Study on Sound Insulation of Integrated Composite Wallboard Made of ALC and Rock Wool Panel

Abstract

The integrated composite wallboard is a new type of prefabricated building enclosure wallboard made of autoclaved aerated concrete (ALC) and rock wool panel, which can meet the thermal requirements of cold areas in China without additional insulation. The ALC of the integrated composite wallboard is divided into local four-sided supported plates by vertical and horizontal ribs, which makes the wallboard have a different sound insulation performance from the wallboard of single uniform material and the composite wallboard of double-layer lightweight plates. The authors investigate the sound insulation performance of the integrated composite wallboard and compare it with other lightweight wallboards. They have found an apparent coincidence frequency region of air-borne sound insulation, which coincides with the natural vibration frequency of the local four-sided supported panel of ALC. Such an anastomosis effect seriously affects the weighted sound reduction index Rw, which reduces the weighted sound reduction index by 6 ~ 8 dB. The sound insulation experiment of integrated composite wallboard of ALC and rock wool panel objectively reflects the adverse effects of the sandwiched wallboard structure and provides a reference for improving the sound insulation performance by structurally upgrading the integrated composite wallboard.

1 Introduction

1.1 The Template Files

Prefabricated buildings have been developing in China in recent years, and the prefabricated envelope structure is an important part of prefabricated buildings. According to the Standard for Evaluation of Prefabricated Building GB/T51129-2017, the external envelope and internal partition wall account for 20 out of 100 points in the prefabricated building. Lightweight concrete insulation integrated composite wallboard is an important form of prefabricated building envelope structure, which has been developed with many types of composite wallboard products in China.

Autoclaved aerated concrete (ALC) is a porous concrete product made of fly ash (or silica sand), lime, cement, aerating agent, and other raw materials cured by high-pressure steam, which features lightweight, high strength, heat preservation, and insulation, fire resistance, and sound insulation, easy processing, etc. Autoclaved aerated concrete slabs have been widely used in building envelope structures, and their applications have been studied extensively. However, in the cold areas of northern China, the autoclaved aerated concrete slabs cannot meet the thermal insulation requirement, and buildings still need to add insulation layers. In the research and experimental building project of China Metallurgical Construction Research Institute Co., Ltd., combined with the subject “Technology and Products of Lightweight and Environment-friendly Envelope System for Steel Structure Building” under the National Key Research and Development Program “Key Technology and Demonstration for Industrialization of Steel Structure Building,” we have developed an integrated composite insulation exterior wallboard of ALC and rock wool, using autoclaved aerated concrete as the load-bearing material and rock wool as the sandwich insulation material. The composite exterior wallboard can meet the insulation requirements in cold areas without additional insulation [1, 2]. In this paper, its sound insulation performance will be studied.

For ordinary reinforced concrete, the exterior wall with a thickness of 180 ~ 200 mm can achieve good sound insulation performance. While lightweight concrete has low density, the exterior wall of the same thickness will have much lower sound insulation performance, so it needs to add sound insulation panels to meet sound insulation requirements [3]. The sound insulation of single-layer uniform lightweight concrete wallboard basically meets the mass law of sound insulation [4]. The composite wallboard consists of two layers of thin plates, an air layer, and a layer of sound-absorbing material, and there have been numerous studies on the sound insulation of double-layer composite wallboard [5, 6]. Similar to the integrated wallboard structure presented in the paper, there have been studies on two-layer LSP panels composite exterior walls [7] and the prefabricated composite wall with a layer of rock wool sandwiched between the two-layer ALC panels [8]. Among them, the composite wallboard of ALC with rock wool panels is widely used, and the sound insulation has an obvious coincidence frequency region.

The ALC + rock wool integrated composite wallboard we have developed has a standard width of 600 mm, longitudinal ribs of 75 mm width on both sides of the wallboard, and transverse ribs at both ends and in the middle span of the wallboard. In the middle of the composite panel lies the rock wool sandwich panel, which not only plays the role of heat preservation but also improves sound insulation performance. The structural form of ALC + rock wool integrated composite wallboard will affect its sound insulation performance. Its structure does not conform to the characteristics of a two-layer thin panel structure [5, 6] or two-layer thick plates + interlayer [7, 8]. This paper will study the sound insulation performance of ALC + rock wool integrated composite wallboard.

