Effects of Fly Ash on Mechanical Properties of PC Girder Using Reac-tive Andesite Aggregates

Abstract

In the Hokuriku region, alkali-silica reaction (ASR) caused severe degradations in many concrete bridges. However, criteria for repair and replacement works of these structures are still unclear. For the development of damage evaluation procedure, it is necessary to investigate the load-carrying capacity of prestressed concrete (PC) girders affected by ASR-induced deterioration in actuality. This study constructed two full-size PC specimens from the high-early-strength Portland cement and reactive aggregates, and then exposed them to outdoor environmental conditions. One of them was specially mixed with a controlled amount of fly ash. After one and a half years of outdoor exposure, destructive loading tests were carried out to investigate the difference in loading capacity of the girders. From results of the long-term exposure and the tests, the flexural strength and the rigidity of the specimen with fly ash were not degraded while ASR was also effectively suppressed. In addition, cylindrical concrete cores were taken at different positions of both girders to analyze the relationship between mechanical properties of concrete such as compressive strength, static elastic modulus, and ultrasonic wave propagation speed. Results of the coring test showed that the mechanical properties of concrete cores varied according to their collecting positions and directions.

Stiffness Evaluation and Current Status of a Degraded Road Bridge Slab Located in a Mountainous Area

“…Regarding the static elastic modulus, the results obtained from the water-leakage part showed that it decreased to about half of that obtained from the dry part. Previous studies pointed out that the elastic modulus was significantly degraded by the ASR-induced deterioration (Kubo et al 2006;Ha et al 2017). This outcome was also confirmed by the results on the RC slab of the test bridge.…”

“…The ASR gel increases in volume, exerting a significant pressure within the material, which causes spalling, cracking, and loss of strength in the concrete and rebar. The relationship between the characteristics of ASR-induced damage and the reduction in the elastic modulus have been proved by many previous studies (Giaccio et al 2008;Ha et al 2017). Over the years, many researchers have performed loading tests on both ASR-degraded PC and RC specimens.…”

“…In the Hokuriku region, salt damage, alkali-silica reaction (ASR), and frost damage cause early severe degradation of the bridges in the mountainous area without warning (Katayama et al 2004;Torii et al 2008;Arima et al 2016;Ha et al 2017). Although traffic volume is small, the influence of overloaded vehicles is also a safety concern.…”

“…Their results showed that the decreases in Young's modulus and tensile strength were more obvious than that in the compressive strength and that the decreased rate was higher in the vertical cores in which confinement was absent than in the longitudinal cores. In another study by Ha et al (2017), two PC girders, which were constructed and placed outside the laboratory, had been exposed to weather conditions for 1.5 years. The H girder was affected by ASR, whereas the FA girder was kept at an inactive state with ASR acceleration due to the addition of fly ash.…”