Because of its affordability and longevity, sand asphalt concrete is a popular and adaptable building material. This kind of concrete provides a sturdy and smooth surface for automobiles and is mostly used in road construction and repair. Sand, asphalt, and other materials are mixed to create a composite that is weather-resistant and flexible.
To ensure a consistent and uniform product, the components of sand asphalt concrete are heated and thoroughly mixed during the manufacturing process. Achieving the ideal balance between strength and flexibility is made possible by this process, which is important for surfaces that are subjected to environmental factors and traffic.
Anyone working in construction or road maintenance needs to understand the technology underlying sand asphalt concrete. Every stage of the process, from choosing the best ingredients to mixing them, is vital to the end product’s durability and quality. This article aims to examine the essential elements involved in the production of sand asphalt concrete, offering guidance on optimal outcomes and best practices.
Process | Description |
Material Selection | Choosing quality sand, bitumen, and fillers. |
Mixing | Combining materials at controlled temperatures. |
Heating | Heating the mix to improve bonding. |
Transportation | Transporting the hot mix to the site. |
Compaction | Compressing the mixture to achieve desired density. |
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General information
Sand asphalt concrete is classified into the following types based on the type of sand used:
- D and Dx – hot sand asphalt concrete mixture type D and cold, type Dx. The main filler is sand from crushed stone screenings, content 70% and higher.
- G and Gx – hot and cold asphalt with a natural sand content of 30% or more.
According to GOST 9128-2013, sand-filled asphalt concrete is categorized into the following grades:
- Gx – cold asphalt, grades I and II;
- Dx II – sand asphalt concrete mixture type "D" grade 2, cold.
Hot asphalt compositions are made with viscous or liquid bitumen solutions, and they must be installed at a minimum temperature of 110 °C. Liquid petroleum bitumen is the basis for the production of cold materials, and a minimum installation temperature of 5 °C is advised (see photo).
The most homogeneous structure is found in sand mixtures when compared to other varieties of asphalt concrete. As a result, they are able to effectively compete with crushed stone coatings in terms of cost, resistance to corrosion, and durability.
Materials
The following components make up the mixture of sand and asphalt concrete:
- petroleum bitumen;
- mineral powder;
- sand;
- modifying additives (surfactants).
Bitumen
According to GOST 11955–82 and GOST 22248–90, liquid and viscous road bitumens are used as binders for the preparation of sand asphalts.
- For hot compositions, viscous petroleum products of the following grades are used: BND 40/60, BND 90/130, BN 90/130, BN 60/90. For cold ones, liquid grades are used: SG 70/130, MGO 70/130, MG 70/130.
- BND grades are characterized by a high temperature range of plasticity, higher heat resistance in comparison with BN bitumens.
- They have good low-temperature characteristics, as well as adhesion to the surface of mineral fillers. Among the disadvantages is low resistance to aging.
- Liquid bitumens SG and MG for cold mixtures are obtained by liquefying viscous road bitumen with liquid petroleum products of verified fractional composition. Technical kerosene is used as solvent for SG grades, and diesel fuel for MG grades.
- MGO grades are partially oxidized or residual petroleum products. Compared to the SG and MG brands, they are characterized by a high speed of structure organization, stable composition and, as a rule, high-quality adhesion to the surface of the aggregates.
- To guarantee the required durability of road pavements. The grade of petroleum bitumen must be selected depending on the temperature and climatic conditions of the region, construction and design category of the road.
- Recommended conditions for the use of petroleum bitumen of different grades when laying road pavements are given in the table below.
Structure-forming materials
Mineral powder is the primary active structuring agent in asphalt concrete.
Asphalt concrete gets the required properties because of its adsorbent surface, which actively absorbs and binds the majority of the bitumen present into a single structural framework. We thus have a material that is resistant to different plastic deformations, high mechanical loads, etc.
