What are the advantages and disadvantages of recycled asphalt concrete

At present, the regeneration technology of asphalt mixture is mainly hot recycling (Hot Recycling) and cold recycling (Cold Recycling), two ways, due to their respective defects and did not get along the development.

Hot recycling has high energy consumption, heavy pollution, low recovery rate, and other shortcomings; cold recycling long-term road performance is not good, generally used only for the middle and lower layers.

In thermal regeneration, the amount of recycled material is generally mixed in 10-30%. Due to the mixing in the heated state, the old asphalt mixture and new aggregates, new asphalt in the process of mixing can be fully integrated, so the material performance of this mixture can reach or even exceed the conventional asphalt concrete, can repair most of the road surface with deformation, cracks, and other defects, but compared with cold regeneration, will cause some pollution to the surrounding environment.

First, plant mix hot regeneration (surface material)

Introduction: The old recycled asphalt pavement material (RAP), choose the appropriate proportion of mixing with the new material, add some regenerant if necessary, and then use intermittent or continuous plant mixing equipment to produce a unique hot mix asphalt mixture.

Advantages: plant mix hot regeneration process is easier to control, the regeneration of the mix performance is better, quality assurance, a wide range of applications.

Disadvantages: asphalt pavement materials need to be transported back and forth, the requirements of the mixing equipment are high, the current amount of old materials mixed with less, generally 20-30%.

Scope of application: regeneration of asphalt mixture for all highway asphalt pavement construction and maintenance projects, can be used for asphalt surface and flexible base.

Second, the asphalt pavement in situ thermal regeneration (surface layer)

Introduction: Using special in-situ hot regeneration equipment, the asphalt pavement is heated and softened, then raked loose (or milled) to a certain depth, mixed with a certain amount of new asphalt, regenerant, new asphalt mixture, etc., to form a unique hot mix regenerated asphalt mixture.

Advantages: to achieve local recycling and save material transfer costs, the original pavement material utilization rate is high.

Disadvantages: regeneration depth of only 20-50 mm, construction quality control is rugged, easy to produce inhomogeneity, and performance is not as good as the plant mix hot regeneration mixture.

Scope of application: the pavement has sufficient bearing capacity; only a shallow layer of minor defects is generally used for highway, one or two highway asphalt pavement surface layer maintenance.

Third, asphalt pavement plant mix cold regeneration (surface materials, grass-roots materials)

Introduction: The old asphalt pavement materials and new aggregate, emulsified asphalt or foam asphalt bonding material, water hardening active filler, water for room temperature mixing, room temperature paving to form the pavement structure layer.

Advantages: plant mix cold regeneration process is easier to control, the regeneration of the mix performance is better, a wide range of applications, low energy consumption, low pollution, emission reduction effect is evident.

Disadvantages: the formation of the strength of the mixture takes a long time, the need to add a certain thickness of the cover layer.

Scope of application: all levels of highway asphalt pavement recycling of old materials, recycled asphalt pavement materials for asphalt pavement in the lower layer and flexible base layer; grass-roots recycled materials can be used as the subgrade or base layer.

Four, asphalt pavement in situ cold regeneration (surface layer, grass-roots level, surface layer, and grass-roots level composite regeneration)

Introduction: Using special in-situ cold regeneration equipment, in-situ cold milling, crushing and sieving of asphalt pavement, mixed with a certain amount of new aggregate, emulsified asphalt or foam asphalt bonding material, water hardening class active filler, water, after room temperature mixing, room temperature paving to form the pavement structure layer. According to the different regeneration layers and thicknesses, cold regeneration is divided into in-situ ground layer complex regeneration, in-situ base layer cold regeneration, full depth (surface layer and base layer composite material) complex regeneration.

Advantages: realize in-situ regeneration, save material transfer cost; low energy consumption and pollution in the construction process; wide application range.

Disadvantages: construction quality control is more complex; generally need to add a thicker pavement structure layer.

Scope of application: all levels of highway asphalt pavement regeneration of old materials, regeneration of the surface mixture for asphalt pavement in the middle and lower layers and flexible base layer; grass-roots regeneration or full-deep regeneration material can be used as the sub-base or base layer.       

The above several regeneration technology selections, according to the highway level, pavement condition, maintenance project nature, traffic volume situation, construction environment, production capacity and other factors, careful consideration and selection.

Generally divided into the following cases:

Asphalt surface material and subgrade material – should be recovered and recycled separately.

Surface overhaul project recycled asphalt surface material – should prioritize plant mix regeneration.

Used for the middle and lower layers of recycled asphalt mixture – can give priority to plant mix cold regeneration.

Recycled asphalt mixes used for the upper layers – plant-mix hot regeneration technology is chosen.

Restoration works of road surface functions – to choose in-situ thermal regeneration technology.

Base material recycling – mainly choose in-situ or plant mix cold regeneration technology.