Huigang Xiao

Microstructure of cement mortar with nano-particles

The mechanical properties of nano-Fe2O3 and nano-SiO2 cement mortars were experimentally studied. The experimental results showed that the compressive and flexural strengths measured at the 7th day and 28th day of the cement mortars mixed with the nano-particles were higher than that of a plain cement mortar. Therefore, it is feasible to add nano-particles to improve the mechanical properties of concrete. The SEM study of the microstructures between the cement mortar mixed with the nano-particles and the plain cement mortar showed that the nano-Fe2O3 and nano-SiO2 filled up the pores and reduced CaOH2 compound among the hydrates. These mechanisms explained the supreme mechanical performance of the cement mortars with nano-particles.

Self-monitoring Properties of Concrete Columns with Embedded Cement-based Strain Sensors

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.

Effects of nano-SiO2 on the permeability-related properties of cement-based composites with different water/cement ratios

To find the suitable conditions under which nano-SiO2 can exhibit a significant impermeability enhancement effect and the mechanism underlying this effect, comparisons between the permeability-related properties of a nano-SiO2-filled cement paste and those of a reference cement paste composed of different water/cement (W/C) ratios were carried out in this research. Permeability-related properties of cement paste, such as the chloride-ion penetration coefficient (Dnssm), water permeability coefficient (Kp), and initial water sorptivity coefficient (Si), were tested. Furthermore, Power’s model, mercury intrusion porosimetry data, and the general effective media theory were also applied to analyse the evolution mechanism. The results indicate that the effect of nano-SiO2 on the enhancement of the impermeability becomes more remarkable at a lower W/C ratio. The decreasing rates of Dnssm, Kp, and Si increase as the W/C ratio decreases. Furthermore, it can be concluded that the effects of nano-SiO2 on promoting the hydration, refining the pore structure, narrowing the width of microcrack and thus enhancing the impermeability of cement paste become much clearer as the W/C ratio decreases.

Nanomaterials-Enabled Multifunctional Concrete and Structures

Nanomaterials-enabled multifunctional concrete that has self-sensing ability and high mechanical properties is attractive for guaranteeing the safety of infrastructure. Self-sensing ability of nanoconcrete which is based on its piezoresistivity is obtained by adding appropriate concentration of nano-carbon black into concrete. Effect of various loading states on pieroresistivity of nanoconcrete was studied experimentally, and a theoretical model was proposed to predict and modify the strain gauge factor of nanoconcrete under various loading or environmental conditions. Effect of moisture on resistance of nanoconcrete was studied and a water-proof method was proposed to eliminate the unfavorable effect of polarization on resistance measurement. Finally, a cement-based strain sensor was fabricated and used in monitoring the strain of concrete column. Other benefits from inclusion of nanomaterials in concrete include enhancement in mechanical properties, including strength, abrasion resistance and fatigue properties. Microstructures of nanoconcrete was studied with help of SEM pictures, which showed that the hydration product of nanoconcrete was more uniform and compact than that of normal concrete.

A scouring sensor by using the electrical properties of carbon nanotube-filled cement-based composite

This paper investigates a scouring sensor using electrical properties of carbon nanotubes(CNTs)-filled cement-based composite. First, for specimens filled with different amount of CNTs, the electrical behavior and the principle which it followed were studied. The effect of the different magnetic field intensity on the arrangement of CNTs in the base was presented. Furthermore, the environment effects (temperature and humidity) on sensors and its causes were revealed. Also, the design of the temperature and humidity self-compensation sensor based on separated electrode was proposed. Finally, by comparison of the sensitivity of the scouring electrode and the stability of the reference electrode, the optimal scheme of the electrode was determined.

A study on ductility of nano-particles reinforced cement-based composites

The ductility of high strength nano-TiO2 reinforced cement-based composites were experimentally studied and compared with that of plain cement-based composite and cement-based composite containing silica fume by stress-strain relationship. The results showed that the ductility of high strength cement-based composite containing nano-TiO2 were better than that of plain cement-based composite and cement-based composite containing silica fume, which demonstrated that it is an available and effective way to improve ductility of high strength cement-based composite by means of mixing nanophase materials into cement-based composite. The origin of nanoparticles improving ductility of high strengthen cement-based composite was also preliminary interpreted.

