Foamed concrete admixtures are surfactants that are diluted with water before passing through a foam generator to produce a stable foam, similar to shaving cream. This is then blended into a cementitious mortar in a quantity that produces the required density for the foamed mortar (more usually called foamed concrete).
Polymer dispersion admixtures are aqueous dispersions of synthetic polymers that form a continuous film when sufficient water is lost from the system. Concrete modified with polymer dispersion is known as polymer cement concrete (PCC). Polymer dispersions reduce the permeability of concrete (improving durability), give a more reliable bond to base materials (concrete and steel), increase toughness and resistance to abrasion/dusting and freeze-thaw action.
Modern pumps are able to cope with most concrete mixes but difficulties can be experienced with concretes made from aggregates that are poorly graded, elongated or flaky. Pumping for large distances horizontally or vertically can lead to high pump pressures and the need for improved lubrication within the lines. Adding a polymer-based pumping aid can modify the cement paste rheology to help provide this enhanced lubrication. Pumping aids can also provide better workability retention for long pumping distances and can be particularly effective if interruptions to pumping are likely and when segregation or stiffening in the line could prevent a restart.
With careful mix design, self-compacting concrete (SCC) admixtures produce a concrete that is fully flowing and self-compacting and which can be placed with no vibration.
There is a growing problem with disposal of washwater from cleaning the inside of truck mixer drums at many ready-mixed concrete plants. The Landfill Tax and the prohibition on disposal through the drainage system have increased the cost of disposal. One solution is to recycle the water by the use of a truck washwater admixture.
Steel fibres mixed into the concrete can provide an alternative to the provision of conventional steel bars or welded fabric in some applications. The concept has been in existence for many years (the first patent was applied for in 1874) and it has been used in a limited range of applications: among the first major uses was the patching of bomb craters in runways during World War II. However, it was during the 1970s that commercial use of this material began to gather momentum, particularly in Europe, Japan and the USA.
Cement Rock is the term given to a limestone containing up to 25% clayey (argillaceous) material. By calcining and grinding this naturally occurring rock, a material known as Natural Cement or Roman Cement is produced. No additional constituents are added to the production process. Its properties are between that of a Portland cement and hydraulic lime.
Martensitic Microcomposite Formable Steel, (MMFX) have a patented chemical composition and proprietary steel microstructure that is formed during the production associated with controlled rolling and cooling of the steels. This minimizes the initiation of corrosion and can therefore be used as reinforcement in concrete in aggressive environments. MMFX reinforcement is not as expensive as stainless steel reinforcement and has been used in the USA and the Middle East but is not currently available in the UK.
Water is needed in concrete for two reasons, firstly to hydrate the cement and secondly to provide mobility when the concrete is in its fluid state (workability). Generally the amount of water needed for mobility purposes is greater than that required for hydration only. The water used should be clean, i.e. of drinking water quality, but other water is allowed by concrete producers by following BS EN 1008.
Polymers are chemicals which can be added to concrete like an admixture, and undergo a reaction which changes them into long chain polymer molecules in the concrete. Most proprietary repair mortars contain polymers.