This extends the coating’s service life and has a significant positive operational economic impact. Two types of powders are used to prepare sand asphalt compositions: activated and non-activated compositions.
Structure-forming elements are produced using carbonate rocks as a base:
- limestones;
- dolomite;
- dolomite limestones;
- shell rock, etc.
Mineral powders are frequently made using industrial waste in addition to natural materials:
- fly ash;
- ash and slag waste from thermal power plants;
- cement plant dust;
- asbestos production waste;
- flotation tailings (sulfur production);
- ferro dust, etc.
Take note! It is important to remember that waste industrial powder has been overly ground, which accounts for the high porosity of these materials and raises the amount of petroleum bitumen used in the creation of sand and asphalt mixtures.
Physicochemical activation of mineral components is one way to enhance their properties.
The fundamental idea behind activation is that powder is simultaneously treated with surface-active substances (SAS) and raw materials are crushed. The material’s previously hydrophilic surface becomes hydrophobic as a result, improving the conditions for its reaction with petroleum bitumen.
The surface of the grains is better wetted by bitumen and is not wetted at all by water as a result of this change in properties.
- increased density;
- water resistance;
- frost resistance;
- crack resistance;
- shear resistance.
When preparing compositions on activated powder, less binder (10–20%) is used than when preparing a similar composition on non-activated powder. Sand asphalt concrete is made, laid, and compacted at a temperature drop of 20 °C on mineral powder that has been treated with modifying additives.
Sand
When making sand asphalt concrete, the following substances are added as filler:
- sands of natural origin;
- sands obtained by crushing sedimentary rocks, volcanic rocks, gravel;
- filler from crushed stone screenings;
- finely ground slag materials.
The properties of asphalt concrete are significantly impacted by the filler’s quality.
Pavements become much rougher and more resistant to wear when crushed fillers or materials from crushed stone screenings of volcanic rocks are used.
Take note! The mobility and workability of solutions as well as the final pavement’s water resistance may decrease as a result of the uncontrolled use of crushed sands.
Activated mineral powder, tar additives, hydrated lime, modifying additives, and raising the percentage of natural sand to 30% of the product’s mass are all advised when designing sand asphalt with a higher percentage of crushed components.
Sand and asphalt concrete mixtures on crushed material are advised for building the upper waterproof layers of class II and III car surfaces.
Mixtures made with natural ingredients are utilized to build bike lanes and walkways as well as equip local roadways.
Preparation
Sand composition for asphalt concrete can only be created in a factory.
The following are the primary tasks involved in the preparation process:
- Dried and heated to the design temperature crushed screenings or natural sand are fed by an elevator to a mixing unit equipped with a batcher.
- Mineral powder, in a cold aggregate state, is loaded into the main weigh batcher.
- Dosed mineral powder and sand from a common weigh bin are fed to the mixer, where they are thoroughly mixed (dry materials).
- Then bitumen heated to the required temperature is added to them, and they continue to mix already in a wet state.
- If the introduction of modifying additives is envisaged, they are loaded at the end of dry mixing of mineral materials.
- The duration of mixing the composition is determined by the process chart of the product and the technical parameters of the mixing plant. But in any case, the process continues until the surface of the aggregate grains is completely coated with bitumen.
In conclusion, precise mixing methods and careful material selection go into the creation of sand asphalt concrete. In order to make a long-lasting, flexible paving material, bitumen is blended with fine aggregates, such as sand. This kind of asphalt works especially well for areas and road surfaces that need a more polished, smooth finish.
A high-quality product is ensured by being aware of the crucial steps in this manufacturing process, such as heating bitumen properly and measuring ingredients correctly. The end product is a pavement that is resilient to weather and traffic while also providing an affordable option for a range of building projects.
Because of its ease of application and versatility, sand asphalt concrete is still a popular choice in the construction industry. Builders and engineers can produce dependable and long-lasting results and help create safer and more effective roads and infrastructure by following the established manufacturing techniques.