Keywords

1 Introduction

In recent years, with the vigorous promotion of the national “dual carbon” policy, the guidance and incentives from local policies, as well as the driving force of the transformation and development needs of the construction and engineering industry, net-zero buildings have gradually become a significant hotspot for the industry [1]. Designing and constructing new materials and structures that balance energy consumption and generation, reducing greenhouse gas emissions and overall energy consumption throughout the construction process and the entire lifespan of the building, and achieving precise monitoring and in-depth data analysis are necessary conditions for achieving net-zero building technology [2, 3].

Building zero carbon is a systematic project, rather than the independent operation of each link and each component [4, 5]. Aiming at the pain points of low energy consumption structure, such as low industrialization degree and limited safety recognition degree, the prefabricated hemispherical cavity plate structure with stable mechanical properties, high safety and reliability and low energy consumption was developed through the combination of prefabricated construction technology and hollow inner membrane structure and optimization and improvement of hollow inner membrane parameters [6, 7]. The main innovation points of the research are: the node construction mode is independent cast-in-place, the semi-spherical hollow inner membrane provides better bearing capacity, the thermal bridge effect of the cavity structure partition plate, the development of efficient green building materials with highly industrialized traditional building materials [8], the application of energy saving and heat insulation technology in the building structure to the prefabricated building system, to achieve the balance and coordination of technical adaptability and economic sustainability [9].

2 Structure Introduction

Fig. 1.
figure 1

The structure diagram of fabricated cavity structure

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The prefabricated cavity floor structure is made by prefabricated cavity intimal members combined with concrete laminated floor fabrication technology. The specific structure is shown in Fig. 1.

Compared with solid plate, under the premise of similar mechanical properties, the body weight of assembled cavity structure can be reduced by 30%–60%. Save steel 20%–30%, concrete 40%–50%, formwork 60%–70%; Shorten the construction period by 1–1.5 days/flow time [10, 11].

3 Mechanical Property Test

3.1 Experimental Design

In this paper, the full size test of 8700mmx8700mm prefabricated laminated cavity floor is carried out to evaluate the bearing capacity and service performance of cavity floor structure through the observed deflection deformation, stress and strain of each measuring point and the crack development of the floor during load application [12]. The specific static loading test process and measuring point arrangement are shown in Fig. 2.

The specific loading process is as follows:

  1. 1.

    Preload: preload before loading, apply the load 0.5 kN/m2, the duration is 15 min, and then unload to ensure that all the test instruments can work normally.

  2. 2.

    Formal loading: formal loading from the plate across the central position gradually spread to all sides, forming uniform loading. The load of the first stage is 1.0 kN/m2, and then each stage is increased by 1 kN/m2 until the eighth stage; The ninth stage starts to load in increments of 2 kN/m2 per stage to the eleventh stage; The twelfth level load is 15 kN/m2; The final stage load is 16 kN/m2. After each stage of loading is completed, stand for 20 min to start reading, observe the cracks at the bottom of the board, and make a mark.

  3. 3.

    Static observation: Stop loading after loading to the last level of load, and observe and read again after 12 h of load, and then unload to understand the load holding capacity and recovery of the board.

Fig. 2.
figure 2

Test design and measuring point layout

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3.2 Experimental Analysis

The test site layout is shown in Figs. 3, 4 and 5. The maximum deflection value at the center of the plate is 13.245 mm, and the standard deflection limit is L/250, that is, 34.8 mm. The deflection of the test plate does not exceed the limit value to meet the bearing capacity requirements, and the crack development also meets the normal use requirements, indicating that the structural safety of the floor can fully meet the use requirements.

The deflection value of the floor gradually decreases from the center point outward and is evenly distributed. The stress characteristics are similar relative to the center symmetric position, and the deformation trend is the same in the vertical and horizontal direction. All these characteristics indicate that the prefabricated composite cavity floor has good integrity and bidirectional stress [13].

Fig. 3.
figure 3

Deflection deformation curve under different loads

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Fig. 4.
figure 4

Deflection deformation after unloading

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4 Thermal Performance

4.1 Experimental Design

Two newly built 3 m × 3 m × 3 m experimental prototypes were used for comparative tests, respectively using assembled integral multi-ribbed cavity floor (no insulation layer but waterproof layer in the floor) and traditional cast-in-place concrete floor (with waterproof layer and insulation layer in the floor).

Hygrograph: used to determine the temperature and relative humidity of the environment, where the allowable error of temperature is ±2 °C, and the error of humidity indication is ±5%RH.

Anemometer: An instrument used to measure the velocity of air. Low speed is 0–5 m/s, medium speed is 5–40 m/s, and high speed is 40–100 m/s.

Specific test arrangement:

  1. 1.

    Make two experimental rooms with identical size, dimension and wall thickness.

  2. 2.

    The cavity structure experiment room is not equipped with thermal insulation materials, and the cast-in-place concrete structure experiment room is equipped with roof insulation layer.

  3. 3.

    Set the same orientation, shading and other boundary adjustment,

The test time is different time periods in March, May and August, and the test content is outdoor temperature, indoor temperature of cast-in-place structure and indoor temperature of cavity structure.

Fig. 5.
figure 5

Infrared thermometer

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4.2 Test Data Analysis

The temperature data of March and May are listed in Figs. 6, 7 and 8. By comparing the temperature conditions of outdoor, precast cavity experiment and traditional concrete experiment, it can be found that: when the outdoor temperature fluctuates in March, the temperature of prefabricated structure changes more gently, and the overall temperature data are higher than that of traditional concrete structure; In May, when the outdoor temperature is higher, different outdoor temperatures will also bring different performance of the assembled structure. When the outdoor temperature is about 19 °C, the overall temperature of the assembled structure is lower than that of the traditional structure, but when the outdoor temperature exceeds 23 °C, the assembled structure will have a higher room temperature than the traditional structure.

In order to better understand the difference between the performance of the cavity structure and conventional concrete under high temperature conditions, temperature tests were conducted on a single day in August, from 11:40 PM to 15:40 PM, with a time interval of one hour. The obtained internal temperature data of the experimental body are shown in Fig. 9. It can be found that the cavity structure can not exceed the performance advantage of thermal insulation materials for the time being from the temperature comparison in each period, but the cavity structure shows a more gentle performance in the temperature development trend of one day.

Fig. 6.
figure 6

Temperature data for March

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Fig. 7.
figure 7

Temperature data for May 22

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Fig. 8.
figure 8

Temperature data for May 23

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Fig. 9.
figure 9

Temperature data for August

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5 Conclusion and Prospect

In this paper, the performance of a prefabricated cavity structure is studied from both mechanical and thermal aspects. The deformation and crack development analysis of the cavity structure is carried out by full-scale static loading test. The test results show that the structure has sufficient bearing capacity and the deformation and crack development meet the requirements of the concrete structure code. Thermodynamic performance is compared between the test house made by prefabricated cavity structure and the house made by traditional concrete structure by means of thermal test. The results show that prefabricated cavity structure can show better ability to cope with temperature changes, and it is more in line with the characteristics of warm winter and cool summer than traditional structure. Prefabricated structures can become poorly equipped to handle high temperatures.

After the preliminary verification that the assembled structure is safe enough, what factors cause the sensitivity of the assembled cavity to high temperature becomes the focus of future research, and how to improve the better temperature control ability of the assembled structure will become the key factor to promote the assembled cavity structure to meet the low-carbon development.