Category: HIGHWAY

The best articles about highways conception, construction and maintenance

Benefits of Using AI in Highway Design

Benefits of Using AI in Highway Design

 

Artificial Intelligence (AI) is revolutionizing highway design and management by introducing advanced methodologies and tools that enhance efficiency, accuracy, safety, and sustainability. Here are several key applications of AI in highway design:

1. Optimizing Route Selection

  • Geospatial Analysis: AI algorithms analyze geospatial data, including topography, land use, and environmental constraints, to optimize route selection for new highways.
  • Cost-Benefit Analysis: AI can evaluate multiple routing options considering cost, construction feasibility, environmental impact, and social factors to determine the most beneficial route.

2. Predictive Maintenance

  • Condition Monitoring: AI systems use data from sensors and IoT devices embedded in highways to monitor conditions in real-time.
  • Failure Prediction: Machine learning models predict the likelihood of pavement failures, structural damage, and other issues before they occur, enabling proactive maintenance.
  • Resource Allocation: AI helps prioritize maintenance activities and allocate resources efficiently based on predicted needs.

3. Traffic Flow Optimization

  • Traffic Simulation: AI-driven traffic simulation models analyze current traffic patterns and predict future traffic flows, helping in the design of highway features like lanes, ramps, and intersections.
  • Adaptive Traffic Management: AI algorithms optimize traffic signal timings, ramp metering, and variable speed limits to enhance traffic flow and reduce congestion.

4. Safety Enhancements

  • Accident Prediction: AI models analyze historical accident data, traffic conditions, and environmental factors to predict high-risk areas and times for accidents.
  • Design for Safety: Using AI insights, designers can incorporate safety features like better signage, improved lighting, and safer road geometry.
  • Autonomous Vehicle Integration: AI supports the design of highways compatible with autonomous vehicles, ensuring safe interaction between human-driven and autonomous cars.

5. Sustainability and Environmental Impact

  • Environmental Monitoring: AI systems monitor environmental parameters (e.g., air quality, noise levels) during and after highway construction.
  • Eco-Friendly Design: AI assists in designing highways that minimize environmental impact by optimizing material use, reducing emissions, and preserving natural habitats.
  • Sustainable Materials: AI helps identify and evaluate sustainable construction materials and techniques that reduce the carbon footprint of highway projects.

6. Design Automation

  • Generative Design: AI-driven generative design tools create multiple design alternatives based on specified criteria (e.g., cost, safety, aesthetics), allowing engineers to explore a wide range of options quickly.
  • BIM Integration: AI enhances Building Information Modeling (BIM) by automating the integration of complex data sets and improving collaboration across different phases of highway design and construction.

7. Project Management

  • Scheduling and Planning: AI tools optimize construction schedules, manage logistics, and forecast potential delays or cost overruns.
  • Risk Management: AI identifies and assesses risks in highway projects, helping managers mitigate them effectively.

8. User Experience and Feedback

  • Crowdsourced Data Analysis: AI analyzes data from social media, mobile apps, and other sources to gather user feedback on highway conditions and design.
  • Enhanced User Interfaces: AI improves the design of user interfaces in traffic management systems, making them more intuitive and responsive to user needs.

Examples of AI Applications in Highway Design

  • Waycare: Uses AI to predict traffic incidents and optimize traffic management.
  • RoadBotics: Employs AI to assess road conditions using smartphone data, helping cities prioritize maintenance.
  • Automated Pavement Evaluation: AI systems like those developed by startups and research institutions evaluate pavement conditions using computer vision and machine learning.

Benefits of Using AI in Highway Design

  • Improved Efficiency: Reduces time and effort in design and maintenance processes.
  • Cost Savings: Optimizes resource allocation, reducing construction and maintenance costs.
  • Enhanced Safety: Proactively addresses safety concerns, reducing accidents and fatalities.
  • Better Decision-Making: Provides data-driven insights for more informed decision-making.
  • Environmental Protection: Supports sustainable practices and minimizes environmental impacts.

Incorporating AI in highway design leads to smarter, safer, and more sustainable infrastructure, meeting the evolving needs of modern transportation systems.

Why Are Spiral Curves Important? Benefits And Elements Of Spiral Curve

Why Are Spiral Curves Important? Benefits And Elements Of Spiral Curve

 

1. Introduction:

 

Spiral curves are an important feature in the design and construction of roads and highways. They are used to provide a smooth and gradual transition between two straight sections of road. They allow vehicles to maintain a consistent speed and direction.

Spiral curves are an essential component of highway design. They improve safety, increase traffic flow, and reduce wear and tear on vehicles and road surfaces.

