Mechanical Properties of Cement Concrete with Waste Rubber Powder

Abstract

To investigate the mechanical properties of cement concrete incorporating waste rubber powder, the response surface methodology was employed. The Box–Behnken central composite design was applied to analyze the three primary factors influencing the road performance of cement concrete containing waste rubber powder: the water–cement ratio, sand ratio, and waste rubber powder content. The study determined the impact of these factors on the flexural strength of waste rubber powder cement concrete at both 7 and 28 days. Additionally, the effects of the water–cement ratio, sand ratio, and waste rubber powder content on the performance of cement concrete were analyzed. To investigate the impact of waste rubber powder on cement concrete, various mechanical property tests were conducted, including compressive, flexural, dynamic elastic modulus, and impact performance tests. Furthermore, the study explored the influence of waste rubber powder on the noise reduction capacity of cement concrete using both the rubber ball impact method and ultrasonic method. Lastly, the durability of cement concrete with added rubber powder was assessed through shrinkage tests, frost resistance tests, and chloride ion penetration tests.

1. Introduction

The construction industry is one of the largest consumers of resources and energy [1], and concrete is the second most widely used construction material after water [2]. Due to its cost efficiency and ease of manufacturing, concrete can be molded into various forms to meet a wide range of specifications [3]. The incorporation of waste rubber powder into concrete can decrease landfill and incineration volumes, while also minimizing the extraction of raw materials [4,5].

Since the early 1990s, scholars have investigated waste tire rubber powder in cement concrete. Most studies suggest that the mechanical strength of concrete typically decreases with the addition of rubber, and this trend exacerbates as rubber content increases [6,7,8,9]. Adding rubber powder tends to reduce the strength and other mechanical properties of cement concrete, but this effect can be mitigated by the inclusion of silica fume [10,11]. Additionally, Shengtian Zhai et al. [12] noted that the interface between rubber and cement, along with the distribution of rubber particles, play pivotal roles in shaping the mechanical properties of rubber aggregate concrete.

Crumb rubber concrete demonstrates notable resistance to chloride ion erosion [13]. According to most studies, rubberized concrete treated with NaOH shows enhanced mechanical properties [13,14]. Experimental results conducted by Ruizhe Si et al. [15] showed that the durability of rubberized concrete or mortar samples with 15% or 25% NaOH-treated rubber replacement is enhanced. Danyang Su et al. [16] discovered that incorporating rubber into concrete enhances both its compressive strength and compactness in chloride salt-corroded environments. Yang Li et al. [17] concluded that employing a low W/C ratio in crumb rubber concrete significantly enhances resistance to chloride penetration.

The study by Iker Bekr Topcu and Abdullah Demir [18] revealed that the inclusion of waste rubber powder reduces the elastic modulus of cement concrete, with a lesser impact on compressive strength observed with larger mesh sizes of waste rubber powder. Following this, J. Retama and A. G. Ayala [19] noted the influence of crumb rubber size on concrete’s elastic modulus, observing a decrease in concrete with fine crumb rubber while enhancing its ductility. Tran Van Cuong et al. [20] demonstrated that incorporating rubber flakes or granules to partially replace the aggregate effectively lowers the static elastic modulus of concrete. Ttilok Gupta et al. [21] proposed that utilizing rubber as aggregate could notably improve concrete durability. Shengtain Zhai et al. [22] observed that the increase in abrasion resistance of crumb rubber concrete is primarily due to the absorption of wear energy by the rubber particles. Wrya A. Abdullah et al. [23] determined that rubberized concrete mixes were functional up to a certain sand replacement level, yielding lighter concrete. Consequently, rubberized concrete presents advantages for lightweight building construction [6].

