Optimizing the Sulphates Content of Cemen tUsing Multivariable Modelling and Uncertainty Analysis
This study aims at determining the effect of the cement composition and mortar age on the optimum content of sulphates using maximization of compressive strength as a criterion. Extensive experimentation has been performed to achieve this purpose by utilizing four cement types and measuring the strength at ages ranging from 2 days up to 63 months. Strength is correlated with the ratio of sulphates to clinker content, SO3/CL and moles SO3/ moles C3A. A generalized model correlating SO3, cement composition and curing time is developed, intensely indicating the necessity of placing the SO3 target within the optimum region and realizing it as well. The set of four equations involves polynomial and logarithmic equations correlating the variables. A variance analysis based on error propagation technique, proves that SO3 affects not only average value of strength but also its variability.
Effects of sulfates on the hydration of Portland cement – A review
Abstract Presented within is a critical overview of the effect of sulfates on cement hydration, properties, and optimum sulfate content in Portland cement. Calcium sulfate is used in Portland cement to control the C3A reaction to induce the optimum hydration of C3S to occur. The amount of calcium sulfate in the Portland cement influences the hydration, rheology, setting, phase assemblage, porosity distribution, and strength in cementitious materials. If added in excess, it can also lead to durability problems, thus a better understanding is needed about the mechanisms of sulfate on C3A and C3S hydration. The optimum sulfate content is well known as a key pathway to produce workable, good strength, and durable concretes. Despite many years of research, questions regarding sulfate optimization remain. Further investigation on the influence of clinker and calcium sulfate characteristics, the use of different supplementary cementitious materials and chemical admixtures, and the curing conditions on the sulfate demand of Portland cement are needed. The main methods used to determine the optimum SO3 content are reported, and the advantages and disadvantages are examined. Finally, recommendation for future research is also discussed.
The peculiar thermo-structural behavior of the anionic lipid DMPG.
Aqueous dispersions of the anionic phospholipid dimyristoyl phosphatidylglycerol (DMPG), around 100 mM ionic strength, are known to exhibit a thermal behavior similar to that of the largely studied lipid dimyristoyl phosphatidylcholine (DMPC), which undergoes a gel to liquid crystalline phase transition at 23 degrees C, well characterized by differential scanning calorimetry (DSC), and other methods. However, at low ionic strength, DMPG has been shown to present a large gel-fluid transition region, ranging from 18 to 35 degrees C. This intermediate phase is optically transparent and characterized by a continuous change in membrane packing. Structural properties of the DMPG gel-fluid transition region will be discussed, based on results obtained by several techniques: electron spin resonance (ESR) of spin labels at the membrane surface and intercalated at different depths in the bilayer; light scattering; DSC; small angle X-ray scattering (SAXS); and fluorescence spectroscopy of probes in the bilayer.