The Application of Resonance Crushing Technology in the Reconstruction of Old Cement Concrete Pavements into Asphalt Pavements

This article mainly discusses several common methods used in converting old concrete pavement to asphalt, as well as the advantages and processes of the resonance crushing technology.

I. Common Processing Methods

The most common approach is to excavate the existing concrete structural layer and repave the road surface.

This method removes the existing concrete layers, thereby completely resolving the issue of reflective cracks in the old cement slabs. The technique is simple, mature, and requires minimal equipment. However, it has a longer construction period, extended road closures, which can easily lead to traffic congestion on busy highways, thereby increasing social costs; simultaneously, it requires a significant amount of space for disposing of old concrete slabs, which is不利于 environmental protection.

2. Reflective cracks are set on the original concrete pavement to delay structural degradation, such as by applying glass fiber cloth, rubber asphalt layers, etc., followed by the application of the surface layer.

This method has a shorter construction period, produces little waste, and generates minimal noise and vibration. Its drawbacks include the necessity for treating damaged sections, such as grouting for hollowed-out areas, which is also complex. The main drawback is that it can only delay the formation of reflective cracks, not eliminate them completely, resulting in a shorter service life. Additionally, the post-construction maintenance is more complicated and costly.

3. Utilizing the technology of crushing, stabilization, and resurfacing of old concrete road pavements

It refers to a construction method in the process of reconstructing old concrete road surfaces, where specialized concrete panel crushing equipment is used to break and stabilize the old concrete road surface before adding a new structural layer. This method significantly reduces the thermal expansion and contraction of the concrete panels due to their reduced size after crushing; then, by using rollers to eliminate the sag difference between the panels, the likelihood of reflective cracking is decreased.

There are generally three types of crushing technology: impact compaction technology, crack and stabilize technology, and stone crushing technology.

The first two methods, including the multi-impact hammer technology in the crushing technology, can help suppress the formation of reflective cracks; however, due to the insufficiently thorough crushing of the cement slabs, these techniques cannot completely eliminate reflective cracks. Additionally, the high impact force during construction can affect surrounding houses, retaining walls, and more. The disturbance and damage to the old pavement structure layers are severe, which may lead to insufficient load-bearing capacity of the old road and necessitate reinforcement.

Resonant Crushing Technology Overview

The technology of resonance crushing for cement road surfaces was first developed and used in the United States in 1986. In 2004, the American company Ament introduced this technology to China. Starting from 2005, it was gradually applied in regions such as Shanghai and Zhejiang.

This technology primarily relies on a resonant device to emit vibrations at a specific harmonic frequency, which matches the concrete's frequency. When this occurs, it induces resonance in the concrete slab, causing it to rapidly crack and break, thereby achieving the goal of破碎ing old concrete slabs. This method significantly differs from other crushing technologies in terms of its mechanism, as it does not solely rely on sheer impact force.

Resonant Crushing and Screening Technology Advantages

Compared to other crushing technologies, Resonant Crushing Technology boasts several advantages:

1. The new board has minimal disturbance and damage to its layers, thereby maintaining the load-bearing capacity of the existing road. Due to its use of resonance principle, the energy is absorbed by the cement concrete, preventing shattered stone pieces from being embedded into the original base layer, thus preserving its load-bearing capacity. Field construction observations and comparative tests indicate that the resonance construction generates less vibration than other crushing processes.

2. The new design features a more thorough crushing of the old slab, with a more rational structure. After crushing, the upper layer has particle sizes predominantly under 4 centimeters, effectively preventing reflective cracks; the lower layer, predominantly below 15 centimeters, forms a layer with good body integrity but numerous cracks. The cracks are at a specific angle, creating an interlocking structure. This structure, compared to the vertical crack structures formed by other crushing methods, offers greater load-bearing capacity. In other words, it ensures that the crushed layer maintains a certain level of strength while also preventing reflective cracks—a structure that cannot be achieved by other methods.

This method has a short construction period, with a maximum daily crushing capacity of 4,000 to 5,000 square meters. After crushing, the road surface can be laid immediately, reducing the traffic closure time by 3 to 5 times compared to the method of removing the existing concrete layer and resurfacing.