2 Sound Insulation Requirements and Measurement of Enclosure Walls

With the development of the economy and science and technology, more vehicles and outdoor recreational activities increase noise sources continuously. At the same time, many new lightweight building materials weaken the ability of sound insulation and noise reduction of civil buildings. Improving the sound insulation index of the building envelope is an important measure to solve the noise interference problem in civil buildings. The standards of foreign developed countries have high requirements for building sound insulation. For example, the British standard is $D_{{\text{nt,w}}} + C_{{{\text{tr}}}} = 43{\text{dB}}\sim 45{\text{dB}}$, the Australian standard is $D_{{\text{nt,w}}} + C_{{{\text{tr}}}} = 45{\text{dB}}$, and the American standard is STC 45, equivalent to $D_{{\text{nt,w}}} + C_{{{\text{tr}}}} = 45{\text{dB}}$. Code for Design of Sound Insulation of Civil Buildings (GB50118-2010) of China stipulates the air sound insulation index of the exterior wall: the air sound insulation single value evaluation + traffic noise correction should be more than 45 dB.

The measurement of sound insulation of the outer envelope consists of field measurement and laboratory measurement. The field measured data results can be evaluated by the single value of standardized sound pressure level difference $D_{{{\text{nT}}}}$:

$$D_{{{\text{nT}}}}^{{}} = L_{{1}} - L_{2} + 10{\text{lg}}\frac{T}{{T_{0} }}$$

(1)

The data results measured in the laboratory can be evaluated by the single value of weighted sound insulation $R_{{\text{w}}}$:

$$R_{{\text{W}}}^{{}} = L_{{1}} - L_{2} + 10{\text{lg}}\frac{ST}{{0.161V}}$$

(2)

where, $L_{1}$ is the average sound pressure level in the sound chamber(dB); $L_{2}$ is the average sound pressure level in the sound receiving chamber(dB); T is the reverberation time of the sound receiving chamber (s); $T_{0}$ is the reference reverberation time (s), which is generally 0.5 s for residential buildings; $S$ is the area of the specimen (m²), which is equivalent to the area of the test hole; V is the volume of the sound receiving chamber (m³). According to Eqs. (1) and (2), the air sound insulation of the 1/3 frequency band can be calculated. With the sound insulation characteristic curve drawn on the sound insulation value-frequency coordinate system, the weight of a single value of sound insulation evaluation can be calculated according to the code Rating Standard of Sound Insulation in Buildings GB 50121.

3 Comparison of Sound Insulation Performance of Lightweight Concrete Walls

3.1 Foamed Cement Composite Wallboard

The research group has conducted sound insulation research on foamed cement composite wall panels. The bulk density of foamed cement is 680 kg/m³, the wall thickness is 250 mm, and the surface density is 170 kg/m². The size of a piece of wallboard is 1965 × 2500 mm, two pieces are put together for the test, and the gap is filled with cement mortar. The size of the wall for the sound insulation test is 4000 × 2500 mm, and the total area is 10m². The experimental data are shown in Fig. 1. The single value evaluation of air sound insulation obtained is $R_{{\text{w}}} ({\text{C}}\,{;}\,\,{\text{C}}_{{{\text{tr}}}} ){ = }47(0\,; - 2{)}$dB, and the curve has no obvious coincidence frequency valley.

Fig. 1

Sound insulation frequency characteristic curve of foamed cement composite wallboard

3.2 ALC Block Wall

The autoclaved aerated concrete block size is 600 × 180 × 240 mm, and the density grade is 750 kg/m³. The weight of the single block is 19.8 kg. After the putty is put on the wall for 10 mm, the thickness of the wall is 200 mm, and the surface density is 170 kg/m². The sound insulation test hole size is 3585 × 2800 mm, and the total area is 10.04 m².

The experimental data [3] are shown in Fig. 2. The single value evaluation of air sound insulation is $R_{{\text{w}}} {\text{(C;}}\,\,{\text{C}}_{{{\text{tr}}}} {) = }48( - 1; - 4)$dB, and the curve has no obvious coincidence frequency valley. The surface densities of the ALC block wall and foamed cement wall are 170 kg/m², and since they are made of uniform material, their sound insulation values are the same, with only a 1 dB difference.

Fig. 2

Sound insulation frequency characteristic curve of ALC block wall

3.3 Composite Wall with Rock Wool Panel Sandwiched Between Two-Layer ALC Panels 

Reference [6] presents an experimental study of sound insulation for the composite wall of 75 mm thick ALC panel + 50 mm rock wool panel + 75 mm thick ALC panel. The wall structure is shown in Fig. 3, and the ALC density is 650 kg/m³, the rock wool panel density is 100 kg/m³, and the wall surface density is 102.5 kg/m². The experimental curve is shown in Fig. 3. As seen from the curve, there is an obvious sound insulation anastomosis valley near 630 Hz, which ranges from 500 to 800 Hz. When the frequency passes the anastomosis zone, the sound insulation increases with the increase of the sound frequency.

