How Do You Select The Best Driveway or Asphalt Driveway?
Driveway to a farm Driveway apron and sloped curb to a public street, all under construction
A driveway (also called drive in UK English) Asphalt Driveway in River Club is a type of private road for local access to one or a small group of structures, and is owned and maintained by an individual or group.
Driveways rarely have traffic lights, but some that bear heavy traffic, especially those leading to commercial businesses and parks, do.
Driveways may be decorative in ways that public roads cannot, because of their lighter traffic and the willingness of owners to invest in their construction. Driveways are not resurfaced, snow blown or otherwise maintained by governments. They are generally designed to conform to the architecture of connected houses or other buildings.
Some of the materials that can be used for driveways include concrete, decorative brick, cobblestone, block paving, asphalt, gravel, decomposed granite, and surrounded with grass or other ground-cover plants.
Driveways are commonly used as paths to private garages, carports, or houses. On large estates, a driveway may be the road that leads to the house from the public road, possibly with a gate in between. Some driveways divide to serve different homeowners. A driveway may also refer to a small apron of pavement in front of a garage with a curb cut in the sidewalk, sometimes too short to accommodate a car.
Often, either by choice or to conform with local regulations, cars are parked in driveways in order to leave streets clear for traffic. Moreover, some jurisdictions prohibit parking or leaving standing any motor vehicle upon any residential lawn area (defined as the property from the front of a residential house, condominium, or cooperative to the street line other than a driveway, walkway, concrete or blacktopped surface parking space). Other examples include the city of Berkeley, California that forbids “any person to park or leave standing, or cause to be parked or left standing any vehicle upon any public street in the City for seventy-two or more consecutive hours.” Other areas may prohibit leaving vehicles on residential streets during certain times (for instance, to accommodate regular street cleaning), necessitating the use of driveways.
Residential driveways are also used for such things as garage sales, automobile washing and repair, and recreation, notably (in North America) for basketball practice.
Another form of driveway is a ‘Run-Up’, or short piece of land used usually at the front of the property to park a vehicle on.
Interesting Facts About Asphalt Driveway in Boksburg:
About Asphalt Driveway in Boksburg:Macadam country road[dubious – discuss]
Macadam is a type of road construction, pioneered by Scottish engineer John Loudon McAdam around 1820, in which single-sized crushed stone layers of small angular stones are placed in shallow lifts and compacted thoroughly. A binding layer of stone dust (crushed stone from the original material) may form; it may also, after rolling, be covered with a binder to keep dust and stones together. The method simplified what had been considered state of the art at that point.
Pierre-Marie-Jérôme Trésaguet is sometimes considered the first person to bring post-Roman science to road building. A Frenchman from an engineering family, he worked paving roads in Paris from 1757 to 1764. As chief engineer of road construction of Limoges, he had opportunity to develop a better and cheaper method of road construction. In 1775, Tresaguet became engineer-general and presented his answer for road improvement in France, which soon became standard practice there.
Trésaguet had recommended a roadway consisting of three layers of stones laid on a crowned subgrade with side ditches for drainage. The first two layers consisted of angular hand-broken aggregate, maximum size 3 inches (7.6 cm), to a depth of about 8 inches (20 cm). The third layer was about 2 inches (5 cm) thick with a maximum aggregate size of 1 inch (2.5 cm). This top level surface permitted a smoother shape and protected the larger stones in the road structure from iron wheels and horse hooves. To keep the running surface level with the countryside, this road was put in a trench, which created drainage problems. These problems were addressed by changes that included digging deep side ditches, making the surface as solid as possible, and constructing the road with a difference in elevation (height) between the two edges, that difference being referred to interchangeably as the road's camber or cross slope.Laying Telford paving in Aspinwall, Pennsylvania, 1908
Thomas Telford, born in Dumfriesshire Scotland, was a surveyor and engineer who applied Tresaguet's road building theories. In 1801 Telford worked for the British Commission of Highlands Roads and Bridges. He became director of the Holyhead Road Commission between 1815 and 1830. Telford extended Tresaguet's theories, but emphasized high-quality stone. He recognized that some of the road problems of the French could be avoided by using cubical stone blocks.
Telford used roughly 12 in × 10 in × 6 in (30 cm × 25 cm × 15 cm) partially shaped paving stones (pitchers), with a slight flat face on the bottom surface. He turned the other faces more vertically than Tresaguet's method. The longest edge was arranged crossways to the traffic direction, and the joints were broken in the method of conventional brickwork, but with the smallest faces of the pitcher forming the upper and lower surfaces.
Broken stone was wedged into the spaces between the tapered perpendicular faces to provide the layer with good lateral control. Telford kept the natural formation level and used masons to camber the upper surface of the blocks. He placed a 6-inch (15 cm) layer of stone no bigger than 6 cm (2.4 in) on top of the rock foundation. To finish the road surface he covered the stones with a mixture of gravel and broken stone. This structure came to be known as "Telford pitching." Telford's road depended on a resistant structure to prevent water from collecting and corroding the strength of the pavement. Telford raised the pavement structure above ground level whenever possible.
Where the structure could not be raised, Telford drained the area surrounding the roadside. Previous road builders in Britain ignored drainage problems and Telford's rediscovery of these principles was a major contribution to road construction. Though notably of around the same time, John Metcalf was a strong advocate that drainage was in fact an important factor to road construction, and astonished colleagues by building dry roads through marshland. He accomplished this by installing a layer of brushwood and heather.John Loudon McAdam (1756–1836)
John Loudon McAdam was born in Ayr, Scotland, in 1756. In 1787, he became a trustee of the Ayrshire Turnpike in the Scottish Lowlands and during the next seven years this hobby became an obsession. He moved to Bristol, England, in 1802 and became a Commissioner for Paving in 1806. On 15 January 1816, he was elected Surveyor-General of roads for the Turnpike Trust and was now responsible for 149 miles of road. He then put his ideas about road construction into practice, the first 'macadamised' stretch of road being Marsh Road at Ashton Gate, Bristol. He also began to actively propagate his ideas in two booklets called Remarks (or Observations) on the Present System of Roadmaking, (which ran nine editions between 1816 and 1827) and A Practical Essay on the Scientific Repair and Preservation of Public Roads, published in 1819.Photograph of macadam road, ca 1850s, Nicolaus, California
McAdam's method was simpler, yet more effective at protecting roadways: he discovered that massive foundations of rock upon rock were unnecessary, and asserted that native soil alone would support the road and traffic upon it, as long as it was covered by a road crust that would protect the soil underneath from water and wear.
Unlike Telford and other road builders of the time, McAdam laid his roads as level as possible. His 30-foot-wide (9.1 m) road required only a rise of 3 inches (7.6 cm) from the edges to the centre. Cambering and elevation of the road above the water table enabled rain water to run off into ditches on either side.
Size of stones was central to the McAdam's road building theory. The lower 20-centimetre (7.9 in) road thickness was restricted to stones no larger than 7.5 centimetres (3.0 in). The upper 5-centimetre (2.0 in) layer of stones was limited to 2 centimetres (0.79 in) size and stones were checked by supervisors who carried scales. A workman could check the stone size himself by seeing if the stone would fit into his mouth. The importance of the 2 cm stone size was that the stones needed to be much smaller than the 10 cm width of the iron carriage tyres that travelled on the road.
McAdam believed that the "proper method" of breaking stones for utility and rapidity was accomplished by people sitting down and using small hammers, breaking the stones so that none of them was larger than six ounces in weight. He also wrote that the quality of the road would depend on how carefully the stones were spread on the surface over a sizeable space, one shovelful at a time.
McAdam directed that no substance that would absorb water and affect the road by frost should be incorporated into the road. Neither was anything to be laid on the clean stone to bind the road. The action of the road traffic would cause the broken stone to combine with its own angles, merging into a level, solid surface that would withstand weather or traffic.
Through his road-building experience, McAdam had learned that a layer of broken angular stones would act as a solid mass and would not require the large stone layer previously used to build roads. Keeping the surface stones smaller than the tyre width made a good running surface for traffic. The small surface stones also provided low stress on the road, so long as it could be kept reasonably dry.Construction of the first macadamized road in the United States (1823). In the foreground, workers are breaking stones "so as not to exceed 6 ounces [170 g] in weight or to pass a two-inch [5 cm] ring".
