7 Key Points for Controlling the Asphalt Mixture Quality

How to control the quality of the asphalt mixture? The quality of the asphalt mixture is mainly reflected in its indicators – stability and flow value. The stability and flow values characterize the stability and deformation resistance of the mixture at high temperatures. In fact, it is an indicator that reflects the material strength of asphalt concrete and the deformation ability of the material after formation. So we control the quality of the asphalt mixture should be done from the following main aspects.

Mineral material of asphalt mixture

Coarse aggregate is gravel with a particle size of 2.36 to 25mm. It needs to provide stability in the concrete surface layer through the role of embedded locking of aggregate particles and resistance to displacement through the role of friction. This requires that its mechanical properties should meet the technical requirements of asphalt concrete and have a certain shape (shape affects the concrete compactness, high-temperature stability, and pavement structural strength). The coarse aggregate is required to be a square particle with a rough surface and angularity after crushing. The content of the needle flake should be low, and there should be high internal friction between the aggregates.

Fine Aggregate of asphalt mixture

Fine aggregate is the crushed rock with particle size between 0.075 and 2.36mm. The ballast and mineral powder should be clean and free from clay and other harmful substances. It should be angular so as to increase the embedded locking effect between the particles and reduce the pore space between the aggregates and increase the stability of the mix.


In the use of asphalt before checking whether the indicators meet the technical requirements of traffic petroleum asphalt, including needle penetration, strength, softening point, flash point, melting degree, wax content, and film oven heating test indicators.

Asphalt grade should be selected according to the local climate. The higher the chosen asphalt grade, the greater the needle penetration, the lower the consistency, which is suitable for regions with lower temperatures. So that the pavement built into the lower temperature crack resistance is better, but the high temperature stability is poor.

Usually according to the level of different types of asphalt, the surface layer should be used thinner asphalt to improve the crack resistance of the surface layer. And the middle and lower layers use thicker asphalt to improve its rutting resistance. The higher the consistency of asphalt, the higher the needle penetration PI index, the higher the high temperature stability and rutting resistance of the pavement, but the temperature crack resistance is poor.

So the construction can be mixed with various modifiers in petroleum asphalt to improve the high-temperature stability and low-temperature cracking of asphalt pavement. Wax content should also be controlled at 3% or less. Wax content is too high, will affect the high temperature stability and low temperature crack resistance of the pavement, will also affect the adhesion of asphalt.

Matching ratio control of asphalt mixture

The design of the target mix ratio should be selected from repeated tests. After setting out the quantity of all levels of the mix, Marshall test is conducted to determine the best amount of asphalt, so as to determine the proportion of ingredients in each specification bin.

After the feeding time sequence, so that the new mineral material being heated in the burning port end of the drying cylinder of the discharge from the inner cylinder flow to the outer cylinder in the inner compartment. The mixed materials such as filling materials arriving at the same time are dry stirred and discharged from the discharge port. The mixture is sieved and the ratio of each specification bin and filler material is adjusted until the error between the key sieve passage rate and the median value of the target gradation range is within the specified value.

Temperature Control of asphalt mixture

In the specification, asphalt heating is controlled at 150 to 170°C. The mineral temperature is 10 to 20°C higher than the asphalt. Mix factory temperature of 140 ~ 155 ℃. The factory temperature of the finished asphalt mixture directly affects the quality of paving and rolling. When it is transported to the paver for use, the temperature is controlled to be between 135 and 150°C. The initial rolling temperature should not be lower than 135℃. The final rolling temperature should not be lower than 110℃. The open traffic is not higher than 60℃. The temperature of the finished material is detected at any time during the production process and fed back to the operation room in time to control the temperature.

Oil-to-stone ratio control of asphalt mixture

The oil-to-stone ratio is the ratio of the mass of asphalt and the mass of sand and other additives in asphalt concrete. It is the most important indicator to control asphalt concrete. If the oil-to-stone ratio is too large, after paving and rolling up the “oil cake”. If the oil-to-stone ratio is too small, the concrete material is scattered, and rolling is not formed, which are quality accidents.

Mixing of asphalt mixture

It is required that all mineral particles are wrapped in asphalt, with no uneven wrapping phenomenon, no white material, no lumps, or serious segregation phenomenon. The mixture with burnt carbonization blistering and water content are to be discarded. Usually, the mixture mixing time is between 45 and 90s. Every day, every week, we should always sample test the technical indicators of the material and report to the engineer for approval.

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