A New Method to Quantitatively Characterize the Porosity of Fiber/Matrix Interfacial Transition Zone (ITZ) via Longitudinal Cross-Sections
Shan He, Minfei Liang, En-hua Yang and Erik Schlangen
Abstract: The properties of the interfacial transition zone (ITZ) between microfiber and cement-based matrix are of primary significance for the overall behavior of strain hardening cementitious composites (SHCCs). However, due to the relatively small diameter of polymeric microfibers (e.g., PVA fiber), it is technically difficult to obtain quantitative and representative information of the properties of the ITZ. In the current study, a new method that is able to quantitatively characterize the microstructural features of the ITZ surrounding a well-aligned microfiber was reported. With the method, the porosity gradients within the ITZs between PVA fiber and cement paste matrices with different water to cement (w/c) ratios were determined. The results show that the matrix surrounding a microfiber were more porous than the bulk matrix. The thickness of this porous region can extend up to 100 microns away from the fiber surface even at a relatively low water to cement ratio (w/c = 0.3). It is thus believed that the method could facilitate the investigation and modification of fiber/matrix bond properties and also contribute to the development of SHCC with superior properties.
Reference of this article: He, S., Liang, M., Yang, Eh., Schlangen, E. (2023). A New Method to Quantitatively Characterize the Porosity of Fiber/Matrix Interfacial Transition Zone (ITZ) via Longitudinal Cross-Sections. In: Kunieda, M., Kanakubo, T., Kanda, T., Kobayashi, K. (eds) Strain Hardening Cementitious Composites. SHCC 2022. RILEM Bookseries, vol 39. Springer, Cham. https://doi.org/10.1007/978-3-031-15805-6_14
Affiliations:
Shan He,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, 639797, Singapore
The full article can be found here: https://doi.org/10.1007/978-3-031-15805-6_14
Predicting micromechanical properties of cement paste from backscattered electron (BSE) images by computer vision
Minfei Liang, Shan He, Yidong Gan, Hongzhi Zhang, Ze Chang, Erik Schlangen, and Branko Šavija
Abstract: Although grouting is a widespread process mainly used for soil treatment and for filling cracks/voids in concrete structures, grout injection is still a challenging step. Due to the different performance required for the numerous fields of application, encompasThis paper employs computer vision techniques to predict the micromechanical properties (i.e., elastic modulus and hardness) of cement paste based on an input of Backscattered Electron (BSE) images. A dataset comprising 40,000 nanoindentation tests and 40,000 BSE micrographs was built by express nanoindentation test and Scanning Electron Microscopy (SEM). A Residual Convolutional Neural Network (Res-Net) model, which differs from a typical Convolutional Neural Network (CNN) architecture by a shortcut connection, was employed and compared with a simple table model. The models were trained, tuned, and tested over a training, validation and testing set comprising 70%, 15% and 15% of the 40,000 data pairs, respectively. The following conclusions were drawn: 1) Express nanoindentation tests can provide reliable information for cement paste. Deconvolution based on Gaussian Mixture Model (GMM) can obtain almost invariant statistics for each phase; 2) Based on averaged greyscale values of each BSE image, a table model can predict the elastic modulus and hardness with R2 of 0.80 and 0.83, respectively; 3) Based on the intensity of each pixel as well as their patterns in each BSE image, the Res-Net model can predict the elastic modulus and hardness with a R2 of 0.85 and 0.88, respectively. Deconvolution of the Res-Net prediction obtains similar invariant statistics as derived by the nanoindentation tests, which gives strong evidence of the applicability of the Res-Net model.