The first macadam road built in the United States was constructed between Hagerstown and Boonsboro, Maryland and was named at the time Boonsborough Turnpike Road. This was the last section of unimproved road between Baltimore on the Chesapeake Bay to Wheeling on the Ohio River. Stagecoaches traveling the Hagerstown to Boonsboro road in the winter took 5 to 7 hours to cover the 10-mile (16 km) stretch. This road was completed in 1823, using McAdam's road techniques, except that the finished road was compacted with a cast-iron roller instead of relying on road traffic for compaction. The second American road built using McAdam principles was the Cumberland Road which was 73 miles (117 km) long and was completed in 1830 after five years of work.
McAdam's renown is due to his effective and economical construction, which was a great improvement over the methods used by his generation. He emphasized that roads could be constructed for any kind of traffic, and he helped to alleviate the resentment travelers felt toward increasing traffic on the roads. His legacy lies in his advocacy of effective road maintenance and management. He advocated a central road authority and the trained professional official, who could be paid a salary that would keep him from corruption. This professional could give his entire time to his duties and be held responsible for his actions.
McAdam's road building technology was applied to roads by other engineers. One of these engineers was Richard Edgeworth, who filled the gaps between the surface stones with a mixture of stone dust and water, providing a smoother surface for the increased traffic using the roads. This basic method of construction is sometimes known as water-bound macadam. Although this method required a great deal of manual labour, it resulted in a strong and free-draining pavement. Roads constructed in this manner were described as "macadamized."New macadam road construction at McRoberts, Kentucky: pouring tar. 1926
With the advent of motor vehicles, dust became a serious problem on macadam roads. The area of low air pressure created under fast-moving vehicles sucked dust from the road surface, creating dust clouds and a gradual unraveling of the road material. This problem was approached by spraying tar on the surface to create tar-bound macadam. On March 13, 1902 in Monaco, a Swiss doctor, Ernest Guglielminetti, came upon the idea of using tar from Monaco's gasworks for binding the dust. Later a mixture of coal tar and ironworks slag, patented by Edgar Purnell Hooley as tarmac, was introduced.
A more durable road surface (modern mixed asphalt pavement) sometimes referred to in the US as blacktop, was introduced in the 1920s. This pavement method mixed the aggregates into the asphalt with the binding material before they were laid. The macadam surface method laid the stone and sand aggregates on the road and then sprayed it with the binding material. While macadam roads have now been resurfaced in most developed countries, some are preserved along stretches of roads such as the United States' National Road.
Because of the historic use of macadam as a road surface, roads in some parts of the United States (as parts of Pennsylvania) are often referred to as macadam, even though they might be made of asphalt or concrete. Similarly, the term "tarmac" is sometimes colloquially misapplied to asphalt roads or aircraft runways.
Asphalt Driveway in BoksburgA high-speed toll booth on SR 417 near Orlando, Florida, United States. A toll collection area in the United Kingdom. Hong Kong toll booth.
A toll road, also known as a turnpike or tollway, is a public or private road for which a fee (or toll) is assessed for passage. It is a form of road pricing typically implemented to help recoup the cost of road construction and maintenance.
Toll roads have existed in some form since antiquity, with tolls levied on passing travellers on foot, wagon or horseback; but their prominence increased with the rise of the automobile, and many modern tollways charge fees for motor vehicles exclusively. The amount of the toll usually varies by vehicle type, weight, or number of axles, with freight trucks often charged higher rates than cars.
Tolls are often collected at toll booths, toll houses, plazas, stations, bars, or gates. Some toll collection points are unmanned and the user deposits money in a machine which opens the gate once the correct toll has been paid. To cut costs and minimise time delay many tolls today are collected by some form of automatic or electronic toll collection equipment which communicates electronically with a toll payer's transponder. Some electronic toll roads also maintain a system of toll booths so people without transponders can still pay the toll, but many newer roads now use automatic number plate recognition to charge drivers who use the road without a transponder, and some older toll roads are being upgraded with such systems.
Criticisms of toll roads include the time taken to stop and pay the toll, and the cost of the toll booth operators—up to about one third of revenue in some cases. Automated toll paying systems help minimise both of these. Others object to paying "twice" for the same road: in fuel taxes and with tolls.
In addition to toll roads, toll bridges and toll tunnels are also used by public authorities to generate funds to repay the cost of building the structures. Some tolls are set aside to pay for future maintenance or enhancement of infrastructure, or are applied as a general fund by local governments, not being earmarked for transport facilities. This is sometimes limited or prohibited by central government legislation. Also road congestion pricing schemes have been implemented in a limited number of urban areas as a transportation demand management tool to try to reduce traffic congestion and air pollution.A table of tolls in pre-decimal currency for the College Road, Dulwich, London SE21 tollgate.
Toll roads have existed for at least the last 2,700 years, as tolls had to be paid by travellers using the Susa–Babylon highway under the regime of Ashurbanipal, who reigned in the 7th century BC. Aristotle and Pliny refer to tolls in Arabia and other parts of Asia. In India, before the 4th century BC, the Arthashastra notes the use of tolls. Germanic tribes charged tolls to travellers across mountain passes.
A 14th-century example (though not for a road) is Castle Loevestein in the Netherlands, which was built at a strategic point where two rivers meet. River tolls were charged on boats sailing along the river. The Øresund in Scandinavia was once subject to a toll to the Danish Monarch, which once provided a sizable portion of the king's revenue.
Many modern European roads were originally constructed as toll roads in order to recoup the costs of construction, maintenance and as a source of tax money that is paid primarily by someone other than the local residents. In 14th-century England, some of the most heavily used roads were repaired with money raised from tolls by pavage grants. Widespread toll roads sometimes restricted traffic so much, by their high tolls, that they interfered with trade and cheap transportation needed to alleviate local famines or shortages.
Tolls were used in the Holy Roman Empire in the 14th and 15th centuries.
Industrialisation in Europe needed major improvements to the transport infrastructure which included many new or substantially improved roads, financed from tolls. The A5 road in Britain was built to provide a robust transport link between Britain and Ireland and had a toll house every few miles.
In the 20th century, road tolls were introduced in Europe to finance the construction of motorway networks and specific transport infrastructure such as bridges and tunnels. Italy was the first European country to charge motorway tolls, on a 50 km motorway section near Milan in 1924. It was followed by Greece, which made users pay for the network of motorways around and between its cities in 1927. Later in the 1950s and 1960s, France, Spain and Portugal started to build motorways largely with the aid of concessions, allowing rapid development of this infrastructure without massive State debts. Since then, road tolls have been introduced in the majority of the EU Member States.
In the United States, prior to the introduction of the Interstate Highway System and the large federal grants supplied to states to build it, many states constructed their first controlled-access highways by floating bonds backed by toll revenues. Starting with the Pennsylvania Turnpike in 1940, and followed by similar roads in New Jersey (Garden State Parkway (1946) and New Jersey Turnpike, 1952), New York (New York State Thruway, 1954), Massachusetts (Massachusetts Turnpike, 1957), and others, numerous states throughout the 1950s established major toll roads. With the establishment of the Interstate Highway System in the late 1950s, toll road construction in the U.S. slowed down considerably, as the federal government now provided the bulk of funding to construct new freeways, and regulations required that such Interstate highways be free from tolls. Many older toll roads were added to the Interstate System under a grandfather clause that allowed tolls to continue to be collected on toll roads that predated the system. Some of these such as the Connecticut Turnpike and the Richmond–Petersburg Turnpike later removed their tolls when the initial bonds were paid off. Many states, however, have maintained the tolling of these roads, however, as a consistent source of revenue.
As the Interstate Highway System approached completion during the 1980s, states began constructing toll roads again to provide new controlled-access highways which were not part of the original interstate system funding. Houston's outer beltway of interconnected toll roads began in 1983, and many states followed over the last two decades of the 20th century adding new toll roads, including the tollway system around Orlando, Florida, Colorado's E-470, and Georgia State Route 400.
London, in an effort to reduce traffic within the city, instituted the London congestion charge in 2003, effectively making all roads within the city tolled.
