Concrete surface flatness error is a key factor affecting the appearance quality of building structures and subsequent finishing effects, and the rationality of the design of the beam bottom template panel system directly determines the accuracy of concrete forming. By optimizing template materials, splicing methods, support systems, detail processing, and construction control, the flatness error of the beam bottom concrete surface can be effectively reduced, improving the overall construction quality.
The selection of template materials is fundamental to controlling flatness error. Beam bottom template panels must possess high rigidity and low deformation rate characteristics. Multi-layer plywood or bamboo plywood are preferred, as their tight interlayer bonding and strong bending resistance reduce surface unevenness in the concrete caused by template deformation during pouring. Simultaneously, the template surface should be flat and smooth, free from warping, cracks, and other defects to prevent unevenness of the template itself from being directly reflected on the concrete surface. Furthermore, the edges of the template must be sealed to prevent moisture intrusion leading to delamination or expansion, further ensuring the dimensional stability of the template.
The design of the splicing method is crucial for reducing local errors. Straight-line butt joints should be avoided at the bottom formwork joints of beams. "Tick-and-groove" or "stepped" joints can be used, utilizing the natural interlocking of the formwork edges to enhance the joint's resistance to slippage. During splicing, double-sided tape or sponge strips should be applied to the gaps to fill tiny gaps and prevent concrete grout leakage that could cause burrs or rough surfaces. Simultaneously, the splicing direction should be consistent with the beam's length to avoid excessive cumulative errors caused by lateral splicing, which would affect overall flatness.
The stability of the template panel system is crucial for ensuring formwork flatness. The bottom formwork of beams must be connected to the full-span scaffolding via adjustable supports. U-shaped supports should be installed at the top of the supports to ensure tight contact between the formwork and the supports, preventing localized suspension. The spacing of the support uprights should be rationally arranged according to the beam cross-section dimensions. For larger spans, independent supports should be added within the beam to reduce formwork sagging deformation. Furthermore, the support system must have sufficient rigidity to prevent formwork displacement or twisting due to lateral pressure during concrete pouring, which would affect surface flatness.
The appropriateness of formwork reinforcement measures directly affects the quality of concrete molding. At the joints of the beam bottom formwork, square timber backing ribs should be used for reinforcement. These ribs should be straight and without bending, and tightly fitted to the formwork, secured with nails or bolts to enhance the tensile strength of the joints. For beams with significant height, tie rods can be added to both sides of the formwork. The tension of the tie rods reduces lateral deformation of the formwork, ensuring the perpendicularity of the beam bottom to the side formwork. The spacing of the reinforcement components should be even to avoid formwork deformation due to insufficient local reinforcement.
Detailed processing is crucial for reducing flatness errors. Continuous backing ribs should be installed at the junctions of the beam bottom formwork and the column/wall formwork to ensure a smooth transition at the junctions, preventing unevenness on the concrete surface due to formwork misalignment. Before formwork installation, beam edge lines should be marked on the support system, and the formwork position adjusted according to these lines to reduce manual installation errors. Simultaneously, the formwork joints should be sanded smooth to remove burrs or protrusions, preventing joint marks on the concrete surface.
Dynamic management during construction is indispensable. After the formwork is installed, a comprehensive inspection is required, focusing on the flatness of the formwork, the tightness of the joints, and the stability of the supports. Any uneven areas should be adjusted promptly. Before pouring concrete, the formwork must be moistened to prevent water absorption, which could cause the concrete surface to shrink and affect flatness. During pouring, layered vibration is necessary to avoid excessive vibration that could cause formwork displacement. The pouring speed should also be controlled to reduce the lateral pressure of the concrete on the formwork.
By optimizing formwork materials, splicing methods, support systems, reinforcement measures, attention to detail, and construction management, the flatness error of the concrete surface at the bottom of the beam can be systematically reduced. During construction, strict adherence to design requirements is essential, along with strengthened process inspections and dynamic adjustments to ensure quality control at every stage, ultimately achieving a smooth and even concrete surface.