Reference of this article: Minfei Liang, Shan He, Yidong Gan, Hongzhi Zhang, Ze Chang, Erik Schlangen, Branko Šavija, Predicting micromechanical properties of cement paste from backscattered electron (BSE) images by computer vision, Materials & Design, Volume 229, 2023, 111905, ISSN 0264-1275
Affiliations:
Minfei Liang, Shan He, Ze Chang, Erik Schlangen, and Branko Šavija: Faculty of Civil Engineering and Geosciences, Delft University of Technology, Delft 2628 CN, the Netherlands
Yidong Gan: School of Civil and Hydraulic Engineering, Huazhong University of Science and Technology, Wuhan 430074, China
Hongzhi Zhang: School of Qilu Transportation, Shandong University, Jinan 250100, China
The full article can be found here: https://doi.org/10.1016/j.matdes.2023.111905
A comprehensive review of cementitious grouts: Composition, properties, requirements and advanced performance
Suelen da Rocha Gomes, Liberato Ferrara, Luis Sánchez and Mercedes Sánchez Moreno
Abstract: Although grouting is a widespread process mainly used for soil treatment and for filling cracks/voids in concrete structures, grout injection is still a challenging step. Due to the different performance required for the numerous fields of application, encompassing several injection methods and different design approaches, it is essential to understand how the components of the grout (cement, aggregates, supplementary cementitious materials, chemical admixtures) affect the workability, stability, injectability, consistency, rheology and, as a result both the composition and the aforesaid properties, also the mechanical strength of the material and the effectiveness and long term performance of the overall grouting application. As a matter of fact, all cementitious materials can suffer deterioration processes that affect the serviceability and durability of structures and jeopardizing their safety, requiring maintenance/recovery works whose cost can, overall the structure life cycle, result even higher than the construction one. This may be especially true in the case of grouting applications, e.g. in prestressed concrete structures, where the state of deterioration is not visible and its non-inspectable progress might lead to catastrophic structural failures. To address all these issues, researchers have developed self-healing cementitious materials which have proved to be an interesting option, as they are able to prolong the lifetime of structures, reducing the environmental impact all along its life cycle. The literature points out that many self-healing mechanisms are effective in concrete and mortars. However, this technology has been barely applied in grouts. In this context, this work presents a comprehensive overview of cementitious grouts with focus on their composition, properties, application technologies and conditions that can affect the overall material and application performance. In addition, this review also provides an overview of self-healing technologies applied to grouts as well as the research gaps in the field of self-healing grouts that should be desirably filled to exploit their benefits in structural and infrastructural applications.
Reference of this article: Suelen da Rocha Gomes, Liberato Ferrara, Luis Sánchez, Mercedes Sánchez Moreno, A comprehensive review of cementitious grouts: Composition, properties, requirements and advanced performance, Construction and Building Materials, Volume 375, 2023, 130991, ISSN 0950-0618,
Affiliations:
Suelen da Rocha Gomes, Luis Sánchez, Mercedes Sánchez Moreno,: Department of Inorganic Chemistry and Chemical Engineering, Chemical Institute for Energy and Environment, IQUEMA. University of Córdoba, Córdoba, Spain
Liberato Ferrara: Department of Civil and Environmental Engineering, Politecnico di Milano, Milan, Italy
The full article can be found here: https://doi.org/10.1016/j.conbuildmat.2023.130991
Self-healing Capabilities of Ultra-High Performance Fiber Reinforced Concrete with Recycled Aggregates
Niranjan Prabhu Kannikachalam, Ruben Paul Borg, Estefania Cuenca, Nele De Belie, and Liberato Ferrara
Abstract: This study examines the effect of recycled aggregates on the stimulated autogenous self-healing of Ultra-High Performance Fiber Reinforced Concrete (UHPFRC) when exposed to wet and dry conditions. Recycled aggregates have been produced by crushing four months old UHPFRC specimens with an average compressive strength of 150 MPa. Two different percentages (50% & 100% by weight) of recycled aggregate (0–2 mm) have been used as a substitute for the natural aggregate in a reference UHPFRC mix to produce recycled UHPFRC. After an assessment of the overall mechanical properties of the recycled UHPFRC mixes, one year old notched beam specimens were pre-cracked to the width of 150 µm through a three-point flexural test. The self-healing capacity of recycled UHPFRCs has been investigated in terms of water absorption tests, regain in flexural strength and microscopic crack healing, at scheduled times after pre-cracking (0 days, 1 month, 3 months and 6 months). Constant wet/dry healing conditions were maintained throughout the experiment. The specimens with recycled UHPC aggregate showed better and longer self-healing than the specimens with natural aggregate, which provides additional value to the overall environmental sustainability of the investigated category of materials.
