engleski

Kinetics of cement hydration with replacement addition of fly ash into aqueous suspension systems

Fly ash is a waste material formed by combustion in coal fired thermal power plants. It is usually used as a replacement material for cement in the cement industry, in this way is solved the environmental problem of waste disposal, are reduced CO2 emissions from cement production, protected natural resources and reduced the production cost of cement. In this paper is presented the influence of the addition of fly ash (from the Thermal power plant Plomin2, HEP) as replacement material on the kinetics in the early phase of cement hydration (type CEM IIA-S 42.5 N). Hydration was carried out in isothermal conditions (20 ± 1 ° C) and till 72 hours of hydration in aqueous suspensions with and without the addition of fly ash in the amount of 5 and 10 wt.%. Aqueous suspensions were prepared with weight ratio of w/s=4 (water/solid (solid = cement + fly ash)). Hydration in aqueous suspensions was stopped in specific times after 30 min., 1, 3, 5, 7, 9, 11, 15, 17, 20, 24, 48 and 72 hours. The content of hydration produced portlandite (Ca(OH)2) was determined by using thermal methods (TG / DTG-DTA). The results of mathematical modelling of hydration indicate that an increasing replacement addition of fly ash increases the hydration degree of cement. The observed change is a direct consequence of extending the duration of hydration in which the slowest processes that determine the speed of the reactions are the processes of nucleation and growth and interaction at boundary interfaces.

fly ash; cement; portlandite; hydration; kinetics; TG/DTG

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