Laboratory testing of asphalt concrete: a brief overview of control methods

When building a road, asphalt concrete is essential because it offers a smooth driving surface and durability. Testing its composition and quality is essential to make sure it functions as planned. An important part of this process is laboratory testing, which confirms that the asphalt concrete can tolerate a range of stresses and meets industry standards.

The primary techniques for testing asphalt concrete in laboratories will be discussed in this article. These control techniques are intended to evaluate various material properties, including strength, resilience to abrasion, and resistance to environmental influences. Knowing how these tests are conducted can help guarantee the durability and dependability of asphalt concrete.

We’ll go over the fundamental methods for assessing asphalt concrete, giving a concise rundown of how these tests are carried out and what the results indicate about the material’s functionality. This summary will provide you with a thorough understanding of the main control techniques employed in the road construction industry, regardless of your involvement in the process or just your curiosity about how asphalt concrete is tested.

What is an asphalt concrete mixture, its types and technical characteristics subject to testing

Sand and crushed stone or gravel, either with or without mineral powder, are combined to make asphalt concrete mixture.

As per GOST 9128-2013, the following surfaces can be used to make asphalt concrete mixture:

• On crushed stone;
• On gravel;
• On sand.

It is possible for the mixture to be either hot or cold depending on the temperature. The mixture can be sandy, fine-grained, or coarse-grained, depending on the size of the mineral grain.

The following mixture types are determined by the amount of residual porosity: dense, highly porous, highly dense, and porous.

Depending on how much crushed stone is present, the hot mix of gravel and crushed stone is:

1. With a crushed stone content of 50-60%;
2. With a gravel or crushed stone content of 40-50%;
3. With the content of the above in the amount of 30-40%.

At least 50–70% of the mixture should consist of crushed stone to be classified as high-density. Crushed stone and highly porous sand are the subsequent divisions of the highly porous mixture.

Cold mixtures of gravel and crushed stone are classified into types Bx and Vx based on the percentage of crushed stone in the mixture.

Depending on the kind of sand used, cold and hot mixtures are separated into different types:

1. Gx and G. This type of asphalt concrete mixture is made on the basis of natural sand from crushing screenings;
2. Dx and D are made on the basis of natural sand or a mixture of them with crushed screenings.

It is essential to test asphalt concrete in laboratories to guarantee the longevity and quality of road surfaces. This article gives a quick rundown of the primary control techniques utilized in these experiments, emphasizing how they contribute to the evaluation of the material’s durability and performance. Professionals can more effectively guarantee that asphalt concrete satisfies the requirements and functions dependably in a variety of scenarios by being aware of these techniques.

Preparatory work

According to GOST, testing asphalt concrete is done in multiple steps, the first of which is sample collection and preparation. Let’s get started with this.

Sampling and preparation of the mixture

Our consideration of this matter will be guided by GOST 12801-84’s requirements. The mixture is prepared in a specialized laboratory mixer that has a heating device as part of the composition selection process.

After being pre-dried and put in a container, sand, crushed stone, and mineral powder are heated to a specific temperature. The binder is then added, albeit in a heated state.

The type of mixture (hot, warm, or cold) determines the appropriate temperature to heat the material to. It needs to match the value listed in Table 1.

Testing of asphalt concrete pavement in laboratories: specifications for the heating temperature of raw materials for various kinds of mixtures:

Type of asphalt concrete mixture	The temperature of mineral raw materials	The temperature of the astringent	The temperature of the mixture during the manufacture of the sample
Cold	100-120	80-90	18-22
Hot	100-110	80-90	90-100
Warm	120-130	100-120	120

Note: You can lower the temperature of the mixture and the astringent by roughly 15-20 degrees if you use mineral powders or surface-active substances.

Raw material mixing takes place for three to six minutes; the precise duration is typically determined experimentally. If there are no clots in the solution and the astringent has completely covered the mineral filler, the mixture is said to be ready. The final step is the creation of the mold.

Depending on the amount of crushed stone in the solution, multiple techniques are used to seal subsequent samples that will be examined for strength, swelling, and water supply.

Two possibilities could exist:

• The content of crushed stone is less than 35%. In this case, pressing is carried out under a pressure of 40 MPa;
• If the crushed stone content is more than 35%, compaction is carried out by vibration, and then by pressing under a pressure of 20 MPa.

A much lower pressure of only 0.5 MPa is used to compaction a sample taken from a cold mix that will later be tested for caking. Within the first 30 minutes, samples from the mixture must be made.

Samples are cut or drilled out in order to assess the final coating’s quality. This situation calls for the use of either a drilling rig or a pneumatic hammer for drilling.

Sample manufacturing

As was previously mentioned, cylindrical samples created by compacting the solution in particular forms are used for tests of the mechanical and physical characteristics of asphalt concrete. Cores or cut samples can also be applied.

The process of pressing for compaction looks like this:

• The press can be mechanical or hydraulic. It should provide pressure up to 40 MPa;
• The press is equipped with a special device that allows you to simultaneously prepare 3 cylinder samples;
• The molds are located in a box that is equipped with a heating mechanism;
• To extract samples, such equipment for testing asphalt concrete is equipped with a stop device;
• If the press power is not enough to simultaneously produce three samples, only one mold is placed in it;
• The electric motor is turned on, the pressure is brought to 40 MPa. At the last stage, the finished samples are extracted.

