Whenever alkali-reactive aggregates are encountered, it has been customary to use cement of low alkali content-the limit being 0.6% Na2O eq. As elsewhere in the world, availability of low-alkali ordinary Portlant cement in India has been somewhat limited. Figure 11.18 indicates that the average level of alkalis in cements in India has increased during the […]

From Table 11.3, it can be seen that, except for aggregates 1 and 4 (Table 11.2), the maximum expansion with 1.00% alkali cement at 38°C was generally within the limit of 0.05% at 3 months that is stipulated for reactive aggregates. The rapid chemical tests also failed to indicate the potential reactivity of these aggregates […]

From the foregoing, it would transpire that most of the reactive aggregates in India are those containing strained quartz as the reactive component. In addition, reactivity of granitic rock aggregates is also partly due to the presence of alkali feldspar, which can undergo alterations as a result of the action of hydrothermic solution and the […]

The presence of secondary silica minerals had been known to be responsible for the reactivity of common aggregates for 40 years or more, and the first comprehensive assessment of certain Indian aggregates was made from this chemical point of view19. Accordingly, the following common rock types were identified as potentially reactive on the basis of […]

In view of the vast size of the country and the wide variations in the geomorphological characteristics of natural rocks from one location to another, any generalisation as to the reactivity of Indian aggregates could be misleading. A broad classification of the common rock types used as natural aggregates for concrete in different parts of […]

Long-term observations on concrete core samples immersed in KOH solution at different temperatures indicated that the expansion potential of the concretes was not yet exhausted14. The repair techniques, therefore, had to take into account the present state of distress as well as possible aggravation in future. Analyses of stability against overturning as well as sliding […]

The general description of the microstructure of reaction products as observed by SEM has been mentioned already. Since these were the first reported cases of ASR in India, detailed examination of the reaction products was undertaken in order to compare them with the features reported in the literature6715. A composite gel sample was made in […]

The concrete gravity dam and adjacent powerhouse of this hydroelectric project, 25 years after their construction, showed extensive distress, which was attributed to ASR4. External manifestations included cracking of concrete, misalignment of machinery and difficulties in the operation of gates, cranes and passenger lifts as a result of movements in concrete. In the powerhouse, the […]

The first investigation relates to a concrete spillway in one of the longest earth dams in the world. The structure at the time of investigation was nearly 27 years old. It had suffered extensive cracking, mostly in the walls of openings like galleries, shafts and adits. Typical ‘map’ cracking was superimposed with longitudinal horizontal cracks. […]

Some of the earliest references to the occurrence of ASR in concrete structures in India were made in 19622; however, few details were documented. The first reported cases of distress in a concrete spillway and a concrete gravity dam and the powerhouse structure can be found in Refs. 3 and 4 along with details of […]