The use of high-strength mass concrete has increased in recent years, with a tendency toward constructing tall and large-scale reinforced concrete structures. At an early age, the interior of mass concrete is heated and cured at high-temperature by internal storage of the heat of cement hydration. High-temperature curing at an early age causes a peculiar strength development in mass concrete. Especially, this tendency is remarkable in high-strength mass concrete, because of the increase of cement content per unit volume of concrete. This paper summarizes the general tendencies about the temperature history and the strength development of high-strength mass concrete, with statistical analysis of the experimental data from the previous studies.

View full abstract

Acoustic emission (AE) techniques are extensively studied in concrete engineering and are recently going to be applied to practical use. In particular, the increase of aging structures and the disastrous damage due to earthquakes substantially demand for the maintenance of reinforced concrete (RC) structures in service. It results in the need for the development of advanced and effective inspection techniques. Accordingly, AE techniques draw an attention for diagnostic applications to RC structures. By several authorities, activities for the standardization of AE testing procedures are in progress. Taking into account these activities, the updated findings and trends on AE research are summarized.

View full abstract

The optical fiber sensor based on Brillouin scattering is the state of the art for measuring the continuous strain in structures. Since the fibers are originally designed for telecommunications, it was difficult to apply them to strain sensor in that the fibers might be easy to break and hard to bond to concrete. To overcome these problems, we coated the optical fiber with fiber reinforced plastic and roughened the surface with the additional coating. According to a series of tests, to investigate the mechanical properties and workabilities, this sensor turned out to be effective for measuring the strain and the deflection of the structures.

View full abstract

Harmonization of JIS with International Standards has been commenced. Since ISO standards for chemical admixtures for concrete have not been constituted yet, CEN is now preparing European Standards on which the ISO drafts are to be based. Therefore, Japan Concrete Admixture Association has researched the European Standards and compared JIS with them, and then describes some problems for the future.

View full abstract

The Hokuriku Expressway's Daikeiji Bridge was completed in 1972. Since 1983, repair and inspection have been conducted several times. However salt-induced corrosion had severely progressed, so repair and retrofit programs were performed to recover the bridge's durability and strength capacity. The automatic concrete removal method using high-pressure water, which is called “water-jet method”, was adopted to remove the damaged concrete of the girders. Before the construction, the experiment using the test girder was conducted by the water-jet method, and the prestress redistribution in the girder was investigated. This paper mainly reports the experiment results, outline of construction and quality control.

View full abstract