Cracking and leakage of external walls of buildings has always been a technical problem that plagues building construction, especially in areas with large differences in temperature between winter and summer and strong monsoons. Due to the different thermal expansion coefficients of concrete (including mortar) and masonry walls, it is easy to Shrinkage cracks occur between concrete and masonry walls, between external wall masonry and external wall mortar, and common quality problems such as cracking and leakage of external walls are prone to occur.

In recent years, with the vigorous development of aluminum alloy formwork construction technology, advanced construction concepts such as plaster-free and dry work have begun to sprout and have been initially developed. Aiming at a series of common problems such as cracking and leakage of external walls of buildings, aluminum mold technology is adopted. The all-concrete exterior wall can be better solved.

1. Current Status of the Construction Industry

▪ The construction speed is slow and the construction period is long;

▪ Insufficient construction workers and high labor costs;

▪ The use rate of wooden formwork is low, the damage rate is high, and there are problems with the construction quality.

2. Technology and Process Innovation

▪ Make the entire exterior wall of the building a concrete wall, and the impermeability of concrete itself is better than that of masonry, and it also avoids shrinkage cracks caused by different thermal expansion coefficients of different materials.

▪ Measures such as measuring the construction quality of the aluminum alloy formwork through the external wall angle elastic control line and actual measurement to ensure the construction quality of the physical structure and achieve the purpose of plaster-free external walls.

▪ The exterior wall is equipped with an EPS exterior wall line every two floors, and the verticality and flatness of the exterior wall structure are controlled between the two-story structure. The construction quality is easier to guarantee, and it also plays a positive role in the control of the chromatic aberration of the wall.

▪ After the construction of the main body, the subsequent processes are arranged in layers and rationally, so that the main body-periphery-public-indoor construction is completed in layers, so as to improve efficiency and shorten the construction period.

Using aluminum formwork technology, the concrete for the secondary masonry exterior wall is cast together with the main body, and the connection is flexible to meet the design requirements, simplify the process, and improve efficiency.

3. Aluminum Formwork Construction Technology

Aluminum formwork is mainly composed of formwork system (aluminum profile or aluminum sheet), support system, fastening system, and accessory system. The picture below shows the assembly of aluminum formwork at the construction site.

The four major components of the construction site aluminum formwork include:

▪ Formwork system: Form the closed surface required for construction to ensure that the building structure takes shape when concrete is poured.

▪ Support system: Play a supporting role in the construction process to ensure the support of the floor, the bottom of the beam and the cantilever structure is stable.

▪ Attachment system: It is the connecting component of the formwork, which connects the single-piece formwork into a system to form a whole (pins, pins, bolts).

▪ Fastening system: It is to ensure that the width of the structure of the formwork is formed, and no deformation occurs during the pouring of the concrete, and the formwork does not appear to expand or burst.

The components of the aluminum formwork system need to be designed according to the characteristics of the floor, which requires high design and technical personnel. Each module of the aluminum formwork can be recycled in multiple projects. Its outstanding technical advantages include:

▪ Short construction period. Quick dismantling and quick construction in assembly line greatly improve the construction schedule and save management costs.

▪ There are many times of repeated use, and the average use cost is low. The standard construction of aluminum formwork can be turned over and used more than a hundred times.

▪ Convenient construction and high efficiency. The aluminum formwork system is simple and convenient to assemble, and it can be completely handled and assembled manually.

▪ Good stability and high bearing capacity. The bearing capacity of most aluminum formwork systems can reach 60KN per square meter, which is sufficient to meet the bearing capacity requirements of most residential buildings.

▪ Few joints, high precision, and good concrete surface effect after mold removal. After the aluminum building formwork is demolished, the surface quality of the concrete is smooth and clean, so that plaster-free is realized, which can save the cost of batching.

▪ Standards, strong versatility, and high recycling value. There are many specifications of aluminum formwork, which can be assembled with different specifications according to the project, and the recycling value is high.

▪ Energy saving and environmental protection. All materials of the aluminum formwork system are renewable materials, which greatly reduces the waste of resources such as traditional wood materials, and is energy-saving, environmentally friendly and low-carbon.

4. Design Principles of All-concrete Exterior Walls

Structural Adjustment

▪ When determining the structural scheme, the external wall should be set as a fully cast-in-place concrete wall under the premise of satisfying the seismic design;

▪ The wall under the window is designed as integral connecting beam or double connecting beam;

▪ Avoid opening structural holes, if openings are necessary, window openings should be combined with the building;

▪ There is no small wall stacking masonry connected with the main structure on the external wall;

▪ Reduce secondary pouring components, such as construction columns, etc.;

▪ In the design, consider the added value of the load after the masonry is converted to a concrete wall, and no longer consider the load of the plastering surface;

▪ Peripheral decorative components involved in area calculation need to be poured into one at a time.

Structure Drawing

▪ When the structural adjustment method cannot realize the full cast-in-place exterior wall, the remaining masonry shall be replaced by the concrete structure wall and the main structure integrally cast-in-place in the form of structural draw joints;

▪ Structural joints refer to the installation of vertical and horizontal flexible materials between the structural concrete wall and the shear wall, so that the structural wall does not participate in the structural calculation;

▪ The increase in wall stiffness caused by the construction of the wall can be solved by setting the cycle reduction factor;

▪ The dividing lines of the exterior wall should be set in conjunction with the structural drawing joints;

▪ Structural drawing seams are generally composed of U-shaped fixed water-stop grooves inside and outside and drawing seam materials;

▪ The draw seam material should meet the requirements of fireproof, waterproof, elasticity, strength and weather resistance.

5. Conclusion

Through the introduction of aluminum formwork construction technology and the economic comparison between aluminum formwork combined with full external wall concrete design and traditional design, this paper concludes that the application of aluminum mold construction technology combined with full concrete external wall system (considering the construction of concrete walls), the overall structure contains steel Compared with the ordinary shear wall system, the cost has not increased significantly, especially for super high-rise residential buildings. Due to the need of structural rigidity, the structural layout is basically a full concrete exterior wall.

The overall cost increase per square meter of the all-concrete exterior wall system using aluminum formwork technology is limited, but it greatly improves efficiency, shortens the construction period, reduces labor costs, and is low-carbon and environmentally friendly. This is inevitably the development trend of the construction industry.