2. Spiral Curves Benefits:

 

One of the primary benefits of spiral curves is improved safety. When a road or highway changes direction suddenly, it can be difficult for drivers to navigate the turn safely. Spiral curves provide a more gradual transition, reducing the risk of accidents caused by sudden changes in direction or speed. This is especially important on highways, where vehicles are traveling at high speeds and any sudden changes can have serious consequences.

Another benefit of spiral curves is that they increase traffic flow. When a road or highway has a series of sharp turns, it can slow down traffic and cause congestion. Spiral curves allow vehicles to maintain a more consistent speed and direction, reducing the need for drivers to slow down and speed up constantly. This improves traffic flow and reduces congestion, making it easier for people to get where they need to go.

Spiral curves also reduce wear and tear on vehicles and road surfaces. When a vehicle has to make sudden turns, it puts additional strain on the tires, suspension, and other components. This can cause increased wear and tear on the vehicle, leading to more frequent repairs and maintenance. Spiral curves reduce this strain by providing a smoother transition between sections of road, which reduces the amount of stress placed on the vehicle. This also helps to reduce the amount of damage that is done to the road surface, which can save money on maintenance and repairs in the long run.

 

3. Spiral curve length:

 

The length of a spiral curve is an important consideration in highway design, as it can affect a range of factors including driver comfort, vehicle wear and tear, and overall highway efficiency.

The length of a spiral curve is determined by several factors, including the radius of the curve, the desired speed limit, and the terrain.

In general, longer spiral curves provide a smoother transition between two straight sections of road, which can improve driver comfort and reduce wear and tear on vehicles. However, longer spiral curves also require more space, which can be a limiting factor in some areas.

One of the main benefits of longer spiral curves is increased driver comfort. When a vehicle transitions from a straight section of road to a curve, there is often a jarring sensation as the vehicle is forced to change direction quickly.

Longer spiral curves provide a more gradual transition, which can reduce this jarring sensation and make the driving experience more comfortable for passengers. This is especially important on highways, where high speeds can amplify the effects of sudden changes in direction.

Another benefit of longer spiral curves is reduced wear and tear on vehicles. When a vehicle makes sudden turns or changes direction quickly, it puts additional stress on the tires, suspension, and other components. This can cause increased wear and tear on the vehicle, which can lead to more frequent repairs and maintenance. Longer spiral curves reduce this stress by providing a smoother transition between sections of road, which can help to extend the life of the vehicle.

In addition to these benefits, longer spiral curves can also improve the overall efficiency of a highway. When a highway has a series of sharp turns or sudden changes in direction, it can slow down traffic and cause congestion. Longer spiral curves allow vehicles to maintain a more consistent speed and direction, which can help to reduce congestion and improve traffic flow. This can save time and fuel for drivers, as well as reduce emissions from idling or stop-and-go traffic.

4. Spiral Curve Elements:

 

The figure below illustrates the standard components of a spiral curve connecting tangents with a central circular curve. The back and forward tangent sections intersect one another at the PI.
The alignment changes from the back tangent to the entrance spiral at the TS point. The entrance spiral meets the circular curve at the SC point. The circular curve meets the exit spiral at the CS point.

The alignment changes from the exit spiral to the forward tangent at the ST point. The entrance and exit spiral at each end of the circular curve are geometrically identical.

 

Below is a list of term and abbrievations of a spiral curve and the definition of each.

 

In conclusion, spiral curves are an essential component of highway design. They provide a smoother transition between sections of road, improving safety, increasing traffic flow, and reducing wear and tear on vehicles and road surfaces. When designing and constructing roads and highways, it is important to consider the benefits of spiral curves and incorporate them into the design to ensure that they are as safe and efficient as possible.

 

Suggested Read:

Road Spiral Curve (Clothoid Calculation) Spreadsheet

Highway Design – Introduction to Horizontal and Vertical Alignment

 

 

The Main Types of Traffic Barriers for Roads and Highways

The Main Types of Traffic Barriers for Roads and Highways

 

Road barriers are a critical component of transportation infrastructure. They are important to prevent vehicles from crossing over into oncoming traffic, to protect pedestrians and cyclists, and to delineate lanes on highways and roads. In this article, we will explore the different types of road barriers and their uses, as well as their benefits and potential drawbacks.

Types of Road Barriers:

There are several types of road barriers, each designed for a specific purpose. The most common types of road barriers include:

  • Steel highway barriers

Metal road barriers are becoming more popular as an option for roadwork crews working in the road corridor. This is because some models on the market feature one of the highest possible MASH ratings, being rated at TL-4.

