Carbon Fiber Reinforced Concrete Research Articles

A Nondestructive Testing Method for Crack in Carbon Fiber Reinforced Concrete with Infrared Thermography

Based on the functional characteristics of carbon fiber reinforced concrete (CFRC), an improved infrared nondestructive testing method, to detect crack in CFRC by using infrared thermography, is presented in this paper. The principle is that when a CFRC specimen is applied a low voltage, crack existing in the specimen will result in non-homogeneous surface temperature distribution due to the electro-thermal effect of the material. Monitoring the temperature difference on the surface, the crack under the observed surface can be inspected by using infrared thermography. In theory, the mechanism causing the temperature difference comes down to an unsteady heat transfer problem with internal energy sources. In the case of the thermo-physical property of CFRC as given, the sensitivity of this method to the depth of the crack is analyzed by numerical computation.

Prediction of Bond Failure and Deflection of Carbon Fiber-reinforced Plastic Reinforced Concrete Beams

Prediction of Bond Failure and Deflection of Carbon Fiber-reinforced Plastic Reinforced Concrete Beams

Influence of carbon fiber contents on the temperature sensibility of CFRC road material

The relationship between the electrical resistivity of carbon fiber reinforced concrete (CFRC) containing different carbon fiber contents and temperature was studied. it is found that carbon fiber contents influence greatly on the temperature sensibility of CFRC road material. Only with a certain amount of carbon fiber can CFRC show a sensitive and stable temperature sensibility.

A study of piezoelectric properties of carbon fiber reinforced concrete and plain cement paste during dynamic loading

Carbon fiber reinforced concrete (CFRC) is an intrinsically smart material, which can be used to realize the self-monitoring of concrete structures based on its piezoresistance effect and the Seebeck effect. An experimental study was made to examine the piezoelectric properties of CFRC and plain cement paste. The results show that both CFRC and plain cement paste exhibit piezoelectric behavior, which can be explained in terms of a solid–liquid interface double-layer model. Furthermore, they can sense a large range of loading rates with high sensitivity. The materials are good sensors for monitoring the dynamic loading. Therefore, a new method to make smart concrete structures can be developed.

A study on thermal self-diagnostic and self-adaptive smart concrete structures

Smart structures are made by embedding sensors, actuators, and controllers into the structure during manufacture. Carbon fiber reinforced concrete (CFRC) can be used as both thermal sensor and thermal actuator because of the Seebeck effect and electrothermal effect, which have been reported. In this paper, two kinds of thermal smart concrete structure are designed using CFRC. First, the smart concrete beam embedded with four CFRC sensors is studied. Experimental results show that the smart concrete beam with CFRC sensors can monitor the process of the heat transfer and temperatures inside concrete. Then, embedding a CFRC sensor into a CFRC plate and connecting it to a controller result in a smart concrete system. Results show that it operates in situ, in-line temperature measurement and control with excellent stability.

Damage in carbon fiber-reinforced concrete, monitored by electrical resistance measurement

Damage of carbon fiber-reinforced concrete was revealed by an increase in the DC electrical resistance in the stress direction during dynamic compression. Minor damage that did not involve a change in modulus resulted in a partially reversible increase in resistance during loading at a stress above that in prior loading. Major damage that involved a decrease in modulus resulted in resistance increase occurring in every loading cycle irrespective of prior loading and in an irreversible increase in the baseline resistance.

A study on thermal self-monitoring of carbon fiber reinforced concrete

Carbon fiber reinforced concrete (CFRC) is an intrinsically smart material that can sense not only compressive or tensile stress, but also temperature. The thermal self-monitoring ability is associated with the Seebeck effect. An experimental study was made to examine the relationship between the temperature differential (ΔT) and thermoelectric force (TEF)—its sensitivity and repeatability, its response time and the influence of ambient temperature (T a) on TEF. The results show that TEF is proportional to ΔT over a wide range of temperature, and the thermal self-monitoring CFRC possesses high sensitivity and good repeatability. The T a has no influence on TEF. Although the response time of CFRC is not fast enough because of its low heat conductivity, it can be used as a thermal sensor embedded in massive concrete structures, such as water dams and bridges, where the temperature changes slowly.

