Road

Stable structures require stable foundations. Nature does not always provide the ideal ground conditions – whether for civil engineering or structural engineering projects. Quite often, the existing soil requires preliminary treatment to improve its bearing capacity. In other places, massive rock formations need to be levelled. What methods are used for laying the foundations?

Soil and rock construction 1.

Soil compaction

2. Soil stabilization 3. Routing operations

1.Roads require a stable foundation to be built on. That is why earthmoving operations need to be carried out prior to paving a road’s base, binder and surface course layers. What are the rolling techniques used in soil compaction? In which way will the ground structure influence compaction results? Nature doesn’t always provide the ideal foundation for the construction of roads: natural rock. In the majority of cases, the ground is unstable, offering insufficient bearing capacity. Earthmoving operations are therefore usually the first step in the construction of a new road. When the course has been defined and set out, the ground underlying the new road needs to be prepared. Stable ground will carry the road Compaction is the single most important process in soil construction. Its job is to reduce the volume of pores in the soil to be compacted, which are filled with water and air. Compaction will give soil the desired properties: Its resistance to stresses induced by traffic and climate will be improved by increasing its stability while simultaneously reducing its tendency to swell due to water absorption. The latter will additionally make the soil resistant to frost. Cohesive and non-cohesive soils The process is different for different types of soil. Experts distinguish between cohesive and non-cohesive soils. In cohesive soils like loam, clay or silt, the particles in the soil bond to one another. In non-cohesive soils like gravel or sand, the particles lie side by side without bonding. Soil types can be distinguished as follows in terms of compactability: water-retaining soils, fine grained cohesive soils, coarse grained noncohesive soils, fine and coarse grained mixed soils, and rock. Dynamic compaction is highly effective Dynamic compaction of soils by means of vibrating or oscillating compaction equipment has proved to be particularly effective in earthmoving operations. Compaction is generated by the combined action of the vibrating or oscillating roller drum and the weight of the machine itself. Applying a dynamic load achieves significantly higher compaction effects than applying just the weight force. Compaction requires more than just weight The intensity of compaction is governed by three influencing factors: displacement of the roller drum, meaning the amplitude of the vibration or oscillation, rate of recurrence of the vibration or oscillation, meaning the frequency, and duration, meaning the roller’s travel speed. When these parameters are set correctly, the specified density can be achieved in considerably less roller passes. The right technique for any type of soil Cohesive soils are compacted most effectively using single-drum compactors with padfoot drums applying high amplitudes of approx. 1.8 mm. Non-cohesive soils are best compacted using smooth drums and low amplitudes of between 0.5 mm and 1 mm. The ground has now been prepared to serve as a base for the

upper road structure – unless its moisture content is too high. Excessively wet soils require additional stabilizing.

Single-drum compactors with padfoot drum play their ace in particular when working on wet mixed soils: Trapezoidal studs on the drum produce impressions in the soil, increasing the total surface and enabling the soil to dry.

2. Getting the water out. Road construction requires a stable base. How to improve the nature of existing soil? What are the binding agents used for this purpose. Extremely cohesive and wet soils are not suitable for compaction by rollers. In such cases, the existing soil needs to be stabilized first to improve its bearing capacity and prepare it as a suitable base for the upper pavement structure. Stabilization is a method of soil improvement, its goal being to permanently bind the water in the soil. Lime and cement provide stability This goal is achieved by mixing binding agents – in particular lime or cement – into the soil. Cement stabilization is particularly suitable for making subsoils permanently resistant to traffic loads, ingressing water and frost. Soils that require stabilizing are often very muddy, so that the stabilizing operation needs to be carried out by powerful, all-wheel driven machinery. Wirtgen soil stabilizers are therefore equipped with large, deep-treaded tyres, offer excellent traction, and feature a powerful travel drive system. Their mixing rotors are capable of mixing pre-spread binding agents into the soil at depths of up to 50 cm in one single working pass. Soil stabilization reduces the water content, turning the soil into a crumbly, stabilized mixture that is ideally suited for compaction by single-drum compactors.

Stabilizing the subgrade: The milling and mixing rotor installed in the Wirtgen soil stabilizer is mixing the soil with pre-spread cement.

3. Building roads through stone and rock. Before commencing the actual road building operation, the prerequisites for doing so need to be established first. Heavy equipment is used where roads are to be built on rocky ground. How to create a precise ground level in hard rock? What are the methods used? Hard rock to the core Road builders are confronted not only with subsoils that are excessively soft or instable, but also with bases that are extremely hard – too hard for roads to be built to the specified level without preparing the ground first. This difficulty typically arises when a road is to be built in mountainous terrain or in other areas where the ground is rocky or extremely hard. When that is the case, routing operations need to be carried out first. Cutting through rock with no explosion, no dust Routing operations are frequently carried out on ground which consists of limestone, slate, or granite, but also in other types of rock. Blasting is a common method for removing hard rock, and is accompanied by the inevitable nuisances of noise, dust, and heavy vibrations. Being gentle on the mountains Where blasting is not feasible because houses, industrial estates or railway lines are located in the immediate vicinity of the job site, routes are often produced by cutting through the rock with surface miners. This environmentally friendly method is capable of cutting rock without causing any damaging vibrations and is therefore gentle both on the mountains and on their inhabitants. Carved in stone with pin-point precision Routing operations involve cutting a path through hard rock. Surface miners cut the rock by means of a cutting drum fitted with tungsten carbide tools, and load it onto trucks or dumpers via their slewing discharge conveyor, all in one single working operation. Reusing the cut material The cut material is of uniform size and can therefore be reused as backfill without requiring additional treatment. Surface miners produce a clean and precisely levelled surface which is ideally suited as a base for the road to be built. Producing a stable floor in the tunnel

