The machinery used during road construction is diverse, each with its unique function and purpose, jointly ensuring the efficiency, safety, and quality of road construction. Here is an introduction to some commonly used machines:
1. Subgrade Construction Machinery
1.1 Bulldozer
The bulldozer primarily cuts or short-distance transports soil and loose materials. It is a self-propelled earth-moving and transporting machine, characterized by flexible operation, convenient rotation, and a small required working face. Depending on the walking device, bulldozers can be divided into crawler and tire types. Their production capacity is mainly determined by engine power, and bulldozers used in road construction are divided into medium (59~103kW), large (118~235kW), and extra-large (greater than 235kW). Bulldozers are generally suitable for construction environments with strong seasonality and concentrated workload. They are mainly used for short-distance operations of 50~100m, such as subgrade construction, pit excavation, site leveling, tree root removal, stone slag pushing, etc., and can also loosen soil for shovel transport machinery and digging machinery, assist in shoveling, and tow various towed work devices. When a bulldozer pushes uphill, it uses the minimum economical operating distance, and when it pushes downhill, it uses the maximum economical operating distance. The economical operating distance of the bulldozer, when chosen appropriately, can maximize its efficacy. Under normal circumstances, the bulldozer has a higher productivity within a distance of 100m, but productivity will significantly decrease beyond 100m. Within the economical operating distance, the bulldozer has higher productivity than the shovel transport machine. Bulldozers are generally operated by two drivers.
1.2 Scraper
The scraper is a cyclic operation earth-moving transport machinery, which can be divided into towed and self-propelled types based on the walking method. Its shovel is located between the forward and backward movement devices, and its working method is cyclic operation, composed of three parts: earth digging, earth transporting, and back driving. The production capacity of the scraper is mainly determined by the volume of the shovel. It is generally divided into small (less than 5m³), medium (5~15m³), large (15~30m³), and extra-large (greater than 30m³) according to the shovel volume. The economical operating distance for small and medium-sized shovel volumes is 100~350m, while for large and extra-large shovel volumes, it is 800~1500m. The scraper is mainly used for medium-distance large-scale earthwork transfer projects and is widely used in road and railway construction. The scraper should work in Class I soil, and if it encounters Class II or III soil, it should be loosened in advance. In terms of soil moisture, it is most suitable for construction in loose sand and clay with a small humidity (water content below 25%), but it is not suitable for work in dry silty sand and wet clay, let alone in areas with high groundwater levels, wetlands, and rock areas. The scraper is generally operated by two drivers.
1.3 Excavators
Excavators are mainly used for the excavation and loading of earth and stone, including single-bucket excavators and multi-bucket (wheel bucket type) excavators, with single-bucket excavators generally being used in road construction. A single-bucket excavator works with either a rigid or a flexible continuous bucket in an intermittent and repetitive cycle, and it is a type of self-propelled earth-moving machinery that operates in cycles. Single-bucket excavators are suitable for digging and loading all types of earth as well as blasted rock. The production capacity of an excavator is mainly determined by the bucket capacity, which ranges from 0.1 to 3m³, with more than twenty different models. Based on the type of undercarriage, single-bucket excavators can be divided into crawler type, tire type, and truck type. Based on the working device, they can be categorized into four types: front shovel excavators, backhoe excavators, dragline excavators, and clamshell excavators.
The characteristics of digging with a front shovel excavator are: digging upwards while moving forward, with forced cutting into the soil. These excavators have great digging force and high productivity, and they can dig earth types I to IV above the machine's standing surface.
The characteristics of digging with a backhoe excavator are: digging downwards while moving backward, with forced cutting into the soil. These excavators have a smaller digging force compared to front shovel excavators and can dig earth types I to II below the machine's standing surface, suitable for digging pits, trenches, and ditches about 4 meters deep, as well as excavation in areas with a high groundwater level.
The characteristics of digging with a dragline excavator are: digging downwards while moving backward, cutting into the soil with its own weight. These excavators have greater digging depth and radius, capable of digging earth types I to II below the machine's standing surface, but they are not as flexible and accurate as backhoe excavators. They are suitable for excavating large pits and underwater soil.
