ICE - Institution of Civil Engineers - Virtual Library

The results of a study on creep of D-dried hydrated C₃S paste after exchange of water in saturated samples with organic solvent are presented. Length and mass changes were also measured when saturated C₃S paste prepared at a water-solid ratio of 0·4 was immersed in both methanol and isopropanol. A differential thermogravimetric technique was used in order to determine the effect of solvent treatment on dehydration of C₃S paste, and its correlation with pore structure, modulus of elasticity and microhardness. Methanol and isopropanol exchanges prior to drying reduce the magnitude of creep in the dry state, suggesting an irreversible interaction of solvent with C-S-H.

The influence of microsilica, ground granulated blast-furnace slag (ggbs) and a set-retarding superplasticiser on the setting of pastes at different curing temperatures was studied. The replacement level of ordinary Portland cement (OPC) by microsilica was 10%. Replacement levels of OPC by ggbs were 30, 50 and 70%. In addition to this, three different sources of ggbs from three countries were tested. Ambient temperatures of 25, 35 and 50°C were simulated. The results show that at 25°C, microsilica retarded setting only slightly whereas the ggbs and the set-retarding superplasticiser resulted in significant retardation. At the other two curing temperatures, the retardation effects of the ggbs and the superplasticiser diminished.

This paper describes a method of producing compacts from cement mixes with extremely low water-cement ratios by isostatic compaction. The main advantage of this procedure is the fact that such compacts exhibit a greater uniformity in the degree of compaction than those produced by unidirectional pressing. The resultant strength increases with increasing pressure of compaction and is higher if high-strength, rather than ordinary Portland cement, is used as a starting material. The strength also increases if silica fume or natural wollastonite with acicular crystal morphology is added to the starting mix

Unlike blast-furnace slags, steel-making slag is not a normal admixture for Portland cement. However, recent work has suggested that by adjusting the chemistry and the cooling rate to generate a substantial glassy phase, the potential for hydration and strength development for the granulated product is enhanced. In order to better understand the role of glassy phases in the hydration process, isothermal calorimetry was used to determine the heat release and the rate of hydration within the 25–70°C range. Synthetic slags, of varying glass:crystal ratios, were used along with Portland cement as a reference. The reactivity of the synthetic slags was found to increase with glassy content which is in agreement with the lower activation energies calculated for these slags. Activation energies for slags were found to be greater than for Portland cement.

The overall aim of this paper is to establish the engineering properties and material durability of Portland limestone cements, particularly when they are exposed continually to an environment rich in magnesium sulphate ions, and conducive to thaumasite formation. In particular, non-destructive and destructive tests were used to identify and examine the interaction of the changes in mechanical properties with the onset of sulphate attack. To achieve these objectives, 40 × 40 × 160 mm mortar specimens were subjected to air curing at 5°C and 20°C, and also immersed in 1·8% MgSO₄ solution, again at 5°C and 20°C. The limestone content in the test specimens was kept at 0%, 5%, 15% and 35% replacement of cement by mass. The formation of thaumasite was checked and confirmed by x-ray diffraction supported by thermal analysis and scanning electron microscopy. The non-destructive tests used in the study included pulse velocity, dynamic modulus, shrinkage, expansion and changes in mass. In addition, flexural and compressive strengths were determined. All the tests were carried out up to one year. The results obtained from the tests have then been critically analysed. It is shown that mortar prisms containing 35% limestone and exposed to magnesium sulphate solution at 5°C suffered extensive damage and deterioration within one year. In addition, prisms containing 15% limestone gave strong signs of impending damage due to sulphate attack. The results of the non-destructive and destructive tests were highly complementary, and confirmed each other. The major mechanical deterioration occurred through the loss of compressive strength of almost 75% of that of the original unaffected mortar, whilst the loss in flexural strength was relatively small. The results strongly indicate that compression members, containing 35% limestone and exposed to aggressive sulphate environment at temperatures of about 5°C, can be seriously at risk in their ability to carry loads. On the other hand, it is unlikely that flexural members under these conditions would suffer the same degree of serious structural damage.