What we saw at the scene was a large mixer, and many heavy vehicles were waiting to be loaded. According to the introduction of the project chief engineer, the cement stabilized macadam used in this project is 5:95 for the upper base and 4: 96 for the lower base, in which the gradation of the material is 20-30mm 7%.
10-20mm 42%
5 5- 10/0mm 27%
Stone chip powder 24%
Maximum dry density of upper base: 2.32; maximum dry density of lower base: 2.34.
The upper base bears a pressure of 3Mpa and the lower base bears a pressure of 4Mpa.
The optimum water content of 5% will increase the water content of 1-3% when mixing, so as to ensure that the water content of the county is about 5% during construction.
After arriving at the site, the chief engineer of the project introduced some indicators of the project to us:
This project is divided into three layers: 20cm stone subgrade and 18cm cement stabilized macadam for upper and lower subbases. There are 6cm AC-20 and 4cm AC- 13 emulsified asphalt on the surface. Primer 1- 1.2Kg/m? The speed of the paver is 3m/min, and the interval between two pavers is about 10m. After the upper and lower subbases are paved, they are rolled by rubber-tyred roller and vibratory roller respectively.
The following is a summary of today's internship content:
First, cement stabilized macadam
(1) Action principle of cement stabilized macadam: Cement stabilized macadam takes graded macadam as aggregate, fills the gap of aggregate with a certain amount of cementing material and sufficient mortar volume, and spreads and compacts it according to the principle of embedding. Its compactness is close to its compactness, and its strength mainly depends on the interlocking principle between crushed stones. At the same time, there is enough mortar volume to fill the gap of aggregate. Its initial strength is high, and the strength increases with age, and soon forms a plate shape, so it has higher strength, better impermeability and frost resistance. The cement content of cement stabilized macadam is generally 3%∽7% of the mixture, and the 7-day unconfined compressive strength can reach 5∽0%mpa, which is higher than other subgrade materials. After surviving, cement stabilized macadam is not muddy in the rain and has a solid surface, so it is an ideal base material for advanced pavement.
According to the Technical Specification for Highway Pavement Base Construction issued by the Ministry of Communications, cement stabilized macadam belongs to medium-grained soil. Because cement and other cementitious materials are contained in water-stabilized macadam, it is required that the whole construction process should be completed before the final setting of cement, and the quality standard should be reached at one time, otherwise it will be difficult to repair. Therefore, it is required to strengthen the construction organization design and plan management, increase the sense of urgency and responsibility of on-site construction personnel, speed up the construction progress, increase the degree of mechanized construction and improve the mechanical efficiency. The construction method of water stabilization is also in line with the development direction of modern large-scale mechanization. Therefore, the application of water stabilization technology in municipal engineering will be popularized soon.
(2) Material requirements: Cement stabilized macadam material is mainly composed of aggregate and mortar volume. The granular material is graded macadam, and the mortar volume includes water and cementitious materials, and consists of cement and mixed materials.
Cement: ordinary portland cement, slag portland cement and pozzolanic portland cement are all acceptable, but the cement with long final setting time should be selected. Fast hardening cement, early strength cement and cement deteriorated by moisture should not be used. Low grade cement should be used. Cement quality must meet the national standards.
Mixed materials: Mixed materials can be divided into two categories: active and inactive. Active substances refer to substances such as fly ash that can react with calcium oxide precipitated in cement. Inactive materials refer to artificial or natural mineral materials with no activity or low activity. The quality requirements for this kind of materials are fine and free from harmful components.
Water: Water that is usually suitable for drinking can be used for mixing and curing cement stabilized macadam. If there is doubt about the water quality, it is necessary to carry out tests to determine whether there are substances in the water that have a significant impact on the development of cement strength. When the ratio of compressive strength of cement mortar made of source water to that made of distilled water is less than 90%, this water is used for water stabilization construction.
