Jian Lin Luo

Hybrid Effect of Carbon Fiber on Piezoresistivity of Carbon Nanotube Cement-Based Composite

Cement-based nanocomposite filled with only 0.1 wt.% multi-wall carbon nanotube (MWNT) (MNFRC), or hybrid with 0.1 wt.% MWNT and 0.5 wt.% microsized short carbon fiber (SCF) (SF/MNFRC), were prepared employing surfactant ultrasonic dispersion and high-speed mixing process. The electrical resistivities (ρ), compressive stresses (σ), and longitudinal strains (εl) of these cured nanocomposites under cyclic uploading/unloading were simultaneously collected, to characterize their stress/strain-sensitive properties. There exists good piezoresisitivity and high strain sensitivity for MNFRC. The fractional change in ρ (Δρ) regularly descends or ascends following the σ, or the εl of MNFRC (the Δρ/εl sensitivity near 68). Hybrid of SCF is found to be more effective to improve the self-sensing repeatability and variation stability of the SF/MNFRC rather than the self-sensing sensitivity (the Δρ/εl sensitivity only about 64).

Damping Performances of Carbon Nanotube Reinforced Cement Composite

Multi-walled carbon nanotubes (MWCNTs) were dispersed in an aqueous cement matrix using surfactant decoration, ultrasonic treatment, and, subsequently, intensive mixing to fabricate MWCNT/cement composites with six different MWCNT concentrations. Damping performances of these cured nanocomposites were studied with forced vibration testing, half-power bandwidth, and Morlet wavelet transform identification methods. The micro-crack bridging and interfacial “stick-slip” capacity of nanotubes among cement matrix contributes to balanced enhancement on structural damping capacity and flexural strength of the nanocomposite. With the addition of 2.0% nanotubes, the fundamental frequency, damping ratio, and flexural strength of the nanocomposite increases around 13 Hz, 60, and 32%, as compared to the reference, respectively.

Effect of Multi-Wall Carbon Nanotube on Fracture Mechanical Property of Cement-Based Composite

Cementitious composites reinforced with multi-wall carbon nanotube (MWNT) (MWFRC) were prepared with surfactant dispersion, ultrasonication, and subsequently high-speed mixing process. Fracture mechanical performance of the cured MWFRC was characterized according to three-point bending method (ASTM 399). It is found that the addition of nanotubes significantly improve the flexural strength, the stress-intensity factor of the nanocomosites with dispersed MWNT fiber, the maximal enhancement amplitude is near to 45%, 80% with respect to the baseline, respectively. The superior fiber bridging capability of the dispersed MWNTs upon the micro-cracks contributes to the reinforcement to cement matrix.

Effect of Compressive Strain on Electrical Resistivity of Carbon Nanotube Cement-Based Composites

Multi-walled carbon nanotube (MWCNT) fiber reinforced cement-based composites (MWFRC) with 0.1 wt.% and 0.5 wt.% weight concentration of MWCNT (wcM)were prepared, associated with the reference. The electrical resistances and compressive strains of these cured nanocomposites under cyclic uploading/unloading were real-time collected, to explore their stress/strain-sensitive properties. Results reveal as follows, there is no self-sensing trait for the reference, but exists good piezoresisitivity and high strain sensitivity (above 110) for MWFRC; the fractional change in resistivity (Δρ) regularly descends or ascends following the compressive stress, or the longitudinal strain of MWFRC; the resistance caused by pore electrolyte polarization has obvious impact on the time-stability of the Δρ trendline of MWFRC with 0.1 wt.% wcM, similar to the reference, but negligible effect on that of MWFRC with 0.5 wt.% wcM.

Orthogonal experimentation for optimization of TiO2 nanoparticles hydrothermal synthesis and photocatalytic property of a TiO2/concrete composite

An orthogonal experimental design was applied to optimize the hydrothermal preparation parameters of TiO2 nanoparticles by the analysis of means (ANOM) and variances (ANOVA). The ANOM & ANOVA results on crystalline and size show that the optimal process of synthesized TiO2 nanoparticles is 5.0% TBT, an alkalescent environment (pH = 9), 160 °C reaction temperature, and 3 h reaction time. The main factors affecting the photocatalytic properties of TiO2 nanoparticles were explored by measuring the UV light absorbance index, and the results show that their photocatalytic performance are excellent when methyl orange (MeO) concentration is 2.5 mg L−1, the pH value is 6, and the Ag-doped amount is 5.0%. Then optimal TiO2 nanoparticles aqueous suspensions with varied concentration (cTiO2) were sprayed on permeable concrete to fabricate TiO2/concrete composites, and their photocatalytic activity was evaluated by measuring the degradation rate of soaked MeO along the UV radiation time. It is concluded that when cTiO2 is 2.0 g L−1 with above fixed conditions, the produced TiO2/concrete composite has an optimal capacity (35.7%) in the photo-degradation of azo pollutants.

