Common problems and solutions of hot-melt road marking coatings

The main function of road markings is to implement lane separation driving, guiding vehicles of different types and speeds to follow the designated route through traffic markings on the road, in order to improve road transportation capacity and reduce traffic accidents. The purpose is to instruct and warn drivers to predict the road situation through traffic markings, Clarify one’s rights, obligations, and methods of using and passing highways to provide legal basis for law-abiding and law enforcement personnel.
The coatings used for highway markings mainly include the following types of solvent based coatings, heating based coatings, hot melt coatings (also known as melt based coatings), two component coatings, water-based coatings, and so on.
In the construction of highways, there is a high requirement for the performance of coating materials used for road markings in traffic engineering. Firstly, it requires a short drying time and simple operation to reduce traffic interference. Secondly, it requires strong retroreflective ability, bright colors, and high reflectivity to ensure good visibility during the day and night. Thirdly, it has good anti slip and wear resistance to ensure driving safety and the service life of the markings. The characteristic of hot-melt reflective coating is that it has fast drying performance and a drying time of 1-3 minutes. Synthetic resin combines colored pigments, physical pigments, reflective materials, and other materials with road surfaces. It has strong adhesion performance, stable performance, long-lasting color, brightness, and reflectivity, and also has good wear resistance and skid resistance. So in the construction of highways in China, road marking materials mainly use hot-melt reflective coatings and hot-melt vibration coatings.
Due to the vast territory of our country, with East Tide and West Dry, South Hot and North Cold, the climate conditions and environment are diverse. In the construction of highway road markings, we often encounter some problems of one kind or another. I have accumulated some experience through learning and practice in long-term highway construction. Below, I will discuss several common problems and solutions of hot melt coatings in construction with everyone:

1、 Discoloration issues

During the melting process, the temperature is too high or the bottom of the hot melt kettle is burnt. The solution is to strictly control the temperature and clean the bottom of the hot melt pot before operation.

If the quality of the product itself is unqualified, it is likely that the coating has deteriorated. Before the construction of bulk products, they should be tested by a professional testing department and can only be used after passing the inspection

2、 Poor reflection effect at night

During construction, glass beads are blown away due to strong winds; The uneven distribution of glass beads on the surface is caused by factors such as the swaying and tilting of the spreader. The solution is to install a wind shield on the glass wave spreader and prepare for the coating operation, so as to control the construction progress speed.

Excessive impurities in glass beads scattered on the premixed surface, low roundness, poor particle size distribution, coating flowability not meeting technical requirements, insufficient viscosity, low softening point, and other reasons can all lead to poor reflection effect at night. These are all products with substandard quality. Qualified products should be used during construction.

During construction, the road surface is uneven and uneven. Construction technology and adaptability should be improved to allow experienced technicians to operate the construction.

3、 Crack problem

During winter construction, the coating contracts when cold, resulting in internal stress. When this stress is concentrated in one location, it is easy to produce cracks; The cracks that occur due to cold conditions are related to the construction season and the performance of the paint, as well as to the condition of the road surface. Especially when the newly laid cement pavement has a fragile mortar layer or curing film, it is easy to produce cracks. How to prevent cracks caused by cold weather, the first step is to choose a suitable construction season and try to avoid marking construction in cold winter. At the same time, it is important to pay attention to the reasonable use of hot melt coatings and choose the appropriate coating ratio for different seasons. The newly laid cement pavement should be cured for at least 2 weeks, and the fragile mortar layer or curing film on the pavement should be cleaned before the construction of road markings.

Reflection cracks caused by roadbed cracks. Cracks in road markings caused by the expansion or contraction of roadbed materials, or uneven settlement. Generally, it is unavoidable and can enhance the construction quality of the roadbed.

Cracks caused by the softening of the road surface. In some places, the temperature in summer can reach over 40 ℃, and in scorching sun, the high temperature of the asphalt road surface can reach over 60 ℃. The asphalt becomes soft, while the paint is relatively hard, which may cause cracks on the soft road surface under wheel impact loads. The direct cause of soft road surface cracks is the mismatch between the softness and hardness of the coating and the road surface. It is caused by impact loads and can be alleviated by adjusting the formula appropriately.

Surface cracks on coatings are irregular network cracks that appear on the surface after coating construction. These cracks are shallow in depth, but often further develop into aging cracks on this basis, causing damage to the coating. To prevent the surface of the coating from drying and cracking, it is necessary to start with selecting resins and additives with good compatibility, and pay attention to controlling the construction temperature.

Strong lines appear due to aging markings. The deterioration and natural weathering of the surface material of the coating cause cracks in the markings. Aging cracks are also caused by the long-term exposure of the marking coating to the road surface, which is exposed to sunlight and rain, spring, summer, autumn and winter, temperature differences between day and night, and seasonal temperature changes. They are also affected by ultraviolet radiation and undergo periodic expansion and contraction. The strong lines caused by aging can only be started by selecting appropriate coatings to prevent premature aging of the coatings. During the construction of marking lines, strict temperature control is required to ensure the quality of road surface treatment before construction and prevent foaming.

