Alemayehu Moges Kebede

The improvements show that the sound absorption capacity of the SPMs is more than double that of the porous concrete with 25% design porosity. Therefore, the micropores were generated using aluminum powder and the sound absorption was then compared with SPM without aluminum powder. Effects of the different hole depth combinations on SPM sound absorption: (a) without Al and (b) with 0.2% Al.

Chapter 1-Introduction

Furthermore, no studies have been reported on the effect of macro-sized holes on the sound absorption of cementitious materials. The effect of different parameters (hole size, hole depth and surface porosity) on the sound absorption performance and its compressive strength was compared with that of porous concrete, and methods to increase the sound absorption of SPM were also presented. . Chapter 4, discusses the synergistic effect of micropores and macro-sized holes on the sound absorption performance of surface perforated mortar.

Chapter 2-Literature Review

Sound and Noise

Definition
Impact of Noise on Human Life and the Environment

According to some WHO results, noise is the second biggest environmental cause of health problems after air pollution (fine dust) [1]. There are many sources of noise, but the most important are traffic, air traffic, buildings and nightlife as well as animal noise. Psychologically, noise can cause stress, malaise, depression, anxiety and hysteria and affect humans and animals.

Transmission of Sound and Noise in Buildings

Acoustic Measurement Methods

Reverberation Chamber Method
Impedance Tube Method
In-situ Surface Impedance Method
Sound Absorption Data Analysis

Over the years, many methods have been developed to measure the sound absorption of materials. SAAR is calculated by the ratio of the area of the sound absorption coefficient curve to the total background area[20]. Where Ai is the area of the sound absorption coefficient curve, Ao is the background area, and f(x) is the absorption coefficient at frequency x.

Figure 2-2. Schematic representation of reverberation chamber method [47].

Optimization of Sound Absorption by Modified Concrete

Pervious Concrete
Concrete With Lightweight Aggregates
Foamed/ Cellular Concrete
Aerated Concrete

Using more cenosphere causes the pore in the matrix to slip and fill, reducing sound absorption [59]. 81] where the fine aggregate requires water, which will affect pore formation, which will affect sound absorption. The main advantage of using aerated concrete over foamed concrete is the greater number of open pores in the matrix, which improves sound absorption.

Methods to Reduce Railway Noise

Noise Barriers
Sound-Absorbing Materials
Rail Dampers and Rail Pads

79,80] found that the sound absorption is dependent on the dosage of the foaming agent, in which a higher dosage provided better sound absorption due to the increase in the porosity and tortuosity in the matrix. For cement-based materials, two key methods are typically considered: improving the material's sound absorption capacity and designing the acoustic surface shape of the concrete structure. To improve the sound absorption performance and mechanical properties of the porous concrete, different methods were used as discussed in the previous section.

Introduction

Materials and Methods

Surface Perforated Mortar
Porous Concrete
Sound Absorption Test
Compressive Strength

The porosity of the porous concrete was designed to be 25%, and the actual porosity was measured as 24.5% using a water absorption test according to ASTM C642 [100]. The water-to-binder ratio is 0.25, 20% cement is replaced with silica fume to increase the binder strength, and a polycarboxylate superplasticizer is applied to adjust the fluidity of the binder to 170 mm, which can generate the uniform pore structure of the concrete. . The size of the SPM sample used for the sound absorption test is determined to be 300 x 300 x 150 mm3 following the suggestion by Li et al.

After samples dried at room temperature for two days, as shown in Figure 3-1, the sound absorption performance at the center of the upper surface was measured using an in-situ sound absorption instrument [10,18]. The sound absorption performance level is determined in this study by the sound absorption area ratio (SAAR) obtained from Eq 2.6 because the SAAR indicates the overall sound absorption performance within the frequency range of material.

Table 3-2. Mix design of the porous concrete (kg/m 3 )

Results and Discussion

Comparison between SPM and Porous concrete
Sound Absorption Mechanism of SPM
Improvement of the Sound Absorption Performance of SPM

Therefore, it can be inferred that the sound absorption data for SPM can be decomposed into the mortar and the hole. Finally, the sounding of the resonant frequency of each hole results in the negative SAC values. The effect of the hole's three design parameters on the sound absorption of SPM is investigated: the hole size, the hole depth and the surface porosity.

Therefore, the sound absorption performance of SPM may be improved by increasing the hole size. The sound absorption test results on the SPMs with different hole depths shown in Figure 3-8, for the case of the surface porosity of the SPMs, are 15%. These experimental findings indicate that the resonant frequency depends on the depth of the holes.

Effect of hole depth on sound absorption capacity at 15% porosity: (a) SAC of 15 mm holes and (b) SAC of 8 mm holes [Note: SAC of SPM holes obtained by subtracting SAC of solid mortar from SAC of SPM]. The sound absorption test results of samples with a hole size of 15 mm are shown in Figure 3-9, and the depth of the hole combines the data. Effect of porosity on sound absorption performance of SPM with 15 mm hole size: (a) 80 mm depth, (b) 60 mm depth, (c) 40 mm depth, and (d) 20 mm depth [Note: SACs of SPM hole obtained by subtracting the SAC of solid mortar from the SAC of SPM].

Effect of the combination of two different depths on the sound absorption performance of SPM: (a) Comparison of SAC data between the combination of different depths and single depths (b) Comparison of SAC data between the porous reference concrete and the SPM with the combination of different depths.

