Effect of different factors on sound absorption property of porous concrete

Highlights

• Impact of aggregate size and cement to aggregate ratio on sound absorption property of porous concrete.

• Effect of porosity and thickness on the sound absorption property of porous concrete.

• Influence of temperature on the sound absorption performance of porous concrete.

• Different humidity of porous concrete effect on its sound absorption performance.

Abstract

As a functional pavement material with a large number of pores, porous concrete (PC) pavement exhibits a good sound absorption performance. Limited experimental studies focused on the effects of aggregate size, cement to aggregate ratio, and pavement thickness of porous concrete on its sound absorption in a wide range of sound frequencies. Besides, the effects of temperature and humidity on the sound absorption performance of porous concrete are still unclear. In this study, one hundred and thirty-five samples of porous concrete were prepared that consist of three aggregate gradations, three cement to aggregate (C/A) ratios and three thicknesses to investigate the sound absorption property of porous concrete considering the effects of temperature and humidity. These samples were tested at different temperatures (−10, 5, 20, 35 and 50 °C) and with different humidity (dry, inundated and saturated) using impedance tubes method with varied sound frequencies (200–2000 Hz). The results demonstrated that: under the same conditions, the sound absorption property of porous concrete decreases with the increase of aggregate size and cement to aggregate ratio, and increases with the increase of thickness. In addition, the temperature and presence of water have significant effects on the sound absorption property of porous concrete.

Introduction

With the rapid development of the urbanization process, a large number of evaluated roads and expressways have been constructed to meet the driving needs of urban residents. Followed by the traffic noise caused by the rapid increase of vehicle speed, which has brought great trouble to the lives of residents along the road (Cackler et al., 2006, Sirin, 2016). In order to elevate/solve this problem, a large number of low-noise roads and noise barriers have been constructed and applied. Porous concrete (PC) materials exhibit a good sound absorption property due to a large number of interconnected pores inside them, which is used in the construction of porous concrete pavement and sound barrier materials (A.Offenberg, 2011, Tian and Niu, 2008, Wang and Zhao, 2015). Moreover, for sponge city construction in China, as one of the important technologies for sponge city construction, porous concrete pavement has unprecedented opportunities for research, development and application (China, 2014).

At present, the research on the sound absorption performance of porous concrete is mainly based on experiments, and other scholars used theoretical modeling to analyze the sound absorption model of porous concrete and compared it with the test results to analyze the reliability of the obtained models (Kim and Lee, 2010a, Leandri, 2012, Neithalath et al., 2005). The test and evaluation methods of the sound absorption property of porous concrete include impedance tube (Kim and Lee, 2010a, Leandri, 2012, Nelson et al., 2008), reverberation chamber (Park et al., 2005), simulated reverberation chamber (Zhong, 2011), sound pressure (P) and acoustical particle velocity (U) setup (Kim and Lee, 2010a) methods.

The main factors that effect on the sound absorption property of porous concrete are: porosity (Lu, 2013, Bérengier et al., 1997, Ni et al., 2014), aggregate size (Marolf et al., 2004, Olek et al., 2003, Rios et al., 2019), aggregate gradation (Kim and Lee, 2010a, Marolf et al., 2004), aggregate type (Kim and Lee, 2010b, Ngohpok et al., 2017), specimen thickness (Jin et al., 2010, Zhao and Yin., 2009), additives (Kim and Lee, 2010b, Neithalath et al., 2004, Wang and Zhao, 2015) and double-layer structure (Jin et al., 2010, Wang and Zhao, 2015), while other factors such as aggregate shape (Kim and Lee, 2010a) and air humidity(Zhong, 2011) have been studied by few studies.

As the most important internal pore characteristics of porous concrete, porosity is a very important factor for the sound absorption performance of porous concrete. In previous studies, three different views have been mentioned about the effect of porosity on the sound absorption property of PC. Firstly, it is considered that as the porosity increases, the sound absorption performance of porous concrete increases. This refers to that the increase of porosity will increase the probability of sound entering into the pavement, and the sound propagation in the pores will also increase the energy consumption of sound, which improves the sound absorption performance (Bérengier et al., 1997, Ni et al., 2014). Secondly, the sound absorption performance of PC shows a trend that it firstly increases and then decreases with the increase of porosity, and these studies recommended a range of porosity with the best sound absorption performance based on the research results. This is owing to when the aggregate size is the same, the increase of porosity will increase the pore size, while the energy consumption of sound propagating in the pore with a larger pore diameter is less than that in the pore with smaller pore diameter (Park et al., 2005, Zhao and Yin., 2009). The main reason for the previous views is that some researchers analyze the influence of porosity on the sound absorption performance and its porosity range was limited. The porosity in this area is in the rising range of the porosity-sound absorption curve. In that range, the sound absorption performance increase with the increase of porosity. After the peak point, with the increase of porosity, the sound absorption performance shows a downward trend. Finally, some scholars think that the effective porosity is only a macroscopic property of porous concrete, and the pore distribution and pore size of porous materials are the main factors affecting their sound absorption performance (Jin et al., 2010).