Routing operations in tunnel construction are no different from those in open terrain. Drilling or blasting of the tunnel tube creates an uneven floor surface that needs to be both lowered and levelled. The same method is applied when lowering the floor of an existing tunnel for the purpose of increasing the tunnel’s headroom. Surface miners remove the existing rock layer by layer until a clean and stable floor surface has been produced, enabling the construction work to continue on a precisely profiled ground level.

A surface miner carrying out routing operations on rocky ground.

New road construction New roads open up the world. The construction of a new road – whether from asphalt or concrete – requires the production of an excellently bonded pavement structure, beginning with a stable base layer and going all the way to a precisely levelled surface course. What are the most important criteria to be considered? What methods need to be applied? What machines used?

1.construction of base layers Base layers are the foundation. The base layer of a road lays the foundation for the upper pavement structure. It must offer excellent bearing capacity, be capable of withstanding a broad range of different climatic conditions, and remain functional over several decades. What materials are used for the construction of base layers? What properties do they need to possess? A strong base for the upper road structure Roads must be capable of withstanding the loads imposed by traffic irrespective of weather conditions. The body of a road is constructed from different layers of different thicknesses, depending on the anticipated traffic load. A layer for the tough job The lowest layer in the upper road structure is built mainly from granular mineral aggregate. The main function of base layers is to reduce the loads induced by traffic to such an extent that the underlying

subgrade is protected from deformation. The required bearing capacity is achieved by using a mixture of gravel, chippings and crushed sand that needs to be compacted to the required density. A gravel layer to protect against frost Roads are exposed to particularly high stresses when the water contained in the pavement structure begins to freeze. Water expands when freezing, which can lead to frost damage that will sooner or later have an impact also on the road surface. This is prevented by a so-called frost blanket which usually consists of a mixture of gravel and sand, supplemented by crushed mineral aggregate. When compacted, these layers of frost-resistant materials conduct water away from the upper pavement layers, reducing tensions very effectively at the same time. The mix makes all the difference Granular base layers are often overlaid with a bituminous or hydraulically bound base layer, with either bitumen, or cement or lime respectively, used as binding agents. A well-graded mixture of mineral aggregate with a fairly high percentage of crushed stone is characteristic of bound base layers. Bituminous bound base layers When using mixes containing bitumen as a binding agent, the resulting base layer is called an asphalt base layer in hot or cold application – depending on whether hot mix or cold mix is used. Bituminous base layers in hot application consist of well-defined mineral aggregate mixtures and road bitumen. Hydraulically bound base layers When the mineral aggregate mixture is bound with cement or lime, the resulting base layer is called a hydraulically bound base layer. Mineral aggregate mixtures used for this type of base layer consist of uncrushed gravel or coarse aggregate, chippings, and crushed or natural sand. Ever more frequently, these mixes also contain a percentage of recycled construction materials.

There are many ways to build a base layer: Placing a base layer with a Vögele road paver.

2. asphalt paving Asphalt paving requires an exceptionally high degree of meticulous logistical planning and management. Care needs to be taken that sufficient quantities of mix are available on site all the time, and that the mix will not cool down prematurely. What types of machines are used for asphalt paving? What is the sequence of operations? There is one machine team which has made itself indispensable to asphalt paving for many decades: road paver and road roller. Very simply put, asphalt is placed by the paver and compacted by the roller. Conveying in longitudinal direction

The asphalt paving gang is always “headed” by the truck driver. He reverses his truck up to the paver to dump the asphalt material into the paver’s receiving hopper. Two independently operating, slightly inclined scraper conveyors then transport the material to the rear part of the machine. Using slightly inclined conveyors permits increased discharge heights, while additionally enabling increased paving thicknesses without pressing the mix into the auger chamber. Reversing the direction of movement The belt speed is controlled in proportion to the filling level at the end of the scraper conveyor. To prevent the loss of paving mix when repositioning the machine, the material can be drawn back by briefly reversing the belt’s direction of movement. Conveying in transverse direction Two independently controlled, rotating feeding augers located between the paver and paving screed spread the material evenly in front of the screed. The augers can be extended so as to fully adapt the conveying width to the machine’s paving width. Sensor control of feeding auger The auger’s speed of rotation is controlled by sensors in proportion to the head of mix in front of the screed. This feature enables the mix quantity to be fully adapted to requirements when paving in bends or at varying paving thicknesses. The auger’s direction of rotation can be reversed if necessary, transporting the mix from the periphery towards the centre. Supply of mix and job site logistics The hot mix should be covered when delivered by charging trucks to ensure that the paving operation is carried out in the most suitable time frame. To guarantee continuous paving, the capacity of the asphalt mixing plant always needs to be higher than the paver’s laydown capacity. Continuous supply of material If the paver stops moving due to lack of material, disruptive lateral joints occur as a result of the paved layer cooling down. When paving standard mix, the paving temperature should be higher than 110°C to allow an as large time frame as possible for compaction. Pre-heating the paving units All paving units need to be heated prior to commencing the paving operation to prevent the mix from sticking to sensitive parts of the machine. Last but not least, the screed needs to be adjusted to the correct paving width. Using the screed for pre-compaction Modern road pavers allow the compaction systems of the paving screed to be controlled in accordance with specific requirements. High-density screeds, in particular, are capable of achieving excellent density values. Optimum final compaction Compaction effected by the high-density screed enables the rollers which follow behind the paver to achieve the overall final density specified by the client in fewer roller passes. In most cases, the road paver is geared for either high density or fast advance speed, both of which have an effect on the number of roller passes required.