In the United States, as states looked for ways to construct new freeways without federal funding again, to raise revenue for continued road maintenance, and to control congestion, new toll road construction saw significant increases during the first two decades of the 21st century. Spurred on by two innovations, the electronic toll collection system, and the advent of high occupancy and express lane tolls, many areas of the U.S saw large road building projects in major urban areas. Electronic toll collection, first introduced in the 1980s, reduces operating costs by removing toll collectors from roads. Tolled express lanes, by which certain lanes of a freeway are designated "toll only", increases revenue by allowing a free-to-use highway collect revenue by allowing drivers to bypass traffic jams by paying a toll. The E-ZPass system, compatible with many state systems, is the largest ETC system in the U.S., and is used for both fully tolled highways and tolled express lanes. Maryland Route 200 and the Triangle Expressway in North Carolina were the first toll roads built without toll booths, with drivers charged via ETC or by optical license plate recognition and are billed by mail.19th-century toll booth in Brooklyn, New York Toll bar in Romania, 1877 Plaque commemorating the suppression of toll on a York bridge in 1914. Main article: Toll roads in Great Britain
Turnpike trusts were established in England and Wales from about 1706 in response to the need for better roads than the few and poorly-maintained tracks then available. Turnpike trusts were set up by individual Acts of Parliament, with powers to collect road tolls to repay loans for building, improving, and maintaining the principal roads in Britain. At their peak, in the 1830s, over 1,000 trusts administered around 30,000 miles (48,000 km) of turnpike road in England and Wales, taking tolls at almost 8,000 toll-gates. The trusts were ultimately responsible for the maintenance and improvement of most of the main roads in England and Wales, which were used to distribute agricultural and industrial goods economically. The tolls were a source of revenue for road building and maintenance, paid for by road users and not from general taxation. The turnpike trusts were gradually abolished from the 1870s. Most trusts improved existing roads, but some new roads, usually only short stretches, were also built. Thomas Telford's Holyhead road followed Watling Street from London but was exceptional in creating a largely new route beyond Shrewsbury, and especially beyond Llangollen. Built in the early 19th century, with many toll booths along its length, most of it is now the A5. In the modern day, one major toll road is the M6 Toll, relieving traffic congestion on the M6 in Birmingham. A few notable bridges and tunnels continue as toll roads including the Severn Bridge, the Dartford Crossing and Mersey Gateway bridge.
Some cities in Canada had toll roads in the 19th century. Roads radiating from Toronto required users to pay at toll gates along the street (Yonge Street, Bloor Street, Davenport Road, Kingston Road) and disappeared after 1895.
19th-century plank roads were usually operated as toll roads. One of the first U.S. motor roads, the Long Island Motor Parkway (which opened on October 10, 1908) was built by William Kissam Vanderbilt II, the great-grandson of Cornelius Vanderbilt. The road was closed in 1938 when it was taken over by the state of New York in lieu of back taxes.Main article: Road pricing
Road tolls were levied traditionally for a specific access (e.g. city) or for a specific infrastructure (e.g. roads, bridges). These concepts were widely used until the last century. However, the evolution in technology made it possible to implement road tolling policies based on different concepts. The different charging concepts are designed to suit different requirements regarding purpose of the charge, charging policy, the network to the charge, tariff class differentiation etc.:
Time Based Charges and Access Fees: In a time-based charging regime, a road user has to pay for a given period of time in which they may use the associated infrastructure. For the practically identical access fees, the user pays for the access to a restricted zone for a period or several days.
Motorway and other Infrastructure Tolling: The term tolling is used for charging a well-defined special and comparatively costly infrastructure, like a bridge, a tunnel, a mountain pass, a motorway concession or the whole motorway network of a country. Classically a toll is due when a vehicle passes a tolling station, be it a manual barrier-controlled toll plaza or a free-flow multi-lane station.
Distance or Area Charging: In a distance or area charging system concept, vehicles are charged per total distance driven in a defined area.
Some toll roads charge a toll in only one direction. Examples include the Sydney Harbour Bridge, Sydney Harbour Tunnel and Eastern Distributor (these all charge tolls city-bound) in Australia, the Severn Bridges where the M4 and M48 in Great Britain crosses the River Severn, in the United States, crossings between Pennsylvania and New Jersey operated by Delaware River Port Authority and crossings between New Jersey and New York operated by Port Authority of New York and New Jersey.This technique is practical where the detour to avoid the toll is large or the toll differences are small.
.Balintawak toll plaza of the North Luzon Expressway in Caloocan, Philippines. The toll barrier has both electronic toll collection and cash payment in the same barrier, before a new toll plaza was added. Tipo toll plaza in Subic–Clark–Tarlac Expressway, Hermosa, Bataan The open road tolling lanes at the West 163rd Street toll plaza, on the Tri-State Tollway near Markham, Illinois, United States
.Overhead cameras and reader attach to gantry on Highway 407 in Ontario. See also: Electronic toll collection
Traditionally tolls were paid by hand at a toll gate. Although payments may still be made in cash, it is more common now to pay by credit card, by pre-paid card, or by an electronic toll collection system. In some places, payment is made using stickers which are affixed to the windscreen.
Three systems of toll roads exist: open (with mainline barrier toll plazas); closed (with entry/exit tolls) and open road (no toll booths, only electronic toll collection gantries at entrances and exits, or at strategic locations on the mainline of the road). Modern toll roads often use a combination of the three, with various entry and exit tolls supplemented by occasional mainline tolls: for example the Pennsylvania Turnpike and the New York State Thruway implement both systems in different sections.
On an open toll system, all vehicles stop at various locations along the highway to pay a toll. (Not to be confused with "open road tolling", where no vehicles stop to pay toll.) While this may save money from the lack of need to construct toll booths at every exit, it can cause traffic congestion while traffic queues at the mainline toll plazas (toll barriers). It is also possible for motorists to enter an 'open toll road' after one toll barrier and exit before the next one, thus travelling on the toll road toll-free. Most open toll roads have ramp tolls or partial access junctions to prevent this practice, known in the U.S. as "shunpiking".
With a closed system, vehicles collect a ticket when entering the highway. In some cases, the ticket displays the toll to be paid on exit. Upon exit, the driver must pay the amount listed for the given exit. Should the ticket be lost, a driver must typically pay the maximum amount possible for travel on that highway. Short toll roads with no intermediate entries or exits may have only one toll plaza at one end, with motorists traveling in either direction paying a flat fee either when they enter or when they exit the toll road. In a variant of the closed toll system, mainline barriers are present at the two endpoints of the toll road, and each interchange has a ramp toll that is paid upon exit or entry. In this case, a motorist pays a flat fee at the ramp toll and another flat fee at the end of the toll road; no ticket is necessary. In addition, with most systems, motorists may pay tolls only with cash and/or change; debit and credit cards are not accepted. However, some toll roads may have travel plazas with ATMs so motorists can stop and withdraw cash for the tolls.
The toll is calculated by the distance travelled on the toll road or the specific exit chosen. In the United States, for instance, the Kansas Turnpike, Ohio Turnpike, Pennsylvania Turnpike, New Jersey Turnpike, most of the Indiana Toll Road, New York State Thruway, and Florida's Turnpike currently implement closed systems.
The Union Toll Plaza on the Garden State Parkway was the first ever to use an automated toll collection machine. A plaque commemorating the event includes the first quarter collected at its toll booths.
The first major deployment of an RFID electronic toll collection system in the United States was on the Dallas North Tollway in 1989 by Amtech (see TollTag). The Amtech RFID technology used on the Dallas North Tollway was originally developed at Sandia Labs for use in tagging and tracking livestock. In the same year, the Telepass active transponder RFID system was introduced across Italy.
Highway 407 in the province of Ontario, Canada, has no toll booths, and instead reads a transponder mounted on the windshields of each vehicle using the road (the rear licence plates of vehicles lacking a transponder are photographed when they enter and exit the highway). This made the highway the first all-automated toll highway in the world. A bill is mailed monthly for usage of the 407. Lower charges are levied on frequent 407 users who carry electronic transponders in their vehicles. The approach has not been without controversy: In 2003 the 407 ETR settled a class action with a refund to users.
Throughout most of the East Coast of the United States, E-ZPass (operated under the brand I-Pass in Illinois) is accepted on almost all toll roads. Similar systems include SunPass in Florida, FasTrak in California, Good to Go in Washington State, and ExpressToll in Colorado. The systems use a small radio transponder mounted in or on a customer's vehicle to deduct toll fares from a pre-paid account as the vehicle passes through the toll barrier. This reduces manpower at toll booths and increases traffic flow and fuel efficiency by reducing the need for complete stops to pay tolls at these locations.E-ZPass lanes at a New Jersey Turnpike (I-95) Toll Gate for Exit 8A in Monroe Township, New Jersey, United States
By designing a tollgate specifically for electronic collection, it is possible to carry out open-road tolling, where the customer does not need to slow at all when passing through the tollgate. The U.S. state of Texas is testing a system on a stretch of Texas 121 that has no toll booths. Drivers without a TollTag have their license plate photographed automatically and the registered owner will receive a monthly bill, at a higher rate than those vehicles with TollTags.
