Description:

Surfactant admixture to entrain micro air bubbles in concrete exposed to freeze/thaw cycles.

Technical Characteristics :

The main technological characteristics of cementitious mixes with aerating agents are as follows:
resistance to freeze-thaw cycles;
better pumping properties for lean concrete with a low fine sand content;
lower segregation in concrete made from lightweight aggregates.
Mortar and concrete do not have the capacity to resist to cyclic stresses deriving from alternating freeze/thaw cycles. In
fact, the formation of ice, which leads to an increase in volume (approximately 9%), provokes high stresses in mortar and concrete saturated with water or exposed to rainwater (open-air car parks, airport runways, tunnels, etc). In these cases,
the most efficient form of prevention to contrast fatigue failure due to freeze/thaw cycles is to absorb a small volume of air (3-6%) in the form of stable micro bubbles with a diameter of between 100 and 300 µm and at an even pitch of between 100 and 300 µm: in such conditions, when the first ice crystals form, the increase in volume deriving from them pushes the water in liquid form which has not yet frozen into the adjacent micro bubbles to ease the internal stresses. In the phase after thawing, the capillary suction effect causes the water to be released by the micro bubbles and to flow towards the pores in the surrounding cementitious mix. This movement leaves the micro bubbles empty and ready to host water in the freezing state again the next time the natural thermal cycle comes around. As well as helping to reduce the effect of the stresses caused by the formation of ice, unfortunately the absorbed micro air
bubbles reduce the strength of the concrete by about 20%. Therefore, the water/cement ratio must be reduced to increase the strength of the concrete to compensate for this reduction due to air bubbles being absorbed.
For this reason, the use of Mapeair AE 20 in concrete resistant to freeze/thaw cycles must always be accompanied by the use of a super-plasticising agent (Dynamon or Chronos) according to the performance characteristics required.
Thanks to the development of deformable, spherical micro air bubbles, Mapeair AE 20 compensates for the lack of finegrained material in the sand (100-300 µm) which is indispensable for pumping purposes, especially in the case of lean
concrete with a low cement content. Also, by absorbing air in concrete made using expanded clay or polystyrene, there is a reduction in the tendency of the aggregates to “float” (segregation) due to the lower difference between the density of
the aggregates and the cementitious mix, which is also lightened. As a result, the conglomerate is more homogenous and, therefore, the thermo-insulating characteristics are also more uniform.