The poorly crystalline calcium silicate hydrate (C‐S‐H) is the primary binding phase in portland cement concrete. In this paper, the influence of adding anatase phase nano‐TiO2, nano‐SiO2, graphene ...oxide (GO), and multiwalled carbon nanotubes (CNT) on the crystallization and morphology of C‐S‐H are systematically investigated through tests. C‐S‐H gels were prepared using the double decomposition method, and the nanomaterial additions of nano‐TiO2, nano‐SiO2, GO, and CNT were 2 wt%, 2 wt%, 0.5 wt%, and 0.5 wt%, respectively. X‐ray diffraction (XRD) results show that a more crystalline nanostructure of C‐S‐H is induced by the addition of nano‐TiO2 or GO. This phenomenon is further confirmed by the transmission electron microscopy (TEM) observations. The TEM observations demonstrate that C‐S‐H would grow on the crystal face of TiO2 to form nanocrystalline regions with a lattice fringe spacing of 3.0 Å. When incorporated with GO, it will form a square lattice structure with a lattice constant of 3.1 Å on the surface of GO and later change to the lattice fringe structure with a spacing of 3.1 Å on the region bit away the GO surface. However, when adding nano‐SiO2 or CNT, these nanocrystalline regions are not observed. Further characterization through scanning electron microscopy (SEM) and atomic force microscopy (AFM) has been performed to investigate the effect of nanomaterials on C‐S‐H morphology. Different nanomaterials take a different morphology of C‐S‐H: sheet‐shape structures for pure C‐S‐H, rod‐shape with for C‐S‐H with nano‐TiO2, and granular agglomeration for C‐S‐H with nano‐SiO2. C‐S‐H with GO or CNT forms a structure of C‐S‐H growing on the templates.
In this study, the enhancement mechanism of steel fiber reinforced cement-based composite was investigated by quantitative analysis of the fiber-matrix interfacial transition zone (ITZ) and the ...corresponding fiber pull-out behavior. Silica fume was selected as a typical mineral admixture with modification effects. The fiber-matrix ITZ microstructure was innovatively characterized by backscattered-electron image analysis, EDS map scanning mode combined with image analysis, and micro-hardness test. Pull-out tests were performed to determine the bond strength and pull-out energy, and the anchorage force and normalized slip-hardening shear stress during fiber pull-out were calculated. The macro mechanical performances were also analyzed and discussed. The results showed that although the improvement effect of silica fume was less significant in the ITZ than in the bulk paste, the gaps, defects, and aggregated calcium hydroxide around the fiber were improved effectively. The increased calcium silicate hydrate and contact area strengthened the bonding established between fiber and matrix, and the denser microstructure and harder matrix resulted in the enhanced anchorage force and slip-hardening effect. The flexural performance was improved by strengthening interfacial bond properties by silica fume, whereas silica fume increased the compressive strength through improving matrix microstructure.
A novel self-deicing road system with utilization of solar energy was proposed in this paper, this system is consisted of a carbon nano-fiber polymer (CNFP) thermal source, an AlN-ceramic insulated ...encapsulation layer, a multiwall carbon nanotube (MWCNT)/cement-based thermal conduction layer and a thermally insulated substrate. The electric and thermo-electric properties of a CNFP, which is composed of individual carbon nano-fibers (10–200nm), were tested. The property of high thermo-electric efficiency was verified, and the resistivity of the CNFP exhibited piecewise linear temperature-dependent characteristics within a certain temperature range (0–280°C). The MWCNT/cement-based composite, which was filled with 3% by weight MWCNT, was proposed as the thermal conduction layer because its thermal conduction properties are superior to those of cement with other fillers and to those of common cement-based composites. To ensure the efficient operation of the CNFP, an AlN-ceramic wafer (0.5mm) was employed as the electro-insulated layer because of its favorable insulating and thermo-conductive properties. The constructed system was applied in deicing and field snow-melting studies, in which the effects of ambient temperature, heat flux density and ice thickness on the deicing and snow-melting performance of the self-deicing system were investigated. The efficiency, repeatability, cost and feasibility of the self-deicing road system in both deicing and snow-melting applications were analyzed. Indices for evaluating the deicing or snow-melting performance of the self-deicing road system were proposed and the optimal values for each parameter are presented.
