Types:
There are generally three types of wood plywood formwork
1.Plywood formwork without surface treatment (referred to as plain board);
2.Plywood formwork treated with resin finish (referred to as coated board);
3.Plywood formwork treated with impregnated film paper veneer (referred to as film faced board)
Structural requirements of boards
1) The wood grains of two adjacent layers of veneers should be perpendicular to each other, and the veneers of the symmetrical layers on both sides of the center layer should be of the same tree species or tree species with similar physical and mechanical properties and the same thickness.
2) The uniformity of the finished product structure should be considered. When assembling, the total thickness of the surface board and the veneers of each layer with the same fiber direction as the surface board should not be less than 40% of the thickness of the slab and not more than 60%. The number of layers of the board should be no less than 7. The thickness of the surface board should not be less than 1.2mm, and the thickness of the surface board of the film-coated board should not be less than 0.8mm.
3) The surface boards of the same layer should be of the same tree species.
4) No inclusions that affect the use of the board should be left in the board. The non-porous adhesive tape used for splicing should not be used inside the plywood. If it is used to splice or repair the panel, in addition to not modifying, the adhesive tape should be removed and no obvious adhesive tape marks should be left.
Tree species requirements
The tree species used for plywood formwork are: pine, poplar, birch, oak, eucalyptus, etc.
Adhesive requirements
1) The adhesive for plywood formwork should be phenolic resin or resin with equivalent performance.
2) Phenolic resin or resin with equivalent performance should be used for resin finishing.
3) Phenolic resin or resin with equivalent performance should be used for laminating.
Note: Phenolic resin is a resin made by polycondensation of phenol and formaldehyde under catalyst conditions, neutralization, and water washing.
The formwork and its support should be designed according to the conditions such as the engineering structure form, load size, foundation soil type, construction equipment and material supply. The formwork and its support should have sufficient bearing capacity, rigidity and stability, and can reliably bear the weight of poured concrete, lateral pressure and construction load.
Note: This article puts forward the basic requirements for the formwork and its support, which is a project that ensures the safety of the formwork and its support and plays an important role in the quality of concrete molding. Years of engineering practice have proved that these requirements are necessary to ensure the construction quality of concrete structures. This article is a mandatory provision and should be strictly implemented.
Before pouring concrete, the formwork project should be inspected and accepted.
When the formwork is installed and concrete is poured, the formwork and its support should be observed and maintained. In case of abnormal conditions, they should be handled in time according to the construction technical plan.
Note: When pouring concrete, the formwork and support often expand (deform), run (displace) or even collapse under the action of concrete gravity, lateral pressure and construction load. In order to avoid accidents and ensure the quality of the project and construction safety, requirements are put forward for observing, maintaining and handling the formwork and its supports when abnormal situations occur.
The order and safety measures for removing the formwork and its supports should be implemented according to the construction technical plan.
Note: The order of removing the formwork and its supports the corresponding construction safety measures are very important to avoid major engineering accidents, and should be considered carefully when formulating the construction technical plan. When the formwork and its supports are removed, the concrete structure may not have formed the force system required by the design, and temporary support should be added if necessary. The removal and support of the post-casting strip formwork are easy to be neglected and cause structural defects, so special attention should be paid. This article is a mandatory provision and should be strictly enforced.
Precautions for formwork construction
Before pouring concrete, the position, verticality and flatness of the formwork, the beam and slab mark should be carefully checked and verified. Check whether the position and size of the reserved holes are accurate and meet the design requirements, whether the formwork support is firm, and whether the joints are tight.
All formworks should be painted with release agent before use, and sponge strips should be pasted at the joints.
Before concrete construction, the debris in the formwork should be cleaned and moistened with water. During concrete construction, arrange carpenters to follow up and check, and solve problems in time.
The removal of the formwork must be approved by the technical person in charge, and the removal must comply with the regulations.