Nobuyuki HIRAKAWA

Crack Control by Expansive Additive for RC Jacketing Method

SupervisorFKyuichi MARUYAMA

In this study, the effect of expansive additive on crack prevention is clarified experimentally. Thermo-dynamic parameters are evaluated by the comparison between experimental data and thermal stress analysis. Referring to those determined values, full-scale thermo-dynamic analysis is executed to estimate the effect of expansive additive on crack preventive control.
We made four kinds of concrete specimens jacketing to steel-piped pier. Parameters were reinforcement and expansive additive. Dimensions of specimen were 0.8m~1.7m~0.9m. Temperature, strain and effective stress of concrete were measured from early age to discuss the effect expansive additive. Through the experiment, following conclusions were obtained.

1)Maximum temperature was reduced by 4Ž both at internal center and at the surface of the specimen in case expansive additive (hydration heat control type) was applied compared with normal cement concrete.
2)Linear expansion coefficient of expansive-concrete was larger than normal concrete in temperature rise phase.
3)In the four specimens which designate reinforcement and expansive additive as parameter, cracks were observed only in the normal concrete specimen without reinforcement in circumferential direction around the steel-pipe from early age.

Thermo-dynamic parameters were determined both from experimental results and thermal stress analysis. Adiabatic temperature rise property, heat transfer coefficient and linear expansion coefficient were evaluated. Especially, the way to include the effect of expansive additive was discussed on the thermal stress analysis. In consequence, that effect of expansive additive was simulated as the difference of probability of crack occurrence, analytically.