Reconstruction of Old Pavements Based on Resonant Rubblization Technology: A Review of Technological Progress, Engineering Applications, and Intelligent Development

Abstract

With the continuous expansion of highway networks and rapid advancements in the transportation industry, the need for highway maintenance and reconstruction has become increasingly urgent. Resonant rubblization technology generates an interlocking structure within the pavement layer by producing diagonal cracks at angles of 35–40°, thereby significantly enhancing load-bearing capacity and structural stability. As a result, this technique offers substantial benefits, including a marked reduction in reflective cracking, efficient reuse of existing concrete slabs (with a utilization rate exceeding 85%), reduced construction costs (by 15–30% compared to conventional methods), and faster construction speeds—up to 7000 square yards per day. Consequently, resonant rubblization has emerged as a key method for rehabilitating aging cement concrete pavements. Building on this foundation, this paper reviews the fundamental principles of resonant rubblization technology by synthesizing global research findings and engineering case studies. It provides a comprehensive analysis of the historical development, equipment design, construction principles, and practical application outcomes of resonant rubblization, with particular attention to its effects on pavement structure, load-bearing capacity, and long-term stability. Future research should focus on developing more realistic subgrade models, improving evaluation methods for post-rubblization pavement performance, and advancing the intelligentization of resonant equipment. The ultimate goal is to enhance the quality of road maintenance and repair, ensure road safety, and promote the development of long-life, sustainable road infrastructure through the continued advancement and application of resonant rubblization technology.

1. Introduction

In the 21st century, the deterioration of transportation infrastructure has emerged as a critical global challenge [1,2,3,4]. Cement concrete pavements, once valued for their high strength and cost-effectiveness, are nearing the end of their service life due to long-term exposure to repetitive traffic loads [5,6,7,8], thermal fluctuations [9,10,11,12,13], and material degradation [14,15,16,17]. Aging concrete pavements often develop structural defects like sub-slab voids, cracks, and faulting, which significantly reduce ride quality and compromise traffic safety [18]. Engineers and policymakers worldwide face a crucial challenge: how do we rehabilitate the deteriorating road network efficiently, sustainably, and cost-effectively?

Conventional pavement rehabilitation methods primarily involve replacing damaged slabs, applying asphalt overlays, or building new concrete surfaces. However, these approaches have significant drawbacks: slab replacement is expensive and labor-intensive; asphalt overlays are susceptible to reflective cracking due to differential movement at slab joints, which shortens their service life; and constructing new concrete surfaces results in resource waste and higher carbon emissions [19]. In response to these challenges, resonant rubblization technology (RRT) has gained prominence as an innovative and eco-friendly pavement rehabilitation approach in global road engineering, thanks to its key benefits of “efficient fragmentation and structural regeneration”.

Since its proposal in the late 20th century, resonant rubblization technology (RRT) has evolved from an experimental niche technique to a globally recognized solution. The technology induces controlled fractures by applying high-frequency mechanical vibrations tuned to the natural frequency of concrete slabs, transforming rigid pavements into interlocked aggregate bases. This process not only addresses the core defect of reflective cracking in traditional overlays but also facilitates the recycling of existing materials, aligning with the principles of a circular economy. From the US Interstate Highway System [20] to Argentina’s national highways [21] and China’s expressways [22], RRT has demonstrated its broad applicability across various climatic conditions, traffic loads, and pavement structures.

In-depth research on resonant rubblization technology can significantly enhance the quality of road maintenance and rehabilitation, contributing to improved road safety and longevity. This paper will begin with an investigation into the principles of resonant rubblization technology, followed by an examination of the equipment, procedures, and standards involved in its application. By analyzing the practical outcomes of using this technique in the rehabilitation of old cement concrete pavements, it aims to facilitate the mature application and widespread adoption of resonant rubblization technology in “white-to-black” road projects.

This paper comprehensively summarizes the advancements in and limitations of resonant rubblization technology in the rehabilitation of old roads and outlines the future development trends in this field. The aim is to provide potential research directions for scholars in this field, promoting the refined design and wider adoption of this technology.

The methodology for this study is illustrated in Figure 1. This paper reviews the recent developments in, as well as progress in the application research of, resonant rubblization technology and related equipment. It aims to provide researchers and construction units with a systematic introduction to the knowledge on resonant rubblization technology. Section 2 provides a brief introduction to the fundamental principles of resonant rubblization, including forced vibration, resonance, and fragmentation of pavement slabs. Section 3 discusses the development history, engineering applications, and post-rubblization pavement structure studies of resonant rubblization technology. Section 4 reviews the optimization of components and algorithms for the load-bearing structure, vibration system, and hydraulic control system of resonant rubblization equipment. Section 5 and Section 6 highlight potential areas for future research and present the conclusions, respectively.

2. Basic Principles of Resonant Rubblization Technology

During the process of breaking old cement concrete pavements using resonant rubblization technology, the pavement slabs are fragmented into smaller pieces within a short time after being excited by a vibrating hammer. This process can be divided into three stages: forced vibration of the pavement slab under the hammer’s oscillation, the onset of resonance in the slab, and the formation of the rubblized layer.

2.1. Forced Vibration of the Pavement Slab Under the Hammer’s Oscillation

Both the RPB series resonant breakers designed by RMI Corporation and the GZL series girder-type resonant breakers developed by China Railway Science & Industry Group operate by using an excitation source to achieve a specific vibration frequency in the breaking hammerhead and imparting a certain level of vibrational force to it. The collision between the hammerhead and the concrete induces forced vibrations in the concrete structure.

For typical highway cement concrete pavement slabs, dimensions usually range from 3 m × 4 m to 4.5 m × 6 m, with thicknesses generally between 200 mm and 300 mm. The ratio of the slab’s thickness to its smallest dimension is less than 0.2. When the vertical displacement of the concrete slab is less than one-fifth of the slab’s thickness, the highway cement concrete pavement slab can be modeled as a Kirchhoff thin plate [23,24,25,26], characterized by continuously distributed mass and elasticity with small deformations.

