Modern cement-based waterproofings for hydraulic structures protection

Abstract

Hydrotechnical structures of water management and land reclamation complex from the moment of commissioning are subject to aggressive environmental effects: hydrostatic water pressure, alternating freezing and thawing, moistening and drying, corrosive action of salts dissolved in water, dynamic action of ice. The trouble-free operation of structures with long-term aggressive environmental factors is possible only in the case of providing their protection (reinforcement) with effective insulating, anticorrosive, high-strength, wear-resistant and cavitation-resistant composite materials.

Waterproofing coatings, which arrange on the surface of reinforced concrete structures, plays an important role in ensuring operational reliability and durability of hydraulic structures. Having rather low cost of waterproofing coatings as compared to the cost of structures the fate of their responsibility in terms of ensuring the durability and operational reliability of the structures is high enough. Waterproofing coatings serve as a barrier to an aggressive environment and thus protect structures from destruction.

Notwithstanding the importance of waterproofing protection, this issue is not given due attention today. Therefore, filtration of water through the structures of water-reclamation facilities is a common phenomenon. Water filtration through damaged concrete of hydraulic structures causes dissolution and leaching of water with calcium hydroxide (leaching), which further causes the decomposition of other components of the cement stone and leads to the dilution of the concrete structure and to the strengthening of drip filtration. Drip filtration increases over time, then jet filtration develops, which can lead to complete destruction of the structure. Therefore, providing waterproofing protection of structures is an important engineering task in their construction and operation.

One of the determining factors for the effectiveness of waterproofing is the right selection of material. Traditional waterproofing materials on a bituminous basis have insufficient physical-mechanical properties and durability. However, modern technologies of waterproofing protection of concrete and reinforced concrete structures are based on the use of effective composite materials with high physical, mechanical and protective properties. Depending on the type of binder, waterproofing materials can be based on bitumen, bituminous-mineral, bitumen-polymer, coal, polymer compositions, as well as on the basis of cements and polymer cements.

The selection of a waterproofing material should be made taking into account the specifics of the operating environment and the conditions of use. The most common in the construction of gluing roll materials on a bituminous basis can only partially satisfy the need for hydraulic engineering, as for the waterproofing of hydraulic structures. There are high requirements with regard to the aggressiveness of the environment and their low repairsability.

The most promising for use in the technology of arrangement of waterproofing coatings on concrete and reinforced concrete structures of hydraulic engineering facilities of water management and reclamation complex are polymer cement mixtures, binders in which are Portland cement modified with polymer latex dispersion powder (for two-component).

Creation of effective polymer cement waterproofing compositions is based on optimization of the ratio of interpenetrating meshes of polymers and crystal matrix hydrates. Modification of cement systems by polymers allows to increase adhesion and deformation characteristics, fracture resistance and corrosion resistance of polymer cement composites. Depending on the components included in the mixture, waterproofing coatings may be rigid or elastic. Rigid formulations are a water-mixed, dry mixture that includes a vinyl acetate copolymer and designed for waterproofing concrete and reinforced concrete structures with low water filtration. Elastic waterproofing materials are usually two-component. These materials are used for waterproofing structures that are susceptible to deformation, as well as surfaces with a high degree of water filtration and where cracks up to 1 mm are formed. Elastic two-component formulations are dry mixtures with the addition of redispersible polymer powders. They consist of two components: a dry mixture of modified fine cement and aqueous latex polymer, usually acrylic.

The content of polymer latex in the mixture has a significant effect on the rheological properties of polymer-cement mixtures and on the physical and mechanical properties of waterproofing coatings made of them. Thus, the introduction of a redispersible polymer powder Axilat L 8262 in a waterproofing mixture in the amount of up to 10% by weight of cement increases the mobility of the mixture from 3,2 to 8,0 cm, increases the adhesive strength of the coating to concrete from 0,45 to 1,95 MPa, increases its bending strength from 6,9 to 7,9 MPa, reduces its water absorption in 24 hours from 7,02% to 0,35% .