Evaluation of Skid Resistance and Comfort of Pedestrian Pavement with Asphalt-Based Wood Chip

Abstract

This paper conducts an in-depth study and evaluation of pedestrian paths, with a particular focus on the anti-slip performance and walking comfort of wooden chip pedestrian walkways. Through controlled experiments, a comparative analysis was performed between wooden chip pedestrian walkways and ordinary paved brick walkways. The experimental results indicate that under dry conditions, the anti-slip performance of various road surfaces is good. However, in wet environments, the anti-slip performance of paved brick roads deteriorates significantly. In contrast, wooden chip pedestrian walkways, especially those mixed with asphalt and wood chips, exhibit excellent anti-slip properties and comfort. Additionally, the study reveals that the comfort of wooden chip pedestrian walkways is significantly better than that of paved brick walkways, and the comfort of asphalt materials is slightly better than emulsified asphalt. It is worth mentioning that fine wood chips provide less comfort than coarse wood chips. Although reducing the thickness can enhance comfort, considering the service life of the road, a thickness of 4–6 cm is most suitable. Finally, asphalt and wooden chip mixtures with coarse wood chips possess good water permeability, making them suitable for permeable drainage pavement designs, effectively reducing road surface water accumulation.

1. Introduction

With the acceleration of urbanization, sidewalks, as a crucial component of urban transportation, have garnered increasing attention for their safety and comfort. Traditionally, sidewalk paving materials such as bricks and cement, despite their simplicity and economy in construction, are prone to cracking and damage over time. Moreover, these materials often overlook anti-slip properties and walking comfort [1]. Consequently, finding novel paving materials to enhance anti-slip performance and walking comfort has become a focal point of current research. Asphalt-based wooden chip pavement, combining the flexibility of asphalt with the environmental friendliness and comfort of wooden chips, holds promise for excellent performance in sidewalk paving. This study aims to systematically evaluate the anti-slip properties and comfort of asphalt-based wooden chip sidewalks, providing a theoretical basis for their practical engineering applications [2]. Assessing the anti-slip performance of asphalt-based wooden chip sidewalks aids in understanding and optimizing their friction coefficient under various environmental conditions. This enhancement improves pedestrian safety on sidewalks and reduces accidents caused by slipping. Comfort is a crucial indicator for evaluating the quality of sidewalk pavement [3]. This study compares the comfort differences between wooden chip sidewalks and traditional brick-paved walkways. The goal is to identify paving materials that offer a superior walking experience, making pedestrians feel more comfortable and pleased during their journeys. As an innovative paving material, asphalt-based wooden chips exhibit environmental friendliness and renewability. Through this research, we hope to promote the widespread application of this novel material in sidewalk paving, thereby advancing the goals of green building and sustainable development [4].

Research on anti-slip and shock-absorbing roads has been conducted both domestically and internationally [5]. According to the Occupational Safety and Health Regulations in the United States, the anti-slip friction coefficient standard for all grounds and sidewalks providing walking and activity spaces in public institutions, schools, commercial areas, tourist attractions, and transportation sectors must reach 0.60 (measured value) or above, and 0.8 (measured value) for sloping areas [6]. The American Society for Testing and Materials (ASTM) states that a static friction coefficient of 0.50 or above for ground materials in a dry state can be considered safe. If the friction coefficient is below 0.50, it is deemed unsafe [7]. In China, some parks and specific venues use anti-slip coatings for pavement, such as the pedestrian walkway in Kunming’s Haigeng Park [8]. However, due to cost considerations, these materials have not been widely promoted or applied to all existing sidewalks. Research on anti-slip measures, such as engraving anti-slip patterns on cement roads or creating significant protrusions on brick-paved roads, has not achieved the ideal anti-slip effect, resulting in slippery roads [9]. Numerous studies on anti-slip measures have been conducted in China, including research on anti-slip and noise-reducing asphalt, environmentally friendly anti-slip road surfaces, and anti-slip measures for cement concrete roads [10]. These studies exhibit scientific rigor and operability, but research specifically focused on anti-slip measures for sidewalks remains limited [11]. Similarly, while some domestic research has touched on shock-absorbing road surfaces, such as a new type of shock-absorbing road structure invention applied for in China, this type of structure is designed for motor vehicle traffic and is not suitable for sidewalks. Therefore, research on shock-absorbing sidewalks remains a relatively unexplored area [12].

