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Eco-UHPC as Repair Material-Bond Strength, Interfacial Transition Zone and Effects of Formwork Type
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.ORCID iD: 0000-0001-5136-9412
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.ORCID iD: 0000-0001-8039-692X
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.ORCID iD: 0000-0003-0459-7433
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.ORCID iD: 0000-0001-7279-6528
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2020 (English)In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 13, no 24, article id 5778Article in journal (Refereed) Published
Abstract [en]

A reduced carbon footprint and longer service life of structures are major aspects of circular economy with respect to civil engineering. The aim of the research was to evaluate the interfacial bond properties between a deteriorated normal strength concrete structure and a thin overlay made of Eco-UHPC containing 50 wt% of limestone filler. Two types of formwork were used: untreated rough plywood and surface treated shuttering plywood. The normal strength concrete elements were surface scaled using water jets to obtain some degradation prior to casting of the UHPC overlay. Ultrasonic pulse velocity (UPV), bond test (pull-off test), and Scanning Electron Microscopy (SEM) combined with Energy Dispersive Spectrometry (EDS) were used for analysis. Elements repaired with the Eco-UHPC showed significantly improved mechanical properties compared to the non-deteriorated NSC sample which was used as a reference. The bond strength varied between 2 and 2.7 MPa regardless of the used formwork. The interfacial transition zone was very narrow with only slightly increased porosity. The untreated plywood, having a rough and water-absorbing surface, created a surface friction-based restraint which limited microcracking due to autogenous shrinkage. Shuttering plywood with a smooth surface enabled the development of higher tensile stress on the UHPC surface, which led to a more intensive autogenous shrinkage cracking. None of the formed microcracks penetrated through the entire thickness of the overlay and some were partly self-healed when a simple water treatment was applied. The project results showed that application of UHPC as repair material for concrete structures could elongate the lifespan and thus enhance the sustainability.

Place, publisher, year, edition, pages
MDPI, 2020. Vol. 13, no 24, article id 5778
Keywords [en]
Eco-UHPC, NSC (normal strength concrete), UPV, bond test (pull-off), SEM-EDS, ITZ, formwork, self-healing
National Category
Other Materials Engineering
Research subject
Building Materials
Identifiers
URN: urn:nbn:se:ltu:diva-82205DOI: 10.3390/ma13245778ISI: 000602864400001PubMedID: 33348899Scopus ID: 2-s2.0-85098280741OAI: oai:DiVA.org:ltu-82205DiVA, id: diva2:1515271
Funder
Swedish Transport AdministrationVinnova
Note

Validerad;2021;Nivå 2;2021-01-08 (johcin)

Available from: 2021-01-08 Created: 2021-01-08 Last updated: 2024-04-16Bibliographically approved
In thesis
1. Low Portland cement content concretes at freezing and subfreezing temperatures
Open this publication in new window or tab >>Low Portland cement content concretes at freezing and subfreezing temperatures
2024 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Concrete is the most used building material. With the increasing growth of industries and urbanization globally; the demand for concrete is increasing significantly. Ordinary Portland Cement (PC) is the binder used to produce typical concrete. Unfortunately, for every ton of manufactured cement about 0.61-ton CO2 is emitted into the earth’s atmosphere. As a result, several solutions have been implemented to reduce the usage of this material in the production of concrete. This includes its partial or full replacement with supplementary cementitious materials (SCMs) or alternative binders. Some of these combinations could be problematic to be used in cold climates due to a lower developed hydration heat, slower setting, or worse frost durability.

In winter the immediate exposure of fresh concrete to freezing temperatures results in pore ice formation and could delay or completely stop the hydration process. This is commonly prevented by using an additional heating system installed in concrete or the formwork. Unfortunately, usually, it adds complexity, increases the price, and depending on the used power source, could increase the CO2 footprint. Another potentially simpler and more sustainable solution is to modify the concrete itself by adjusting the mix design, by using certain chemical admixtures and special cementitious binders.

This research aimed to better understand how partial replacement of Portland cement with GGBFS and/or CSA cement affects the properties of concretes exposed to freezing and subfreezing temperatures in a fresh state and at a young age. The secondary aim was to evaluate a possible application of UHPC to protect new and existing concrete structures from frost damage.

The research included a literature review of methods used to produce concrete structures at zero and subzero temperatures. A special emphasis was on the application of chemical and mineral admixtures that could eliminate the need to use heat treatments. The output of this analysis enabled to narrow the scope of the research.

The experimental program focused on the optimization, testing, and analysis of mixes containing various combinations of chemical admixtures, CSA cement, and Portland cement. Tests included exposure to freezing and subfreezing temperatures. The aim was to lower the freezing point of water and promote faster hydration and strength gain. Fresh and hardened properties were determined for all produced concretes. The phase transition of pore water into ice, the ice-forming temperature, and their effects on the binder matrix were studied using differential scanning calorimetry (DSC). Other tests included ultrasonic pulse velocity measurements (UPV), bond test (pull-off), scanning electron microscope (SEM) for analysis of the microstructure and phase composition, frost durability evaluation with Båras test, semi-adiabatic calorimetry to study hydration processes, compressive strength measurements.

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2024
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
National Category
Building Technologies Composite Science and Engineering
Research subject
Building Materials
Identifiers
urn:nbn:se:ltu:diva-105133 (URN)978-91-8048-540-1 (ISBN)978-91-8048-541-8 (ISBN)
Public defence
2024-06-18, F1031, Luleå University of Technology, Luleå, 10:00 (English)
Opponent
Supervisors
Funder
InterregVinnovaSvenska Byggbranschens Utvecklingsfond (SBUF)Swedish Transport AdministrationSwedish Energy Agency
Available from: 2024-04-17 Created: 2024-04-16 Last updated: 2024-05-28Bibliographically approved

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Kothari, AnkitRajczakowska, MagdalenaBuasiri, ThanyaratHabermehl-Cwirzen, KarinCwirzen, Andrzej

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