Effect of Polyoxymethylene Fiber on the Mechanical Properties and Abrasion Resistance of Ultra-High-Performance Concrete.

It is necessary to prepare marine UHPC with synthetic fibers instead of steel fibers, owing to the corrosion risk of steel fibers in marine environments. Currently, the performance of UHPC prepared with different types of fibers has not been comparatively investigated. This work prepared UHPC with steel fiber, polyoxymethylene (POM) fiber, polypropylene (PP) fiber, and polyvinyl alcohol (PVA) fiber. The effects of different fibers on the mechanical properties, impact, and abrasion resistance of UHPC were studied and compared. The results showed that increasing POM fiber can increase the mechanical strength, flexural toughness, impact, and abrasion resistance of UHPC. When its content reaches 2%, the adsorbed-in-fracture energy and abrasion strength of UHPC are 2670 J and 105 h/(kg/m2), respectively. At the same fiber content, POM fiber-reinforced UHPC shows better mechanical strength, toughness, and impact- and abrasion-resistance than the polypropylene (PP)- and polyvinyl alcohol (PVA)-fiber-reinforced UHPCs. Microstructure investigation found that PP fiber has the weakest binding with UHPC paste, which would directly pull out of the matrix under external tensile loading. This weak connection limits the strengthening and toughening effect on the UHPC. PVA fiber has an excellent interfacial connection with the UHPC paste. However, the low tensile strength of PVA fiber limits the strength and toughness of UHPC. POM fiber has a high tensile strength and can absorb tensile loading through debonding, fracture, and tearing. The fracture interface of POM fiber is large, indicating its significant role in strengthening and toughening the UHPC.

The Application of Heat-Shrinkable Fibers and Internal Curing Aggregates in the Field of Crack Resistance of High-Strength Marine Structural Mass Concrete: A Review and Prospects.

High-strength large-volume marine concrete is a critical material required for the construction of large-span sea-crossing bridges. However, the widespread issue of cracking in this concrete type significantly impacts the durability and load-bearing capacity of concrete structures. Dealing with these cracks not only delays construction schedules but also increases project costs. Addressing these pressing technical issues, this project proposes the use of newly developed high-modulus heat-shrinkable fibers (polyethylene terephthalate fiber, also known as PET fiber) from the textile industry. These fibers utilize the heat generated during the hydration of large-volume concrete to trigger its contraction, applying three-dimensional micro-prestressing stress to enhance its crack resistance, while simultaneously incorporating prewetted aggregates with high-performance micro-porous structures and utilizing their internal curing effect to reduce concrete shrinkage. This helps to minimize the loss of micro-prestressing stress caused by concrete shrinkage and creep. This synergistic approach aims to improve the crack resistance of high-strength large-volume marine concrete. By employing modern testing and simulation analysis techniques, this study aims to uncover the mechanism by which the heat-shrinkable fibers exert micro-prestressing stress on concrete and the water release mechanism of internal curing aggregates during the temperature rise and fall stages of large-volume concrete. It seeks to elucidate the cooperative regulation of the microstructure and performance enhancement mechanisms of high-strength large-volume marine concrete by the heat-shrinkable fibers and internal curing aggregates. This research will lead to the development of novel methods for the design and crack control of high-strength large-volume marine concrete, which will be validated through engineering demonstrations. The outcomes of this study will provide theoretical foundations and technical support for the preparation of the crack-resistant large-volume marine concrete used in large-span bridges.

The Application of Self-Healing Microcapsule Technology in the Field of Cement-Based Materials: A Review and Prospect.

This review provides an overview of microcapsule self-healing technology and its application in the field of cement-based materials, as well as future prospects. The presence of cracks and damage in cement-based structures during service has a significant impact on their lifespan and safety performance. Microcapsule self-healing technology shows promise in achieving self-healing by encapsulating healing agents within microcapsules, which are released upon damage to the cement-based material. The review starts by explaining the fundamental principles of microcapsule self-healing technology and explores various methods for preparing and characterizing microcapsules. It also investigates the influence of incorporating microcapsules on the initial properties of cement-based materials. Additionally, the self-healing mechanisms and effectiveness of microcapsules are summarized. Finally, the review discusses the future development directions for microcapsule self-healing technology, outlining potential areas for further research and advancement.

Improving Surface Wear Resistance of Polyimide by Inserting KH550 Grafted GO.

To improve the wear resistance of polyimide (PI), surface modification was developed. In this study, the tribological properties of graphene (GN), graphene oxide (GO), and KH550-grafted graphene oxide (K5-GO) modified PI were evaluated by molecular dynamics (MD) at the atomic level. The findings indicated that the addition of nanomaterials can significantly enhance the friction performance of PI. The friction coefficient of PI composites decreased from 0.253 to 0.232, 0.136, and 0.079 after coating GN, GO and K5-GO, respectively. Among them, the K5-GO/PI exhibited the best surface wear resistance. Importantly, the mechanism behind the modification of PI was thoroughly revealed by observing the wear state, analyzing the changes of interfacial interactions, interfacial temperature, and relative concentration.