The characteristics of digging with a clamshell excavator are: moving straight up and down, cutting into the soil with its own weight. These excavators have a smaller digging force and can only dig earth types I to II, used for digging narrow and deep isolated pits and trenches, caissons, and are suitable for underwater excavation, as well as for digging trenches for continuous wall construction.
Single-bucket excavators have strong digging capabilities, good versatility, and can meet different operational requirements. In highway construction, when encountering large excavation volumes, it is reasonable to use excavators in combination with transport vehicles for organized construction.
Single-bucket excavators generally require two operators.
1.4 Loaders
Loaders are commonly used in highway construction for the shoveling and transportation of earth and stone, as well as for bulldozing, lifting, and various other operations. Based on the characteristics of the undercarriage, they can be divided into tire type and crawler type.
When the transport distance is short or when the distance and road gradient frequently change, such as when using loaders in combination with dump trucks for transport operations, work efficiency may decrease and costs may increase. In such cases, loaders can be used independently as self-loading equipment. Based on experience, if the entire loading and transporting operation cycle is less than 3 minutes, then it is advisable to use the loader as self-loading equipment.
The bucket capacity of the loader should match the bin volume of the dump truck, and it is generally appropriate to fill the truck with 3 to 5 buckets.
Crawler type loaders generally require two operators, tire type loaders with a capacity of 2m³ or less generally require one operator, and tire type loaders with a capacity of 3m³ or more and equipped with excavating functions generally require two operators.
1.5 Grader
A grader is a road construction machinery equipped mainly with a soil scraping blade and other interchangeable working devices for continuous land leveling and shaping operations. Based on the different modes of locomotion, it can be divided into towed and self-propelled types. The towed type, due to its poor mobility and strenuous operation, is rarely used. The self-propelled grader has a tire walking device, is flexible and mobile, has a high productivity, and is widely used. The productivity of a grader is determined by the length of the scraper and the power of the engine, which are divided into light type: scraper length less than 3m, engine power 44~66kW; medium type: scraper length 3~3.7m, engine power 66~110kW; heavy type: scraper length 3.7~4.2m, engine power 110~220kW.
The grader is mainly used for leveling the subgrade and gravel road surface, shaping the site in earthwork projects, and leveling operations. It can also be used to trim the cross-section of the subgrade, repair the embankments and slopes of the road, excavate side ditches and road grooves, etc. In addition, it can be used to mix and stabilize soil or other pavement materials on the subgrade, spread materials, repair and maintain dirt roads, loosen soil, backfill, remove weeds, and clear snow, etc. Self-propelled graders are usually operated by two drivers.
1.6 Roller
1.6.1 Classification of Compaction Machinery
According to the principle of compaction force, it can be divided into static rolling machinery, vibrating rolling machinery, and tamping machinery.
- Static rolling machinery
Includes various models of smooth wheel rollers, tire rollers (commonly known as tire rollers), sheep foot rollers (commonly known as sheep foot rollers), block rollers (commonly known as block rollers), and various types of towed rollers.
- Vibratory rolling machinery
Single drum vibratory rollers usually weigh between 10~25t or 30~50t. With the development of highways, large-tonnage vibratory rollers are widely used.
Double drum vibratory rollers are mainly divided into light (2~4t), medium (5~8t), and heavy (10~14t) types.
- Tamping machinery
Mainly used for compacting soil, it can be divided into vibratory compaction and impact compaction. Mainly used for compacting soil layers on narrow work surfaces.
1.6.2 Applicable Scope of Compaction Machinery
- Smooth wheel roller
Smooth wheel rollers have a small linear pressure per unit and shallow compaction depth. Light and medium smooth wheel rollers are suitable for compacting general soil subgrade, gravel, and crushed stone base layers. Heavy and extra heavy smooth wheel rollers can compact block stone filled subgrades and crushed stone structural layers.
- Sheep foot roller
Sheep foot rollers have a large unit pressure (including the squeezing force of the sheep's foot), large and uniform compaction depth, and can crush soil blocks, so they have good compaction effect and high productivity. They are widely used for layered rolling of cohesive soil. Because of these advantages, sheep foot rollers can also adjust the unit pressure of the sheep's foot by adding or removing weights, and are often used to roll impermeable cohesive soil in earth dam construction. Sheep foot rollers are not suitable for compacting non-cohesive soil and high water content clay because of their poor compaction effect.
