The Improvement in the Floor Impact Noise with Changes in the Glass Transition Temperature of an SBR Latex Mortar

Abstract

It is most effective to reduce floor impact noise as close to the sound source as possible. In apartments, there are multiple layers in the floor system, from floor finishing to the structural concrete slab. Apart from the floor finishing, mortar lies at the top layer of the floor system, followed by autoclaved lightweight concrete, insulation, and the concrete slab. The present study aims to identify the reduction characteristics of light and heavy floor impact noises by changing the glass transition temperature of an SBR (styrene–butadiene rubber) latex mortar. To achieve this, structural tests were undertaken to find the appropriate mix proportions of SBR latex in the mortar, meeting the glass transition temperature based on the physical test results regarding the latex mortar. As seen in the study method and process, because this study aimed to both increase and decrease the strength compared to general mortar, a 7% mixture ratio of Tg 4 °C SBR latex was decided upon for the strength increase, while a 5% mixture ratio of Tg −16 °C SBR latex was chosen for the strength reduction. A mock-up specimen was created using the SBR latex-modified mortar according to the identified mix proportions, and the characteristics of light- and heavy-weight floor impact noises of the SBR latex-modified mortar were then examined. Comprehensive analysis of the reduction performance of the floor impact noise revealed that the Tg −16 °C SBR latex-mixed mortar showed a reduction effect of about 2–5 dB for light-weight impact noise and about 7–10 dB for heavy-weight impact noise.

1. Introduction

In Korea, more than 65% of the population lives in apartment houses, which means the probability of exposure to floor impact noise is very high. In fact, complaints about floor impact noise collected from 16 cities and provinces are steadily increasing [1]. According to a survey by the Ministry of Environment, 76.2% of respondents indicated that the major source of noise came from upper-story apartments, highlighting the seriousness of the floor impact noise issue. Statistics from the “Neighbors Center”, operated by the Ministry of Environment of the Republic of Korea, show a steady annual increase in consultations received through call centers and websites. The severity of floor impact noise is evident from the sharp increase in telephone consultations, which rose from 8795 in 2012 to 28,231 in 2018 [2]. A survey conducted on households affected by floor impact noise found that heavy-weight impact noise accounts for more than 90% of the reported noise, indicating an urgent need for a solution to this problem [1].

Since 2003, the Korean government has enacted and reformed laws to reduce floor impact noise in apartments. To more precisely measure the noise experienced by residents, the noise produced by running children, which is regarded as the most serious noise source, was analyzed [3]. Additionally, the measurement results under various conditions were compared with the noise generated by an impact ball [4]. A similarity in noise transmission was found between the impact ball and running children, which is why the impact ball is currently used as a standard heavy-weight impact source along with tapping and bang machines [5].

Lee undertook floor impact noise tests using 19 different resilient materials, including EVA, PET, PP, and PS sheets. The results showed that a maximum reduction of 5 dB in heavy-weight floor impact noise could be achieved compared to a bare concrete slab [6]. Similarly, Kim measured the dynamic elastic modulus of nine specimens, comprising EVA, EPS, PE, crumb rubber, and glass fiber materials. He found that the dynamic elastic modulus decreases with increasing thickness of the composite materials, regardless of the type of resilient material used [7]. Another similar experiment used 20 mm of EVA resilient material with a concrete slab of 180 mm thickness, resulting in a 2 dB reduction in heavy-weight floor impact noise [8].

The management regulations for the “certified slab structure”, a floor structure system suitable for reducing floor impact noise, were established in 2000 [9]. However, the actual floor impact noise reduction effect was insignificant. To address these issues, the Ministry of Land, Infrastructure and Transport of the Republic of Korea has operated a “pre-certification system” since 2005 to control floor impact noise in newly built apartments. The pre-certification system involves certifying the floor impact noise insulation performance of apartment floors in a laboratory setting. However, due to discrepancies between laboratory measurement results and actual performance, it was difficult to achieve realistic floor impact noise reductions. For this reason, the Korean government is currently implementing a “post-certification system”, which evaluates the floor impact noise insulation performance after construction [10].

