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A new surfactant combination compatible with concrete formulation is proposed to avoid unwanted air bubbles created during mixing process in the absence of a defoamer and to achieve the uniform and the maximum possible dispersion of multiwalled carbon nanotubes (MWCNTs) in water and subsequently in concrete. To achieve this goal, three steps have b...
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Citations
... Adresi et al. [172][173][174][175][176][177][178] used multi-wall carbon nanotubes to induce Piezoresistance properties in concrete. Fig. 12 shows the steps of the explained process. ...
... According to the authors Sobolkina et al. [49], the effective dispersion of CNTs can increase compressive resistance by 40%. In a work by Adresi et al. [50], a surfactant and superplasticizer are combined for efficient dispersion. Bundles are one manifestation of the CNTs agglomeration issue in the cementitious substrate [51]. ...
Alkali-activated material (AAM) is a potential sustainable substitute for normal Portland cement-based concrete, but the composition of the material and the design of the mixture have a significant impact on fresh and hardened properties. This research describes the formulation and mechanical behavior of a multi-walled carbon nanotube-reinforced-based alkali-activated nanocomposite. Multiwall carbon nanotubes (MWCNTs) were incorporated into the FA/hydrated lime-based alkali-activated material at concentrations of 0.1%, 0.2%, 0.3%, and 0.35% by weight of the binder. The significant dispersion of MWCNTs within the matrix was achieved in an aqueous solution of surfactant and superplasticizer by employing both magnetic stirring and sonication procedures. The fresh-state characteristics of the MWCNT-based AAM were evaluated in terms of setting time and rheology parameters. Notably, samples containing 0.3% and 0.35% MWCNTs exhibited setting times of 26 and 25 minutes, respectively. The rheological behavior of the nanocomposite adhered to Modified Bingham's model, displaying shear-thinning properties. Moreover, an increase in MWCNT content led to an augmentation in yield stress, with the highest enhancement of 11.1% and 13.1% in yield stress and plastic viscosity, respectively, observed for mortar samples with 0.3% MWCNTs. Mechanical assessments were performed at 7, 14, and 28 days to investigate the compressive and flexural strengths of the specimens. The addition of approximately 0.3% MWCNTs resulted in an impressive boost of up to 14% in compressive strength and an even more remarkable increase of 28% in flexural strength. Furthermore, after exposure to acid and sulfate attacks, the ACN3 samples (0.3% wt. of MWCNTs) exhibited minimal strength loss, with only 5.1% and 3.9% decrease in compressive strength after acid and sulfate attacks, respectively. According to these results, the MWCNTs can function as effective bridges to reduce and limit the progression of microcracks through the AAM-based nanocomposite under the circumstances of homogeneous distribution and good adhesion between both the MWCNTs and the adjacent AAM paste.
... A suitable concentration of such dispersing agents may improve CNT dispersion [30,31] while at the same time, preserving or improving the physical and chemical properties of the cement mortar [32,33].However, the existing findings concerning surfactants on CNT dispersion modification vary significantly among different studies, showing the lack of consistency [34]. In addition, some dispersion agents may induce negative influences on cement hydration or void density [35,36]. Recently, a different CNT surface modification method using carboxymethyl cellulose (CMC) has been investigated and showed promising effectiveness in improving CNT dispersion consistently while increasing the piezoelectric sensitivity in cement mortar [37]. ...
... For the NaDDBS surface treatment, a critical micelle concentration of NaDDBS in water of 1.4 × 10 −2 mol/L (approximately equal to 0.4875% by weight) was set as the input surfactant concentration [35]. First, 1.17g of NaDDBS was mixed with 120 mL of water using a magnetism stirrer for 15 min. ...
... Then, the NaDDBS/CNT solution was mixed with 200 g of cement. A previous study found that air bubbles can appear in the cement paste [35] with NaDDBS addition. Therefore, 0.25% of defoamer (by volume) was utilized to decrease the air bubbles in the CNT-filled cement pastes. ...
