Effect of Carbon Fiber and Graphite Powder on Resistivity of Cement-based Sensor under Compression

Abstract

Structural health monitoring currently becomes an important part in the maintenance of concrete structures. Thus, using of sensors to monitor the structural behavior is necessary. Cement-based sensors have been developed recently to be embeddable in structures and to be implemented by measuring the change in their resistivity. In this research, the electrical resistivity and compressive strength of the cement-based sensors with the addition of carbon fiber (2% and 4% by volume fraction) and graphite powder (2%, 4%, and 10% by weight of cement) were studied. Three water to binder ratios (w/b) that are 0.3, 0.4 and 0.5 were varied. For 28 days after demolding, the resistivity of the non-load-bearing sensors was monitored to determine the influence of their maturity. At the age of 28 days, their compressive strength was evaluated. Subsequently, the fractional change in resistivity (FCR) of the sensors was measured under a set of compressive loading, which comprised of three cycles of loading; first loading to the strain of 0.0025, then to 0.005 and 0.01. From the test results, it is showed that the carbon fiber was more favorable than the graphite powder. Although the addition of graphite powder could reduce the resistivity, it dropped the compressive strength and highly fluctuated the resistivity results of the cement-based sensors. In term of the piezoresistivity, all of the sensors when loaded provided good responses only when the compressive strain was less than 0.005.

Electrical and piezoresistive properties of cement composites with carbon nanomaterials

“…11,13 On the other hand, this value was higher than that of cement-based composites with carbon black (37.71 ≤ GF ≤ 55.28) and with low volume fraction (2%) of carbon fibers ( GF = 20). 6,12 Of course, the GFs are influenced by the loading rate (LR) (they are smaller for low loading rates) and suffer from a lack of accuracy and repeatability. 11 Thus, it appears that the use of MWCNTs is more effective in developing cement-based sensors for strain measurements under compression than the use of carbon black and carbon fibers, but further research is required to confirm this hypothesis.…”

“…In recent years, many studies have been performed to develop a conductive cement-based composite for self-sensing purposes, 5,6–16 as they have several advantages compared to conventional strain sensors embedded or attached to the structures. These advantages include high durability, low cost, no degradation of mechanical properties, and large possible sensing volume.…”

Experimental Investigation of the Piezoresistive Properties of Cement Composites with Hybrid Carbon Fibers and Nanotubes

“…Metal sensors attached to or embedded in concrete can easily separate and corrode over time. The high cost of adhesive bonding and their low sensitivity and low survival rate are also drawbacks of such sensors [ 8 , 9 ].…”

“…A cement-based sensor that uses piezoresistivity to sense strain could be a good alternative to those sensors. Because concrete is considered an insulator, conductive fillers are incorporated to obtain conductivity for sensing [ 8 , 9 , 10 , 11 , 12 , 13 ]. Chen and Chung had been investigated carbon fiber reinforced concrete to monitor flaws in a concrete structure in 1993 [ 14 ].…”

“…Therefore, micro- or nano-scale fillers are commonly used, rather than macro-scale fillers, due to their enormous potential area for connecting with one another. More than 10 types of conductive fillers are available at the micro- or nano-scale, including carbon fiber (CF), graphite powder (GP), and nickel powder at the micro-scale and carbon nanofiber, carbon nanotube (CNT), titanium dioxide, and iron(III) oxide at the nano-scale [ 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 22 , 23 , 24 ].…”