Durability and Impermeability
Concrete possesses a pore structure which distinguishes concrete from metals and makes it airtight and watertight. The capillary pore structure of concrete allows the permeation of gas or liquid, especially under pressure. The macrostructure of concrete reveals that it consists of
(a) coarse and fine aggregates
(b) hydrated cement paste, and
(c) entrapped air voids.
The low durability that we witness in many concrete structures, which gets manifested in the form of cracking, and spalling due to poor quality of materials or workmanship and corrosion of steel, is principally due to inferior design, specification or construction.
Certain parts of a concrete structure may also be subjected to physical wear and tear. Parking garages, concrete roads, and breakwater wall are examples of structures subjected to repeated wear.
The factors governing the permeability of concrete can be summarized as follows:
- The quality of materials, e.g., Cement, sand and aggregates
- The quality of pore structure, based on w/c ratio, the admixtures used and the degree of hydration
- The quality of interfacial transition zone
- The degree of compaction
- The cracking arising because of structural loading
- The adequacy of curing It is also true that all concretes produced for different application may not be designed to be completely impermeable.
Products Selection and System
The problem is neatly summed up in a quote by John Ruskin (1819–1900): “There is hardly anything in the world that some man can’t make just a little worse and sell just a little cheaper, and the people who buy on price alone are this man’s lawful prey” Multichem manufactures wide range of waterproofing systems which are classified into (a) Membrane Waterproofing (b) Waterproofing by crystallization. Under membrane waterproofing, an external layer is formed by way of application and water is not allowed to enter the structure. Multiguard A (Figure 2) is a two component, thixotropic, cementitious modified polymer coating with high adhesion to both steel and concrete, which falls into this category. It has high level of impermeability of more than 6.00 X 10–16 m/sec. Multiguard A forms a hard, highly alkaline coating with a degree of elasticity which not only protects the concrete, or other substrates, from the effects of aggressive acidic gases, moisture and chlorides, but also has greatly enhanced chemical resistance.
There include: Rigid waterproofing of water tanks, sealing internal basement and cellar walls against dampness, protection of concrete structures in marine environment, external tanking of substructure concrete such as foundations and basement walls in new buildings.
Under Waterproofing by Crystallization, structure is waterproofed in-depth. The active ingredients create catalytic reaction generating billions of crystals to block cracks and capillaries in the concrete. Multichem manufactures (a) Multiguard In-depth TA/TB for surface application (b) Multiguard In-depth Premix, additive to be added to the concrete. Multiguard In-Depth (Figure 3) contains active waterproofing chemicals which create catalytic reaction when in contact with moisture, and cementitious products in the concrete, generating insoluble crystalline complexes which seal the capillaries tracks, pores and minor shrinkage cracks. They penetrate even against strong hydrostatic pressure, becoming an integral part of the concrete. As the reaction is catalytic in nature the waterproofing chemicals remain active for the life of the structure, permanently sealing it from water and waterborne chemicals penetration. The crystals continue to grow as long as moisture is present, often reaching several feet in length. Once moisture is removed, the chemicals remain dormant in the concrete, ready to be reactivated by water even years later if new non-structural cracks (which are <0.4mm) develop through natural settling or other factors.
- Swimming pools
- Tunnels and subway systems
- Parking garages
- All below grade concrete foundations
- Dry vaults
- Water towers and water reservoirs
- Marine structures
- Bridge decks
- Concrete walls and floor
- Sewage and water treatment plants