Numerous surveys and polls have revealed that residents in apartments experience significant stress due to floor impact noise. Although material developments have been conducted to reduce floor impact noise, these efforts have not efficiently mitigated both light- and heavy-weight impact noise simultaneously, highlighting limitations in materials and technology. It was also found that noise buffering on floor surfaces, including flexible floor finishes, effectively reduces only light-weight floor impact noise, with minimal impact on heavy-weight noise. This limitation has led to expanded research into ceiling-slab configurations, aimed at reducing low-frequency impact sound [11]. Additionally, research has been conducted to develop a new rating factor to quantify and evaluate low-frequency impact noise [12,13].

Latex-modified concrete undergoes changes in properties based on the water–cement ratio, aggregate–cement ratio, and polymer–cement ratio, making it necessary to design mixes suitable for the intended purpose. In latex-modified concrete, the polymer–cement ratio has a more significant influence on its properties than the water–cement ratio, which typically determines the properties of ordinary concrete [14].

The polymer–cement ratio is expressed as the mass ratio of the total solids content in the polymer admixture to the cement. The water–cement ratio is determined by the required workability, such as slump or flow values. Generally, the water–cement ratio calculation includes both the moisture in the polymer admixture and the amount of added water. It is desirable to keep the water–cement ratio as low as possible, within a range of 30–60%. Typically, the polymer–cement ratio ranges from 5 to 20%. As the polymer–cement ratio increases, properties, such as tensile and flexural strength, adhesion, impermeability, chemical resistance, abrasion resistance, and impact resistance, improve, but surface hardness decreases. In latex-modified concrete, the cement hydration process forms a binder that connects the aggregates. The latex strongly bonds with the hydrated cement particles, forming a polymer–cement co-matrix with a network structure.

Meanwhile, research has been conducted to use SBR latex as a sound insulation material for floor impact noise. To determine the proper mixing ratio of mortar with SBR latex, changes in compressive and tensile strength and floor impact noise were observed for each mortar curing time. The results showed that floor impact noise was reduced when 5% of SBR latex was mixed into the mortar. Specifically, a reduction of about 2–3 dB in floor impact noise at 125–500 Hz was achieved when a tapping machine was used, and about 2–4 dB at 125–250 Hz with impact balls.

It was also found to be very effective in reducing vibration. When vibration was measured from the bottom of the slab on which the SBR Latex mortar was installed, the impact was reduced by about 3 to 5 dB in the 500 Hz to 1 kHz band when using a tapping machine. When a bang machine and impact ball were used, floor impact noise was reduced by 1 to 3 dB in the 63 Hz to 1 kHz band [15,16,17]. Additionally, floor impact noises were measured using mixed SBR latex mortar, with admixtures having various glass transition temperatures. The results showed that mortar containing only SBR latex with a glass transition temperature of −11 °C exhibited the highest dynamic modulus of elasticity and the greatest reduction in floor impact noise [18,19].

In general, it is most effective to reduce impact noise near the point of the noise source. Since the mortar layer commonly lies just beneath the floor finish, it is expected to be highly effective in reducing floor impact noises. The present study aims to identify the reduction characteristics of light- and heavy-weight impact noises by examining changes in mortar strength after mixing SBR latex.

2. Study Methods and Process

The present study aimed to enhance sound insulation performance against floor impact noise by mixing SBR latex with different glass transition temperatures into the mortar. This approach seeks to alter the material properties of the finish mortar within the existing floor structural engineering framework. The study methods and processes are as follows:

(1)

Physical tests: We conducted physical tests to determine the compressive and tensile strength of latex mortar with different glass transition temperatures, identifying the properties of each mixture.

(2)

Selection of Mix Proportion: We selected the appropriate mix proportion based on the glass transition temperature through the results of the physical tests on latex mortar.

(3)

Mock-Up Specimen: We created mock-up specimens using the SBR latex-modified mortar according to the identified mix proportion, then assessed the characteristics of light- and heavy-weight floor impact noise of the SBR latex-modified mortar.

(4)

Comprehensive Conclusion: We derived a comprehensive conclusion based on the experimental results regarding floor impact noise using the SBR latex-modified mortar and outlined future study assignments.

By following these methods and processes, this study’s aim was to identify the most effective SBR latex formulation for enhancing the sound insulation performance of floor impact noise in apartment buildings.

2.1. SBR Latex-Modified Mortar

Polymer compounds can be largely divided into four categories: water polymer dispersion, re-emulsification-type polymer powder, water-soluble polymer (monomer), and fluid polymer. Among these, the most commonly used polymer is polymer latex, such as copolymers, including SBR latex, PAE, and EVA emulsion [14].