Improving Thermal Conductivity and Tribological Performance of Polyimide by Filling Cu, CNT, and Graphene.

The thermal conductivity, mechanical, and tribological properties of polyimide (PI) composites filled by copper (Cu), carbon nanotube (CNT), graphene nanosheet (GNS), or combination were investigated by molecular dynamics simulation (MD). The simulated results suggested that Cu can improve thermal stability and thermal conductivity, but it reduces mechanical properties and tribological properties. CNT and GNS significantly improved the thermal and tribological properties at low content, but they decreased the properties at high content. In this study, the modification mechanism, friction, and wear mechanism of different fillers on polyimide were revealed by observing the frictional interface evolution process from the atomic scale, extracting the atomic relative concentration, the temperature and velocity distribution at the friction interface, and other microscopic information.

Chloride Ion Transport Properties in Lightweight Ultra-High-Performance Concrete with Different Lightweight Aggregate Particle Sizes.

In this paper, the microstructure and resistance to chloride ion penetration of ultra-high-performance concrete (UHPC) prepared from lightweight aggregate (LWA) were studied through simulation and experiment. The effects of LWA with different particle sizes on the chloride ion transport properties of lightweight ultra-high-performance concrete (L-UHPC) were discussed through simulation test results. The random delivery model of LWA in L-UHPC was established by MATLAB, and the model was introduced into COMSOL. Through the comparative analysis of experimental data and simulation results, the repeatability of the proposed model and the simulation accuracy were verified. The results show that when the LWA particle size changes from 0.15-4.75 mm to 0.15-1.18 mm, the width of interfacial transition zone (ITZ) and the overall porosity of L-UHPC decrease. This is because the large particle size LWA has more open pores with larger pore diameters and related interconnections, which are potential channels for chloride ion transport. Therefore, the chloride ion transport properties in L-UHPC are inhibited, which is manifested by the "tortuosity effect" of the LWA.

Effect of Shale Powder on the Performance of Lightweight Ultra-High-Performance Concrete.

In this study, lightweight ultra-high-performance concrete (L-UHPC) was prepared by using SP to replace part of the cement. The main study investigated the effect of the amount of SP on the spread diameter, apparent density and mechanical properties of L-UHPC. The mechanism of the effect of SP on the hydration product of L-UHPC was studied and the pore structure of L-UHPC was also analyzed. The results show that the incorporation of SP can effectively improve the spread diameter and reduce the apparent density of L-UHPC to a certain extent. With the increase in SP content, the compressive strength of L-UHPC at 7 days of age did not change significantly. However, the compressive strengths at 3 and 28 days of age changed significantly. When the amount of SP was less than 12%, there was no significant decrease flexural and compressive strength at 28 days of age. However, the flexural and compressive strength of L-UHPC gradually decreased when the amount of SP was greater than 12%. The microstructure shows that SP can reduce the content of portlandite. This is mainly due to the fact that the addition of SP improved the stacking compactness of L-UHPC and promoted secondary hydration reactions. The content of portlandite and the hydration degree of cement were reduced. At the same time, the exothermic hydration of L-UHPC with SP was less, the hydration process was slow, and the exothermic rate of initial hydration was low. An appropriate amount of SP can effectively improve the pore structure of L-UHPC and significantly reduce the pore volume of harmful pores (50~200 nm). SP can make the L-UHPC structure more compact and has a positive effect on the development of L-UHPC strength.

Influence of Structural Characterization of C3S-C3A Paste under Sulfate Attack.

The durability of C3S-C3A paste with varied C3A content (0%, 5%, 10%, and 20%) against sulfate attack at various attack ages (3 d, 7 d, 28 d, and 180 d) was investigated in this study through the examinations of corrosion product composition, Ca/Si and Al/Si of calcium-(aluminum)-silicate-hydrate (C-(A)-S-H) gel, formation and evolution of microstructure, migration and transformation of Al containing phase products, and pore structure. The results indicated that sulfate attack can promote the hydration reaction in C3S-C3A paste, thus accelerating the production of C-(A)-S-H gel in the paste. With the increase of C3A content, the acceleration effect becomes more significant. In addition, sulfate attack led to the dealumination and decalcification of C-(A)-S-H gel, resulting in the reduction of the gelling power of C-(A)-S-H gel. The degree of dealumination and decalcification of C-(A)-S-H gel increases with the increase of C3A content. At the same time, free Al and Ca promote the formation of expansive products such as ettringite and gypsum. Finally, under the action of sulfate, the pore characterization of C3S-C3A paste deteriorated, showing a decrease in specific surface area, cumulative pore volume and average pore diameter.

Influence of Submicron Fibrillated Cellulose Fibers from Cotton on Hydration and Microstructure of Portland Cement Paste.