This rating refers to the ability of the roadside safety barriers to deflect and control out of control vehicles, and generally the higher the MASH rating, the faster the speed zone it can be used in. This makes steel barriers a good choice for the fastest road speeds such as those found on freeways, motorways and highways.

Steel road barriers are generally sold in 6m long units which are easy to install using a T shaped connecting pin.

  • Plastic jersey barriers

Barriers made from polypropylene or blow moulded plastic are generally only suitable for lower speed areas. This limits their use on highways or faster speed roads, as many of these barricades are rated to a maximum of 70km/hr. This means they are probably not the best choice for highway use, as speeds would generally be well above this level.

However, you might see plastic barriers used on worksites at the side of a highway: they are a great all rounder and can be used to create temporary worksite carparks and walkways.

They are also used to barricade items such as power poles or electrical boxes so that worksite plant such as excavators does not accidentally bump into these obstacles.

  • Concrete barriers

These roadside safety barriers are one of the most common to be used around temporary road work, new road construction and infrastructure sites. Also known as jersey barriers, these barriers are TL-3 rated making them suitable for use on most Australian highways.

Jersey barriers are constructed with a steel bar running through the middle of the concrete, giving it extra strength and rigidity and helping to link all of the barriers together in a long line.

 

 

Uses of Road Barriers:

Road barriers are used for a variety of purposes, including:

  1. Separating opposing lanes of traffic: Jersey barriers and cable barriers  separate opposing lanes of traffic on highways and prevent head-on collisions.
  2. Protecting pedestrians and cyclists: Bollards  protect pedestrians and cyclists from vehicles by creating a physical barrier between them.
  3. Channelizing traffic: Barriers are often used to create lanes of traffic and prevent vehicles from veering into other lanes.
  4. Protecting work zones: Water-filled barriers are often used in construction zones to separate traffic from work areas, keeping workers safe.

Disadvantages of Road Barriers:

 

The benefits of road barriers are numerous. They can help prevent accidents by separating opposing lanes of traffic and protecting pedestrians and cyclists from vehicles. Road barriers can also reduce the severity of accidents by absorbing the impact of a collision, potentially saving lives.

Another benefit of road barriers is that they can be cost-effective. While the initial cost of installing barriers can be high, they can save money in the long run by reducing the cost of accidents and the associated medical bills, property damage, and legal fees.

Disadvantages of Road Barriers:

 

Despite their benefits, road barriers can have drawbacks. They can obstruct the view of drivers, making it difficult for them to see oncoming traffic or pedestrians. Additionally, road barriers can limit the ability of emergency vehicles to respond to accidents.

Road barriers can also create traffic congestion, particularly in urban areas limited with limited spaces. They can make it difficult for vehicles to merge or change lanes, leading to backups and delays.

Conclusion:

Road barriers are a crucial component of transportation infrastructure, providing safety and protection for motorists, pedestrians, and cyclists. There are several types of road barriers, each designed for a specific purpose. They can offer numerous benefits, including preventing accidents, reducing the severity of collisions, and saving money in the long run.

However, road barriers can also have drawbacks, including obstructing views, limiting emergency vehicle access, and creating traffic congestion. As with any transportation infrastructure, it is essential to weigh the benefits and drawbacks of road barriers carefully. It is always a good practice to consider their use on a case-by-case basis.

The Common Types of Bridge Railings

The Common Types of Bridge Railings

 

A bridge’s railing depends on various factors such as location, material, and purpose. The railing adds safety for pedestrians, aesthetics, and a custom touch to bridge construction.

Guardrails for bridges are located prominently to make the public stay alert and safe during their drive through bridges. These railings not only keep the traffic within the boundaries but also improve the bridge aesthetics.

Types of Bridge Railings

The common types of railings used for bridges are:

  1. Steel bridge railings
  2. W-Beam railings
  3. Thrie-Beam railings
  4. Concrete beam railings

1. Steel Bridge Railings

 

Steel railings come in different cross-sections and designs. The most common type of steel bridge rail is a tubular rail system. These types of railings can be built alone or integrated into the concrete curb or on a low barrier wall.

For bridges with low-vehicular traffic and for pedestrians, architectural steel railings are commonly used. Architecturally important bridges do not have a bulky and heavy design. They incorporate decorative railings without compromising pedestrian safety.

 

2. W-Beam Bridge Railings

 

W-Beam railings are used for bridges with less traffic. As shown in the figure-2, W-Beam railings have a two-wave design and are attached to steel posts or truss girders.

W-Beam is a simple steel railing system that can be designed for higher strength.

 

3. Thrie Beam Bridge Railings

 

Thrie beams are high-strength guard rail systems designed for highways, especially on sharp curves and slopes.

