Deterioration Prediction Model of Multi-Layer Coating Material and its Reference Service Life Evaluation in Terms of Carbonation Control Effect

In this paper, authors propose a method to predict deterioration of exterior finishes using Markov Chain Model based on field survey results on cracks of exterior finishes of existing RC buildings. There existed correlation between degradation of finishing and carbonation progress. Authors propose the service life prediction approach to focus on the carbonation suppression effect into the concrete considering progress of exterior finish deterioration

Compressive Strength Improvement and Water Permeability of Self-Healing Concrete Using Bacillus Subtilis Natto

In recent years, many projects have been carried out to enhance the durability of concrete structure from the influence of cracks. Generally, managing cracks should be a rather preventative method for sustainable development. Based on that, Bacillus subtilis natto - a local bacterium in Japan was found to have the ability to form CaCO3, which can be used as healing materials for cracks in the concrete structure. The bacterial biomineralization immobilized in lightweight aggregate was studied to improve the compressive strength by healing the cracks and densifying the structure. Moreover, as an essential parameter for durability enhancement, the water permeability of self-healing concrete through a water-flow system was carried out. Experimental results on the behavior of the materials indicate that Bacillus subtilis natto could lead the compressive strength to 40 % higher than the controls. Promising result in preventing the water through the cracks confirmed the self-healing effect with more potential in larger-scale

Synthetic Resin Reinforcement of Timber Joints Deteriorated by Termites

Timber has been widely adopted as a global structural material. However, timber sometimes deteriorates due to various factors such as termite infestation, which may reduce its strength and durability. It is difficult to ascertain the degree of deterioration of timbers by visual inspection because deterioration by termites causes severe damage to the inner parts of the timber. Therefore, the damage is often discovered after the deterioration progresses. The restoration and refurbishment method currently implemented is removing the degraded parts and partially replacing them with new healthy wood. Although it is as desirable to reinforce the original part as it is to restore its strength, especially for historical timber structures, this approach has not yet been put into practical use. This study investigates the possibility of restoring timber deteriorated by termites with little changes in its appearance by using resin filling. Deterioration by termites occurs at the base of the timber. Therefore, the specimen is assumed to be the joint of a foundation and column. First, the deteriorated specimen was filled with epoxy resin, and then, the effectiveness of the filling was confirmed by a nondestructive test method using ultrasonic pulse velocity. Finally, shear strength test was performed for the joint. As a result, ultrasonic velocity significantly increased because of the resin filling. The strength of the specimen filled with epoxy resin was restored and was close to the strength of a healthy one. It was confirmed that this strengthening method with resin filling was useful for improving the structural performance of timber deteriorated by termites with little change in appearance

Effects of Finishing Materials against Carbonation and Corrosion Condition of Model Building Exposed to Outdoor Conditions for 30 Years

A model building made out of concrete block specimens whose surfaces were coated with various finishing materials was constructed for the outdoor exposure test. After 30 years of outdoor exposure, the deterioration of finishes and their carbonation and corrosion inhibition effects were investigated. As a result, the following conclusions were obtained: Though the deterioration levels differed depending on their types and thickness, all finishing materials showed some kind of deterioration after 30 years‘ long-term outdoor exposure. The progress of carbonation and corrosion are prevented when the surface is coated with finishing materials of sufficient thickness or waterproof effect. Regarding the relationship between corrosion depth and carbonation depth, corrosion is initiated after the carbonation front reaches the area. It usually takes a while to initiate corrosion in the carbonated area, not immediately after the carbonation reaction. When the concrete surface is properly coated with finishing material, corrosion may not be initiated in non-carbonated area in concrete where the pH level is not lowered

Post Peak Behavior of Carbonated Concrete Structure - A Case Study of the Former Shime Mining Office Vertical Derrick in Japan

This paper is a report on the investigation results of the Former Shime Mining Office Vertical Derrick, which was built in 1943 and was 75 years old at the time of the investigation. The building suffered from serious deterioration including rebar corrosion, which led to large area of concrete spalling. In this report, aggregation data of concrete spalling has been presented along with the investigation results of cover thickness. According to the investigation results, concrete spalling occurred in places where cover thickness was less than 25 mm. And According to the aggregation data, concrete spalling flakes increased by approximately 200 pieces per year, with the average size of 10 cm in diameter. Also, a possible relation between concrete spalling and rainfall was observed during the investigation. Equations using the proportion of wet area affected by rainfall to estimate the area of spalling are proposed, although the value of empirical coefficientαneeds further discussion, including collecting data from other buildings where spalling occurs