An effective method for hybrid CNT/GNP dispersion and its effects on the mechanical, microstructural, thermal, and electrical properties of multifunctional cementitious composites

"Article ID 6749150"This paper reports a study undertaken to achieve a compatible and affordable technique for the high-quality dispersion of carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs) in an aqueous suspension to be used in multifunctional cementitious composites. In this research work, two noncovalent surfactants with different dispersion mechanisms (Pluronic F-127 (nonionic) and sodium dodecylbenzene sulfonate (SDBS) (ionic)) were used. We evaluated the influences of various factors on the dispersion quality, such as the surfactant concentration, sonication time, and temperature using UV-visible spectroscopy, optical microscopic image analysis, zeta potentials, and particle size measurement. The effect of tributyl phosphate (TBP) used as an antifoam agent was also evaluated. The optimum suspensions of each surfactant were used to produce cementitious composites, and their mechanical, microstructural, electrical, and thermal behaviors were assessed and analyzed. The best dispersed CNT+GNP aqueous suspensions using Pluronic and SDBS were obtained for concentrations of 10% and 5%, respectively, with 3 hours of sonication, at 40°C, with TBP used for both surfactants. The results also demonstrate that cementitious composites reinforced with CNT+GNP/Pluronic showed better mechanical performance and microstructural characteristics due to the higher quality of the dispersion and the increasing hydration rate. Composites prepared with an SDBS suspension demonstrated lower electrical and thermal conductivities compared to those of the Pluronic suspension due to changes in the intrinsic properties of CNTs and GNPs by the SDBS dispersion mechanism.This work was supported by the European Commission-Shiff2Rail Program under the project “IN2TRACK2–826255-H2020-S2RJU-2018/H2020-S2RJU CFM-2018"

Effects of multiscale carbon-based conductive fillers on the performances of a self-sensing cementitious geocomposite

In this study, the effects of multiscale conductive carbon fillers, including carbon nanotubes (CNTs), graphene nanoplatelets (GNPs), and carbon fibres (CFs), on the mechanical and microstructural properties, durability, and piezoresistivity of cementitious stabilised sand (CSS) were investigated. In this route, the surface of the CFs was modified via an oxidation process to improve their interfacial performance and dispersion. An optimum amount of hybrid CNT/GNP with different concentrations of CFs was incorporated into the CSS, and specimens were fabricated using the standard compaction method at the optimum water content. The interfacial properties of the CFs were studied by performing pullout tests and several chemical analyses. The variations in the mechanical and microstructural, durability, and piezoresistivity of the CSS, were investigated by various tests. In addition, the status of the specimens in terms of residual strain and damages was identified by the digital image correlation technique. The results showed a considerable improvement in the interfacial properties of the modified CFs in terms of physical and chemical bonding with the cement matrix. In addition, a combination of 0.17% CNT/GNP (1:1, by weight of dry sand) with 0.75% CF can improve the maximum dry density and mechanical properties, as well as the ductility and durability of the CSS. In addition, using multiscale conductive fillers resulted in a considerable enhancement in the electrical conductivity and piezoresistivity of the CSS. The outcomes indicate the immense potential of CNT/GNP/CF for the development of a sustainable self-sensing cementitious geocomposite.This work was supported by the European Commission-Shift2Rail Program under the project “IN2TRACK3, H2020–S2RJU-CFM-2020, S2R-CFMIP3- 01–2020”. Furthermore, it is partly financed by FCT/ MCTES through national funds (PIDDAC) under the R&D Unit of the Institute for Sustainability and Innovation in Engineering Structures (ISISE), under reference nº. 101012456, as well as under the R&D Unit of the Centre for Textile Science and Technology (2C2T)

Development of a novel multifunctional cementitious-based geocomposite by the contribution of CNT and GNP

