Structurally dense lightweight concrete
In fabric density lightweight concrete (also construction lightweight concrete ), it is a concrete , the oven-dry in the state of a bulk density of at least 800 kg / m³ and a maximum of 2000 kg / m³ has and a closed structure comprising.
The composition of dense lightweight concrete corresponds to that of normal concrete . As the aggregate , however, porous grains such. B. from expanded clay or pumice , used, whereby the lower bulk density is achieved. The achievable strengths are comparable to those of normal concrete. Structurally dense lightweight concrete is therefore suitable for reinforced and prestressed concrete structures .
properties
Bulk density
Structural lightweight concrete is normatively divided into the bulk density classes 1.0 - 1.2 - 1.4 - 1.6 - 1.8 - 2.0, which correspond to the bulk densities between 800 and 2000 kg / m³. The raw density achieved depends on the aggregate selected.
Compressive strength
The compressive strength is one of the important characteristics of the concrete. DIN EN 206 prescribes a test after 28 days for the classification, which is carried out using cubes with an edge length of 15 cm (test cubes) or 30 cm long cylinders with a diameter of 15 cm. With the determined compressive strength, the lightweight construction concrete can be assigned to one of the strength classes shown in the table below. A lightweight construction concrete of strength class LC12 / 13 then has the characteristic cylinder compressive strength of 12 N / mm² and a characteristic cube compressive strength of 13 N / mm². The letters “LC” in the nomenclature stand for English: “Light Concrete”.
For the compressive strength of lightweight construction concrete, the grain strength of the aggregate is decisive, as this is usually smaller than that of the cement stone. A high compressive strength is therefore linked to a higher bulk density.
Compared to normal concrete, lightweight concrete with a dense structure has a lower modulus of elasticity .
| Compressive strength classes for lightweight concrete according to DIN EN 1992 | ||||
| Strength class | characteristic cylinder compressive strength (N / mm²) |
Average cylinder compressive strength (N / mm²) |
||
| LC12 / 13 | 12 | 17th | ||
| LC16 / 18 | 16 | 22nd | ||
| LC20 / 22 | 20th | 28 | ||
| LC25 / 28 | 25th | 33 | ||
| LC30 / 33 | 30th | 38 | ||
| LC35 / 38 | 35 | 43 | ||
| LC40 / 44 | 40 | 48 | ||
| LC45 / 50 | 45 | 53 | ||
| LC50 / 55 | 50 | 58 | ||
| LC55 / 60 | 55 | 63 | ||
| LC60 / 66 | 60 | 68 | ||
| LC70 / 77 | 70 | 78 | ||
| LC80 / 88 | 80 | 88 | ||
Thermal conductivity and thermal expansion
The lower thermal conductivity of structural lightweight concrete compared to normal concrete is due to the porosity of the aggregate. It is therefore determined by the type and quantity of the aggregate. The thermal conductivity increases with increasing bulk density. The coefficient of thermal expansion is smaller than that of normal concrete and can be set at 8 · 10 −6 1 / K.
| Thermal conductivity of lightweight concrete according to DIN 4108 | ||||
| Bulk density class | Gross density (kg / m³) | Thermal conductivity (W / (m K)) | ||
| D 1.0 | 800 | 0.39 | ||
| D 1.0 | 900 | 0.44 | ||
| D 1.0 | 1000 | 0.49 | ||
| D 1.2 | 1100 | 0.55 | ||
| D 1.2 | 1200 | 0.62 | ||
| D 1.4 | 1300 | 0.70 | ||
| D 1.4 | 1400 | 0.79 | ||
| D 1.6 | 1500 | 0.89 | ||
| D 1.6 | 1600 | 1.0 | ||
| D 1.8 | 1800 | 1.15 | ||
| D 2.0 | 2000 | 1.35 | ||
Norms
- DIN EN 1992-1-1 and NA
- DIN EN 206 / DIN 1045-2
Web links
literature
- Verein Deutscher Zementwerke eV: Cement information sheet for concrete technology B13. Lightweight concrete 2014
- W. Scholz: Knowledge of building materials. Werner Verlag, Neuwied 2007, ISBN 978-3-8041-5227-4 .
- G. Neroth: Wendehorst building materials science. Basics - building materials - surface protection. Vieweg + Teubner, Wiesbaden 2011, ISBN 978-3-8351-0225-5 .