Figure 3-4. Picture of Specimens for sound absorption test: (a) porous concrete of 25% design porosity and (b) SPM of P30-D15-H80

Chapter 4-Synergistic Effect of Micro-Sized Pores and Surface Holes of SPM

Introduction

Materials
Sample Preparation
Testing Methods

4.1) Different Al dosages are used to investigate the effect of micro-sized pores on the sound absorption performance of SPM. Based on the results, the minimum amount of SPM micro-sized pores that have a synergistic effect with macro-sized pores can be determined. The effect of SPM design variables on the magnitude of the synergistic effect is also examined, for example, SPM surface porosity and macro-sized hole size and depth to provide evidence for SPM design guidelines.

Dosages of superplasticizers ranged from 0.5% to 1.25% of the cement weight to achieve the same fluidity between samples. For compressive strength and porosity measurements, cube molds of 50 x 50 x 50 mm3 were used, while for the sound absorption test, molds of 300 x 300 x 150 mm3 were used. The averages of the three replicates were then used as representative test results for both compressive strength and density tests.

The porosity of the samples was calculated by X-Y plane images, the number of which is more than 900. The region of interest was fixed at 80% of the inner rectangular region, excluding about 20% of the outer region. The pore surface area was determined based on image histogram analysis, where the largest peak of the histogram corresponds to the mortar structure.

An example of the threshold analysis result of the 0.20% Al mortar sample: (a) the original CT scan image and (b) the image in which the pores are colored in blue.

Figure 4-1. Picture of surface perforated mortar with Al (SPM-Al).

Results and Discussion

Effects of Al Dosage on Porosity
Effects of Al in SPM on Sound Absorption
Effects of Geometrical and Numerical Parameters of Macro Holes on SPM Sound
Enhancement of Sound Absorption

By subtracting the mortar data from the SPM data, the sound absorption of holes is obtained. The effects of surface porosity on SPM sound absorption were investigated using design surface porosities of and 30%. The results of the sound absorption tests for SPM with different hole depths are shown in Figure 4-11.

The results of sound absorption tests for SPM with different hole sizes are shown in Figure 4-12. The effect of hole size on sound absorption is minimal when design surface porosity is 7.5%. Design variable studies found that surface porosity was not always correlated with sound absorption of SPM with 0.2% Al.

This implies that the distribution of macro-sized holes is a significant factor in SPM sound absorption. This implies that the internal surface area of the macro-sized holes must exceed a certain level to have effective SPM sound absorption. As the hole size increases, the distance between the holes also increases, which degrades the SPM sound absorption.

Summary of sound absorption test results for SPM specimens with 0.2% Al and their design properties. The results of sound absorption tests on SPM with and without Al are shown in Figure 4-14. The effects of sound absorbing filler on the sound absorption of SPM with 0.2% Al are shown in Figure 4-15.

Figure 4-5. Effects of different Al dosages on the pore size distribution and pore sphericity in mortar specimens: (a) pore size distribution; (b) sphericity

Chapter 5-Conclusions

SPM without Al was used as a control sample to compare its sound absorption results with those of SPM with Al. Although the amount of micro-sized pores in mortar increases, which reduces the density and deterioration of the compressive strength of mortar samples. If the sound absorption performance is compared between mortar with and without Al, the increase in sound absorption is only 40%, but when SPM having both macro and micropores is compared to SPM without Al, then sound absorption increases by 133%.

Experimental studies of design variables of SPM with Al show that 1) sound absorption improves as surface porosity increases because macro-sized holes can absorb some of the sound;. Higher surface porosity can improve SPM sound absorption because it includes a larger hole area of the inner surface. Smaller hole size can improve SPM sound absorption because it reduces the gap between the holes when the surface porosity is the same.

Their results showed that combining different hole depths does not increase sound absorption as significantly as SPM. In addition, these studies showed that the sound-absorbing filler is beneficial to improve the sound absorption of SPM with Al because the filler increases the tortuosity of the void structure. However, filling more than half of the hole deteriorates the sound absorption of SPM with Al because the efficiency of the macro-sized holes in sound absorption is reduced.

Some future works are needed to improve the sound absorption performance of SPM: 1) optimization of the hole design parameters, 2) the method to increase the SAC in low frequency, 3) the sound absorption expectation model for SPM, 4) additional sound absorption test using international standard methods such as the reverberation chamber method to compare the sound absorption performance of the SPM with other materials, and 5) development of theoretical models to explain extraordinary acoustic phenomena of the SPM made of cement-based materials.

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Hernández-Olivares, “Influence of fibers partially coated with recycled tire rubber as aggregate on the acoustic properties of rubberized concrete,” Constr. Sukontasukkul, “Use of crumb rubber to improve thermal and acoustic properties of precast concrete panels,” Constr. Peña, “Glass-reinforced concrete panels containing recycled tires: Evaluation of the acoustic properties for their use as sound barriers,” Constr.

Wang, “Mechanical, thermal insulation, thermal resistance and acoustic absorption properties of geopolymer foam concrete,” Cem. Illikainen, “Mechanical and acoustic properties of fiber-reinforced alkali-activated slag foam concrete containing lightweight structural aggregates,” Constr. Yılmaz Demirkale, "Investigation and Development of Sound Absorption of Plasters Prepared with Pumice Aggregate and Natural Hydraulic Lime Binder," Appl.

Deckers, “Sound absorption of micro-slit backed plates with air voids: analytical estimates, numerical calculations and experimental validations,” Appl.