(3) Composition design of cement stabilized macadam mixture: cement, fly ash, stabilized macadam, sand, stone chips and other road materials are used as cement stabilized macadam base. First of all, through a certain number of raw material tests, laboratory mix design and compaction tests to determine the maximum dry density and the best water content. Then, the specimens were made according to this ratio, kept moist for 6 days at the specified temperature, and soaked in water for 65438 0 days, and then the unconfined compressive strength test was carried out.
(4) Brief introduction of cement stabilized macadam construction method: First, check the subbase and recheck the elevation of control piles. Before laying cement stabilized macadam, the subbase should be cleaned and properly watered to keep it moist. Mixing: Before using the factory-run equipment, the factory-run equipment and various metering systems should be debugged to ensure that the water content, aggregate gradation and cement content of the mixed mixture meet the matching requirements, so that the machine can operate normally and the output of the mixer is consistent with the paving production capacity used. When paving and rolling, the paving coefficient is between 3∽5. The principle of "rather high than low, rather scraping than mending" must be implemented in the construction, and all construction projects must be completed before the final setting of cement. After rolling, the compactness test shall be conducted immediately. If the test result is not up to standard, roll again. In general, cement stabilized macadam can not be constructed until 24 hours after the operation is completed. The interval between it and the kerb should not be too long, otherwise the slab will be hard after the mixture is formed, which will increase the construction difficulty and the integrity of the slab will be easily destroyed by knocking and chiseling. The curing time shall not be less than 7 days. Vehicles are prohibited from passing during this period. Sprinkle water for curing 2∽4 times a day to keep it moist.
Second, the subgrade pavement
Subgrade is a structure that directly supports the track formed by filling or excavation. Also known as line substructure. Subgrade, bridge and tunnel are connected together to form a line. There are two basic forms of subgrade according to the different terrain conditions: embankment and cutting, commonly known as filling and excavation. The function of subgrade is to directly lay track structure on the surface of subgrade. Therefore, the subgrade is the foundation of the track, which not only bears the weight of the track structure, that is, the static load, but also bears the dynamic load transmitted through the track when the train is running (see subgrade load). This kind of line structure composed of subgrade and track is a loose connection structure, and its ability to resist dynamic load is weak. The materials for subgrade construction, whether filling or excavation, are mainly earth-rock granular materials, so the subgrade is a geotechnical structure. Therefore, the subgrade is often attacked and destroyed by the changes of its own conditions such as geology, water, rainfall, climate and earthquake, and its resistance is poor. Therefore, the subgrade should have sufficient firmness, stability and durability. For high-speed railway, the subgrade should also have reasonable stiffness to ensure the stability and comfort of the train at high speed.
Pavement pavement refers to one or more layers of road structure paved with road building materials on the top surface of subgrade for vehicles to travel directly on its surface. Pavement structure According to the design requirements and the principle of using local materials, the pavement can be paved with different materials in layers. Generally, middle and low grade pavements have few structural layers, including surface layer, base layer and cushion layer. Advanced pavement structure has many layers, generally including surface layer, connecting layer, base layer, subbase layer and cushion layer. The surface layer is the layer in direct contact with the atmosphere. It bears the vertical force, horizontal force and impact force of traffic load, and is also affected by precipitation erosion and temperature change. Therefore, the surface layer should have higher structural strength, stiffness, impermeability and temperature stability than other layers, and the surface should also have good flatness, roughness and wear resistance. The surface layer sometimes adopts a double-layer structure of upper and lower layers. The connection layer is set to strengthen the connection between the surface layer and the base layer and improve the fatigue resistance of the surface layer, which is also the surface layer.
Part of the pavement structure. Often used in roads with heavy traffic, sometimes in order to prevent or reduce the impact of cracks on the surface, connecting layers are also used.
Pavement structure: According to the design requirements and the principle of using local materials, the pavement can be paved in layers with different materials. Generally, middle and low grade pavements have few structural layers, including surface layer, base layer and cushion layer. Advanced pavement structure has many layers, generally including surface layer, connecting layer, base layer, subbase layer and cushion layer.
