The alkali-aggregate reaction in concrete involves natural siliceous minerals in aggregates reacting with alkaline hydroxides derived from cement alkalis. This reaction forms an alkali-silica gel that absorbs water, swells, and increases in volume, which is confined by the surrounding cement paste, creating internal pressures that crack and disrupt the concrete. The extent of expansion and damage can be partly attributed to the alkali-silica reaction's osmotic hydraulic pressure and the swelling pressure of the solid products formed.
The rate of reaction is influenced by the size of the siliceous particles; finer particles may cause expansion in a matter of weeks, whereas larger particles could take years to manifest similar damage. Factors such as the porosity of the aggregates, the alkali content of the cement, the amount of water in the paste, and the permeability of the cement paste all affect the progression of this reaction. This reaction typically occurs on the surface of concrete under continuous moisture or during wetting and drying cycles, especially at temperatures between 50 and 100 degrees Fahrenheit. To mitigate these reactions, it is advisable to use low-alkali cement, incorporate a pozzolan, and use at least 30 percent limestone coarse aggregate by mass in the concrete mix.
Aggregates naturally contain siliceous minerals that react with the alkaline hydroxides from cement alkalis.
The alkali-silica gel formed attracts water and swells, which is constrained by the cement paste around it, leading to internal pressure, causing the cement paste to crack and disrupt, evidenced by expansion.
Expansion is partly due to the alkali-silica reaction's osmotic hydraulic pressure and swelling pressure of solid products.
The size of the siliceous particles influences the reaction rate, with fine particles causing expansion in weeks, while larger ones may take years to cause damage.
The progression of the alkali-aggregate reaction is affected by factors like aggregate porosity, cement alkali content, water in the paste, and cement paste permeability.
This reaction occurs mainly on concrete's surface under continuous moisture or during wetting and drying cycles, particularly at temperatures between 50 and 100 degrees Fahrenheit.
If avoiding harmful cement-aggregate combinations is difficult, incorporating a pozzolan and at least 30 percent limestone coarse aggregate by mass is advisable. Using low-alkali cement also helps reduce the alkali aggregate reactions.
繁體中文