Regarding foundation models, common types include the elastic half-space model [27,28,29], Pasternak model [30,31,32,33], layered foundation model [34,35,36,37], nonlinear foundation model [38,39,40,41], and viscoelastic foundation model [42,43,44,45], among others. For subgrade supporting highway cement concrete pavement slabs, the Winkler elastic foundation assumption [46,47,48,49,50,51] is typically adopted. This assumption posits that the foundation consists of unconnected springs, where the displacement $w$ at any point on the foundation is proportional to the stress $F$ at that point, with the ratio being $k$, known as the foundation reaction coefficient, independent of other points. The relationship is expressed as follows:

$$F(x,y)=kw(x,y)$$

(1)

In summary, in this resonant rubblization model, the effect of the hammerhead’s vibration on the concrete slab is considered as an external harmonic excitation force. The original cement concrete pavement structure is treated as a Kirchhoff thin plate undergoing small-deflection bending vibrations on a Winkler elastic foundation [52,53]. This simplifies the resonant rubblization problem into a single-degree-of-freedom vibration system model of a thin plate with small deflections on an elastic foundation under harmonic excitation (as shown in Figure 2). For this model, the dynamic differential equation can be formulated as follows:

$$m\ddot{x}(t)+c\dot{x}(t)+kx(t)=F_0\sin {\omega }_{0}t$$

(2)

In the above equation, $m$ denotes the mass of the concrete slab, $c$ is the system damping coefficient, $k$ represents the stiffness coefficient of the elastic foundation, $F_0$ is the maximum value of the excitation force, and ${\omega }_0$ is the angular frequency of the hammerhead’s vibration.

By solving the above equation, the following result is obtained:

$$x(t)=A{e}^{-\xi {\omega }_{n}t}\sin ({\omega }_{d}t+\phi )+B\sin ({\omega }_{0}t-\theta )$$

(3)

According to the above equation, the vibration of this model can be divided into two components: one is the transient vibration $x_1(t)=A{e}^{-\xi {\omega }_{n}t}\sin ({\omega }_{d}t+\phi )$ of the pavement slab after being excited by the vibrating hammer; the other is the steady-state forced vibration $x_2(t)=B\sin ({\omega }_{0}t-\theta )$ under the continuous action of the hammer. The parameters $A$ and $\phi$ represent the initial amplitude and phase angle of the pavement slab after excitation, respectively, which are determined by the initial displacement $x(t=0)$ and initial velocity $\dot{x}(t=0)$; $B$ and $\theta$ denote the amplitude and phase difference under steady-state vibration conditions; ${\omega }_d$ and ${\omega }_n$ are the damped and undamped natural frequencies of the pavement slab system, respectively; and $\xi$ represents the damping ratio.

Through analysis of the above equation [54,55,56], it can be seen that the transient vibration decays rapidly to zero under the influence of damping, leaving only the steady-state forced vibration as the displacement response of the pavement slab. The steady-state vibration induced by the harmonic excitation of the vibrating hammer is itself a harmonic motion with a constant amplitude that does not decay over time. The frequency of the pavement slab’s vibration matches that of the hammerhead, while its phase angle lags behind that of the excitation force by $\theta$.

2.2. The Onset of Resonance in the Slab

Based on the above analysis, the theoretical condition for resonance of the pavement slab under excitation by the vibrating hammer is given by

$$\beta ={\displaystyle \frac{B}{B_0}}={\displaystyle \frac{1}{\sqrt{{(1-s^2)}^2+4{\xi }^2{s}^2}}}$$

(4)

In the above equation, $\beta$ represents the amplitude ratio—the ratio of the harmonic displacement amplitude to the static displacement—indicating the magnification factor of the vibration displacement relative to the static displacement under excitation by the hammerhead; $s={\omega }_0/{\omega }_n$ denotes the frequency ratio, which is defined as the ratio of the excitation frequency of the hammerhead to the natural frequency of the pavement slab system.

Through analysis of the above equation, it can be observed that when the frequency ratio approaches 1—that is, when the excitation frequency of the hammerhead is approximately equal to the natural frequency of the pavement slab—the amplitude of the displacement response increases rapidly and reaches a maximum value. This phenomenon is referred to as “resonance” (as shown in Figure 3). Resonant rubblization technology exploits this principle to achieve effective fragmentation of old cement concrete pavements [57,58,59,60].

In mechanical vibration theory, the range 0.7 ≤ $s$ ≤ 1.3 is defined as the resonance zone. Therefore, when the excitation frequency applied by the vibrating hammer falls within this range (0.7 ${\omega }_n$ ≤ ${\omega }_0$ ≤ 1.3 ${\omega }_n$), the pavement slab will experience intense forced vibration. At this point, the vibration can be regarded as resonance, and the amplitude of the vibration will increase significantly.

Hence, the theoretical condition for the pavement slab to enter resonance is met when the excitation frequency of the vibrating hammer lies between 0.7 and 1.3 times the natural frequency of the pavement slab [54,61].

2.3. The Formation of the Rubblized Layer

During the formation of the rubblized layer, the excitation force applied by the vibrating hammerhead causes the pavement slab to vibrate. When this vibration frequency approaches the natural frequency of the pavement slab, resonance occurs. At this point, the impact energy generated by the vibration propagates downward in the form of waves, with the energy gradually diminishing as it travels.

This characteristic results in a particle size distribution where finer particles are at the top and larger ones are at the bottom: the upper layer’s concrete fragments become relatively smaller as they absorb more energy, whereas the lower layer’s chunks remain relatively larger. This unique particle size distribution not only helps mitigate the risk of reflective cracking [55,56,62] when overlaying asphalt layers but also allows the finer upper structure to relieve internal stresses while the larger lower particles create a stable interlocking structure, providing solid support for the overlay.

The pavement structure after resonant rubblization can be roughly divided into three layers: the loosened surface zone, the upper rubblized zone, and the lower rubblized zone. The thickness of the loosened surface zone typically ranges from 3 to 8 cm, while both the upper and lower rubblized zones are approximately 10 cm thick (as shown in Figure 4). The fine particles in the loosened surface zone become more compact under the action of a roller, effectively releasing the internal stress of the old concrete slab, thereby reducing the likelihood of reflective cracking in the new asphalt layer [63]. The larger particles in the upper rubblized zone form a stable interlocking structure. An increase in particle size corresponds to an increase in the internal friction angle, which enhances the inter-particle stability and structural strength. The lower rubblized zone exhibits a “cracked but not fragmented” plate-like structure that generates an “arching” effect. This interlocked blocky structure demonstrates higher strength compared to conventional interlocking structures, ensuring the entire rubblized layer possesses excellent stability and sufficient load-bearing capacity [64,65].

