“Development and introduction of technology of stabilization and de-dusting of gravel roads with the use of magnesium chloride”
Objective of the project:
The purpose of this project is to develop a technology for reducing the level of dustiness of gravel roads, which, in turn, will lead to:
Reduction of the harmful effect on the health of residents of the settlements adjacent to the road;
Reducing the number of road accidents;
Reducing losses of construction soil, which occur when removing dust particles from the coating.
Properties of MgCl2 (magnesium chloride).
Magnesium chloride is salt. Manufactured by industrial method from natural brines. Can be sold as a clear solution, white flakes or granules.
Three important properties of magnesium chloride provide a variety of ways to use it:
The first property is the ability to dissolve, attracting moisture from the air.
The second – hygroscopicity, a strong ability to absorb moisture, without turning into a liquid. This ability to attract moisture even from relatively dry air ensures the optimum moisture content of the road surface. Water binds the dust particles, providing certain stabilization and preventing the formation of dust.
The third important property is exothermy, i.e. heat release during dissolution. This property allows the use of magnesium chloride as an antifoaming agent.
The technology of dust removal with the use of magnesium chloride.
MgCl2 can be distributed along the road surface during or after profiling, at any time of the year. The best results are observed with the spring production of works, when the road is already sufficiently moistened. The work should include the addition of gravel material (if necessary) and the correction of the transverse profile of the road. The best shape of the diameter is a gable width with a slope of 40% from the axis to the roadside.
The required rate of salt distribution depends on the traffic intensity and width of the carriageway, as well as on the proximity of the forest, the direction of the road, the earth base, the road structure and the quality of the wear layer material.
When drawing up instructions on the distribution of salt on the road surface, it is necessary to take into account the influence of all the above factors. In table shows the factors determining the recommended distribution rates, only the width of the carriageway and the traffic intensity are presented. However, the required rate may be greater when processing open plots or near residential buildings, or farms for growing berries and cereals. Accordingly, the required norm may be less in a wooded area, in areas with thin structural layers and with a capillary earth base.
Intensity of movement, car/day
Width of carriageway, m
Norm of consumption of magnesium chloride, t/km
De-dusting work was carried out on the experimental site on May 31, 2005. During the production of works, it was decided to scatter 3 tons per km, which is 0.438 kg per 1 sq. M. In this case, the rate of consumption is lower than required, but according to the results of the experiment it was sufficient for the summer season.
The technology of de-dusting the road section consists of several stages.
Stage 1. Watering.
To ensure that the salt is not carried off the road section, it is necessary to wet the coating before rinsing out the magnesium chloride. The number of passes depends on the degree of wetting of the coating, during the experiment on the site from 226 to 227 km water was watered in 2 passes on each strip, since it was raining recently, so the cover was already sufficiently moistened. In the case of dry weather, the number of passes should be increased to achieve the best result.
Stage 2. Distribution of magnesium chloride.
The distribution was carried out using a conventional distributor machine.
When distributing the material, it should be taken into account that the material consumption is large enough, therefore it is necessary to open the shutters as much as possible, otherwise the number of passes will increase. If the distribution is correct, you need 2 passes for each strip.
Stage 3. Moistening of magnesium chloride.
The road surface must be sprinkled with water in order to ensure a better solubility of the salt in the wear layer, as well as for the best adhesion of the material and its mixing with the coating after its distribution. After watering the water, the granules dissolve and are subsequently better contacted with water.
The recommended number of passes is 2, but depending on the actual conditions, the quantity can be reduced or increased.
Stage 4. Mixing of material, grading.
After distribution, the wear layer is mixed with magnesium chloride so that there are no free particles of chloride. During grading, magnesium chlorine particles are mixed with the top layer forming a homogeneous layer, which, as the experiment showed, subsequently darkens and visually differs from other untreated sections. During planning it is necessary to pay attention to that there are no high edges that prevent drainage. The number of main passes is 2, the remaining passes are necessary to remove the remaining flaws, if any.
Stage 5. Sealing.
From the consolidation of the wear layer depends on how long the wear layer will retain a good condition, and how much of the mineral material will come off. After sealing the wear layer with the optimum calculated humidity, it well withstands traffic, rain and long periods without rain. Consequently, the compaction of the wear layer must be carried out carefully, not paying attention to the lack of means for compaction. However, the separate use of a pneumatic wheel road roller or a roller with smooth rolls is uneconomical. In the case of the experimental site, dump trucks were used in 4 passes.
On roads with high traffic intensity or in open areas, additional magnesium chloride treatment may be required in the summer. The distribution norms with additional de-dusting in summer are less than those used in the spring. If there are potholes and sweating on the road surface, which requires profiling, then additional treatment with magnesium chloride is carried out in the form of mixing with the material of the wear layer. Otherwise, de-dusting is carried out by distributing magnesium chloride on the road surface, in which magnesium chloride is distributed over the surface without mixing with the mineral material.
Additional de-dusting, especially when using dry magnesium chloride, is produced immediately after the rain in order to reduce the required amount of water to moisten the surface.
Also, for additional de-dusting, brine can be used, applied in the same way as in the spring period.
The rate of consumption of magnesium chloride with additional de-dusting is determined separately for each specific case. If additional de-dusting should be carried out in the spring, then it is necessary to use as much magnesium chloride as is enough until the fall.
Safety and liquidation of consequences:
Magnesium chloride and its solutions create some problems when used, like all salts. Contact with solids in the eyes may cause irritation. Continuous contact with the skin may cause a small burn. Proper storage, cleanliness and care plus the use of protective glasses – this is enough to prevent harm to health.
If there is a large area of exposure and duration of contact of the skin and magnesium chloride, it is necessary to rinse the affected area under a stream of clean water.
If magnesium chloride enters the eyes, they should be rinsed for at least 15 minutes.
Caution is needed when mixing flakes or granules with water, because magnesium chloride dissolves heat when dissolving flakes in a strong concentration, the temperature can rise by 31 ° C. When dissolving granules under the same conditions, the temperature can rise by 70 ° C. Always use only cold water to dissolve magnesium chloride to prevent effervescence of the solution. In a tightly closed container, such a rise in temperature can lead to a rise in pressure, and, as a consequence, to rupture the container and spray the solution.
If there is a leak, it is necessary to prevent a large amount of magnesium chloride solution from entering the reservoirs with drinking water, as well as plants and shrubs. Dilution with a sufficiently large amount of water can reduce the concentration of the solution to a safe one.
For the same reasons, care should be taken when cleaning the mixing and distribution equipment.
Corrosion and deterioration of equipment:
After distribution and mixing with the pavement material, the degree of concentration of magnesium chloride becomes very low. Salt remains in road clothing, and direct contact with transport or the surrounding nature does not occur. For this reason, the concentration of magnesium chloride solution is much lower than when using dry salt for winter maintenance, when it simply crumbles down the road. If distribution, humidification and mixing are carried out correctly, no harm to health, cars or the environment is applied.
After conducting an experiment on de-dusting at the road section.