Modern road pavers achieve tremendous performance rates: The Super 2500 from Vögele is capable of paving at widths of up to 16 m, and can achieve paving rates of up to 1,500 tons per hour.

3.asphalt compaction

Packing strength into the asphalt road. Compaction is the final procedure in road construction, its goal being to produce a surface texture of high quality. What aspects need to be considered in asphalt compaction? When compacting an asphalt road, what impact will the road’s location or ambient temperatures have on the compacting operation? The goal of asphalt compaction is to create a pavement that offers maximum evenness and stability, while simultaneously increasing both traffic safety and riding comfort. Compaction aims at producing a road surface of maximum regularity and skid resistance, and at creating a permanent bond between the various asphalt layers. Compaction by rollers results in an extremely tight interlock between the individual particles of the mineral aggregate, which enables a high degree of stability, excellent resistance to wear, and permanent evenness to be achieved. Rollers reduce the void content in the asphalt, making it more resistant to loads and more durable. Questions to be clarified prior to commencing work What type of mix will be compacted, and what are the thicknesses of the individual layers? Where’s the job location? On a motorway, in a residential area, on a bridge? The answers to these questions will determine the type of roller to be used for compaction. What will be the paving width and paving speed? That will determine the number of rollers to be used. Getting the rollers ready Rollers are heavy road construction machines used for compacting hot and therefore flexible asphalt pavements. To prevent them from causing damage to the new asphalt surface, they must not come to a halt during the compacting operation. For precisely that reason, machine maintenance is of particular importance. In addition to that, checks need to be carried out prior to commencing work to make sure that the drum is clean, that fuel and engine oil are available in sufficient quantities, and that the water tank has sufficient water for the drum spray system. The effect of temperature on the compaction result The basic rule applies that the higher the temperature of the paved mix, the better will be the compaction result. However, there are no generally applicable rolling temperatures. The ideal temperature range depends on the composition of the asphalt mix, layer thickness, and type of binding agent used.

The different roller passes An experienced roller driver begins compaction at the seams – for instance, the lateral joints to the existing lane. Starting from there, he compacts along the edge of the pavement. In bends, the lane with the smallest radius is compacted first. The next pass is to press down the pavement. In most applications, dynamic compaction is used for the subsequent main compaction phase. Dynamic compaction means that the roller drums are made to vibrate either horizontally (oscillation) or vertically (vibration), thus achieving a significantly higher compaction effect. The operation is completed by a final roller pass that will “iron out” any remaining irregularities in the asphalt pavement or surface to produce a perfect surface finish.

The manoeuvrable small tandem rollers with operating weights ranging from 1.4 to 4.2 tons impress with their high power of compaction.

4.inset concrete paving

Building concrete pavements with modern road construction plant. Concrete is an exceptionally durable material, and is therefore highly suitable in particular for arterial roads that need to withstand extremely high loads caused by heavy traffic. What is the sequence of operations when paving concrete slabs? What machines are used for concrete paving? The standard method of slipform paving is used mostly for large-scale paving applications. Roads, airport runways, and other large traffic surfaces exposed to exceptionally high loads are usually built with the inset paving method. The following sequence of operations is typical of inset paving: Trucks dump the concrete in front of the machine. The slipform paver then performs the following work steps: It distributes the concrete material across the full paving width by means of a spreading auger or spreading plough, and shapes the concrete slab by means of the paving mould. Concrete vibrators inside the mould vibrate at high frequencies, consolidating the concrete by expelling the air entrapped in the material. On dowel bars, tie bars, and joints The slipform paver keeps moving all the time during the paving operation, its working speed ranging from 1 to 2 m per minute. The machine is capable of inserting dowel bars or tie bars into the freshly paved concrete in the same operation, their purpose being to reinforce the new pavement. Joints will be cut into the concrete above these equally spaced reinforcing elements later to ensure that cracks, which are inevitably caused by loads and temperature fluctuations, are transmitted into the concrete pavement in a controlled manner.

A burlap drag finish produces the required grip A finishing beam and super smoother mounted at the rear of the slipform paver remove any irregularities in the new concrete pavement. A burlap drag finish is often applied to produce the required grip, resulting in a surface texture of precisely defined roughness. Uniform hardening is ensured by spraying a curing compound on the freshly paved concrete using a texture curing machine.