3. Application of Resonant Rubblization Technology

Resonant rubblization is a technique specifically designed for old concrete pavements. It applies high-frequency, low-amplitude impact forces through a vibrating hammerhead, inducing resonance between the old concrete slab and the resonant equipment. This process fractures the existing cement concrete pavement into a granular layer composed of interlocking particles in the upper zone and tightly interlocked blocks in the lower zone. The resulting fragments are small in size and complementary in shape, forming a stable interlocked structure that resembles well-graded aggregate. Compared to conventional graded aggregates, however, this structure exhibits superior load-bearing capacity and stability due to its loose top layer (approximately 5 cm thick) and structurally embedded layers with 35–40° inclined cracks. Therefore, resonant rubblization is an effective solution for mitigating reflective cracking commonly encountered during asphalt overlay on existing concrete pavements.

For the rehabilitation of old cement concrete pavements, two common approaches are typically adopted: “white-over-white”, which involves placing a new concrete overlay on the existing surface, and “white-to-black”, where an asphalt overlay is applied instead. Both of these overlay methods are generally implemented after treating the original concrete slabs. For old cement concrete slabs, three typical treatment options are available: full slab removal and replacement, surface milling and cleaning, or resonant rubblization. The advantages and disadvantages of these approaches are summarized in

Table 1. Disposal options for old cement concrete slabs.

Plan	Applicable Road Conditions	Effect on Reflective Crack Prevention	Construction Characteristics	Construction Cost
Full Slab Removal and Repaving	Pavement condition rating (PCR) is poor	Only delays reflective cracks, cannot prevent them completely	Long construction period, noisy and dusty	High cost, generates waste material
Milling and Removal	Pavement condition rating (PCR) is excellent	Poor effect on reflective crack prevention	Short construction period, noisy and dusty	Low cost
Resonant Rubblization	Pavement condition rating (PCR) is fair or better	Significantly reduces reflective cracks	Moderate construction period, relatively noisy and dusty	Moderate cost, reuses old pavements, no waste generated

.

3.1. Research on Resonant Rubblization Technology

Rubblization technology originated in the United States during the 1980s and was initially used to separate concrete from internal rebar. It was later applied to the rehabilitation of transportation roads. Rubblization can be divided into resonant rubblization and multi-hammer rubblization. Both methods utilize the impact force from hammerheads for breaking but differ significantly.

Multi-hammer rubblization employs multiple hammerheads operating at a low frequency and high amplitude. The impact force is determined by the drop height of the hammerheads, leading to significant energy levels that can disturb the pavement base and subgrade. For weaker sections, this can reduce load-bearing capacity and damage the pavement structure, posing certain risks.

In contrast, resonant rubblization uses high-frequency, low-amplitude impacts. By matching the excitation frequency of the equipment with the natural frequency of the concrete slab, it induces resonance, effectively breaking the old cement concrete pavement. Each impact involves lower energy, causing minimal disturbance to the road base and subgrade [66,67]. Consequently, resonant rubblization has seen wider application over time.

The concept of resonant rubblization was introduced by Raymond in the US [68]. He designed a resonant breaker in 1983 and filed for related patents. In 1985, he first applied resonant rubblization on I-76 near Sterling, Colorado, to test its efficacy on old cement concrete pavements [69]. Long-term service data showed that resonant rubblization outperformed multi-hammer rubblization in preventing reflective cracking and reducing construction costs. Subsequently, resonant rubblization technology saw widespread adoption across various states in the US and other Western countries during the 1990s, leading to the establishment of relevant standards and guidelines.

After conducting a comprehensive follow-up investigation and study of 118 asphalt overlay projects following rubblization across the United States [70], PCS (Pavement Consultancy Services) Law Engineering concluded that rubblization technology is the best method for preventing reflective cracking in cement concrete pavement rehabilitation. The National Asphalt Pavement Association (NAPA) conducted related research on reflective cracking issues in asphalt overlays after resonant rubblization, concluding that using resonant rubblization to break up old cement concrete pavements before applying an asphalt overlay is the most effective method of preventing reflective cracking.

Subgrade conditions and environmental factors such as road temperature and humidity affect the effectiveness of resonant rubblization. Rada [70] detailed the process of implementing resonant rubblization and drainage improvement techniques on severely damaged concrete pavements in a technical report, noting that resonant rubblization enhances overall pavement performance by providing a more stable and uniform base layer, reducing maintenance costs, and extending pavement life. Additionally, the report emphasized the importance of improved drainage systems, highlighting that effective drainage is crucial to preventing water infiltration into the subgrade, thereby avoiding premature pavement damage. Figure 5 shows a crushed stone slab technology with an added side drainage system, which can ensure smooth drainage and ensure the safety of the road surface after resonance crushing [71]. Ksaibati et al. [72] conducted a comprehensive evaluation of resonant rubblization-treated sections across various states in the US. Their findings indicated that the application of this technology generally yielded excellent overall performance in most areas. However, in a few specific regions, some limitations were observed with the resonant rubblization process, primarily attributed to poor subgrade conditions characterized by inadequate soil bearing capacity.

In road rehabilitation projects, crack and seat (C&S), break and seat (B&S), and rubblization are three commonly used concrete pavement breaking techniques, and their related technical parameters and engineering effects are compared in

Table 2. Comparison of common concrete pavement rubblization techniques.

Concrete Pavement Rubblization Technique	Fragment Size	Applicable Thickness	Risk of Reflective Cracking	Construction Speed
Crack and Seat [73,74,75]	30–60 cm	<20 cm	High	Fast
Break and Seat [76,77]	15–30 cm	20–30 cm	Medium	Moderate
Rubblization	<15 cm	Unlimited (including severely damaged pavements)	Low	Slow

. These methods are primarily employed to convert old Portland cement concrete (PCC) pavements into a stable base for asphalt concrete (AC) overlays.

