The alkali–silica reaction in concrete is normally associated with alkalis from cement. However, some aggregates have alkalis in their crystalline or amorphous phases that can be released during long-term exposure to the water in concrete structures. Previous research has demonstrated that alkaline feldspars in aggregates can supply a significant amount of alkalis when exposed to alkaline solutions. Other research indicates that micas can release alkalis and promote alkali–silicate reaction. The main problem is the evaluation of the potential contribution of the alkalis released by aggregates during the service life of a concrete structure. This paper describes accelerated tests that can determine the level of alkalis released from aggregates, but finds that the results are not representative of the long-term behaviour of concrete structures. Alternative tests are being developed, but these could take much longer, and it is concluded that numerical methods may be the most practical solution.
The increased use of industrial wastes and by-products to produce concretes and blended cements is a lever to achieve carbon neutrality. Furthermore, they could improve their durability. Some pozzolanic additions can minimize the alkali-silica reaction (ASR), which is a well-known deleterious process that occurs between some reactive aggregates and the alkaline pore solution found in mortars and concretes. This work quantifies the efficiency of four pozzolanic materials (natural pozzolan, P, siliceous coal fly ash, V, silica fume, D, and blast-furnace slag, S) assessed by means of compressive strength testing, open porosity, ASR-expansion measurements, and SEM microscopy. Accelerated expansion tests were performed in mortar bars with a cement/sand ratio of 1/2.25 and a water/cement ratio of 0.47, two reactive aggregates and a non-reactive one. The major contributions of this paper are: (i) The more aggregate reactivity is, the higher ASR mitigation level was found when additions were added and (ii) The best additions for ASR inhibition are silica fume and fly ash.
The alkali-silica reaction has been studied in depth due to the evolution in the knowledge of the expansive phenomenon. One of its most important aspects is the reaction rate of the aggregates. In Spain, at the early 90s of the 20th century, aggregates were considered almost non-reactive. However, the use of accelerated curing and other environmental factors revealed that there were potentially reactive siliceous aggregates. Nevertheless, there are several siliceous and limestone aggregates with siliceous inclusions that show reactivity over long period. In the present work, open porosity, expansion and petrography with quartz reactivity index have been determined, in 68 siliceous, limestone and dolomitic aggregates, from quarries located in areas with diagnostic reactivity. Based on these parameters and their interrelation, a classification method is proposed to detect slow-reacting aggregates.
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