Admixtures for road construction are preferably used for production of concrete mixes of enhanced frost resistance and water impermeability.
These admixtures are classified as air-entraining agents and plasticizers and refer to the category of surfactants.
The class of air-entraining admixtures was discovered by chance in the late 30-s, when it was discovered that road slabs produced in New-York state and containing some types of cement turned out to be more frost resistant and watertight compared to concrete slabs containing other cements. The analysis showed, that in the course of cement grinding, substances containing fish and animal fats and calcium stearate were added producing air-entraining action. Since that time, air entrainment has become a significant factor in increasing the frost resistance of concrete under cyclic freezing and thawing.
Molecules of admixtures are adsorbed at the air-water interface, while the surface tension of water decreases significantly and micro foam occurs, with a large number of tiny air bubbles trapped between thin layers of liquid. Thus, the volume of cement paste in concrete mix increases to 6-8%. Since the rheological and technological properties of concrete mix mainly depend on the volume of cement paste and its viscosity, the fluidity of concrete mix increases, and most significantly in mixes with relatively low cement consumption ratio.
However, these admixtures somewhat reduce the strength of concrete (1% of entrained air reduces the compressive strength of concrete by 3%), therefore, it is not necessary to introduce a large amount of air-entraining agent into concrete for the purposes of its plasticizing. In case the content of entrained air is 4 … 5%, the strength of concrete practically does not decrease, since the negative effect of the entrained air is neutralized by increase of cement stone strength because of water-cement ratio decrease due to plasticizing effect of the admixture. The air-entraining admixture makes pores and capillaries of concrete water-repellent, and air bubbles serve as a reserve volume for water freezing without causing large internal stresses. This results in significant increase of concrete water and frost resistance.
MasterAir 114 — additive that increases the air content of the concrete mix for concrete with high grade for frost based…
MasterAir 125 — Additive based on an aqueous solution of surfactants, increasing the air content of the concrete mix, for concrete…