Short-fiber-mixed concrete and shotcrete
Photo 1 Poly-vinyl alcohol short fibers
(click to enlarge)
Photo 2 Falling prevention experiment
(click to enlarge)
Photo 3 Shear capacity improvement
experiment (click to enlarge)
Concrete is made from stone and sand mixed with cement and water, and hardens as a result of a chemical reaction. With high compressive strength and low tensile strength, it is generally used in combination with reinforcing bars to compensate for its material weakness, and is widely applied in reinforced concrete for civil engineering structures and buildings. However, reinforced concrete structures in cold regions gradually deteriorate as a result of their water content repeatedly freezing and thawing due to changes in ambient temperature, and reinforcing bars rust due to the accumulation of chloride ions from sea breezes or deicing salts. Additionally, concrete lumps may fall from structures in response to impacts by earthquakes or accidents. To prevent these problems, fine short fibers are mixed into concrete to improve its performance by preventing disintegration. Although such fibers have conventionally been made of steel, this type rusts easily due to sea breezes or deicing salts. Against such a background, joint research was performed with the Muroran Institute of Technology, Hokkaido University, Sumitomo Mitsui Construction Co., Ltd. and DPS Bridge Works Co., Ltd. with a focus on poly-vinyl alcohol (PVA) short fiber, which is rust-resistant and adheres to concrete.
The results of PVA short-fiber-mixed smart concrete testing in this study showed that concrete falling was prevented (falling prevention effect) and that concrete was more resistant to large forces (shear capacity improvement effect). Although the pump hoses used to convey concrete clogged easily due to its short-fiber, it was also found possible to increase the material’s properties of flow for pumping and spraying by improving the materials used and adjusting the mix ratio. Based on such materials, the smart shot method is used to repair deteriorated reinforced concrete by spraying fresh concrete over a grid-form plastic reinforcement member as fiber mesh, supporting the treated concrete to resist large forces.
The Materials Research Team summarizes key points in the design and construction of PVA short-fiber-mixed concrete, such its limit of application and the estimation method of its reinforcement effects. And the team plans to expand the usage of PVA short-fiber-mixed concrete based on trial construction.
(Contact: Materials Research Team, CERI)