Self-Sensing Property of Cementitious Nanocomposites Hybrid with Nanophase Carbon Nanotube and Carbon Black

Cementitious composite filled with only 0.1 wt% multi-walled carbon nanotube (MWCNT) (MNTCC), or hybrid with 0.1 wt% MWCNT and 0.5 wt% nanophase carbon black (NCB) (NB/MNTCC), were prepared employing surfactant ultrasonic dispersion and subsequently high-speed mixing process. The electrical resistivities (ρ), compressive stresses (σ), and longitudinal strains (εl) of these cured nanocomposites under cyclic loading (10 times) were simultaneously collected, to investigate their piezoresistivty properties. Results revealed that, hybrid of NCB is very effective for enhancement on the stress/strain sensitivity of NB/MNTCC (the strain sensitivity up to 107, much higher than that of MNTCC 67), but there is almost no improvement on the self-sensing repeatability and variation stability of the corresponding nanocomposite.

Cement-Based Composite with Carbon Nanotubes Reinforcement Tailored for Structural Damping

Cement-based composites filled with some multi-walled carbon nanotubes (MWNTs) (MWNT/CC) were fabricated using surfactant enwrapping, ultrasonic treatment, and subsequently intensive shear mixing. The damping capacities of the cured nanocomposites were characterized with forced vibration testing and half-power bandwidth identification method. Results show that, the MWNTs can greatly enhance the structural damping capacity of the MWNT/CC beam with balanced strength reinforcement. There exists 44.5%, 10% increase in the damping ratio, and fundamental frequency of the MWNT/CC with 1.0 wt% MWNTs addition, along with strength reinforcement, as compared to the reference, respectively.

Influence of Preparation Process on the Performance of Strain Hardening Cementitious Composite

The modification of matrix is an important method to improve the mechanical properties of strain hardening cementitious composite (SHCC). The influence of the properties of the matrix water binder ratio (W/B) and fresh state rheology on SHCC tensile behaviors are useful for the SHCC design. The W/B influences only on tensile strength, but not the stain capacity, if the fresh state workability remains uniform. On the other hand, the workability has a significant influence on SHCC strain capacity through its influence on the fiber distribution. Consequently, it is important to cast SHCC carefully and make sure the even fiber distribution to insure the bridging function and mechanical properties of SHCC.

Improvement on Mechanical and Piezoresistivity Properties of Cementitious Binder by Using Surface Oxidized Multi-Wall Carbon Nanotubes

Two types of the cementitious binders (MWNT/CB, AMNT/CB) filled with 0.5 wt.% multi-wall carbon nanotube (MWNT), and acid-treatment MWNT (AMNT) were prepared. The surfaces of MWNT and AMNT were firstly characterized with TEM micrograph and FT-IR spectrum before and after acid oxidation. The electrical resistivities (ρ) and the longitudinal strains (εl) of two cured nanocomposites under cyclic compressive stress (σ) are real-time collected, in order to investigate their piezoresistivity properties, associated with mechanical behaviors. On one hand, acid treatment can enhance interface bonding between AMNT and cementitious binder decorated with some hydrophilic groups, resulting in some mechanical improvements; on the other hand, it causes better distribution and more network pathway, AMNT/CB has resultantly balanced piezoresistivity property with regular and consistent variation of ρfollowing the σ, or the εl, and fixed stress/strain sensitivity (around 62), compared to that of MWNT/CB.

Piezoresistive Effect of Multi-Wall Carbon Nanotube Reinforced Epoxy Resin Coating

Some conductive MWNT with different loading was filled in epoxy resin through the dispersion technique of surfactant-decoration, high-intensive shear mixing, and bath sonication process. This kind of conductive functional resin coating was then simply brushed on a FRP sheet surface. The electrical conductivity of the cured nanocomposite coating was acquired by four-electrode method to explore the percolation threshold and piezoresistive effect. The change in its longitudinal strain of the coating and FRP sheet was simultaneously sampled under three-point bending. Results reveal that, at the onset percolation threshold (2.0%), the nanocomposite possesses superior piezoresistive effect with high strain-sensitivity (up to 27), which favors to health monitoring to FRP structure used as a novel self-sensing coating.