Abstract
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.
Highlights
Ultra-high performance concrete (UHPC) has received vast attention over the past three decades since its introduction in the 1990s [1,2,3]
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 results showed that the amounts of the unhydrated cement in samples
Summary
Ultra-high performance concrete (UHPC) has received vast attention over the past three decades since its introduction in the 1990s [1,2,3]. This material offers a very high compressive strength, exceeding 150 MPa, and exceptional durability and good workability [3,4,5]. One of the main reasons behind the excellent mechanical properties of the UHPC is the high cement content and a very low water-to-cement ratio (w/c) This type of concrete is not an environmentally friendly material due to the high CO2 footprint. The calculation clearly shows that the total CO2 emissions of UHPC is twice as high as ordinary concrete
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