Internationally, standards have been established for anti-slip measures. For instance, the ASTM F1677 standard outlines a test method using a Portable Inclinable Articulated Strut-Type Friction Tester (PIAST) [13,14]. Other relevant standards include ASTM F1679 for the Coefficient of Retroreflection Test Method for Variable-Angle Gloss Meters (CVIT), ANSI A1264.2 for specifying the anti-slip performance of walking and working surfaces, and NFPA 901 for automated instrumentation [15]. Yin conducted friction and anti-slip research on ordinary artificial ceramic tiles using a simple friction testing device. Wang Qi used a pendulum friction tester to study the friction coefficient and anti-slip properties of wooden floors in gymnasiums [16]. For road surfaces, Qin employed a vehicle-mounted road surface horizontal force coefficient testing vehicle to investigate the friction coefficient and anti-slip characteristics of various road surface types and grades (generally high-grade road surfaces) on cement or asphalt roads [17].

Good comfort on the road surface is a prerequisite for healthy pedestrian walking [18]. Walking or running on the road can cause some damage to the knees, and comfortable shock-absorbing shoes can reduce knee joint damage [19]. A highly comfortable road surface can further minimize joint wear and tear, achieving healthy walking. Numerous scholars have conducted research on road surface comfort [20]. For instance, Mo You, Yang, Xia, Cao, Sun, Dai, and Zhang have all investigated the shock absorption and comfort of roads. They replaced materials to improve the shock absorption effect of roads, utilizing inherently elastic rubber materials to enhance elasticity and shock absorption. The shock absorption effect was evaluated using a drop ball impact vibration test [21,22,23,24,25,26,27,28,29].

As asphalt-based wooden chip sidewalks are still in the early stages of research, relevant testing methods and structural forms are relatively rare. In this paper, wooden chips are used to create sidewalks, and the skid resistance of the specimens is tested. A comparison with traditional brick-paved roads provides a comfort evaluation for wooden chip sidewalks. A controlled experiment is conducted to compare the comfort of different road surfaces. This approach aims to verify the road performance of asphalt-based wooden chip sidewalks.

2. Materials and Methods

The main experimental materials used in this article include three types of binders and two types of aggregates. The binders are asphalt, emulsified asphalt, and cement, while the aggregates are coarse wood chips and fine wood chips. In addition, sand is used as an additional material.

2.1. Materials

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Asphalt

This article selects 70#A asphalt from Maoming, Guangdong, as shown in Figure 1. All asphalt indicators meet the technical requirements of highway asphalt construction technology, as shown in

Table 1. Technical indicators of matrix asphalt.

Indicators	Actual Measured Value	Technical Standard	Experimental Methods
Penetration (25 °C, 5 s, 100 g)/0.1 mm	65.9	60~80	T0604-2011
Softening point (R&B)/°C	47.9	≥46	T0606-2011
Ductility (15 °C)/cm	126	≥100	T0605-2011
Solubility/%	99.89	≥99.5	T0607-2011
Wax content (distillation method)/%	0.9	≤2.2	T0615-2011
Flash point (COC)/°C	279	≥260	T0611-2011
RTFOT quality loss/%	−0.03	≤±0.8	T0610-2011

.

(2)

Emulsified Asphalt

This article uses SBR-modified emulsified asphalt, as shown in Figure 2. All emulsified asphalt indicators meet the technical requirements of road construction technology.

(3)

Cement

The cement used is slag Portland cement, grade P·S·A 32.5.

(4)

Wood Chips

Both the coarse and fine wood chips are produced by Xinzexing Wood-Based Panel Co., Ltd., Kunming, China. The wooden debris is mainly needle-shaped, with a maximum particle size of 18 mm in length and 4 mm in width. It is finely ground (fibrous length ≤ 3 mm, width ≤ 0.2 mm) and sieved for later use. The natural moisture content is 8.66%, and the water absorption rate is around 1.46, as shown in Figure 3 and Figure 4.

