The so-called preventive maintenance refers to the maintenance of roads before serious diseases occur or will occur. Different from corrective maintenance, preventive maintenance is a proactive maintenance in advance. Preventive maintenance can not only maintain the good service level of roads all the time, but also save money in the life cycle of roads, which has good social and economic benefits and has been recognized by developed countries such as Europe and America.
For example, the highway department in Arizona, USA, made the following comparison on the project cost:
(1) After the asphalt concrete pavement is paved, it will be overhauled after 20 years of driving without any intermediate maintenance;
(2) After paving the asphalt concrete pavement, after driving for 10 years, do a maintenance and then do an asphalt concrete overlay;
(3) According to the requirements of preventive maintenance, timely and regularly maintain the paved asphalt concrete pavement according to the pavement test results.
The economic analysis of three maintenance methods shows that the maintenance cost of the first method is 163% of that of the third method, and that of the second method is 155% of that of the third method. Therefore, preventive maintenance is the most economical.
For preventive maintenance technology, foreign developed countries have formed a set of standardized and scientific systems. The technical characteristics, applicable conditions and construction technology of various preventive maintenance technologies are introduced below.
1 joint filling
This maintenance method is suitable for transverse and longitudinal cracks and small block cracks on closed pavement. The main purpose is to prevent water from invading the structure through existing cracks. Sealant should be able to seal cracks well. This maintenance method requires high-quality materials and good construction technology. The sealant used must be a thermoplastic material, which softens when heated and hardens when the temperature drops.
This maintenance method is not suitable for structural cracks in pavement. For example, a large area of fatigue cracks, a large area of network cracks and so on. Cracks are treated in a cool and dry climate. In order to achieve better bonding effect, it is necessary to clean the cracks, such as using hot compressed air to clean the cracks.
2 fog seal coat
Fog seal coat is mainly used to seal the surface layer, prevent or reduce water infiltration, prevent road deterioration and improve the performance of aging hardened asphalt. Fog seal coat technology is a preventive maintenance measure of spraying a small amount of diluted modified emulsified asphalt directly on the pavement without using aggregate. The general usage is 0.23-0.45 L/m, and the fog seal coat is suitable for diseases such as poor pavement oil quality and fine particles falling off, as well as slight longitudinal, transverse or massive cracks on the pavement. This method is very important for choosing the right maintenance opportunity. If the curing time is too late, the disease will develop seriously and the use effect of fog seal will be greatly reduced.
Fog seal layer, a maintenance measure, does not contribute to the structural strength, but can reduce the water damage caused by fatigue cracks.
Because fog seal will reduce the friction coefficient of pavement, this maintenance technology is not suitable for sections with low friction coefficient. Because the emulsifier in emulsified asphalt used in fog seal coat is retarded emulsifier, it takes time to cure, and it usually takes 2 hours to stop traffic to stay healthy.
3 slurry seal coat
Slurry seal technology is to spread the mixture composed of well-graded aggregate (fine aggregate and mineral filler) and emulsified asphalt evenly on the whole road surface. The advantage of this technology is that it can effectively close the cracks on the pavement surface, improve the waterproof performance of the surface layer and improve the anti-sliding ability of the surface layer. According to the engineering particle size of the mixture, the slurry seal mixture is divided into type I, type II and type III, and the paving thickness is 5 ~ lomm.
The types of pavement diseases applicable to this technology are:
(1) Pavement transverse cracks, longitudinal cracks and unstructured block cracks.
(2) The pavement is slightly damaged (the dropped materials need to be cleaned before paving).
(3) The surface asphalt of asphalt pavement is aging and short of oil.
(4) The friction coefficient of pavement decreases.
(5) Water seepage on the pavement.
Slurry seal technology has no contribution to the structural strength of pavement. When there are large fatigue cracks or serious ruts on the pavement, this maintenance technology cannot be used for maintenance. In order to harden emulsified asphalt, it is often necessary to close the road for several hours. During construction, it should be noted that the road surface must be kept clean, the stone should be angular, durable and well graded, and it must be cleaned before mixing. Construction in hot weather conditions should be avoided, and sufficient open traffic time should be maintained according to the type of emulsifier. In the case of preventive maintenance, the expected life of slurry sealing technology is generally 3 ~ 5 years.
4 micro-surfacing
Micro-surfacing is a special slurry sealing technology. Compared with the traditional slurry sealing technology, the bonding material of micro-surfacing mixture is modified emulsified asphalt. The whole mixture consists of polymer modified emulsified asphalt, graded macadam, mineral filler, water and additives.
Micro-surfacing technology can solve the diseases of asphalt pavement such as aging, poor oil quality, non-structural damage, cracks, pavement seepage and wear reduction. In addition, in addition to the above advantages, the micro-surfacing can also fill the rut separately, and the sections with deep rut can also be filled twice.
The construction of micro-surfacing can be applied to all climatic conditions. But the effect will be better in a warm climate. The construction temperature is low and the strength rises slowly. Micro-surfacing is generally considered to be very limited to improve the bearing capacity of the structure.
For structural damage such as fatigue cracks on pavement, pretreatment is needed before construction, and then micro-surfacing is carried out after treatment. In the case of preventive maintenance, the life expectancy is 4 ~ 7 years.