is an insulating concrete form (ICF) used to make walls for buildings. It is composed of concrete
Concrete is a composite construction material, composed of cement and other cementitious materials such as fly ash and slag cement, aggregate , water and chemical admixtures.The word concrete comes from the Latin word...
and thastyron. Thastyron is a mixture of plastic foam and binder that is composed of eighty-five percent recycled post consumer polystyrene
Polystyrene ) also known as Thermocole, abbreviated following ISO Standard PS, is an aromatic polymer made from the monomer styrene, a liquid hydrocarbon that is manufactured from petroleum by the chemical industry...
waste that are molded into blocks. The main components of rastra are cement, water and expanded polystyrene.
Rastra is sustainable in its production because no energy is used in the curing process, and only one to three kilowatt hour (kWh) is required to make each block. After the blocks are trimmed to exact size, the remaining debris are recycled to create new blocks. No byproducts are released in the production process that are considered a burden to the environment.
Rastra blocks come in different sizes, and can be easily cut with woodworking tools to form the desired shape. These blocks are commonly attached together with clamps or glue to form a grid-like system. Rebar
A rebar , also known as reinforcing steel, reinforcement steel, rerod, or a deformed bar, is a common steel bar, and is commonly used as a tensioning device in reinforced concrete and reinforced masonry structures holding the concrete in compression...
is then run through the grid, which is then filled with concrete.
Polystyrene concrete was invented in 1960. BASF
BASF SE is the largest chemical company in the world and is headquartered in Germany. BASF originally stood for Badische Anilin- und Soda-Fabrik . Today, the four letters are a registered trademark and the company is listed on the Frankfurt Stock Exchange, London Stock Exchange, and Zurich Stock...
, a German chemical conglomerate originally created this product, but found no successful applications. An Austrian/Swiss-based company modified the product and created what is known as Rastra.
As a thermal barrier Rastra has a four-hour fire rating with no flame spread and no smoke development. A five-hour fire endurance test of a ten-inch-thick wall with temperatures exceeding two thousand degrees Fahrenheit on the face of the wall showed that the wall did not conduct heat. This lowers the number of health hazards during a fire and also makes building repairs easier afterwards.
Thastyron has a compressive strength of 56 pound-force per square inch (psi) and a tensile strength
Ultimate tensile strength , often shortened to tensile strength or ultimate strength, is the maximum stress that a material can withstand while being stretched or pulled before necking, which is when the specimen's cross-section starts to significantly contract...
of 43 psi. Rastra has a low toxicity level. Rastra is highly frost, fungus, and mildew resistant. The sound insulation is greater than 50 decibel
The decibel is a logarithmic unit that indicates the ratio of a physical quantity relative to a specified or implied reference level. A ratio in decibels is ten times the logarithm to base 10 of the ratio of two power quantities...
As a heat insulation rastra keeps a room at a constant temperature and evens out temperature changes both of which can lower energy use. It also has a low heat penetration depth.