This paper reports on the components and required qualities of frost-resistant accelerators used for cold-weather concreting, as well as the properties of concrete containing a frost-resistant accelerator, such freezing temperature, setting/hardening, compressive strength gains, and the effect of inhibiting early frost damage. Suggestions for use are given as well.

View full abstract

Superretarders are used for retarding setting of concrete for a desired period to integrate construction joints and extending the placeable time of concrete. This paper describes the components, performance and mechanism of superretarders and properties of concrete containing a superretarder based on the literature and state-of the-art technology in anticipation of expanding the horizons of their conventional and new applications.

View full abstract

Reinforced concrete infilled shear wall is one of the seismic strengthening methods for existing R/C buildings. But bad environment and long construction period are problems of this method. A Method using installed precast concrete panels was developed to solve this problem. Precast concrete panel is manufactured as divided panels due to installation and transportation requirements. Divided panels are formed as one by prestressing at the reinforcement construction site. After precast panel is attached to the existing frame, four laps of the wall are filled with mortar, and joined to the existing frame.
To develop a seismic strengthening method for installing precast concrete panel, lateral loading tests were conducted. Specimen shear walls, 1 story by 1 span, scaled down to 1/3 were prepared. Three specimens were tested. One was a reinforced concrete infilled shear wall. The others were installed precast concrete shear walls. The two precast specimens consist of three sheets of panels, the amount of connecting anchoring varied between them. The test results showed that the precast concrete wall had same strength and ductability as R/C walls.

View full abstract

Concrete waste is hardly recycled to be aggregate for concrete by only normal crushing, because the micro cracks remain in the crushed concrete and the particles consists of only mortar or cement paste are included. Thus many techniques to produce recycled aggregate are proposed and used, but these techniques need significantly much energy and may cause much CO₂. In this paper, effects of the processes for recycled aggregate to absorb a part of mixing water or Pozzolanic material, ex. colloidal silica, on the properties of concrete were reported. One of these processes can be achieved by soaking the recycled aggregate in mixing water or Pozzolanic liquid before mixing concrete. The other process is the mixing procedure for recycled aggregate to soak up a part of mixing water with or without Pozzolanic liquid. In this investigation, the vacuuming sequence before or during mixing of concrete is also evaluated. The absorbed water or Pozzolanic liquid is expected to fill up the micro cracks in recycled aggregate with cement gel by cement hydration or Pozzolanic reaction. Thus the strength of recycled aggregate concrete can be improved, even though the only crushed concrete wastes are used.

View full abstract

[in Japanese]

View full abstract

[in Japanese]

View full abstract