How to Make Asphalt Concrete and How to Use It to Pave a Driveway?
Three things you must know about asphalt concrete
1. What is the difference between asphalt and asphalt concrete?Asphalt concrete
Asphalt concrete is a composite material which is consisting of mineral aggregate bound together with asphalt.
It is widely used in driveway pavement after being laid in layer and compacted.
Usually there are four components of asphalt concrete: sand, stone chips, 5-10 mm stone, and 10-15 mm stone.
asphalt and asphalt concrete are all widely used in road pavementAsphalt
Asphalt is sticky, dark brown to black, highly viscous liquid produced from petroleum distillation residue. Asphalt is refined from the heavy component of crude oil and does not come from tar.
Although being used in dam proofing, coatings, paints, and waterproofing, it is mainly applied for road pavement.
2. Different types of asphalt concrete
Asphalt concrete can be divided into two categories: petroleum asphalt and coal asphalt according to the different binders used.
According to the different types of materials used, it can be divided into aggregate, gravel, and mineral slag types of asphalt concrete.
According to the maximum particle size of the mixture, it can be divided into the following particle sizes:
|coarse granularity||medium granularity||fine granularity||sand grains|
|<35-40 mm||<20-25 mm||<10-15 mm||< 5-7 mm|
According to the different density of the mixture, it can be divided into dense gradation, semi-open gradation and open gradation.
There's a very direct relationship between the density and permeability, the higher density, the lower permeability.
Lower permeability keeps water and air out of pavement structure to prevent moisture damage from stripping standpoint, and to reduce oxidation of the binder that being coated the aggregate with.
So, if you get more a percent more density, you add 10 percent more longevity in the field.
3. Physical properties of asphalt concrete
Stability of asphalt refers to the ability of resisting deformation.The concrete road always cracks and breaks as the increase of temperature.
While different with concrete, the asphalt concrete with physical property of asphalt can withstand the temperature at the range of 64°C to -16°C.
That's why the asphalt concrete driveway is more durable.Waterproof Property
The asphalt is water-repellent material, and it has compact structure and can't dissolve in water, and meanwhile it has good plasticity, adhesion ability and bond force with mineral materials so that it makes asphalt concrete to be well waterproof.Plasticity
The plasticity asphalt concrete increases with composition, temperature, thickness and stretching speed. The greater the elongation, the better the plasticity.
How to make asphalt concrete?
Excavation and transportation
Use heavy machinery to dig out large blocks of rocks, and then transport them by truck to a paving plant which is right on the quarry site.
Because the volume of the rock is too large, it is necessary to use crushers to reduce it into small pieces of material.
The crushing process is mainly divided into three levels:Primary crushing:
The huge-block should be crushed into smaller than 20 centimeters by a jaw crusher.
When it's time to make the crushed rocks travel via a conveyor belt from the storage area to a screening building to be classified by size, there the rocks tumble downward over a series of incline screens whose largest holes at 10 centimeters across.
it's necessary to crusher rocks into small piecesSecondary crushing:
Pieces which is still large are drop through and go to a secondary crushers like impact stone crusher or cone crusher that reduces the rocks to 10 centimeters or smaller.Tertiary crushing:
Then send rock of secondary stage to a third or tertiary crusher that further reduces them to 2 centimeters or smaller.
Rock which is already small enough to pass through the screen, bypass the secondary crusher and go directly to the tertiary crusher.
After the last crushing stage, the largest stone size is about 2 cm. Materials smaller than 5mm, 5-10mm, 10-14mm are separated by conveyor belt after screening.
Then the material of a specific size is sent to the dryer through a conveyor belt. The main purpose is to reduce the humidity of the material and better bond with the asphalt during the period.
Then, the screening equipment can screen the materials again to meet people's more precise needs.
The dried material should be fully stirred in the mixer, which is designed for the surface layer, and then pumping into the hot asphalt.
This fine mix is less permeable and keeps water from penetrating down and causing cracks to form.
How to install the asphalt concrete driveway?
Installing the asphalt driveway properly means the difference between a driveway that will last just a few years and a driveway that can last up to 20 or even 30 years. You only get one chance to get the job done right.
The correct way to install the asphalt concrete driveway
Preparation of the subgrade
Proper subgrade preparation is extremely important for a driveway that will last a lifetime. The better the subgrade preparation, the better the driveway.