This paper reports the influence of submicron hydrophilic fibers on the hydration and microstructure of Portland cement paste. Submicron fibrillated cellulose (SMC) fibers was prepared by the acid hydrolysis of cotton fibers in H2SO4 solution (55% v/v) for 1.5 h at a temperature of 50 °C. The SMC fibers were added into cement with a dosage of 0.03 wt.%, and the effect of SMC on the hydration and microstructure of cement paste was investigated by calorimeter analysis, XRD, FT-IR, DSC-TG, and SEM. Microcrystalline cellulose (MCC) fibers were used as the contrast admixture with the same dosage in this study. The results show that the addition of SMC fibers can accelerate the cement hydration rate during the first 20 h of the hydration process and improve the hydration process of cement paste in later stages. These results are because the scale of SMC fibers more closely matches the size of the C-S-H gel compared to MCC fibers, given that the primary role of the SMC is to provide potential heterogeneous nucleation sites for the hydration products, which is conducive to an accelerated and continuous hydration reaction. Furthermore, the induction and bridging effects of the SMC fibers make the cement paste microstructure more homogeneous and compact.

An Optical Fiber Sensor Based on Fluorescence Lifetime for the Determination of Sulfate Ions.

A new optical fiber sensor based on the fluorescence lifetime was prepared for specific detection of sulfate ion concentration, where 1,1'-(anthracene-9,10-diylbis(methylene))bis(3-(dodecylcarbamoyl)pyridin-1-ium) acted as the sulfate fluorescent probe. The probe was immobilized in a porous cellulose acetate membrane to form the sensitive membrane by the immersion precipitation method, and polyethylene glycol 400 acted as a porogen. The sensing principle was proven, as a sulfate ion could form a complex with the probe through a hydrogen bond, which led to structural changes and fluorescence for the probe. The signals of the fluorescence lifetime data were collected by the lock-in amplifier and converted into the phase delay to realize the detection of sulfate ions. Based on the phase-modulated fluorometry, the relationship between the phase delay of the probe and the sulfate ion concentration was described in the range from 2 to 10 mM. The specificity and response time of this optical fiber sensor were also researched.

Model compounds-based study on adsorption and dispersion properties of lignin-based superplasticizer.

The chemical modifications of lignin-based superplasticizers have attracted extensive attentions during recent years. The comprehending of the structure-activity relationship of lignin-based superplasticizer is important to promote the modification and application research of lignin resources. However, lignin features complex and variable molecular structure, which is not conducive to study on structure-activity relationship of lignin-based superplasticizer as well as development and application of new lignin-based superplasticizer. However, the related research work can be simplified by selecting small molecular compound with appropriate molecular structure as the lignin model compound. This article intends to study the structure-activity relationship of lignin-based superplasticizer by using dihydroeugenol as the lignin model compound. Through the substitution of lignin by dihydroeugenol during the synthesis process, a model compound lignin-based superplasticizer (DAFS) was synthesized. The adsorption and dispersion properties of this superplasticizer and reference sample (LAFS) were investigated by fluidity test, Zeta-potential measurement, Total organic carbon analysis and others. The results suggest that the adsorption behavior of both DAFS and LAFS conformed to the Langmuir isotherms and Pseudo-second order kinetic. In cement paste, added with 1 g/L of LAFS and DAFS, Zeta potential were reduced from +3.5 to -15.2 mV and -18.7 mV, respectively. The substitution of lignin by dihydroeugenol has no significantly influence on the dispersive property, but differences on rheological properties which need to be optimized in the future. All the tests confirmed that dihydroeugenol is suitable to replace lignin on exploring the structure-activity relationship of lignin-based superplasticizer. This research work provides new insight on model study of lignin-based superplasticizer.

Analysis of wireless power transmission system with negative impedance converter.

In this study, we analyze a resonant coupled wireless power transmission system with a negative impedance converter (NIC). The expressions for the output power of this system are obtained. The constraints of system parameter selection are determined according to the practical limitations of the NIC. The energy efficiency ratio (EER) is introduced to represent the relationship between the increase in system output power and the additional loss caused by the introduction of the NIC. The influence of the NIC on the EER was tested by changing the negative resistance. The experimental results show that the NIC reduces the loop impedance, increases the loop current, and improves the output power of the system. In addition, setting the appropriate parameters of the NIC can effectively increase the EER of resonant coupled radio power transmission by more than 4%.

Anisotropic Properties of Polylactic acid⁻carbon Fiber Composites Prepared by Droplet spray Additive Manufacturing.

Anisotropic materials are important functional materials in many fields. The use of these materials is currently being expanded through the rapid development of additive manufacturing. However, there is still no universal method for fabricating two-dimensional anisotropic polymer composites. Here, polylactic acid⁻carbon fiber composites were prepared using the droplet spray method, and their mechanical and friction properties were studied. The tensile strength in the X⁻Y plane perpendicular to the direction of the droplet spray was significantly higher than that in the direction of droplet ejection. Similar trends were observed for the elongation at breaking and the impact strength. The friction coefficient was smallest in the X⁻Y plane. Scanning electron microscopy showed that carbon fibers were oriented in the X⁻Y plane, which enhanced the mechanical and friction properties in this plane.