residuaalkaitselülititeks

Residual Alkali-Silica Reaction (RASR) is a type of concrete deterioration that occurs over time, typically after the initial curing period. It is a form of alkali-silica reaction (ASR), where the alkali hydroxides in the cement react with the silica in certain aggregates, forming a gel that expands and causes cracking and other forms of damage. Residual alkali-silica reaction refers to the continued expansion and damage that occurs after the initial reaction has been mitigated or controlled.

The primary cause of RASR is the presence of reactive silica in the aggregates used in concrete. This silica can be in the form of opal, chalcedony, or other forms of amorphous silica. The alkali hydroxides in the cement, primarily from the portlandite (Ca(OH)2) formed during hydration, react with the silica to form a gel. This gel absorbs water and expands, exerting pressure on the surrounding concrete and causing cracks and other forms of damage.

RASR can occur in concrete that has been previously treated to mitigate ASR, such as through the use of low-alkali cement or the addition of lithium compounds. However, the residual alkali hydroxides and the reactive silica can still react, leading to continued expansion and damage. The rate of expansion and the extent of damage can vary depending on factors such as the type and amount of reactive silica, the alkali content of the cement, and the moisture conditions in the concrete.

The diagnosis of RASR typically involves visual inspection, petrographic examination, and chemical analysis. Treatment options for RASR may include further mitigation of the alkali content, the use of lithium compounds, or the application of external pressure to counteract the expansion. However, the effectiveness of these treatments can be limited, and in some cases, the damage may be irreversible. Therefore, it is important to consider the potential for RASR during the design and construction of concrete structures.