Now the most important aspect of the grading process is drainage planning. The soil should be excavated in fine grade for proper water drainage.Here you should make sure two things be done
- 1Make sure that the water runs off the asphalt
- 2Avoid water pooling and sitting on the surface of the asphalt to avoid pavement failures and premature deterioration
Material like rocks or gravel should be removed prior to grading and paving a driveway. Now if the driveway consists of any soft or unstable material like clay, sand or topsoil, they should also be removed.
In a strong base material like road base, recycled concrete, or limestone just name a few should be installed prior to installing the new hot asphalt, and this will help stabilize the subgrade and make the driveway much stronger and much more durable.
Install the driveway with no crown
When it comes to a long driveway, contrary to popular belief, long driveways should not be graded with a crown in them. Long driveways should be graded flat with a slight pitch to each side to get the water to run off the surface of the asphalt.
There is absolutely no advantage of installing a driveway with a crown in it. as a matter of fact, crowning can actually cause premature deterioration and pavement failures.
The crowning long driveway is also a very common way for asphalt contractors to rip homeowners off, so avoid crowns at all costs.
Once the grading is complete the subgrade should then be compacted with the rollers before installing the asphalt concrete. Next, an herbicide should be put down to minimize vegetation growth.
Weeds grow up through the asphalt can cause irreparable damage and eventually pavement failure so a quality herbicide should be put down prior to installing the asphalt.
Lay the asphalt concrete
Next step is laying the asphalt concrete. Asphalt should be installed with an asphalt paving machine and not by hand. This is going to provide a consistent average depth of asphalt throughout the driveway and a much smoother finish to the surface.
Some areas that are too small for the equipment to get when need to be installed by hand, which can slightly add to the overall cost.
Experienced asphalt rakers are also an integral part of a nicely finished surface.
When asphalt concrete is being laid out of the paving machine, it's not compacted yet, therefore, it needs to be compacted. The asphalt should be compacted soon after it's laid out of the paving machine while it's still hot.
If the asphalt cools down too much before rolling it, it's not going to get compacted well enough.
- 1Too little compaction will allow water to penetrate the asphalt and cause it to deteriorate much faster, cutting the life expectancy dramatically.
- 2On the other hand, too much compaction while it's still hot can cause the asphalt to stretch and crack causing premature pavement failures.
Compact the edges
Compacting the edges will help strengthen them and make them less prone to cracking and deterioration.
During the grading process, some of the subgrade material should left along the edges so that once the driveway is complete, that material can be pulled up to the edge of the asphalt.
This gives the driveway the appearance of sitting down in the soil rather than just being laid out on top or leaving edges exposed.
Doing so also helps to enhance the firmness of both sides, thereby minimizing cracks when the vehicle is off the driveway.
Once the asphalt installation is complete, caution tape or cones should be put up at the end of the driveway to keep people from driving on it until it's completely cool down.
Another paving choice
Some contractors may also offer to install a driveway into two layers. What this means is they'll install one layer of asphalt concrete compacted then start at the beginning of the driveway again and install the second layer of asphalt concrete and compact that layer.
But this is not a requirement and in most cases is really overkill for a residential driveway but it makes for a much more durable driveway with a much smoother ride and a beautiful finished surface.
While it does cost more money since there is more time labor and materials required, so be prepared to pay additional costs for the two-layer driveway.
FAQ about the asphalt concrete
How to calculate the density of asphalt/bitumen?
Weight of Pycnometer with Bitumen (W2) =23g
Weight of Empty and Dry Pycnometer(W1) =14g
Weight of Pycnometer with Distilled Water and Bitumen(W4) =50g
Weight of Pycnometer with Full of Water at Temperature 25°C(W3) =60g
Density of Bitumen/Asphalt=(W2-W1)/(W3-W1) -(W4-W2)
Asphalt Density = (23-14)/ [(60-14) -(50-23)]
Which is cheaper concrete or asphalt driveway?
From international market prices of 2019-2020, asphalt is between 4$-8$ per square foot while concrete is from 8$ to 12$.
The asphalt concrete driveway may need maintenance every 3-5 years, but concrete would be degraded by salt very quickly is as little as one or two seasons whether the salt is applied on sidewalks or other flat surfaces, or if you building a retaining wall made out of concrete masonry unit.
How much area can be covered by 1ton asphalt?
One ton of asphalt can be covered 80 square feet area with 2 inches thickness material, which is best for frequently used driveway.
One ton of asphalt can be covered 160 square feet area with 1inch thickness material, which is for unfrequently used driveway.
One ton of asphalt can be covered 320 square feet area with 1/2 inches thickness material, which is for roof or floor painting.