In this study, a self-sensing cementitious stabilized sand (CSS) was developed by the incorporation of hybrid carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs) based on the piezoresistivity principle. For this purpose, different concentrations of CNTs and GNPs (1:1) were dispersed into the CSS, and specimens were fabricated using the standard compaction method with optimum moisture. The mechanical and microstructural, durability, and piezoresistivity performances, of CSS were investigated by various tests after 28 days of hydration. The results showed that the incorporation of 0.1%, 0.17%, and 0.24% CNT/GNP into the stabilized sand with 10% cement caused an increase in UCS of about 65%, 31%, and 14%, respectively, compared to plain CSS. An excessive increase in the CNM concentration beyond 0.24% to 0.34% reduced the UCS by around 13%. The addition of 0.1% CNMs as the optimum concentration increased the maximum dry density of the CSS as well as leading to optimum moisture reduction. Reinforcing CSS with the optimum concentration of CNT/GNP improved the hydration rate and durability of the specimens against severe climatic cycles, including freeze–thaw and wetting–drying. The addition of 0.1%, 0.17%, 0.24%, and 0.34% CNMs into the CSS resulted in gauge factors of about 123, 139, 151, and 173, respectively. However, the Raman and X-ray analysis showed the negative impacts of harsh climatic cycles on the electrical properties of the CNT/GNP and sensitivity of nano intruded CSS.This research was funded by European Commission-Shiff2Rail Program under the project “IN2TRACK2–826255-H2020-S2RJU-2018/H2020-S2RJU CFM-2018”. It was also partly financed by FCT/MCTES through national funds (PIDDAC) under the R&D Unit Institute for Sustainability and Innovation in Engineering Structures (ISISE), under reference UIDB/04029/2020, as well as under the R&D Unit Centre for Textile Science and Technology (2C2T)

Geotechnical and piezoresistivity properties of sustainable cementitious stabilized sand reinforced with recycled fibres

In this study, the geotechnical and piezoresistivity properties of a sustainable self-sensing cementitious stabilised sand reinforced with recycled fibres (self-sensing cementitious geocomposite, SCG) were extensively investigated. In this route, different concentrations of recycled glass, polypropylene, and ultra-high-molecular-weight polyethylene (GF, PP, and UHMWPE) fibres were incorporated into the conductive stabilised sand with 10% cement composed of 0.17% hybrid (1:1) carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs). The specimens were fabricated using the standard Proctor compaction method at optimum water content, and their mechanical, hydraulic, microstructural, durability, and piezoresistivity properties were investigated after 28 days of hydration using different laboratory test methods. The test results indicate that the maximum dry densities of all SCGs were obtained with a degree of saturation of approximately 85%. For these moisture conditions, there are well-defined relationships between the maximum dry density and strength, permeability, and ultrasonic pulse velocity for SCGs. The GF and UHMWPE fibres exhibited the best performances in terms of strength, durability in climatic cycles, as well as a reduction in permeability. A unique relationship between the ratio of tangent modulus and strength with the strain was defined for all the SCGs that can be of practical use in geocomposite. Furthermore, the piezoresistivity and sensitivity of the SCGs were also increased by reinforcing the geocomposites with fibres, due to increasing their ductility. In summary, we believe that this novel approach contributes to a new era of smart geocomposite materials in sustainable intelligent transport infrastructures.This work was supported by the European Commission-Shiff2Rail Program under the project “IN2TRACK2–826255-H2020-S2RJU-2018/ H2020-S2RJU CFM-2018′′. It was also partly financed by FCT/MCTES through National Funds (PIDDAC) under the R&D Unit Institute for Sustainability and Innovation in Engineering Structures (ISISE) under reference UIDB/04029/2020, and under the R&D Unit Centre for Textile Science and Technology (2C2T)

A review of intrinsic self-sensing cementitious composites and prospects for their application in transport infrastructures

Monitoring of transport infrastructures, in terms of early damage detection, can prevent the loss of life and economic damage associated with sudden infrastructure collapse and inform timely intervention, such as repair, to increase the sustainability and service life of infrastructures. Self-sensing cementitious geocomposites with the ability to detect stress, strain, and damage based on a piezoresistive mechanism enable the development of more integrated and viable geomaterial monitoring solutions than existing monitoring technologies. Self-sensing cementitious geocomposites are composed of conductive phases embedded in cementitious geomaterials that exhibit both sensing ability and superior mechanical properties. The states of stress, strain, displacement, and damage in infrastructures can be investigated by analysing the change in their electrical resistance. In this review, different types of self-sensing composites, their preparation, influential parameters, and associated theoretical investigations are discussed in detail to inform future advances in the development of self-sensing geocomposites. The challenges of this technology have also been summarised. This review is expected to stimulate and inform research that explores the development and application prospects of self-sensing cementitious geocomposites.This work was supported by the European Commission-Shiff2Rail Program under the project “IN2TRACK2–826255-H2020-S2RJU-2018/H2020-S2RJU CFM-2018”. It is also partly financed by FCT/MCTES through national funds (PIDDAC), under the R&D Unit of the Institute for Sustainability and Innovation in Engineering Structures (ISISE; reference UIDB/04029/2020), as well as under the R&D Unit of the Centre for Textile Science and Technology (2C2T)