Concrete roads were first built in the 19th century. Today, the highly stable material is laid in an economically efficient and highly precise paving operation by giant “road building plant”, the so-called slipform pavers.

5.Offset concrete paving

Slipforming special jobs like bicycle paths, traffic barriers or kerbs. Instead of placing pre-fabricated concrete parts in a manual operation, the required profiles can also be produced by slipform pavers in offset application. What applications can offset concrete paving be used for? What are the advantages of slipform paving when compared to manual construction? Kerbs, barriers in the central reservation of motorways, gutters for water drainage – moulded concrete parts are available in many different shapes. It is, however, much easier and more economically efficient to produce such profiles using the slipform paving technology. Slipform pavers typically produce these socalled monolithic profiles in offset application. A broad variety of special jobs Offset paving offers a tremendous variety of profile shapes and sizes, as the paving mould is mounted on the side of the paver and can have nearly any given contour. Standardized moulds are available for commonly used shapes like the New Jersey profile used for traffic barriers on motorways. For all other profiles, the moulds are customized to the application in question. Economically efficient method Offset applications range from road boundaries and safety barriers with a maximum height of 2 m to artificial runoffs or narrow paths. Offset paving using slipform pavers is an extremely fast and efficient method when compared to manual construction with pre-fabricated concrete parts.

Cast into a homogeneous whole: 2-m high concrete noise barrier.

Road rehabilitation

A new life cycle for worn-out roads.

Roads are exposed to tremendous loads that will sooner or later leave their marks on them. A time will come when every road will be in need of a general overhaul. But no two damage patterns are alike. Which rehabilitation methods offer a cure for distressed roads? What are the differences between them? Which are suitable to be carried out as mobile roadworks?

1.replacing the pavement Replacing the pavement is one of the standard methods in road rehabilitation. What are the challenges posed by this rehabilitation method? What machines are used for replacing the road pavement? What are the methods used for building a new pavement? The challenge of road rehabilitation lies in removing only those layers of a road structure that are actually damaged. Additional conditions frequently stipulate that the flow of traffic must be maintained in spite of extensive reconstruction measures. In view of these prerequisites, the choice of suitable rehabilitation methods in a construction project is often narrowed to one single option: removing the damaged pavement layers by means of cold milling machines. Milling and loading in one operation The tools that cold milling machines use for removing road layers were originally developed for the mining industry. So-called point-attack cutting tools, fitted to a rotating milling drum on the underside of the machine, bite into the road at precisely the specified depth. No material is too hard for these tools: Cold milling machines are even capable of rehabilitating concrete pavements. Whether asphalt or concrete: The material is milled and then directly loaded on trucks to be transported from site, all in one single pass. Ahead of the traffic jam Because traffic is often slow-moving in the area of the job site, car drivers mock the massive cold milling machines by saying that they’re always first in the traffic jam. Few bear in mind, however, that rehabilitation projects using cold milling machines are mostly carried out as mobile roadworks. Alternative

methods would involve a much greater effort. Cold milling of road pavements is unrivalled in terms of both logistics and speed of execution. Road milling machines are team players Not all cold milling machines are as big as a whole apartment. Some models are as small as a passenger car. On many job sites, machines of different sizes frequently work as a team, each one playing its own aces: The large milling machine removes the large surfaces, while the small one takes care of milling off the pavement around “nuisances”, such as manhole covers or kerbstones. Paving and compacting using pavers and rollers Typical of rehabilitation methods using cold milling is that the damaged pavement layers are usually replaced with asphalt – irrespective of whether the distressed pavement consisted of asphalt or concrete. The new surface course or asphalt road structure is paved by road pavers prior to conventional compaction by rollers.

2.fine milling

New grip for old roads. In many road rehabilitation projects, fine milling offers an economically efficient alternative to expensive, time-consuming full rehabilitation measures. What damage patterns are suitable for rehabilitation by fine milling? What are the special characteristics of fine milling drums? Many countries are investing less money in maintaining their road network despite increasing traffic loads. The result is a growing demand for fast and economically efficient solutions that are capable of taking the edge off hazardous stretches of road. Fine milling is such a method, and is predominantly used where bumps and wheel ruts, or slippery surfaces pose an acute danger to traffic safety. Large numbers of tools improve the surface texture Fine milling is a modification of the standard cold milling method, the difference being that the cutting tools on the drum are arranged at much narrower intervals. One speaks of fine milling when the so-called tool spacing is 8 mm or less. These special milling drums are fitted with a much larger number of cutting tools than standard milling drums. New grip for the road The goal of fine milling is to produce a new, precisely defined surface texture. Even though fine milling drums are not capable of eliminating damages that are located deep within the pavement structure, they can produce an even pavement surface with excellent grip. Rehabilitation in one single pass After installing a fine milling drum in the milling drum housing, the cold milling machine cuts grooves into the pavement at intervals of between 8 mm and 3 mm and at a maximum depth of 50 mm, producing a fine surface texture in just one machine pass. Additional work steps, such as paving a new surface layer, are usually not required.

Restoring the skid resistance: new grip for slippery surfaces.

