1960 Volume 68 Issue 780 Pages 307-318
In order to investigate the hydration product of blast furnace slag under the coexistence of stimulating agents such as Ca(OH)2, Ca(OH)2 and CaSO4, Ca(OH)2 and CaSO3⋅1/2H2O the slag and synthetic gehlenite were subjected to hydration during a month, and the reaction products appeared were studied using several methods.
(A) Both in blast furnace slag and gehlenite the hydration products, 2CaO⋅SiO2⋅H2O, 3CaO⋅Al2O3 8-12H2O, 4CaO⋅Al2O3⋅13H2O, 3CaO⋅Al2O3⋅CaSO3⋅7H2O, etc., the same compounds in the hydration of portland cement, were confirmed by X-ray analysis.
(B) Using quantitative X-ray analysis and the measurement of ignition loss the rate of chemical reaction was estimated. It was found that the hydration of slag came to only 20% after 28 days, while gehlenite was so active that 50-60% hydration was observed after 3 hours.
(C) The differential thermal analysis of hydrated gehlenite showed the increase of the amount of heat absorption at 100-200°C along with the progress of hydration, which indicates the formation of the hydrates losing water at lower temperatures.
(D) Slag and gehlenite were remelted and quenched to form disks of 3/4″ in diameter. The disks were polished to mirror surface in order to observe the change of appearance during the hydration under electron microscope. In the initial stage the hydration products crystallized out leaving the mirror surface unchanged. After 3 days in slag, and 5 hours in gehlenite the film of the hydration products separated out on the surface with the appearance of silk crape or fish scale. The authors consider that these film takes part in the increase of adhesive strength.
(E) Suspension of slag powder in solution containing stimulating agents showed the increase with time of sedimentation volume, the trend becomming more remarkable with increasing basicity. Based on this fact the authors have worked out a new method of estimating the hydrauric property of blast furnace slag.