The SBR latex was used as the polymer compound in this test. Since the properties of latex-modified concrete are influenced by the ratios of water to cement, aggregate to cement, and polymer to cement, it is necessary to design the mixture appropriately for its intended purpose. While the properties of general cement are primarily determined by the water-to-cement ratio, the properties of latex-modified concrete are governed by the polymer-to-cement ratio. Therefore, it is crucial to calculate the appropriate mixture proportion to achieve the desired performance.

In general, polymers are used in resin concrete or resin mortar to enhance compressive and tensile strength. Typically, this involves improving the adhesion strength between materials by forming a polymer film between recycled aggregate and cement sand. According to preliminary tests and study papers, it is common to test with a polymer inflow rate of 5%. However, this study focused on finish mortar to reduce direct floor impact noise, without the help of buffering materials. An economic review concluded that it is economically viable to mix SBR latex at less than 10%, compared to using current buffering materials or SBR latex-mixed mortar.

The mixture ratios of 5%, 7%, and 9% were calculated, increasing the mix inflow rate by 2% increments starting from 5%, using SBR latex with a glass transition temperature of 4 °C. A strength test was planned to identify the most appropriate mixture ratio by testing the material properties at each mix inflow ratio, with a non-mixed mortar serving as the control group [20]. In addition, since SBR latex with a glass transition temperature of −16 °C is not commonly used, this study conducted strength tests with mixture ratios of 5%, 10%, and 15%.

2.2. Materials Used for SBR Latex Mortar

2.2.1. Cement

The cement used in this test is general Portland cement from S company, regulated by KS L 5201. The physical properties are detailed in

Table 1. Physical properties of cement.

Density (g/cm3)	Fineness (cm2/g)	Setting		Stability (%)	Compressive Strength
		Initial Setting (min)	Final Setting (min)		3 days	7 days	28 days
3.15	3331	190	250	0.13	26.7	38.1	51.0

. These values provide a baseline for evaluating the impact of SBR latex on the mortar’s performance.

2.2.2. Sand

The sand used in this test was sourced from G company located in Daejeon City. The grading chart of the sand is presented in Figure 1. This grading chart indicates the particle size distribution of the sand used in the test, which is essential for understanding its suitability for use in the mortar mix.

2.2.3. SBR Latex

Latex is a synthetic rubber manufactured through emulsion polymerization, using styrene and butadiene as the main raw materials from the overseas company G. Since water is used as the solvent, it has excellent dispersibility in water and demonstrates stable nonionic properties with cement. Its physical properties are shown in

Table 2. Physical properties of SBR latex.

Appearance	Glass Transition Temperature (Tg)	Solid Content (%, tsc)	Specific Gravity (20 °C)	Particle Size (μm)	pH (25 °C)	Viscosity (25 °C, cP)	Surface Tension (dyne/cm)
Milky white suspension	+4 °C	47.5	1.010	0.20	10.3	70	35
	−16 °C

, and its chemical composition is presented in

Table 3. Chemical composition of SBR latex.

Styrene	Butadiene	Nonionic Surfactant	Anionic Surfactant	Potassium	Persulfate
58.3%	35%	6%	0.2%	0.3%	0.2%

. These tables provide essential information about the physical properties and chemical composition of the synthetic rubber latex used in this study, ensuring a comprehensive understanding of its characteristics and potential impact on the mortar mix.

2.2.4. Mixture Water

The water regulated at KS F 4009 was used in the tests.

2.3. Mortar Mixture

The mortar mixture was prepared according to the material-inputting order shown in Figure 2, following the mixture ratio of the test plan. The preparation process involved the following steps. This process ensured a consistent and homogeneous mortar mixture for the subsequent tests.

(1)

The sand and cement were added to the mixing container in the specified order.

(2)

The materials were mixed with a hand mixer at low speed for 30 s to ensure an even distribution of the dry components

(3)

Water was then poured into the mixture and mixed for an additional 30 s at low speed.

(4)

SBR latex was added to the mixture according to the specified input ratio.

(5)

The mixture was then mixed at high speed for 60 s to ensure thorough blending of all components.

(6)

The final mortar mixture was then ready for use in the tests.

Figure 2. Mortar-mixing method and order.

Figure 2. Mortar-mixing method and order.

