Reaction alkali-aggregate

The reactions alkali-aggregate constitute a family of reactions in the Béton between the alkaline ions contained in the Pore S of the Ciment and the Granulat S.

They lead to the attack of the aggrégats and with the formation of gels Hydrophile S. This attack results by a reduction in the mechanical properties of the concrete (resistance to the Compression, with the Flection, modification of the Modulus Young) and in a characteristic swelling.

This reaction occurs only if three conditions are met:

the aggregates are reactive,
there are suffisemment the alkaline ones,
there is suffisemment water to allow the migration of ion.

Types of Reactions alkali-aggregate

Alkali-silica

The aggregates, primarily made up of Silice are sometimes vulnerable there: silica badly crystallized is most liable to deterioration and reacts with the alkaline ions of the intersticielle solution of the pores of cement. The kinetics of the attack is managed by a whole of parameters such as the pH, the concentration of alkaline (in particular), the quality of the structure of the SiO2 aggregate…

The bridges Silanol S If-OH structure graulaire are destroyed and of the Siloxane S - If-O-Na-OH or - If-O-K-OH are created. This new compound is a strongly absorbent gel which inflates in the presence of water. The products which one names " gels" CKSH and HSC in the jargon cement-manufacturer are also called. It is about hydrated phase made up of potassium and/or calcium, silicon.

Alkali-carbonate

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