Crack and Seat (C&S) [73,74,75]: This method involves creating controlled cracks in the concrete slab using specialized equipment such as multi-hammer breakers without fully fracturing it. The cracked slabs are then compacted to form a stabilized base layer before an asphalt overlay is applied.

Break and Seat (B&S) [76,77]: This technique uses heavy machinery, such as portal crushers, to break the concrete slabs into larger chunks (approximately 15–30 cm). After compaction, these fragments form an interlocking base structure, followed by the application of an asphalt overlay.

Rubblization: This method employs high-frequency resonant breakers or multi-hammer equipment to completely fracture the concrete slab into particles smaller than 7.5 cm, forming a flexible base similar to a gravel layer, which is then overlaid with asphalt.

Gu et al. [78] evaluated three concrete pavement breaking techniques (crack and seat (C&S), break and seat (B&S), and rubblization) through long-term pavement performance monitoring. Their study found that rubblization technology nearly eliminates reflective cracking issues (as shown in Figure 6): when the rubblized slab modulus exceeds 560 MPa, a 20 cm asphalt overlay can achieve a long-life state; if the modulus is greater than 840 MPa, a 15 cm asphalt overlay can also reach a long-life state. Increasing the elastic modulus of the rubblized layer effectively extends the fatigue life of composite pavements and reduces rutting depth. However, if the slab modulus is too high, it may indicate insufficient rubblization, potentially leading to transverse cracking problems.

Both resonant rubblization and multi-hammer rubblization are types of rubblization technologies, but they exhibit significant differences in practical application outcomes. Akentuna et al. [79] compared multi-hammer rubblization with resonant rubblization in four PCC pavement rehabilitation projects in Louisiana, USA, focusing on reflective cracking issues when hot mix asphalt (HMA) overlays are applied to Portland cement concrete (PCC) pavements. The results indicated that the elastic modulus of existing subgrades significantly affects the structural and functional performance of evaluated sections; sections with weak subgrade conditions are not suitable for slab-breaking repair techniques. Among all evaluated projects, sections treated with resonant rubblization showed higher crack resistance compared to control groups, while multi-hammer rubblization failed to consistently improve or reduce crack resistance relative to the controls.

As a crucial branch of machine learning, deep learning has seen significant advancements alongside rapid developments in computing technology, particularly in the study of resonant rubblization, which relies on powerful computational algorithms. Kim et al. [80] conducted an in-depth investigation of the resonant rubblized layer in Iowa by using a synthetic database to correlate structural responses (strain and deflection) with layer thickness and modulus values. They designed a reverse engineering approach based on neural networks to evaluate the material properties of this layer. In addition, they quantified the mechanical attributes of the rubblized layer, determining its average elastic coefficient and modulus to be 0.19 and 539 MPa, respectively. Utilizing mechanistic–empirical pavement design methods, they accurately predicted the optimal thickness of HMA overlay layers, providing a theoretical foundation for planning and implementing actual road projects.

Ozdemir et al. [81] used numerical simulation techniques to investigate the impact of resonance breaking equipment on the vibration response of nearby pipelines during concrete pavement fragmentation operations. Their findings revealed that the internal stress induced in steel pipes by resonance breaker operation was significantly lower than the stress levels caused by normal operational pressures. Under the combined effects, the deformation of steel pipes remained within the linear elastic range, indicating that the operation of resonance breakers is unlikely to cause damage to nearby underground pipes, thereby validating their safety and reliability in practical applications.

Reflective cracking is a direct consequence of stress concentration at existing cracks on old pavements and is one of the most common pavement distresses. To date, five primary approaches have been commonly used to mitigate reflective cracking: increasing the thickness of asphalt overlays [82,83], installing geosynthetic interlayers [84], applying stress-absorbing layers [82,85], constructing graded aggregate intermediate layers [86], and placing large-aggregate asphalt mixtures as interlayers. Resonant rubblization technology falls under the category of implementing a graded aggregate interlayer. It not only offers lower construction costs but also significantly reduces both the likelihood and severity of reflective cracking. Dhakal et al. [86] surveyed current practices employed by highway agencies in the United States and Canada. Figure 7 presents a comparison of nearly all methods used to mitigate reflective cracking, with resonant rubblization emerging as the most effective and proactive solution.

Fitts [20] reviewed and analyzed the evolution and industry trends of resonant rubblization technology since 1980. His study revealed that the technology has evolved from an initial method for removing old concrete pavements into an effective solution for transforming these waste materials into unbound base or sub-base layers. Notably, resonant rubblization has been proven to significantly reduce the occurrence of reflective cracking in hot mix asphalt (HMA) overlays. This characteristic allows the reuse of old pavement materials without further processing, greatly simplifying construction procedures and reducing overall costs.

Martins et al. [87] analyzed the successful application of resonant rubblization in the rehabilitation of the old concrete runway at Shaybah Airport, led by Saudi Aramco. This project successfully recycled resources and demonstrated sustainable development principles. The technology involved breaking the severely worn surface of the original runways into small fragments while preserving the integrity of the underlying structure, which was then reused as a stable base layer for the new HMA overlay. This approach not only effectively enhanced the runway’s load-bearing capacity but also significantly reduced reflective cracking, ensuring durability and safety. More importantly, the application of resonant rubblization aligns with circular economy principles, enhances economic efficiency, conserves natural resources, and improves environmental performance—marking a significant advancement over traditional pavement rehabilitation methods.

Furthermore, as a key construction technique in pavement rehabilitation, resonant rubblization exhibits environmentally friendly characteristics. Bin Lei et al. [88] proposed a pavement rehabilitation strategy that utilized resonantly crushed old concrete as recycled base material and replaced the lower HMA layer with cold-recycled emulsified asphalt mixtures. Using life cycle assessment (LCA) and a quantitative environmental impact evaluation model, they achieved a 57.97% reduction in total energy consumption and a 71.45% decrease in carbon emissions. This study provides valuable insights for future research on sustainable pavement rehabilitation strategies.

