Manote Sappakittipakorn

Corrosion of Rebar and Role of Fiber Reinforced Concrete

Recent studies have shown that fiber reinforcement of concrete reduces its permeability to water and enhances its service life. In this study, this finding was extended to determine if fiber reinforcement can also control corrosion of reinforcing steel in traditionally reinforced concrete. Two fiber types, cellulose and polypropylene, at 0.1 % and 0.3 % volume fraction, were examined. Two series of tests were performed. In the first series, chloride transport characteristics were determined by using the Bulk Diffusion Test, the Silver Nitrate Spray Test and the Rapid Chloride Permeability Test. In the second series, corrosion activity in reinforcing steel was monitored in loaded RC beams with and without fiber reinforcement for a year in a simulated marine environment. Results demonstrated that while the presence of fibers increased the coefficient of chloride diffusion based on total chlorides, there was a decrease in the coefficient related to free chlorides. Fibers therefore appear to bind the chlorides and inhibit their transport through concrete. Corrosion tests further corroborated these findings and indicated that fibers delayed the onset of corrosion in RC beams as long as the applied load did not exceed a certain threshold value.

Resistance to Underwater Abrasion of Fiber Reinforced Cement Mortar

Surfaces of hydraulic concrete conduits where significant abrasion of waterborne sediment can occur often degrade and need a regular repair to maintain their serviceability. In this research, thin overlay made of fiber reinforced cement mortar was introduced as a repair measures. Its resistance to underwater abrasion was therefore experimentally evaluated following the procedures of ASTM C 1138. This research utilized three types of fiber: steel fiber, polypropylene fiber, and micro polypropylene fiber (the micro polypropylene fiber was used only in a combination with either the steel or the polypropylene fiber). The influence of these fibers on the abrasion resistance of fiber reinforced cement mortar was then determined in terms of weight loss. The weight loss results showed that the fibers added to mortar specimens can enhance the abrasion resistance. Between the steel and polypropylene fiber, the latter provided better abrasion resistance. In case of the combination mixes, the micro polypropylene fiber increased abrasion resistance when combined with the polypropylene fiber but had no benefit when combined with the steel fiber.

Electrical Resistivity of Cement-Based Sensors under a Sustained Load

This research was to study the influence of a sustained load on the electrical resistivity of a cement-based sensor. The cement-based sensor in this study was made of cement paste having water to cement ratio of 0.4 with the addition of graphite powder at 2% and 4% by weight of cement and carbon fibers at 2% and 4% by volume. The sustained load was applied on the cement-based-sensor using a sustain machine to control a compressive force continually at 30% of its ultimate compressive strength for a period of 30 days. The test results showed that the sustained load induced a creep strain on the cement-based-sensor. The graphite incorporated cement-based sensor showed higher creep strain than the plain cement-based sensor while the carbon fiber cement-based sensor showed lesser. In addition, it was shown that the creep strains affect the electrical resistivity of the cement-based sensors.

Application of Cement-Based Sensor on Compressive Strain Monitoring in Concrete Members

The aim of this research was to implement cement-based sensors in monitoring the change of strain in concrete structures in particular where a compression applies. The experiment was conducted in a laboratory by embedding a cement-based sensor in a 150x150x150 mm normal strength concrete cube. When the sensor-installed concrete cube was loaded, the relation between the fractional change in resistivity (FCR) and strain of the sensors was evaluated. In this study, all cement-based sensors were made of cement paste containing carbon fiber at 2% by volume fraction. They were then varied with the addition of graphite powder at 4% and silica fume at 15% by weight of cement. Thus, there were total four mix proportions. From the experimental results, all sensors provided a good corelation between the FCR and compressive strain. Among them, the carbon fiber plus graphite powder (no silica fume) cement-based sensor yielded the most excellent piezoresistive response.