It was generally believed that when the porosity of the porous concrete is the same, the smaller the aggregate particle size, the better the sound absorption performance. This is attributed to when the particle size is smaller, the number of pores in porous concrete will increase, and the sound transmission channel will increase. Therefore, the energy consumption in the process of sound transmission will increase, thus the sound absorption capacity will be improved (Kim and Lee, 2010b, Rios et al., 2019, Zhao and Yin., 2009). The aggregate gradation has a significant impact on the sound absorption performance of porous concrete. However, it only affects the maximum sound absorption coefficient, and has no substantial effect on the peak frequency (Kim and Lee, 2010b, Rios et al., 2019). The studies that focused on the influence of aggregate types on the sound absorption property of PC are mainly divided into two aspects: the effects of different types of recycled aggregates and their blending ratios on sound absorption performance, and the sound absorption performance of stone materials with internal pores such as Perlite and Zeolite. As a part of aggregate to replace the new aggregate, porous concrete prepared with recycled aggregate has good sound absorption ability than the new aggregate. Also, the aggregate with pores inside can significantly improve the sound absorption ability (Kim and Lee, 2010b, Neithalath et al., 2005, Ngohpok et al., 2017, Oancea et al., 2018). Regarding the impact of the shape of aggregate, it has little effect on the sound absorption performance of PC (Kim and Lee, 2010b). As an important part of porous concrete, additives can also affect its sound absorption performance. Researchers consider that fiber and aluminum powder can significantly improve the sound absorption property of porous concrete, but the reason for this promotion was not clearly provided (Kim et al., 2018, Neithalath et al., 2004, Wang and Zhao, 2015).

When using the simulated reverberation chamber method to test the sound absorption performance of porous concrete, it was found that the increase in air humidity could improve its sound absorption performance. This refers to the increase in air humidity increases the viscosity of the air and causes frictional energy between the air that is also increased, which in turn increase the sound absorption coefficient of the PC materials (Zhong, 2011).

While the porous concrete materials are determined, the influence of the material thickness on the sound absorption performance of porous concrete is reflected in the absorption effect of different frequencies of sound. Generally, with the increase of thickness, the sound absorption property of porous concrete increases in the full frequency range, however the absorption effect of noise caused by vehicle driving becomes low (Jin et al., 2010, Neithalath et al., 2005, Tao, 2006). With the increase of thickness, the dominant absorption frequency (the frequency with the highest absorption coefficient) of porous concrete was transferred from high to low. This makes its absorption effect on the frequency that close to the traffic frequency (in the range of 650–1250 Hz) lower, therefore its absorption capacity for driving noise becomes lower (Tao, 2006). Based on the previous studies, some scholars recommended the optimum thickness of porous concrete pavement for different types of traffic loads (Jin et al., 2010, Tian and Niu, 2008). In addition, some scholars have explored the effect of double-layer structure on the sound absorption property of porous concrete and recommended a suitable combination of double-layer structure and thickness (Jin et al., 2010, Wang and Zhao, 2015).

In summary, the current research on the sound absorption property of porous concrete was mainly focused on the porous concrete materials itself. However, the influence of external environment such as temperature and water on the sound absorption performance of porous concrete has received less attention.

The objective of this study is to analyze the influence of temperatures and humidity on the sound absorption performance of porous concrete. Therefore, a method of measuring the sound absorption property of porous concrete with varying states of temperature and water is proposed in this study. In addition, the impact of aggregate particle size, cement to aggregate ratio (C/A), and thickness on the sound absorption performance of porous concrete in the full frequency at 20 °C was first investigated. Then, the effect of temperature on the sound absorption property of porous concrete with different types and thicknesses were examined. Finally, the sound absorption effect of the inundated and saturated porous concrete specimens at −10 °C and 20 °C was investigated, and the effect of water in different states on the sound absorption property of porous concrete was also analyzed.