In conclusion, the development of resonant rubblization technology represents a significant advancement in road reconstruction practices. However, it is essential to recognize that its effectiveness is closely tied to site-specific construction conditions. Factors such as insufficient subgrade bearing capacity, the dimensions, and the structural integrity of existing concrete slabs can significantly influence the performance of this technique and potentially lead to suboptimal outcomes. Therefore, future efforts should focus on developing more accurate methods for evaluating pavement structural characteristics. Approaches such as neural network modeling and finite element simulations offer promising potential to provide more scientific and data-driven guidance for both pavement construction and structural design.

3.2. Resonant Rubblization Construction

Before designing a resonant rubblization construction plan, it is essential to conduct a comprehensive investigation of the construction section. This includes collecting data on the original pavement structure and distress conditions, surrounding and underground utilities, and the drainage system setup.

Xia Hongyu [89] conducted a detailed analysis of a test section in the Dong’erhuan Road renovation project in Fuzhou City, investigating methods for determining construction parameters of the resonant breaker. He also analyzed the strength formation mechanism of the fractured layer and the impact of construction-induced vibrations on the surrounding environment. It was pointed out that a comprehensive survey and proper handling of the existing concrete pavement are prerequisites for successful resonant rubblization. Reasonable excitation force and travel speed ensure both fragmentation effectiveness and production efficiency. The safe impact range of construction vibration on the surrounding environment is within 5 m. A mean compaction measurement value of 70 is adopted as the compaction acceptance criterion. Locations with deflection values less than 70 (0.01 mm) require reinforcement treatment.

After completing the survey of the old cement concrete pavement intended for resonant rubblization, a preliminary construction plan can be developed based on past experience [90]. A test section should then be established for trial vibration. By continuously optimizing construction parameters during the trial phase, the design requirements for the resonant section can be met, allowing for the finalization of the resonant rubblization construction plan.

Zhao et al. [91] conducted trial vibration experiments to analyze the dynamic response of tunnel linings to vibrations induced by resonant rubblization. The results showed that the peak vibration velocity caused by the construction on the lining structure was 17.2 mm/s, with maximum vibration velocities of 2.3 mm/s and 10.3 mm/s observed in the 10–30 Hz and 30–60 Hz frequency bands, respectively. These findings provide valuable reference data for evaluating the safety and feasibility of applying resonant rubblization in roadway rehabilitation within mountain tunnels.

During resonant rubblization construction, the first step is to treat the old cement concrete pavement by removing any existing asphalt overlays or patches and other debris. Additionally, level control points should be established outside the affected construction area to monitor elevation changes during construction, guiding the process of resonant rubblization. Simultaneously, for underground structures, pipelines, and critical facilities around the construction section, clear signs with relevant information and precautions should be placed at corresponding station numbers on the road surface. According to regulations, vibration isolation trenches or stress relief channels should also be set up to minimize damage to surrounding facilities during the resonant construction process.

Peng et al. [92] analyzed the dynamic response of tunnel linings to vibrations induced by resonant rubblization techniques used in road renovation through numerical simulations and field tests. The study showed that the peak additional stresses on the tunnel invert and lining were approximately 2 MPa and 1.5 MPa, respectively, significantly decreasing along the transverse, longitudinal, and vertical directions of the tunnel. The effectiveness of vibration isolation trenches was also discussed, revealing that such trenches could reduce peak additional stresses in the invert and lining by 31.7% and 16.0%, respectively, demonstrating their efficiency in mitigating vibration propagation.

When beginning construction with a resonant breaker, work should proceed from lower to higher areas of the pavement, typically starting from the outer edge of the lane and moving inward, ensuring complete coverage without skipping sections. After completion of the breaking process, it is necessary to clean out joint fillers and exposed rebars on the surface of the rubblized layer and refill any vibration isolation trenches (pavement structure, field construction). Nair et al. [93] conducted a detailed analysis of a resonant rubblization project at Terminal Boulevard (SR 406). This project utilized resonant rubblization technology to transform the old damaged concrete pavement into a stable base for subsequent asphalt overlay. By inducing resonance through high-frequency, low-amplitude vibrations, the old concrete slabs were fragmented into smaller pieces, forming an interlocking gravel layer. This method effectively reduces reflective cracking and extends pavement life. The report showcased performance differences between resonant rubblized sections and untreated sections in terms of crack development, smoothness, and rut depth, confirming the significant benefits of resonant rubblization in enhancing pavement quality and durability. Furthermore, the report highlighted key operational parameters during project execution, such as equipment frequency settings and depth control, along with considerations for minimizing impacts on the surrounding environment and underground facilities, providing valuable insights for future similar projects.

Finally, a roller is used to perform multiple passes of static and vibratory compaction on the rubblized layer, starting from the edges towards the center and from the lower to the higher areas. During compaction, water should be sprayed appropriately to keep the rubblized layer moist and control dust. After compaction is completed, the asphalt overlay should be laid as soon as possible in to complete subsequent road construction operations. The construction process of resonant rubblization for all old cement concrete pavements is shown in Figure 8.

3.3. Study on Pavement Structure After Resonant Rubblization

The enhanced load-bearing capacity and ability to eliminate reflective cracking of resonant rubblized sections compared to conventional pavements [94,95] are attributed to the physical and mechanical properties of the resonant rubblized layer itself.

One of the most apparent physical characteristics of a resonant rubblized layer is the gradation of crushed stone and its spatial distribution [78,96]. Stone gradation refers to the shape, size, and grading relationship of crushed stones from the old concrete structure; the spatial distribution among crushed stones includes the void ratio, directional locking angles, and vertical distribution ratios of different-sized stones within the rubblized layer.

Evaluating the mechanical performance of pavement structures after resonant rubblization forms the basis for subsequent asphalt overlay design. Field deflection testing is a common technique that is efficient, non-destructive, and convenient, capable of accurately back-calculating the modulus of each pavement layer through inverse calculation methods [97,98,99,100]. Zhang [101] conducted a systematic study on the resilient modulus of urban roads where old cement concrete pavements were treated with resonant rubblization, focusing on the interaction between the rubblized layer and the asphalt overlay surface. The study found that if the top surface of the compacted resonant rubblized layer achieves or exceeds a resilient modulus of 200 MPa, an asphalt overlay can be directly applied without additional base treatment. However, if the resilient modulus is below 200 MPa, it is recommended to use this layer as a sub-base, with an additional semi-rigid or flexible base layer above to enhance overall pavement structure performance. Subsequently laying the asphalt overlay ensures that the final acceptance deflection value meets the design standards, thereby guaranteeing pavement durability and traffic safety.

