Heat of Hydration and Characterization of Reaction Products of Adiabatically Cured Fly Ash and Slag Mixtures
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HEAT OF HYDRATION AND CHARACTERIZATION OF REACTION PRODUCTS OF ADIABATICALLY CURED FLY ASH AND SLAG MIXTURES S. KAUSHAL,* D.M. ROY and P.H. LICASTRO Materials Research Laboratory, The Pennsylvania State University,
University Park, Pennsylvania 16802 Received 5 January,1988; refereed
ABSTRACT The hydration of cementitious materials is an exothermic process which results in significant temperature increases in large masses of these materials. The thermal environment under these conditions is nearly adiabatic. The heat of hydration of cementitious aluminosilicate blend materials incorporating fly ash and granulated blast-furnace slag was calculated from the adiabatic temperature rise. Additional reaction of siliceous fly ash with alkaline solutions results in the formation of zeolitic reaction products. Studies were carried out to characterize the hydration products by X-ray diffraction and through analysis of solutions. In addition, zeolitic reaction products were prepared by reacting the pure Class F fly ash at 90 0 C with NaOH and different anions. This study has implications for general thermal properties of hydrating cementitious materials, and for costeffective immobilization of radioactive and chemical waste cations and anions. INTRODUCTION The hydration of cementitious materials is the result of a series of complex exothermic chemical reactions. As a result of these hydraulic reactions, the temperature of a cementitious monolith increases significantly within hours to days [1]. Similarly, large temperature increases have been predicted as well as reported in complex blended cements [2-4]. Studies have predicted the development of temperatures as high as 100 0C in cementitious materials in large monoliths. The temperature reached in the material depends not only on the material itself, but also on the thermal conductivity and diffusivity of the hydrating and the surrounding media. It is governed by the heat of hydration of the cementitious material and the boundary conditions. Studies that have been undertaken to predict the temperature rise due to the exothermic nature of cement hydration have typically input isothermal data, which is an inherent shortcoming when simulating a massive structure. Accurate prediction of temperature rise is desirable in view of concern about thermal cracking due to the large temperature differentials between the interior and exterior of concrete bodies [5]. Prediction of temperature differentials between interior and surroundings is also believed to be important in other applications such as in highway uses [6]. The objectives of this study, therefore, were (a) to investigate the thermal properties of Portland cement and blended cements to determine the effect of these characteristics (heat of hydration, thermal conductivity and diffusivity) on: the temperature rise in large monoliths, and the strength, microstructure and phase changes in these materials; and (b) to suggest conditions under which such aluminosilicate blends would be suitable for mass emplacement. The general hy
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