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Sand

The sand used is ordinary construction sand. After being sieved through a sieve, sand with a particle size of 0.15–0.6 mm is selected, as shown in Figure 5.

The experimental method used in this article is a controlled experiment, where variables are controlled to conduct a preliminary analysis and comparison of the test specimens. Subsequently, the mix proportion, construction steps, and materials used in the experiment are determined.

2.2. Preparation of Test Specimens

2.2.1. Preparation Method

In this article, hot mixing is used for asphalt specimens, where mixing and vibration are performed at high temperatures using a flat vibratory compactor for 30 s. For emulsified asphalt and cement specimens, cold mixing is employed, where mixing and vibration are conducted at room temperature using the same flat vibratory compactor for 30 s. During the preparation process, the final specimens are made to have the same thickness within a range where the thickness tolerance does not exceed ±2 mm.

2.2.2. Mix Design

To investigate the impact of the mix proportion between the components of the mixture on the basic properties of asphalt–wood chip composites, this experimental study first tentatively determines the range of mix proportions. Then, specimens with asphalt-to-wood chip ratios of 0.6:1, 0.8:1, 1:1, 1.2:1, and 1.4:1 are prepared (as shown in

Table 2. Various mix proportions and specimen forming diagrams.

Mix Proportion (g/cm3)	Forming Test Piece
	Facade	Top Face
0.6:1
0.8:1
1:1
1.2:1
1.4:1

), with three specimens for each ratio, to measure density and dimensions. Due to the poor mechanical properties of specimens made from wood chips, increasing the temperature may cause specimens with suboptimal mix proportions to lose strength, rendering the test results invalid. Therefore, the step of placing the upper and lower pressure heads in a constant temperature water bath at 60 °C for 30–40 min is omitted, and this experiment is conducted at room temperature. To simulate the actual weather conditions during the service life of the mixture, the prepared specimens are placed in an indoor environment at room temperature and a fully immersed environment to mimic typical sunny and rainy weather conditions, respectively. The mass and height of the specimens are measured at regular intervals until neither changes, and the data are recorded.

2.2.3. Preparation Process

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Preparation Process for Asphalt Specimens:

Asphalt is roasted in an oven at 150 °C (Figure 6) to soften it into a liquid state. The mixer is heated to 120 °C. While the asphalt is being roasted and the mixer is heating up, other materials are prepared. The mold is cleaned and Vaseline is applied to the inner surface of the mold to ensure smooth demolding without damaging the specimen. Then, 500 g of fine wood chips are weighed, heated in the oven for 1 min (note: heating time should not be too long as high temperatures can cause the spontaneous combustion of the wood chips), and any moisture is removed. Next, 500 g of sand is also weighed, heated in the oven for 2 min to remove moisture, and 750 g of liquid asphalt is poured into the mixer, followed by the dried sand. The sand and asphalt are mixed for 2 min at 120 °C to ensure the asphalt coats the sand surface evenly. The dried fine wood chips are then added, and the mixer is started for 2 min of mixing at 120 °C. Meanwhile, the mold is placed in the oven for 2 min to prevent the premature cooling of the aggregate due to the fast heat dissipation of the metal mold. The uniformly mixed aggregate is poured into the mold (Figure 7), spread evenly, and the surface is leveled. The mold is then vibrated using a flat vibratory compactor (Figure 8) for 30 s (±5 s). After vibration, the specimen is allowed to cool at room temperature for over 12 h. After 12 h, the specimen is removed from the mold, resulting in an experimental block with asphalt as the binder (Figure 9). For specimens made with coarse wood chips, the preparation steps are the same as that for fine wood chips. The only difference is that the fine wood chips are replaced with coarse wood chips. The appearance of specimens with thicknesses of 2 cm, 4 cm, and 6 cm is shown in Figure 10.

