This is an experimental study showing the effect of four types of polymers (acrylate polymer (AC), polyvinyl alcohol (PVA), styrene–butadiene rubber (SBR), and ethylene-vinyl acetate (EVA)) on the ...mechanical properties of polymer-modified cement mortars (PCMs). One polymer dosage was used in this study (3%), and the effect of this dosage on PCMs was compared with a control mortar mix with 0% polymer. The compressive, flexural, and pull-off bond strengths were measured and compared with previous results in works of literature. The effect of polymer addition on improving the mechanical properties of PCMs was clarified, and this effect was more obvious on the flexural strength than that on the compressive strength. The PCMs containing EVA showed the best performance, with up to 33% and 63% increases in compressive and flexural strengths after 28 days, respectively. In comparison, AC, PVA, and SBR produced smaller (16%–46% compared to control) improvements in the flexural strength after 28 days. In general, PCMs containing EVA showed the best mechanical properties.
In this paper, we present a flexible hybrid energy harvester for single- or multi-source energy collection. To increase harvesting power, piezoelectric and thermoelectric conversions are used ...simultaneously. The piezoelectric portion of the harvester collects energy from low-frequency kinetic motion using frequency up-conversion. The thermoelectric part is suitable for harvesting energy from a curved surface, thanks to its flexibility. By harvesting from two different energy sources (kinetic and thermal), the harvester allows for sustainable energy harvesting. The average power density obtained was 28.57 and 0.64 μW/cm2 by piezoelectric and thermoelectric conversion, respectively.
•Alkali-activated fly ash with pozzolanic reaction reached 60 MPa at ambient condition.•Silica fume enhanced reaction participation of Ca2+ in alkaline environment.•Significant contribution to ...strength development was induced from pozzolanic reaction.•Physical filling effect by addition of silica fume was negligible in tested mix proportions.
Despite considerable efforts focused on the utilization of industrial wastes, the application of low-calcium fly ash to the construction industry is limited to the partial substitution to ordinary Portland cement. High-temperature curing is a method via which fly ash can be completely utilized as an alkali-activated construction material; however, additional energy is required. In this study, the dual reaction of alkali activation and the pozzolanic reaction was proposed to manufacture ambient-condition-curable structural mortars. For this purpose, calcium hydroxide was used in fly ash activated by sodium hydroxide and sodium silicate solutions. A series of experiments, including compressive strength tests, X-ray diffraction, thermogravimetric analysis, heat of reaction, and mercury intrusion porosimetry, were conducted. The continuous pozzolanic reaction on the pre-formulated geopolymeric skeleton was found to significantly enhance the material properties. By the addition of silica fume and a 7:3 mixture of sodium hydroxide and sodium silicate solutions, the material strength increased to greater than 60 MPa at 56 days. The added silica fume as well as the reduced alkali content of the solution enhanced the reactions due to the active participation of the calcium ion supplied by the added hydrated lime in a high pH environment.
Self-powered energy harvesters utilizing triboelectric effect and electrostatic induction have been widely studied, leading in the materials viewpoint to numerous material pairs for facile charge ...separation upon repetitive contacts with elaborate topological structures. Here, we present a simple but robust triboelectric platform based on a molecularly engineered surface triboelectric nanogenerator by self-assembled monolayers (METS). Triboelectric surface charge density of a substrate was readily controlled by the variation of end-functional groups of self-assembled monolayers (SAMs). In particular, by employing fluorine terminated SAMs, we are able to develop a METS with the maximum open circuit voltage and short circuit current of 105 V and 27 μA, respectively, under relatively gentle mechanical contacts with the 3N vertical force at 1.25 Hz. The power density of the device was 1.8 W/m2 at the load resistance of 10 MΩ more than 60 times greater than that of an unmodified dielectric/Al device. Moreover, our approach with SAMs was extended to various types of surfaces including fabrics of silk, cotton, and poly(ethylene terephthalate) (PET) and a PET film, and the results of single-friction-surface triboelectric nanogenerators with these materials offers a facile and universal guideline for designing triboelectic materials.
In this study, recycled waste fishing net (WFN) short fibers were proposed to be used as short fiber reinforcements. The pullout resistance of WFN short fibers embedded in cement mortar was ...investigated by conducting fiber pullout tests. Three types of WFN short fibers and two types of commercial polypropylene (CP) fibers were investigated. To quantitatively compare the pullout resistance of WFN short fibers and CP fibers, pullout parameters, including peak pullout load (peak bond strength), peak fiber stress, slip at peak load, and pullout energy (equivalent bond strength) of the pullout specimens, were analyzed. In addition, the analysis of fiber images, captured by using a stereoscopic digital microscope, before and after pullout tests, elucidated the different mechanisms of fiber pullout corresponding to the type of fibers. The bundled structures of the WFN fibers generated mechanical interaction between fiber and matrix during fiber pullout; consequently, they produced higher bond resistance and more damage on the surface of fibers after the pullout. Therefore, the bundled WFN fibers showed comparable pullout resistance with CP fibers.
