M Nili - Associate Professor, Bu Ali Sina University, Hamedan, I.R.Iran
S Nazari - Msc Student,
A.M Salehi - Msc, Bu Ali Sina University, Hamedan, I.R.Iran

In this paper the effect of different casting temperatures on cracking potential of mass high strength columns were studied. Four mix proportions with 0.3 watercementing ratio were made and two different casting temperatures, 26ºC and 40ºC were applied to simulate moderate and hot climate conditions. Cement was replaced by silica fume at 0%, %5, %8 and %11. Temperature rising of the mixtures, due to hydration, after casting was monitored till 7 days. Furthermore, compressive strength of the specimens was determined at the ages of 1 to 91 days. Thermal analysis of 4 large columns, 600×600×200 to 1800×1800×2000 mm, was carried out by finite element method [3-7]. In this regard, two demolding time, 24 and 48 hours were selected to clarify the effect of ambient temperature on risk of cracking. The results declare that tensile stress of the 600 mm columns with 24 hours demolding time, irrespective of casting temperature, was higher than tensile strength and will be cracked. However, 48 hours demolding time induced lower tensile stress and diminished risk of cracking. Silica fume has no considerable effect on risk of cracking.

mass concrete, casting temperature, risk of cracking, silica fume, demolding time