Effects of bacteria-embedded polylactic acid (PLA) capsules on fracture properties of strain hardening cementitious composite (SHCC)
Abstract: Strain hardening cementitious composite (SHCC) is a special class of ultra-ductile material which has autogenous self-healing capability due to its intrinsic tight crack widths. To further improve its healing ability, healing agent (HA) can be incorporated in SHCC, enabling it also the autonomous self-healing mechanism. In this study, the effects of adding bacteria-embedded polylactic acid (PLA) capsules on the mechanical properties of SHCC with different amounts of HA (i.e., 1.25%, 2.5%, 5% by weight to binder) were investigated. Experiments were conducted to examine the composite performance, matrix properties and single fiber pullout behavior of the SHCCs, followed by microscopy characterization of the fiber/matrix interface microstructure. Results show that the inclusion of the PLA-HA up to 5% by weight to binder influenced the tensile performance (i.e., tensile strength and ductility) of SHCC only to a very small extent but significantly reduced the average residual crack widths. The inclusion of HA at a high dosage (5%) increased the crack tip toughness (Jtip) of the matrix by lowering elastic modulus and increasing fracture toughness. Single fiber pullout results show that the fiber/matrix bond properties were enhanced by the addition of the HA, which can be attributed to the formation of a denser interfacial transition zone (ITZ) with less calcium hydroxide crystals as revealed by the scanning electron microscope (SEM) micrographs. The improved bond properties led to higher fiber bridging complementary energy and thus partially sustained the tensile strain capacity as verified by the micromechanical model.
Reference of this article: Shan He, Shizhe Zhang, Mladna Lukovic and Erik Schlangen (2022), Effects of bacteria-embedded polylactic acid (PLA) capsules on fracture properties of strain hardening cementitious composite (SHCC) , Engineering Fracture Mechanics, Volume 268, Elsevier, ISSN 0013-7944
Shan He, Shizhe Zhang and Erik Schlangen: Microlab, Faculty of Civil Engineering and Geosciences, Delft University of Technology, 2628 CN Delft, the Netherlands
Mladena Lukovic: Concrete Structures, Faculty of Civil Engineering and Geosciences, Delft University of Technology, 2628 CN Delft, the Netherlands
Understanding the Impacts of Healing Agents on the Properties
of Fresh and Hardened Self-Healing Concrete: A Review
Abstract: Self-healing concrete has emerged as one of the prospective materials to be used in future constructions, substituting conventional concrete with the view of extending the service life of the structures. As a proof of concept, over the last several years, many studies have been executed on the effectiveness of the addition of self-healing agents on crack sealing and healing in mortar, while studies on the concrete level are still rather limited. In most cases, mix designs were not optimized regarding the properties of the fresh concrete mixture, properties of the hardened concrete and self-healing efficiency, meaning that the healing agent was just added on top of the normal mix (no adaptations of the concrete mix design for the introduction of healing agents). A comprehensive review has been conducted on the concrete mix design and the impact of healing agents (e.g., crystalline admixtures, bacteria, polymers and minerals, of which some are encapsulated in microcapsules or macrocapsules) on the properties of fresh and hardened concrete. Eventually, the remaining research gaps in knowledge are identified.
Reference of this article: Hermawan, H.; Minne, P.; Serna, P.; Gruyaert, E. Understanding the Impacts of Healing Agents on the Properties of Fresh and Hardened Self-Healing Concrete: A Review. Processes 2021, 9, 2206.
Keywords: self-healing concrete; crystalline admixture; bacteria; microcapsules; macrocapsules; fresh properties; hardened properties
Harry Hermawan, Peter Minne & Elke Gruyaert: Department of Civil Engineering, Materials and Constructions, Ghent Technology Campus, KU Leuven, Gebroeders De Smetstraat 1, 9000 Ghent, Belgium
Pedro Serna: Instituto de Ciencia y Tecnología Del Hormigón (ICITECH), Universitat Politècnica de València, Camino de Vera S/n, 46022 Valencia, Spain
An Investigation of Suitable Healing Agents for Vascular-Based
Self-Healing in Cementitious Materials
Abstract: Self-healing cementitious materials can extend the service life of structures, improve safety during repair activities and reduce costs with minimal human intervention. Recent advances in self-healing research have shown promise for capsule-based and intrinsic healing systems. However, limited information is available regarding vascular-based self-healing mechanisms. The aim of this work is to compare different commercially available healing agents regarding their suitability in a selfhealing vascular network system by examining a regain in durability and mechanical properties. The healing agents investigated include sodium silicate, two polyurethanes, two water repellent agents and an epoxy resin. Sealing efficiencies above 100% were achieved for most of the healing agents, and both polyurethanes and the epoxy resin showed high regain in strength. The results obtained from this study provide a framework for selecting a healing agent given a specific application, as a healing agent’s rheology and curing properties can affect the optimal geometry and design of a vascular network.