It has been observed that concrete incorporating elastic materials like crumb rubber exhibits a high fracture toughness. Aijiu Chen et al. [24] demonstrated that pretreating rubber particles enhances the strength, ductility, and crack resistance of rubberized concrete. Moataz Badawi et al. [25] discovered that rubber-treated concrete samples display increased ductility under pressure testing compared to ordinary concrete, and they exhibit slower fracture rates. Research indicates that the addition of waste rubber powder substantially reduces the thermal conductivity of concrete and significantly improves its sound absorption [26].

In summary, although numerous studies have delved into rubber concrete, the bulk of them center on mechanical properties. However, research on the durability of rubber concrete remains inadequately thorough, yielding divergent and inconclusive outcomes. The introduction of rubber powder may reduce the strength of concrete. The shape and surface characteristics of rubber powder may affect the workability of concrete. The aging and decomposition of rubber powder may impact the service life of concrete. Currently, the application of rubber concrete lacks unified specifications and standards, hindering its promotion and application. This discrepancy impedes the practical utilization of waste rubber concrete in engineering applications. This study conducted indoor experiments to select materials meeting specifications and designed the mix proportions for cement concrete. Utilizing response surface methodology, the Box–Behnken central composite design was employed to optimize the water–cement ratio, sand ratio, and waste rubber powder, each at three levels. Subsequently, response surface analysis was performed to elucidate the influence of the water–cement ratio, sand ratio, and waste rubber powder on the flexural strength of cement concrete at 7 and 28 days. Finally, the mechanical properties of cement concrete mixed with waste rubber powder were experimentally evaluated, providing a reference for design purposes.

2. Materials and Methods

2.1. Materials

The materials used in the tests included rubber powder, cement, coarse aggregate, sand, and superplasticizer. The rubber powder particle sizes were categorized into four groups: 10-mesh, 20-mesh, 30-mesh, and 60-mesh, as illustrated in Figure 1. Portland cement (Type P.O. 42.5) was utilized in the tests. The coarse aggregate particle sizes were classified into three grades: 5–10 mm, 10–20 mm, and 20–30 mm, mixed at a ratio of 2:5:3. The fineness modulus of the medium sand was determined to be 2.74. The grain size distribution curve of the coarse aggregate and medium sand are shown in Figure 2 and Figure 3. The technical specifications of the superplasticizer are provided in

Table 1. Technical indexes of superplasticizer.

Items	Plasticizer
Water-reducing rate (%)	25.6
Shrinking percentage	72
Chloridion content (%)	0.01
Total alkali content (%)	0.36
Sodium sulfate content (%)	1.232
PH	7.1

. And, the concrete mixtures used in the tests are given in

Table 2. The concrete mixtures of the tests.

Items	Content
Water–cement ratio	0.38
Cement (kg/m3)	375
Water (kg/m3)	150
Sand ratio (%)	34
Aggregate quantity (kg/m3)	1925
Superplasticizer (%)	1.28

.

2.2. Response Surface Methodology (RSM)

Response surface methodology (RSM) is an optimization technique that aims to find the optimal experimental design with a minimal number of samples. Despite the limited sample size, RSM effectively captures the complex non-linear relationships between the response and parameters with satisfactory precision [27]. RSM can optimize multiple responses or fulfill specific requirements [28,29,30]. The Box–Behnken design (BBD) is a quadratic response surface design that operates independently. The BBD necessitates three levels for each factor and yields fewer experimental runs compared to the central composite design, with an equivalent number of factors [31,32]. All combinations in the BBD are contained within the region of interest. While less costly than the central composite design, the BBD is unsuitable for sequential experiments [33]. The Box–Behnken design, with its absence of axis points, ensures that all design points remain within their boundaries and prevents the simultaneous elevation of all factors to high levels. This unique characteristic makes it a suitable choice for optimizing the mix ratio of waste rubber powder cement concrete.

Design-Expert software (version 12) was employed in this study to identify the optimal conditions. Three independent variables—the water–cement ratio (A), sand ratio (B), and 10-mesh waste rubber powder content (C)—were investigated using a three-level, full-factorial Box–Behnken design. A total of 17 experiments were conducted, and the factors and their levels are detailed in

Table 3. The factors of Box–Behnken design.

