Temperature effect on the pore solution chemistry in contaminated cements

The combined effect of chloride and sulphate contamination and temperature on the pore solution chemistry, particularly the OH, Cl and SO42 concentration, in plain and blended cements was evaluated. The cement mortar specimens were contaminated with sodium chloride and sodium chloride plus sodium sulphate and exposed to temperatures in the range 25 to 70°C. Results indicate that the chloride binding capacity of cement is affected by both the temperature and the sulphate contamination. In the chloride contaminated specimens, the chloride binding was influenced by the exposure temperature, while in those contaminated with sodium chloride plus sodium sulphate, it was affected by the presence of sulphate ions. The sulphare concentration in the plain and blended cements was also influenced by the exposure temperature and chloride contamination. The Cl/OH values increased with temperature in both plain and blended cements, indicating the vulnerability to accelerated steel depassivation in concyete exposed to elevated temperature and contaminated with chloride and sulphute ions. </jats:p

A photoelastic investigation of anchorage bearing stresses

Synopsis This investigation focuses on a number of features which have hitherto been less researched but which have been found to be critical in the behaviour and failure mechanism of anchorage zones. These include the mode of load transfer, the proximity of the anchorage unit to the surface plane and the critical role of the high sub-surface shear in the immediate vicinity of the anchorage unit. The results show the significant advantages of the embedded anchorage over the corresponding external unit and the critical dependence of the surface stresses upon the proximity of the anchorage unit. In a typical multi-anchorage end-block. the behaviour of adjacent units is found to be sensibly independent. </jats:p

Influence of chloride ions on sulphate deterioration in plain and blended cements

This investigation was carried out to elucidate the role of chloride ions in sulphate attack in plain and blended cements. Paste and mortar specimens made with Type I and Type I cements as well as with Type I cement blended with fly ash, silica fume and blastfurnace slag (BFS) were exposed to four sulphate and/or chloride environments for a period of two years. The performance of these cements was evaluated through visual inspection and measurement of reduction in compressive strength. X-ray diffraction and scanning electron microscopic techniques were used to study the sulphate attack mechanisms in plain and blended cements in both the presence and the absence of chloride ions. Results indicate that sulphate deterioration in plain cements was mitigated by the presence of chloride ions, whereas in blended cements, particularly those made with silica fume and BFS, the beneficial effect of chloride was only marginal. This is attributed to the Mg-oriented sulphate attack which was more operative in blended cements. In contrast to the gypsum and ettringite-oriented sulphate attacks, this type of attack was not inhibited in the presence of chloride ions. </jats:p