Reference of this article: Shields, Y.; Van Mullem, T.; De Belie, N.; Van Tittelboom, K. An Investigation of Suitable Healing Agents for Vascular-Based Self-Healing in Cementitious Materials. Sustainability 2021, 13, 12948.
Keywords: vascular networks; healing agents; self-healing concrete; durability; mechanical recovery
Yasmina Shields, Tim Van Mullem, Nele De Belie & Kim Van Tittelboom: Magnel-Vandepitte Laboratory, Department of Structural Engineering and Building Materials, Faculty of
Engineering and Architecture, Ghent University, Technologiepark Zwijnaarde 60, B-9052 Ghent, Belgium
Self-healing bacterial concrete exposed to freezing and thawing associated with chlorides
Abstract: Self-healing concrete and preventive repair of structures will slow down the development of cracks and/or arrest the ingress of aggressive agents. When the cracks are closed or a decrease in crack width is achieved, this will be associated with improved durability of the structure. This paper describes the literature review and inter-laboratory comparison carried out within the COST Action CA15202 (SARCOS), as well as the research planned within the recently started International Training Network SMARTINCS.
Reference of this article: Vanessa Giaretton Cappellesso, Tim Van Mullem, Elke Gruyaert, Kim Van Tittelboom and Nele De Belie (2021), Self-healing bacterial concrete exposed to freezing and thawing associated with chlorides, Proceedings Resilient Materials 4 Life 2020 (RM4L2020), Maddalena R, Wright-Syed M, (RM4L Eds), pp. 241-246, Cardiff, UK, 20-22 Sep 2021, ISBN 978-1-3999-0832-0
Vanessa Giaretton Cappellesso, Tim Van Mullem, Nele De Belie, Kim Van Tittelboom: Ghent University, Department of Structural Engineering and Building Materials, Technologiepark Zwijnaarde 60, 9052 Gent, BE
Vanessa Giaretton Cappellesso and Elke Gruyaert: KU Leuven, Department of Civil Engineering, Materials and Constructions, Ghent Technology Campus, Gebroeders De Smetstraat 1, 9000 Ghent, BE
Time dependent micromechanical self-healing model for cementitious material
Abstract: The need for more sustainable systems for construction applications has led researchers to develop a range of self-healing materials for designing or repairing structures. Unsurprisingly, concrete, as the most used construction material, has received considerable attention from the biomimetic research community. Despite much research over the past two decades, there is not yet a comprehensive reliable model for predicting the behaviour of self-healing concrete under a range of conditions. Concrete itself is a complex heterogeneous brittle material that is challenging to simulate. When healing is also considered, its behaviour becomes even more complex. This contribution presents a constitutive model based on a micromechanical formulation, with time dependent cracking and healing functions. The model employs an Eshelbian solution, as well as a range of homogenization techniques, to estimate overall properties and the nonlinear response of self-healing concrete. A key assumption in the formulation is that the new healing material forms in a stress-free state. The initial results show that the mechanical healing efficiency and post-healed response are strongly dependent on the properties of the matrix and healing materials, curing time of the healing agent and the damage threshold at which healing is activated.
Reference of this article: Sina Sayadi, Iulia Mihai and Anthony Jefferson (2021), Self-healing bacterial concrete exposed to freezing and thawing associated with chlorides, Proceedings Resilient Materials 4 Life 2020 (RM4L2020), Maddalena R, Wright-Syed M, (RM4L Eds), pp. 105-109, Cardiff, UK, 20-22 Sep 2021, ISBN 978-1-3999-0832-0
Sina Sayadi, Iulia Mihai and Anthony Jefferson: School of Engineering, Cardiff University, Cardiff CF24 3AA, UK