A highly reliable micromechanical contact based on aligned carbon nanotube (CNT) arrays is demonstrated and characterized. The CNT arrays are synthesized directly on three‐terminal ...microelectromechanical systems, and they are adjusted and simultaneously preloaded during the synthetic process, making intimate micromechanical contacts. It is found that the CNT array‐to‐array contact improves upon conventional solid‐to‐solid micromechanical contact.
A polymer-based tactile sensor with flexibility and multi-directional sensing capability is presented. The proposed sensor consists of a polydimethylsiloxane (PDMS) bump, a polyimide (PI) substrate, ...Cr/Au electrode lines for electrical connection, NiCr piezoresistors, and an SU-8 support structure. The sensing mechanism is based on piezoresistive effect, in which the resistance of NiCr changes under mechanical load. The PMDS bump positioned at the center of the sensor transfers an applied force to the PI film, and the piezoresistors are differently deformed depending on the magnitude and direction of the force. A diaphragm structure formed by the SU-8 support with a trench allows the piezoresistor to be effectively deformed. Simulation and experimental results confirm that magnitude and direction can be obtained from an arbitrarily applied force by comparing the change in resistance of each sensing element. Based on its compatibility with conventional microfabrication, the proposed sensor may be a promising candidate for a low-cost tactile sensing solution for human‒machine interfaces.
The development of fabric‐based triboelectric energy harvesters is of great interest for converting human motion into electricity and is relevant for the development of wearable electronics. However, ...such harvesters exhibit significant degradation in performance under high humidity conditions. To solve this problem, a humidity‐resistant, fabric‐based triboelectric energy harvester by depositing self‐assembled monolayers (SAM) to increase the hydrophobicity of the fabric surface is demonstrated. The SAM coating is compatible with various fabrics and a noticeable improvement in triboelectric performance under high humidity conditions (relative humidity ≈85%) is observed, while the fabric maintains outstanding breathability. Moreover, the harvester exhibits no degradation in the output voltage over 5 × 104 cycles of loading/unloading, indicating excellent stability. The energy harvester is demonstrated as a wearable device by mounting it onto various parts of the human body and it is validated that the harvester successfully generates electrical power from human motion. Based on the humidity‐resistant triboelectric performance and the ease and cost‐effectiveness of the SAM coating, the harvester is expected to provide meaningful opportunities for the development of self‐powered smart clothes or wearable healthcare devices.
A humidity‐resistant, wearable triboelectric energy harvester based on hydrophobic self‐assembled monolayers (SAM)‐coated fabrics is presented. The SAM coating provides a noticeable improvement in triboelectric performance under humidity conditions while maintaining the breathability of fabric. Moreover, a wearable energy harvester that is capable of generating electrical power from various human motions is demonstrated.
•OPC replacement shows 31% strength gain at 28days compared to control sample.•Strength enhancement was explained by delayed dissolution & activation of the OPC.•Geopolymeric reaction is strongly ...influenced by OPC substitution.
Despite the considerable attention being paid to geopolymer concrete, its application has been limited due to its requirement of high temperature curing. In this study, we aim to increase the reactivity of fly ash at ambient condition by substituting OPC in high-alkaline medium. A series of experiments of compressive strength test, heat flow measurement, XRF, XRD, and SEM analysis is conducted to understand the mineralogical and microstructural impacts of the substituted OPC. The XRD experiments reveal that abundant Ca source in fly ash and OPC transforms to katoite and amorphous phases of C-A-S-H and C-S-H. The formation of zeolite precursors was also influenced by the OPC substitution. Furthermore, the delayed dissolution and activation of OPC in high-alkaline medium that observed by reaction heat measurement, play a positive role of filling existing voids which can efficiently enhance mechanical strength of complex system.
Interfacial bond properties of six different epoxy resins used to coat submerged concrete structures were investigated. Test variables included coating type, coating equipment, and underwater curing ...time. Coating thickness and pull-off bond strength were measured using commercially available test equipment. Coating thickness and bond strength varied greatly depending on the manufacturer. The standard (control) coating equipment positively influenced the bond strength compared to other equipment. The effect of curing time on the bond properties was not significant within the range of 24 to 72 h. Lastly, some important considerations for the underwater coating of actual marine and coastal concrete structures were discussed, and suggestions for future research are presented.
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