Effects of electrodes layout and filler scale on percolation threshold and piezoresistivity performances of a cementitious-based geocomposite

An extensive experimental study was conducted to investigate the co-effects of surface area and distance between electrodes as well as filler scales on the percolation threshold of piezoresistive cement-stabilised sand. In this route, the electrical resistivity of numerous specimens of different sizes and composed of different content of carbon-based conductive fillers was measured, including carbon nanotubes (CNTs), graphene nanoplatelets (GNPs), and carbon fibres (CFs) with different aspect ratios. In addition, the numerical relations between the electrical percolation threshold and matrix dimensions were expressed for different conductive fillers. Furthermore, the electrical percolation threshold of two large-scale specimens with different shapes (a 10 × 10 × 85 cm3 beam, and a 15 cm size cube) were predicted through numerical relations, and their piezoresistivity performances were investigated under compression cyclic loading (cube) and flexural cyclic loading (beam). The mechanical properties of the specimens were also evaluated. The results showed that the changes in the length, width, and thickness of the matrix surrounded between electrodes had a significant effect on the electrical percolation threshold. However, the effects of length changes on the percolation threshold were greater than the width and thickness changes. Generally, increasing the aspect ratio of the conductive fillers caused a reduction in the electrical percolation threshold of the cementitious geocomposite. The appropriate piezoresistivity response of the large-scale specimens composed of filler content equal to their percolation threshold (obtained by the numerical relation presented in this study) showed the adequacy of the results in terms of threshold dosage prediction and self-sensing geocomposite design. The results of this study addressed a crucial factor for the design of self-sensing composites and pave the way for the development of field-applicable, smart, cementitious geocomposite.European Commission-Shift2Rail Program under the project “IN2TRACK3, H2020-S2RJU-CFM-2020, S2R-CFMIP3-01-2020”. Furthermore, it is partly financed by FCT/MCTES through national funds (PIDDAC) under the R&D Unit of the Institute for Sustainability and Innovation in Engineering Structures (ISISE), under reference nº. 101012456, as well as under the R&D Unit of the Centre for Textile Science and Technology (2C2T). The first author also acknowledges the support provided by the FCT/PhD individual fellowship with the reference of “2021. 07596.BD”

Innovative self-sensing fiber-reinforced cemented sand with hybrid CNT/GNP

This study is a systematic attempt to develop a self-sensing fiber-reinforced cemented sand (CS) with high physical, mechanical, durability, and piezoresistivity performances. In this route, different concentrations of Dyneema, glass, and polypropylene (PP) fibers were incorporated into CS containing 0.17% hybrid carbon nanotubes and graphene nanoplatelets. The specimens were fabricated using the standard Proctor compaction method and tested at the optimum water content. The mechanical, microstructural, and durability performances of the specimens were evaluated through various types of tests. Further, the piezoresistivity of the specimens was evaluated under compression cyclic loads using the four probes method. The incorporation of 1.0% glass and Dyneema fiber as the optimum percent increased the unconfined compression strength (UCS) (29% and 82%, respectively) and the maximum dry density of the CS; however, reinforcing of the specimens with PP fiber at a concentration in the range of 0.5%-1.5% generally reduced the UCS of the specimens. The pullout test results exhibited a considerable interfacial performance for the Dyneema fiber. The CS reinforced with 1.0% Dyneema and glass fiber demonstrated a lower weight loss after 12 wetting and drying cycles compared to other specimens. The maximum gauge factors were also achieved for Dyneema fiber-reinforced CS. The outcomes of this study, balanced with sustainable issues, contribute to the development of the new era of smart structures, with applications to roller-compacted-concrete dams, rammed earth, and particularly in structural layers in transportation infrastructure.This work was supported by the European CommissionShiff2Rail Program under the project ‘IN2TRACK2–8262 55-H2020-S2RJU-2018/H2020-S2RJU CFM-2018’. It is also partly financed by FCT/MCTES through national funds (PIDDAC) under the R&D Unit Institute for Sustainability and Innovation in Engineering Structures (ISISE), under reference UIDB/04029/2020, as well as under the R&D Unit Centre for Textile Science and Technology (2C2T)

Thermophysical properties of compressed earth blocks incorporating natural materials