Thrie-Beam features ‘three’ waves across its section versus ‘two’ on W-Beam and therefore provides greater rigidity, which in turn means lower deflections and higher containment that is more suitable for heavier vehicle protection.

Thrie beam rail systems can absorb the impact of out-of-control vehicles and guide them to a safer stop. These rail systems provide excellent performance and versatility.

It has an added corrugation that gives an advantage for use in transitions to bridges and along high volume, high speed roadways.

 

4. Concrete Bridge Railings

 

Concrete is the most common material used for bridge construction. Concrete railings are attached to the bridge’s deck slab to create a strong vehicle barrier.

A concrete railing attaches to the bridge’s deck slab and creates a powerful vehicular barrier. These sturdy railings are ideal for high traffic roadways or areas where run-off the road accidents are frequent.

The initial construction cost of concrete railings is high. Huge concrete railings in some situations can impede an open road view. In such situations, concrete railings with high strength can be combined with a tubular railing system.

The dimensions and construction of bridge railings are dependent on the construction budget, the bridge deck material, and the mandated state specifications.

Highway Design – Introduction to Horizontal and Vertical Alignment

Highway Design – Introduction to Horizontal and Vertical Alignment

 

The layout of a highway is comprised of two components: A horizontal component which is viewed from above and the vertical component which is viewed from the side.

The horizontal alignment dictates the left or right turning required to remain on the roadway, while the vertical alignment exerts forces on the vehicle as the grade along the roadway changes.

Horizontal Alignment:

In the horizontal perspective, a roadway is primarily comprised of tangent, or straight, sections which are smoothly connected by curves.

The horizontal curves that are used to provide drivers with the transition from one tangent to the next tangent are typically simple curves which are an arc of circle.

These curves have a single radius value which represents the sharpness or flatness of the curve.

Highway Geometric Design – Horizontal Curve Equations

A tangent roadway section has an infinite radius, since it is a straight line and a horizontal curve has a single, finite radius. Therefore, a spiral transition is used in some instances to help make the shift from a tangent to a curve a little smoother.

Geometric relationships and equations can be used to find important information for reach curve. This information includes the radius, the length of the curve, the change in direction of the two tangents, and other factors depending on our needs.

Several points of interest along the curve include the location where the tangents intersect, which is known as the Point of Intersection. The location where the vehicle leaves the tangent section and begins to drive along the curve, is known as the point of curvature.

Types Of Horizontal Curves:

Horizontal curves are of different types as follows:

1.Simple circular curve

2.Compound curve

3.Reverse curve

4.Transition curve

 

1. Simple Circular Curve

Simple circular curve is normal horizontal curve which connect two straight lines with constant radius.

2. Compound Curve

Compound curve is a combination of two or more simple circular curves with different radii. In this case both or all the curves lie on the same side of the common tangent.

3. Reverse Curve

Reverse curve is generated when two simple circular curves bending in opposite directions are meet at a signle point and that points is called as point of reverse curvature. The center of both the curves lie on the opposite sides of the common tangent such that the radii of both the curves may be same or different.

Types of horizontal curves

4. Transition Curve

A curve of variying radius is termed as transition curve. It is generally provided on the sides of circular curve or between the tangent and circular curve and between two curves of compound curve or reverse curve etc. Its radius varies from infinity to the radius of provided for the circular curve.

Transition curve helps gradual introduction of centrifugal force by gradual super elevation which provides comfort for the passengers in the vehicle without sudden jerking.

Spiral Curve

Spiral is a type of transition curve which is recommended by Indian Road Congress as ideal transition curve because of its smooth introduction of centrifugal acceleration. It is also called as clothoid.

  • TS = Tangent to spiral
  • SC = Spiral to curve
  • CS = Curve to spiral
  • ST = Spiral to tangent
  • LT = Long tangent
  • ST = Short tangent
  • R = Radius of simple curve
  • Ts = Spiral tangent distance
  • Tc = Circular curve tangent
  • L = Length of spiral from TS to any point along the spiral
  • Ls = Length of spiral
  • PI = Point of intersection
  • I = Angle of intersection
  • Ic = Angle of intersection of the simple curve
  • p = Length of throw or the distance from tangent that the circular curve has been offset
  • X = Offset distance (right angle distance) from tangent to any point on the spiral
  • Xc = Offset distance (right angle distance) from tangent to SC
  • Y = Distance along tangent to any point on the spiral
  • Yc = Distance along tangent from TS to point at right angle to SC
  • Es = External distance of the simple curve
  • θ = Spiral angle from tangent to any point on the spiral
  • θs = Spiral angle from tangent to SC
  • i = Deflection angle from TS to any point on the spiral, it is proportional to the square of its distance
  • is = Deflection angle from TS to SC
  • D = Degree of spiral curve at any point
  • Dc = Degree of simple curve

Bernoulli’s lemniscate

In this curve, the radius decreases as the length increases and this causes the radial acceleration to keep on falling. The fall is, however, not uniform beyond a 30 o deflection angle. We never use this type of curve on railways.

