Distribution of porosity surrounding a microfiber in cement paste
Shan He, Yu Chen, Minfei Liang, En-Hua Yang and Erik Schlangen
Abstract: This study investigates the microstructural changes of cement paste due to the inclusion of polymeric microfiber at different water-to-cement (w/c) ratios. A procedure to quantify the porosity of epoxy impregnated interfacial transition zone (ITZ) is also presented. Results show that the microstructures of the ITZ beneath and above a microfiber, with respect to the gravity direction, are largely different. Though the ITZ at both sides of the fiber are more porous than the bulk matrix, the porosity of the lower ITZ (i.e., the ITZ beneath a fiber) is significantly higher than the upper side (i.e., the ITZ above a fiber). This difference can be attributed to the combined effects of fiber on the initial packing of surrounding cement grains and on the settlement of the fresh mixture. The porosity gradients of the upper ITZs are found to be nearly identical for all the tested w/c ratios, while the porosity gradients of the lower ITZs become steeper when the w/c is higher. The lower side is also found to be the preferred location for the precipitation of calcium hydroxide crystals. Results of energy-dispersive X-ray spectroscopy (EDS) and nano-indentation analyses confirm that the chemical and mechanical properties of the ITZ are also asymmetric.
Reference of this article: Shan He, Yu Chen, Minfei Liang, En-Hua Yang, Erik Schlangen, Distribution of porosity surrounding a microfiber in cement paste, Cement and Concrete Composites, Volume 142, 2023, 105188, ISSN 0958-9465,
Affiliations:
Shan He, Yu Chen, Minfei Liang and Erik Schlangen: Faculty of Civil Engineering and Geosciences, Delft University of Technology, Delft 2628 CN, the Netherlands
En-Hua Yang: School of Civil and Environmental Engineering, Nanyang Technological University, Singapore, 639798, Singapore
The full article can be found here: https://doi.org/10.1016/j.cemconcomp.2023.105188
Ultra-thin Strain Hardening Cementitious Composite (SHCC) layer in reinforced concrete cover zone for crack width control
Shan He, Shozab Mustafa, Ze Chang, Minfei Liang, Erik Schlangen and Mladena Luković
Abstract: In the current study, experiments and numerical simulations were carried out to investigate the cracking behavior of reinforced concrete beams consisting of a very thin layer (i.e., 1 cm in thickness) of SHCC in the concrete cover, tension zone. A novel type of SHCC/concrete interface that features a weakened chemical adhesion but an enhanced mechanical interlock bonding was developed to facilitate the activation of SHCC. The study involved testing hybrid SHCC/concrete beams that have various types of interfaces. The results were compared to the control reinforced concrete beams that do not have SHCC in the cover. Four-point bending tests were performed with the beams and Digital Image Correlation (DIC) was utilized to track the development of crack pattern and crack width. Results show that hybrid beams possessed similar load bearing capacity but exhibited a significantly improved cracking behavior as compared to the control beam. With a 1-cm-thick layer of SHCC, the maximum crack width of the best performing hybrid beam exceeded 0.3 mm at 53.3 kN load, whereas in the control beam the largest crack exceeded 0.3 mm at 32.5 kN load. The hybrid beam with the proposed new interface formed 10 times more cracks in SHCC than the hybrid beam with a simple smooth interface and had an average crack width less than 0.1 mm throughout the loading. The lattice model has successfully showcased its ability to predict and offer valuable insights into the fracture behavior of hybrid systems. The simulation results indicate that the presence of a weak interface bond, coupled with mechanical interlocking, can effectively facilitate the activation of SHCC, resulting in the formation of more cracks and a delayed progression towards the maximum crack width. As the volume ratio of SHCC used in the hybrid beams is only 6%, the current study highlights the strategic use of minimum amount of SHCC in the critical region to efficiently enhance the performance of hybrid structures.