4. Minimal waste generation, benefiting environmental protection.

5. In terms of cost, it is comparable to, if not slightly lower than, the expense of removing the existing concrete structural layer and resurfacing. Compared to other resonance technologies, its lifespan is significantly longer due to its reasonable reflection crack control.

Resonant Crushing Technology for Pavement Structure Layer Design

In the design of concrete pavement overlays following破碎改造, we have adopted the elastic layered system theory method from the "Highway Asphalt Pavement Design Specification" to ensure alignment with our current standards. This choice is due to the varying national conditions and pavement design approaches across countries, which result in diverse methods.

The crushed stone structure is distinct from our commonly used semi-rigid subgrade pavement structure and differs from flexible subgrade pavements, being most similar to the overseas "inverted structure." To ensure compatibility with existing regulations, in accordance with domestic research findings, calculations can be based on either the flexible subgrade or the composite subgrade.

Ensure the modulus of the subgrade, base course, and crushed stone layer is determined. It is best to use measured values; the modulus of the crushed stone layer is generally 500~1000 MPa, with a common calculation range of 600~800 MPa.

The overlay thickness typically needs to be greater than 12 centimeters, with the most common range being 12 to 25 centimeters. This project utilizes a thickness of 15 centimeters.

Resonant Crushing and Paving Construction Techniques

Prior to the crushing and screening construction, we must conduct surveys and prepare accordingly.

Preliminary treatment must be applied to road sections with poor geological conditions. Additionally, to ensure the safety of bridge and culvert structures, a certain distance must be maintained at both ends of the structures, and the碎石化 (crushing) process cannot be used. Based on our actual construction experience, round culvert pipes buried 50 centimeters below the subgrade will generally not cause any impact.

Additionally, due to the expansion of the old concrete after crushing, it is necessary to consider longitudinal cutting of the old cement concrete pavement for surfaces with strong plate-like properties (such as reinforced concrete), wider widths, or limited crushing expansion space.

The requirement for the stone mastic asphalt (SMA) in drainage systems is quite high. Its ability to provide sufficient load-bearing capacity and prevent or eliminate reflective cracking is greatly related to whether a drainage system is installed and its rationality. After the old road surface is crushed, it acts as a subgrade drainage system. Our task is to divert the water from the crushed stone layer to outside the subgrade. Generally, this can be achieved by setting blind gutters or collecting pipes at the road edge. The asphalt patches on the old road need to be removed as they can affect the working efficiency of resonance machinery.

Before the formal crushing, a trial vibration and excavation trial pit inspection must be conducted. Through excavation, check the particle size distribution and uniformity, and determine the construction parameters of the crushing equipment and the construction organization measures.

3. After crushing, the material should be compacted using a roller with high frequency and low amplitude, ensuring the tonnage is not excessive and the number of passes is limited. Pay attention to avoid over-compaction.

4. The asphalt paving process is similar to other asphalt pavement processes, but it is important to lay the material within 48 hours after the crushing layer has been compacted to minimize the impact of vehicle traffic and rain on the crushed layer. After the crushing layer is compacted, it is generally not necessary to apply priming oil, nor is it required to set up stress-absorbing layers, stress-absorbing membranes, or geotextiles. The material can be directly laid and compacted. Additionally, you may refer to the experience of multi-rammer crushing for laying and compacting emulsified asphalt priming oil on the surface after the crushing layer has been compacted.

Reference:

Wu Qingfeng, Ling Jianming. Research and Application of Stone Paving Technology for Concrete Pavement Resonant Fragmentation. Shanghai Municipal Public Works Administration Bureau Science and Technology Development Fund Project.

Wang Songgen et al. Guide to the Application of Stone Paving Technology for Old Concrete Road Surfaces. People's Communications Press, 2007.1

[3] Ministry of Transport of the People's Republic of China. Design Specifications for Highway Cement Concrete Pavements (JTG D40-2002). People's Traffic Publishing House.

[4] Ministry of Transport of the People's Republic of China. Highway Asphalt Pavement Design Specification (JTG D50-2006). People's Communications Press