 

Vertical Alignment:

 

In the vertical perspective, a roadway is also comprised of tangents which are smoothly connected by curves. For vertical alignment, the tangents represent grades which can either be flat, uphill or downhill.

The typical vertical curve is a symmetric, parabolic curve whose shape is defined by the parabolic equation.

The information required to fully define a vertical curve is the elevation of the beginning of the curve, the grades of the two tangents that are connected ad the length of the curve.

The naming convention of vertical alignment is similar to horizontal alignment. Several points of interest along the curve include that the location where the tangents intersect, which is known as the Point of Vertical Intersection.

The location where the vehicle leaves the tangent grade and begin to drive along the curve, is known as the point of vertical curvature.

The point where the curve ends and the vehicle returns back to the tangent grade is known as the Point of Vertical Tangency.

Highway Geometric Design – Vertical Curve Equations

 

Types Of Vertical Curves:

In general parabolic curve is preferred as vertical curve in the vertical alignment of roadway for the ease of movement of vehicles. But based on the convexity of curve vertical curves are divided into two types

1.Valley curve

2.Summit curve

1. Valley Curve (sag curve)

Valley curve connects falling gradient with rising gradient so, in this case convexity of curve is generally downwards. A second name for valley curve is sag curve.

They are formed when two gradients meet as any of the following four ways:

  • When a negative gradient meets another mild negative gradient
  • When a negative gradient meets a level zero gradient
  • When a negative gradient meets with a positive gradient
  • When a positive gradient meets another steeper positive gradient

2. Summit Curve (crest curve)

Summit curve connects rising gradient with falling gradient hence, the curve has its convexity upwards. A second name for summit curve is crest curve.

They are formed when two gradients meet as in any of the following four ways:

  • When a positive gradient meets another positive gradient.
  • When positive gradient meets a flat gradient.
  • When an ascending gradient meets a descending gradient.
  • When a descending gradient meets another descending gradient.

Suggested Read:

Why Are Spiral Curves Important? Benefits And Elements Of Spiral Curve

 

What is a Highway Impact Attenuator?

What is a Highway Impact Attenuator?

 

Highway impact attenuators are devices which are generally used to reduce the impact resulting from a motor vehicle collision, where those impacts might damage other vehicles, motorists, or structures nearby.

In some cases, they are also designed to redirect a colliding vehicle away from roadway machinery, workers, or some other fixed structure. Impact attenuators be classified into three distinct categories, which are based on the engineering method which is used to reduce the kinetic energy of a colliding automobile.

Impact Attenuator Categories:

Momentum transfer, in which the impacting vehicle’s momentum is transferred to containers having sand or water in them, thereby successively lowering the speed of a colliding vehicle.

Material deformation, this category uses crushable materials which absorb energy by creating a crumple zone.

Friction: these work by causing a steel cable to be pushed through an angled slot, thereby transforming kinetic energy into harmless heat.

Impact Attenuator Types:

There are several types, and most of these can be frequently seen along roadsides at locations where it is necessary to protect those kinds of objects and individuals.

Crash cushions:

These attenuators are constructed of several segments, all of which crumple into each other when struck by a colliding automobile, and these are often used because of their reusable nature.

After being struck by a colliding vehicle, they can return to their original form and can be used again. Fitch barriers are sand-filled plastic containers, most often colored yellow with a black lid.

They are generally set up in a triangular arrangement between a highway and an exit line, also known as the gore point, and always along the most likely collision line.
The containers which are most forward usually have the least amount of sand in them, with each successive barrel having a higher level of sand.

This allows an impacting vehicle to decelerate more or less smoothly, rather than striking a solid obstruction in a violent manner.

Crash cushions are often implemented along the shoulders of a roadway where it is necessary to protect against collisions with the hazard directly behind them. They can be ground-mounted or surface-mounted and situated on top of a concrete pad.

Water-filled impact attenuators:

They are filled with water which absorbs the force of a colliding auto. Since these are not anchored to the ground, they can easily be redeployed to locations where they are needed.

The water in the containers helps absorb all the kinetic energy so that there is less damage to objects behind the containers, and to the occupants of the colliding vehicle. In cold climates, when water-filled options are used, it will be necessary to include an additive such as magnesium chloride to prevent them from freezing.