In order to achieve effective monitoring of concrete structures for sound structural health, the addition of carbon nanotubes (CNTs) into cementitious materials offers a promising solution for fabricating CNT-modified smart concrete with self-sensing ability. This study investigated the influences of CNT dispersion method, water/cement (W/C) ratio, and concrete constituents on the piezoelectric properties of CNT-modified cementitious materials. Three CNT dispersion methods (direct mixing, sodium dodecyl benzenesulfonate (NaDDBS) and carboxymethyl cellulose (CMC) surface treatment), three W/C ratios (0.4, 0.5, and 0.6), and three concrete constituent compositions (pure cement, cement/sand, and cement/sand/coarse aggregate) were considered. The experimental results showed that CNT-modified cementitious materials with CMC surface treatment had valid and consistent piezoelectric responses to external loading. The piezoelectric sensitivity improved significantly with increased W/C ratio and reduced progressively with the addition of sand and coarse aggregates.
... The absorption bands in these areas indicate a higher degree of crystallization of the above calcium hydrosilicates in the presence of a complex modifier. 1,39 More complete hydration of clinker minerals is determined in the presence of carbon nanotubes in the amount of 0.1 mass. %. ...
... Thus, the use of a complex polymer additive with multilayer carbon nanotubes significantly changes the structure of hardened cement paste due to the directional crystallization of calcium hydrosilicate neoplasms, accelerates the hydration of silicate clinker minerals and the crystallization of hydrosilicates and the basicity of hydrosilicates operational properties. 1,38,39 The results obtained by IR spectroscopy are confirmed by the method of determination of hardened cement paste mass loss by thermogravimetric analysis (TGA) ( Table 6). Losses in the 110-570°C range indicate the amount of hydration products produced -hydrosilicates and calcium hydroxide, and indirectly the rate of hydration. ...
... Such conclusions are confirmed by experimental results in numerous works. 29,36,39,[41][42][43][44] To obtain a high dispersion of CNTs and subsequent uniform distribution in the cement matrix, ultrasonic treatment of carbon nanotubes in acrylic acid solutions was carried out. Results from Raman Spectroscopy (RS) and Transmission Electron Microscopy (TEM) showed that polyacrylic chains were covalently bound to carbon nanotubes rather than adsorbed. ...
In accordance with the principles of sustainable development, improving the quality and durability of structural elements and coatings, the construction industry requires the development and the implementation of resource-and energy-efficient building materials, as well as innovative technologies for their production. The use of complex modifiers for no-slump concrete mixtures and concrete is becoming increasingly widespread in modern materials science. The article presents the studies of influence of polymer additive structured carbon nanomaterials on physical and mechanical characteristics of no-slump concrete mixtures. The methods of infrared spectroscopy and thermogravimetric analysis showed that the use of carbon nanomaterials alters the structure of no-slump concrete mixtures significantly. As a result of the fact that the high-strength nanomaterial is the centre of crystallization of cement stone neo-formation, a denser reinforced microstructure is formed, which increases significantly the strength properties of no-slump concrete mixtures. The inclusion of a complex polymer additive in no-slump concrete mixtures leads to higher and longer plasticizing, which plays an important role in the production of monolithic products. It was determined that, in the presence of a complex modifier (a polymer additive structured by carbon nanotubes), the crystalline structure of calcium silicate hydrate is compacted, which determines high physical and mechanical characteristics of modified no-slump concrete mixtures. It was experimentally shown that the additive acted as an accelerator of a setting and hardening cement test and also increases its strength characteristics. In general, in this study, there is a water-reducing effect from the application of the additive for all no-slump concrete mixtures. Water consumption is reduced by 5% of the mass, while the strength is increased by 19%. No-slump concrete mixtures recipes modified by polymer additives, structured by carbon nanotubes, with high performance were developed.
... Although scanning electron microscopy (SEM) has been used to provide images of nanostructures, spectroscopic methods such as Raman and UV-vis, are used to measure nanotube scattering properties and determine the relationship between the light absorption/scattering rate and the size of particles [47,48]. UV-vis spectroscopy is used to measure the CNT dispersion rate in aqueous solutions [42,49] because dispersed CNTs are very active at 200-1200 nm in wavelength and individual CNTs show specific bands in the UV region [50][51][52]. Jiang et al. [53] used the UV-vis method to determine the dispersion quality of multiwalled carbon nanotubes (MWCNT) quantitatively and observed the maximum absorption in the CNT aqueous solution at 253 nm in wavelength. ...