Factors	Factor Levels and Ranges
	−1	0	1
A water–cement ratio	0.35	0.40	0.45
B sand ratio (%)	32	34	36
C 10 mesh waste rubber powder content (%)	5	10	15

. Using a three-factor, three-level Box–Behnken central composite design of the water–cement ratio, sand ratio, and 10-mesh waste rubber powder dosage, 17 groups of experimental schemes were obtained, as shown in

Table 4. Response surface test design mix design scheme (kg/m³).

Number	Cement	Water	5∼10 mm	10∼20 mm	20∼30 mm	Sand	Plasticizer	Crumb Rubber
1	375	131.25	385	962.5	577.5	616	4.8	37.5
2	375	168.75	385	962.5	577.5	616	4.8	37.5
3	375	150	385	962.5	577.5	654.5	4.8	37.5
4	375	131.25	385	962.5	577.5	693	4.8	37.5
5	375	168.75	385	962.5	577.5	693	4.8	37.5
6	375	150	385	962.5	577.5	654.5	4.8	37.5
7	375	131.25	385	962.5	577.5	654.5	4.8	18.75
8	375	150	385	962.5	577.5	654.5	4.8	37.5
9	375	168.75	385	962.5	577.5	654.5	4.8	18.75
10	375	131.25	385	962.5	577.5	654.5	4.8	56.25
11	375	150	385	962.5	577.5	654.5	4.8	37.5
12	375	168.75	385	962.5	577.5	654.5	4.8	56.25
13	375	150	385	962.5	577.5	616	4.8	18.75
14	375	150	385	962.5	577.5	654.5	4.8	37.5
15	375	150	385	962.5	577.5	616	4.8	56.25
16	375	150	385	962.5	577.5	693	4.8	56.25
17	375	150	385	962.5	577.5	693	4.8	18.75

.

2.3. Methods

2.3.1. Specimens Preparation

It can be inferred from the Testing Methods of Cement and Concrete for Highway Engineering that cubic specimens measuring 150 mm × 150 mm × 150 mm were utilized for the compression strength, impact resistance, and noise reduction tests. Cylindrical specimens with a diameter of 100 mm and a length of 200 mm were employed for the impermeability tests. Cuboid specimens measuring 100 mm × 100 mm × 400 mm were used for the flexural strength, elastic modulus, and freezing resistance tests. Another set of cuboid specimens measuring 100 mm × 100 mm × 515 mm was designated for the shrinkage testing. All specimens, except those for shrinkage testing, were demolded after 24 h and cured in a standard curing room.

The compressive strength, flexural strength, and dynamic modulus of the mixes were determined at the concrete ages of 7, 14, 21, and 28 days, with the impact resistance, noise reduction, and impermeability tests conducted at 28 days. Each specimen underwent three replicates, and the average strength values were reported.

2.3.2. Impact Resistance

The study replaced 5%, 10%, and 15% of the cement mass with waste rubber powder of four different particle sizes and incorporated them into the concrete mix. Impact tests were performed on 60 mm concrete slabs obtained by cutting standard compressive test specimens, using a self-made drop hammer impact test device. Finally, regression analysis was conducted on the initial and final crack times using the Weibull distribution. The cast concrete specimens were sliced into 60 mm thick test samples, resulting in two pieces from each standard specimen, yielding 10 specimens in each group. A custom-made impact testing apparatus, as illustrated in Figure 4, was employed to release a 1.2 kg steel ball from a vertical height of 80 cm. The impact times, N₁ and N₂, were then recorded when the initial crack appeared and the final failure occurred, respectively.

