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.
Influence of the SO3 Content of Cement on the Durability and Strength of Concrete Exposed to Sodium Sulfate Environment
The objective of this investigation was to assess the influence of the SO3 content on the durability and strength of portland cement. Four portland cements were used in this study. The cements had a variable tricalcium silicate, tricalcium aluminate, and alkali contents, as well as differences in the amount and form of calcium sulfates. The SO3 content of the cements was increased by replacing part of the cement by gypsum according to ASTM C 452-95. Mortar bars and cubes were prepared for the as-received as well as for the cements with an SO3 content of 3.0% and 3.6%. The durability of the as-received and doped cements was determined by measuring the length change of the mortar bars that were exposed to sodium sulfate environment. The compressive strength of the mortar cubes prepared for the same mixes was measured at different ages for sets of cubes cured both in sodium sulfate solution and in saturated lime solution. It was concluded at the end of this study that there is an optimum SO3 content for the lowest expansion that is different from that determined for the highest compressive strength. Optimum values also differed from one cement to another and from one age to
The deterioration of mortar in sulphate environments
Abstract The skin of concrete plays an important role in the durability of cementitious materials. In a sulphate environment this surface reaction can cause deterioration or in some cases protection. Surface properties of mortars, which are exposed to sulphate environments, have been studied using SEM, microanalysis, X-ray diffraction and Vickers’ hardness testing. When cement mortar is exposed to sulphuric acid a dense layer of gypsum is formed; this is capable of retarding the deterioration process by acting as a surface sealing layer. Gypsum also exists in pores and fissures in the surface zone, indicating that the attack is due to expansive crystallisation. In ammonium sulphate the surface deposit of gypsum is sparse and the damage to the concrete occurs to a greater depth. The lack of sulphur found in the surface zone indicates that the mechanism of deterioration is due to the dissolution of Ca 2+ .