Traditional applications of AAC panels mainly concern the enclosure of buildings, as well as interior and exterior wall panels and floor panels, with limited use in load-bearing walls. There has been extensive research on the flexural resistance of reinforced AAC panels in China, with analytical models for flexural load-bearing capacity proposed as early as the 1980s. Compared to concrete blocks and reinforced concrete structures, AAC panel-structured buildings offer the advantages of low weight, good seismic performance, economic efficiency, minimal on-site wet work, low noise, recyclability of materials, ease of factory production, standardization, and fast on-site assembly. These advantages align with the requirements for energy-saving, carbon reduction, green building, and ecological low-carbon housing, meeting the demands of building industrialization and prefabricated buildings, consistent with the carbon neutrality strategies in construction.

The application of AAC blocks in low-rise residential buildings has matured with respect to masonry systems. However, in comparison, the use of AAC panels as structural components in prefabricated systems is lagging. Panels are still used as load-bearing walls in a horizontal large block format, and floors primarily consist of cast-in-place reinforced concrete, resulting in very low assembly efficiency. This paper introduces a demonstration project involving a single-storey and a double-storey AAC panel-structured residential building, with a focus on research and application of key technologies such as modular building design, structural assembly, integrated enclosure insulation, and construction joints, proposing practical design and construction methods to guide the design and construction of AAC panel-structured residential buildings.

Building design

Floor plan design

AAC panel-structured residential buildings differ from traditional residences, requiring modular design to facilitate component processing and on-site installation. Modular design connects building design, construction, and component production, creating a highly efficient and high-quality pathway, essential for standardized, serialized, and industrialized building design.

The building floor plan of the demonstration project is shown in Figure 1, divided into two small residences. The left side shows Unit 1, and the right side shows Unit 2. Unit 1 has a one-room, one-living room, one-kitchen, and one-bathroom layout on the first floor, and three bedrooms and one bathroom on the second floor, with a total floor plan area of 105 m². Unit 2 is a single storey building with two bedrooms, one living room, one kitchen, and one bathroom, with a total floor area of 60 m². The design strictly follows a 600 mm panel width. In actual production and construction, the building plan will be flexibly adjusted based on the panel layout and wall thickness.

In the demonstration project, ALC panel widths typically follow a 600 mm module. Modular design reduces panel cutting and waste, improves material utilization, and saves costs while making construction more convenient and efficient. It also enhances the stability of the building structure.

Wall panels in the demonstration project are primarily designed using a 600 mm module, with internal spans of 3900, 3300, 3000, 2400, 2100, 1800 mm, etc., in full and half modules. For example, the floor areas of the kitchen, bedroom and bathroom are 3000 x 2400 mm, 3000 x 3900 mm, and 3000 x 2100 mm, respectively. Modular design facilitates standardized positioning within functional rooms.

Elevation design

The building elevation is designed with a module height of 100 mm. The sample house project has a floor height of 3 m, a parapet height of 0.8 m, and a total building height of 6.8 m.

Demonstration project design

Structural design

The main structure of this project uses an AAC panel-structured system. The layout of AAC load-bearing walls is shown in Figure 2. The structural safety level is Grade 2, with a design service life of 50 years. The seismic intensity is 7 degrees, the seismic group corresponds to Level 3, the basic seismic acceleration is 0.10 g, and the characteristic period is 0.45 s. The foundation uses a reinforced concrete strip foundation with a characteristic bearing capacity of 100 kPa.

The design thickness of the AAC load-bearing wall panels is 240 mm. Floor and roof panels use both AAC single panels and AAC composite panels, with the floors connected to the tie beams with reinforcing bars. Both the wall and floor panels use B06A5.0 grade materials.

The structural analysis for this project was conducted using the ABAQUS finite element software, with the AAC modelled using C3D8R elements. Variable standard loads were selected as follows: floor 2.0 kN/m², stairwell 2.5 kN/m², non-accessible roof 0.5 kN/m², bathroom 2.0 kN/m², terrace 2.0 kN/m², basic snow load 0.25 kN/m², and basic wind load 0.35 kN/m².