The initial crack impact energy and final crack impact energy of the test piece are represented by E₁ and E₂, respectively. The calculation formula is as follows:

$$E_1=N_{1}mgh$$

(1)

$$E_2=N_{2}mgh$$

(2)

where E₁ = the initial crack impact energy of the test piece, J; E₂ = the final crack impact energy of the test piece, J; N₁ = the impact times of the initial crack, times; N₂ = the impact times of final crack, times; m = the mass of the falling hammer, 1.2 kg; g = the gravitational acceleration, 9.8 m/s²; and h = the height of the falling hammer, 0.8 m.

2.3.3. Noise Reduction

The rubber ball impact test assessed the noise reduction capabilities of the waste rubber powder cement concrete. A 1 kg rubber ball was released vertically from a 1 m distance above the test specimen, and the noise level was gauged using a noise detector positioned 1.5 m horizontally from the test piece. The schematic diagram of this test is illustrated in Figure 5.

2.3.4. Shrinkage

Three standard specimens were cured in the curing room for one day before demolding. Subsequently, they were transferred to the drying shrinkage chamber after three days, and their initial lengths were measured. Length measurements were taken on days 1, 3, 7, 14, 28, 45, 60, 90, and 120 post placement in the drying shrinkage chamber. The drying shrinkage rate was calculated with a precision of 0.0001%. Figure 6 depicts the drying shrinkage test of the waste rubber powder cement concrete.

2.3.5. Impermeability

To assess the impermeability of the waste rubber powder cement concrete, the electrical flux method was deployed. Chloride ion permeability testing was conducted using an NJW-AB computer-controlled vacuum water absorption machine (Figure 7) and an NJW-RCP-6B concrete chloride ion electrical flux determination device (Figure 8). The test principle relied on the migration of chloride ions from the negative to the positive electrode through the waste rubber powder concrete under the influence of direct current. The quantity of chloride ions penetrating the waste rubber powder concrete was assessed by measuring the electric charge within the material. Figure 9 depicts the schematic diagram of the chloride ion penetration test device.

2.3.6. Freezing Resistance

Following a 24-day standard maintenance period, the specimens were immersed in water for four days. After removal, the surface moisture was wiped off, and the specimens were weighed and measured for transverse fundamental frequency using a D7-16 dynamic meter. Subsequently, they underwent concrete rapid freezing-thawing tests, with mass and dynamic modulus measurements recorded after every 25 freeze-thaw cycles. The experiment ceased if the mass loss exceeded 5%, after 300 freeze-thaw cycles, or if the threshold was met after 200 cycles. Figure 10 illustrates the D7-16 dynamic modulus tester and the concrete rapid freezing-thawing test machine utilized in this research. Formula (3) shows the calculation of the mass loss rate.

$$\mathrm{Mess} \mathrm{loss} \mathrm{rate} (\%)={\displaystyle \frac{{\mathrm{m}}_0-{\mathrm{m}}_n}{{\mathrm{m}}_0}}\times 100\%$$

(3)

where m₀ = the mass of the sample before freeze-thaw cycles and m_n = the mass of the sample after n freeze-thaw cycles.

3. Results and Discussion

3.1. Optimal Design Based on the Mix Design of the RSM

The experimental and predicted responses of the 17 runs of experiments on 7 d and 28 d flexural strength are provided in

Table 5. The results of Box–Behnken design.

Number	Water–Cement Ratio	Sand Ratio (%)	10-Mesh Waste Rubber Powder Cement (%)	Flexural Strength (MPa)
				7 d	28 d
1	0.35	32	10	5.45	5.98
2	0.45	32	10	4.92	5.45
3	0.4	34	10	5.32	5.84
4	0.35	36	10	5.37	5.92
5	0.45	36	10	4.69	5.27
6	0.4	34	10	5.24	5.82
7	0.35	34	5	5.58	6.13
8	0.4	34	10	5.26	5.74
9	0.45	34	5	5.03	5.56
10	0.35	34	15	5.16	5.65
11	0.4	34	10	5.21	5.73
12	0.45	34	15	4.47	5.01
13	0.4	32	5	5.26	5.78
14	0.4	34	10	5.23	5.78
15	0.4	32	15	4.78	5.32
16	0.4	36	15	4.57	5.12
17	0.4	36	5	5.29	5.83