Specimens were prepared with varying SBR latex incorporation rates and were examined using a scanning electron microscope (SEM) to observe the composition and manifestation process within the cement matrix. The specimens were photographed at 14 days of age, a point at which significant strength development is evident. Figure 3 shows the internal images of the specimens taken at 5000× magnification using an SEM for different SBR latex incorporation rates.

These SEM images provide a detailed look at how different incorporation rates of SBR latex influence the internal structure and properties of the modified mortar. The increased porosity and the formation of a polymer network within the cement matrix contribute to the material’s ability to mitigate noise and vibration.

As shown in Figure 3, it was observed that the number of pores increases with the incorporation rate of SBR latex. Additionally, Figure 4 shows a specimen with a 7% SBR latex incorporation rate at 5000× magnification, illustrating the mechanism by which SBR latex bonds with cement. These pores act as air layers within the cement, and the latex binding within the cement gaps manifests the rubber properties of the latex. This interaction suggests that the latex-modified mortar can help reduce noise and vibration from floor impacts.

3. The Results of SBR Latex Mortar Strength Tests

The structural strength tests of the modified mortar were conducted following the KS F 2476 standard. The structural strength tests provided valuable data on the performance of the modified mortar. The inclusion of SBR latex at varying rates demonstrated how different proportions affect both compressive and tensile strength, contributing to the overall understanding of the material’s suitability for reducing floor impact noise and vibration.

3.1. Compressive Strength of SBR Latex Mortar

The compressive strength of the mortar specimens mixed with SBR latex at different glass transition temperatures was measured at 7 and 28 days to observe the development of strength over time. The mix inflowing ratios for the SBR latex were varied, and the results are presented in Figure 5.

As displayed in Figure 5, the mortar mixed with 7% SBR latex showed higher compressive strength at 28 days compared to the non-mixed mortar. However, the mortar mixed with 5% and 9% SBR latex demonstrated lower compressive strength than the non-mixed mortar, indicating that the strength improvement effect was not observed for these proportions. Particularly, the mortar mixed with 9% SBR latex exhibited significantly lower compressive strength due to excessive flexibility.

The compressive strength of the mortar mixed with Tg +4 °C SBR latex at a 7% incorporation rate was observed to be the highest, indicating that this mixture ratio achieves high strength. Conversely, the compressive strength of the mortar mixed with Tg −16 °C SBR latex was found to be lower than that of the non-mixed mortar.

Figure 6 compares the compressive strength of mortar specimens mixed with 4 °C SBR latex and −16 °C SBR latex, both at a 5% mixture ratio. This comparison serves as a control group to examine the impact of the glass transition temperature on compressive strength.

The compressive strength of Tg −16 °C SBR latex was found to be lower by approximately 5 MPa at 7 days and by about 9 MPa at 28 days compared to Tg 4 °C SBR latex. The comparison indicates that the glass transition temperature of SBR latex significantly affects the compressive strength of the modified mortar. At a 5% mixture ratio, the 4 °C SBR latex provides better strength performance than the −16 °C SBR latex. This finding emphasizes the need to carefully select the glass transition temperature of SBR latex to match the desired mechanical properties of the mortar.

3.2. Tensile Strength of SBR Latex Mortar

Figure 7 presents the tensile strength of mortar specimens mixed with SBR latex at various mixture ratios, measured at different ages (7 and 28 days). This comparison helps to explain how the incorporation of SBR latex affects the tensile strength development over time.

It was found that the mortar mixed with 5% SBR latex exhibited higher initial tensile strength compared to mortars with other mixture ratios. However, at 28 days, the tensile strength of the 5% SBR latex mortar was lower compared to the mortars mixed with 7% and 9% SBR latex. The mortar mixed with 9% SBR latex was measured to have lower tensile strength than the mortar mixed with 7% SBR latex due to excessive flexibility.

Figure 7b shows the tensile strength of the mortar specimens mixed with Tg −16 °C SBR latex to the mixture ratio according to ages of 7 and 28 days. Based on the mortar mixed with Tg −16 °C SBR latex, as seen with the result of compressive strength, it was shown that the higher the mixture ratio, the higher the tensile strength. The tensile strength data from Figure 7 suggest that a 7% mixture of SBR latex provides the best balance for enhancing the tensile strength in mortar. Higher ratios, such as 9%, may reduce the tensile strength due to increased flexibility. This information is crucial for optimizing mortar formulations to achieve the desired mechanical properties.

