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The level of complexity in modern-day infrastructure is increasing by leaps and bounds. From bridges to buildings, tunnels to dams, there is a high level of pressure in all of them due to environmental factors, usage, and natural calamities. This is where environmental and structural monitoring plays a crucial role.

There are a number of engineers and experts in infrastructure who are now working towards real-time monitoring technologies that can sense any potential problems before they occur. Rather than waiting for a structure to get damaged, monitoring technologies are proving to be effective in keeping them safe for a longer period of time.

What Is Environmental and Structural Monitoring?

Environmental and structural monitoring is a technique that constantly monitors the state of a structure and its environment. Sensors are placed on structures such as bridges, buildings, railways, dams, and many other structures of critical importance.

These sensors are equipped to pick up vital information such as:

Vibration levels

Movement of structures

Temperature fluctuations

Wind pressure

Moisture and environmental conditions

These help engineers to understand how a structure is performing in a particular state. If anything untoward occurs, it can trigger alarms immediately.

Why Monitoring Infrastructure Is So Important

In the past, monitoring of infrastructure has always been done manually. This means that an engineer would have to go to the location of the infrastructure and visually check the state of the infrastructure. Although this has its own advantages, it does not guarantee the monitoring of the infrastructure at all times.

Currently, there are several advantages of using monitoring systems for infrastructure, including:

1. Early Detection of Damages

The monitoring systems can detect early damage to the structures, such as cracks, which are not visible to the naked eye. This helps to prevent major catastrophes from occurring.

2. Enhanced Public Safety

Damaged infrastructure can cause major accidents, especially for structures such as bridges, buildings, and tunnels. This can be prevented by using the monitoring systems to ensure the infrastructure is safe for use by the public.

3. Cost Savings

It is always cheaper to maintain infrastructure than to repair major damage to structures. This can be made easier by the monitoring systems.

4. Data-Driven Decision Making

The engineers can use this data to make better decisions regarding repairs, upgrades, and other improvements to the structures.

Technologies Used in Structural Monitoring

The new monitoring systems use different technologies to obtain precise data.

Smart Sensors

Sensors are the heart of any monitoring system. They detect stress, strain, and vibrations, and other environmental factors influencing structures.

IoT Connectivity

The Internet of Things helps these sensors send data to the cloud, where engineers can access the data and process it remotely.

Data Analytics

Data analytics helps process the data obtained from the monitoring systems and detect any patterns or risks.

Remote Monitoring Platforms

The monitoring systems enable engineers to remotely access the structures, eliminating the need to visit the structures physically.

Real-World Applications

Environmental and structural monitoring systems have numerous applications in various fields.

Bridges:

Monitoring helps in measuring and monitoring the level of vibration and movement of structures.

Buildings:

Taller buildings require monitoring for better knowledge of wind forces and stability.

Dams:

Monitoring systems help in measuring pressure and structural stress.

Railway Infrastructure:

Sensors help in monitoring tracks, tunnels, and bridges for smooth transportation.

The Future of Smart Infrastructure Monitoring

As more and more cities are being built, the need to monitor our infrastructure is also on the rise. Smart cities are built with the intention of developing a safe and well-maintained infrastructure through data-driven technology.

The future is sure to bring more of the following:

Artificial Intelligence

Predictive Maintenance Systems

Cloud-Based Monitoring Solutions

Smart Sensor Solutions

This will allow engineers to be able to foresee failures before they happen.

Conclusion

Environmental and structural monitoring has changed the face of how engineers maintain and keep our infrastructure safe. This has allowed engineers to build safer bridges, buildings, and roads.

Asian Construction Equipment Group Co., Ltd. (abbreviated as​ ACE Group) has been deeply involved in the road engineering field for many years. Relying on advanced construction equipment and a mature technical system, it has accumulated rich practical experience in the construction of hot-mix asphalt pavement. This specification, based on the current “Technical Specification for Construction of Highway Asphalt Pavement” (JTG F40–2004) and the latest industry technical standards, combined with practical data from hundreds of the company’s road engineering cases, systematically outlines the key technical points, critical control parameters, and special working condition handling solutions for the entire process of hot-mix asphalt pavement construction. It aims to provide construction teams with scientific, standardized, and practical technical guidance to ensure that project quality meets the core requirements of “high strength, high smoothness, and high durability.”