. The flexural strength was correlated with the water–cement ratio, sand ratio, and 10-mesh waste rubber powder content. The obtained quadratic regression models are given in Formulas (4) and (5).

$$\begin{gathered} 7 \mathrm{d} \mathrm{flexural} \mathrm{strength}=-34.13+17.55A+2.13B+0.34C-0.38AB-0.14AC \\ -6.00\times {10}^{-3}BC-11.9A^2-0.03B^2-6.49\times {10}^{-3}{C}^2 \end{gathered}$$

(4)

$$\begin{gathered} 28 \mathrm{d} \mathrm{flexural} \mathrm{strength}=-28.46+13.25A+1.88B+0.32C-0.3AB-0.07AC \\ -6.25\times {10}^{-3}BC-10.4A^2-0.03B^2-6.74\times {10}^{-3}{C}^2 \end{gathered}$$

(5)

where A = water-cement ratio; B = sand ratio; and C = 10-mesh waste rubber powder content.

Diagnostic plots were employed to assess the adequacy of the chosen model [33]. The model volatility was illustrated through residuals, indicating the variance between the predicted and calculated values. The association among the model residuals, calculated values, and predicted values is illustrated in Figure 11 and Figure 12.

Figure 11 and Figure 12 illustrate the residuals of each experimental scheme in the model, showing consistently small deviations. Both the experimental and predicted results followed a similar pattern, displaying a predominantly linear distribution. This uniformity indicates the model’s high accuracy and its suitability for predicting and optimizing flexural strength at 7 and 28 days. Utilizing the constraints outlined in Formula (6), the optimal mix proportion of waste rubber powder cement concrete was derived from the model. Subsequently, 10 sets of optimized schemes were chosen and are detailed in

Table 6. Response surface optimization scheme table.

Number	Water–Cement Ratio	Sand Ratio (%)	10-Mesh Waste Rubber Powder Content (%)	7 d Flexural Strength (MPa)	28 d Flexural Strength (MPa)
1	0.35	34	5	5.6	6.18
2	0.35	33	8	5.57	6.14
3	0.36	33	7	5.56	6.12
4	0.35	33	8	5.55	6.12
5	0.35	35	8	5.56	6.10
6	0.37	35	5	5.53	6.07
7	0.36	34	9	5.51	6.04
8	0.37	33	9	5.47	6.01
9	0.36	36	9	5.47	6.00
10	0.35	35	10	5.45	5.98

.

$$\{\begin{array}{l}0.35\le \mathrm{Water-cement} \mathrm{ratio}\le 0.45\\ 32\%\le \mathrm{sand} \mathrm{ratio}\le 36\%\\ 5\%\le 10-\mathrm{mesh} \mathrm{waste} \mathrm{rubber} \mathrm{powder} \mathrm{content} \le 15\%\\ 4.47\le 7\mathrm{d} \mathrm{flexural} \mathrm{strength}\le 5.6\\ 5.01\le 28\mathrm{d} \mathrm{flexural} \mathrm{strength}\le 6.18\end{array}$$

(6)

Analysis of the optimization design results in Table 6 revealed that with a constant water–cement ratio and a sand ratio within the range of 33% to 36%, the waste rubber powder content should not surpass 10%.

3.2. Influence of Waste Rubber Powder Concrete Composition Materials

The response surface analysis elucidated the response behavior concerning variable alterations [29]. The 7-day and 28-day flexural strength were scrutinized concerning variations in the input variables, namely the water–cement ratio (A), sand ratio (B), and waste rubber powder content (C). Figure 13, Figure 14 and Figure 15 depict the response surface plots delineating the concrete strength derived from the multivariate regression equations (Formulas (4) and (5)). These plots facilitated discerning the influence of any two factors on the 7-day and 28-day flexural strength, thereby identifying the optimal range of component materials based on these strengths.

