|Budget Amount *help
¥2,000,000 (Direct Cost : ¥2,000,000)
Fiscal Year 1995 : ¥600,000 (Direct Cost : ¥600,000)
Fiscal Year 1994 : ¥1,400,000 (Direct Cost : ¥1,400,000)
In this study, prevention method for early age crack at surface layr of concrete slab placed in hot weather ambience was discussed by experiment and numerical analysis on properties of temperature and water vaporization.
At first, as basic experiment of thermal crack, time-dependent change of temperature distribution and water vaporization at mortar specimens were measured from immediately after placing toward twenty four hours, and effect of outer conditions (ambient temperature, ambient humidity, wind, solar radiation) and inner conditons (materials, mix proportion) were quantitatively discussed.
Next, flow chart for prevent thermal crack was shown. Further, analysis method of thermal strain used in flow chart, estimation method of water vaporizing rate used in analysis were shown, coefficient of thermal expansion of specimens at young age to calculate thermal strain at surface layr from temperature distribution, and tensile capacity as border line of crack occurence were measurd.
Using these results, tensile strain at surface layr of slab specimens due to temperature distribution was analyzed, and it was clarified that tensile strain bacame maximum at the same time when tensile capasity became minimum. So it was obvious that crack due to temperature difference between outermost and central layrs was most liable to occur at above mentioned period. And effect of outer conditons and inner conditions were quantitatively clarified.
At the end, effect of curing as prevention of thermal crack was discussed. Immediately after starting of curing, tensile strain at surface layr bacame smaller. In the other words, it was cirtificated that curing was very effective to prevent thermal crack. And it was clarified that starting time of curing was important, and it must be started before the period when tensile capasity became minimum.