I. Construction Preparation Phase (Core Controls: Foundation Guarantee and Parameter Calibration)

1.1 Raw material quality control (source control, performance compliance)

• Asphalt materials: Base asphalt (70#, 90#) or modified asphalt (SBS, SBR type) that meet the design requirements should be given priority. Before entering the site, key indicators such as penetration (25℃, 0.1mm), softening point (ring and ball method, ℃), ductility (10℃/5℃, cm), and film oven aging test (mass loss rate, penetration ratio) must be tested. The test results must meet the corresponding grade requirements of JTG F40–2004 specification. It is strictly forbidden to use asphalt with indicators exceeding the standard or deteriorated.

• Aggregate selection: Coarse aggregates are hard rocks such as basalt and granite produced by impact crushing, with a crushing value ≤26%, Los Angeles abrasion loss ≤28%, needle-like and flaky particle content ≤15%, mud content ≤1%, and particle angularity (flow time) ≥30s; Fine aggregates are manufactured sand or clean natural sand, with gradation meeting design requirements, mud content ≤3%, and apparent relative density ≥2.60; Aggregate gradation must be verified through standard sieve analysis tests to ensure a smooth continuous gradation curve without obvious discontinuities in gradation.​

• Mineral powder compatibility: The mineral powder should be ground from limestone, with a hydrophilicity coefficient <1, a fineness modulus (passing rate on a 0.075mm sieve) ≥75%, and a moisture content ≤1%. The use of fly ash or cement as substitutes for mineral powder is strictly prohibited to avoid affecting the bonding performance between asphalt and aggregates.

1.2 Construction equipment commissioning (precise calibration, stable performance)

· Paver: Select a high-grade paver with automatic leveling and vibratory compaction functions (such as Volvo ABG or Dynapac SD series). Before construction, calibrate the vibration frequency (2000~3000 times/min) and screed angle (preset according to the loose paving thickness), and check the matching of the auger distributor speed and paving speed to ensure uniform mixture distribution and no segregation. Equip with a non-contact leveling beam or laser leveling system, with accuracy error controlled within ±1mm.

· Road rollers: Equipped with double-drum vibratory rollers (working weight ≥12t) and rubber-tired rollers (working weight ≥26t). Vibratory rollers require calibration of amplitude (0.3~0.8mm) and vibration frequency (30~50Hz). Rubber-tired rollers require strict control of tire pressure between 0.5~0.7MPa, with uniform tire wear and no localized damage. All rollers must have their travel speed calibrated (0~6km/h steplessly adjustable) to ensure uniform speed during compaction.

· Mixing equipment: An intermittent asphalt mixing plant (production capacity ≥ 240 t/h) is used, equipped with a computer-controlled automatic metering system (metering accuracy: asphalt ±0.3%, aggregate ±0.5%). During commissioning, the feeding speed of the cold aggregate bins and the screening efficiency of the hot aggregate bins need to be verified to ensure gradation stability; the fuel system and heating devices should be checked to ensure that the heating temperature of the aggregate and asphalt meets the standards.

1.3 Substrate pretreatment (base layer meets standards, interlayer bonding)

· Base layer acceptance: The flatness deviation of the base layer surface is ≤3mm/3m (measured with a 3m straightedge), the compaction degree is ≥98% (measured by sand filling method), and the deflection value meets the design requirements (≤design deflection value); the surface is free of defects such as loose material, cracks, and pits. Locally loose areas must be repaired with cement-stabilized crushed stone, and cracks with a width ≥5mm must be treated with sealant.

· Tack coat construction: After the base layer passes inspection, spray slow-cracking emulsified asphalt (PC-2 type) evenly, with the dosage controlled at 0.7~1.5L/m² (calculated based on the solid content of emulsified asphalt). After spraying, use a spreader to evenly spread 3~5mm stone chips (dosage 3~5kg/m²) to ensure that the penetration depth of emulsified asphalt is ≥5mm. After demulsification and curing, proceed to the next process.

· Sealing Coat Construction: For heavy-load roads such as highways and Class I roads, a synchronous chip seal coat (chip size 5~10mm, asphalt dosage 1.2~1.6kg/m², chip seal dosage 8~12kg/m²) or a slurry seal coat (thickness 3~5mm) needs to be added on top of the prime coat. After sealing, it must be cured for at least 24 hours to ensure interlayer bond strength ≥0.6MPa (pull-out test).

II、Mixing stage (core control: uniform gradation, temperature meets standard)

2.1 Selection and Parameter Setting of Mixing Equipment

An intermittent mixing plant with secondary screening function should be selected, equipped with an asphalt heat transfer oil heating system and an aggregate drying drum (thermal efficiency ≥85%). The computer control system must have automatic recording functions for batching, temperature, and mixing time, allowing traceability of production data for each batch of mixture.