To compare the tensile strength of Tg 4 °C SBR latex to Tg −16 °C SBR latex at a 5% mixture ratio, the results from the pre-test indicate that the tensile strength of Tg −16 °C SBR latex is lower by about 0.9 MPa at 7 days and by about 0.8 MPa at 28 days compared to Tg 4 °C SBR latex. This comparison is illustrated in Figure 8.

The comparison highlights that Tg 4 °C SBR latex at a 5% mixture ratio provides better tensile strength, both initially and over time, compared to Tg −16 °C SBR latex. The difference in tensile strength, though not drastic, indicates that the higher glass transition temperature latex (Tg 4 °C) is more effective in enhancing the tensile properties of the mortar.

3.3. Brief Conclusion

The most effective method to reduce floor impact noise is to block the noise transfer at the point of impact. Therefore, the material properties of the mortar that first encounters the impact source should be modified. There are two methods to alter the mortar properties to achieve this:

(1)

Enhancing Mortar Strength: Increasing the strength of the mortar compared to general mortar to block the impact transfer.

(2)

Reducing Mortar Strength: Decreasing the strength of the mortar to absorb the impact.

As for the methods to change the strength for modifying the properties of mortar, there are two approaches: enhancing the mortar strength to block impact transfer compared to general mortar and reducing the mortar strength to absorb the impact [21]. Accordingly, in this test, the optimal mixture ratio was analyzed by reviewing the test values for compressive and tensile strength as well as the economic validity.

Through the compressive strength tests of the mortar mixed with Tg 4 °C SBR latex, it was found that only the mortar mixed with 7% SBR latex showed higher strength compared to the non-mixed mortar. In terms of tensile strength, all mortars mixed with SBR latex exhibited higher strength than the non-mixed mortar. Accordingly, the mixture ratio of 7% SBR latex was selected as the optimal mixture ratio because it surpassed the flexibility problem and provided higher compressive and tensile strength.

On the contrary, in order to reduce the strength, this test tried to identify the optimal mixture ratio through the tests of the compressive and tensile strength of the mortar mixed with Tg −16 °C SBR latex. According to the test results, it was found that, starting with a 5% mixture of Tg −16 °C SBR latex, the higher the mixture ratio, the higher the compressive and tensile strength.

As seen in the study method and process, this study aimed to both increase and reduce the strength of mortar compared to general mortar. Therefore, the mixture ratio of Tg 4 °C SBR latex at 7% was selected to increase the strength, while the mixture ratio of Tg −16 °C SBR latex at 5% was chosen to reduce the strength. These findings provide valuable insights for selecting appropriate SBR latex formulations and mixture ratios to tailor the mortar properties for specific construction needs.

4. The Floor Impact Noise Tests of SBR Latex-Modified Mortar

Table 4. The floor impact noise standards of Korea [22].

Classification	Light-Weight Impact Sound (L′nT,w)	Heavy-Weight Impact Sound (L′I,Fmax)
1st grade	L′nT,w ≤ 37	L′I,Fmax ≤ 37
2nd grade	37 < L′nT,w ≤ 41	37 < L′I,Fmax ≤ 41
3rd grade	41 < L′nT,w ≤ 45	41 < L′I,Fmax ≤ 45
4th grade	45 < L′nT,w ≤ 49	45 < L′I,Fmax ≤ 49

shows the floor impact noise standards of Korea for light-weight and heavy-weight impact sound, with four different grades that have been implemented since 2006. These standards have been implemented to ensure acceptable levels of noise within residential buildings, improving the quality of living by mitigating floor impact noise.

According to the ‘Report on the Operational Status of the Apartment Floor Impact Sound Reduction System’ conducted by the Board of Audit and Inspection of Korea as shown in

Table 5. Operational status of the apartment floor impact sound reduction system.

Light-Weight Impact Sound (L′n,Aw)			Heavy-Weight Impact Sound (L′I,Fmax, AW)
Classification	Number of Household (n)	Number of Household (%)	Classification	Number of Household (n)	Number of Household (%)
≤43 dB	39	24	≤40 dB	0	0
≤48 dB	72	45	≤43 dB	1	1
≤53 dB	28	18	≤47 dB	21	11
≤58 dB	7	4	≤50 dB	67	35
58 dB<	14	9	50 dB<	102	53
Total	160	100	Total	191	100

, approximately 69% of the floor impact sound performance in multi-family housing was found to be 48 dB or less for light-weight impact sound (L′n,Aw). For heavy-weight impact sound (L′I, Fmax, AW), about 46% was evaluated to be 50 dB or less, while the proportion exceeding 50 dB was approximately 53% [23].

