Tomoyuki Sakurada

Bond Splitting Strength of High–quality Recycled Coarse Aggregate Concrete Beams

Abstract This study concerns high–quality recycled coarse aggregate concrete which was recently specified in Japanese Industrial Standards (JIS). The objective of this study is to determine the basic properties of recycled aggregate concrete when used for the beams of reinforced concrete structures. During a period of one year after the placement of concrete, regular observations were made to identify the magnitude of drying shrinkage cracks generated in the beams. Furthermore, for the beams in which drying shrinkage cracks were generated, the bond splitting strength was investigated. The study found that the drying shrinkage cracks at the material age of one year were slight, showing that the generation of drying shrinkage cracks was suppressed compared with when using an intermediate–quality recycled coarse aggregate. The observed bond splitting strength was equivalent to that of normal concrete, unaffected by the formation of slight drying shrinkage cracks. When the high–quality recycled coarse aggregate of the study was used for reinforced concrete beams, the bond splitting strength was equivalent to that of normal concrete even when recycled coarse aggregate was substituted entirely for normal coarse aggregate. These findings suggest that reinforced concrete beams made using high–quality recycled coarse aggregate can be used as members of architectural structures.

AN EXPERIMENTAL STUDY ON THE BOND PROPERTIES OF LAP SPLICES OF RECYCLED AGGREGATE CONCRETE HALF PRECAST BEAMS APPLIED ULTRA HIGH STRENGTH FIBER REINFORCED CONCRETE FORM

The bond properties of recycled aggregate concrete half precast beams using ultra high strength fiber reinforced concrete form were studied. This study aimed to increase the scope of application of recycled aggregate concrete. The high fluidity recycled aggregate concrete with a medium-quality recycled coarse aggregate used as site placed concrete. The four-point bending tests were conducted on recycled aggregate concrete half precast beams. The results showed that the load carrying capacity of the half precast beams using the ultra high strength fiber reinforced concrete form was higher than monolithic beams. Thus, high concrete strength of fiber reinforced form can be effectively used for the bond splitting strength of lap splices. Furthermore, the bond splitting strength of lap splices of recycled aggregate concrete half precast beams was estimated from the past bond splitting strength equation considering the strength difference of form and recycled aggregate concrete.

STUDY ON APPLICATION OF RECYCLED AGGREGATE CONCRETE TO THE COMPOSITE STRUCTURES

It is known that the axial strength of composite columns could be calculated by the strength superposing method due to the many experimental results of axial compression of composite columns. However, in case of the composite columns in which recycled concrete are used, the contribution of the confinement effect to the structural performance has not yet been clarified. Therefore, twenty-one composite columns were tested under axial compression loading to investigate the effects of concrete type, such as normal concrete, recycled aggregate concrete and fiber reinforced concrete. The application of recycled aggregate concrete to the composite structures are discussed in this paper based on test results.