Fig. 3

Sound insulation characteristic curve of two-layer ALC panel with rock wool

4 Integrated Composite Wallboard ALC + Rock Wool Sound Insulation

4.1 ALC + Rock Wool Integrated Composite Wallboard Structure

ALC (Autoclaved Aerated Concrete) + rock wool integrated composite wallboard is incorporated by autoclaved aerated concrete and rock wool and placing reinforcement to improve the bearing capacity and crack resistance, as shown in Fig. 4. The density of ALC is controlled from 500 to 800 kg/m³, and the strength is not less than 3.5 MPa, which can meet the strength requirements of the wallboard. The density of rock wool is not less than 120 kg/m³. The composite density of ALC and rock wool panel is generally 400 ~ 600 kg/m³, equivalent to the weight of wallboard is 100 ~ 150 kg/m², which can effectively reduce the weight of the wall and the seismic response of the structure. The thermal conductivity of ALC is no more than 0.15 W/(m·K), the thermal conductivity of rock wool is no more than 0.04 W/(m·K), and the heat transfer coefficient of composite wallboard can reach 0.31 W/(m²·K) [9]. Rock wool is water-repellent and has the highest fire rating, with a combustion performance rating of A1.

Fig. 4

Structure of ALC + rock wool integrated composite wallboard

4.2 Sound Insulation Experimental Scheme

The sound insulation experiment is carried out on ALC + rock wool composite wallboards according to the standard method. The measured wall is installed with five standard panels and one non-standard panel, as shown in Fig. 5. The gaps are sealed by cement mortar, as shown in Fig. 6.

Fig. 5

Layout of wallboard for sound insulation experiment

Fig. 6

Installation of wallboard for sound insulation experiment

The weight of each piece of each wallboard is 278 kg on average, and the surface density of the wallboard is 157 kg/m². The volume density of rock wool panels is 140 kg/m³, the volume density of ALC is 750 kg/m³, and the density of cement mortar is 1800 ~ 1900 kg/m³. The average surface density of the whole wall is 182 kg/m².

4.3 Prediction of Sound Insulation Experimental Results

When the sound waves incident at an irregular angle, the mass law of sound insulation of a single-layer homogeneous solid wall can be expressed as:

$$R = {20}\lg f + {\text{20lgm}} - {48}$$

(3)

where f— the frequency of the incident wave; m—the mass of the unit area of the wall. When the surface densities and the material properties are relatively similar, the sound insulation values of two wallboards have the following relationship:

$$R_{2} = R_{1} + {\text{20lg}}\frac{{{\text{m}}_{2} }}{{{\text{m}}_{1} }}$$

(4)

Firstly, the integrated wallboard is considered single material wallboard. According to the experimental data of Sect. 3.1 of cement foamed concrete wallboard and Sect. 3.2 of ALC block wall, the surface densities are 170 kg/m², and the sound insulation is 47 dB and 48 dB, respectively. According to Eq. (4), it can be approximately obtained that when the surface density is 182 kg/m², the sound insulation is:

$$R_{{\text{A}}} = {47} + {\text{20lg}}\frac{{{182}}}{{{170}}} = 4{7}.{6}({\text{dB)}}$$

(5)

The sound insulation will be increased if the sandwiched rock wool panel is considered.

4.4 Experimental Results of Sound Insulation

The sound insulation experiment is carried out four days after the installation of the experimental wallboard, and the experimental results are shown in Table 1 and Fig. 7. $R_{{\text{w}}} { = }43.8{\text{dB}}$ is obtained, and the integer number is $R_{{\text{w}}} {\text{(C}},{\text{C}}_{{{\text{tr}}}} ){ = }4{3(}0, - 2)$dB. Compared with $R_{{\text{w}}} { = }4{7}.{\text{6dB}}$ predicted by the previous theoretical analysis, it is 4 dB smaller, and the sound insulation is significantly reduced. The abnormal reduction of sound insulation of ALC + rock wool integrated composite wallboard must be related to the structure of the composite wallboard, which needs further analysis and research.

Table 1 Experimental data of ALC + rock wool composite wallboard sound insulation

Fig. 7

Sound insulation frequency characteristic curve of ALC + rock wool integrated wallboard

As can be seen from Fig. 7, an anastomosis valley appears between 315 and 400 Hz. Compared with Fig. 4, the range of the anastomosis valley is larger. After the coincidence frequency, the sound insulation is proportional to the logarithm of the frequency, and the fitting relationship is shown in Eq. (6):

$$R_{2} = R_{1} + 25.{\text{1}} \times \lg \frac{{f_{2} }}{{f_{1} }}$$

(6)

According to Eq. (3), the logarithmic relationship between sound insulation value and frequency is shown as Eq. (7):

$$R_{2} = R_{1} + 20 \times \lg \frac{{f_{2} }}{{f_{1} }}$$

(7)

By comparing Eqs. (6) and (7), it can be found that the sound insulation value of the integrated composite wallboard is proportional to the logarithm of the frequency after the coincidence frequency of 400–5000 Hz, but the proportional coefficient changes from 20 to 25 in the mass law, reflecting the influence of the sandwich rock wool panel on the sound insulation.