Based on the results of the material property test, this study used a 7% mixture of Tg 4 °C SBR latex to enhance the strength and a 5% mixture of Tg −16 °C SBR latex to reduce the strength. The finish mortar for the mock-up was composed, as shown in Figure 9. The mock-up was constructed to simulate a typical apartment floor in Korea, and the floor impact noise-insulating performance was then measured.

This study targeted deteriorated apartments scheduled for remodeling, focusing on apartments over 10 years old with an average floor slab thickness of 150 mm. The thickness of insulated materials used in the specimen was decided based on the thermal conductivity of each part, as specified in the ‘Energy-saving Design Standard in Buildings’ (Publication No. 2008-652 by the Ministry of Land, Transportation, and Maritime Affairs). The thickness of insulators was calculated to achieve a total height of 110 mm, considering the following configurations:

(1)

Wet structure: insulator + light-weighting bubbles + finish mortar;

(2)

Semi-dry structure: buffering materials + insulators + finish mortar.

Given the field construction conditions, the mock-up was constructed with an error margin of ±3 mm in thickness for the insulator, buffering materials, light-weight concrete, and finish mortar. This precision ensures that the mock-up closely simulates real-world conditions and provides reliable results for assessing floor impact noise insulation performance.

The measurements were conducted at the Korea Institute of Machinery & Materials (KIMM) in Daejeon, within a lab volume of 87.7 m³. The testing adhered to KS standards, using various impact sound sources, including an impact ball (newly regulated by JIS in 2000), tapping machine, and bang machine. All experiments followed the KS F ISO 717-2 standards. Figure 10 and Figure 11 show the lab top, mock-up specimen size, and lab summary for floor impact noise-insulating performance within KIMM.

The test for floor impact noise was conducted by adjusting the reverberation time to 4.2 s (±0.04) within the lab, in accordance with KS regulations. This was done after measuring the initial reverberation time of the lab and calculating the sound-absorbing power. Microphones were installed at four sound-absorbing points, spaced 70 cm apart, and positioned 50 cm away from the ceiling, walls, and floor.

For the hitting points of the standard impact source, both light-weight and heavy-weight impact sound sources were spread across five points, including the center point. The measurements of the floor impact noise-insulating performance were carried out following the lab measurement method of KS F 2856 for light-weight impact noise and the field measurement method of KS F 2810-2 for heavy-weight impact noise.

4.1. Light-Weight Floor Impact Noise

The test results for the light-weight impact noise of floor structures using Tg 4 °C and Tg −16 °C SBR latex-mixed mortar, illustrated in Figure 12, indicate that the mortar mixed with SBR latex at frequencies below 500 Hz showed a superior noise reduction performance of approximately 3–5 dB compared to general mortar. This suggests that incorporating SBR latex in the mortar enhances its ability to reduce low-frequency impact noise more effectively.

Especially, the mortar mixed with Tg 4 °C SBR latex demonstrated superior noise reduction characteristics, achieving about a 2 dB improvement at the frequency bands of 125 Hz, 500 Hz, 1000 Hz, and 2000 Hz, compared to the Tg −16 °C SBR latex-mixed mortar. However, this improvement did not extend to the 250 Hz frequency band.

4.2. Heavy-Weight Floor Impact Noise

4.2.1. Bang Machine

The test results on the heavy-weight impact noise of the mock-up using SBR latex-mixed mortar with different glass transition temperatures, as shown in Figure 11, indicate that the characteristics of heavy-weight floor impact noise for the mock-up using Tg 4 °C SBR latex are similar to those of the mock-up using general mortar. This suggests that the Tg 4 °C SBR latex-mixed mortar does not significantly differ from general mortar in terms of heavy-weight impact noise reduction.

Even with slight differences, the mock-up using Tg 4 °C SBR latex showed a better reduction effect of about 0.5 dB at frequencies between 63 Hz and 125 Hz compared to general mortar. This indicates a marginally improved performance in reducing heavy-weight impact noise within this frequency range.

As seen in Figure 13, the characteristics of heavy-weight impact noise differ significantly between the mock-up specimen using Tg −16 °C and Tg 4 °C SBR latex-mixed mortars. This indicates that the two types of SBR latex-mixed mortars have distinctly different effects on reducing heavy-weight impact noise.

