Investigation of the hydration process in 3CaO·Al 2O 3–CaSO 4 · 2H 2O–plasticizer–H 2O systems by X-ray diffraction

Abstract

The development of the hydration process in 3CaO·Al 2O 3–CaSO 4 · 2H 2O–H 2O system is studied by X-ray diffraction in the presence of varying contents of new plasticizer admixtures belonging to the lignosulphonates class (calcium lignosuphonate-LSC) and condensates melamine formaldehyde sulfonated class-MSF (VIMC-11). The plasticizer admixtures were added in proportion of 0.1–1% solid substance. The influence of the plasticizer admixtures on the hydration process with increasing time is observed and it is shown to depend on the nature and content of the admixtures and the reaction time. The strong adsorption of admixtures on the surfaces on the anhydrous or partially hydrated particles of the system can explain the influence of the admixtures upon the kinetics of the hydration process retardation or acceleration. These plasticizer admixtures influence also the evolution of the hydrated compounds and forming of the hardening structure in the 3CaO·Al 2O 3–CaSO 4 · 2H 2O–H 2O system; their proportion in the system and the considered length of hardening are correlated. In the 3CaO·Al 2O 3–CaSO 4 · 2H 2O–H 2O system there are two different influences of the plasticizer admixtures upon the hydration process. One is a delaying action, as a result of plasticizer adsorption on the surface of the anhydrous and hydrated compound particles and another one is the intensifying action due to the stronger dispersion of the particles in aqueous medium.