* Road Maintenance
Emulsified asphalt is an oil-in-water asphalt emulsion formed by hot melting asphalt, high-speed mechanical shearing, and dispersing it in an aqueous solution containing emulsifier as fine particles.The asphalt of this dispersion system is the dispersed phase and water is the continuous phase, which has good fluidity at normal temperature.Its main characteristics are its storage stability, stability during mixing, surface treatment, viscosity characteristics and curing speed.Many of these characteristics are related to particle size and particle distribution in the emulsion.This change depends on the asphalt type and the stability of the equipment and chemical reagents used in the production of graded emulsion.
The particle size of the emulsion is a relatively important parameter, because the more single and dispersed the particle size becomes, the better the viscosity of the emulsion, the more suitable the demulsification rate and the bonding performance are.However, this also limits the asphalt content in the emulsion and can affect the curing speed. under normal circumstances, the particle diameter has the best characteristics in the range of 1 μ m to 5 μ m..
In general, the dosage of emulsion is controlled by equipment and formula.It is very important to use proper emulsifier and proper emulsion formula to control the emulsifier effect in order to produce the emulsion that meets the needs.
1. Application of Emulsified Asphalt
The application of emulsified asphalt in various engineering parts of road construction will now be described as follows:
1.1 transparent layer
Interlaminar treatment of asphalt pavement mainly refers to the transitional connection treatment between base layer and surface layer, surface layer and surface layer, surface layer and structure, which is used to strengthen the adhesion between layers so as to form a complete stress system for each layer of asphalt pavement and improve the bearing capacity and durability of pavement structure.Secondly, the interlayer treatment makes the pavement structure consistent with the theoretical hypothesis of pavement design ( multi-layer continuous elastic layered body ) in theory, and makes the pavement design conform to the actual stress state of pavement.Good interlayer treatment measures can effectively prevent semi-rigid base layer from reflecting on shrinkage cracks and prevent surface water infiltration and subgrade water rise.The requirements of each treatment layer for material properties and construction points are described below.The asphalt permeable layer construction is suitable for the non-asphalt lower bearing surface under the asphalt surface layer to increase the mutual bonding force. the main functions are as follows:
(1) penetrating into the pores on the surface of the base layer to enhance the bonding between the base layer and the asphalt surface layer;
(2) it is helpful to combine the fine materials in the aggregate on the surface of the base layer;
(3) after the paving of the base layer is completed, timely spraying of oil through the layer can also reduce the cost of keeping in good health at the base layer and improve the quality of keeping in good health;
(4) filling the opening gap on the surface of the base layer after the penetration molding of the permeable layer oil to obtain a waterproof layer at the penetration depth;
(5) under the condition that the paving of the surface layer is delayed for some reason, the permeable layer can provide temporary protection to the grassroots to prevent the damage caused by rain and temporary driving.
In all interlayer treatment methods, the transparent layer has its special requirements for materials.The ideal penetration depth should be 3 mm to 5 mm through the base layer. for this purpose, low viscosity kerosene is traditionally used to dilute the asphalt, but the viscosity of the asphalt after the light oil in the diluted asphalt is completely volatilized is low.It is very difficult to ensure the bonding strength between the base layer and the surface layer and has adverse effects on the environment. therefore, emulsified asphalt should be used as the permeable layer material.After the base course is paved, the oil penetration construction should be followed up in time, which can not only achieve the best penetration effect of oil penetration, but also help the base course keep in good health.For the surface of the base layer where there is laitance and pollution, it is necessary to carry out strict cleaning before spraying oil through the layer. the road section where there is laitance should be closed to traffic after cleaning. if necessary, the surface of the base layer can be moistened by sprinkling water. it is advisable to control the amount of sprinkling water so as to make the surface of the base layer moist without accumulated water. through the infiltration of water, the pores on the surface of the base layer can be opened, which is beneficial to the penetration of oil through the layer.After the surface water evaporates, it can start spraying through the layer. the spraying amount should be kept between 0.6 kg / m and 1.1 kg / m and should not be too high.Therefore, the amount of modifier should not increase the viscosity of emulsified asphalt too much. generally, it should be controlled below 3 %, and the graded crushed stone base can be appropriately increased.
1.2 adhesive layer
The role of the adhesive layer is to bond the surface layers and the surface layers with the structure into a + whole.The asphalt adhesive layer is suitable for increasing the adhesive force between the asphalt paving layer and the contact surface of its lower layer and adjacent structures.The asphalt adhesive layer material is called " asphalt paint" and is also used as a spacer for cement slabs adjacent to side walls and dowel bars.The adhesive layer shall be evenly painted on the lower bearing surface or side wall within 3 hours to 4 hours before paving the asphalt mixture. the painted surface shall be clean, dry and free of dirt and other impurities. the layer must be cleaned. the spreading of the adhesive layer emphasizes " thin" and " pass".The general dosage of spreading is 0.4 kg / ㎡ to 0.6 kg / ㎡ between each surface layer. the specific dosage can be adjusted according to the concentration of emulsified asphalt. the adjustment principle is to ensure that no more than 0.2 kg / ㎡ of residual asphalt will be provided on the entire surface layer for continuous cover.In the actual construction, judging from the splitting test results of the core sample, the fracture surfaces at the joints of each surface layer are irregular, which indicates that the bonding strength of the joint surface is greater than or equal to the bonding strength of the mixture itself, which is superior to the bonding strength of the oil layers that have not been treated with the adhesive layer.
