In winter construction, what key points should be paid attention to at all stages of the building formwork and plate project?
1、 Formwork construction management
The formwork works mainly follow the principles of practicality, safety, economy, etc., fully consider the main points such as the dead weight of the formwork and its support, the construction load, the load of construction personnel and construction equipment, the lateral pressure of the formwork caused by concrete pouring and vibration, so as to ensure that the formwork has sufficient load-bearing capacity, rigidity and stability, so that it will not deform, damage or collapse during construction, so as to formulate a reasonable and effective formwork scheme.
In case of construction in winter, the technical disclosure of winter construction shall also be made in time to ensure that each process of formwork works is organized according to regulations, specifications and technical measures, and corresponding winter construction records shall also be made to provide basis for the arrangement of subsequent formwork construction schemes. At the same time, special personnel shall also be designated to grasp the temperature change, timely convey the meteorological information, make weather records, and take corresponding technical measures and material preparation in case of sudden temperature drop, so as to do a good job in the protection of the formwork construction in winter and ensure the smooth progress of the project.
2、 Template material management
For the management of formwork materials, the formwork materials shall be selected according to different engineering conditions and different construction positions. For example, the beam and column formworks can adopt medium combined formworks; The wall formwork can be made into large formwork by using medium combined formwork, or large formwork by using the whole multi-layer formwork, or permanent all-steel large formwork; The floor formwork can be made of wood, bamboo and other whole multi-layer boards; High-rise buildings can adopt hydraulic climbing formwork which combines the advantages of large formwork and sliding formwork to facilitate construction, save the lifting time of site and tower crane, and ensure the safety of aerial work.
In the construction process, on the premise of ensuring the quality and safety of the construction period, the one-time investment shall be reduced as much as possible, the turnover of formwork shall be increased, and the labor for supporting and dismantling shall be reduced. The formwork shall be removed without damaging the formwork as much as possible, and the formwork removal fasteners shall be recycled as required, and shall not be littered for recycling. The removed formwork shall be cleaned, corrected and painted with release agent in time. The formwork with unclear identification shall be re-identified and carefully maintained to extend the service life.
During winter construction, dry and ventilated places shall also be selected to classify and store the unused building formwork in time, and the formwork shall not be directly exposed to the outside, so as to avoid the deformation, deterioration, discoloration and other problems of the formwork caused by frost, rain and snow or the impact of low temperature, which will affect the subsequent use.
3、 Key points of formwork installation
1. In case of construction in winter, the ice, snow and soil on the formwork shall be cleaned before use, and the debris, ice and snow in the formwork shall be cleaned after the formwork is erected, and no watering is allowed. In case of strong wind (above Level 5), the assembly and hoisting of large formwork shall not be carried out.
2. Before the installation of column formwork, the axis column sideline must be snapped, and the elevation should be set on the reinforcement. In addition to ensuring that the column formwork and support are firm and stable, the upper and lower formwork should also be supported on the same vertical centerline.
3. The back of the wall and column formwork can be pasted with 50mm thick flame retardant polystyrene board for thermal insulation, and the relative gap of the thermal insulation board can be increased by 1~2cm to ensure that the thermal insulation board does not fall. At the same time, the outside of the thermal insulation board should be sealed with bamboo plywood or plywood, and the bamboo plywood or plywood should be disassembled and assembled at the same time with the formwork.
4. The beam side formwork shall be 18mm thick multilayer plate; The beam bottom formwork shall be planed with 50mm thick pine wood; The floor formwork of the floor shall adopt seven plywood or 18mm thick multilayer board.
5. The formwork support shall be set up according to the requirements of the formwork scheme, and the elevation and camber height of the support shall be checked after the completion of the erection, and the slab formwork shall be paved flush to the outer opening of the beam side formwork, and shall not be paved on the beam side formwork.
4、 Key points of formwork removal
1. When the formwork is removed in winter, the formwork removal application shall be submitted in accordance with the regulations, and the pressure test report of the formwork removal test block shall be included. The formwork removal operation can only be carried out after the formwork removal application is approved.
2. The correct formwork removal sequence and method shall be selected according to the provisions of the formwork design. If there is no specific provisions, the formwork shall be removed according to the principle of first supporting and then removing, and the formwork at non-bearing parts shall be removed first, and then the formwork at load-bearing parts.
3. Under the positive temperature environment, the formwork can be removed if the edges and corners of the concrete and the surface layer will not be damaged due to the wall formwork removal; In the negative temperature environment, the formwork can be removed only when the compressive strength of the formwork removal test block reaches 4MPa and the concrete is not frozen. At the same time, the removal time should be strictly controlled.
4. When the temperature difference between the concrete and the outside environment is greater than 20 ℃, the concrete surface shall be covered with polyethylene plastic cloth after the formwork is removed, and the surface shall be temporarily covered with straw bags to make it cool slowly.