3.paving thin layers hot

Perfectly bonded layers withstand traffic loads. Replacing the entire pavement at full depth is not necessary when damages are limited to the road surface. Paving thin layers in hot application is a viable option for rehabilitating such roads. How does the method work? What are the advantages of paving thin layers in hot application? Rehabilitation methods that can be carried out both quickly and with economic efficiency are becoming increasingly important worldwide. Paving thin layers in hot application is such a method, offering an exceptionally economical alternative to full pavement rehabilitation. Paving thin layers in hot application is eminently suitable for roads in need of rehabilitation but with damages limited to the surface, or poor grip, or pronounced surface irregularities. The surface properties of worn-out roads, such as grip, evenness and noise reduction, can be improved significantly for extended periods of time. Perfect bond between layers is vital In a preliminary operation, surface deformations are removed by cold milling machines fitted with fine milling drums to create an even, slightly roughened road surface. The road texture produced by fine milling offers an ideal base which ensures an excellent bond with the thin pavement layer to be applied. Paving thin layers in hot application is typically carried out by a road paver with an integrated spray module. Spraying the tack coat When using a paver with integrated spray module, the paver seals the base by spraying a tack coat of polymer-modified bitumen emulsion with a minimum bitumen content of 60% in an automated operation, and then applies a 1.2 cm to 2.0 cm thin asphalt surface course in a second operation immediately afterwards, but all in one single pass. When a conventional road paver is used, the bitumen emulsion needs to be sprayed in a separate operation prior to applying the new, thin pavement layer. Rollers create an even road surface Compaction is a big challenge when paving thin layers in hot application, as it requires the layers to be compacted uniformly but without causing irregularities in the surface. Moreover, the specified density needs to be achieved without damaging the underlying, cold pavement layers. These prerequisites require the use of high-quality rollers. Dynamic compaction with oscillation is the ideal compaction method. Alternatively, such layers can be compacted using static rollers, whereas compaction with vibration is not allowed. Economical use of material saves costs

The small layer thickness of the new surface course helps to keep the costs of this method of rehabilitation fairly low. Paving thin layers in hot application uses 30 kg to 50 kg of asphalt mix per m² of the new surface course, which is up to 50% less when compared to conventional “mill and fill” measures. Because it helps to save natural resources, paving thin layers in hot application is also beneficial to the environment.

4.paving thin layers cold

Extending the life cycle of worn-out roads. Paving thin layers in cold application offers a fast and economically efficient alternative to replacing the entire road pavement. What damage patterns are suitable for this application? How to produce a perfect bond between layers? Traffic safety is jeopardized when the road surface gets slippery, when wheel ruts have dug into the pavement, or when the road is covered with bumps and deformations. Paving thin layers in cold application is a method that is increasingly used for restoring road surfaces to good evenness and skid resistance. Known as “microsurfacing” in many countries around the globe, paving thin layers in cold application prolongs the service life of damaged asphalt roads without the need for replacing the entire road pavement. Fine milling paves the way Cold milling machines fitted with fine milling drums prepare the road surface for application of the thin, cold pavement layer. Fine milling removes deformations in the pavement surface. It works at a maximum milling depth of 50 mm, reprofiling the pavement by means of modern levelling technology to produce a level surface. Optimum bond between layers The slightly roughened surface texture produced by fine milling offers the perfect base for creating an excellent bond with the thin layers paved in cold application. The grooves in the fine-milled profile firmly interlock with the thin layers paved in cold application, resulting in excellent layer adhesion. Mix for the new pavement Once the fine milling machines have completed their preliminary operations, the paving mix for the thin, cold pavement layer is produced directly on site by means of automotive mixing and laying machines. It consists of a well-graded mineral aggregate mix with particle sizes ranging from 3 to 8 mm, polymermodified cationic bitumen emulsion, cement and water. Two layers for a new pavement surface The cold paving mix is distributed across the full width in two separate layers, the first being the profile, the second the surface course layer. Economical alternative to full pavement rehabilitation Ever more rarely does the strained financial situation of public budgets permit cost-intensive full rehabilitation measures to be carried out on a large scale. To ensure that the road network is maintained in good condition, alternative methods, such as paving thin layers in cold application, are therefore more popular than ever. Thin layers in cold application offer an economically efficient, but also fast-paced solution. Paving as mobile roadworks Paving thin layers in cold application is suitable to be carried out as mobile roadworks, and the road can be reopened to traffic quickly. More than 5 million square metres of thin layers in cold application are paved in Germany alone each year.

5.inline pave

Asphalt paving technology on the fast lane. The demands placed on pavement rehabilitation keep growing all the time. Jobs need to be completed ever more quickly, but with traffic continuing to move along smoothly all the same. This is where InLine Pave plays its aces. What is the sequence of operations? What are the logistical prerequisites that need to be met? Road construction is facing ever-greater challenges: Roads are exposed to ever-increasing stresses caused by ever-increasing numbers of vehicles. Rehabilitation measures need to be carried out both quickly and with economic efficiency. Placing asphalt pavements in “hot-on-hot” application offers an efficient solution to this problem. Paving hot-on-hot With InLine Pave, the binder and surface courses are paved “in line”, meaning in immediate succession, “hot-on-hot”. The machines used for this application need a maximum space of just 3 m in width, so that traffic can continue to move along on the adjoining lanes. Perfect bond between layers for an extended lifespan Very high pre-compaction of the binder course prevents the materials of binder and surface course layers from getting mixed, guaranteeing the clean separation of both layers and an optimum surface seal. “Hot-onhot” paving achieves an excellent bond between the binder and surface course layers, which not only dispenses with the need for applying a bitumen emulsion but also extends the service life of the road.