Reference of this article: Kannikachalam, N.P., Borg, R.P., Cuenca, E., De Belie, N., Ferrara, L. (2023). Self-healing Capabilities of Ultra-High Performance Fiber Reinforced Concrete with Recycled Aggregates. In: Escalante-Garcia, J.I., Castro Borges, P., Duran-Herrera, A. (eds) Proceedings of the 75th RILEM Annual Week 2021. RW 2021. RILEM Bookseries, vol 40. Springer, Cham.
Affiliations:
Niranjan Prabhu Kannikachalam, Estefania Cuenca and Liberato Ferrara: KDepartment of Civil and Environmental Engineering, Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133, Milan, Italy
Niranjan Prabhu Kannikachalam and Nele De Belie: Department of Structural Engineering and Building Materials, Ghent University, Magnel-Vandepitte Laboratory, Tech Lane Ghent Science Park, Campus A, Technologiepark Zwijnaarde 60, 9052, Ghent, Belgium
Ruben Paul Borg: Faculty for the Built Environment, University of Malta, Msida, 2080, MSD, Malta
The full article can be found here: https://doi.org/10.1007/978-3-031-21735-7_38
Experimental investigation on the bond behaviour of steel reinforcement in self-healing concrete
Harry Hermawan, Virginie Wiktor, Elke Gruyaert and Pedro Serna
Abstract: The appearance of cracks in structural reinforced concrete is inevitable and when out of control, it can be the cause of concrete failure. The ingress of water and harmful substances via the cracks is critical as the embedded steel reinforcements in the concrete can be corroded. Crack formation will directly weaken the bond between the reinforcing bar and concrete. To mitigate this issue, cracks should be repaired and closed relatively fast and this can potentially be obtained by incorporating self-healing technologies. Self-healing concrete demonstrates a good healing efficiency by the use of smart materials which allow for autonomous healing or enhance the autogenous healing mechanism of concrete. However, it is questioned whether the precipitates only artificially close the crack or also contribute to improve the bond with the reinforcement. In this study, an experimental investigation was conducted to evaluate the bond properties of self-healing concrete by means of pull-out tests. Four types of healing agents were used including two non-axenic biomass agents (HTN and YEAST) and two commercial agents (crystalline admixture and bacteria (CA and BAC)). The fresh properties and mechanical properties of the concrete including the healing agents were initially investigated. Pull-out tests were executed on uncracked, cracked and healed specimens. Two healing periods (28 and 112 days water immersion) were considered to evaluate the effect of healing time on bond recovery. Test results confirm that the addition of healing agents induced a better improvement of bond properties of steel reinforcement in uncracked concretes with respect to the reference concrete (no healing agent added). The highest bond strength enhancement by 57% on uncracked concrete was obtained with the addition of CA, while the inclusion of other agents such BAC, HTN and YEAST also possessed the bond strength improvement by 47, 21 and 7%, respectively. The presence of a longitudinal crack in concrete significantly reduced the bond strength up to 80% and this effect was not significantly affected by the crack size, when considering cracks in the range of 200─500 µm, and the introduction of healing agents. Nevertheless, the bond properties were slightly recovered after healing due to self-healing effects and formation of healing products in the crack was clearly visible.
Reference of this article: Harry Hermawan, Virginie Wiktor, Elke Gruyaert, Pedro Serna, Experimental investigation on the bond behaviour of steel reinforcement in self-healing concrete, Construction and Building Materials, Volume 383, 2023, 131378, ISSN 0950-0618
Affiliations:
Harry Hermawan and Elke Gruyaert: KU Leuven, Ghent Technology Campus, Department of Civil Engineering, Materials and Constructions, Gebroeders De Smetstraat 1, 9000 Ghent, Belgium
Virginie Wiktor: Cugla B.V., R&D center, Rudonk 6b, 4824 AJ Breda, the Netherlands
Pedro Serna: Instituto de Ciencia y Tecnología Del Hormigón (ICITECH), Universitat Politècnica de València, Camino de Vera S/n, 46022, Valencia, Spain
The full article can be found here: https://doi.org/10.1016/j.conbuildmat.2023.131378