The first all-electric toll road in the eastern United States, the InterCounty Connector (Maryland Route 200) was partially opened to traffic in February 2011, and the final segment was completed in November 2014. The first section of another all-electronic toll road, the Triangle Expressway, opened at the beginning of 2012 in North Carolina.
Some toll roads are managed under such systems as the Build-Operate-Transfer (BOT) system. Private companies build the roads and are given a limited franchise. Ownership is transferred to the government when the franchise expires. This type of arrangement is prevalent in Australia, Canada, Hong Kong, India, South Korea, Japan and the Philippines. The BOT system is a fairly new concept that is gaining ground in the United States, with California, Delaware, Florida, Illinois, Indiana, Mississippi, Texas, and Virginia already building and operating toll roads under this scheme. Pennsylvania, Massachusetts, New Jersey, and Tennessee are also considering the BOT methodology for future highway projects.
The more traditional means of managing toll roads in the United States is through semi-autonomous public authorities. Kansas, Maryland, Massachusetts, New Hampshire, New Jersey, New York, North Carolina, Ohio, Oklahoma, Pennsylvania, and West Virginia manage their toll roads in this manner. While most of the toll roads in California, Delaware, Florida, Texas, and Virginia are operating under the BOT arrangement, a few of the older toll roads in these states are still operated by public authorities.
In France, all toll roads are operated by private companies, and the government takes a part of their profit.
Toll roads have been criticized as being inefficient in various ways:
- They require vehicles to stop or slow down (except open road tolling); manual toll collection wastes time and raises vehicle operating costs.
- Collection costs can absorb up to one-third of revenues, and revenue theft is considered to be comparatively easy.
- Where the tolled roads are less congested than the parallel "free" roads, the traffic diversion resulting from the tolls increases congestion on the road system and reduces its usefulness.
- By tracking the vehicle locations, their drivers are subject to an effectual restriction of their freedom of movement and freedom from excessive surveillance.
A number of additional criticisms are also directed at toll roads in general:
- Toll roads are a form of regressive taxation; that is, compared to conventional taxes for funding roads, they benefit wealthier citizens more than poor citizens.
- If toll roads are owned or managed by private entities, the citizens may lose money overall compared to conventional public funding because the private owners/operators of the toll system will naturally seek to profit from the roads.
- The managing entities, whether public or private, may not correctly account for the overall social costs, particularly to the poor, when setting pricing and thus may hurt the neediest segments of society.
AsphaltNot to be confused with cement or mortar (masonry). Exterior of the Roman Pantheon, finished 128 AD, the largest unreinforced concrete dome in the world. Interior of the Pantheon dome, seen from beneath. The concrete for the coffered dome was laid on moulds, probably mounted on temporary scaffolding. Opus caementicium exposed in a characteristic Roman arch. In contrast to modern concrete structures, the concrete used in Roman buildings was usually covered with brick or stone.
Concrete is a composite material composed of fine and coarse aggregate bonded together with a fluid cement (cement paste) that hardens over time. Most concretes used are lime-based concretes such as Portland cement concrete or concretes made with other hydraulic cements, such as calcium aluminate cements. However, asphalt concrete, which is frequently used for road surfaces, is also a type of concrete, where the cement material is bitumen, and polymer concretes are sometimes used where the cementing material is a polymer.
When aggregate is mixed together with dry Portland cement and water, the mixture forms a fluid slurry that is easily poured and molded into shape. The cement reacts chemically with the water and other ingredients to form a hard matrix that binds the materials together into a durable stone-like material that has many uses. Often, additives (such as pozzolans or superplasticizers) are included in the mixture to improve the physical properties of the wet mix or the finished material. Most concrete is poured with reinforcing materials (such as rebar) embedded to provide tensile strength, yielding reinforced concrete.
Famous concrete structures include the Hoover Dam, the Panama Canal, and the Roman Pantheon. The earliest large-scale users of concrete technology were the ancient Romans, and concrete was widely used in the Roman Empire. The Colosseum in Rome was built largely of concrete, and the concrete dome of the Pantheon is the world's largest unreinforced concrete dome. Today, large concrete structures (for example, dams and multi-storey car parks) are usually made with reinforced concrete.
After the Roman Empire collapsed, use of concrete became rare until the technology was redeveloped in the mid-18th century. Today, concrete is the most widely used human-made material (measured by tonnage).
The word concrete comes from the Latin word "concretus" (meaning compact or condensed), the perfect passive participle of "concrescere", from "con-" (together) and "crescere" (to grow).
Small-scale usage of concrete has been documented to be thousands of years old. Concrete-like materials were used since 6500 BC by the Nabataea traders or Bedouins, who occupied and controlled a series of oases and developed a small empire in the regions of southern Syria and northern Jordan. They discovered the advantages of hydraulic lime, with some self-cementing properties, by 700 BC. They built kilns to supply mortar for the construction of rubble-wall houses, concrete floors, and underground waterproof cisterns. They kept the cisterns secret as these enabled the Nabataea to thrive in the desert. Some of these structures survive to this day.
In the Ancient Egyptian and later Roman eras, builders re-discovered that adding volcanic ash to the mix allowed it to set underwater.
German archaeologist Heinrich Schliemann found concrete floors, which were made of lime and pebbles, in the royal palace of Tiryns, Greece, which dates roughly to 1400–1200 BC. Lime mortars were used in Greece, Crete, and Cyprus in 800 BC. The Assyrian Jerwan Aqueduct (688 BC) made use of waterproof concrete. Concrete was used for construction in many ancient structures.
The Romans used concrete extensively from 300 BC to 476 AD, a span of more than seven hundred years. During the Roman Empire, Roman concrete (or opus caementicium) was made from quicklime, pozzolana and an aggregate of pumice. Its widespread use in many Roman structures, a key event in the history of architecture termed the Roman Architectural Revolution, freed Roman construction from the restrictions of stone and brick materials. It enabled revolutionary new designs in terms of both structural complexity and dimension.
Concrete, as the Romans knew it, was a new and revolutionary material. Laid in the shape of arches, vaults and domes, it quickly hardened into a rigid mass, free from many of the internal thrusts and strains that troubled the builders of similar structures in stone or brick.
Modern tests show that opus caementicium had as much compressive strength as modern Portland-cement concrete (ca. 200 kg/cm2 [20 MPa; 2,800 psi]). However, due to the absence of reinforcement, its tensile strength was far lower than modern reinforced concrete, and its mode of application was also different:
Modern structural concrete differs from Roman concrete in two important details. First, its mix consistency is fluid and homogeneous, allowing it to be poured into forms rather than requiring hand-layering together with the placement of aggregate, which, in Roman practice, often consisted of rubble. Second, integral reinforcing steel gives modern concrete assemblies great strength in tension, whereas Roman concrete could depend only upon the strength of the concrete bonding to resist tension.
The long-term durability of Roman concrete structures has been found to be due to its use of pyroclastic (volcanic) rock and ash, whereby crystallization of strätlingite and the coalescence of calcium–aluminum-silicate–hydrate cementing binder helped give the concrete a greater degree of fracture resistance even in seismically active environments. Roman concrete is significantly more resistant to erosion by seawater than modern concrete; it used pyroclastic materials which react with seawater to form Al-tobermorite crystals over time.Smeaton's Tower
The widespread use of concrete in many Roman structures ensured that many survive to the present day. The Baths of Caracalla in Rome are just one example. Many Roman aqueducts and bridges, such as the magnificent Pont du Gard in southern France, have masonry cladding on a concrete core, as does the dome of the Pantheon.
After the Roman Empire, the use of burned lime and pozzolana was greatly reduced until the technique was all but forgotten between 500 and the 14th century. From the 14th century to the mid-18th century, the use of cement gradually returned. The Canal du Midi was built using concrete in 1670.
Perhaps the greatest driver behind the modern use of concrete was Smeaton's Tower, the third Eddystone Lighthouse in Devon, England. To create this structure, between 1756 and 1759, British engineer John Smeaton pioneered the use of hydraulic lime in concrete, using pebbles and powdered brick as aggregate.
Developed in England in the 19th century, a method for producing Portland cement was patented by Joseph Aspdin in 1824. Aspdin named it due to its similarity to Portland stone which was quarried on the Isle of Portland in Dorset, England. His son William Aspdin is regarded as the inventor of "modern" Portland cement due to his developments in the 1840s.