Piezoresistance property of cement-based composites filled with carbon black and the application of it for strain sensing

Cement-based composite filled with nanophase carbon black (CCN) was found the promising strain sensor material candidate. Experimental results showed that temperature had obviously influence on the initial resistivity of CCN, but nearly no effect on the strain-sensing property of CCN. Resistivity of CCN decreases linearly upon compressive strain, and the strain gauge factors measured under various temperatures were all about 55. Strain sensor was made with CCN and applied in concrete beam for strain monitoring, the results monitored by CCN sensor agreed well with that of strain gauge. The results of this paper suggested CCN sensor a practicable strain sensor.

Improving the microstructure of ITZ and reducing the permeability of concrete with various water/cement ratios using nano-silica

The interfacial transition zone (ITZ) between an aggregate and a cement matrix is known to be the weakest component of concrete; hence, its microstructure is the key factor determining its performance in terms of permeability. The objectives of this study are to strengthen the ITZ and reduce the permeability of concrete using nano-silica, and explore its improvement features under different water-to-cement ratios (W/Cs) between 0.3 and 0.5. An innovative testing and characterization methodology is adopted to quantitatively evaluate the properties of the ITZ. The results indicate that nano-silica can reduce both the width and formation of abrasion cracks in the ITZ. Further, the role of nano-silica is especially effective when the W/C of concrete is reduced. Small hydration products growing on the surface of the aggregate and cement matrix of nano-concrete with a reduced W/C can overlap each other and effectively fill the gap, resulting in enhanced densification of the ITZ by the nano-silica at reduced W/C ratios. Further, the enhancement rate of the anti-permeability of concrete also becomes significant. It can be concluded that nano-silica can effectively improve the performance of concretes, especially those with reduced W/C.

Self-sensing of nano-carbon black concrete

Nano-carbon black concrete (CBCC) that has self-sensing ability is attractive for guaranteeing the safety of infrastructure. The self-sensing ability of nanoconcrete is based on the piezoresistivity, which is obtained by adding an appropriate concentration of nano-carbon black into concrete. This chapter presents a comprehensive knowledge of the piezoresistive property of CBCC material, modeling of the piezoresistivity of CBCC, and the performance of a CBCC-based strain sensor embedded in a concrete beam. Specifically, Section 4.2 gives the fabrication and resistance-measuring method of CBCC, and the piezoresistivity of CBCC under monotonic and cycle loading, respectively. Section 4.3 describes the modeling of piezoresistivity of CBCC, which can help us to understand, optimize, and predict the strain-sensing property of CBCC. Section 4.4 is about the application of CBCC-based strain sensors in monitoring the strain state of concrete beam under flexural loading, in which CBCC-based strain sensors are embedded at different strain state zones.

Piezoresistivity of Nickel Powder Filled Cement-based Composite

This paper studied the piezoresistivity of cement-based composite filled with nickel powder. Cement-based composites filled various content of nickel powder were fabricated. During the hardening procedure of cement-based composite, various strength of magnetic fields were applied on the composites with a set of Helm-holtz coils, which can generate an adjustable uniform magnetic field through changing the electric current. The aligning level of nickel powder was characterized with the scanning electron microscopy (SEM) pictures, which indicated that the aligning level of nickel powder increased upon the magnetic field strength, and the alignment of nickel powder leaded to a remarkable change in the characteristics of conductive network. The electrical property of cement-based composite filled with randomly distributed nickel powder is isotropic. After aligning the nickel powder, it becomes anisotropic. Furthermore, the anisotropic level is not only dependent on the magnetic field strength (alignment level), but also related to the content of nickel powder. An interesting finding given in this paper is that the highest anisotropic level of electrical conductivity is reached at the threshold content of nickel powder, which is the critical content of nickel powder to form a connected conductive network. Piezoresistivity of cement-based composite is also dependent on both the content and alignment level of nickel powder. When the content of nickel powder was lower than the threshold, the strain gauge factor of the cement-based composite increased upon its alignment level. However, for a large content of nickel powder that exceeded the threshold, the alignment of the nickel powder reduced the strain gauge factor. doi: 10.12783/SHM2015/278