Building materials are responsible for significant CO2 emissions and energy consumption, both during production and operational phases. Earth as a building material offers a valuable alternative to conventional materials, as it naturally provides high hygrothermal comfort and air quality even with passive conditioning systems. However, disadvantages related to high density, conductivity, and wall thickness prevent its effective inclusion in the mainstream. This research explores enhancing the thermophysical properties of compressed earth blocks (CEBs) by using locally sourced natural materials. The study is framed in the Portuguese context and the natural materials involved are wheat straw (WS) as a by-product of wheat harvesting, cork granules (CGs) from bottle caps, and ground olive stone (GOSs) residues from olive oil production. Blocks were produced with different mixtures of these materials and the thermal response was examined in a hot box apparatus. Best results include a 20 and 26% reduction in thermal conductivity for mixtures with 5v.% CG and 10v.% GOS, respectively, and an associated reduction in bulk density of 3.8 and 5.4%. The proposed approach therefore proves to be effective in improving the key thermophysical characteristics of CEBs. The article includes a comparative analysis of the experimental data from this study with those from the literature. The study contributes to the growing knowledge of sustainable materials, providing insights for researchers and practitioners looking for innovative solutions for low-carbon and energy-efficient materials.This work is funded by national funds through FCT, Foundation for Science and Technology, under grant agreement UIBD/150874/2021 (https://doi.org/10.54499/UI/BD/150874/2021, accessed 23 April 2024), attributed to the first author. The work is partly financed by Fundação “La Caixa” (Programa Promove) under the project BTCpro with the reference PV20-00072. The work is also partly financed by FCT/MCTES through national funds (PIDDAC) under the R&D Unit Institute for Sustainability and Innovation in Structural Engineering (ISISE), reference UIDB/04029/2020 (https://doi.org/10.54499/UIDB/04029/2020, accessed 23 April 2024), and under the Associate Laboratory Advanced Production and Intelligent Systems ARISE, reference LA/P/0112/2020

Unified compressive strength and strain ductility models for fully and partially FRP-confined circular, square, and rectangular concrete columns

Determination of fiber-reinforced polymer (FRP) confinement-induced improvements in the mechanical properties of concrete columns under compression is a current concern, particularly if partial confinement applied on a noncircular cross-sectional shape is to be considered. Although several design-oriented predictive formulations have been proposed for the calculation of axial strength and axial strain ductility of FRP-confined concrete, their applications are, in general, limited to a specific cross-sectional shape (circular, square, or rectangular cross section) and a certain confinement arrangement (fully or partially confining system). Accordingly, the aim in this study is to establish new unified strength and ductility models for concrete columns of circular or noncircular cross sections with fully or partially confining FRP systems. To achieve the highest level of predictive performance through a nonlinear regression technique, two datasets, consisting of 2,117 test data of peak strength and 2,050 test data of strain ductility, available in the literature, were collected. The dominance degrees of size effect, sectional noncircularity (corner radius ratio), cross-sectional aspect ratio, and confinement configuration type on confinement effectiveness were evaluated and reflected in the development of these regression-based models. Through predictions of test data compiled in the datasets and a comparison with the performances of available predictive models, the proposed unified formulations demonstrated a high level of reliability and were found to be proper for design purposes.FCT -Fundação para a Ciência e a Tecnologia(SFRH/BD/148002/2019

Ultra-sensitive affordable cementitious composite with high mechanical and microstructural performances by hybrid CNT/GNP

In this paper a hybrid combination of carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs) was used for developing cementitious self-sensing composite with high mechanical, microstructural and durability performances. The mixture of these two nanoparticles with different 1D and 2D geometrical shapes can reduce the percolation threshold to a certain amount which can avoid agglomeration formation and also reinforce the microstructure due to percolation and electron quantum tunneling amplification. In this route, different concentrations of CNT + GNP were dispersed by Pluronic F-127 and tributyl phosphate (TBP) with 3 h sonication at 40 °C and incorporated into the cementitious mortar. Mechanical, microstructural, and durability of the reinforced mortar were investigated by various tests in different hydration periods (7, 28, and 90 days). Additionally, the piezoresistivity behavior of specimens was also evaluated by the four-probe method under flexural and compression cyclic loading. Results demonstrated that hybrid CNT + GNP can significantly improve mechanical and microstructural properties of cementitious composite by filler function, bridging cracks, and increasing hydration rate mechanisms. CNT + GNP intruded specimens also showed higher resistance against climatic cycle tests. Generally, the trend of all results demonstrates an optimal concentration of CNT (0.25%) + GNP (0.25%). Furthermore, increasing CNT + GNP concentration leads to sharp changes in electrical resistivity of reinforced specimens under small variation of strain achieving high gauge factor in both flexural and compression loading modes.This research was funded by European Commission-Shiff2Rail Program under the project“IN2TRACK2–826255-H2020-S2RJU-2018/H2020-S2RJU CFM-2018