Gating impact attenuators:

They permit vehicles that collide with them from the side, to pass right through, and are often used because they’re so economical. However, they do require more clearing space around them in order to be effective, because, without sufficient space, it might be possible for an impacting automobile to pass through and collide with another hazard.

Non-gating impact attenuators:

They do stop the motion of head-on impacts, but also deflect vehicles which strike the sides of the barrier. These types are more expensive because they are anchored, but they require less space than gating versions.

 

Fitch barriers:

They are most often used at temporary construction worksites, for example at the end of a concrete barrier. They are also used at bridge piers, wide medians, and for two-sided protection.

Where are These Cushions Placed?

Highway impact attenuators are often placed forward of objects along the freeway such as overpass supports, crash barrier introduction, and gore points.

They are frequently used at the side of road construction projects, where there is a greater likelihood of collision with construction equipment and or individuals. Truck-mounted versions is another type which are deployed on vehicles that happen to be susceptible to being hit from behind, for example, maintenance vehicles, road construction vehicles, and snowplows.

 

 

 

What is Warm Mix Asphalt (WMA) ?

What is Warm Mix Asphalt (WMA) ?

 

The increase of scheduled commercial flights at busy civil airports have made it imperative that airfield pavement rehabilitation and asphalt overlay be performed without disrupting airport operations.

For this purpose, the off-peak period (nighttime) construction has become one practical solution for airport authorities. Using this approach, the airfield facilities are closed at night for a few hours when the flight volume is at the lowest, and then quickly opened to air traffic in the next morning.

During this closed period, aircraft will use other runway facilities, if parallel runways are available, or airport operation will be postponed. Time is the essence of the construction during the off-peaktime.

The typical unoccupied time of airfield pavement rehabilitation is as short as 6–8 h per night. It is a period from 23:00 to 6:00 that was specified for runway overlay in Fukuoka airport. The similar night time construction period can also be found in these following airport projects: San Diego International airport in1980 (8 h), Frankfurt airport, Germany, in 2005 (8 h)and Hong Kong airport in 2006 (8 h).

However, with the increase of 24-hour airport operation, the period for night time construction has become limited. The decrease was observed in the largest Australian airports, where the available night time construction was generally reduced from eight hours in 2005 to five hours in 2015.

Rapid construction is expected to reduce the disruption due to the airport closure and allow more time for contractors to produce the maximum volume of asphalt each night to achieve satisfactorily constructed pavement.

One of the approaches for rapid night time construction is to shorten the cooling time of freshly paved asphalt overlay. In this case, with its advantage of lower production and compaction temperature, warm mix asphalt (WMA) gives an advantage of a lower cooling time of asphalt; thus, the pavement can be quickly opened to traffic.

In the situation where the closure of the runway is substantially critical, the use of WMA is expected to shorten the runway closure time each night. In addition, in the case that the closure hours are fixed for each night, the use of WMA would enable more volume of asphalt to be laid each night, increase the target length of pavement to be done each night, thus, shortening the overall project time, compared to HMA.

The use of WMA technology for airport pavements has been few until now. The technology has more popularly been adopted for road pavement projects than airfield pavements. However, extensive research has been carried out in the last few years on the use of WMA for airside applications.

Recent evidence suggests the suitability of using WMA for airfield pavement. Although considerable researches have been done, there has been no detailed investigation into the advantages of the use of WMA on shortening the construction time of pavement.

Description And Uses Of Bituminous Binders

Description And Uses Of Bituminous Binders

 

 Bituminous binders can be classified into three general groups: asphalt cement, asphalt cutbacks, and emulsified asphalt.
Blown asphalt and road tars are also other types of bituminous material that now are not used commonly in highway construction.

Asphalt Cements

 

Asphalt cements are obtained after separation of the lubricating oils. They are semisolid hydrocarbons with certain physiochemical characteristics that make them good cementing agents. They are also very viscous, and when used as a binder for aggregates in pavement construction, it is necessary to heat both the aggregates and the asphalt cement prior to mixing the two materials.

For several decades, the particular grade of asphalt cement has been designated by its penetration and viscosity, both of which give an indication of the consistency of the material at a given temperature. The penetration is the distance in 0.1 mm that a standard needle will penetrate a given sample under specific conditions of loading, time, and temperature.

The softest grade used for highway pavement construction has a penetration value of 200 to 300, and the
hardest has a penetration value of 60 to 70. For some time now, however, viscosity has been used more often than penetration to grade asphalt cements.


Asphalt cements are used mainly in the manufacture of hot-mix, hot-laid asphalt concrete, which is described later in this chapter. Asphalt concrete can be used in a variety of ways, including the construction of highways and airport pavement surfaces and bases, parking areas, and industrial floors. The specific use of a given sample depends on its grade. 