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Preparation Process for Emulsified Asphalt Specimens:

In this study, the emulsified asphalt specimens are mixed through a cold mixing process. Under room temperature conditions, the mold is first prepared by cleaning the inner surface and lining it with a layer of newspaper to facilitate easy demolding. Subsequently, 162 g of cement and 300 g of sand are mixed. Then, 81 g of water and 750 g of emulsified asphalt are added and mixed uniformly to obtain a liquid mixture (Figure 11). Next, 330 g of fine wood chips are added to the mixing bowl and mixed thoroughly, ensuring that the mixture does not form clumps. The uniformly mixed aggregate is poured into the mold, spread evenly, and the surface is leveled (Figure 12). The aggregate is then compacted by a flat vibratory compactor for 30 s (±5 s). The compacted aggregate, along with the mold, is placed in a room at room temperature for curing for 12 h. After 12 h, the specimen is demolded. Since the specimen has not fully hardened, care should be taken during demolding. The resulting specimen with emulsified asphalt as the binder is shown in Figure 13.

When using coarse wood chips to make specimens, the preparation steps are the same as that for fine wood chips. The only difference is that the fine wood chips are replaced with coarse wood chips. The appearance of the resulting specimens is shown in Figure 14.

2.3. Design of Slip Resistance Test

In this study, the slip resistance of the specimens is measured by a pendulum friction tester (Figure 15).

Test Procedure: Under room temperature conditions, the surface of the specimen is cleaned to avoid any debris that could affect the test results. The instrument is leveled and calibrated to zero, and the sliding length of the pendulum tester is set to the standard 126 mm. Then, the friction coefficient of the specimen is measured. The data about the first release of the pendulum are not recorded. Subsequently, five consecutive tests are conducted, and the temperature at the test point is measured. The data are recorded, and the average value is taken as the BPN value at that point and temperature. The same specimen is also tested under different environmental conditions (dry, wet, lubricated).

After the above preparations are completed, the BPN value of the specimen is measured. First, the dry surface is tested (Figure 16), and the data are recorded. Then, the surface of the same specimen is cleaned again, and the pendulum friction tester is adjusted. Water is sprayed on the same location to make the surface wet, and the BPN value under wet conditions is measured and recorded (Figure 17). Next, the same location on the same specimen is wiped clean to remove any surface moisture. After adjusting the pendulum friction tester, a lubricating substance (Vaseline) is applied to the surface of the specimen, and the BPN value under lubricated conditions is measured (Figure 18). As a control experiment, the BPN value of a brick-paved surface is also tested under the same conditions (Figure 19). The ambient temperature during the test is 25 °C.

3. Results and Discussion

3.1. Impact of Compaction Frequency on Splitting Strength

Considering the water absorption characteristics of wood chips themselves, we reduced the number of blows to conduct splitting tests and explored the effect of the number of blows on their splitting strength.

Figure 20 showed the splitting strength of specimens with different compaction cycles under standard curing conditions. According to the results in the figure, except for a few specimens, the splitting strength of the specimens increases with the number of blows. To further analyze the influence law between the number of blows, the growth ratio of splitting strength with the number of blows was calculated, and the results are shown in

Table 3. Growth of splitting strength with different compaction times.

Water Cement Ratio	Cement Aggregate Ratio	7 d			28 d
		F20/MPa	K (35/20)	K (50/35)	F20/MPa	K (35/20)	K (50/35)
1	0.4	0.6	1.67%	1.64%	0.91	13.19%	−10.68%
	0.5	0.64	9.37%	2.86%	0.92	19.57%	8.18%
	0.6	0.82	6.10%	2.30%	0.97	15.46%	7.14%
0.8	0.4	0.97	6.19%	0.97%	1.08	12.04%	1.65%
	0.5	1.02	8.82%	0.90%	1.19	11.76%	0.00%
	0.6	0.97	4.12%	5.94%	1.15	6.96%	1.63%
0.6	0.4	0.27	7.41%	3.45%	0.5	82.00%	5.49%
	0.5	0.42	16.67%	20.41%	0.98	4.08%	7.84%
	0.6	0.67	8.96%	−1.37%	1.02	5.88%	4.63%

Note: The splitting strength is denoted as F, and the growth rate is denoted as K. F20 represents 20 splitting strengths, K (35/20) = (35 splitting strengths − 20 splitting strengths)/20 splitting strengths, K (50/35) = (50 splitting strengths − 35 splitting strengths)/35 splitting strengths.

.