• Temperature control standards: Aggregate heating temperature 160~190℃ (10~20℃ higher than asphalt heating temperature); asphalt heating temperature (base asphalt 150~170℃, modified asphalt 160~180℃); mixture delivery temperature (base asphalt mixture 145~165℃, modified asphalt mixture 160~180℃); The mixture temperature must not exceed 195℃ (critical aging temperature).

2.2 Key Points for Mixing Quality Control

• Mixing time: 5–10 seconds for the dry mixing stage (to ensure uniform preheating of the aggregate), 35–45 seconds for the wet mixing stage (stirring after adding asphalt), with a total mixing time of no less than 45 seconds, ensuring the mixture is free of white speckles and asphalt clumps, and has a uniform color.

• Gradation and Asphalt-Aggregate Ratio Control: Before starting work each day, the gradation of the hot aggregate bins must be tested, and the feeding ratio of the cold aggregate bins adjusted according to the test results; the asphalt and aggregate usage should be recorded for each batch, with an allowable deviation of ±0.3% for the asphalt-aggregate ratio; at least one Marshall test of the mixture should be conducted daily to test indicators such as stability, flow value, and void ratio to ensure compliance with design requirements.

• Waste disposal: If problems such as excessive temperature, deviation of gradation, or uneven mixing occur during the mixing process, the mixture must be disposed of as waste and is strictly prohibited from being used for road paving.

III. Mixed Material Transportation Stage (Core Controls: Insulation to Prevent Segregation, Continuous Supply)

3.1 Technical requirements for transport vehicles

Dump trucks with a rated load capacity of ≥20t should be used. The inner walls of the truck bed must be evenly coated with a diesel-water mixture release agent (volume ratio 1:3). The amount applied should be such that the mixture does not stick to the material; excessive application is strictly prohibited as it may cause the asphalt film to peel off. Vehicles must be equipped with double-layered rainproof and heat-insulating tarpaulins (inner layer of insulation cotton, outer layer of waterproof cloth), ensuring the tarpaulin is completely covered and free from damage or air leakage.The number of transport vehicles should be rationally configured according to the mixing plant’s production capacity and paving speed, ensuring that there are always 3–5 vehicles waiting to unload in front of the paver to avoid the paver stopping due to lack of material. Each vehicle’s cab should be equipped with a thermometer to monitor the mixture temperature in real time.

3.2 Transportation and Unloading Control

• Control vehicle speed during transportation, avoiding sudden acceleration and braking to reduce segregation of the mixture; the transportation time of the mixture should not exceed 1 hour (at normal temperature), and in high-temperature weather (≥35℃), the transportation time should not exceed 40 minutes, with the temperature drop controlled at ≤10℃/h.

• Upon arrival at the site, the asphalt mixture must be immediately tested for temperature: ≥135℃ for base asphalt mixtures and ≥150℃ for modified asphalt mixtures. Mixtures failing to meet these standards must be discarded. During unloading, transport vehicles must maintain a distance of 10–30cm from the paver, which should push the vehicles forward slowly, strictly prohibiting collisions with the paver. The tarpaulin should be gradually uncovered during unloading to prevent a sudden drop in mixture temperature.

IV. Paving Operation Stage (Core Controls: Smooth and Uniform, Suitable Temperature)

4.1 Preparations before paving

• Clean the base surface to ensure it is free of dust and debris; based on the design elevation and paving thickness, use a total station to set up control points at intervals of 5–10m, and hang steel strand baselines (tension ≥15kN) to ensure that the paving elevation deviation is ≤±2mm.

• Paver preheating: The screed preheating temperature should be ≥100℃ (base asphalt) or ≥120℃ (modified asphalt), and the preheating time should be no less than 30 minutes to avoid the mixture sticking or unevenness deviation caused by a low-temperature screed.

4.2 Paver Parameter Settings and Operation

• Paving speed: 2~6m/min for base asphalt mixture, 1~3m/min for SMA mixture. Maintain a constant speed and do not change speed or stop the machine at will. The speed fluctuation range is ≤±0.5m/min.

• Loose paving coefficient: determined through test sections, 1.15~1.35 for ordinary dense-graded asphalt concrete (AC), 1.1~1.2 for SMA mixture, loose paving thickness = design thickness × loose paving coefficient, with deviation controlled within ±5mm.

• Paving temperature: Base asphalt mixture ≥130℃, modified asphalt mixture ≥150℃, SMA mixture ≥160℃. The mixture temperature should be checked every 20 minutes during paving to ensure it meets the standards.

