Contrary to appearances, the technological process of building asphalt pavements is complicated. Starting from ordering the material, through its transport, pouring and compaction, to final processing and commissioning. What seems simple to average drivers is a challenge and risk for construction teams each time.
In today's article, we will discuss in detail the asphalt pavement construction process, the compaction technique, and the types of equipment used throughout the process. But first, let's check what the asphalt consists of and what its properties are.
What is asphalt?
If we want to define asphalt, it is a mineral-asphalt mixture. The asphalt itself is obtained from the fraction of crude oil processing and is most often used in road construction and as an insulating material, i.e. asphalt mastic. Asphalt is sometimes incorrectly equated with tar, which, unlike asphalt, is the result of degassing wood or coal.
Asphalt plays the role of the so-called binder that binds the mineral mixture consisting of sand, grits, and limestone flour. Asphalt constitutes approx. 5% of the mineral-asphalt mixture, which is used for the construction of the wearing course, binding course, and the main foundation. Asphalt can be divided into 4 types that are used in the construction of road surfaces. It is conventional, hard, multi-grade, and polymer-modified asphalt. It can also be classified according to a more general application. It will be road, industrial and special purpose asphalt
Classes and categories of public roads
Following the Regulation of the Minister of Transport and Maritime Economy, issued on March 2, 1999, public roads were divided into appropriate classes to define specific technical and operational requirements:
- Symbol A - highway
- Symbol S - expressways
- Symbol GP -fast traffic trunk roads
- Symbol G - main roads
- Symbol Z - collector roads
- L symbol - local roads
- Symbol D - access roads
Public roads have also been properly sorted according to their functions in the road network:
- Classes A, S, GP - national roads
- Class GP or G - voivodeship roads
- Gp, G, Z classes - district roads
- Classes GP, G, Z, L, D - municipal roads
Laying asphalt - step by step
The asphalt paving process consists of several stages that are closely interconnected. Even a small mistake in the initial phase can have a huge impact on the further development of the tasks performed. For this reason, each such investment is quite a big logistical and organizational challenge.
The first step is to prepare an order for the asphalt mix. The material must then be transported to the construction site as quickly as possible. The time intervals between consecutive deliveries are very important here. Then the mixture is evenly spread with a machine called an asphalt spreader and the whole is compacted until a compact and stable surface is obtained. The whole thing does not seem so complicated, but each stage requires proper preparation and compliance with strictly defined technological rules.
Stage I - collection and transport of the mixture
Before commencing activities on the construction site, the contractor places an order for an asphalt mix. This document must contain information such as:
- company name
- construction details
- designation of the mixture
- planned delivery date
- the total amount of material / possible daily amount
- type of vehicle for transporting the mixture (capacity, quantity)
- details of the person responsible for the coordination of activities
The collection of the material and its transport to the place of installation is a considerable logistical challenge. Subsequent deliveries must take place at strictly defined time intervals, taking into account the efficiency of paving on the construction site. You also have to bear in mind the changing weather conditions, traffic difficulties, detours for trucks, and drivers' breaks.
Why is it so important? Because the mixture dries and cools down every minute. It must be delivered to the construction site within a strictly defined time to ensure smooth unfolding. The transport of the mixture itself also involves the proper preparation of, for example, load boxes, which must be covered with a special anti-adhesive agent.
Stage II
Before implementing the mixture, its prior visual assessment is very important. The most important parameter that determines whether the imported material will be on the substrate is its temperature. For this purpose, readings are made with fast-reacting depth thermometers or a probe. The correct temperature of the asphalt mix is from approx. 140 to even 190 °C. How to visually identify if the imported material is fit for use?
- Correct mixture temperature - asphalt fills the space between the aggregate well. The whole thing is black and slightly shiny. Slightly specific vapors are visible and felt.
- Mixture temperature too low - a solid shell is visible on the truck's load box and the mixture does not emit fumes. The mass does not maintain a more fluid consistency and forms characteristic lumps during unloading. The cooled mixture should not be unloaded, but the further course of the procedure should be agreed with the plant.
- The temperature of the mixture is too high - specific yellow vapors are visible, which appear even before unloading. The mass is slightly brown and dull. Generally, the overheated mix should not be unloaded, although it can be used for the construction of e.g. a shoulder or a slope.
Stage III - asphalt pouring
Before starting the unloading of the asphalt mass into the paver box, the efficiency of this machine should be precisely determined depending on the thickness and width of the layer to be laid. Then, the building material is unloaded, which is evenly laid and pre-compacted by the paver.
