Workability of concrete varies during pumping. Even though concrete satisfies the required workability before pumping, it often does not satisfy the required standard after pumping. Moreover, serious...

When cement-based materials are transported at a construction site, they undergo high pressures during the pumping process. The rheological properties of the materials under such high pressures are unknown, and estimating the workability of the materials after pumping is a complex problem. Among various influential factors on the rheology of concrete, this study investigated the effect of mineral and chemical admixtures on the high-pressure rheology. A rheometer was fabricated that could measure the rheological properties while maintaining a high pressure to simulate the pumping process. The effects of superplasticizer, silica fume, nanoclay, fly ash, or ground granulated blast furnace slag were investigated when mixed with two control cement pastes. The water-to-cement ratios were 0.35 and 0.50.

A new prestressing strand was recently developed. The objective of this study is to investigate and provide the mechanical properties of the new strand, as these properties are essential in the design and construction of prestressed concrete structures. The experimental program includes a tensile test, a fatigue test, a relaxation test, and a stress corrosion test. In the tensile test, an optimal gripping method was initially determined and the measured ultimate strength was found to be higher the nominal strength of the new strand. The new strand does not exhibit any degradation in its mechanical performance after fatigue loading. Compared to the existing strand with the strength of 1,860 MPa, the new strand also showed equal or enhanced performance in the stress relaxation and the stress corrosion tests.

The purpose of this study is to suggest a new partially precast pier cap system and to experimentally verify its structural performance. The optimum shape and reinforcement detail of the partially precast pier cap were first derived and an improved manufacturing process in the precast plant and on-site was suggested. The new pier cap system offers benefits in terms of economy and quality management, and it can be constructed more rapidly than the conventional pier cap and fully precast pier cap. The specimens were manufactured at a one-half size of the original scale for structural tests. The tests highlighted that the loads at cracking, yielding and failure of the partially precast pier cap were almost identical to those of the conventional pier cap. Consequently, this study verified that the partially precast pier cap system can be applied for actual design and construction of the pier caps.

Deteriorated facility maintenance is a critical social issue in advanced countries. Its cost increases when considering the social consequences in terms of asset value and direct maintenance costs. Data from Korea’s Ministry of Land, Infrastructure, and Transport shows that there were 3454 bridges aged 30 years or over in Korea in 2017; this number will increase to 10,961 by 2027. In thirty years, maintenance costs will be incurred for more than 32,000 old bridges in Korea. These trends are also observed in the US, Japan, and Korea. Diverse studies have been conducted to predict the residual life of old bridges via bridge performance evaluation and load-carrying capacity assessments. However, criteria for evaluating bridge performance and verifying the effect of bridge maintenance are yet to be established due to two reasons. First, most studies on performance evaluation, maintenance, and rehabilitation techniques have been performed on limited specimens from building elements or through small-scale simulations that do not reflect the deterioration factors of complex materials in diverse environments. Second, the performance evaluation of bridges is difficult compared to quantitative state evaluations. As a method of predicting the future performance of aged concrete bridges, it is effective to understand the actual aged bridges through experiments, and this study intends to propose the method.