Surface layer: the layer that is in direct contact with the atmosphere. It bears the vertical force, horizontal force and impact force of traffic load, and is also affected by precipitation erosion and temperature change. Therefore, the surface layer should have higher structural strength, stiffness, impermeability and temperature stability than other layers, and the surface should also have good flatness, roughness and wear resistance. The surface layer sometimes adopts a double-layer structure of upper and lower layers. The connection layer is set to strengthen the connection between the surface layer and the base layer, improve the fatigue resistance of the surface layer, and is also a part of the surface pavement structure. Often used in roads with heavy traffic, sometimes in order to prevent or reduce the impact of cracks on the surface, connecting layers are also used. Base: It is the load-bearing part of pavement structure. Mainly bear the vertical force of vehicle load, and disperse the force handed down from the surface to the cushion or soil foundation, so the base should also have sufficient strength and stiffness. Although the influence of natural factors on the base course is not as strong as that on the surface course, there should be enough water stability to prevent the base course from being deformed too much after it is wet and soft, which will lead to the damage of the surface course. Subbase: it is a layer below the base, which is used to strengthen the role of the base in bearing and transmitting loads, and is often used on roads and highways with heavy traffic. The strength and stiffness requirements of subbase material can be slightly lower than that of subbase. The materials that make up the base and subbase are: mixtures made of various industrial waste residues, or crushed gravel mixtures stabilized with cement, lime or asphalt, various crushed gravel mixtures or natural gravel, flaky and boulder, etc. Cushion: It is a layer between the base (or subbase) and the foundation. Its main function is to improve the humidity and temperature of the soil foundation, ensure the strength stability and frost heaving resistance of the surface layer and the base layer, and disperse the load from the base layer to reduce the deformation of the soil foundation, so the cushion layer is often laid in the area with poor water temperature of the soil foundation. The cushion layer that can play an anti-freezing role in areas with large freezing depth is called anti-freezing layer; Laying a cushion that can prevent water leakage or surface water from penetrating downwards in areas with high groundwater level is called isolation layer. Commonly used cushion materials include sand, gravel, slag, lime soil, slag lime soil and other materials with good water permeability or stability.
Soil foundation is the foundation of pavement, which bears wheel load and pavement self-weight. It does not belong to the pavement structure level, but the pavement design must be based on the soil foundation conditions, and the subgrade and pavement are comprehensively designed.
Pavement according to its mechanical properties can be divided into:
Rigid pavement: it can produce slab effect under traffic load and has high bending strength, such as cement concrete pavement.
Flexural and tensile strength of flexible pavement is small, mainly relying on compressive strength and shear strength to resist the action of driving load, and residual deformation will occur under repeated loads, such as asphalt pavement and gravel pavement.
Some pavement materials have the characteristics of flexible pavement in the early stage of construction, and almost have the characteristics of rigid pavement in the later stage. This kind of pavement is sometimes called semi-rigid pavement, such as pavement made of lime stabilized soil, cement stabilized soil, lime fly ash, lime slag and other materials.
Third, asphalt pavement.
Asphalt binder asphalt binder binds mineral aggregate into a whole, increases strength, enhances the ability of pavement to resist traffic damage, and makes pavement waterproof. Asphalt materials suitable for pavement construction are mainly petroleum asphalt and coal asphalt, in addition to natural asphalt. The nature and label requirements of asphalt vary with asphalt pavement type, regional climate and road traffic conditions. Hot mixing or pouring by hot method, thick asphalt should be used in hot areas and busy roads; Cold mixing or cold sprinkling, as well as cold areas and light traffic roads, should choose thinner asphalt.