The mock-up specimen using the Tg −16 °C SBR latex-mixed mortar showed a significantly better reduction performance, achieving about a 10 dB improvement at the 63 Hz frequency band, which is critical for controlling heavy-weight impact noise, compared to the mock-up using the Tg 4 °C SBR latex-mixed mortar. It can be inferred that the mock-up using the Tg −16 °C SBR latex-mixed mortar achieves higher reduction performance at the 63 Hz frequency band and subsequently maintains higher performance at 125 Hz compared to other specimens, likely due to the energy balance.

4.2.2. Impact Ball

The major test on the impact ball excitation was conducted using the field measurement method of KS F 2810-2, similar to the test method for heavy-weight impact noise. The results of heavyweight impact noise using the impact ball are shown in Figure 14. As seen in Figure 14, the results of heavy-weight floor impact noise through impact ball excitation are similar across all mock-ups in the frequency range of 125–1000 Hz. This indicates consistent performance in noise reduction within this frequency band for the different mock-ups tested.

Similarly to the results obtained with the bang machine excitation, the Tg −16 °C SBR latex-mixed mock-up exhibited a higher reduction performance by about 7 dB at the 63 Hz frequency band, which is crucial for controlling heavy-weight floor impact noise compared to the other mock-ups.

According to the test results on light-weight floor impact noise, it was found that mortar with high strength is more effective in reducing light-weight impact noise. Conversely, for heavy-weight floor impact noise, mortar with low strength enhances the reduction effect. To comprehensively analyze the reduction performance of floor impact noise, it was observed that the Tg −16 °C SBR latex-mixed mortar showed a reduction effect of about 2–5 dB for light-weight impact noise and about 7–10 dB for heavy-weight impact noise.

5. Conclusions

This study constructed mock-up specimens resembling the wet floor structures used in apartments, incorporating SBR latex-mixed mortar to understand the characteristics of floor impact noises. To achieve an effective reduction performance for the floor impact noise, this study mixed SBR latex with different glass transition temperatures and analyzed both the physical properties and the noise characteristics. The results are as follows:

(1)

Mortar strength: The mixture of Tg 4 °C SBR latex is effective in enhancing the compressive and tensile strength, while the mixture of Tg −16 °C SBR latex is effective in reducing the strength. According to the comprehensive analysis of the test values for compressive and tensile strength, along with an evaluation of economic validity, it was determined that the optimal mixture ratio is approximately 7% Tg 4 °C SBR latex and 5% Tg −16 °C SBR latex.

(2)

Light-weight impact noise: Mortar with high strength was more effective in reducing light-weight impact noise. The Tg −16 °C SBR latex-mixed mortar showed a reduction effect of about 2–5 dB for light-weight impact noise compared to general mortar

(3)

Heavy-weight impact noise: Mortar with low strength enhanced the reduction effect of heavy-weight impact noise. The Tg −16 °C SBR latex-mixed mortar showed a significant reduction effect of about 7–10 dB for heavy-weight impact noise, particularly at the critical 63 Hz frequency band.

(4)

Glass transition temperature of SBR latex: The Tg 4 °C SBR latex-mixed mortar demonstrated better reduction characteristics by about 2 dB at frequency bands of 125 Hz, 500 Hz, 1000 Hz, and 2000 Hz (except 250 Hz) compared to Tg −16 °C SBR latex-mixed mortar. The Tg −16 °C SBR latex-mixed mortar exhibited a significantly better reduction performance at the 63 Hz frequency band for heavy-weight impact noise, outperforming Tg 4 °C by about 10 dB.

(5)

Heavy-weight impact sound sources: The results of heavy-weight impact noise through impact ball excitation showed similar performance across all mock-ups at 125–1000 Hz. The Tg −16 °C SBR latex-mixed mortar consistently showed a better reduction performance, by about 7 dB at 63 Hz, in tests with both the impact ball and bang machine excitation methods.

As a result of these test results, it can be that the Tg −16 °C SBR latex, which can more significantly reduce the strength compared to general mortar, is effective for floor impact noises, and in addition to this study, studies to identify the economic optimal mixture ratio while acquiring the effective sound-insulating performance and to focus on the characteristic changes in floor impact noises while applying the dry as well as the wet floor construction method should be conducted.