Carbon fiber-reinforced concrete for traffic monitoring and weighing in motion

The use of carbon fiber (5 mm long, 0.5% or 1.0% by weight of cement) reinforced concrete for traffic monitoring and weighing in motion was demonstrated in the laboratory for stresses up to 1 MPa and speeds up to 55 mph. The DC electrical resistance decreased with increasing stress and was independent of speed. Resistance was measured with the four-probe method, using continuous carbon fibers together with silver paint as electrical contacts. The resistance change was reversible upon unloading.

Thermoelectric percolation phenomena in carbon fiber-reinforced concrete

The measurements of thermoelectric power (TEP) and conductivity on carbon fiber-reinforced concrete (CFRC) containing short polyacrylonitrile-based carbon fibers (0.2–2.0 wt.%) were conducted. Percolation phenomena in CFRC associated with TEP were observed. TEP in CFRC increases, with the content of short carbon fiber increasing from 0.2 to 1.0 wt.%. As the content of carbon fiber reaches 1.2 wt.%, TEP decreases abruptly. In the end, TEP is almost maintained marginally with increasing content of carbon fiber from 1.4 to 2.0 wt.%. Therefore, the threshold is 1.2 wt.%, which is the same as the percolation content associated with conductivity. The results provide an important guide for the manufacture of smart concrete that has the ability for thermal self-diagnosis.

Study on the Hole Conduction Phenomenon in Carbon Fiber-Reinforced Concrete

The thermoelectric force (TEF) measurements on carbon fiber-reinforced concrete (CFRC) containing short PAN-based carbon fibers (0.2 ∼ 1.2 wt.%) and plain concrete are conducted. TEF is observed in CFRC specimens but not in plain concrete specimens, and the cold end is the positive electrode of TEF while the warm end is the negative electrode. This phenomenon stems from the motion of positive hole in carbon fiber. Therefore, besides ion conduction and electronic conduction, hole conduction exists in CFRC, and hole conduction is the most important of the three. As a result, the conductivity of CFRC(σ) is made up of ionic conductivity (σ i), hole conductivity (σ h), and electronic conductivity (σ e); that is, σ = σ i + σ e + σ h. A new conduction model of CFRC is proposed at the end of the paper.

粗骨材混入炭素繊維補強コンクリートの調合と力学的特性に関する実験的研究

Applications of carbon fiber reinforced concrete (CFRC) to various building materials have been progressed because of its excellent mechanical characteristics. The conventional CFRC made of mortar with no coarse aggregate has some defects such as large drying shrinkage and low modulus of elasticity, which will be reduced by substituting concrete-mix including coarse aggregate for the mortar. In this study, in order to develop the CFRC using concrete-mix, experimental investigations were conducted concerning evaluations of an optimum mix proportion and various mechanical characteristics of the CFRC. As the results, it was shown that the CFRC of concrete-mix was superior in modulus of elasticity, flexural and fracture toughnesses to that of the mortar-mix and the mechanical characteristics of the former was, if anything, similar to those of steel fiber reinforced concrete.

調合因子がCFRCのフレッシュ時および硬化時の特性に及ぼす影響 : 軽量炭素繊維補強コンクリート(CFRC)の調合と基礎物性に関する実験的研究(その1)

Light-weight carbon fiber reinforced concrete (CFRC) is a new building material with light weight and high tensile strength. This study aims at obtaining an optimum mix proportion of the CFRC. The used materials are low-shrinkage cement, high-performance pitch-based carbon fibers, silica sands plus Sirasu balloon and some admixtures. The parameters of the experiments are unit cement content, grain size of silica sand, water-cement ratio, fiber volume fraction, fiber length and mix ratio of silica sand and Sirasu balloon. Fiber dispersion, flow and air content of the fresh CFRC, and specific gravity, compressive and flexural strengths of the hardened one were evaluated.

硬化CFRCの基礎物性における各種力学的特性 : 軽量炭素繊維補強コンクリート(CFRC)の調合と基礎物性に関する実験的研究(その2)

In this study, in order to obtain mechanical properties of hardened carbon fiber reinforced concrete (CFRC), compression, bending, fracture toughness and flexural fatigue testings were conducted. From the results, following items were investigated and discussed: 1) fundamental mechanical properties such as Young's modulus and compressive and flexural strengths, 2) tension-softening curves and J-integral values estimated by means of an inverse analytical approach using the cohesive force model, 3) evaluation of size effects on flexural strength based on a highly-stressed volume concept, and 4) flexural fatigue endurance and residual flexural strength after fatigue testing.