Asphalt pavement aggregate is the general name of mineral aggregate in asphalt pavement materials, which plays the role of skeleton and filling in pavement materials. Sometimes it is necessary to mix several kinds of coarse and fine granular materials together to form the required particle size gradation. Among aggregates, those with a particle size of 19~26.5 mm are called coarse aggregates, those with a particle size of 13.2~ 19 mm are called medium aggregates, those with a particle size of 4.75~ 13.2 mm are called fine aggregates, and those with a particle size of 4.75 mm or less are called sand aggregates. According to different sources, aggregate can be divided into natural aggregate and artificial aggregate. Natural aggregates include gravel, gravel, sand, stone chips, etc. Artificial aggregates include calcined bauxite and stabilized solid metallurgical slag. Aggregate used for asphalt pavement should be clean and mud-free. Coarse aggregate particles should be close to the cube, with more edges and corners and less flat belts. Its compressive strength should not be less than 60 MPa, the road surface of heavy vehicles should not be less than 80 MPa, and it can wear. Aggregate and asphalt materials should have good adhesion and are not easy to peel off due to water erosion. If the adhesion between aggregate and asphalt is poor, effective anti-stripping agent should be added to improve it. When selecting aggregate, aggregate with similar particle size and the same particle size should be paved in layers; When mixing the mixture, it is usually necessary to use graded aggregates of different sizes and sizes according to the specifications. This kind of aggregate can also be mixed with different grades of aggregate with the same size in proportion. The particle size of mineral powder is less than 0.074 mm, which is mostly used in asphalt concrete and asphalt macadam pavement. Its function is to fill gaps, prevent hot asphalt from flowing, and enhance the cohesive force and thermal stability of asphalt materials. Mineral powder should also have good affinity (i.e. adhesiveness) with asphalt and can resist water erosion. The most commonly used mineral powder is limestone powder.
The asphalt structure layer of asphalt pavement belongs to the category of flexible pavement, but its base can also use rigid cement concrete or semi-rigid hydraulic materials besides flexible materials. There are many classification methods of asphalt pavement, including asphalt sand, asphalt soil and asphalt macadam mixture. According to different aggregate types; According to the different types of asphalt materials, it can be divided into petroleum asphalt pavement, coal asphalt pavement, natural asphalt pavement and residual oil pavement. However, the common classification methods are divided into asphalt concrete pavement, factory-mixed asphalt macadam pavement, asphalt permeable pavement, road-mixed asphalt macadam mixture pavement and asphalt surface treatment pavement according to their construction methods, technical quality and application characteristics. Asphalt concrete pavement is a pavement surface layer made of aggregate, mineral powder and asphalt with different particle sizes in a proper proportion, heated to a certain temperature, mixed, spread and compacted.
① Rolling type. Asphalt concrete mixture is mostly prepared by hot mixing and hot paving method, which has good road performance, so it requires higher preparation technology and raw materials, and mostly adopts centralized factory mixing method. The asphalt concrete mixture that is widely used now is roller compacted, that is, the mixture can only be shaped after heavy mechanical compaction, so some countries call it roller compacted asphalt. After molding, the road surface is smooth, dense, less dust and not rough, so it has better driving comfort and appearance. And has good aging resistance, wear resistance, temperature stability and driving damage resistance. General service life is long. When petroleum asphalt is used as binder, the overhaul life is often longer than 15 years.
② Cold paving type. Hot-mixed cold paving of asphalt concrete, also called cold asphalt in some countries, is often used for minor repairs or projects that need long-distance transportation of mixture. The asphalt used is thinner than the asphalt used by the hot-mix hot-spread machine, and the dosage is less, so as to have appropriate looseness and viscosity at room temperature, but the service life is not as good as that of the hot-mix hot-spread machine.
③ Paving type. Hot-mixed hot-laid asphalt concrete mixture can be formed without heavy mechanical compaction, which is usually called road asphalt. In order to make the paving asphalt mixture have proper fluidity and can be lightly rammed, leveled and compacted, it is required that there is more mixture of asphalt and mineral powder in the mixture, that is, asphalt binder, and its strength mainly depends on the cohesive force of asphalt binder. Because the particle surface of aggregate has been separated by thick cement, its locking force and internal friction resistance are reduced, so paving asphalt is rarely used in roadway, but some European and American countries also use it in roadway. At this time, the performance requirements of asphalt materials are very strict. To avoid softening in summer, it is necessary to spread a layer of anti-skid layer or add anti-skid aggregate to prevent the surface from slipping.