Asphalt Cutbacks

 

The asphalt cutbacks are slow-curing asphalts, medium-curing cutback asphalts, and rapid-curing cutback asphalts. They are used mainly in cold-laid plant mixes, road mixes (mixed-in-place), and as surface treatments.


Slow-Curing Asphalts


Slow-curing (SC) asphalts can be obtained directly as slow-curing straight run asphalts through the distillation of crude petroleum or as slow-curing cutback asphalts by “cutting back” asphalt cement with a heavy distillate, such as diesel oil.

They have lower viscosities than asphalt cement and are very slow to harden. Slow-curing asphalts usually are designated as SC-70, SC-250, SC-800, or SC-3000, where the numbers relate to the approximate kinematic viscosity in centistokes at 60°C (140°F). Specifications for the use of these asphalts are no longer included in The American Association of State Highway and Transportation Officials (AASHTO) Standard Specifications for Transportation Materials.


Medium-Curing Cutback Asphalts


Medium-curing (MC) asphalts are produced by fluxing, or cutting back, the residual asphalt (usually 120 to 150 penetration) with light fuel oil or kerosene. The term medium refers to the medium volatility of the kerosene-type diluter used. Mediumcuring cutback asphalts harden faster than slow-curing liquid asphalts, although consistencies of the different grades are similar to those of the slow-curing asphalts.


However, the MC-30 is a unique grade in this series as it is very fluid and has no counterpart in the SC and RC series.
The fluidity of medium-curing asphalts depends on the amount of solvent in the material. MC-3000, for example, may have only 20 percent of the solvent by volume, whereas MC-70 may have up to 45 percent. These medium-curing asphalts can be used for the construction of pavement bases, surfaces, and surface treatments.

 

Rapid-Curing Cutback Asphalts


Rapid-curing (RC) cutback asphalts are produced by blending asphalt cement with a petroleum distillate that will evaporate easily, thereby facilitating a quick change from the liquid form at the time of application to the consistency of the original asphalt cement. Gasoline or naphtha generally is used as the solvent for this series of asphalts.

The grade of rapid-curing asphalt required dictates the amount of solvent to be added to the residual asphalt cement. For example, RC-3000 requires about 15 percent of distillate, whereas RC-70 requires about 40 percent. These grades of asphalt can be used for jobs similar to those for which the MC series is used. Specifications for the use of these asphalts are given in AASHTO’s Standard Specifications for Transportation Materials.

 

Emulsified Asphalts

 

Emulsified asphalts are produced by breaking asphalt cement, usually of 100 to 250 penetration range, into minute particles and dispersing them in water with an emulsifier.

These minute particles have like-electrical charges and therefore do not coalesce. They remain in suspension in the liquid phase as long as the water does not evaporate or the emulsifier does not break.

Asphalt emulsions therefore consist of asphalt, which makes up about 55 to 70 percent by weight, water, and an emulsifying agent, which in some cases also may contain a stabilizer.


Asphalt emulsions generally are classified as anionic, cationic, or nonionic. The first two types have electrical charges surrounding the particles, whereas the third type is neutral. Classification as anionic or cationic is based on the electrical charges that surround the asphalt particles.

Emulsions containing negatively charged particles of asphalt are classified as anionic, and those having positively charged particles of asphalt are classified as cationic.

The anionic and cationic asphalts generally are used
in highway maintenance and construction, although it is likely that the nonionics may be used more frequently in the future as emulsion technology advances.


Each of these categories is further divided into three subgroups based on how rapidly the asphalt emulsion returns to the state of the original asphalt cement. These subgroups are rapid-setting (RS), medium-setting (MS), and slow-setting (SS).


A cationic emulsion is identified by placing the letter “C” in front of the emulsion type; no letter is placed in front of anionic and nonionic emulsions. For example, CRS-2 denotes a cationic emulsion, and RS-2 denotes either an anionic or nonionic emulsion.


Emulsified asphalts are used in cold-laid plant mixes and road mixes (mixedin-place) for several purposes, including the construction of highway pavement surfaces and bases and in surface treatments.

Note, however, that since anionic emulsions contain negative charges, they are more effective in treating aggregates containing electropositive charges (such as limestone), whereas cationic emulsions are more effective with electronegative aggregates (such as those containing a high percentage of siliceous material).

Also note that ordinary emulsions must be protected during very cold spells because they will break down if frozen. Three grades of high-float, medium-setting anionic emulsions designated as HFMS have been developed and are
used mainly in cold and hot plant mixes and coarse aggregate seal coats. These highfloat emulsions have one significant property: They can be laid at relatively thicker films without a high probability of runoff.