From Table 3, it can be seen that regardless of the curing age of 7 days or 28 days, the number of compaction times for each mix proportion during molding increased from 20 to 35, and the increase in specimen splitting strength was the most significant. However, increasing from 35 to 50 times had a relatively low increase in specimen splitting strength, and even had a negative impact on specimen splitting strength reduction, indicating the existence of the optimal number of compaction times. This was because the newly mixed mixture was in a loose state, and within a certain range of compaction times (20–35 times), the randomly distributed wood chips were gradually compacted with the increase in compaction times (compaction work) under the infiltration of cement (sand) slurry. The increase in density had a positive effect on the significant improvement of the splitting strength of hardened specimens. However, wood chips had their own high water absorption characteristics. Generally speaking, excessive compaction times would increase the probability of cement slurry loss in the mixture (or wood chips), leading to a significant decrease in the growth rate of splitting strength in most mix proportions, resulting in zero growth (Ww/C = 0.8, C/A = 0.5 mixture) and negative growth (Ww/C = 1, C/A = 0.4 mixture), which was quite special.

These special phenomena were not only caused by the loss of cement slurry in the general sense, but also related to its 20 cycles of strength as the reference value. A mixture with a mix ratio of Ww/C = 0.8 and C/A = 0.5 exhibited the maximum splitting strength at 20 cycles, indicating that its composition was well proportioned and could achieve higher compactness than other mix ratios under smaller compaction work. However, excessive compaction times (50 cycles) made the increase in splitting strength less significant. The mixture with a mix ratio of Ww/C = 0.6 and C/A = 0.5 had a splitting strength of only 0.29 MPa after 20 cycles, indicating a low water cement ratio and a relatively small amount of cement slurry. The amount of mortar in the mixture was not enough to wrap the surface of the wood debris, making it easy for the aggregates to separate and reduce their cohesion, resulting in the lowest strength. However, as the number of compaction cycles (compaction work) increases, the splitting strength of the wood debris under the infiltration of cement slurry improves.

3.2. Study on the Slip Resistance of Wood Chip Sidewalks

When the surface temperature of the specimen was t °C, the pendulum value measured was BPNt, which was converted to the pendulum value BPN20 at a standard temperature of 20 °C using the following formula:

BPN20 = BPNt + ΔBPN

During the ceremony:BPN20—pendulum value at standard temperature 20 °C;

BPNt—the pendulum value measured at the pavement temperature t;

ΔBPN—temperature correction values are used as per

Table 4. Temperature correction values.

Temperature (°C)	0	5	10	15	20	25	30	35	40
Temperature correction value ΔBPN	−6	−4	−3	−1	0	+2	+3	+5	+7

.

After the above experimental steps, the BPN values of asphalt specimens, emulsified asphalt specimens, cement specimens, and brick laying specimens under different environments are shown in

Table 5. BPN20 values in different environments.

Surface State	Bitumen		Emulsified Asphalt		Laying Bricks
	Fine Sawdust	Crude Wood Chips	Fine Sawdust	Crude Wood Chips
dry	66	61	61	58	62
moist	53	51	53	48	34
oil	31	31	26	24	17

. The data changes are shown in Figure 21.

Analysis and comparison of the BPN values from the above table revealed that there was not a significant difference between the BPN value of brick paving in a dry state and the BPN values of asphalt and emulsified asphalt specimens in a dry state. However, there was a change in the BPN value of brick paving after treating its surface.

The BPN value in the fine sawdust state was 66, and in the coarse sawdust state it was 61. Both of these values indicated that the skid resistance of asphalt pavement was relatively superior in dry environments. The type of wood chips (fine or coarse) had a certain impact on the skid resistance of asphalt pavement, but the effect was not significant. The BPN values in the state of fine wood chips and coarse wood chips were 61 and 58, respectively. Although slightly lower than pure asphalt specimens, it still maintained a high level of skid resistance. This may mean that emulsified asphalt could be an effective choice when dealing with certain road conditions. The BPN value of the brick paving specimen was 62, which was similar to that of the asphalt specimen, indicating that the brick paving pavement also had good skid resistance under dry conditions. However, it should be noted that the performance of paved roads may undergo significant changes in other environmental conditions, such as wet or oily environments.