Yu et al. [102] analyzed the sensitivity of mechanical indicators in pavement structures after rubblization using the finite element method. They found that for pavement structures with graded aggregate base layers, every 5 cm increase in the thickness of the graded aggregate layer reduced pavement deflection by 0.4–1.2%. The theoretically optimal solution involves using a 20 cm thick graded aggregate layer with a modulus of 500–600 MPa and a surface modulus greater than 1300 MPa.

Reflective cracking is a common form of pavement distress that originates in the upper base layer. Under external loads, it causes stress concentration and propagates upward, inducing other types of pavement damage. The primary external forces responsible for crack initiation include thermal loading and traffic loading [103,104,105,106].

Gou [54] conducted an in-depth study on resonant rubblization technology for old cement concrete pavements. Through theoretical analysis and simulation modeling, he explored the mechanism of resonant fragmentation of thin plates on elastic foundations. He pointed out that effective fragmentation can be achieved when the excitation frequency is maintained within 0.7 to 1.3 times the natural frequency of the plate. Using ABAQUS 6.14-4 software, simulations under different boundary conditions revealed that the first-order natural frequency ranges from approximately 50 Hz to 100 Hz, confirming that high-frequency, low-amplitude vibrations have minimal impact on the underlying pavement structure. Field sampling analysis indicated that the rubblized layer formed after resonant rubblization exhibits excellent gradation characteristics and strength mechanisms, demonstrating flexible base behavior compared to sections backfilled with graded aggregates. Finite element analysis showed that under load, the bottom of the overlay layer experiences tensile stress, while the rubblized layer remains in compression—indicating its flexible base-like nature, which enhances the overall performance of the asphalt pavement structure. Ground-penetrating radar (GPR) and falling weight deflectometer (FWD) test results further verified the structural integrity of the rubblized layer, showing that the treated crushed concrete layer exhibits clear flexible base characteristics and enables better flexural–tensile performance of the asphalt surface when used as the base layer.

The rubblized layer generated by resonant fragmentation of old concrete slabs serves as a flexible base for the asphalt overlay. The interfacial mechanical interaction between the rubblized layer and the overlay effectively prevents the occurrence of reflective cracks, thereby enhancing the serviceability and durability [107] of the resonant rubblized asphalt pavement.

Meng et al. [108] analyzed the resonant rubblization mechanism of elastic foundation plates using vibration theory for long-serving and severely damaged old cement concrete pavements. By establishing four plate models under different constraint conditions, they investigated the frequency response characteristics of the plates and the subgrade response under dynamic compaction forces. Based on field data, they revealed the particle size distribution and strength mechanisms of the fractured layer. The study found that the fragmented layer after resonant rubblization exhibits distinct flexible base characteristics. When used as a base for overlays, the entire system remains in a compressive state, allowing better utilization of the flexural and tensile resistance of the asphalt overlay and helping to prevent reflective cracking. These findings provide theoretical support and reference values for applying resonant rubblization in the rehabilitation of old cement concrete pavements.

In the application research of resonant rubblized pavement structures, traditional asphalt pavement design often emphasizes strong bases with relatively weak surface layers, leading to premature structural failures [109,110,111]. Resonant rubblization technology transforms the original rigid concrete pavement into a semi-rigid and semi-flexible base, enriching the pavement structural system and demonstrating improved durability and environmental sustainability. Liu [112], through comparative analyses with several typical pavement structures, found that resonant rubblized pavements exhibit structural advantages under moving loads. Elastoplastic analysis of the rubblized layer was conducted using the Drucker–Prager yield criterion, which effectively distributes stress and strain, reducing tensile stress and strain at the bottom of the asphalt layer. Applying fracture mechanics principles, the stress intensity factors at the bottom of both resonant rubblized and directly overlaid asphalt layers were calculated and analyzed. The results showed that resonant rubblized pavements have significantly longer residual fatigue lives. Regarding rutting, viscoelastic theory analysis demonstrated that resonant rubblized pavements possess higher bearing capacity, with rutting development similar to that of asphalt surfaces over rigid bases. Overall, resonant rubblized pavements show significant advantages in structural mechanics, fatigue life extension, and rutting control, offering an efficient and environmentally friendly solution for rehabilitating old cement concrete pavements.

Regarding the microstructure of pavements after resonant rubblization, micro-crack treatment relies on the significant impact force generated by free-falling weights to crack semi-rigid bases. The fracture characteristics, dynamic response, energy transmission, and dissipation of the matrix under falling weight impact are key issues in studying pavement microstructure features. Zhao [113] et al. used three types of falling weights (flat-bottomed, small protrusion, and large protrusion) to investigate the cracking patterns and mechanical responses of the matrix through field and simulation tests. Figure 9 shows the surface and internal cracking distribution of the matrix when the falling weight is dropped from a height of 2.2 m. The large protrusion weight caused the maximum vertical displacement of the base, resulting in more extensive cracking, extending into interlocking small pieces within the semi-rigid base.

In conclusion, resonant rubblization significantly enhances pavement load-bearing capacity and extends service life, especially by nearly eliminating reflective cracking. Moreover, the application of asphalt overlays further improves the mechanical behavior of the entire pavement structure. Future research should aim at better characterizing the material properties of the rubblized layer, particularly its mechanical behavior, to inform pavement design methodologies so that they are more accurate. Additionally, further investigation into the interaction mechanisms between the resonant rubblized layer and newly constructed layers—especially their long-term performance under dynamic loading—is essential.

4. Resonant Rubblization Equipment

The world’s first resonant pavement breaker (RPB) used in practical demolition was invented by Resonant Machine Incorporation (RMI) in the USA. It was officially applied to the demolition of old cement concrete pavements in actual projects in 1986. The working principle of this type of resonant pavement breaker is as follows: the vibration source and the breaking hammer are located on one side of a beam, with the vibration source driving the beam to induce vibrations in the hammer. When the excitation frequency approaches the natural frequency of the cement concrete slab, resonance occurs, leading to the fragmentation of the panel. The width of the hammerhead is approximately 20 cm [114,115].