The process of laying and pouring the mineral-asphalt mixture from the truck's load box to the paver basket requires quite a precise procedure. Please note that:
- The delivery trucks were positioned parallel to the axis of the paver load box (any deviation should be corrected);
- Keep the set feed rate as constant as possible;
- Do not allow the filling box of the paver to be completely emptied (it will result in a break in the paved surface, which requires supplementing later);
- All adjustments of the paver finisher should be set as precisely as possible before starting work. Improvements in the operation of the machine during pouring must be kept to an absolute minimum;
- Do not sprinkle the mixture directly behind the paver to even out the losses in the pavement. This is only done in exceptional circumstances;
- Be especially careful when working in close contact with the hot mixture. A great risk is not only its high temperature but also the ability to stick to clothing and skin, which increases the effects of burns.
The ongoing control of the asphalt paving process is very important. As we mentioned earlier, the asphalt mix changes its properties over time. Therefore, it is important to identify any discrepancies as early as possible.
Asphalt installation in the rain - is it possible?
For many reasons, the mineral-asphalt screed is usually not made during rainfall and on a wet substrate. A humid environment has a negative effect on the ability to evenly compact the asphalt floor. Nevertheless, it is permissible to lay thick layers of asphalt during light rainfall, e.g. drizzle. If necessary, the surface can be heated with heat radiators.
Stage IV - Mix compaction
Asphalt compaction is critical to its final strength. Unfortunately, classic compactors will not work on such a large surface. Therefore, to thicken it, well-known compaction rollers are used. Both single-drum rollers and tandem rollers (double-drum) rollers are available in use.
The number of rollers used depends mainly on the type of asphalt mix, its total area, thickness, width, and temperature. Compaction is carried out as soon as possible after the asphalt has been poured out by the paver. The first run (rollover) is made by driving as close to the paver as possible. Compaction should not be continued if the temperature of the mixture is lower than 90 °C.
The most common mistakes during asphalt installation
Construction equipment operators are required to have excellent knowledge of the rules that are assigned to a specific technological process. It is no different in the case of compacting the asphalt surface with the use of rollers.
Cracks visible at the beginning of compaction are the most common and visible defects. The reason may be, among others selection of a roller that is too heavy for the first pass, a too abundant sprinkling of the roller surface, the too low load-bearing capacity of the foundation, or inappropriate composition of the mixture.
Stage V - giving the appropriate roughness
The final stage of construction is sprinkling the asphalt surface with aggregate to give it the appropriate roughness. This treatment increases the road durability and affects the safety of its users. For this purpose, aggregate with a gradation of 1 to 5 mm is used, which is installed before the second pass of the roller. The road should be put into operation not earlier than after 24 hours of surface cooling.
Cracks in the asphalt - important information
When talking about laying asphalt roads, it is hard not to mention the gaps (or rather longitudinal joints) formed in this process. The difference between the joints and the welds is that the joints are formed during the passage with two pavers in a tandem system - hot joining. On the other hand, joints are formed when one paver is used, which pours first one lane of the road, and then the other.
The hot-to-hot joint shows the greatest durability. However, this requires the closure of vehicle traffic over a larger area, since asphalt is poured simultaneously from two pavers. If there is no such possibility, the so-called 'hot to cold' laying. At this point, it should be noted that the resulting joint should not be in the place of the planned horizontal marking, i.e. white stripes.
Equipment and machinery for road construction - what will you find with us?
In our store you will find professional and comprehensive equipment for construction companies. We offer an extensive range of compactors, including vibratory rammers, single direction vibratory plate compactors and reversible vibratory plate compactors. We have products from renowned brands such as Husqvarna, Wacker Neuson, Ammann and Bomag. Road workers will appreciate the power, reliability and versatility of road rollers available in our offer. We also have a comprehensive range of measuring instruments such as rotating levels or theodolites.
The innovative tandem rollers from Wacker Neuson
When browsing the offer of our shop, we also recommend taking a look at the range of articulated and universal Wacker Neuson tandem rollers of the RD45 series. These modern machines are characterized by enormous versatility and the highest reliability. This equipment has several functionalities that affect the efficiency of road works. They can include, among others edge pressure and cutting system, safe ROPS (Roll Over Protective Structure) protective bar and the possibility of moving the drums (creeping motion) - which is especially useful when compacting the substrate along walls.
The technical parameters of this series of rollers are also an advantage. For example, the Tandem roller Wacker Neuson RD 45-140 C is equipped with a reliable 50.9 HP diesel engine. The machine has a turning radius of 2650 mm and a drum diameter of 900 mm. The operating speed, depending on the prevailing environmental factors, is 183 m / min.
Construction of roads with iSPRZET
Our clients can also count on professional advice on the selection and operation of equipment as well as favorable financing conditions, such as leasing in 15 minutes and 100% online. By ordering products for the construction industry in our store, you can be sure that your company will receive fully original equipment with a complete manufacturer's warranty.
