Concrete

Concrete is a composite from cement, sand, gravel, water and additives. The strength varies in classes (C12 to B60). Usually the concrete is reinforced. The components are: AIR (without air entraining agents ca. 2% and with these agents ~3.5% in the shape of air spheres), WATER (has an important role in the strength and time behaviour), CEMENT (e.g. Portland with various part. size and composition, Hoogoven, Portland flyash cement, specialties (heat, color, sulphate resistance)), SAND (mostly siliceous compositions), GRAVEL (river gravel, broken rock, crushed concrete, artificial gravel (mostly light weight), heavy gravel). FILLERS (microsilica, flyash, limestone flower, pigments, ground blast furnace slag), ADDITIVES (accelerators, retarders, plasticisers, superplasticisers, air entrainment agents, thickeners, inhibiters, polymers). The hardening process is a chemical process and may require up to one month to reach its full strength. Crucial for the characterization and determination of the strength B(sigma) is the K-value. K is the statistical value depending on the test circumstances and the number of specimen.