Factory-mixed asphalt macadam pavement: also called black macadam pavement or open graded asphalt concrete pavement. Its processing technology and paving technology are close to those of asphalt concrete pavement, but the porosity is large (the boundary between them is not strict, and the boundary is porosity 10% in China). Asphalt macadam mixture can be hot-mixed and hot-paved, or hot-mixed and cold-paved; Hot paving has good quality and wide application. Aggregate particles can be divided into homogeneous particles and graded particles, and graded particles are mostly used at present. Compared with asphalt concrete, the content of fine aggregate and mineral powder in asphalt macadam is less, the proportion of coarse aggregate is larger, and the asphalt consumption is correspondingly less. The thermal stability of asphalt macadam mixture mainly depends on the locking force between aggregate particles, so the variation range of asphalt content, consistency, mixture ratio and aggregate gradation can be wider than that of asphalt concrete, and its thermal stability can still be maintained. However, due to its porosity, the pavement is prone to water seepage and aging, so asphalt macadam is often used in the lower layer, connecting layer, leveling layer and base layer of the surface. If it is used in the upper layer of pavement, it must be sealed with asphalt or embedded with fine asphalt mixture. But it is also laid on the dense asphalt surface as a waterproof and anti-slip layer. The service life of asphalt macadam pavement is generally shorter than that of asphalt concrete pavement, but its engineering cost is often cheaper.
Asphalt permeable pavement: It is a kind of cast asphalt pavement. Asphalt is poured on the paved main aggregate, then caulking stone chips and asphalt are paved in layers, and compacted in layers to form a dense asphalt structure layer. The advantages of pouring construction are simple equipment and convenient transportation of materials; Its disadvantage is that the construction is greatly influenced by the climate, and the final molding takes a certain time. The molded pavement is not as smooth and beautiful as the factory-mixed asphalt mixture pavement, and there are more lime sand floating during molding, which may be flooded. In order to overcome this shortcoming, the last layer of asphalt and stone chips can be poured instead of pre-mixed fine asphalt mixture, which can speed up molding, reduce floating dust and facilitate surface drainage. The thermal stability of permeable pavement mainly depends on the locking force between coarse aggregates, so it is not as sensitive to asphalt content and asphalt consistency as asphalt concrete pavement, and its road performance and applicable horizon are close to asphalt macadam pavement. Asphalt permeable pavement can be constructed by hot method or cold method. In hot construction, the heated viscous asphalt is poured on the cold aggregate, which makes the pavement form quickly and is suitable for urban roads and roads with heavy traffic. In cold construction, emulsified asphalt is used for cold pouring, but it can not be formed until the emulsified asphalt is separated from oil and water and evaporated, which is suitable for long-distance roads with small maintenance and difficult heating equipment. Aggregate particles used for prime coat should be close to the same particle size, so that asphalt can fully penetrate into the main coat and make the thickness of seal coat uniform; The maximum particle size of aggregate in the main layer should be close to or 0.7 ~ 0.8 times of the thickness of the surface layer; Aggregate should be clean and ash-free, and the surface should be dry.
Road-mixed asphalt crushed (gravel) mixture pavement: Road-mixed method is to pile materials on the road bed, sprinkle a proper amount of asphalt, and then mix them mechanically or manually, level and compact them. Because the aggregate on subgrade can't be heated, it is necessary to use asphalt emulsion or liquid asphalt with thinner consistency as binder. Emulsified asphalt is not heated frequently when it is stirred, and liquid asphalt with high flash point can be heated. When the climate is wet, it is necessary to add anti-stripping agent or cationic asphalt emulsion to asphalt, or mix cement and lime into the mixture to increase the adhesion between wet aggregate and asphalt. Due to various conditions, road-mixed asphalt mixture is not as good as factory-mixed asphalt mixture, but it can save the round-trip transportation fee and energy consumption of sand and gravel on site, and is often used in secondary roads or rural roads.
