Crushing concrete and recycling waste concrete into valuable building material
Concrete ranks among the most important recycled raw materials. It can be found virtually everywhere, is particularly high in quality and is very strong. This means that it can be reused in an extremely wide variety of ways.
Here are only some of the many opportunities: aggregate in the concrete industry, road substructures, ready-mixed concrete industry, concrete blocks, paving, prefabricated concrete elements and many more.
After tearing down a building using specialized equipment, such as high-reach excavators, our crew places concrete into discrete piles and removes extraneous materials. Using an excavator, workers load the salvaged pieces of concrete into a crusher.
The machine grinds the pieces of concrete into gravel-sized chunks that are great for structural fill, pipe bedding, road compaction and other applications. You can also mix crushed concrete with sand, water, Portland cement and aggregate to make new concrete that’s stronger and lighter than using concrete made of materials. After concrete passes through a crusher, workers separate the pieces by size and remove any scrap metal using strong electromagnets.
Jaw crusher is mainly used as coarse crusher and medium crusher in mining, building materials, infrastructure and other departments. It is divided into three types: large, medium, and small according to the width of the inlet. The machine with a width of more than 600MM is a large machine, the machine with a width of 300-600MM is a medium-sized machine, and the width of the inlet is less than 300MM. machine. Jaw crusher has simple structure, easy manufacture and reliable work.
The working part of the jaw crusher is two jaws, one is a fixed jaw (fixed jaw), is fixed vertically (or the upper end is slightly inclined) on the front wall of the machine body, and the other is a movable jaw (movable jaw). It is inclined to form a large and small crushing cavity (working cavity) with the fixed jaw plate. The movable jaw plate periodically reciprocates against the fixed jaw plate, sometimes separated and sometimes approached. When separated, the material enters the crushing cavity, and the finished product is discharged from the lower part; when approaching, the material installed between the two jaws is crushed by squeezing, bending and splitting.
Jaw crushers use two vertically-oriented tapered “jaws” that work similarly as a nutcracker’s jaws. A flywheel makes the jaws open and close, allowing only small pieces of concrete to pass.
The impact crusher can handle materials with a side length of 100-500 mm, with a pressure resistance of up to 350 MPa. It has the advantages of large crushing ratio and cubic particles after crushing. Widely used in building materials, ore crushing, railway, highway, energy, transportation, energy, cement, mining, chemical and other industries for medium and fine crushed materials. The size of the discharge granularity can be adjusted, and the crushing specifications are diversified.
The impact crusher is named according to the working principle, that is, the material is crushed by the principle of impact crushing. It is a crusher equipment that is finer than the jaw crusher. It is mainly used for fine crushing in stone production lines The crusher performs cooperative crushing.
Some impact crushers fling pieces of concrete against a hard surface at a high velocity, causing the material to break naturally along internal fissures. Other types of impact crushers use a hammer to break concrete placed on the outer edge of a spinning rotor. This type of crusher is great for concrete with wire mesh or rebar.
When the water content of the processed material is too large, the feeding chute and the impact plate of the impact crusher can be equipped with heating devices to prevent the material from sticking. The impact crusher does not need to be equipped with a bottom sieve plate to effectively prevent clogging.
The hammer of the impact crusher is mechanically clamped on the rotor and has a large moment of inertia when rotating with the rotor. Compared with the hammer crusher (the hammer head is in a suspended state), the rotor of the impact crusher has greater momentum, which is suitable for crushing harder materials, and they also have lower energy consumption.
The impact crusher can adjust the discharge granularity in various ways, such as adjusting the rotor speed, adjusting the gap between the impact plate and the grinding chamber. The clearance adjustment can be adjusted mechanically or hydraulically. The hydraulic adjustment system can be used to conveniently adjust the clearance by operating the button or the travel control system on the spot.
The wear of the hammer of the impact stone breaker only occurs on the side facing the material. When the rotor speed is normal, the feed will fall to the surface of the hammer (hitting surface), and the back and sides of the hammer will not be worn. Even the wear on the side facing the material is minimal. And the bottom grinding rod is easy to replace. The metal utilization rate of the impact crusher hammer can reach 45% -48%.
Only 6 plate hammers are installed on the impact crusher rotor, and the plate hammer can be easily replaced with the designed special tools. It only takes one shift time to replace a set of plate hammers.
