This paper describes a study on the fundamental physical properties of concrete with rice husk ash, which a number of other researchers have already investigated. The study used Southeast Asian non-crushed rice husk ash (primary components: SiO2, density: 2.41g/cm3, average size of aggregate: 80.1μm, specific surface area: 321,000 cm2/g). The purpose of this study was to examine suitable utilization forms of rice husk ash blended concrete. The test results show that rice husk ash can be blended in concrete as binder in the range of 25 to 80 kg/m3 and as mineral admixture in the range of 50 to 75 kg/m3.
To understand the conditions of frost damage in concrete, a freezing and thawing test was executed on microchannels. During the test, the straight channels stayed intact while the channels with ink bottle geometries suffered frost damage. The channels with ink bottle geometries avoided frost damage when air remained in their cavities. After water permeation, air remained in the channels having a large ratio of cavity to neck volume. Usually, air is entrained to fresh concrete to improve frost damage resistance. However, the above results indicate the important role of the air trapped during water permeation. On the basis of the results obtained for microchannels, cement paste was cured under reduced pressure to reduce frost damage. Freezing and thawing of hardened cement paste with AE water reducing agent caused surface deterioration. On the other hand, vacuumed cement paste suffered almost no damage. The above results indicate, under our experimental conditions, that vacuum curing is effective to reduce frost damage, and they validate the observed results for microchannels.
Cathodic protection controls the corrosion current of steel in concrete by polarizing the steel potential in the less noble direction. Furthermore, cathodic protection is accompanied by spin-off reactions such as increase in pH by the generation of OH- ion and decrease in chloride ion concentration near the steel surface. In this study, a cathodic protection test was conducted to maintain depolarization values of 25 mV, 50 mV, and 100 mV for the steel in concrete specimens with different levels of chloride ion concentration. The protection effect was examined on the basis of the corrosion rate of the steel bars in concrete. The corrosion rate of the steel bars under cathodic protection was observed to decrease to less than 1.0 mA/m2, indicating a passive condition. The results also showed that the corrosion rate of steel decreases under cathodic protection even for depolarization values of less than 100 mV, which is the standard value under cathodic protection conditions.
The purpose of this study was to investigate a method to estimate the deterioration area of fire-damaged concrete by the impact elastic wave method, performing measurement from the surface of the concrete. Based on the findings of this study, it is considered that the measured contact time between the surface of the concrete and the hitting hammer can be used to estimate the area of deterioration on the surface, and that multipoint measurement of the propagation time of the elastic wave on the surface of the concrete can estimate the depth of deterioration. However, the estimation accuracy was found to be lower in the case of slight deterioration.