Reinforced concrete was invented in 1849 by Joseph Monier. In 1889 the first concrete reinforced bridge was built, and the first large concrete dams were built in 1936, Hoover Dam and Grand Coulee Dam.
Many types of concrete are available, distinguished by the proportions of the main ingredients below. In this way or by substitution for the cementitious and aggregate phases, the finished product can be tailored to its application. Strength, density, as well chemical and thermal resistance are variables.
Aggregate consists of large chunks of material in a concrete mix, generally a coarse gravel or crushed rocks such as limestone, or granite, along with finer materials such as sand.
Cement, most commonly Portland cement, is associated with the general term "concrete." A range of other materials can be used as the cement in concrete too. One of the most familiar of these alternative cements is asphalt concrete. Other cementitious materials such as fly ash and slag cement, are sometimes added as mineral admixtures (see below) - either pre-blended with the cement or directly as a concrete component - and become a part of the binder for the aggregate.
To produce concrete from most cements (excluding asphalt), water is mixed with the dry powder and aggregate, which produces a semi-liquid slurry that can be shaped, typically by pouring it into a form. The concrete solidifies and hardens through a chemical process called hydration. The water reacts with the cement, which bonds the other components together, creating a robust stone-like material.
Chemical admixtures are added to achieve varied properties. These ingredients may accelerate or slow down the rate at which the concrete hardens, and impart many other useful properties including increased tensile strength, entrainment of air and water resistance.
Reinforcement is often included in concrete. Concrete can be formulated with high compressive strength, but always has lower tensile strength. For this reason it is usually reinforced with materials that are strong in tension, typically steel rebar.
Mineral admixtures have become more popular over recent decades. The use of recycled materials as concrete ingredients has been gaining popularity because of increasingly stringent environmental legislation, and the discovery that such materials often have complementary and valuable properties. The most conspicuous of these are fly ash, a by-product of coal-fired power plants, ground granulated blast furnace slag, a byproduct of steelmaking, and silica fume, a byproduct of industrial electric arc furnaces. The use of these materials in concrete reduces the amount of resources required, as the mineral admixtures act as a partial cement replacement. This displaces some cement production, an energetically expensive and environmentally problematic process, while reducing the amount of industrial waste that must be disposed of. Mineral admixtures can be pre-blended with the cement during its production for sale and use as a blended cement, or mixed directly with other components when the concrete is produced.
The mix design depends on the type of structure being built, how the concrete is mixed and delivered, and how it is placed to form the structure.Main article: Cement A few tons of bagged cement. This amount represents about two minutes of output from a 10,000 ton per day cement kiln.
Portland cement is the most common type of cement in general usage. It is a basic ingredient of concrete, mortar and many plasters. British masonry worker Joseph Aspdin patented Portland cement in 1824. It was named because of the similarity of its colour to Portland limestone, quarried from the English Isle of Portland and used extensively in London architecture. It consists of a mixture of calcium silicates (alite, belite), aluminates and ferrites - compounds which combine calcium, silicon, aluminium and iron in forms which will react with water. Portland cement and similar materials are made by heating limestone (a source of calcium) with clay or shale (a source of silicon, aluminium and iron) and grinding this product (called clinker) with a source of sulfate (most commonly gypsum).
In modern cement kilns many advanced features are used to lower the fuel consumption per ton of clinker produced. Cement kilns are extremely large, complex, and inherently dusty industrial installations, and have emissions which must be controlled. Of the various ingredients used to produce a given quantity of concrete, the cement is the most energetically expensive. Even complex and efficient kilns require 3.3 to 3.6 gigajoules of energy to produce a ton of clinker and then grind it into cement. Many kilns can be fueled with difficult-to-dispose-of wastes, the most common being used tires. The extremely high temperatures and long periods of time at those temperatures allows cement kilns to efficiently and completely burn even difficult-to-use fuels.
Combining water with a cementitious material forms a cement paste by the process of hydration. The cement paste glues the aggregate together, fills voids within it, and makes it flow more freely.
As stated by Abrams' law, a lower water-to-cement ratio yields a stronger, more durable concrete, whereas more water gives a freer-flowing concrete with a higher slump. Impure water used to make concrete can cause problems when setting or in causing premature failure of the structure.
Hydration involves many different reactions, often occurring at the same time. As the reactions proceed, the products of the cement hydration process gradually bond together the individual sand and gravel particles and other components of the concrete to form a solid mass.
Reaction:Cement chemist notation: C3S + H → C-S-H + CH Standard notation: Ca3SiO5 + H2O → (CaO)·(SiO2)·(H2O)(gel) + Ca(OH)2 Balanced: 2Ca3SiO5 + 7H2O → 3(CaO)·2(SiO2)·4(H2O)(gel) + 3Ca(OH)2 (approximately; the exact ratios of the CaO, SiO2 and H2O in C-S-H can vary) Crushed stone aggregate Main article: Construction aggregate
Fine and coarse aggregates make up the bulk of a concrete mixture. Sand, natural gravel, and crushed stone are used mainly for this purpose. Recycled aggregates (from construction, demolition, and excavation waste) are increasingly used as partial replacements for natural aggregates, while a number of manufactured aggregates, including air-cooled blast furnace slag and bottom ash are also permitted.
The size distribution of the aggregate determines how much binder is required. Aggregate with a very even size distribution has the biggest gaps whereas adding aggregate with smaller particles tends to fill these gaps. The binder must fill the gaps between the aggregate as well as pasting the surfaces of the aggregate together, and is typically the most expensive component. Thus variation in sizes of the aggregate reduces the cost of concrete. The aggregate is nearly always stronger than the binder, so its use does not negatively affect the strength of the concrete.
Redistribution of aggregates after compaction often creates inhomogeneity due to the influence of vibration. This can lead to strength gradients.
Decorative stones such as quartzite, small river stones or crushed glass are sometimes added to the surface of concrete for a decorative "exposed aggregate" finish, popular among landscape designers.
In addition to being decorative, exposed aggregate may add robustness to a concrete.Constructing a rebar cage. This cage will be permanently embedded in poured concrete to create a reinforced concrete structure. Main article: Reinforced concrete
Concrete is strong in compression, as the aggregate efficiently carries the compression load. However, it is weak in tension as the cement holding the aggregate in place can crack, allowing the structure to fail. Reinforced concrete adds either steel reinforcing bars, steel fibers, glass fibers, or plastic fibers to carry tensile loads.
Chemical admixtures are materials in the form of powder or fluids that are added to the concrete to give it certain characteristics not obtainable with plain concrete mixes. In normal use, admixture dosages are less than 5% by mass of cement and are added to the concrete at the time of batching/mixing. (See the section on Concrete Production, below.)The common types of admixtures are as follows:
Inorganic materials that have pozzolanic or latent hydraulic properties, these very fine-grained materials are added to the concrete mix to improve the properties of concrete (mineral admixtures), or as a replacement for Portland cement (blended cements). Products which incorporate limestone, fly ash, blast furnace slag, and other useful materials with pozzolanic properties into the mix, are being tested and used. This development is due to cement production being one of the largest producers (at about 5 to 10%) of global greenhouse gas emissions, as well as lowering costs, improving concrete properties, and recycling wastes.Concrete plant facility showing a Concrete mixer being filled from the ingredient silos.
Concrete production is the process of mixing together the various ingredients—water, aggregate, cement, and any additives—to produce concrete. Concrete production is time-sensitive. Once the ingredients are mixed, workers must put the concrete in place before it hardens. In modern usage, most concrete production takes place in a large type of industrial facility called a concrete plant, or often a batch plant.
In general usage, concrete plants come in two main types, ready mix plants and central mix plants. A ready mix plant mixes all the ingredients except water, while a central mix plant mixes all the ingredients including water. A central mix plant offers more accurate control of the concrete quality through better measurements of the amount of water added, but must be placed closer to the work site where the concrete will be used, since hydration begins at the plant.
A concrete plant consists of large storage hoppers for various reactive ingredients like cement, storage for bulk ingredients like aggregate and water, mechanisms for the addition of various additives and amendments, machinery to accurately weigh, move, and mix some or all of those ingredients, and facilities to dispense the mixed concrete, often to a concrete mixer truck.
Modern concrete is usually prepared as a viscous fluid, so that it may be poured into forms, which are containers erected in the field to give the concrete its desired shape. Concrete formwork can be prepared in several ways, such as Slip forming and Steel plate construction. Alternatively, concrete can be mixed into dryer, non-fluid forms and used in factory settings to manufacture Precast concrete products.