► A CNFP-based deicing system utilizing solar energy was developed. ► The remarkable electro-thermal propertied were investigated. ► The Cement-based composite with high thermal conductivity was developed. ► Deicing investigations of CNFP-based deicing system were implemented in freezer. ► CNFP-based deicing system was applied to the field test of snow-melting.
The advantage of concrete containing nano-TiO2 in resisting the coupled effects of chloride diffusion and scouring with respect to pure concrete was studied in this paper. Because of the movement in ...exposed concrete surface induced by scouring and the deterioration in concrete microstructure caused by chloride salt accumulation, an increasing mutual accelerative effect between the chloride diffusion and the scouring abrasion was experimental observed, which agreed with the theoretical simulation results. Benefited from the improvement in microstructure and porosity compared with the pure concrete, concrete containing 1% nano-TiO2 in the weight of cement showed a better impermeability as well as the abradability. Correspondingly, a better performance in resisting the coupled effects of chloride diffusion and scouring was founded for the concrete containing nano-TiO2 compared to the pure concrete, and this advantage increased upon the time.
To study the influence of different water–binder ratios on the corrosion, permeability, and freezing properties of concrete, we produced different strengths of concrete with respective water–binder ...ratios of 0.32, 0.38, 0.50, and 0.66. The corrosion resistance of the concrete was studied via three corrosion methods: full immersion, half immersion, and dry and wet cycles. The impermeability and frost resistance of concrete with different water–binder ratios were tested and analyzed. The test results show that the corrosion modes in order from strong to weak were dry and wet cycles, half soaking, and full soaking. The relative dynamic elasticity modulus and freeze–thaw index were used to evaluate the frost resistance of concrete based on the analysis of three indices of frost resistance. To study the internal mechanism of corrosion of concrete with different water–binder ratios, microscopic pore structure testing of the concrete was conducted using a Micromeritics AutoPore IV 9500 Series instrument. The porosimeter studies show that the smaller the water–binder ratio, the more small pores and the denser the concrete. The smaller the water–binder ratio, the higher the strength and the better the corrosion, permeability, and frost resistance.
Addition of fibers can give brittle material extrinsic toughness, mainly because of the bridging effects. However, such behavior is highly dependent on the interfacial interaction between fiber and ...brittle matrix. In order to optimize both the strength and ductility of cement, which is the most extensively used brittle material on this planet, here we propose a new strategy to control the interfacial property in the fiber-cement matrix. Silica-coated polyvinylalcohol fibers were successfully synthesized by a sol-gel method with controlled silica thickness, and then incorporated into cement paste. The interaction between fibers and cement matrix was significantly enhanced due to the greatly increased hydrophilicity and roughness of silica-coated fibers, as well as the pozzolanic reactivity of silica nanoparticles. Therefore, the interfacial region between fiber and cement becomes much more compact, promoting the fiber-cement interaction both physically and chemically. As such, the crack propagation would be severely constrained, resulting in the strength and ductility of cement significantly increased. We showed that the ultimate flexural strength and ultimate deflection of the cement composites reinforced by silica-coated polyvinylalcohol fibers increase by 187% and 980% with respect to pristine cement, and increase by 28% and 74% compared to cement reinforced by polyvinylalcohol fibers without silica, at the fiber content of 1 wt.%. This study illustrates the potential and effectiveness of interfacial design to overcome the mechanical dilemma of strength and ductility increase simultaneously, and open a new dimension to further improve the mechanical properties of cement.
Cement-based composite filled with 120
nm carbon black (CBCC) in the amount of 15% by weight of cement was a promising strain sensor material candidate, of which the resistance was sensitive to ...strain. This paper showed that the initial resistance of CBCC not only increased with water content, but also increased with the measurement time. These two phenomena were mainly attributed to a polarization effect which strengthened with water content. A waterproof measurement, i.e. a specimen encapsulated by epoxy resin, was developed to insulate the composite from ambient moisture. The effects of full water absorbing capacity of epoxy, creep behavior of CBCC and environmental temperature on the waterproof efficiency were studied. The results indicated that the effects of creep strain and temperature on resistance could be compensated and an epoxy with full water absorbing capacity less than 1.83% could meet the waterproof requirement of CBCC that guaranteed the accuracy of the resistance measurement.