6.hot recycling

Old pavements re-mixed. Porous and deformed surface courses can be rehabilitated using the hot recycling method. How does hot recycling work? What prerequisites need to be fulfilled for the application of hot recycling? Many asphalt pavements deform or become brittle over time when exposed to heavy loads, with cracks developing in the upper layers. Such distressed surface courses can be cured by a special recycling method: hot recycling – a method that is always carried out in a mobile operation. Heating the existing pavement In a first step, a heating machine heats the surface course to up to 150°C by means of gas-operated infrared heater panels, softening it so as to enable the recycler to scarify, remove, recycle and re-place it. New surface course from old Hot recycling is used solely for the rehabilitation of damaged asphalt surface courses, which is why an intact layer structure is of vital importance. The pavement structure underlying the surface course must fully comply with all requirements in terms of bearing capacity and frost resistance. The hot recycler processes the existing road pavement, improving it with virgin mix, if necessary. After completion of the recycling operation, the new surface course will fully comply with all requirements once again. Improving the surface texture Hot recycling improves all relevant properties of both the surface and the pavement profile, as well as the composition of the aggregate fractions in the surface course layer. It helps to restore lacking skid resistance, to ensure water drainage, and to eliminate wheel ruts. Economical recycling

Hot recycling offers a tremendous saving potential. Around 85% of truck transports, and 70% of virgin mix can be saved in comparison to replacing the pavement using a milling machine and road paver. A practical example An approximately 5 km long section of road is to be recycled across a width of 5 m, which equals a total area of some 25,000 m². Assuming a weight of 200 kg per m² of surface course, the “classical” method – replacing the pavement – would require around 200 truck transports: 100 for transporting the milled material from site, and 100 for supplying virgin asphalt mix. 30 kg of virgin mix per m² of surface course are added when adhering to the standards of hot recycling, which requires just 30 truck loads of 25 tons each – 170 less than with conventional rehabilitation methods.

Old becomes new: Paving the recycled mix with the Remixer.

7.cold recycling in situ

A cold recycling train builds new roads from old. Cold recycling in-situ is just the right technology when it comes to building a new road from old. It is mostly carried out as mobile roadworks. What are the advantages of “in-situ” cold recycling? How does the method work? In roads which are exposed to very high loads by heavy traffic, damages frequently extend all the way into the pavement subgrade. To repair these damages, the pavement structure needs to be rehabilitated at full depth. Cold recycling gives roads new stability and strength. In contrast to “in-plant” cold recycling, the entire “in-situ” cold recycling process is carried out in one single operation as follows: Special cold recyclers granulate the damaged road layers – usually the surface and binder courses, as well as part of the base layer –, mix the milled material with new binding agents, and place the recycled mix again immediately. Adding precise quantities of binding agents Milling and pulverizing of the existing pavement is carried out by a milling and mixing rotor fitted with tungsten carbide tools similar to those used for cold milling. Inside the machine, the material is then processed in a mixing chamber or compulsory mixer, in which binding agents are added by means of microprocessor control. Some recycler models feature a so-called “variable mixing chamber”: The larger the working depth, the larger is also the mixing chamber volume. The quantity of binding agents to be added increases at the same time, controlled by a computer, in accordance with the machine’s working depth and advance speed. This concept permits optimum processing of the recycling mix. Types of binding agents to be added include bitumen emulsion, foamed bitumen, and cement.

Slurry mixer meters cement quantities Hot bitumen for the production of foamed bitumen, bitumen emulsion, and water – which is always mandatory – are delivered by tanker trucks. Cement can either be pre-spread as a powder ahead of the cold recycler or added using a so-called slurry mixer. The slurry mixer precisely meters the correct quantity of cement, mixes it with water to obtain a cement slurry, and then transfers the liquid binding agent directly into the mixing chamber of the recycler. Pre-spreading of the cement can then be dispensed with. The slurry mixer prevents the development of dust and loss of material, and helps to improve the quality of the recycled layer. Economical and environmentally friendly The tanker trucks supplying binding agents and water travel ahead of and are pushed by the cold recycler, forming a so-called “cold recycling train”. Some Wirtgen cold recycler models are equipped with a paving screed at the rear of the machine for placing the recycled mix. With all other Wirtgen cold recyclers, heavy tandem rollers and single-drum compactors are used for compaction of the recycled mix. A paving screed builds the new road A thin surface course of virgin asphalt mix is usually applied on top of the cold recycled layer by standard road pavers, and is then compacted by rollers. Short construction times and high economic efficiency are marks in favour of this method. The fact that cold recycling “in-situ” helps to save some 600 truck transports of construction material per kilometre of road built clearly shows the tremendous saving potential when compared to the conventional method of replacing the pavement, which requires a much bigger effort in terms of both logistics and personnel.