A wide variety of equipment is used for processing concrete, from hand tools to heavy industrial machinery. Whichever equipment builders use, however, the objective is to produce the desired building material; ingredients must be properly mixed, placed, shaped, and retained within time constraints. Any interruption in pouring the concrete can cause the initially placed material to begin to set before the next batch is added on top. This creates a horizontal plane of weakness called a cold joint between the two batches. Once the mix is where it should be, the curing process must be controlled to ensure that the concrete attains the desired attributes. During concrete preparation, various technical details may affect the quality and nature of the product.
When initially mixed, Portland cement and water rapidly form a gel of tangled chains of interlocking crystals, and components of the gel continue to react over time. Initially the gel is fluid, which improves workability and aids in placement of the material, but as the concrete sets, the chains of crystals join into a rigid structure, counteracting the fluidity of the gel and fixing the particles of aggregate in place. During curing, the cement continues to react with the residual water in a process of hydration. In properly formulated concrete, once this curing process has terminated the product has the desired physical and chemical properties. Among the qualities typically desired, are mechanical strength, low moisture permeability, and chemical and volumetric stability.See also: Volumetric concrete mixer and Concrete mixer
Thorough mixing is essential for the production of uniform, high-quality concrete. For this reason equipment and methods should be capable of effectively mixing concrete materials containing the largest specified aggregate to produce uniform mixtures of the lowest slump practical for the work.
Separate paste mixing has shown that the mixing of cement and water into a paste before combining these materials with aggregates can increase the compressive strength of the resulting concrete. The paste is generally mixed in a high-speed, shear-type mixer at a w/cm (water to cement ratio) of 0.30 to 0.45 by mass. The cement paste premix may include admixtures such as accelerators or retarders, superplasticizers, pigments, or silica fume. The premixed paste is then blended with aggregates and any remaining batch water and final mixing is completed in conventional concrete mixing equipment.Decorative plate made of Nano concrete with High-Energy Mixing (HEM) Pouring and smoothing out concrete at Palisades Park in Washington DC. Main article: Concrete slump test
Workability is the ability of a fresh (plastic) concrete mix to fill the form/mold properly with the desired work (vibration) and without reducing the concrete's quality. Workability depends on water content, aggregate (shape and size distribution), cementitious content and age (level of hydration) and can be modified by adding chemical admixtures, like superplasticizer. Raising the water content or adding chemical admixtures increases concrete workability. Excessive water leads to increased bleeding or segregation of aggregates (when the cement and aggregates start to separate), with the resulting concrete having reduced quality. The use of an aggregate blend with an undesirable gradation can result in a very harsh mix design with a very low slump, which cannot readily be made more workable by addition of reasonable amounts of water. An undesirable gradation can mean using a large aggregate that is too large for the size of the formwork, or which has too few smaller aggregate grades to serve to fill the gaps between the larger grades, or using too little or too much sand for the same reason, or using too little water, or too much cement, or even using jagged crushed stone instead of smoother round aggregate such as pebbles. Any combination of these factors and others may result in a mix which is too harsh, i.e., which does not flow or spread out smoothly, is difficult to get into the formwork, and which is difficult to surface finish.
Workability can be measured by the concrete slump test, a simple measure of the plasticity of a fresh batch of concrete following the ASTM C 143 or EN 12350-2 test standards. Slump is normally measured by filling an "Abrams cone" with a sample from a fresh batch of concrete. The cone is placed with the wide end down onto a level, non-absorptive surface. It is then filled in three layers of equal volume, with each layer being tamped with a steel rod to consolidate the layer. When the cone is carefully lifted off, the enclosed material slumps a certain amount, owing to gravity. A relatively dry sample slumps very little, having a slump value of one or two inches (25 or 50 mm) out of one foot (305 mm). A relatively wet concrete sample may slump as much as eight inches. Workability can also be measured by the flow table test.
Slump can be increased by addition of chemical admixtures such as plasticizer or superplasticizer without changing the water-cement ratio. Some other admixtures, especially air-entraining admixture, can increase the slump of a mix.
High-flow concrete, like self-consolidating concrete, is tested by other flow-measuring methods. One of these methods includes placing the cone on the narrow end and observing how the mix flows through the cone while it is gradually lifted.
After mixing, concrete is a fluid and can be pumped to the location where needed.A concrete slab ponded while curing.
A common misconception is that concrete dries as it sets, but the opposite is true - damp concrete sets better than dry concrete. In other words, "hydraulic cement" needs water to become strong. Too much water is counterproductive, but too little water is deleterious. Curing allows concrete to achieve optimal strength and hardness. Curing is the hydration process that occurs after the concrete has been placed. In chemical terms, curing allows calcium-silicate hydrate (C-S-H) to form. To gain strength and harden fully, concrete curing requires time. In around 4 weeks, typically over 90% of the final strength is reached, although strengthening may continue for decades. The conversion of calcium hydroxide in the concrete into calcium carbonate from absorption of CO2 over several decades further strengthens the concrete and makes it more resistant to damage. This carbonation reaction, however, lowers the pH of the cement pore solution and can corrode the reinforcement bars.
Hydration and hardening of concrete during the first three days is critical. Abnormally fast drying and shrinkage due to factors such as evaporation from wind during placement may lead to increased tensile stresses at a time when it has not yet gained sufficient strength, resulting in greater shrinkage cracking. The early strength of the concrete can be increased if it is kept damp during the curing process. Minimizing stress prior to curing minimizes cracking. High-early-strength concrete is designed to hydrate faster, often by increased use of cement that increases shrinkage and cracking. The strength of concrete changes (increases) for up to three years. It depends on cross-section dimension of elements and conditions of structure exploitation. Addition of short-cut polymer fibers can improve (reduce) shrinkage-induced stresses during curing and increase early and ultimate compression strength.
Properly curing concrete leads to increased strength and lower permeability and avoids cracking where the surface dries out prematurely. Care must also be taken to avoid freezing or overheating due to the exothermic setting of cement. Improper curing can cause scaling, reduced strength, poor abrasion resistance and cracking.
During the curing period, concrete is ideally maintained at controlled temperature and humidity. To ensure full hydration during curing, concrete slabs are often sprayed with "curing compounds" that create a water-retaining film over the concrete. Typical films are made of wax or related hydrophobic compounds. After the concrete is sufficiently cured, the film is allowed to abrade from the concrete through normal use.
Traditional conditions for curing involve by spraying or ponding the concrete surface with water. The picture to the right shows one of many ways to achieve this, ponding – submerging setting concrete in water and wrapping in plastic to prevent dehydration. Additional common curing methods include wet burlap and plastic sheeting covering the fresh concrete.
For higher-strength applications, accelerated curing techniques may be applied to the concrete. One common technique involves heating the poured concrete with steam, which serves to both keep it damp and raise the temperature, so that the hydration process proceeds more quickly and more thoroughly.Main article: Pervious concrete
Pervious concrete is a mix of specially graded coarse aggregate, cement, water and little-to-no fine aggregates. This concrete is also known as "no-fines" or porous concrete. Mixing the ingredients in a carefully controlled process creates a paste that coats and bonds the aggregate particles. The hardened concrete contains interconnected air voids totalling approximately 15 to 25 percent. Water runs through the voids in the pavement to the soil underneath. Air entrainment admixtures are often used in freeze–thaw climates to minimize the possibility of frost damage.Two-layered pavers, top layer made of pigmented HEM Nanoconcrete.
Nanoconcrete is created by high-energy mixing (HEM) of cement, sand and water. To ensure the mixing is thorough enough to create nano-concrete, the mixer must apply a total mixing power to the mixture of 30 - 600 watts per kilogram of the mix. This mixing must continue long enough to yield a net specific energy expended upon the mix of at least 5000 joules per kilogram of the mix. A plasticizer or a superplasticizer is then added to the activated mixture which can later be mixed with aggregates in a conventional concrete mixer. In the HEM process, the intense mixing of cement and water with sand provides dissipation of energy and increases shear stresses on the surface of cement particles. This intense mixing serves to divide the cement particles into extremely fine nanometer scale sizes, which provides for extremely thorough mixing. This results in the increased volume of water interacting with cement and acceleration of Calcium Silicate Hydrate (C-S-H) colloid creation.
The initial natural process of cement hydration with formation of colloidal globules about 5 nm in diameter spreads into the entire volume of cement – water matrix as the energy expended upon the mix approaches and exceeds 5000 joules per kilogram.
