There are three parts to a typical pavement structure: The Sub-Base, The Base, The Asphalt Level.

   While the three components vary from job to job, most paving works usually require 5 simple steps:

  1. Excavation or removal of poor sub-base material
  2. replacing with proper material of a solid base
  3. grading and compacting of the base material
  4. placing of the asphalt
  5. rolling and compacting of the asphalt layer

    1 . Sub-Base

       The Sub base is simply the natural soil that exists in the surrounding area. The Stability of a given soil varies greatly. Most soils contain silt and clay that weaken with ground moisture. Thus moisture-retaining soils are not suitable as a base for asphalt paving. These soils are removed and replaced with some type of gradual (gravel) material.

    2. The Base

       Granular materials are used to replace the excavated soils and serve as the base for which the asphalt will be placed upon. Granular materials do not retain moisture and essentially aid in lowering the water table beneath the pavement structure. The depth or thickness of the base depends on certain factors including the soil type, expected loads and water runoff. As a guideline for residential paving, a base of 200mm to 250mm in thickness is adequate.

       The base material should have a low affinity for holding water. Gravel with larger stones and less sand tend to allow water to permeate at faster rates. However, compacted base may leased to further compression in the future resulting in settlement and failure of the pavement layer. Tri-City Paving Inc. uses properly graded and high quality granular material from only the most reliable suppliers. it cannot be overstated that the base is the most important component to a long lasting driveway.

    3. Grading and Compaction

   Grading or leveling out the granular base is necessary to:

    1. Provide the desired contour or shape
    2. ensure a uniform thickness for the asphalt
    3. ensure proper water runoff is achieved
    4. ensure an optimum riding asphalt is achieved


    The Asphalt layer


       The pavement seen on the roads, parking lots or residential driveways is referred to as Hot Mix Asphalt (HMA). There are two ingredients in HMA. One is the asphalt cement and the second is the aggregate (granular) material. Hot mix asphalt designs combine the proper amounts of asphalt cement and aggregate to produce a high-performing and durable pavement mixture. Asphalt cement is a black-brown thermoplastic compound and is by-product from processing petroleum oil. It typically accounts for 4-8% of the HMA by weight. The aggregate portion makes up 90-95% or the HMA by weight. It is the aggregate portion that is primarily responsible for the load supporting capacity of a pavement.


       Tri-City Paving Inc. uses only OMPHA approved facilities for the batch of hot mix asphalt. Typically mix designs using more coarse aggregate are used on a larger commercial projects. The high content of coarse aggregates aids in the stability of the mixture, which would be necessary for the high level of traffic on a commercial property. For residential paving, Tri-City paving Inc. uses a modified version of the coarse-aggregate mixture. These modified mix designs contain more sand & small aggregates to help give a more cosmetic look at your driveway.

    4. Placing of the Hot Mix Asphalt

       Tri-City Paving Inc. uses an array of sophisticate paving machinery to achieve an aesthetic looking and durable asphalt product. The HMA is removed from large dump trucks and emptied into the mouth of a large self-propelled paving machine. "Feeder" plates guide the asphalt mix downward under "hot" a plate of ‘screed". The screed is flat and can be adjusted to a desired height to determine the thickness of the asphalt layer. The screed can also be tiled, crowned or inverted for drainage purposes in difficult situation. Hydraulic gates allow the paving machine to open to various widths (8’ to 14’) making it very versatile. The end result is a paved area of uniform thickness and optimal smoothness. Difficult to reach areas or items too small for paving machines are spread out by hand and leveled with hand tools (lutes and rakes).

    5. Rolling and Compacting of the Asphalt Layer

       Rolling or compaction of the asphalt layer is the final step in the paving process. Compaction is the process by which the aggregate particles in the mixture are squeezed together. In doing so, the amount of air pockets in the mixture are reduced and the density of the pavement structure increases. The increased density makes the pavement suitable for load bearing. Rolling must occur when the hot mix asphalt is still fluid, between 85 and 150 degrees Celsius.

       Decreasing the air void content in the asphalt mixture is crucial to the durability f the asphalt. Excess air voids allow the penetration of air and water. Air tends to oxidize the asphalt and make it brittle while excessive water will slowly strip the aggregate of the cement causing it to weaken. If the proper density is not achieved during the rolling process, further consolidation may occur in the asphalt layer with load bearing leading to rutting and sinking.

       Numerous factors affect the rolling procedure such as asphalt mix properties, grade of asphalt, mix temperature, environmental conditions, type of rolling machine, speed of application, rolling pattern and asphalt thickness. Tri-City Paving Inc. uses a combination of rolling machines during compaction because different situations call for different applications. Smaller static and vibratory rollers with low dynamic forces are used for rolling of more tender asphalt mixes. Larger pneumatic and steel drum rollers of high vibratory frequency and force are used in larger areas with more course asphalt mixtures. Areas too difficult to reach with motorized rollers are neatly compacted with hand tampers and tools.



 

 
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