Reference of this article: Shan He, Shozab Mustafa, Ze Chang, Minfei Liang, Erik Schlangen, Mladena Luković, Ultra-thin Strain Hardening Cementitious Composite (SHCC) layer in reinforced concrete cover zone for crack width control, Engineering Structures, Volume 292, 2023, 116584, ISSN 0141-0296
Affiliations:
Shan He Ze Chang ,Minfei Liang and Erik Schlangen: Faculty of Civil Engineering and Geosciences, Delft University of Technology, Delft 2628 CN, the Netherlands
Shozab Mustafa and Mladena Loković: Concrete Structures, Faculty of Civil Engineering and Geosciences, Delft University of Technology, 2628 CN Delft, the Netherlands
The full article can be found here: https://doi.org/10.1016/j.engstruct.2023.116584
Optimization of concrete mix designs toward the bond properties of steel reinforcement in self-healing concrete by Taguchi method
Harry Hermawan, Virginie Wiktor, Elke Gruyaert and Pedro Serna
Abstract: The bond of steel reinforcement in normal concrete has been extensively studied, while its bond properties in self-healing concrete has rarely been investigated because the main focus of developing self-healing concrete relies on the improved healing performance such water tightness and strength regain. In fact, the mix design of concrete will greatly affect the bonding. This study elaborates on the optimisation of mix designs for self-healing concrete toward the bond properties of steel reinforcement. The proposed healing agents were bacterial healing agent (BAC) and crystalline admixtures (CA). Mix design parameters include water-cement ratio (w/c) (0.40, 0.50 and 0.60), fine ratio (FR) (0.34, 0.44 and 0.54), and healing agent (HA) (BAC, CA and REF, without healing agent). The Taguchi method was used to formulate nine self-healing concrete mixes by considering three factors and three levels in the design. The compressive strengths of all different concrete mixtures were initially assessed and the pull-out tests on a single steel rebar embedded in concrete were performed in three different states of concrete (uncracked, cracked and healed). The sizes of the cracks were varied and three groups were identified: cracks with a width of 200-300, 300–400 and 400-500 μm. Water immersion was selected as the healing regime with two healing periods lasting 28 and 112 days. The Taguchi analysis and in-depth statistical evaluations were performed for optimisation purpose. Results showed that the compressive strength considerably increased as lowering the w/c, increasing the FR and incorporating the healing agents. The bond of steel reinforcement with the concrete matrix in the uncracked state improved after the BAC or CA was added into the concrete. The formation of cracks in the concrete significantly reduced the bond strength. After being subjected to healing, the bond strength slightly recovered. A longer healing time induced a better bond strength recovery. The phenomenon of crack closure was found at all healed specimens and the healing products were confirmed to be calcium carbonates.
Reference of this article: Harry Hermawan, Virginie Wiktor, Elke Gruyaert, Pedro Serna, Optimization of concrete mix designs toward the bond properties of steel reinforcement in self-healing concrete by Taguchi method, Journal of Building Engineering, Volume 76, 2023, 107294, ISSN 2352-7102,
Affiliations:
Harry Hermawan and Elke Gruyaert: KU Leuven, Department of Civil Engineering, Materials and Constructions, Ghent Campus, Gebroeders De Smetstraat 1, 9000, Ghent, Belgium
Harry Hermawan and Pedro Serna: Instituto de Ciencia y Tecnología Del Hormigón (ICITECH), Universitat Politècnica de València, Camino de Vera S/n, 46022, Valencia, Spain
Virginie Wiktor: Cugla B.V., R&D Center, Rudonk 6b, 4824 AJ, Breda, The Netherlands
The full article can be found here: https://doi.org/10.1016/j.jobe.2023.107294
Preliminary Analysis of Non-destructive Test Methods to Evaluate the Self-healing Efficiency on the Construction Site
Tim Van Mullem, Gerlinde Lefever, Arthur Decuypere, Erik De Vleeschouwer, Yasmina Shields, Laurena De Brabandere, Didier Snoeck, Dimitrios G. Aggelis & Nele De Belie
Abstract: In the last decades major advances have been made in the development of self-healing concrete which is able to heal its own cracks without the need for traditional repair interventions, thereby increasing its durability and service life. Recently, more and more self-healing technologies have been applied in demonstrator projects. These demonstrator projects have made it evident that we need to develop new testing methodologies to evaluate the self-healing performance, as many laboratory test methods cannot be applied on structural elements on the construction site. In the current study different non-destructive test methods have been used to analyse the self-healing performance of concrete beams. These beams were cracked in a three-point bending setup. Part of the beams had a cast-in vascular network allowing the crack to be healed via the injection of polyurethane. The healed beams were compared to the reference beams without the vascular network by applying different test methods: microscopy, concrete moisture content, resistivity, air permeability, water permeability, and ultrasound. Based on the results of these methods which were obtained under laboratory conditions, it was found that the concrete moisture content and the resistivity only provided limited value in terms of conclusions for self-healing. All test methods were also applied to concrete walls on site. Based on this last measuring campaign, recommendations are provided for quantification of the self-healing efficiency on the construction site.