• Auxiliary operations: Mechanical paving is the main method, with manual assistance for edge trimming and segregation treatment; when trimming manually, heat-resistant gloves must be worn, and it is strictly forbidden to step on the high-temperature mixture to ensure a smooth surface.

V. Rolling and shaping stage (core control: compaction degree meets the standard, no wheel tracks)

5.1 Compaction Process and Equipment Combination

Rolling operations must strictly follow a three-stage process of “initial compaction → secondary compaction → final compaction,” scientifically combining equipment characteristics with the type of mixture to ensure a steady improvement in compaction quality.

• Initial compaction stage: Static compaction is performed using a double-drum roller, with a total of two passes. The core objective of this stage is to quickly eliminate paving marks and lay a smooth foundation for subsequent compaction. The temperature control standards are: not lower than 120℃ for base asphalt mixtures and not lower than 140℃ for modified asphalt mixtures.

• Secondary compaction stage: A combination of vibratory roller and rubber-tired roller is used. The vibratory roller operates with high-frequency, low-amplitude parameters (vibration frequency 35~45Hz, amplitude 0.3~0.5mm), compacting 4~6 times; the rubber-tired roller simultaneously performs 2~3 kneading compactions. Through the synergistic effect of the two compaction methods, the maximum compaction degree of the mixture (≥97%) is achieved. The temperature control during this stage is: not lower than 100℃ for base asphalt mixtures and not lower than 120℃ for modified asphalt mixtures.

• Final compaction stage: Static compaction is performed again using a double-drum roller, for a total of 2 passes. The core task is to eliminate wheel tracks generated during the secondary compaction process and ensure that the road surface smoothness meets the standard (requirement ≤1.5mm/3m). The temperature control standard is: not lower than 70℃ for base asphalt mixture and not lower than 80℃ for modified asphalt mixture.

5.2 Key Points of Compaction Operation

• Compaction sequence: Strictly adhere to the technical principles of “edges first, then center; static compaction first, then vibratory compaction; slow compaction first, then fast compaction.” The compaction direction must be consistent with the paving direction; lateral compaction is strictly prohibited to prevent pavement displacement or cracking. When operating a double-drum roller, overlap by 1/3 of the drum width; for a rubber-tired roller, overlap by 1/2 of the drum width to ensure thorough compaction without any omissions or blind spots.

• Speed control: The rolling speed must be kept constant and stable at each stage to avoid sudden acceleration or braking, which would affect the compaction effect. The specific speed standards are: 2~3km/h for the initial compaction stage, 3~5km/h for the intermediate compaction stage, and 4~6km/h for the final compaction stage, with the speed fluctuation range not exceeding ±0.5km/h throughout the entire process.

• Prohibited requirements: Before the road surface temperature cools down to below 50°C, the road roller is strictly prohibited from turning, making a U-turn, or parking on the road surface for a long time to prevent damage to the road structure; during the entire rolling process, water must not be sprayed or any auxiliary materials spread on the road surface to avoid affecting the bonding performance and compaction quality of the asphalt mixture.

VI. Joint Treatment (Core Control: Smooth, dense, and crack-free)

6.1 Longitudinal joints

• Hot joint: Two pavers work in echelon, with the subsequent paving layer overlapping the previous one by 10–15cm. The overlapping area is kept warm (≥100℃). During compaction, the roller applies static pressure once along the joint, then compacts outwards to ensure a tight joint.

• Cold joints: If continuous paving cannot be completed on the same day, the loose parts at the edge shall be cut off before construction on the next day (cutting depth ≥5cm) to make the joint vertical and flat; apply tack coat (emulsified asphalt dosage 0.3~0.5L/m²), and after the emulsion breaks, the new mixture shall be manually paved, and the flatness shall be checked with a 3m straightedge to ensure that the joint is smooth.

6.2 Transverse joints

• Joint type: Vertical flat joints are required; oblique joints are strictly prohibited. After paving, use a cutting machine to vertically cut the edges, remove loose mixture, and apply tack coat.

• Compaction Treatment: Preheat the mixture at the joint to ≥65℃. First, use a double-drum roller for transverse compaction (perpendicular to the road centerline), with a compaction strip width of 20~30cm, gradually advancing towards the new paving layer. Then switch to longitudinal compaction to ensure the joint compaction is consistent with the main pavement, without any stepped appearance.

VII. Quality Inspection and Acceptance (Core Control: Indicators Meet Standards, Appearance is Qualified)

7.1 Detection of Key Control Indicators

• Compaction degree: Core drilling was used for testing, with one point sampled per 2000m². The compaction degree at a single point was ≥97%, and the representative value was ≥98%. Simultaneously, a nucleus-free density meter was used for rapid testing to assist in controlling construction quality.​

• Thickness: Measured using core drilling method. Single-point thickness deviation ≥ design thickness — 5mm, extreme value ≥ design thickness — 10mm, representative value ≥ design thickness — 3mm.