Asphalt surface treatment pavement: the construction technology and road performance of surface treatment are close to infiltration, but because of its thin layer thickness (generally 1 ~ 3cm), asphalt is poured directly on the clean and dry lower layer instead of the main layer aggregate, then the aggregate and asphalt are poured in turn, and finally compacted and formed. Surface treatment can be divided into single layer, double layer and three layers according to the time of pouring asphalt and spreading aggregate. The service life of surface-treated pavement is not as long as that of permeable pavement, and its bearing strength is generally not considered in design. Its function is mainly to protect and prevent the wear of non-asphalt bearing layer, and it is also a common measure for daily maintenance of old asphalt pavement. The aggregate particles distributed for the first time in construction are generally large, and then the particle size gradually decreases; However, there is also the opposite process, that is, first, build a thin surface treatment layer with fine aggregate layer by layer, and then pile it up to a certain thickness, and then press it in with coarse aggregate to form a thick surface treatment layer with good thermal stability; Or treat with fine aggregate to form a watertight seal, and then treat with coarse aggregate to make the surface rough.
Fourthly, the permeable layer
The prime coat is very inconspicuous in the design of pavement structure. Some people even think that it is not a part of pavement structure, but its function has been recognized by more and more people. Because the effect of primer is very important and obvious. But if the construction quality of primer is not guaranteed, it is empty talk to talk about its function. The following are some opinions on the quality control of primer:
1 the function of prime coat and slurry seal coat
The permeable layer mainly has the following three functions: first, it is waterproof and impervious, and the permeable layer with good quality can be basically impermeable, so that the water oozing from the surface layer can be discharged along the surface of the permeable layer, thus ensuring that the base layer does not pump mud and the roadbed does not accumulate water; Second, the bonding effect, for asphalt concrete pavement, can strengthen the bonding between the base and the surface, so that the base and the surface form a whole, thus prolonging the service life of the pavement; The third is to protect the base, which is a cement stabilized material. Under the repeated action of vehicles, it is easy to dust, loosen and penetrate the layer, which can effectively protect the moisture loss of the base, improve the strength of the base and avoid the damage of the base in the construction process.
2. Quality control of primer
2. 1 Main technical indicators
2. 1. 1 mixing ratio
There are two kinds of base oil: diluted asphalt and emulsified asphalt. Kerosene diluted asphalt is used as base oil and road petroleum asphalt as matrix asphalt in Shishi Expressway. The mixing ratio of kerosene and asphalt is an important parameter of prime coat. Whether the ratio is suitable or not largely determines whether the other two important technical indexes, namely viscosity and penetration, meet the requirements. The purpose of adding kerosene is to reduce the viscosity of asphalt and facilitate the penetration of base oil. Too high kerosene content will cause three adverse effects: first, too low asphalt content will affect the bonding and waterproofing of the prime coat; Second, there is no volatile kerosene scattered with rain, which pollutes the local environment; Third, the high price of kerosene increases the production cost. Too low kerosene content will lead to too high asphalt content, high viscosity of base oil and poor permeability.
The blending ratio of kerosene is not fixed, which is related to the label of matrix asphalt and the compactness of base. At the same penetration depth, the higher the asphalt grade, the lower the kerosene content; The thicker the base oil, the higher the kerosene content. Table 1 shows several mixing proportion ranges under general compact conditions.
Table 1 mixing proportion range of kerosene in permeable oil
Proportion range of base asphalt grade kerosene/%
70 55~65
1 10 40~50
140 30~40
2. 1.2 viscosity C25.3(S)
Viscosity is the control index of permeable oil construction technology. According to the test results, when the viscosity is 8 ~ 12s, the bonding effect, waterproof effect and penetration depth of the base oil are good. Because the blending amount of kerosene is difficult to measure and the viscosity test is very easy, the blending ratio of kerosene can be controlled by viscosity index. When the viscosity value is greater than 12s, it means that the base oil has high viscosity, high asphalt content and low kerosene content. When the viscosity value is less than 8s, it means that the viscosity of base oil is low, the asphalt content is low and the kerosene content is high.
