.

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