When the road surface was in a wet state, the BPN values of all specimens showed a significant decrease. Under wet conditions, the BPN values of asphalt specimens in fine wood chips and coarse wood chips decreased to 53 and 51, respectively. This indicated that moisture had a significant negative impact on the skid resistance of asphalt pavement. This decrease may be due to the decrease in moisture, which reduced the friction coefficient between the road surface and tires. The BPN value of emulsified asphalt specimens also showed a similar downward trend under wet conditions, indicating that emulsified asphalt pavement was also affected by moisture. The BPN value of the brick laying specimen decreased to 34 under wet conditions, and the decrease was significantly greater than that of asphalt and emulsified asphalt pavement. This indicated that the skid resistance of brick pavement was relatively poor in humid environments, and additional anti-slip measures may be required to ensure safety.

Under the condition of oiling, the BPN values of all roads decreased significantly, showing that the oil pollution had a serious impact on the skid resistance of roads. The BPN values of both asphalt and emulsified asphalt specimens, whether in the state of fine wood chips or coarse wood chips, decreased to around 31. This indicated that oil pollution had a significant negative impact on the skid resistance of asphalt and emulsified asphalt pavement. The BPN value of the brick laying test piece dropped to 17 in the oiling condition, which was the lowest value of all test conditions. This further confirmed the extreme adverse effect of oil pollution on the skid resistance of brick pavement.

Through detailed analysis of BPN values in different environments, the following conclusion could be drawn: under dry conditions, the skid resistance of various road surfaces was good. Wet conditions could significantly reduce the skid resistance of the road surface, especially when paving with bricks. Oil pollution had the most serious impact on the skid resistance of road surfaces, especially on paved roads. In humid or oil-contaminated areas, special road materials or designs may be needed to improve skid resistance and ensure pedestrian safety.

3.3. Study on the Comfort of Wood Chip Sidewalks

This study evaluated the comfort of road surfaces by measuring the gravitational acceleration. The principle behind this test was that the different stiffnesses of road surfaces affected the rebound effect of an identical sphere dropped from the same height. When the sphere rebounded, it experienced a gravitational acceleration, which was analyzed and compared to determine the comfort level of the road surface. A smaller acceleration indicated a softer road surface and, therefore, better comfort.

For this study, an acceleration sensor (Figure 22) was used. The sensor was connected to a computer, and the test specimens were used to calibrate the sensor (Figure 23). After calibration, the sensor head was placed on the edge of the test specimen. To ensure that the sphere always landed on the same point of the specimen, a PVC tube with a diameter slightly larger than the sphere was used as a guide. Initially, a 50 g golf ball was dropped freely from a height of 0.8 m onto a 2 cm thick asphalt specimen (Figure 24). Subsequently, a 250 g steel ball was dropped from the same height onto the same point of the same specimen (Figure 25). Finally, a 500 g steel ball was dropped from the same height onto the same point of the same specimen (Figure 26).

For the emulsified asphalt specimens, the same testing procedures were followed to obtain the experimental data under the same conditions as mentioned earlier. The data are presented in

Table 6. Acceleration sensing data.

Type	Thickness	Types of Sawdust	Peak Value	50 g Golf Ball	250 g Small Steel Ball	500 g Large Steel Ball
Binder	2 cm	Fine sawdust	Maximum peak value	0.015	0.015	0.017
			Minimum peak value	−0.016	−0.016	−0.02
		Coarse sawdust	Maximum peak value	0.009	0.034	0.02
			Minimum peak value	−0.013	−0.02	−0.032
	4 cm	Fine sawdust	Maximum peak value	0.037	0.132	0.043
			Minimum peak value	−0.025	−0.213	−0.02
		Coarse sawdust	Maximum peak value	0.007	0.027	0.284
			Minimum peak value	−0.026	−0.0112	−0.65
	6 cm	Fine sawdust	Maximum peak value	0.026	0.6	0.039
			Minimum peak value	−0.05	−0.46	−1.036
		Coarse sawdust	Maximum peak value	0.056	0.135	1.177
			Minimum peak value	−0.048	−0.089	−1.018
Emulsified asphalt	2 cm	Fine sawdust	Maximum peak value	0.688	1.893	5.028
			Minimum peak value	−0.864	−1.893	−4.207
		Coarse sawdust	Maximum peak value	0.323	0.84	0.58
			Minimum peak value	−0.353	−1.108	−1.54
	4 cm	Fine sawdust	Maximum peak value	1.041	2.964	3.416
			Minimum peak value	−1.678	−1.631	−3.8
		Coarse sawdust	Maximum peak value	4.816	11.075	4.787
			Minimum peak value	−5.445	−10.38	−5.622
Bricklaying	6 cm	/	Maximum peak value	6.91	15.079	14.235
			Minimum peak value	−5.034	−10.306	−11.06