The liquid activated high-energy mixture can be used by itself for casting small architectural details and decorative items, or foamed (expanded) for lightweight concrete. HEM Nanoconcrete hardens in low and subzero temperature conditions and possesses an increased volume of gel, which reduces capillarity in solid and porous materials.
Bacteria such as Bacillus pasteurii, Bacillus pseudofirmus, Bacillus cohnii, Sporosarcina pasteuri, and Arthrobacter crystallopoietes increase the compression strength of concrete through their biomass. Not all bacteria increase the strength of concrete significantly with their biomass.:143 Bacillus sp. CT-5. can reduce corrosion of reinforcement in reinforced concrete by up to four times. Sporosarcina pasteurii reduces water and chloride permeability. B. pasteurii increases resistance to acid.:146 Bacillus pasteurii and B. sphaericuscan induce calcium carbonate precipitation in the surface of cracks, adding compression strength.:147Main article: Polymer concrete
Polymer concretes are mixtures of aggregate and any of various polymers and may be reinforced. The cement is more costly than lime-based cements, but polymer concretes nevertheless have advantages, they have significant tensile strength even without reinforcement, and they are largely impervious to water. They are frequently used for repair and construction of other applications such as drains.
Concrete, when ground, can result in the creation of hazardous dust. The National Institute for Occupational Safety and Health in the United States recommends attaching local exhaust ventilation shrouds to electric concrete grinders to control the spread of this dust.Main article: Properties of concrete
Concrete has relatively high compressive strength, but much lower tensile strength. For this reason it is usually reinforced with materials that are strong in tension (often steel). The elasticity of concrete is relatively constant at low stress levels but starts decreasing at higher stress levels as matrix cracking develops. Concrete has a very low coefficient of thermal expansion and shrinks as it matures. All concrete structures crack to some extent, due to shrinkage and tension. Concrete that is subjected to long-duration forces is prone to creep.
Tests can be performed to ensure that the properties of concrete correspond to specifications for the application.Compression testing of a concrete cylinder
Different mixes of concrete ingredients produce different strengths. Concrete strength values are usually specified as the lower-bound compressive strength of either a cylindrical or cubic specimen as determined by standard test procedures.
Different strengths of concrete are used for different purposes. Very low-strength - 14 MPa (2,000 psi) or less - concrete may be used when the concrete must be lightweight. Lightweight concrete is often achieved by adding air, foams, or lightweight aggregates, with the side effect that the strength is reduced. For most routine uses, 20 MPa (2,900 psi) to 32 MPa (4,600 psi) concrete is often used. 40 MPa (5,800 psi) concrete is readily commercially available as a more durable, although more expensive, option. Higher-strength concrete is often used for larger civil projects. Strengths above 40 MPa (5,800 psi) are often used for specific building elements. For example, the lower floor columns of high-rise concrete buildings may use concrete of 80 MPa (11,600 psi) or more, to keep the size of the columns small. Bridges may use long beams of high-strength concrete to lower the number of spans required. Occasionally, other structural needs may require high-strength concrete. If a structure must be very rigid, concrete of very high strength may be specified, even much stronger than is required to bear the service loads. Strengths as high as 130 MPa (18,900 psi) have been used commercially for these reasons.The Buffalo City Court Building in Buffalo, NY.
Concrete is one of the most durable building materials. It provides superior fire resistance compared with wooden construction and gains strength over time. Structures made of concrete can have a long service life. Concrete is used more than any other human-made material in the world. As of 2006, about 7.5 billion cubic meters of concrete are made each year, more than one cubic meter for every person on Earth.Main article: Mass concrete Aerial photo of reconstruction at Taum Sauk (Missouri) pumped storage facility in late November, 2009. After the original reservoir failed, the new reservoir was made of roller-compacted concrete.
Due to cement's exothermic chemical reaction while setting up, large concrete structures such as dams, navigation locks, large mat foundations, and large breakwaters generate excessive heat during hydration and associated expansion. To mitigate these effects post-cooling is commonly applied during construction. An early example at Hoover Dam, installed a network of pipes between vertical concrete placements to circulate cooling water during the curing process to avoid damaging overheating. Similar systems are still used; depending on volume of the pour, the concrete mix used, and ambient air temperature, the cooling process may last for many months after the concrete is placed. Various methods also are used to pre-cool the concrete mix in mass concrete structures.
Another approach to mass concrete structures that minimizes cement's thermal byproduct is the use of roller-compacted concrete, which uses a dry mix which has a much lower cooling requirement than conventional wet placement. It is deposited in thick layers as a semi-dry material then roller compacted into a dense, strong mass.Main article: Decorative concrete Black basalt polished concrete floor
Raw concrete surfaces tend to be porous, and have a relatively uninteresting appearance. Many different finishes can be applied to improve the appearance and preserve the surface against staining, water penetration, and freezing.
Examples of improved appearance include stamped concrete where the wet concrete has a pattern impressed on the surface, to give a paved, cobbled or brick-like effect, and may be accompanied with coloration. Another popular effect for flooring and table tops is polished concrete where the concrete is polished optically flat with diamond abrasives and sealed with polymers or other sealants.
Other finishes can be achieved with chiselling, or more conventional techniques such as painting or covering it with other materials.
The proper treatment of the surface of concrete, and therefore its characteristics, is an important stage in the construction and renovation of architectural structures.40-foot cacti decorate a sound/retaining wall in Scottsdale, Arizona Main article: Prestressed concrete
Prestressed concrete is a form of reinforced concrete that builds in compressive stresses during construction to oppose those experienced in use. This can greatly reduce the weight of beams or slabs, by better distributing the stresses in the structure to make optimal use of the reinforcement. For example, a horizontal beam tends to sag. Prestressed reinforcement along the bottom of the beam counteracts this. In pre-tensioned concrete, the prestressing is achieved by using steel or polymer tendons or bars that are subjected to a tensile force prior to casting, or for post-tensioned concrete, after casting.
More than 55,000 miles (89,000 km) of highways in the United States are paved with this material. Reinforced concrete, prestressed concrete and precast concrete are the most widely used types of concrete functional extensions in modern days. See Brutalism.
Extreme weather conditions (extreme heat or cold; windy condition, and humidity variations) can significantly alter the quality of concrete. In cold weather concreting, many precautions are observed. Low temperatures significantly slow the chemical reactions involved in hydration of cement, thus affecting the strength development. Preventing freezing is the most important precaution, as formation of ice crystals can cause damage to the crystalline structure of the hydrated cement paste. If the surface of the concrete pour is insulated from the outside temperatures, the heat of hydration will prevent freezing.
The American Concrete Institute (ACI) definition of cold weather concreting, ACI 306, is:
In Canada, where temperatures tend to be much lower during the cold season, the following criteria is used by CSA A23.1:
The minimum strength before exposing concrete to extreme cold is 500 psi (3.5 MPa). CSA A 23.1 specified a compressive strength of 7.0 MPa to be considered safe for exposure to freezing.
Concrete roads are more fuel efficient to drive on, more reflective and last significantly longer than other paving surfaces, yet have a much smaller market share than other paving solutions. Modern-paving methods and design practices have changed the economics of concrete paving, so that a well-designed and placed concrete pavement will be less expensive on initial costs and significantly less expensive over the life cycle. Another major benefit is that pervious concrete can be used, which eliminates the need to place storm drains near the road, and reducing the need for slightly sloped roadway to help rainwater to run off. No longer requiring discarding rainwater through use of drains also means that less electricity is needed (more pumping is otherwise needed in the water-distribution system), and no rainwater gets polluted as it no longer mixes with polluted water. Rather, it is immediately absorbed by the ground.
Energy requirements for transportation of concrete are low because it is produced locally from local resources, typically manufactured within 100 kilometers of the job site. Similarly, relatively little energy is used in producing and combining the raw materials (although large amounts of CO2 are produced by the chemical reactions in cement manufacture). The overall embodied energy of concrete at roughly 1 to 1.5 megajoules per kilogram is therefore lower than for most structural and construction materials.
Once in place, concrete offers great energy efficiency over the lifetime of a building. Concrete walls leak air far less than those made of wood frames. Air leakage accounts for a large percentage of energy loss from a home. The thermal mass properties of concrete increase the efficiency of both residential and commercial buildings. By storing and releasing the energy needed for heating or cooling, concrete's thermal mass delivers year-round benefits by reducing temperature swings inside and minimizing heating and cooling costs. While insulation reduces energy loss through the building envelope, thermal mass uses walls to store and release energy. Modern concrete wall systems use both external insulation and thermal mass to create an energy-efficient building. Insulating concrete forms (ICFs) are hollow blocks or panels made of either insulating foam or rastra that are stacked to form the shape of the walls of a building and then filled with reinforced concrete to create the structure.A modern building: Boston City Hall (completed 1968) is constructed largely of concrete, both precast and poured in place. Of Brutalist architecture, it was voted "The World's Ugliest Building" in 2008.
