Perforated brick
| Perforated brick | |
|---|---|
|
|
| origin | |
| raw materials | clayey loam , e.g. T. polystyrene , sawdust, paper fiber |
| Material properties | |
| Thermal conductivity λ | 0.07 - 1.00 W / (m K) |
| Specific heat capacity c | 1 kJ / (kg K) |
| Bulk density ρ | 600 to 650 kg / m³ |
| Vapor diffusion resistance μ | 11 |
| commitment | |
| Areas of application | also load-bearing homogeneous walls or ceilings |
Perforated bricks (also hollow bricks or Frewen bricks ) were already known during Roman antiquity . However, their function has changed fundamentally since then.
In ancient Rome, hollow bricks (tubules) were mostly part of the furnishing of heated rooms ( hypocaust ) . These rectangular bricks had no load-bearing function, but were bricked up after a building was erected along the inner walls of a room to be heated above the level of the room. The heat coming from the underfloor heating flowed through them upwards. Nevertheless, the Romans knew methods of reducing the weight of heavy ceilings and domed structures. Secondary use amphorae were placed one inside the other or clay tubes were pushed into one another.
Today's hollow brick is a brick that is perforated to reduce thermal conductivity and weight. A distinction is made between the vertically perforated brick (HLZ), the perforation of which is perpendicular to the bearing surface and which can therefore be used in a load-bearing manner, and the elongated perforated tile (LLZ), the perforation of which runs horizontally to the bearing surface and which therefore has a less good load-bearing capacity. Another differentiation is the shape of the holes, i.e. round, square, slot-shaped and possibly distributed differently on the tile surface.
Manufacturing
Clay is cleaned and processed and, if necessary, mixed with porosity substances. In order to obtain a suitable consistency for processing, the clay is mixed with steam and then pressed and cut through an extrusion tool . The resulting brick blanks are first dried and then fired .
Extrusion tool for perforated brick
Extrusion of perforated bricks
Unburned brick
properties
Dimensions
The mass of the brick is controlled by the proportion of holes (for example 50 percent) and the porosity or the selection of raw materials. The broken brick (solid part of the perforated brick) can be "lightened" with burn- out materials such as foam polystyrene beads, sawdust, paper fiber (and the like) and thus adjusted to be more heat-insulating, for example to 1.4 kg / dm³. In industry, porosity is achieved by adding, for example, polystyrene beads or wood particles, which leave air pores behind during the firing process.
These bricks have a gross density (mass / volume including holes) of less than / equal to 1.0 kg / dm³. In order to express both the lightness and the direction of the perforation, one often speaks of the light vertical perforated brick (LHLZ) or light elongated brick . The slightly elongated brick is hardly used in Germany any more due to its low compressive strength .
Thermal insulation ability
(Top view).
The good thermal insulation properties result from the mechanisms of heat conduction through the webs, convection within the air-filled holes and radiation through the hole areas. The weighting of the individual heat transfer mechanisms essentially depends on the hole design and arrangement (length, width, number of holes in the direction of wall thickness, offset), the web thickness and the fragment properties of the fired clay (pore formation with burn-out substances such as polystyrene beads, sawdust, paper fiber) from.
The thermal conductivity of modern Poroton light vertical perforated bricks for single-shell external masonry without additional insulation (today mostly flat perforated bricks , ground to a height of 249 mm (± 0.5 mm, processed with thin-bed mortar D = 1 mm) reaches values of 0.075 W / (m K) at Brick density (density = mass / volume) of 550 kg / m³. It is mainly used in wall thicknesses of 36.5 cm and 42.5 cm, less often in thicknesses of 30.0 cm and 49.0 cm.
Resilience
The properties are essentially determined by the positioning of the holes (horizontal = elongated hole or vertical = vertical hole). While vertically perforated bricks can assume load-bearing functions, oblong perforated bricks (LLZ) are suitable for partition walls without static functions. In southern countries such as Italy or Turkey, long-hole bricks are used to brick the areas between reinforced concrete pillars of the preferred house construction due to the increased risk of earthquakes.
Elongated brick
Slotted brick wall between poured concrete pillars
Typical house construction in earthquake-prone areas of southern Europe: concrete pillars and ceiling with brick walls
Hollow brick in a small bath building at Eining Fort
application
When building single-family houses and terraced houses, most of the monolithic LHLZ external walls are made 36.5 cm thick. The thermal conductivity λ for Poroton flat bricks T10 is 0.10 W / (m K), T12 at 0.12 W / (m K), T14 at 0.14 W / (m K). The Poroton Plan-T9, -T8 and -T7 (association name) filled with perlite (expanded volcanic rock, 0–3 mm) show the limits of what was technically feasible up to now. The filling has a thermal conductivity of 0.045 W / (m K), while porous brick shards have a thermal conductivity of approx. 0.286 W / (m K). In the course of the CO 2 discussions and the causes of new and existing residential buildings, the U-values are becoming increasingly important as “thermal component parameters” ( KfW subsidy, low-interest loans). The transmission heat losses of the outer walls amount to approx. 30% of the total transmission heat losses of the building envelope, which also includes windows, roof, floor areas, basement ceilings and doors of a residential building. The share of the final energy demand, which results from offsetting ventilation heat losses, solar gains, internal gains and finally system efficiency, is approx. 12%.
These tiles are from the DIBt ( German Institute for Building Technology , Berlin) by building permit. The highest building supervisory authority DIBt demands and checks the usability certificates from the manufacturer such as thermal resistance, sorption moisture content and wall load-bearing capacity.
The bricks still used and in demand in the 21st century have grooves and tongues (mortar-free butt joints). Mortar pocket tiles and wall tiles , as they were used just a few years ago, are no longer of great importance in Germany.
However, the use of perforated bricks also has disadvantages: If you have to drill into this building material, there is a high risk of breakage. In addition, the fastening of heavy objects is only possible with special dowels.
Compared to other building materials for the outer wall, it must be mentioned that the fired clay bricks can achieve compressive strength properties (usually at least 9 N / mm², very often 15 N / mm²). Due to the firing process, the bricks are delivered without residual moisture, which means that the building owner does not have to use any energy for dry heating (apart from the building moisture from mortar and plaster) and the thermal conductivity properties are guaranteed from the start.
The hollow tile should not be confused with the hollow pan , which is a profiled roof tile .
literature
- Hans Christian Grassmann: The function of hypocausts and tubules in ancient Roman buildings, especially in thermal baths. Explanations and calculations , Arceopress, Oxford 2011, ISBN 978-1-4073-0892-0
Web links
Individual evidence
- ↑ sanded to a height of 249 mm (± 0.5 mm, processed with thin-bed mortar D = 1 mm)
- ↑ a b Reinhard Welz: Building science for laypeople , a. a. Fig. Of a Frewen brick and description of multi-hole bricks , p. 95 ; Vermittler Verlag eK, 2005. Accessed October 27, 2017.
- ^ Henner von Hesberg : Römische Baukunst . Beck, Munich 2005, ISBN 3 406 52920 8 , p. 29; Werner Heinz: Roman thermal baths. Bathing and bathing luxury in the Roman Empire . Hirmer, Munich 1983, ISBN 3777435406 , p. 135.
- ↑ Building materials for the masonry of the solid houses. Retrieved August 24, 2016 .