Asphalt concrete mix production process and its control

Asphalt concrete mix production process and its control.  State Standard 9128-97

- Prior to preparation of a/c mix it is necessary to develop its composition in the laboratory (the ratio of sand, mineral dust and bitumen).
- To secure the precise composition of A/C mix the preliminary sorting of these materials is needed (the sorting equipment is installed before the cold vertical elevator).
- The amount of outputted materials from the plant storage bins to the mixer should correspond to the composition of the mix suggested by the laboratory.
-  For the cover rehabilitation of all types of roads the following a/c mix is suggested:
1st grade
A type
where the amount of gravel should be 50-60% (state standard 9128-97).

- For making the mixture, at first gravel, sand, mineral dust is loaded into the mixer.  After getting the aggregate, corresponding amount of bitumen is added for further mixing. 
- When mixing, the temperature of gravel and sand should be 165°-185° C.
- Mineral dust is added cool. 
- Bitumen temperature should be 130°-150° C.
- At the output from the mixer the temperature of a/c mixture should be 140°-160° C.
- The gravel particles should have the size to pass through the:
20mm sieve – 90-100%
15mm sieve – 75-100%
- When making a/c mixture, the error tolerance for the material quantities cannot exceed:
Gravel ± 3%
Sand ± 3%
Bitumen ± 1.5%
Mineral dust ± 1.5%
- Bitumen temperature is checked every two hours.
- Rest of the components are checked continuously.
- Prepared mixture temperature is checked in each truck.
- Quality of a/c mix at every shift is checked once, in the laboratory.
- The distance of the mix transportation should not exceed 1.5 hours in the case the air temperature is over 10° C.
- The proper operation of preliminary sorting equipment and components’ weight measurement devices are checked once in two weeks and, immediately, when there is concern.   
- During the visual observation a/c mix should be homogeneous, slump and should not stick to the truck body.
When there are concerns, it should be checked in the laboratory.
- The a/c particle size is checked once in three shifts and the composition of gravel - during each shift in speeded up manner.
- Gravel hardness used in a/c mix (A type) should be no less than 1000.
- In a/c mix (A type) the amount of flat and needle-like particles should be no more than 15%.
- Amount of clay and dust in the gravel and sand should not exceed 1%.
- Porosity of mineral substances structure should not exceed 23%.
- A/c mix should satisfy the following conditions:

The particle structure of I grade, A type a/c should be:

- Bitumen heated up to the working temperature should be used within 5 hours.
- After making the a/c mix it should be extracted from the mixer onto the trucks for transportation or into the storage silos.
- During mix production, depending on the viscosity of bitumen, the used materials should have the following temperature:

To prepare a/c mix appropriate amount of gravel, sand, mineral dust and bitumen is needed.
- During mix production the preliminary proportioning should be done according to the component volumes and particle sizes identified in the laboratory.
From each surge bin the wet gravel and sand with defined particle sizes are given to drying and heating ovens.  From the oven the aggregate is transported to the double sorting sieves, and from there on to the surge bins.

From these bins the sized gravel, sand and mineral dust is loaded to the mixer by defined proportions (bitumen is given separately).
- The aggregate preparation cycle is considered completed, when it is loaded onto the transporting trucks or in to the storage silos.