• Smoothness: Measured with a 3m straightedge, maximum gap ≤3mm; for highways, a continuous smoothness meter is used, IRI value ≤2.0m/km.

• Permeability coefficient: Tested using a permeability meter; SMA mixture ≤ 120 ml/min, ordinary asphalt mixture ≤ 300 ml/min.

• Texture depth: Tested using the sand-laying method; ≥0.55mm for ordinary asphalt mixtures, ≥0.7mm for SMA mixtures.

7.2 Appearance Quality Acceptance

The surface is free of obvious wheel tracks, cracks, shoving, segregation, looseness, or other defects; joints are smooth with no vehicle bouncing; pavement edges are neat, and elevation meets design requirements. Any localized quality defects discovered are immediately repaired using methods such as cutting and repaving to ensure overall quality meets standards.

VIII. Handling Special Operating Conditions (Core Control: Risk Mitigation and Quality Assurance)

8.1 Construction in Rainy Weather

Laying the asphalt mixture is strictly prohibited in rainy weather or when the base layer is damp. If rain occurs during construction, paving must be stopped immediately. The already laid mixture should be quickly compacted and covered with a rainproof tarpaulin. Rain-soaked mixture must be discarded and must not be used for road paving. After rain, the moisture content of the base layer must be retested. Construction can only resume after the moisture content (≤10%) (for cement-stabilized base layers) and the surface is dry.

8.2 Low-Temperature Construction

Construction is generally prohibited when the ambient temperature is below 10℃ (for ordinary asphalt) or below 15℃ (for modified asphalt). If construction is absolutely necessary, the plant temperature of the mixture must be increased (base asphalt +10℃, modified asphalt +15℃), transportation time shortened (≤30 minutes), and the paving and compaction pace accelerated to ensure the final compaction temperature does not fall below the control standard. During low-temperature construction, the number of rollers should be increased, and the interval between initial and secondary compaction should be shortened to prevent the mixture temperature from dropping too quickly, resulting in substandard compaction.

8.3 High-Temperature Construction

When the ambient temperature is ≥35℃, adjust the construction time (avoiding the midday heat). Strengthen insulation and sun protection during the transportation of the mixture to reduce temperature loss. After paving, accelerate the compaction speed to ensure compaction is completed within the specified temperature range. Increase the frequency of mixture sampling in hot weather, focusing on monitoring asphalt aging to prevent performance degradation due to excessively high temperatures.

IX. Opening to Traffic and Maintenance

After asphalt pavement is compacted, it needs to cool naturally to ambient temperature (generally 24 hours after construction) before being opened to traffic. Driving on the uncooled pavement is strictly prohibited to avoid damage. Initially, heavy vehicles (≤20t) are restricted to a speed of ≤40km/h. Normal traffic can resume once the pavement has fully stabilized (generally after 7 days). Regular pavement inspections should be conducted after opening to traffic, and debris should be removed promptly. Any minor cracks, potholes, or other defects should be immediately addressed with preventative maintenance to extend the pavement’s lifespan.

Conclusion

Hot-mix asphalt pavement construction is a systematic and meticulous project that must strictly adhere to the core principles of “qualified raw materials, compliant equipment, standardized processes, and thorough testing.” Asian Construction Equipment Group Co., Ltd. , driven by technological innovation and focused on project quality, has developed this specification that combines years of construction practice and technological accumulation to provide comprehensive technical reference for related projects.During construction, process parameters must be optimized through test sections based on actual project conditions (such as climate conditions, material properties, and road grade). The “three quicks and two timely actions” principle (quick unloading, quick paving, quick compaction; timely testing, timely repair) must be strictly implemented to ensure the project quality meets design standards and usage requirements.

Learn more about the team of students working behind the scenes at Invent@NMU!

Austin Morris is a mechanical engineering technology major from Johnsburg, Ill. Along with Invent@NMU, Morris works at the NMU Campus Visit Office and serves as vice president of the NMU SAE Baja Team.

Morris said his time spent with both Invent@NMU and the SAE Baja Team are two activities that have been the most rewarding.

“Spending time with these organizations has vastly increased the wealth of knowledge and experience at my disposal in my major field. Both of these experiences have taught me skills that help me to design, fabricate and improve product designs. I am also much more apt to overcome issues and challenges that may be faced when doing so."