Specifications for the use of emulsified asphalts are given in AASHTO M140 and
ASTM D977.

Blown Asphalts

 

Blown asphalt is obtained by blowing air through the semisolid residue obtained during the latter stages of the distillation process.

The process involves stopping the regular distillation while the residue is in the liquid form and then transferring it into a tank known as a converter. The material is maintained at a high temperature while
air is blown through it.

This is continued until the required properties are achieved.
Blown asphalts are relatively stiff compared to other types of asphalts and can maintain a firm consistency at the maximum temperature normally experienced when exposed to the environment.


Blown asphalt generally is not used as a paving material. However, it is very useful  as a roofing material, for automobile undercoating, and as a joint filler for concrete pavements.

If a catalyst is added during the air-blowing process, the material obtained usually will maintain its plastic characteristics, even at temperatures much lower than that at which ordinary asphalt cement will become brittle. The elasticity of catalytically blown asphalt is similar to that of rubber, and it is used for canal lining.

 

Road Tars

 

Tars are obtained from the destructive distillation of such organic materials as coal.
Their properties are significantly different from petroleum asphalts. In general, they are more susceptible to weather conditions than similar grades of asphalts, and they set more quickly when exposed to the atmosphere. Because tars now are used rarely for highway pavements, this text includes only a brief discussion of the subject.


The American Society for Testing Materials (ASTM) has classified road tars into three general categories based on the method of production.

  1. Gashouse coal tars are produced as a by-product in gashouse retorts in the manufacture of illuminating gas from bituminous coals.
  2. Coke-oven tars are produced as a by-product in coke ovens in the manufacture of
    coke from bituminous coal.
  3. Water-gas tars are produced by cracking oil vapors at high temperatures in the
    manufacture of carburated water gas.

Road tars also have been classified by AASHTO into 14 grades: RT-1 through RT-12, RTCB-5, and RTCB-6. RT-1 has the lightest consistency and can be used effectively at normal temperatures for prime or tack coat (described later in this
chapter).

The viscosity of each grade increases as the number designation increases to RT-12, which is the most viscous. RTCB-5 and RTCB-6 are suitable for application during cold weather, since they are produced by cutting back the specific grade of tar with easily evaporating solvent. Detailed specifications for the use of tars are given by AASHTO Designation M52-78.

What is Frost Action In Soils?

What is Frost Action In Soils?

 

When the ambient temperature falls below freezing for several days, it is quite likely that the water in soil pores will freeze. Since the volume of water increases by about 10 percent when it freezes, the first problem is the increase in volume of the soil.

The second problem is that the freezing can cause ice crystals and lenses that are several centimeters thick to form in the soil. These two problems can result in heaving of the subgrade (frost heave), which may result in significant structural damage to the pavement.


In addition, the ice lenses melt during the spring (spring thaw), resulting in a considerable increase in the water content of the soil. This increase in water significantly reduces the strength of the soil, causing structural damage of the highway pavement known as “spring break-up.”


In general, three conditions must exist for severe frost action to occur:
1. Ambient temperature must be lower than freezing for several days.
2. The shallow water table that provides capillary water to the frost line must be
available.
3. The soil must be susceptible to frost action.


The first condition is a natural phenomenon and cannot be controlled by humans. Frost action therefore will be more common in cold areas than in warm areas if all other conditions are the same.

The second condition requires that the groundwater table be within the height of the capillary rise, so that water will be continuously fed to the growing ice lenses.

The third condition requires that the soil material be of such quality that relatively high capillary pressures can be developed, but at the same time that the flow of water through its pores is restricted.


Granular soils are therefore not susceptible to frost action because they have a relatively high coefficient of permeability. Clay soils also are not highly susceptible to frost action because they have very low permeability, so not enough water can flow during a freezing period to allow the formulation of ice lenses.

Sandy or silty clays or cracked clay soils near the surface, however, may be susceptible to frost action. Silty soils are most susceptible to frost action. It has been determined that 0.02 mm is the critical grain size for frost susceptibility.

For example, gravels with 5 percent of 0.02 mm particles are in general susceptible to frost action, whereas well-graded soils with only 3 percent by weight of their material finer than 0.02 mm are susceptible, and fairly uniform soils must contain at least 10 percent of 0.02 mm particles to be frostsusceptible.

Soils with less than 1 percent of their material finer than the critical size are rarely affected by frost action.

Current measures taken to prevent frost action, include removing frost-susceptible soils to the depth of the frost line and replacing them with gravel material, lowering the water table by installing adequate drainage facilities, using impervious membranes or chemical additives, and restricting truck traffic on some roads during the spring thaw.

error: Content is protected !!
Exit mobile version