Figure 13 and Figure 14 indicate that as the water–cement ratio decreased, there was a steady rise in both the 7-day and 28-day flexural strengths of the cement concrete. Meanwhile, adjustments in the sand ratio had a limited impact on these strengths, with a tendency to initially rise before declining.

According to Figure 15 and Figure 16, the 7-day and 28-day flexural strengths of cement concrete decreased progressively with an escalation in the waste rubber powder content. This trend stemmed from the compromised interfacial bonding between the cementitious elements induced by the presence of the waste rubber powder and the consequent reduction in flexural strength.

The data presented in Figure 17 and Figure 18 indicate that changes in sand ratio minimally affected the 7-day and 28-day flexural strengths. In contrast, an increase in waste rubber powder content resulted in a gradual decrease in both the 7-day and 28-day flexural strengths of the cement concrete. Notably, among the three influencing factors, the water–cement ratio demonstrated the most significant impact on flexural strength, while the sand ratio exhibited the least effect.

3.3. Compressive Strength

The results depicted in Figure 19 revealed a noticeable impact of waste rubber powder quantity on the compressive strength of waste rubber powder cement concrete. Specifically, when the particle size remained constant, the compressive strength decreased as the waste rubber powder content increased. Additionally, particle size played a role in influencing the compressive strength, with larger particles causing more pronounced reductions in strength at equivalent contents.

3.4. Flexural Strength

Figure 20 illustrates that the change in flexural strength mirrored that of the compressive strength. As the amount of waste rubber powder increased, the flexural strength of waste rubber powder cement concrete decreased, with larger mesh sizes amplifying this decline. Moreover, the augmentation in weak points within the concrete, induced by higher waste rubber powder quantities, reduced the actual bearing area, thus diminishing the concrete’s bearing capacity.

3.5. Dynamic Modulus

Figure 21 illustrates a consistent trend: as the quantity of rubber powder increased, the mic elastic modulus of the rubber powder concrete gradually diminished, with larger mesh sizes exacerbating this decline. This phenomenon was more pronounced with higher rubber powder amounts. Increased rubber powder content corresponded to greater deformation when the concrete was subjected to pressure. Consequently, larger mesh sizes and higher rubber powder quantities corresponded to a lower dynamic elastic modulus of the rubber powder concrete.

3.6. Impact Resistance

Formulas (1) and (2) were employed to determine the initial crack and final crack impact energy absorption of the test piece. For the test piece lacking waste rubber powder, the initial crack energy absorption and final crack energy absorption stood at 696.19 J and 752.64 J, respectively. The corresponding values for the test piece incorporating waste rubber powder are depicted in Figure 22. The increased waste rubber powder content, coupled with a smaller particle size, correlated with a higher frequency of initial and final cracks in concrete, thereby augmenting both the initial crack energy absorption and the final crack energy absorption. Notably, a higher rubber powder content and a smaller particle size promoted enhanced dispersion of rubber particles, bolstering the impact resistance.

3.7. Noise Reduction

Figure 23 illustrates that the addition of waste rubber powder resulted in a reduction in the decibel level of cement concrete upon impact by rubber balls. Furthermore, an incremental increase in waste rubber powder content corresponded to a more pronounced decrease in concrete decibel levels post impact. Remarkably, concrete containing 10-mesh waste rubber powder exhibited the lowest decibel level post impact, while those with 20-mesh, 30-mesh, and 60-mesh waste rubber powder demonstrated similar decibel levels.

3.8. Shrinkage

Analysis of the drying shrinkage test results (Figure 24) revealed a reduction in the drying shrinkage rate of cement concrete upon the addition of waste rubber powder. Notably, higher waste rubber powder content corresponded to a smaller drying shrinkage rate, while an increase in mesh number was also associated with a decreased drying shrinkage rate. Hence, waste rubber powder exhibits potential for mitigating crack formation, rendering it suitable for road applications.