below. Analysis and comparison of the data resulted in acceleration graphs for various scenarios, as shown in Figure 27, Figure 28 and Figure 29. Figure 27 illustrates the acceleration changes with different thicknesses of the same material (asphalt) and the same wood chip (fine sawdust) thickness. Figure 28 shows the acceleration changes for the same thickness (4 cm) and the same wood chip (fine sawdust) but different materials. Finally, Figure 29 presents the acceleration changes for the same material (emulsified asphalt), the same thickness (2 cm), but different types of wood chips.

As the thickness of asphalt increased (from 2 cm to 6 cm), the peak acceleration generally increased for spheres of the same mass. This indicated that a thicker asphalt pavement layer provides better rebound when subjected to impact, but may also increase the stiffness of the pavement, leading to an increase in acceleration. On asphalt pavement, the influence of fine wood chips and coarse wood chips on the peak acceleration was not significant, but coarse wood chips may slightly reduce the peak acceleration in some cases, especially in thicker cases. Compared with pure asphalt pavement, emulsified asphalt pavement usually exhibits higher peak acceleration under the same conditions. This may mean that the stiffness of emulsified asphalt pavement was greater and the comfort may be relatively poor. Similarly, the type of wood chips had no significant impact on emulsified asphalt pavement. The paved road surface showed the highest peak acceleration under all test conditions, indicating that it has the highest stiffness and may have the worst comfort. From the above table, it could be seen that the average peak acceleration of brick pavement was the highest, followed by emulsified asphalt, and asphalt pavement was the smallest. This indicated that under the same conditions, asphalt pavement may provide better comfort compared to the other two pavement types.

For all types and thicknesses of road surfaces, as the mass of the sphere increased (from 50 g golf balls to 500 g large steel balls), the peak acceleration generally increased. This indicated that heavier spheres generated greater impact force when hitting the road surface, resulting in greater acceleration. According to the testing principle, the smaller the acceleration, the softer the road surface, and the better the comfort. Therefore, from the data, it could be seen that asphalt pavement (especially thinner asphalt layers) and emulsified asphalt pavement (although the peak acceleration is relatively high) may provide better comfort under certain conditions, while brick pavement provides the worst comfort. As the mass of the sphere increases, both the average maximum peak and the average minimum peak increase. This indicates that heavier spheres generate greater impact force when hitting the road surface, resulting in greater acceleration. The type of sawdust had a relatively small impact on comfort, but in some cases, coarse sawdust may slightly improve the comfort of the road surface.

The comfort of the road surface was influenced by various factors, including the road material, thickness, type of wood chips, and mass of the impact sphere. When designing and maintaining the road surface, it was necessary to comprehensively consider these factors to optimize the comfort of the road surface.

4. Conclusions

Through the performance study of wooden chip sidewalks, the following conclusions could be drawn:

• Under dry conditions, the skid resistance of various road surfaces was good. Wet conditions could significantly reduce the skid resistance of the road surface, especially when paving with bricks.
• Wooden debris pedestrian walkways had good skid resistance, and asphalt materials have better skid resistance than emulsified asphalt materials.
• Wooden debris pedestrian walkways had better comfort than brick paved pedestrian walkways. The comfort of asphalt materials was slightly better than that of emulsified asphalt materials, and the comfort of fine wood chips was not as good as that of coarse wood chips.
• Wooden crushed material sidewalks have better comfort with a smaller thickness, but considering the service life of the road surface, a thickness of 4–6 cm was recommended.
• Asphalt wood chips and coarse wood chips had good permeability and could be used in a permeable drainage pavement design to reduce road surface water.