Concrete buildings are more resistant to fire than those constructed using steel frames, since concrete has lower heat conductivity than steel and can thus last longer under the same fire conditions. Concrete is sometimes used as a fire protection for steel frames, for the same effect as above. Concrete as a fire shield, for example Fondu fyre, can also be used in extreme environments like a missile launch pad.
Options for non-combustible construction include floors, ceilings and roofs made of cast-in-place and hollow-core precast concrete. For walls, concrete masonry technology and Insulating Concrete Forms (ICFs) are additional options. ICFs are hollow blocks or panels made of fireproof insulating foam that are stacked to form the shape of the walls of a building and then filled with reinforced concrete to create the structure.
Concrete also provides good resistance against externally applied forces such as high winds, hurricanes, and tornadoes owing to its lateral stiffness, which results in minimal horizontal movement. However this stiffness can work against certain types of concrete structures, particularly where a relatively higher flexing structure is required to resist more extreme forces.
As discussed above, concrete is very strong in compression, but weak in tension. Larger earthquakes can generate very large shear loads on structures. These shear loads subject the structure to both tensile and compressional loads. Concrete structures without reinforcement, like other unreinforced masonry structures, can fail during severe earthquake shaking. Unreinforced masonry structures constitute one of the largest earthquake risks globally. These risks can be reduced through seismic retrofitting of at-risk buildings, (e.g. school buildings in Istanbul, Turkey).Concrete spalling caused by the corrosion of rebar Main article: Concrete degradation
Concrete can be damaged by many processes, such as the expansion of corrosion products of the steel reinforcement bars, freezing of trapped water, fire or radiant heat, aggregate expansion, sea water effects, bacterial corrosion, leaching, erosion by fast-flowing water, physical damage and chemical damage (from carbonatation, chlorides, sulfates and distillate water). The micro fungi Aspergillus Alternaria and Cladosporium were able to grow on samples of concrete used as a radioactive waste barrier in the Chernobyl reactor; leaching aluminium, iron, calcium and silicon.The Tunkhannock Viaduct began service in 1912 and is still in regular use more than 100 years later.
Concrete can be viewed as a form of artificial sedimentary rock. As a type of mineral, the compounds of which it is composed are extremely stable. Many concrete structures are built with an expected lifetime of approximately 100 years, but researchers have suggested that adding silica fume could extend the useful life of bridges and other concrete uses to as long as 16,000 years. Coatings are also available to protect concrete from damage, and extend the useful life. Epoxy coatings may be applied only to interior surfaces, though, as they would otherwise trap moisture in the concrete.
A self-healing concrete has been developed that can also last longer than conventional concrete. Another option is to use hydrophobic concrete.Concrete mixing plant in Birmingham, Alabama in 1936
Concrete is widely used for making architectural structures, foundations, brick/block walls, pavements, bridges/overpasses, highways, runways, parking structures, dams, pools/reservoirs, pipes, footings for gates, fences and poles and even boats. Concrete is used in large quantities almost everywhere mankind has a need for infrastructure. Concrete is one of the most frequently used building materials in animal houses and for manure and silage storage structures in agriculture.
The amount of concrete used worldwide, ton for ton, is twice that of steel, wood, plastics, and aluminum combined. Concrete's use in the modern world is exceeded only by that of naturally occurring water.
Concrete is also the basis of a large commercial industry. Globally, the ready-mix concrete industry, the largest segment of the concrete market, is projected to exceed $100 billion in revenue by 2015. In the United States alone, concrete production is a $30-billion-per-year industry, considering only the value of the ready-mixed concrete sold each year. Given the size of the concrete industry, and the fundamental way concrete is used to shape the infrastructure of the modern world, it is difficult to overstate the role this material plays today.Main article: Environmental impact of concrete
The manufacture and use of concrete produce a wide range of environmental and social consequences. Some are harmful, some welcome, and some both, depending on circumstances.
A major component of concrete is cement, which similarly exerts environmental and social effects.:142 The cement industry is one of the three primary producers of carbon dioxide, a major greenhouse gas (the other two being the energy production and transportation industries). As of 2001, the production of Portland cement contributed 7% to global anthropogenic CO2 emissions, largely due to the sintering of limestone and clay at 1,500 °C (2,730 °F).
Concrete is used to create hard surfaces that contribute to surface runoff, which can cause heavy soil erosion, water pollution, and flooding, but conversely can be used to divert, dam, and control flooding.
Concrete is a contributor to the urban heat island effect, though less so than asphalt.
Workers who cut, grind or polish concrete are at risk of inhaling airborne silica, which can lead to silicosis. Concrete dust released by building demolition and natural disasters can be a major source of dangerous air pollution.
The presence of some substances in concrete, including useful and unwanted additives, can cause health concerns due to toxicity and radioactivity. Fresh concrete (before curing is complete) is highly alkaline and must be handled with proper protective equipment.Recycled crushed concrete, to be reused as granular fill, is loaded into a semi-dump truck. Main article: Concrete recycling
Concrete recycling is an increasingly common method for disposing of concrete structures. Concrete debris was once routinely shipped to landfills for disposal, but recycling is increasing due to improved environmental awareness, governmental laws and economic benefits.
Concrete, which must be free of trash, wood, paper and other such materials, is collected from demolition sites and put through a crushing machine, often along with asphalt, bricks and rocks.
Reinforced concrete contains rebar and other metallic reinforcements, which are removed with magnets and recycled elsewhere. The remaining aggregate chunks are sorted by size. Larger chunks may go through the crusher again. Smaller pieces of concrete are used as gravel for new construction projects. Aggregate base gravel is laid down as the lowest layer in a road, with fresh concrete or asphalt placed over it. Crushed recycled concrete can sometimes be used as the dry aggregate for brand new concrete if it is free of contaminants, though the use of recycled concrete limits strength and is not allowed in many jurisdictions. On 3 March 1983, a government-funded research team (the VIRL research.codep) estimated that almost 17% of worldwide landfill was by-products of concrete based waste.
The world record for the largest concrete pour in a single project is the Three Gorges Dam in Hubei Province, China by the Three Gorges Corporation. The amount of concrete used in the construction of the dam is estimated at 16 million cubic meters over 17 years. The previous record was 12.3 million cubic meters held by Itaipu hydropower station in Brazil.
The world record for concrete pumping was set on 7 August 2009 during the construction of the Parbati Hydroelectric Project, near the village of Suind, Himachal Pradesh, India, when the concrete mix was pumped through a vertical height of 715 m (2,346 ft).
The world record for the largest continuously poured concrete raft was achieved in August 2007 in Abu Dhabi by contracting firm Al Habtoor-CCC Joint Venture and the concrete supplier is Unibeton Ready Mix. The pour (a part of the foundation for the Abu Dhabi's Landmark Tower) was 16,000 cubic meters of concrete poured within a two-day period. The previous record, 13,200 cubic meters poured in 54 hours despite a severe tropical storm requiring the site to be covered with tarpaulins to allow work to continue, was achieved in 1992 by joint Japanese and South Korean consortiums Hazama Corporation and the Samsung C&T Corporation for the construction of the Petronas Towers in Kuala Lumpur, Malaysia.
The world record for largest continuously poured concrete floor was completed 8 November 1997, in Louisville, Kentucky by design-build firm EXXCEL Project Management. The monolithic placement consisted of 225,000 square feet (20,900 m2) of concrete placed within a 30-hour period, finished to a flatness tolerance of FF 54.60 and a levelness tolerance of FL 43.83. This surpassed the previous record by 50% in total volume and 7.5% in total area.
The record for the largest continuously placed underwater concrete pour was completed 18 October 2010, in New Orleans, Louisiana by contractor C. J. Mahan Construction Company, LLC of Grove City, Ohio. The placement consisted of 10,251 cubic yards of concrete placed in a 58.5 hour period using two concrete pumps and two dedicated concrete batch plants. Upon curing, this placement allows the 50,180-square-foot (4,662 m2) cofferdam to be dewatered approximately 26 feet (7.9 m) below sea level to allow the construction of the Inner Harbor Navigation Canal Sill & Monolith Project to be completed in the dry.
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