Micropores and bubbles are caused by the expansion or gasification of air, moisture, or wet undercoating agents in the road surface cavities under the action of high temperature in the coating. Bubbling is caused by expanding gas pushing up the coating, while micropores are holes left by expanding gas penetrating the coating, making the coating a more common defect. The probability of producing micropores and bubbles on wet road surfaces increases because the micropores in the road are filled with water or moisture. High temperature coatings cause the remaining water in the micropores to vaporize and expand, forming micropores and bubbles. The undercoating agent contains certain low boiling point components that are not easy to dry. When the undercoating agent remains in the pores and is not dry, it rapidly vaporizes and expands the active substances when encountering high-temperature coatings, forming microporous bubbles in the undercoating agent. Microcellular foaming not only affects the appearance of the markings, but also reduces the actual bonding area between the coating and the road surface, thus seriously affecting the adhesion and service life of the coating. Therefore, it is necessary to choose coatings with good fluidity. Ensure that the road surface is dry and receive sufficient sunlight after rain before proceeding with construction. Choose a fast drying undercoating agent, strictly control the construction temperature, and pay attention to the coordination of environmental temperature.

4、 Peeling and peeling issues

Peeling at road surface fractures. Adjustable coating formula to increase adhesion and flexibility

The road surface is not cleaned thoroughly, or the coating agent is not used. Strictly follow the construction procedures to ensure construction quality

After applying 3 coats of paint, if the lines are not drawn for a long time (or during construction in windy and sandy weather), it is easy to stick dust, which can cause peeling and peeling of the markings. After the paint dries, the markings should be drawn immediately.

The marking coating is affected by the degree of moisture on the road surface. If there is water on the road surface or it is relatively damp, measures must be taken, and the road surface should be dry before construction. During construction, the road surface should be ensured to be dry. In special circumstances, it is necessary to rush to work and manual methods can be used for drying

If the ambient temperature is below 5 ℃, the construction quality is unstable, which can easily cause peeling and peeling. If the melting temperature is too low, it will seriously affect the adhesion between the markings and the road surface; If there is no coating treatment, the ambient temperature should be above 10 ℃ for construction. The instantaneous temperature of the coating applied to the road surface should not be lower than 180 ℃; Construction in the early winter season should be considered between 10 a.m. and 3 p.m., and the ambient temperature should not be too low.

Insufficient melting of paint and uneven mixing. During construction, the coating should be fully melted, thoroughly stirred and matured before application;

Improper selection of coating agent under cement pavement. Newly laid cement pavement is prone to peeling and peeling due to its high surface alkalinity and brittle layer. Permeable undercoating agents should be used to treat cement pavement to improve adhesion strength. Carefully clean the newly poured cement pavement.

5、 Wear resistance issues

The wear and tear of road markings is directly related to the size of traffic volume. In sections with high traffic volume, a large number of large vehicles, and frequent lane changes, road markings generally wear out quickly. In addition, the presence of dirt, sand, dust, and small stones on the road surface will accelerate the wear of the markings. The wear resistance of the marking is related to the coating itself, which is the adjustment of the production formula by adding some wear-resistant fillers such as quartz sand.

To ensure that the hot melt marking has a longer service life, it is necessary to choose coating formulations based on different climatic conditions and purchase high-quality and stable raw materials. Strictly control the temperature during the melting process, mix evenly, and control the construction speed of the markings during the construction process to ensure the uniformity of thickness and maintain the cleanliness of the road surface.

6、 Line deformation and tooth edge

Mainly tire indentations and spots. High quality coatings with appropriate viscosity and good flowability should be selected. Strengthen construction management and open up traffic after the coating is completely dry.

The horizontal stripes on the surface of the 2 coating are due to the vibration of the coating bucket and the uneven surface due to the high viscosity of the coating. The construction temperature should be well controlled, and the bucket groove scraper should be inspected and handled in a timely manner. Thoroughly clean the road surface and avoid bucket vibration when using construction carts.

There are longitudinal stripes on the surface of the coating, which is due to the local burning of the hot melt coating during the heating process, and there may also be foreign objects mixed in. In addition, defects in the groove of the coating bucket or adhesion of coating slag can also cause longitudinal stripes. Poor surface condition will directly affect the appearance quality of the markings and affect the reflective effect at night. The first step in this regard should be to heat and melt the coating, strictly control the temperature, and prevent burning and foreign objects from entering. Before construction, the machinery and bucket slots should be thoroughly inspected and cleaned to ensure they are in normal condition.

Road markings are an important component of traffic safety facilities and play an irreplaceable role in modern highway transportation. The level of construction and the quality of products are both related to the service life of road markings, and directly affect the transportation safety and efficiency of backbone transportation in a region. Therefore, we must pay attention to various problems that arise in road marking construction, and solve them through learning and mutual communication, so that our road markings can have a qualitative improvement from material quality to construction technology, and play its maximum role.