2. 1.3 penetration depth
Permeability depth is the effect index of permeable layer after construction, and the connection between surface layer and base layer depends on the permeability effect of permeable layer. The penetration depth of permeable oil is generally 1 ~ 2 cm, and the factors affecting the penetration effect are: first, viscosity, which is the main factor affecting the penetration effect; Second, whether the surface of the base is clean, if there is soil and ash layer on the surface of the base, it will affect the infiltration effect; Third, the spraying temperature should generally be controlled at 80 ~ 90℃. If the spraying temperature is too low, it will also affect the penetration effect of the base oil.
2. 1.4 delivery quantity
Coating quantity is also an important index of primer construction. For open structure base, the prescribed dosage is 1.0 ~ 1.5 kg/㎡, and for closed structure base, the prescribed dosage is 0.6 ~ 0.9 kg/㎡. During primer construction, uniform spraying shall be ensured. When the spraying amount is insufficient, yellowing and graying will occur, so that the penetration depth cannot be guaranteed. If the amount of cloth is too much, the oil in the primer will flow, forming oil wax on the surface, affecting the bonding effect and even causing sliding areas.
2.2 Several common quality problems
The following are common quality defects in primer construction.
2.2. 1 The primer oil is a black oil film after spreading.
This phenomenon is usually caused by the following reasons:
(1), low kerosene content, high asphalt content, or insufficient paving temperature, the priming oil cannot completely penetrate into the base;
⑵ If the cloth is too much, the redundant priming oil cannot penetrate into the base, and the remaining asphalt remains on the surface after kerosene volatilizes;
(3) The top surface of the base is not clean, and the permeable oil cannot seep out due to dirt and dust.
2.2.2 Black and yellow appear in the base oil.
There are two reasons for this phenomenon.
(1), uneven distribution, resulting in too much and too little local oil;
(2) Because the distributor is not equipped with asphalt circulating stirring device, kerosene and asphalt are mixed unevenly, and block kerosene and block asphalt are formed during paving.
2.2.3 The bottom oil is yellow.
There are two reasons for this phenomenon: first, there is too much kerosene and too little asphalt; Second, the amount of oil diffused through this layer is too small.
2.3 Key measures to ensure the quality of prime coat construction
(1) Make a good test before construction, decide what material and proportion to use according to the basic structure, and then determine the requirements of each process connection, man-machine combination on site, driving speed and so on through the test road.
⑵ Ensure that the grass-roots surface is clean and dry. Before pouring the priming oil thoroughly, use air compressor or forest fire extinguisher to blow off the floating dust on the surface of the base (when the base is seriously polluted, rinse it with high-pressure water gun first, and then blow off the floating dust on the surface after drying), so that the aggregate on the surface of the base can be exposed as much as possible. At the same time, the surface of the base should be dry, and the water content of the base should not exceed 3%, which is beneficial to the penetration of priming oil and the bonding with the base.
(3) Select the appropriate paving equipment. The choice of machine is very important. At present, there are many old-fashioned dealers in China, and the construction quality is difficult to guarantee. The applicable crude oil distributor should have independent oil pump, nozzle, tachometer, pressure gauge, liquid level gauge, thermometer, bubble level gauge and hose for reading the temperature of materials in the oil tank, and be equipped with asphalt circulating stirring device, all of which should be in good working condition.
(4) control the amount of cloth. During construction, the distributor should drive at a constant speed to ensure the uniform and stable distribution. Be sure to check the cloth quantity with iron plate. When the cloth quantity does not meet the requirements, adjust the cloth quantity in time by changing the driving speed.
5] protection work should be carried out after the completion of the prime coat. Because penetrating oil needs a certain spreading temperature and soaking time. Generally, the paving temperature is 80 ~ 90℃, the paving time is at the highest temperature in a day, the surface temperature is between 55 ~ 65℃, and the asphalt is in a softened state. Generally, the penetration time of the penetrating oil is 5-6 hours. During this period, traffic control should be strictly done to avoid sticking or slipping, which will affect the oil penetration effect.