... Leonavičius et al. [63] reported that the compressive strength increased in cementitious paste containing methylcellulose surfactant and CNTs. Many studies have used superplasticizers as surfactants and have shown that their compatibility with the cement matrix improved the mechanical properties of cementitious composites containing CNTs [52,[67][68][69][70][71][72][73][74][75]. ...
... Adresi et al. [52,76] studied surfactants (NaDDBS, SDS, TX-100, SP) and their combinations. The results showed that the optimal dosage of superplasticizer was 0.5 % (wt), that SDS-superplasticizer was able to disperse the MWCNTs more efficiently than the other surfactants and that 1 SDS to 9 SP was the optimal ratio. ...
When developing cementitious self-sensing composites, a surfactant must provide good CNT dispersion, be compatible with the cementitious matrix and improve the piezoelectric properties of the nanocomposite. This study used CNTs with superplasticizer (SP), carboxymethylcellulose (CMC) and sodium dodecyl sulfate (SDS) and their combinations (SPMC, SPSDS) to compare the dispersion quality of CNTs. SPMC25 showed the best overall results; however, SDS and SPSDS, although showing high levels of UV–vis absorption, also produced good results. The percolation threshold of SPMC25 and SPSDS was 0.025% to 0.1% and the gauge factor of 0.1% SPMC25 reached 126.7. These combinations showed greater sensitivity than sensors made with cement mortar and 0.1% CNT.
... When manufacturing self-sensing concrete, reaching a good dispersion of the conducting nanoparticles is of paramount importance and makes the electrically conductive network more sensitive to the applied load (i.e., the electrical variation will be higher under the same load). To this aim, it is widely reported in the literature that mechanical mixing, sonication, and the addition of dispersants are needed because of a correct dispersion of nanomaterials that easily form agglomerates due to van der Waals forces [67]. Another inconvenience due to the formation of filler clumps because of a poor dispersing process is that they get shrunk under compressive loads and do not recover to their original form when unloading [68]. ...
The importance of the safety and sustainability of structures has attracted more attention to the development of smart materials. The presence of small cracks (<300 µm in width) in concrete is approximately inevitable. These cracks surely damage the functionality of structures, increase their degradation, and decrease their sustainability and service life. Self-sensing cement-based materials have been widely assessed in recent decades. Engineers can apply piezoresistivity for structural health monitoring that provides timely monitoring of structures, such as damage detection and reliability analysis, which consequently guarantees the service life with low maintenance costs. However, concrete piezoresistivity is limited to compressive stress sensing due to the brittleness of concrete. In contrast, engineered cementitious composites (ECC) present excellent tensile ductility and deformation capabilities, making them able to sense tensile stress/strain. Therefore, in this paper, first, the ability of ECC to partly replace transverse reinforcements and enhance the joint shear resistance, the energy absorption capacity, and the cracking response of concrete structures in seismic areas is reviewed. Then, the potential use of natural fibers and cellulose nanofibers in cementitious materials is investigated. Moreover, steel and carbon fibers and carbon black, carbon nanotubes, and graphene, all added as conductive fillers, are also presented. Finally, among the conductive carbonaceous materials, biochar, the solid residue of biomass waste pyrolysis, was recently investigated to improve the mechanical properties, internal curing, and CO2 capture of concrete and for the preparation of self-sensing ECC.
... This was attributed to the strong bond between surfactant and [131,137], sodium dodecylbenzene sulfonate (SDBS) [177,178], polycarboxylate-based superplasticizers [16,176], Lignosulfonate (WDRA) [176], Arabic Gum (AG) [131,178], sodium deoxycholate (NaDC) [178], dodecyl-benzene sodium sulfonate (NaDDBS) [127], Sodium polyacrylate [131], Poly-naphthalene sulfonate sodium salt [179], and sodium alkylbenzene sulfonate [176]. Cationic surfactants: dodecyl trimethylammonium bromide (DTAB) [180] and Cetyltrimethyl ammonium bromide (CTAB) [178,181]. Nonionic surfactants: polyoxyethylene laurylether (Brij35) [137], Pluronic F-127 [177], Methylcellulose [131], Silane [131], Triton X-100 (TX10) [178], propylene glycol aliphatic ether (SR) [176]. ...