8.cold recycling in plant

Transporting the old road to the cold recycling mixing plant. When cold recycling road pavements, contractors can choose between processing the milled material “in-situ”, meaning on the job site, or “in-plant”, meaning in a cold mixing plant. Their decision is influenced, however, not only by the damage patterns of the road to be repaired. What are the advantages offered by “in-plant” cold recycling? How does it work? What kinds of damage patterns can cold recycling “in-plant” be used for? One speaks of cold recycling “in-plant” when the reclaimed asphalt material of roads in need of rehabilitation is recycled in a nearby mixing plant, transported back to the job site, and then placed again by road pavers. The method is often used with roads that are exposed to high loads by heavy traffic, and with damages extending all the way into the pavement subgrade, but where site conditions do not allow the operation of an “in-situ” cold recycling train. Cold recycling mixing plant recycles 100% When cold recycling “in-plant”, a mobile cold recycling mixing plant is usually set up in the vicinity of the job site. Trucks deliver the reclaimed asphalt material from the job site straight to the plant. Technically speaking, the cold recycling mixing plant and “in-situ” cold recycler perform one and the same job: The old asphalt material is recycled 100% by adding one or several binding agents. When recycling is complete, trucks transport the cold recycled mix back to the job site. Road paver places the recycled mix Road pavers use the cold recycled material to replace the old pavement of the road with two new layers. A new surface course meeting all the requirements placed on the surface of the recycled road is placed on top of the cold recycled base layer. The cold recycled base layer is ideally suited for compaction by heavy

vibratory rollers. Final compaction of the surface course is similar to that of other construction methods, using oscillation rollers. Recycling mix for stockpiling Cold mix which has been recycled in the cold recycling mixing plant using foamed bitumen as a binding agent is suitable for stockpiling over extended periods of time. Cold mixes do therefore not have to originate from the same job site that they are used for later. Re-mix aggregate fractions “In-plant” cold recycling is mostly used for smaller contracts where setting up and supplying a recycling train with water and binding agents would be less economically efficient. There is, however, an additional argument speaking in favour of transporting the milled material from site: When access to the job site is difficult from a logistical point of view, it is much easier to recycle the milled material separately in a cold recycling mixing plant.

A Wirtgen cold milling machine is removing the asphalt pavement.

Materials mining and processing Economically efficient mining of rock and useful minerals. Uncrushed rock is the main source material for road construction. How are massive lumps of rock turned into mineral aggregate with a precisely defined particle size? New mining methods offer solutions for the selective mining of different kinds of rock. What types of machines are used for carrying out such extremely hard work? What are the advantages of this method? 1.surface mining

Improving the yield with no explosions or damaging vibrations. It is becoming increasingly difficult to mine the precious raw materials buried in the earth. In what way can surface mining offer solutions to this problem? What are its applications? What advantages does surface mining offer in comparison to conventional mining methods? Mechanical mining of useful minerals There is a growing demand in mineral mining for mining methods that are more economically efficient and more environmentally compatible at the same time. Mechanical mining of useful minerals using surface miners is therefore constantly gaining in importance. The method is applied in newly developed open-cast

mine areas or expansions of existing open-cast mines, as well as in rock construction for precise levelling under space-restricted conditions. Selective mining of useful minerals Increasingly difficult geological conditions result in lower contents of useful minerals both in existing and newly developed mineral deposits. Surface mining increases the exploitation rate of mineral deposits, because it enables the minerals to be mined in a selective operation. Selective mining produces a high yield of useful minerals of high purity, while saving natural resources at the same time. Mineral deposits can be exploited right up to the peripheral areas of the mine. Cut, crush and load in one single operation The operating method of surface miners resembles that of cold milling machines. A special cutting drum cuts and crushes the material before it is loaded on dumpers via a robust conveyor system. The material can alternatively be deposited as a windrow between the miner’s crawler tracks – an option that enables surface miners to not only save time but costs and energy as well. No strains through damaging vibrations The raw mineral materials are mined by cutting, not by drilling and blasting, which prevents damaging vibrations in the immediate vicinity of the mining site. Environmentally compatible mining method The low levels of noise and dust developing during the mining operation are yet another mark in favour when compared to conventional drilling and blasting methods. Surface mining permits useful minerals to be mined effectively and without difficulty right up to residential areas or roads. Increased efficiency Surface miners cut and crush the minerals to be mined, producing small-sized material that is ideal for profitable processing, because it requires only minor additional treatment. Mining bauxite, phosphate, kimberlite or salt becomes increasingly profitable, and surface miners are capable of mining even hard lime or granite rock of up to 260 MPa without the need for drilling and blasting. 2.mobile crushers

Crushers are on the move. Versatility and flexibility in application are the major trump cards that mobile crushers play in comparison to stationary crushing plants. What are mobile crushers used for? What are the differences between the various crushing techniques? What about the hardness of the rock to be processed?

