In the slab foundations from L-blocks in the EPS-shape form, you should take into the account that such structure is designed as an upturned slab with point support. This means, specifically, that the slab is affected by the tension forces and loads of the building structures, which are transmitted through the bearing walls to the foundation slab, resulting in the unfolded slab. The tensile strength of concrete is 10-15 times weaker than the concrete’s compressive strength. The tensile strength of the concrete is achieved by reinforcing, concreting and concrete after-care.
AS Reideni Plaat manufactures L-blocks from EPS 200 material, 300mm, and 400mm high. The upturned blocks 500 mm can be also used. Generally, a structure is planned where the floor heating pipes are immediately mounted inside the plate foundation, but not separately insulated from the plate foundation or mounted onto the second layer. The thickness of the plate-type slab depends largely on the structure and configuration of the building. The thickness of the plate-type slab, where the floor heating pipes are installed, should be minimized to achieve the required tensile strength of the structure. If the plate of the foundation is to be thickened, when it is necessary to ensure the tensile strength, it adds dead weight to the structure and causes an increase in heating costs. As the L-block plate foundation is designed primarily aiming at the tensile strength, the tensile strength of the structure results from a co-work of the concrete and the reinforcement. The vertical pressure of the load-bearing walls on the L-block produces tensile stresses in the plate, in particular, in the upper layer. Reinforcement continuity systems to be installed under the load-bearing walls are connected to the upper reinforcement of the plate, and shear load dowel bars of the band and the plate nodes are installed to stabilize the wall deflection. If a floor heating pipeline is installed in the base plate and for minimizing heating costs the thickness of the plate is minimized, while ensuring the tensile strength of the structure, then the concrete protection layer of the upper reinforcement mesh is no more than 30-40 mm.
Ideally, the concreting of the slab must be a single process. For all concrete to be installed, it is necessary to pour the EPS form without interruption. After installation, concrete must be vibrated to remove air and to completely block the concrete into the reinforcing mesh, thus protecting the concrete against corrosion of the reinforcement. In the non-vibrated or poorly vibrated reinforced concrete, the reinforcement, transmitting the tensile strength, will rust. Then the concrete surface is immediately refined. The idea behind after-care is to provide the strength of concrete and to prevent excessive drying of concrete surfaces. In the first place, aftercare will ensure the development of tensile strength of concrete. Concrete aftercare will be started as soon as possible after concrete consolidation and finishing. If it is necessary to avoid cracking due to plastic volume contraction on free surfaces, it is recommended to start the temporary maintenance even before finishing. Concrete surface durability is also affected by concrete finishing. Excessive brooming or watering fresh concrete to facilitate treatment increases the water-cement ratio, the surface layer of concrete weakens and the risk of damage increases. If the plate foundation is designed in such a way that the upper reinforcement grid is covered with a concrete shield 30 to 40 mm thick, for such construction any finishing with tools creating centrifugal forces („helicopter”-type concrete sliders) should be avoided. In addition to attenuating and damaging the surface layer described above, the finishing techniques where tools creating centrifugal forces are applied on fresh concrete may damage the bond between the concrete and the top layer of the reinforcement mesh.
To ensure the reliability of the L-block EPS in the plated foundation form, the following is required:
1. The bearing structures should be based on the material not lower than EPS 200. Using L-blocks with a material of lower compression strength will cause a higher bend-up of the plate and increase the tensile stress applied to the construction, which is not taken into account when designing the design. L-blocks from EPS 100, EPS 120 materials are not intended to accept the compressive strength of building bearing structures.2. When reinforcing the plate foundation from L-blocks EPS 200, it is needed to consider the fact that the plate works on the basis of tensile strength and the concrete tensile strength is 10-15 times weaker than the compressive strength, so that the forces transmitted through the tension spring will bend the plate up.
3. When concreting the L-blocking EPS 200 foundation, it must be taken into account that a concreting process must be carried out without interruption in order to ensure the homogeneity of concrete, and the concrete must be certainly vibrated.
4. Finishing the L-block EPS 200 plate foundation also requires taking into account that such structure is designed for tensile strength and that the tensile strength of the concrete is 10-15 times weaker than the concrete’s compressive strength. The finishing technique, where the fresh concrete surface is rubbed and watered to facilitate the finishing, raises the water-cement ratio of the surface layer and the surface of the concrete weakens. Besides, the finishing by centrifugal force may worsen the bond of the concrete and the top layer of the reinforcement mesh. In the event of the bond deterioration, the tensile stresses in the reinforcement and in the concrete will affect in a different way, which causes the structure to break.