A novel road deicing system consisting of a carbon nano-fiber polymer (CNFP) thermal source, an AlN ceramic insulated encapsulation layer, a multi-wall carbon nanotube (MWCNT)/cement-based thermal ...conductive layer and a thermal insulated substrate was developed in a previous experimental study. Based on the basic transient heat conduction theory, a mathematical model of composite-media thermal conduction is proposed in this study. Utilizing the orthogonal expansion technique, the non-homogeneous problem is split into the superposition of two steady-state non-homogeneous problems and a homogeneous transient problem; the transient analytic solutions are found in the stage without a phase change. Considering the quasi-steady hypothesis, the other parts of the solutions are determined for the phase change stage. The parameter analyses of the analytic solutions obtained in terms of the time-dependent temperature field reveal the same parameter-dependent influence and curve tendency in the deicing process as in the previous experimental study. To verify the credibility and reliability of the analytic solutions, the results are experimentally confirmed; both the theoretical and experimental approaches present similar trends except for a few slight, acceptable differences. These analytic solutions will be applied for prediction, control and guidance in further deicing studies.
•A theoretical model for CNFP-based self-deicing road system was developed.•A mathematical model of composite-media thermal conduction is proposed.•The perfect transient analytic solutions of non-homogeneous problem were found.•The parameter analysis verified well coincident with experimental study.•Analytic solutions will be applied for prediction and guidance in further studies.
•The slant shear test and splitting tensile test were adopted in this study.•The method of BSE-EDX was used to study the interfacial microstructure.•UHPC is conducive to the full use of the ...mechanical properties of the substrate.•The interface transition zone between UHPC and substrate is dense.
This study aims to investigate the effects of repair materials such as ultra high-performance concrete (UHPC) and normal concrete (NC) on the bond performance and microstructure between a concrete substrate and the repair materials. Specifically, C25, C35, and C45 concretes were used as the substrate materials, and their surfaces were treated with high-pressure water. C45 and UHPC were used as the repair materials. Bond properties were evaluated through slant shear tests with various slant angles and splitting tensile strength tests. Cohesion strength and internal friction were obtained via the slant shear test at three angles using the Mohr–Coulomb approach to reflect the differences between different repair materials. In addition, combining the splitting tensile strength and slant shear tests at three angles, bond failure envelopes were obtained using second-order polynomial and bi-linear models, which can reflect the bond behaviour of repair materials more effectively. The results of the study indicate that UHPC combined with concrete substrates exhibit good interfacial bond performances compared with NC repair materials. Compared with NC, the interface transition zone between UHPC and a substrate is denser, stronger, and more uniform, which results in good bond performance. Using second-order polynomial and bi-linear models, the UHPC repair material are more beneficial to the full utilisation of the mechanical properties of the substrate compared with the NC repair materials. Therefore, it is envisaged that the use of UHPC combined with the high-pressure water treatment of a substrate surface will provide an effective repair.
Cement-based strain sensors (CBCC sensor) were fabricated by taking the advantage of piezoresistivity of CB-filled CBCC. CBCC sensors were centrally embedded into concrete columns (made with C40 and ...C80 concretes, respectively) to monitor the strain of the columns under cyclic load and monotonic load by measuring the resistance of CBCC sensors. The comparison between the monitored results of CBCC sensors and that of traditional displacement transducers indicates that CBCC sensors have good strain-sensing abilities. Meanwhile, CBCC sensors exhibit different failure modes that break later than C40 concrete columns, but a little earlier than C80 concrete columns. Therefore, the strength-matching principle between embedded CBCC sensors and concrete columns is proposed in this article to guarantee the sensing capacity of CBCC sensors in various concrete structures. The analytical results agree well with the experimental phenomena.
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