Prediction model of compressive strength development of fly-ash concrete

Based on experimental results concerning the compressive strength development of concrete containing fly ash, the authors derived an estimation equation for compressive strength development. The equation can express coefficient , which indicates the activity of fly ash as a binder, in the form of a function of age, fly-ash content, and Blaine specific surface area of fly ash.

This equation is capable of explaining the increases in the early strength due to fly ash in place of part of fine aggregate, the decreases in the early strength due to fly ash in place of part of cement, the increases in the long-term strength due to pozzolanic reaction, the relationship between the fly-ash replacement ratio and the ratio of strength increase/decrease, and the effect of fly ash's Blaine specific surface area on the strength.     

Evaluation of the bond properties between concrete and reinforcement as a function of the degree of reinforcement corrosion

In order to investigate the effect of reinforcement corrosion on the bond properties between concrete and reinforcement, the pullout tests were conducted using reinforcements embedded in concrete specimens, which were corroded by an accelerated electric corrosion method. A finite element method (FEM) analysis was also carried out on the basis of the results of the pullout tests. The maximum bond strength (τ_max) and the bond rigidity (D_s) of specimens decreased in proportion to the increase of corrosion percentage (Δ_w), respectively. Also, the curves of bond stress-free end slip could be analyzed by the FEM, if the τ_max and D_s were determined as a function of corrosion percentage. The equations for calculating the maximum bond strength and the bond rigidity necessary for an FEM analysis of RC members with corroded reinforcements were obtained by the experiments and the FEM analysis of the pullout tests.     

An experimental study on the retrofitting effects of reinforced concrete columns damaged by rebar corrosion strengthened with carbon fiber sheets

This paper presents the results of an experiment study on the structural behavior of reinforced concrete (RC) columns damaged by rebar corrosion and the retrofitting effects of damaged RC columns strengthened with carbon fiber sheets (CFS). In the experiment, a cyclic horizontal loading test was carried out using RC columns damaged by different degrees of rebar corrosion and strengthened with CFS. As a result, it was revealed that the deterioration of their structural behavior was mainly caused by the decline in the confining effect due to the falling off of concrete cover and the reduction of mechanical properties of corrosion rebar. In addition, the test proved that shear strengthening using CFS is an very effective retrofit technique that prevents bond splitting cracks and shear cracks from growing and improves the ductility of RC columns with corroded rebars due to the confining effect of CFS.