Title : SEMI - ADIABATIC CALORIMETRIC STUDIES FOR EVALUATING THE EFFECT OF FLY - ASH AS SECONDARY CEMENTITIOUS MATERIAL ON TEMPERATURE RISE DUE TO HYDRATION
Authors : Arun D.Pofale,Keshav C.Tayade,Narendra V.Deshpande
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Price : 250
Abstract : The paper deals with the measurement of temperature rise due to heat evolution because of hydration of cement in concrete. The semi-adiabatic calorimeter was used to record the temperature rise in various samples of cement paste maintaining the water to cement ratio constant at 0.50. Further, keeping the total binder content same the effect of using Type "F" Fly Ash from various sources and of different fineness with 20%, 30%, and 40% replacement levels, on the temperature rise and heat evolution characteristics, was determined on cementitious paste samples. Total 8 such Sets were tested. The study clearly demonstrated the pattern of temperature rise and the heat evolution characteristics of cementitious material. The results showed that the temperature rise was reduced by 18.5 %; 29.2 % and 39.1 %, so also the time to reach the peak temperatures was delayed by 1.4; 2.3 and 3.2 hours for 20%, 30%, and 40% replacement levels. Similarly, the heat of hydration evolved at 7 days was reduced by 13.9 %; 26.39 % and 35.28% for 20%, 30%, and 40% replacement of cement by Fly Ash. The reduced temperatures would mean lower probability of cracking due to internal restraint. The Temperature modeling done based on Degree of Hydration assessed from Av. Heat evolved for various blends showed a decrease in adiabatic rise from 50.90C when only cement is used as binder to a rise of 34.60C when cement with 40%FA is used. The maximum temperature; the time to maximum temperature and the time spent at elevated temperatures so also form removal are critical parameters in predicting the thermal shock susceptibility and the use of fly ash has a reducing effect on this parameter also. Another effect of high temperatures is the formation of delayed ettringite formation (DEF), and to avoid DEF in mass concrete, it is necessary to prevent the temperature rise in the concrete from exceeding the threshold value at which ettringite nucleation occurs and use of fly-ash has shown to reduce the peak temperatures thereby reducing the possibility of formation of DEF. So this study consolidates and shows the importance of using Fly Ash as secondary cementitious material improving the various parameters of concrete such as imperviousness, durability including the thermal characteristics of concrete.