Overview of large template construction details and solutions to common problems

Undoubtedly, large formwork is widely used due to its advantages, including high construction efficiency, low labor intensity, high turnover, and easy installation and removal. Despite these numerous advantages, problems such as inadequate communication and common defects can still lead to substandard concrete quality during construction. To avoid quality issues, what precautions should be taken during large formwork construction? We have compiled a list of potential issues to share with you.

1. Transportation, storage and assembly of large templates

(1) The cylinder mold can be transported as a whole on a trailer, or it can be disassembled into flat molds and transported horizontally on a trailer. When stacking flat molds, the pads must be aligned and tied firmly.

(2) When storing flat formwork, the self-stabilizing angle required by local conditions should be met. Two large formworks should be stored face to face. When storing formwork for a long time, the formwork should be replaced as a whole. Large formworks stored on the construction floor must have reliable anti-tilting measures and must not be placed along the edge of the exterior wall. They must be stored perpendicular to the exterior wall.

(3) Large formwork without support or with insufficient self-stabilizing angle should be stored on a dedicated stacking rack or stacked flat. It should not be leaned against other formwork or objects to prevent it from slipping and tipping over.

(4) When assembling or dismantling the formwork, the personnel who are directing, dismantling and hooking must stand in a safe and reliable place before operating. It is strictly forbidden for personnel to lift with the large formwork.

2. Installation of large template

Installation process: inspection → cleaning → lifting → inspection → filling → adjustment.

Installation details:

(1) To ensure the quality of concrete, the installation quality of the formwork should be guaranteed to be flawless. Therefore, before the formwork is put on the wall, the sponge strips pasted at the formwork joints should be carefully checked; whether the surface is clean; whether the formwork edges are deformed, and if so, they should be leveled; whether the steel bars are out of place, affecting the placement of the formwork; check whether the steel bars, embedded pipes, door openings, etc. affect the passage of the tension bolts, and deal with them in advance.

(2) After checking the formwork support, you should also check whether the wall reinforcement, water and electricity pipelines, embedded parts, door and window opening formwork and through-wall bolts are missing, whether the position is accurate, and whether the installation is firm, and remove the debris in the formwork. Once the concrete is poured, if you want to repair it, you have to destroy the problematic concrete and re-pour it, so you must do a good job of the preliminary work.

(3) When installing large formwork, it should be hoisted into place in the order of the formwork numbers. Before hoisting the formwork, check whether the hoisting ropes, clamps and the lifting rings on each formwork are complete and effective, and remove all temporary supports first. Only after checking that they are correct can the formwork be hoisted. When using a combined flat formwork, first install the formwork on one side of the horizontal wall, then hoist it vertically, insert the through-wall bolts coated with release agent, then install the formwork on the other side, and finally install the vertical wall formwork.

(4) Check the installation accuracy of the formwork at any time to ensure that the formwork is installed in the correct position and the facade is vertical. The formwork that is installed first can be checked with a 2m long straightedge board, and the formwork installed later can be checked for verticality on the back of the formwork with a double cross straightedge. When installing the external formwork of a fully cast-in-place structure, the cantilever must be fixed and the hook can only be removed after the position is adjusted accurately. After the external formwork is installed, the pin rod must be inserted immediately and the bolts must be tightened. Operators installing the external floor slab must wear a safety belt.

(5) When filling the gaps of large formwork, after the formwork is fixed, the gaps around the formwork can be filled with 1:3 cement mortar to prevent the wall from having roots.

(6) When calibrating large formwork, the top of the formwork should be fixed with a clamp after the calibration is qualified, and the through-wall bolts should be properly tightened. After installation, the top of each wall formwork should be aligned, and the fasteners and bolts should be checked for tightness, joints, wall thickness, and tightness with the exterior wall panels. Concrete can only be poured after passing the inspection.

3. Removal of large templates

Dismantling order: dismantle the longitudinal wall formwork → dismantle the transverse wall formwork → dismantle the corner formwork and door opening formwork → demoulding and lifting.

Demolition details:

(1) For single large formwork, the longitudinal wall formwork should be removed first, followed by the transverse wall formwork and door opening formwork. For each large formwork, the connecting parts such as the turnbuckles, upper clips, and through-wall bolts should be removed first and placed in the tool box. Then, the anchor bolts should be loosened to gradually separate the formwork from the wall.

(2) When dismantling a hinged cylinder formwork, remove the connectors and rotate the demoulder to detach the formwork from the wall before hoisting it out. The large cylindrical formwork is heavy and is relatively close to the wall. When hoisting it out, the hooks must be firmly attached and the hoisting must be steady without shaking to prevent damage to the wall.

(3) When removing the corner formwork, first remove the concrete on the surface of the formwork, then use a crowbar to pry it from the bottom to remove the corner formwork. When removing the door opening formwork, be careful not to crack the concrete in the door opening lintel.

(4) Chisel out the concrete at the protruding parts in time, and use cement mortar to repair the recessed parts or corners in time. For door openings with a span greater than 1m, add supports or delay the demolding after demolding.

(5) Before lifting the large formwork after demoulding, carefully check whether all the through-wall bolts have been removed. Only after confirming that there are no omissions and the formwork is completely separated from the wall can it be lifted. When removing the external formwork, first hang the hook, tighten the rope, and then remove the pin rod and the support.

4. Prevention of common quality problems

1. Seam defects

Joint defects can result from gaps between formwork panels or errors during the lifting and installation process. To avoid joint defects, minimize gaps between formwork panels and appropriately increase the width of the assembly adjustment gap between the panels. After hoisting and adjustment, install the joint plate and drive the wedge. While aligning the two panels, the convex rubber strips on the joint plate should be squeezed into the adjustment gap to achieve both leveling and sealing.

2. Concrete damage

During the demolding process, concrete can be easily damaged. Large formwork can be difficult to remove due to installation or other factors. Prying or hitting the formwork with a sledgehammer at the top can damage it and affect the quality of the concrete.

3. Lifting of large templates

(1) When lifting large formwork, do not collide with the wall to prevent wall cracks. Large formwork should be moved directly on the floor without falling to the ground as much as possible to reduce the time occupied by the tower crane.

(2) The hook should be vertical to the formwork and should not be hung at an angle to prevent collision with adjacent formwork and walls. Keep your hands on the hook when removing it. Do not release your hands until the hook is lifted above your head. You can only drive or turn the arm when the height exceeds the allowable height above the obstacle.

4. Subsequent work after demoulding

(1) After the large formwork and its supporting formwork are removed, the cement slurry on the board surface should be cleaned in time and the mold release agent should be applied to prepare for the next use. Apply the mold release agent on the floor to prevent the mold release agent from splashing onto the steel bars. If the large formwork is not cleaned in time, it may reduce the quality and affect its turnover rate.

(2) After the large formwork is removed, the residual concrete on the formwork should be cleaned promptly and the release agent should be applied. When cleaning and applying the release agent, the formwork should be temporarily fixed. A 50-60 cm wide sidewalk should be left between the formworks where the board faces are parked. The top of the formwork should be fixed with a tie rod.