Research On Ettringite Growth Characteristics In Modern Concrete

The hydrated calcium aluminium, ettringite(AFt), one of the primary hydration product of Portland cement, accounts for most of expansive properties of cement-based composite materials. Research on the composition and structure of AFt have an important role in understanding, regulating and controlling the mechanical properties and the volume stability of cement-based composite materials. This paper carried out a systematic study, which focused on the synthesis of AFt, its composition, structure and morphology, dehydration and hydration properties with major work and achieved important results as follows:Several series single-phase AFt samples were prepared by different methods-solid-state reaction of Al2(SO4)3·18H2O and Ca(OH)2, solution reaction of Al2(SO4)3·18H2O and Ca(OH)2, mineral hydration reaction of 3CaO·Al2O3 and CaSO4·2H2O. The AFt samples in actual cement hydration system were prepared through Portland cement hydration, Sulphoaluminate hydration,ordinary portland cement+12% expansion agent hydration. Effect of synthesis methods, temperature, curing age, water cement ratio (W/C) on the structure and morphology of AFt was investigated by the techniques of X-ray diffraction (XRD), Infrared spectrum (IR), Raman spectrum (Raman), Scanning electron microscope (SEM).Microstructures (including the d-space, unit cell parameters and others) of AFt were studied by XRD, IR and Raman, and results indicated that prepared methods effected the structure of AFt. The prepared method with solution reaction of Al2(SO4)3·18H2O and Ca(OH)2 effects the structure of AFt mostly; while the improvement of temperature promoted the formation of ettringite. The change of water-cement ratio does not affect the type of hydration products in cement hydration system, and increasing the water-cement ratio proposed the hydration process and the generation of AFt. The AFt has generated when the hydration time is 1d for sulphoaluminate cement; with the hydration period extended to 3d, the hydration reaction rapidly increased; and the characteristic peak of AFt no significant change in strength for 7d; 28d when the AFt characteristic diffraction peaks decreased compared to 7d. Morphology of AFt was studied through the techniques of SEM. Morphology of AFt depends on the composition, synthesis method and temperature, curing age, and water-cement ratio. There exists several types of AFt in SEM micrograph, such as group bunch of pellet, curl thin laminated shape, stubby needle clavate as well as staggered tall and slender needle clavate.The thermal stability and rehydration capacity of AFt were researched by XRD, TG, IR, and Raman, and founded that the crystal structure of AFt changed under 80℃heated for 9h. In addition, the crystal lattice parameters a0 of AFt increased and co decreases in the process of dehydration. The X-ray diffraction patterns obtained a good recovery at 100℃and 150℃in the dry AFt autoclaved water conservation at room temperature.