Finite element analysis under rare seismic events using the El-Centro wave input indicates that the maximum Mises stress in the structural system does not reach the ultimate compressive strength of the concrete. The structural system demonstrates good load transfer efficiency, with maximum displacement angles within 1/1000, and no structural damage endangering human safety, confirming the overall safety and reliability of the structural system.

Enclosure system design

External wall panel design

The demonstration project adopts high-performance AAC core panels, which have advantages over standard AAC external wall panels in terms of energy efficiency, installation speed, fewer joints, thinner panels, larger effective room area, and better lateral force resistance. The core panels use B06A5.0 grade AAC with a thermal conductivity of 0.13 W/(m·K) and a thickness of 240 mm. The overall heat transfer coefficient of the wall is 0.6 W/(m²·K), meeting the requirements of the "Energy Efficiency Design Standards for Rural Residential Buildings." The core panels feature longitudinal and transverse connecting core holes as shown in Figure 4.

Each building span in this project is composed of assembled wall panels. The floor plan of assembled wall panels is shown in Figure 5. A total of 62 assembled AAC wall panels were produced for this demonstration project, with 42 panels for the first floor and 20 for the second floor. The design of all external wall panels is based on 600 mm modules.

Floor and roof panel design

Currently, floor and roof panels in rural residential buildings in China are mainly cast-in-place reinforced concrete slabs and prefabricated composite slabs. Cast-in-place reinforced concrete slabs require on-site formwork, steel bar tying, and concrete pouring, with formwork removal after the concrete reaches design strength. This process involves extensive on-site wet work, long construction periods, and high labour costs, making rapid assembly in rural housing projects difficult.

The demonstration project uses AAC single panels for floors and composite panels for roofs. The composite panel is a reinforced concrete layer cast on top of an AAC floor panel (175 mm thick). Compared to ordinary prefabricated concrete composite panels, the AAC floor panel used as the base has high overall stiffness during the construction stage, reducing the likelihood of breakage during transportation and installation. This allows for factory-standardized, modular production, eliminating the need for formwork during construction, thereby reducing on-site work and shortening the construction period. The economic benefits are significant, compared to prefabricated composite and cast-in-place slabs. The composite layer facilitates the installation of electrical and plumbing lines, with panel seams forming dowels after concrete pouring to enhance the bond between new and old concrete.

Joint and construction design

Wall panel joints

AAC core panels feature longitudinal and transverse core holes that allow for rebar insertion and grouting, forming a cohesive unit of reinforced panels.

To facilitate on-site construction, individual panels were pre-assembled into wall units at the factory. Each building span comprises of a single wall panel, with corresponding panels placed on each floor. The assembly joints of the wall panels are shown in Figure 7.

Floor panel joint design

AAC single panels and composite panels have good overall stiffness and can be designed as conventional AAC flexural components. Composite panels are designed based on the balance formula of the concrete composite layer under compression and the internal steel bars under tension. The thickness of the AAC bottom panel of the composite floor should not be less than 125 mm as shown in Figure 8.

The total volume of AAC panels used in this project was 104 m³, with a total building area of 165 m². The main on-site construction was completed in 9 days. The final completion is shown in Figures 9 and 10.

Conclusions

Starting from modular design of residential buildings, this project provides a standardized structural system design, adopting a factory-prefabricated large panel method, integrating wall panels as external wall units, and optimizing installation and construction processes to achieve modularization, standardization, serialization, and assembly of urban AAC residential buildings.

1.     For the design, it is recommended to use a 600 mm module, which demonstrates appropriate standardization and relative flexibility during the design process.

2.     High-performance AAC core panels offer excellent insulation and energy efficiency. Horizontal holes in the members provide the opportunity to construct elements consisting of multiple panels with lateral force resistance.

3.     The application of AAC single panels and composite panels improves thermal insulation and sound insulation of floor and roof panels, enabling factory production, scale production, formwork-free and convenient construction with good structural integrity, short construction periods, and highly consistent and well-controlled building quality.

References

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