In this study, in order to establish an estimation method of the compressive strength of ultra high strength mortar using alite cement and pozzolanic fine powder as a binders, equivalent age considering apparent activation energy was adopted to the estimation of the compressive strength. As a result, the estimated apparent activation energy increased depends on the development of the compressive strength and curing temperature. The temperature dependency of the compressive strength can be evaluated with high accuracy when the equivalent age modified by the obtained apparent activation energy was used. In addition, it was shown that the apparent activation energy is strongly influenced by the hydration of pozzolanic fine powder.
This paper proposed a method of Bayes estimation of the corrosion rate of reinforcing bars for each transformation process and prediction of peeling/falling area of covering concrete considering uncertainty based on visual observation information. The proposed method allows to estimate the corrosion rate of reinforcing bars before an d after cracking with accuracy of about -35 to + 35% peeling/falling area can be predicted with accuracy of about -5 to + 15% even if the chloride ion concentration and the neutralization rate is not measured. As a result of applying to the actual structure of 45 years, the standard corrosion rate of internal salt damage and composite deterioration was 30 to 70% and the corrosion rate of the reinforcing bar increased by about 140% on average due to cracking. Based on the deterioration prediction result, the optimum repair area when the sum of maintenance cost becomes the minimum was 10 m2, which is about 40% of the cost saving effect compared with the method of repairing only the visible peeling area.
This study presents fatigue life prediction of steel-concrete joint system based on the experiments of wind turbine model subjected to uniaxial or bi-axial vibration. The wind turbine model was tied to the biaxial shake table, then was vibrated at most 200,000 cycle to induce fatigue damage of concrete in joint system. The model subjected to bi-axial vibration showed rapid increase of horizontal displacement at tower when the number of vibration was about 2/3 or half of the one subjected to uniaxial vibration. Several particular cracks were observed at the cross section of pedestal and footing after the test. The ultimate capacity of the model was estimated by fatigue strength of concrete estimated by JSCE standard. The number of vibration during the variation of input amplitude was converted to the equivalent number by Miner’s low. The S-N diagram for uniaxial vibration obtained in this study showed good agreement of S-N diagram for ordinary concrete.
This paper describes an experimental and analytical study on the influence of crack on drying-wetting behavior of concrete members. Experimental results showed that the drying-wetting is accelerated by the existence of crack. Numerical simulation method was developed, which can well simulate drying and wetting behavior of concrete members with various patterns of cracks. Parametric numerical simulation of long-term behavior of concrete members with cracks revealed that the crack strain, which is defined as crack width divided by crack interval, is an effective index for the influence of crack on long-term drying and wetting behavior of concrete members and that monthly model of environmental action is acceptable to predict long term drying-wetting behavior of concrete under natural environment.
In constructing RC wall structures such as a box culvert, placing mechanical joints in the same section is considered efficient in enhancing productivity. Previous research shows that by placing mechanical joints in the same section of the plastic hinge zone improves the deformation performance of the member. However, the relationship between the characteristics of the mechanical joints and the performance of RC wall member has not been clarified. This report shows deformation performance and crack properties of a full scale sized wall member tested under cyclic seismic loading using mechanical joints classified as “SA”, “A”, “B”, “C” by Japan Society of Civil Engineers. As a result, it was observed that the specimen using mechanical joints of Class B’ or above improves the performance of the wall members compared to the specimen without joints.