During the past decade, researchers investigated the incorporation of carbon nanotubes (CNTs) as a reinforcement for cementitious materials to achieve multifunctional properties. Nevertheless, the mechanisms by which CNTs affect various properties of the cementitious composites including the fresh and hardened states remain elusive. Furthermore, conflicting experimental results have been reported. The discrepancy is attributed to the variability in dispersion, bonding states, and the inconsistencies in the fabrication process (e.g., matrix composition and material characteristics) of the various research conducted. To overcome these challenges, few researchers have investigated the development of analytical equations that could capture the complex interactions between CNTs and the cementitious matrix in order to predict the final properties. This review presents a comprehensive discussion on the research that has been conducted to this date, and provides a detailed insight into the various reinforcing mechanisms of CNTs.
To this extent, first, the extraordinary multifunctional properties of CNTs alongside with their various production methodologies are discussed. Also, potential applications of CNT-reinforced cementitious composites are illustrated. Furthermore, the dispersion methodologies implemented to achieve a well-dispersed and homogenized material are presented including the surfactant-assisted ultrasonication procedure. Moreover, the impact of surface treatment of CNTs on the dispersibility and bonding characteristics of the nano-reinforcement within the cementitious matrix is provided. Then, the latest investigations on the microstructure and fresh properties of CNT-reinforced cementitious composites are discussed. In addition, a statistical analysis on data gathered from the available literature is conducted to search for optimal experimental parameters that can achieve the desired mechanical properties (i.e., compressive strength, flexural strength, elastic modulus, and toughness). Also, recently developed prediction models to estimate the mechanical properties are presented. Finally, the impact of CNTs on the dimensional stability (i.e., shrinkage and creep), durability (e.g., resistance to freezing and thawing and corrosion), and smart applications (i.e., self-sensing, electromagnetic shielding, and energy harvesting) is investigated
... 13 show the correlation between the processing time in the VLA and cubic compressive strength, prismatic compression strength, tensile flexural strength, axial tensile strength, ultimate deformations in axial compression and axial tension of lightweight fiber-reinforced concrete, obtained as a result of the presented experimental research. The polynomial Equations (5)-(11), obtained by interpolating the experimental data, show the relationship between the processing time in the VLA (t) and the strength and deformation characteristics of lightweight fiber-reinforced concrete (Rb,cub, Rb, Rbtb, Rbt, εb, εbt, E) together with the coefficient of determination (Influence of the processing time of the cement-sand mortar in the VLA on the coefficients of the constructive quality of lightweight fiber-reinforced concrete. ...
The relevant problem of choosing effective materials for enclosing structures is compliance with the requirements of increased thermal resistance, reduced mass of buildings and structures, and reduced material consumption, labor intensity, and construction costs. These requirements are satisfied by structures made of lightweight fiber-reinforced concrete, which are the subject of attention of many scientists and engineers. One of the most rational requirements for industrial use is the activation of untreated components of the concrete mixture. This article is devoted to studying the influence of the activation of fiber-reinforced concrete elements in the vortex layer apparatus on concrete strength and structural characteristics. The effect of the raw component processing time of the concrete mixture on the strength and deformation characteristics of the lightweight fiber-reinforced concrete was studied. The optimal processing time for the cement–sand mortar in the VLA-75-85s was determined. It was shown that the activation of the vortex layer in the apparatus leads to an increase in strength from 27% to 61% and an improvement in the deformation characteristics of lightweight fiber-reinforced concrete by up to 12%. Furthermore, it was found that the use of activation in VLA leads to an increase in the coefficient of constructive quality for all experimentally determined strength characteristics of lightweight fiber-reinforced concrete by up to 27%.