Using a combined method for compaction suggests the following:

• Compaction is performed using vibration followed by compaction;
• Samples are manufactured in single molds;
• The mold is filled with a mixture and sent to a vibration platform, on which it is fixed;
• Vibration lasts for about 3 minutes, then the sample is sent for additional compaction under a pressure of 20 MPa. The exposure time is the same;
• Using a squeezing device, the sample is extracted.

In order to prepare samples from a cold mixture that will later be tested for caking, follow these steps:

• The mixture is heated to the temperature specified in Table 1:
• The solution is poured into the mold;
• A load capable of providing a pressure of 0.5 MPa is placed on the upper insert;
• The exposure time is the same 3 minutes;
• The sample is then kept for about four more hours.

GOST also establishes the sample size and required mixture amount, which are dependent on the property to be tested.

Test methods

Now that we have the production and sample selection down, it’s time to think about the test procedures and the indicators that will be put through them.

The essence of the methods for monitoring the main quality indicators

The following phases are present in every test:

• Preparation for testing;
• Conducting it;
• Processing the results.

Using the table as a guide, let’s examine the essential elements of the primary techniques for tracking indicator compliance.

GOST test procedures for asphalt concrete:

Name of the indicator	Instruments for testing asphalt concrete	Briefly about the essence of the method
Average density (bulk density)	Scales equipped with a weighing device (hydrostatic); vessel, with a volume of 1-3 liters.	The essence lies in determining the density value, taking into account the pores contained in samples made in laboratory conditions or in samples removed from the pavement.

A brief set of instructions looks like this:

• During the test, the samples are weighed, after which they are lowered into water, where they are weighed again. The third weighing is carried out after removal from water.
• Subsequently, the results of asphalt concrete tests are recorded and processed.

Asphalt concrete is put into a flask, filled with water, and weighed during the test. After that, they are placed in a drying oven without any heat and subjected to pressures of about 2000 MPa. After 30 minutes, the pressure is brought back to normal, and the material-containing flask is weighed.

After being placed in a water-filled vessel, the samples are sent to a drying oven, where a minimum pressure of 2000 MPa needs to be maintained.

After that, the samples are taken out and weighed.

The outcomes are logged and handled.

• Testing machine;
• mercury thermometer;
• vessels;
• vacuum device.

The sample is stored for fifteen days in order to assess water resistance after extended exposure to water.

• Scales;
• flask;
• extraction nozzle;
• sand bath, drying oven;
• filter paper, porcelain cup;
• solvent;
• cotton wool.

The crushed material or asphalt concrete mixture is poured into a cartridge that has been made.

The extraction nozzle is filled with the cartridge. Place a refrigerator on one side and a solvent-filled flask on the other.

The binder is released by the solvent.

Once the mineral portion has been cleaned and ground in a cup with a petroleum jelly-greased spout, it is sampled by passing it through a sieve.

Test reports are created for the asphalt concrete mixture and pavement sample based on the above control methods and their outcomes.

This article’s "Control and testing methods" video provides the most recent information on testing procedures as well as some tips for using your hands to manually check certain quality indicators.

Accompanying documents issued after testing

For every batch of material, a quality certificate for the asphalt concrete mixture is provided.

The following details are included in the asphalt concrete mixture passport:

• Type, kind, brand of the mixture;
• Name of the manufacturer and its address;
• Standard number;
• Date of issue of the document;
• Product weight;
• Shelf life;
• Tensile strength;
• Water resistance;
• Porosity of both mineral and residual parts;
• Water saturation;
• Shear resistance;
• Radionuclide efficiency;
• Crack resistance;

The primary documents that are shipped with the goods are the passport and the consignment note for the asphalt concrete mixture. The latter includes the following details: product weight, delivery date and time, carrier information, destination and shipment location, product price, mixture temperature, quantity, and type.

Kindly take note! According to GOST, the customer has the right to a control (repeated) inspection of the product even in the presence of documentation, such as a certificate of conformity for the asphalt concrete mixture.

Every manufacturer of asphalt concrete mixture whose products pass all indicators in the test is given a certificate.

Control Method	Description
Visual Inspection	Checking the surface for obvious defects like cracks and deformations.
Density Test	Measuring the density of asphalt concrete to ensure it meets specifications.
Marshall Stability Test	Assessing the strength of asphalt concrete by determining its stability under load.
Fatigue Test	Evaluating how well the asphalt withstands repeated loading over time.
Moisture Sensitivity Test	Testing how the asphalt mix performs when exposed to moisture.

Comprehending the diverse laboratory testing techniques for asphalt concrete is imperative to guaranteeing excellence and longevity in building endeavors. Engineers and construction experts can make well-informed decisions with the use of the distinct insights that each control method offers into the performance of the material.

These tests offer a thorough picture of how asphalt concrete will perform in various scenarios, ranging from determining the mix’s consistency to analyzing its strength and resistance. We are able to address possible problems early on and make sure that the finished product satisfies all requirements by routinely carrying out these tests.

Not only do these testing procedures extend the life of asphalt surfaces, but they also improve overall performance and safety in quality control procedures. In the end, this proactive approach results in pavements and roads that are more dependable and long-lasting.

Video on the topic

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