Mobile crushers are used in quarries, in mining, on job sites, and in the recycling industry. The robust plants mounted on crawler tracks are capable of processing both rock and recycling material, producing mineral aggregate and recycled building materials respectively for the construction industry. When processing natural stone or recycling material like demolition waste, concrete, asphalt, incineration ash or steel slag, an excavator or wheel loader feeds the material into the mobile crusher. The then produced material is used for road construction or other, similar applications. Flexible relocation A major advantage of mobile crushers is their flexibility in terms of moving from one location to the next. They are suitable for transport, but can also cover short distances within the boundaries of their operating site, whether in a quarry or on the job site, on their own crawler tracks. When operating in quarries, they usually follow the quarry face, processing the stone directly on site.

Short setup times Mobile crushers are loaded on low-loaders when transported over longer distances to a new location. No more than 20 minutes to 1 hour is needed for setting the plant up for operation. Their tremendous flexibility enables the mobile crushers to process even small quantities of material with economic efficiency. Different crushing techniques Crushing techniques distinguish between pressure crushing and impact crushing. Jaw crushers or cone crushers use the so-called pressure crushing technique where material is reduced in size mainly by high pressure between slow-moving wear parts. Impact crushers use the so-called impact crushing technique, in which the rock is accelerated by a massive fast-moving rotor and reduced in size by impacting against breaker walls. Depending on material hardness Jaw crushers are widely used for crushing medium-hard to hard rock, and are mostly used as primary crushers. Impact crushers work as both primary and secondary crushers for processing soft to medium-hard rock, producing larger quantities of fines. Cone crushers are used predominantly as secondary crushers for hard rock. Mobile screening technology and grain size Mobile plants allow the combination of pre-screening, which prepares the rock for the crushing process, and grading, which precisely separates defined grain sizes into different end products, to be integrated with the crushing unit into one single machine. In the first stage, the material is screened using an active pre-screen. After pre-screening, it is transferred to the crusher, from where it is either stockpiled via a discharge conveyor or forwarded to a final screen or a secondary crushing stage. Depending on the specified end product, the grains are then either graded by screening units or transported to additional crushing stages by secondary or tertiary impact crushers or cone crushers, if required. Further, downstream screening units are used for grading the final aggregate fractions. Combining different types of plants The process of pre-screening, crushing and grading described above is a common operation in mobile materials processing, and can be varied in a number of ways. Mobile crushers with up to three crushing stages are increasingly used in modern quarries today. Different mobile crushing and screening plants can be combined for managing more complex crushing and screening jobs that would previously have required a stationary crushing and screening plant.

Natural stone processing with a Mobicat MC120 Z jaw crusher.

3.stationary crushing plant

Breaking it big with stationary processing. Stationary processing plants are specially designed for many years of use in one single, fixed location. What types of crushing and screening equipment do they use for processing stones and recycling material? What advantages do they offer? Stationary processing plants are usually operated in large rock deposits. They are typically designed for a useful life of 20 or more years. In addition to large quarries or the mining industry, stationary plants are also used in the processing of recycling materials, such as demolition waste, concrete, asphalt, incineration ash, or steel slag. Made-to-measure design Two questions need to be answered first of all when designing a stationary processing plant: Where will it be located, and what material will be processed? To meet with the individual requirements placed on the stationary processing plant, the entire plant is then designed and set up in accordance with prevailing local conditions. A feature that all stationary plants have in common is that several crushing and screening units co-operate, forming an integrated system. Different crushing techniques Crushing techniques distinguish between pressure crushing and impact crushing. Jaw crushers or cone crushers use the so-called pressure crushing technique where material is reduced in size mainly by high pressure between slow-moving wear parts. Impact crushers use the so-called impact crushing technique, in which the rock is accelerated by a massive fast-moving rotor and reduced in size by impacting against breaker walls. Sophisticated screening technology In materials processing, the quality of an end product is determined, among other things, by the number of crushing stages and by sufficiently dimensioned screening equipment. A basic distinction is made between pre-screening, which is important for separating the material streams prior to crushing, and grading, which separates the different final aggregate fractions. Pre-screening screening separates material streams Pre-screening screening is used for separating the material streams. Contaminations are also eliminated in this first processing stage. The material is separated via the screening surface, which usually consists of a slotted screen or perforated plate. Grading for the fine range Grading determines the screening quality, meaning the quality of the end product. Grading screens have a screening surface which consists of, for instance, a wire screen for precise separation of the medium and fine aggregate fractions. The graded final aggregate fractions are finally discharged via belt conveyors and stockpiled. Use advantages consistently Stationary processing plants enable large amounts of material to be crushed, and complex processes to be managed. End products of superior quality are produced, complying with the standards to be adhered to in terms of grain size and cubicity, which may differ from one market area to the next. Stationary plants play their aces in particular when it comes to flexibility in production. The crushed aggregate can be stored in several silos, enabling the most diverse aggregate mixtures to be produced right at the plant, and in accordance with the requirements of the customer or end user. Yet another advantage of stationary plants: The production can always be adapted to changing requirements in the sales markets. Reducing the burden on the environment

Preventing the emission of dust is an important aspect of materials processing. Stationary processing plants offer two options for doing so: They either feature water spray systems for binding the dust, or special dust extraction systems. The entire plant can also be fully enclosed to protect the environment from dust and noise.

Stationary processing plant, Stevin Rock, UAE.