All About Asphalt
*Information on this page obtained from www.myasphaltpavingproject.com
The Construction Process
Once the pavement and mix designs are completed, planning, asphalt manufacture and construction can begin. Once the mix is manufactured (see How are Asphalt Mixtures Made), the asphalt mix should be put into the trucks in such a way to prevent segregation of the mixture. It is then transported from the plant to the job site. Controlling the temperature throughout the process is very important. Putting tarps on the transport trucks helps hold the heat in. At the job site, the pavement base is prepared with grading and compaction of the subgrade, followed by the subbase, if necessary. A tack layer of liquid asphalt should be put on each layer of asphalt pavement, to make sure there is a strong bonding between the layers. The paver can accept the mix from the transport trucks, or a material transfer device (MTD) can be used. The MTD further mixes the material before depositing it in the paver, helping to reduce segregation and keeping the temperature uniform. Once the asphalt mixture is in the paver, the paver lays it under a screed in a mat of predetermined depth on the prepared base. The paving should be planned so there is a minimum of hand work. Once the mat has cooled to the predetermined compaction temperature, the rollers can begin their work – again according to a predetermined pattern to achieve the design density and air voids. Traffic control should be in place to prevent disrupting each of the layers until they have been compacted and are cool enough to hold traffic, and the tack should never be compromised by traffic.
Hint: Planning, timing, temperature, uniformity and quality control are the keys to your successful asphalt paving project.
Milling / Pulverizing/ Full Depth Reclaimation (FDR)
A milling machine (also known as a cold planer, pavement planer, pavement recycler or rotomill) is a piece of heavy equipment used to remove old asphalt pavements and surfaces from roadways, resulting in an even surface. The machine’s revolving cutting head cuts into the pavement at a predetermined depth and cross slope and removes the reclaimed asphalt pavement (RAP). The milling machine is equipped with a conveyor which deposits the RAP into a transport truck, or the RAP can be left in place (wind-rowed) to be removed at a later date or used in recycling.
Some of the things that milling (cold planning) can do are:
- Improve the pavement profile and cross section
- Restore drainage flow
- Keep overhead clearances under bridges and overpasses
- Keep the curb at the same level
- Texture the surface for skid control and improved bonding with new
Asphalt surface lifts
- Minimize traffic interruption
- Reclaim material for future use
- Lower costs, extending the maintenance budget to provide more miles
of pavement rehabilitation.
Pulverizing or Full Depth Reclaimation (FDR)
Road Reclaimers are machines that are used to pulverize or “reclaim” the full depth of the existing pavement structure. These powerful machines are capable of going through asphalt pavements that are 6 – 10″ in depth. As the material is being reclaimed, additives such as foamed asphalt cement, emulsion or fly ash may be added to help improve overall pavement structure.
The reclaimer is followed by a blade or road maintainer and compaction equipment necessary to get the desired cross slope and in place density.
Some of the things that FDR can do:
- Improve pavement profile
- Minimize traffic disruption
- Remove major pavement distresses such as cracks and pavement fatigue.
- Pavement surface can be pulverized with underlying base course to
increase overall width, depth and structure to meet pavement design needs.
Cold In-Place Recycling
Cold in-place recycling (CIR) uses a train of equipment that mills, screens, and crushes the existing asphalt pavement. Typically a milling machine removes 3-5 inches off the pavement. The milled material is then blended with an asphalt liquid and the recycled mix is laid back down to form a new pavement structure. Additional aggregate or other additives may also be blended in to correct the gradation or improve the mix. The recycled mix may be placed with a paver or it may be bladed. The mat is then compacted. After a curing period (usually 3-5 days), a new surface (typically an asphalt pavement or a seal coat) is applied. The recycling liquid asphalt may be emulsified or turned into a foamed (water expanded) asphalt cement. It may have rejuvenator oils or other additives to improve coating, moisture sensitivity and durability. The process moves quickly with minimal traffic delay.
The Benefits of Cold In-Place Recycling
- Aged, distressed pavements are replaced with recycled asphalt mix.
- In-place recycling reuses the existing aggregate and asphalt, reducing new raw material and hauling costs.
- Cracked pavement is removed, preventing future reflective cracking.
- Deformations such as potholes, ruts, bumps and shoved pavement are removed.
- Crowns can be re-established.
- Clearances under bridges and curb height can be restored.
- With the proper choice of materials, aged asphalt can be rejuvenated, and poor aggregate gradations can be corrected with added aggregate material.
- In-place recycling minimizes the time a lane is closed for re-construction.
- There is excellent public acceptance of recycled materials.
- The recycled pavement can, itself, be recycled when its time has come.
Cold in-place recycling is ideal for severely distressed pavements with potholes, cracking, shoving, ruts, and/or oxidation. The pavement must have a structurally sound base as this process does not correct base failures, and the pavements should be sufficiently thick (5-6 inches) to support the equipment. The existing pavement should be analyzed and the recycled mix designed in a laboratory. CIR can also be used for widening and upgrading pavements.
Hint: It is important to understand the reason for the pavement failure and to correct any deficiencies that may pose problems for the recycled pavement.
Contact us now for a free estimate and quick reliable service. A qualified estimator will meet with you personally to evaluate your asphalt paving needs and promptly provide a free written estimate. Alaniz Construction also excels at developing pavement maintenance plans for your long term needs.
Fremont, CA 94538
(510) 770-5020 FAX