Cone crushers are not commonly used on Oregon demolition sites. They have a conical shape and accept concrete at the base. Two gyrating spindles inside the machine squeeze the pieces of concrete together, causing them to break and exit through an opening in the cone.
The full noise encapsulation of the jaw crusher absorbed the crushing noise so effectively that the only sounds heard at the site were the hum of the diesel engines of the and the excavator, as well as the chink of the steel bars falling onto the pile.
An official crushing noise measurement was taken at the same site, and it proved that the operation noise was significantly lower than with conventional crushers. According to the measurements, the area within 3–5 meters of the machine was the only zone in which the noise exceeded 85 dB, and where hearing protection were needed.
Thanks to the encapsulation of the crusher and the covered conveyor, there was practically no dust during concrete crushing, eliminating the need for the standard high-pressure spraying.
“We’re just learning to use the machine, but we’ve already reached a capacity of more than 200 metric tons per hour and 3,000 metric tons in a 12-hour shift. Who knows where we’ll end up next week, when we start proper work with a machine that is now more familiar to us?” Mikko Mähönen muses.
Aggregates producers and recyclers of concrete and asphalt rubble and C&D (construction and demolition) debris basically use two types of comminution devices: compression crushers and primary impact crushers. The primary impact crusher is far more productive for recycling as well as many aggregate-crushing operations.
Compression crushers are of three varieties--all being designed to handle aggregates and each having its limitations for recycling applications.
Jaws normally are used as primary crushers, handling incoming, previously uncrushed materials. Because of their small reduction ratio, jaws normally find use in combination with cone and roll crushers that further reduce the size of materials coming from the primary and secondary crusher. The jaw/cone (primary/secondary) combination is most common.
Impact crushers shatter materials by striking them with blow bars mounted on a horizontal rotor. Rotor speed can be varied according to the type of application and materials being crushed.
Prior to WWII, impact crushers mainly found use as secondary aggregate crushers. After the war certain horizontal-shaft impact crushers were designed by Hazemag specifically as primary crushers to process rubble in bombed out cities. It has major advantages over any jaw, jaw/cone, or jaw/cone/roll combination for recycling operations.
The recycling impact crusher is much faster and has a larger reduction ratio than a jaw crusher. Thus, it is more efficient and usually does not require a secondary crusher. Generally, a primary impact crusher costs more than a jaw crusher but less than a jaw/cone system, and thus can save money in its purchase as well as in more efficient production.
A jaw crusher bites up large pieces of material, such as concrete slabs and lengths of curbstone, slowly, piece by piece, and often leaves steel mesh and rebar still embedded in the concrete. The recycling impact crusher shatters concrete instantly, leaving steel clean enough to be segregated by an electromagnetic separator on the discharge conveyor for sale to a metals recycler.
Nearly all recycling impactor crushers sold today are road portable—to go where needed and work on site. They range in size from the small, self-contained mini-crusher types designed for use in cramped urban areas to large plants capable of crushing rubble at up to 600 or more tons per hour.
Often recycling impact-crusher plants are set up at road or building demolition and construction sites to crush rubble on the spot for possible immediate use as roadbed, fill, or sub-base for pipelines, buildings, and parking lots. Such availability reduces or eliminates the need to purchase aggregate and results in additional savings in time and hauling costs.
Many quarry operators use the recycling impact crusher instead of jaw crushers and jaw/cone combinations for crushing limestone with a low to normal silica content because of its efficiency and versatility. Some quarry operators also use road-portable impact-crusher plants to disintegrate recyclables, going from quarry to quarry to crush shot limestone as well as accumulations of concrete and asphalt rubble hauled in by local construction and demolition contractors.
Primary impact crushers also find application at landfills for crushing rubble and C&D debris. Materials such as drywall, asphalt shingles, wood, and dirt--often included in C&D debris--pose no problem for properly designed impact-crusher systems that include such attendant operations as picking stations, air classifiers, wood shredders and electromagnetic separators.
Impact crushers are available in primary and secondary varieties. The former's design is suitably substantial to withstand the rigors of continuous large-object breakup. Secondary crushers occasionally are unadvisedly substituted for primary crushers by enlarging their intakes. Each type crusher has its place and should be used accordingly.