Reference of this article: Van Mullem, T. et al. (2023). Preliminary Analysis of Non-destructive Test Methods to Evaluate the Self-healing Efficiency on the Construction Site. In: Jędrzejewska, A., Kanavaris, F., Azenha, M., Benboudjema, F., Schlicke, D. (eds) International RILEM Conference on Synergising Expertise towards Sustainability and Robustness of Cement-based Materials and Concrete Structures. SynerCrete 2023. RILEM Bookseries, vol 43. Springer, Cham.
Affiliations:
Tim Van Mullem, Arthur Decuypere, Erik De Vleeschouwer, Yasmina Shields, Laurena De Brabandere and Nele De Belie: Magnel-Vandepitte Laboratory, Department of Structural Engineering and Building Materials, Faculty of Engineering and Architecture, Ghent University, Technologiepark Zwijnaarde 60, Campus Ardoyen, 9052, Gent, Belgium
Gerlinde Lefever and Dimitrios G. Aggelis: Department Mechanics of Materials and Constructions, Vrije Universiteit Brussel (VUB), Pleinlaan 2, 1050, Brussels, Belgium
Didier Snoeck: Department of Building, Architecture and Town Planning (BATir), École Polytechnique de Bruxelles, Université Libre de Bruxelles, Av. F. Roosevelt 50, 1050, Brussels, Belgium
The full article can be found here: https://doi.org/10.1007/978-3-031-33211-1_33
Experimental Investigation on the Novel Self-healing Properties of Concrete Mixed with Commercial Bacteria-Based Healing Agent and Crystalline Admixtures
Harry Hermawan, Virginie Wiktor, Pedro Serna and Elke Gruyaert
Abstract: Repairing the cracks in concrete structures is relatively difficult and the manual repair techniques are costly and time-consuming. To overcome this obstacle, stimulated autogenous and autonomous self-healing technologies offer a potential benefit. The healing agents are normally added in the concrete during casting. In fact, traditional concrete also has an autogenous healing ability but the self-healing effect is rather limited. In this study, self-healing concretes were made with two commercial healing agents, namely bacteria-based healing agent (BAC) and crystalline admixtures (CA). The fresh and mechanical properties of concrete were initially evaluated. The addition of healing agents increased the 28 d compressive strength of concrete by 4% for CA and 16% for BAC. The self-healing properties of concrete were evaluated by two methods: (1) crack closure measurements by means of optical microscopy and (2) water flow tests by use of the permeability setup. Results showed that the addition of healing agents showed an advanced progress of the crack closure with increasing healing time, and the permeability rate considerably decreased as a result of the crack clogging by healing products. The self-healing concretes showed better healing and sealing efficiencies than the autogenous self-healing in the traditional concrete, showing a promising result to apply the agents in real applications.
Reference of this article: Hermawan, H., Wiktor, V., Serna, P., Gruyaert, E. (2023). Experimental Investigation on the Novel Self-healing Properties of Concrete Mixed with Commercial Bacteria-Based Healing Agent and Crystalline Admixtures. In: Jędrzejewska, A., Kanavaris, F., Azenha, M., Benboudjema, F., Schlicke, D. (eds) International RILEM Conference on Synergising Expertise towards Sustainability and Robustness of Cement-based Materials and Concrete Structures. SynerCrete 2023. RILEM Bookseries, vol 44. Springer, Cham.
Affiliations:
Harry Hermawan and Elke Gruyaert: KU Leuven, Department of Civil Engineering, Materials and Constructions, Ghent Campus, Gebroeders De Smetstraat 1, 9000, Ghent, Belgium
Harry Hermawan and Pedro Serna: Instituto de Ciencia y Tecnología Del Hormigón (ICITECH), Universitat Politècnica de València, Camino de Vera S/n, 46022, Valencia, Spain
Virginie Wiktor: Cugla B.V., R&D Center, Rudonk 6b, 4824 AJ, Breda, The Netherlands
The full article can be found here: https://doi.org/10.1007/978-3-031-33187-9_77