Currently, the latest generation of beam-type resonant pavement breakers produced by RMI in the USA is the RB-700 model (as shown in Figure 10a). Controlled by a single lever, it features a hammerhead width ranging from 50 to 300 mm and operates at a breaking frequency of around 44 Hz. For ordinary concrete up to 660 mm thick, its daily breaking efficiency can reach 7000 m². A key challenge in developing the RMI series of beam-type resonant pavement breakers lies in ensuring that the vibration generated by the vibration source is effectively transmitted through the beam structure to the hammerhead, while also ensuring that the beam components do not suffer damage during the impact between the hammerhead and the road surface.

In 2010, China Railway Scientific Industry Group and China Railway Engineering Machinery Research & Design Institute jointly developed the fully floating resonant pavement breaker model GZL-600 (as shown in Figure 10b), marking a significant breakthrough in China’s road construction machinery field and achieving a milestone in resonant breaking technology [116]. This equipment was applied to the renovation of cement concrete pavements on Bazhou Avenue and National Highway G212 in Sichuan Province, successfully breaking 23 × 10⁴ m² of old cement concrete pavement, thus demonstrating its efficiency and reliability in practical engineering applications. The innovation of the GZL series of fully floating resonant pavement breakers lies in abandoning the traditional suspended beam vibration frequency transmission mechanism and adopting a side-mounted vibration system that directly connects the vibrator to the hammerhead, complemented by a sliding guide rail design to ensure uniform contact pressure between the hammerhead and the pavement under complex road conditions.

Academic exploration and optimization of resonant rubblization machinery continue. JIANG et al. [117] developed an adaptive backstepping sliding mode control strategy for the vibration systems of resonant breakers, aiming to precisely and dynamically regulate the resonance vibration systems within electro-hydraulic proportional control systems, ensuring accurate output frequencies and amplitudes. Their proposed optimization algorithm provides valuable reference for the design of the sliding guide rail system of the GPJ3X-600 series breakers, aiding in enhancing operational efficiency and stability. Huang [118] conducted dynamic modeling of the support structure of resonant beams, analyzing the impact of different excitation frequencies on the system’s breaking performance. This research provides theoretical foundations for designing and optimizing resonant breaker vibration systems, contributing to improved system performance and guiding practical engineering applications. Zhu et al. [119] employed ANSYS and ADAMS software to develop a rigid–flexible coupled dynamic model of the beam-type resonant breaker. They designed a vibration system comprising a resonant beam, breaking shoe, and exciter and conducted a detailed analysis of the system’s free modal characteristics. The seventh-order natural frequency was determined to be 47.0 Hz, which exceeds the optimal fracture frequency. This result verifies that the resonant beam’s natural frequency satisfies the design requirements.

In parallel, to enhance the practical application of resonant rubblization equipment, a more appropriate theoretical basis was adopted to establish an optimized model. The operational process of the equipment was simulated using software such as ANSYS, ADAMS, and CATIA, providing guidance for real-world engineering applications.

In the design of the load-bearing structure for resonant pavement breakers, Wang et al. [120] hinged the front and rear frames to prevent resonance between the front frame and the resonant system. Using a combination of shell elements, beam elements, and rigid elements, they developed a finite element model of the front frame and performed modal analysis to evaluate its dynamic characteristics. Through an optimized Latin hypercube experimental design, the structural parameters of the resonant pavement breaker were refined, resulting in an improved fourth-order modal frequency that is closer to the operational frequency.

Regarding the hydraulic system of resonant breaking systems, Ge [121] conducted optimization and simulation studies on the vibration hydraulic system of resonant breakers. Static parameters of the hydraulic drive system were matched and calculated to establish a vibration hydraulic drive system model. To address hydraulic shock issues during startup conditions, an optimization strategy was proposed that involves inputting segmented current signals to reduce hydraulic shocks. The simulation results confirmed that the optimized signal effectively lowered peak pressure shocks and shortened the startup time. Through Guan Ge’s research, the performance of the vibration hydraulic system in resonant breakers was enhanced, providing strong support for practical engineering applications.

In terms of the dynamics of vibrational forces within resonant breaking systems, Chen [122] conducted an in-depth study on the dynamic performance of the vibration system in fully floating resonant pavement breakers. The role and characteristics of the vibration system were analyzed, and structural improvements were designed. Through theoretical analysis and simulation calculations, key parameters affecting eccentric excitation forces and the motion of the exciter box were identified. A virtual prototype model was established using CATIA, ADAMS, and SimDesigner software, allowing for dynamic performance simulations under various operating conditions. Detailed comparisons were made of the mechanical behavior of the hammerhead at angles of 0° and 8° with different support spring stiffnesses (2.5 × 10⁵ N/mm and 5.0 × 10⁵ N/mm). This research provided theoretical foundations for the design and optimization of fully floating resonant pavement breakers, offering important guidance for the development and manufacturing of subsequent prototypes.

Concerning construction equipment, the quality of devices [123] and how to make construction parameters of critical components, such as resonant beams, adjustable on-site to meet the requirements for cement concrete crushing under varying regional and environmental conditions, remains an area for improvement. Currently, most parameters of existing resonant rubblization equipment are fixed and non-adjustable [124]. Optimization of these parameters could enhance rubblization efficiency and enable on-site reuse of old materials, contributing to environmental protection.

In conclusion, optimizing the mechanical structure and vibration system of resonant rubblization equipment can significantly improve operational efficiency, extend service life, and enhance the quality of resonance-based pavement breaking. However, there remains substantial potential for advancing the level of automation and intelligence in such equipment. Integrating “Internet+” technologies or adopting intelligent, unmanned operation models can enable these systems to adapt to complex and variable construction environments while minimizing the influence of human factors on workmanship and quality. Future research and development should focus on expanding the application of resonant rubblization technology in specialized engineering contexts, such as runway rehabilitation at airports and roadway modifications near bridge structures. Additionally, efforts should be directed toward mitigating the environmental impacts associated with the resonant rubblization process—particularly noise and dust emissions—and ensuring the structural safety of nearby facilities. Ultimately, achieving the effective regeneration and reuse of materials from old cement concrete pavements will further reinforce the energy efficiency, environmental sustainability, and high performance of resonant rubblization technology.