3.9. Impermeability

The electrical flux test results are depicted in Figure 25. The results indicate that impermeability improved with the addition of waste rubber powder. The impermeability of concrete increased as the mesh number of waste rubber powder rose while at constant content levels. Similarly, at consistent mesh numbers, impermeability rose with increasing content. However, the impact of content variation on concrete impermeability was more pronounced. Consequently, higher mesh numbers of waste rubber powder corresponded to increased concrete resistance against chloride ion penetration, while higher waste rubber powder content further bolstered concrete’s ability to resist chloride ion penetration.

3.10. Freezing Resistance

Figure 26 illustrates a decrease in the mass loss rate of cement concrete upon the addition of waste rubber powder. Likewise, the mass loss rate of waste rubber cement concrete decreased with the increasing mesh size of the waste rubber powder, and a higher quantity of waste rubber powder led to a proportionally smaller mass loss rate. These findings suggest that the freezing resistance of waste rubber cement concrete improved as both the mesh size and quantity of waste rubber powder increased. In frozen concrete conditions, waste rubber powder functioned to impede crack formation and development. Moreover, the significance of these effects increased with the quantity of waste rubber powder added.

4. Conclusions

This study used response surface methodology to design the mix proportion of waste rubber powder cement concrete. Subsequently, this study investigated the mechanical properties of waste rubber powder cement concrete using traditional mechanical property tests and impact resistance tests. It also explored its noise reduction performance through rubber ball impact and ultrasonic methods. Moreover, the durability properties of waste rubber powder cement concrete were examined through shrinkage performance tests, chloride ion flux tests, and freeze-thaw resistance tests. The following conclusions are presented:

(1)

Among the three influencing factors—the water–cement ratio, sand ratio, and waste rubber powder content—the optimization design results indicate that when the water-cement ratio was held constant and the sand ratio was maintained between 33% and 36%, the waste rubber powder content should not exceed 10%. Additionally, it was observed that the water–cement ratio exerted the most significant influence on the flexural strength of cement concrete, whereas the sand ratio had the least impact.

(2)

Both the particle size and content of waste rubber powder significantly influenced the mechanical properties of cement concrete. Specifically, under consistent mesh sizes, increasing content led to a decline in compressive strength, flexural strength, and dynamic elastic modulus; conversely, at constant content levels, larger mesh sizes corresponded to lower compressive strength, flexural strength, and dynamic elastic modulus. Furthermore, impact resistance tests revealed that higher content and smaller particle sizes of waste rubber powder enhanced the concrete’s crack resistance. Statistical analysis utilizing the two-parameter Weibull distribution can be employed to assess the initial crack impact number (N₁) and final crack impact number (N₂) of waste rubber powder cement concrete.

(3)

Among the waste rubber powders, the 10-mesh variant exhibited the most pronounced noise reduction effect, whereas the 20-mesh, 30-mesh, and 60-mesh varieties showed comparable noise reduction effects in concrete. Moreover, an increase in waste rubber powder content correlated with improved noise reduction capability.

(4)

Waste rubber powder addition resulted in decreased drying shrinkage of cement concrete. Moreover, larger content and mesh size led to reduced drying shrinkage. Conversely, under constant content, impermeability increased with higher mesh sizes of waste rubber powder; meanwhile, with consistent mesh size, impermeability rose with increasing content, although the impact on concrete impermeability was more pronounced. Additionally, the mass loss rate of waste rubber powder cement concrete decreased with greater mesh size of waste rubber powder, and higher content correlated with lower mass loss rates.

This study delivers a thorough examination of the mechanical properties of waste rubber powder cement concrete, offering a fresh perspective for concrete research and application. It can not only decrease waste rubber pollution of the environment, while also increasing the recycling rate of raw materials, but also potentially broaden the application scope of cement concrete and alleviate its limitations.