4.5 Analysis of Sound Insulation and Coincidence Frequency of Integrated Composite Wallboard

According to the thin panel sound insulation and anastomosis frequency theory [9], the incident frequency is:

$$f_{{\text{c}}} = \frac{{c_{0}^{2} }}{{{2}\pi {\text{sin}}^{2} \vartheta }} \cdot \sqrt {\frac{\rho }{D}}$$

(8)

Where $D = \frac{{h^{3} E_{{}} }}{{{12(1} - \nu^{2} {)}}}$ is the bending stiffness of the single-layer plate, h = 0.075 m is the thickness of the plate, $\nu$ is the Poisson’s ratio, E is the elastic modulus, $\rho$ is the surface density, $c_{0}$ is the sound speed in the air, and $\vartheta$ is the incident Angle. According to Eq. (8), the coincidence frequency is $f_{{\text{c}}} = \frac{{{504}}}{{{\text{sin}}^{2} \vartheta }}$, $f_{{\text{c}}}$ is minimum when $\vartheta { = }\pi /2$, which is 504 Hz. Obviously, the coincidence frequency of composite wallboard cannot be reflected by the thin panel theory.

ANSYS carried out the finite element modeling analysis of single ALC + rock wool composite wallboard. Since there are two hollow-filled rock wool panels in the 610 mm wide and 2900 mm high single-span wall panels, the rock wool panel has almost no stiffness compared with ALC, so the rock wool stiffness can be ignored for analysis. A single hollow surface is the vibration of half a wave with the lowest frequency of 355 Hz. At the fundamental frequency of local vibration of the ALC panel, around 355 Hz, acoustic resonance occurs in the front and rear panels. The sound insulation value shows a coincidence valley, which is completely consistent with the test results.

The experimental results show an obvious sound insulation trough in the frequency 315 ~ 400 Hz, which is located in the coincidence effect area. Compared with Fig. 4, the coincidence effect area has a larger range. The local bending deformation vibration frequency of the composite wallboard is consistent with the acoustic frequency, and the sound insulation ability is significantly reduced, with the reduction amount reaching 6 ~ 8 dB. As the frequency continues to increase, when the sound source frequency passes the anastomosed effect area, the bending vibration frequency of the panel increases and becomes the main contributor to the acoustic impedance rate. The sound insulation quantity continues to increase with the increase of frequency.

5 Conclusions

The sound insulation of the integrated composite wallboard of the ALC + rock wool panel is different from that of a single material wall as well as that of the on-site composite wall with two-layer of ALC panels and one layer of rock wool panel. Both experimental research and theoretical analysis show new sound insulation characteristics, and the following conclusions can be drawn through the experimental research and theoretical analysis:

• (1) The integrated composite wallboard of the ALC + rock wool panel belongs to non-uniform material wallboard due to structural reasons. Therefore, the relationship between the sound insulation volume and the mass surface density of the wallboard does not conform to the law of mass, which should be measured by experiment.

• (2) There are two local four-sided supporting ALC panels on each side of the integrated composite wallboard of the ALC + rock wool panel, and there is local vibration. The vibration frequency of the local four-sided supporting panel calculated by the finite element method is 355 Hz. In this experiment, the thickness of the local ALC panel is 75 mm, and the density is 750 kg/m³. Since there is no experimental measuring point at 355 Hz, the coincidence frequency obtained in the experiment is between 315 and 400 Hz, which is completely consistent with the finite element calculation results.

• (3) The sound insulation single evaluation value of 75 mm ALC + 125 mm rock wool panel + 75 mm ALC integrated composite wall panel is 43.8 dB. Compared with the wallboard with the same mass density and considering rock wool interlayer, the sound insulation single evaluation value is reduced by about 6 ~ 8 dB, which is unfavorable to the wall’s sound insulation.

• (4) It is necessary to improve the structural form of the integrated composite wallboard or add sound insulation measures to meet the standard of sound insulation required by the specification, such as adding a 10 mm thick sound insulation panel, adjusting the thickness of the ALC panel on both sides of composite wallboard rock wool to avoid local resonance before and after.