5. Recommendations for Future Research

This paper reviews the recent research on resonant rubblization technology both domestically and internationally. In summary, regarding the analysis of the underlying principles of resonant rubblization, old concrete pavement slabs are often modeled using the Kirchhoff thin plate model with small deflections, which is reasonably consistent with the actual conditions of cement concrete pavements. For the elastic foundation model, the Winkler foundation assumption is commonly adopted, where displacement occurs immediately under the loaded area and is zero outside this area. This foundation model idealizes the soil medium, offering simplicity and straightforwardness in mathematical solutions, thus gaining widespread popularity in the published literature. However, in reality, the foundation not only displaces directly under the loaded area but also experiences displacement in a certain range beyond the loaded area. Additionally, foundation soils are often deposited in layers, exhibiting stratified distributions with relatively uniform properties within each layer but significant differences between layers. Therefore, it is essential to consider the actual foundation conditions in engineering practice when applying elastic foundation models and correctly assess the continuity and diffusion capabilities of the foundation. It is recommended to further investigate the frequency response and dynamic characteristics of the Kirchhoff thin plate model on elastic continuous media or two-parameter foundation models.

Furthermore, regarding the construction and application of resonant rubblization technology, this paper presents numerous engineering examples since the 1990s. These cases have demonstrated the positive impact of resonant rubblization on pavement structure, load-bearing capacity, and stability over long-term service periods. However, there is limited research on how the extent of pavement damage affects the effectiveness of resonant rubblization. Roads can experience issues such as voids and settlement under slabs or between slabs due to vehicle loads, water erosion, construction processes, and environmental factors, leading to damage in the integrity of pavement slabs. Pavement slabs may also have different boundary conditions depending on their location within the road network or due to failures in dowel bars and tie rods between slabs. These factors significantly influence the natural frequencies of old concrete pavement slabs and their resonance effects with related equipment. Therefore, future research should focus on examining the impact of the condition of old concrete pavement slabs and external conditions on the construction outcomes and practical applications of resonant rubblization.

It should also be noted that in the research on resonant rubblization equipment, extensive studies have been conducted by integrating simulation and field testing to investigate key components and control algorithms, including load-bearing structures, vibration systems, and hydraulic control systems. These studies have provided a theoretical basis and practical guidance for the design and optimization of resonant rubblization equipment. However, there remains room for further improvement in the level of intelligence embedded in such equipment. Therefore, to meet the stringent requirements of modern infrastructure development in terms of efficiency, performance, and safety, future research should focus on advancing the intelligent transformation of resonant rubblization equipment. This can be achieved through the deep integration of technologies such as the Internet of Things (IoT), artificial intelligence (AI), big data analytics, high-precision positioning, and advanced sensing techniques. Such integration can enhance the precision and efficiency of individual machine operations, enable digitalized construction management, and reduce both operational and maintenance costs.

6. Conclusions

Resonant rubblization technology, as an advanced method for renovating old cement concrete pavements, has demonstrated exceptional performance in highway maintenance projects worldwide. By employing precisely controlled high-frequency, low-amplitude vibrations, it effectively fractures old concrete slabs and forms a rubblized layer with excellent interlocking properties, significantly enhancing the pavement’s load-bearing capacity and stability.

The application of this technology not only significantly reduces the occurrence of reflective cracking but also optimizes construction costs and timelines, demonstrating notable economic benefits and environmental value. Compared to multi-hammer rubblization techniques, resonant rubblization offers superior advantages in maintaining base integrity and minimizing disturbance to the subgrade, making it the preferred solution for road rehabilitation projects.

This paper summarizes, analyzes, and provides perspectives on the development of rubblization technologies, the application of resonant rubblization, simulations, and underlying principles. The main conclusions are as follows:

• The old concrete pavement slabs are fractured and transformed into an interlocking rubble structure by receiving impact excitation from the hammerhead at a frequency close to their natural frequency. When resonance occurs in the pavement slab, the excitation frequency of the vibrating hammer should be within the range of 0.7 to 1.3 times the natural frequency of the slab.
• The development of resonant rubblization technology represents an important trend in road rehabilitation engineering. Since its introduction, this technique has been widely applied and promoted globally in the field of road construction, with many countries establishing relevant industry standards. Compared to other concrete pavement breaking techniques, resonant rubblization offers broader applicability and superior performance in mitigating reflective cracking. It enhances the quality of road maintenance and reconstruction, ensures road safety, and supports the long-life development of pavements.
• The mechanism analysis of the resonant rubblization process is well developed but still has some limitations. When vehicular loads act on the edges or corners of finite-sized rectangular slabs, there are no corresponding analytical expressions for the resulting bending moments and deflections. Additionally, the existing theoretical foundation assumptions are inconsistent with actual sub-base structures, especially when slab structures are affected by thermal stresses or warping stresses, or when the subgrade is eroded by groundwater, leading to voids between the slab and the sub-base. These assumptions often fail to accurately reflect the complex working conditions of the foundation slab under such circumstances. There is further room for improvement in optimizing and enhancing the intelligence levels of resonant rubblization equipment. Implementing “Internet+” or intelligent unmanned operation models can allow for adaptation to complex and variable construction environments while reducing the impact of human factors on construction quality.
• The resonant rubblized layer behaves similarly to a flexible base, and its thickness is inversely proportional to the pavement deflection after overlay. Under load, the rubble layer is in a compressive state, while the bottom of the overlay layer is in tension. This structural behavior effectively distributes stress and strain, reducing tensile stress and strain at the bottom of the asphalt layer, thereby extending the remaining fatigue life of the resonantly rubblized pavement.
• The intelligence level of resonant rubblization equipment should be enhanced, with optimization in mechanical structure, signal processing, and algorithm design to prevent damage caused by hammer excitation. At the same time, further exploration should be conducted on the application of resonant rubblization technology in special engineering scenarios, such as road rehabilitation around airport runways and bridges. Research should also focus on minimizing environmental impacts during the rubblization process, including noise and dust control, as well as ensuring the safety of surrounding structures. The regeneration and utilization of waste materials from old cement concrete pavements should be promoted, and the advantages of resonant rubblization in energy conservation, environmental protection, and green efficiency should be highlighted.