What is the alkaline reactivity of aggregates?

Alkaline reactivity of aggregates is a complex phenomenon both in chemical terms and due to many different mineralogical factors and operating conditions affecting its occurrence. The use of reactive aggregates in concrete in unfavorable conditions (e.g. presence of moisture) may lead to ASR (Alkali-Silica Reaction) or ACR (Alkali-Carbonate Reaction) reactions, which result in the destruction of concrete. This destructive process is a serious threat to many buildings, as well as road surfaces and bridge elements

Alkaline reactivity of aggregates - what is this phenomenon?

Alkaline reactivity is susceptibility of certain types of aggregates to reactions with alkalis in concretes. Alkalis are most often introduced into concrete with cement. As already mentioned, many factors influence the occurrence and course of this phenomenon. There are three basic alkaline reactions:

  • reaction between amorphous silica (a component of aggregates) and alkali - the most common;
  • reaction between alkalis and carbonates (mainly in the case of aggregates from carbonate rocks - limestones and dolomites);
  • reaction between alkalis and poorly crystallized forms of silicates.

Alkaline reactions leading to the destruction of concrete can contribute to serious consequences, especially in the case of buildings used by people or constituting an important element in the construction infrastructure. This phenomenon is even more dangerous in the absence of proper technical supervision over concrete objects.

The course of the reactions taking place is slow. Zwykle potrzeba nawet kilku lat, aby rozpoznać, czy do zniszczeń doszło w wyniku reakcji z alkaliami, czy też w wyniku innych procesów destrukcyjnych. Z tego też powodu istotne znaczenie mają badania reaktywności alkalicznej kruszyw.

Tests of alkaline reactivity of aggregates

Aggregate testing in terms of their alkaline reactivity are carried out by various methods. Among the ways to assess alkaline reactivity, the following methods are distinguished:

  • direct, which consist in measuring the expansion of concrete or mortar samples,
  • chemicals, including on leaching alkalis from concrete,
  • petrography, which are aimed at identifying potentially reactive minerals and aggregate-alkali reaction products.

Our company provides services in the field of alkaline reactivity testing of aggregates, offering full service through accredited sampling according to PN-EN 932-1:1999. We perform tests in accordance with the guidelines of the PN-EN 12620 standard - Aggregates for concrete.

The FERROCARBO laboratory is accredited for testing alkaline reactivity using trabecular methods according to the procedures of the General Directorate for National Roads and Motorways PB/1/18 and PB/2/18. We also test the alkaline reactivity of aggregates (alkali-silica ASR and alkali-carbonates ACR). We also carry out accredited reactivity tests according to PN B-06714/46:1992 and ASTM C1260-21 standards. In order to provide comprehensive customer service, we have also implemented reactivity tests according to PN-B-06714-34:1991/AZ1:1997 and ASTM C1293-20 standards (non-accredited methods).