... A dark brown solution of polycarboxylate-based superplasticizer (Sarapush construction chemical manufacture) with 36% solid contents and a density of 1.1 g/cm 3 was used for workability purposes. A combination of polycarboxylate superplasticizer and sodium dodecyl sulfate (SDS) with a ratio of 9:1 was used as a surfactant [42,43]. This paper proposes a novel concept in multifunctional smart concrete that can be used as a new NDT technique to monitor damage propagation in concrete media. ...
... In this study, prismatic concrete sensors suitable to be embedded in self-sensing concrete elements were produced. To this purpose, multi-walled carbon nanotubes (MWCNTs) obtained from the Iranian Research Institute of Petroleum Industry (RIPI) were used and added to the concrete mix in a 0.15% proportion by weight of cement content, in analogy with previous studies [42,43]. Using MWCNTs instead of carbon fibers (CFs) helps to increase the sensor's ability to detect crack initiation and propagation under fatigue conditions. ...
... A dark brown solution of polycarboxylate-based superplasticizer (Sarapush construction chemical manufacture) with 36% solid contents and a density of 1.1 g/cm 3 was used for workability purposes. A combination of polycarboxylate superplasticizer and sodium dodecyl sulfate (SDS) with a ratio of 9:1 was used as a surfactant [42,43]. MWCNTs and surfactants were weighted and mixed in water and the solution was stirred for 10 min with a magnetic stirrer (WIFESTEER MSH-20B); then it was sonicated in an ultrasonic bath for 2 hours and afterward with an ultrasonic probe for a further 90 min. ...
Assessing the damage level in concrete infrastructures over time is a critical issue to plan their timely maintenance with proper actions. Self-sensing concretes offer new opportunities for damage assessment by monitoring their electrical properties and relating their variations to damage levels. In this research, fatigue tests were conducted to study the response of a self-sensing concrete under high-cycle dynamic loading. The concept of G-value was defined as the slope of the voltage response baseline of the self-sensing concrete over time that reflects the damage created under the fatigue-loading test. Based on this definition, log (G)–log (N) curves were obtained using a linear regression approach, with N representing the number of cycles during the fatigue tests. While traditional fatigue curves S-log (N) are used to estimate the remaining life under fatigue loading, log (G)–log (N) diagrams can be used to determine the damage level based on the voltage response of the self-sensing concrete as a function of the loading history. This finding can be useful for the estimation of the lifetime and remaining life of self-sensing concrete structures and infrastructure, eventually helping to optimize the related maintenance operations.
... Similarly, Randhawa et al. [26] investigated the effect of surfactant concentration on dispersion and functionalization using Triton X-100 and suggested better functionalization of CNTs with COOH after dispersion, the optimum surfactant being 1.3 wt%. Various researches have suggested that there should be an optimum surfactant to MWCNTs ratio for the most efficient dispersion [27][28][29]. Konsta-Gdoutas et al. [29] state that a weight ratio of surfactant to MWCNTs close to 4 is required for effective dispersion of nanotubes. They further suggested that improvement of fracture properties was observed by the proper dispersion of MWCNTs even at a very less concentration of 0.048% weight. ...
The development of hybrid fiber reinforced cement composite that has high strength, scope to be used as cement based sensors has been investigated in this study by using a combination of carbon fibers and carbon nan-otubes (CNT) at low volume fraction. The dispersion of CNTs was enhanced by using polycarboxylate based su-perplasticizer that resulted in a homogeneous aqueous stable solution, and profoundly improved dispersion when integrated with the cementitious matrix. Different siliceous additives were also incorporated into the mixes to improve the dispersion of CNTs in the matrix, where micro-silica outperformed as compared to nano-silica, confirmed morphologically. On the other hand, nano-silica enhanced dispersion of milled carbon fibers in the aque-ous state. The sensing behavior was determined by the measurement of bulk resistance of mixes and the samples were subjected to compressive loading to study the strength improvement with the incorporation of fibers. The experimental results reveal that hybrid combination of chopped carbon fibers, micro silica, and low volume fraction of CNTs in a cementitious matrix results in a stronger and durable concrete that holds the potential for sensing applications. Thus, laying a strong foundation for the future of low cost smart cement based materials.