Tire Roller
The tire roller has good maneuverability and is easy to transfer. During compaction work, both the soil and the tires deform simultaneously, resulting in a long duration of full pressure, a large contact area, and a kneading effect, which leads to good compaction. Tire rollers are suitable for compacting cohesive soils and non-cohesive soils, such as clay, sandy clay, sand, and gravel.
Vibratory Roller
The vibratory roller has a high unit line pressure and the vibratory force affects a deep range, thus it has a larger compaction depth, and the number of rolling passes is correspondingly reduced. There are many types of vibratory rollers and they have a wide range of applications. Smooth wheel vibratory rollers are suitable for compacting non-cohesive soils (sand, gravel), crushed stone, and boulders. This type of compaction machinery can also be used as static compaction machinery for leveling operations when the vibration mechanism is disengaged.
Compaction Machinery
Vibratory tampers are suitable for compacting non-cohesive sandy clay, gravel, and crushed stone, while impact tampers are suitable for compacting clay, sandy clay, and loess.
A single operator is required for a smooth wheel roller, while towed sheep's foot rollers, towed vibratory rollers, and vibratory rollers require two operators.
1.7 Rock Drilling and Boring Machinery
Rock drilling and boring machinery includes rock drills, boring machines, and their auxiliary equipment. These are the rock excavation machinery used for drilling blast holes, with rock drills being suitable for drilling small-diameter blast holes and boring machines suitable for drilling large-diameter blast holes.
In highway construction, rock drills are commonly used. Compared with large earth-moving machinery, rock drills are considered small tools. Therefore, in the highway engineering quota, their costs are included in the use of small tools and are not listed as the main machinery.
Rock drills are classified according to the type of working power and are divided into four types: pneumatic rock drills (commonly used in highway engineering), hydraulic rock drills, electric rock drills, and internal combustion rock drills.
2. Pavement Engineering Machinery
Pavement engineering machinery primarily includes stabilized soil mixers and plant mixing equipment, asphalt emulsion equipment, asphalt transport trucks and spreaders, black aggregate mixers, asphalt mixture mixing equipment and pavers, as well as cement concrete pavers, etc.
2.1 Stabilized Soil Mixers and Plant Mixing Equipment
Stabilized soil plant mixing equipment comes in structural forms such as mobile and stationary types. Their production capacities are categorized into small (<200t/h), medium (200-400t/h), large (400-600t/h), and extra-large (>600t/h) sizes. They are widely used for the construction of base and sub-base layers in highways and urban roads. Mobile plant mixing equipment is often used for scattered highway construction projects that require frequent relocation, while stationary plant mixing equipment is suitable for urban road construction or for large and concentrated construction projects.
The production capacity of stabilized soil mixers is determined by the mixing width, depth, and the working travel speed. The general mixing width is 2100mm, with mixing depths ranging from 100 to 485mm, and a working speed of less than 1.5 km/h. They are mainly suitable for in-situ mixing construction methods.
Stabilized soil plant mixing equipment generally requires a team of three operators, while stabilized soil mixers typically require two operators.
2.2 Stabilized Soil Mixers and Plant Mixing Equipment
Stabilized soil plant mixing equipment comes in structural forms such as mobile and stationary types. Their production capacities are categorized into small (<200t/h), medium (200-400t/h), large (400-600t/h), and extra-large (>600t/h) sizes. They are widely used for the construction of base and sub-base layers in highways and urban roads. Mobile plant mixing equipment is often used for scattered highway construction projects that require frequent relocation, while stationary plant mixing equipment is suitable for urban road construction or for large and concentrated construction projects.
The production capacity of stabilized soil mixers is determined by the mixing width, depth, and the working travel speed. The general mixing width is 2100mm, with mixing depths ranging from 100 to 485mm, and a working speed of less than 1.5 km/h. They are mainly suitable for in-situ mixing construction methods.
Stabilized soil plant mixing equipment generally requires a team of three operators, while stabilized soil mixers typically require two operators.
The use of these machines significantly improves the efficiency and quality of road construction, shortens the construction period, and reduces construction costs. When selecting construction machinery, it is necessary to make a rational choice based on the volume of work and the construction progress of the road construction project to ensure the maximization of construction quality and economic benefits.