1.3 pavement waterproof layer
The lower seal coat of road asphalt pavement is suitable for waterproofing of base course.The waterproof layer is generally a waterproof layer with a certain thickness between the organic binder surface layer and the base layer.The waterproof layer is combined with the permeable layer to form a protective layer between the base layer and the surface layer to resist water disasters ( including dynamic water pressure damage ).Waterproof layer should be made of materials with good adhesion and temperature stability.Under the action of load stress and strain, it should not only maintain good water tightness, but also form sufficient bonding force between the surface layer and the base layer to prevent the thin asphalt surface layer from sliding, pushing and other damages.Compared with the case where the surface layer and the base layer are not combined, it can reduce the tensile stress and strain caused by the driving load on the bottom layer of the surface layer, and can obviously reduce the tensile stress and strain in the asphalt surface layer caused by the temperature change.The seal coat oil shall be spread after demulsification of the permeable layer oil, and the spread amount shall be controlled to be 0.8 kg / ㎡ to 1.6 kg / ㎡.When the seal coat oil is not completely demulsified, 0.5 cm to 1 cm of single-particle gravel will be scattered in time.The coverage rate is generally 60 % - 70 % of the whole area, and then the light rubber-tyred roller is used to stabilize the pressure for 1 - 2 times.The immersion depth of stabilized crushed stone particles is 1 / 2 of the particle size.Attention should be paid to the timing of stone spreading during construction, and good results cannot be achieved either too early or too late.
1.4 slurry seal coat
The upper seal coat is suitable for the maintenance of closed road surface pores and fine cracks or old roads.Slurry seal coat construction: before construction, the overall strength of the original road surface should meet the strength requirements, and diseases that affect the use function of the original road surface should be repaired.Before the seal coat, the repaired road surface should be basically stable;During construction, traffic shall be closed, sundries on the road surface shall be cleaned, and the original road surface shall be washed with water when necessary, but there shall be no accumulated water on the road surface.During construction, adjust the opening of each material gate of the seal coat machine according to the design ratio, open the discharge valve, and when the slurry mixture in the paving box reaches 1 / 2 of the volume of the box, start the chassis, travel at low speed, and pave.Maintenance should be carried out after paving. traffic can be opened when the adhesive strength of the seal coat meets the requirements ( ordinary emulsified asphalt seal coat is usually closed for 4h - 5h, when the temperature is low for 8h - 10h, and modified slurry seal is usually only 0.5h - 1h ).The construction temperature of emulsified asphalt slurry seal coat should be above 10 ℃;When the average daily temperature is lower than 5 ℃ in rainy days, the construction should be stopped.Judging from road maintenance, the use of slurry seal for pavement rutting repair does not need to be separated from the mixing equipment site, thus the relative cost is less than that of using hot mix asphalt mixture.Because emulsified asphalt allows wet road surfaces and good adhesion, there is no adhesive layer, and grinding is not required for the surface of common rutted roads.Therefore, the basic cost of materials used on site is relatively low, and construction conditions are improved, labor intensity is reduced, and environmental pollution is reduced.
1.5 bridge deck waterproof layer
Due to the large variety of bridge deck strain and drastic temperature changes, the effect and durability of common waterproof measures are poor.In particular, the modulus of asphalt concrete surface layer and cement concrete bridge surface are quite different, which puts forward higher requirements for waterproof layer materials and process methods that have both waterproof and bonding transition functions.Sbr and SBS modified emulsified asphalt have good effect in bridge deck waterproof engineering.This treatment method has the advantages of good waterproof effect, strong adhesive force, uniform and seamless construction, and fast construction progress, effectively overcoming the problems of hollowing and peeling and interlayer sliding that are easy to occur when using waterproof coiled material and multi-cloth and multi-coating waterproof methods.
2. Concluding Remarks
Emulsified asphalt can be used in cold state construction and has many advantages such as saving energy, facilitating construction, saving asphalt and protecting the environment.In particular, the performance of polymer modified emulsified asphalt has been substantially improved compared with that of emulsified asphalt. it has the effect of preventing pavement asphalt from softening at high temperature and cracking at low temperature, and preventing high temperature rutting and cracking at low temperature. it can not only greatly improve the interlayer bonding condition of asphalt pavement, reduce the occurrence of various diseases during use, but also has greater economic and social benefits in road maintenance, especially in the maintenance of high-grade pavement.The viscosity change of the through-layer oil after modification should be checked during specific application.During interlayer processing.Cleaning is the most crucial link. the cleaning degree of the lower bearing layer will directly affect the effect of interlayer treatment.The current cleaning methods are mainly manual cleaning with brooms and steel brushes, supplemented by flushing with high-pressure water cannons.Various interlayer treatment methods should be applied flexibly and can be combined when necessary.With the continuous development of the performance of the modified emulsified asphalt and its unique advantages, the modified emulsified asphalt will be fully used in future construction.
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