gyratory crusher & cone crusher mantle differences

gyratory crusher & cone crusher mantle differences

Any of you that are at all familiar with the Gyratory crushersand Cone Crushers that the former are used as Primary crushers will probably note many similarities between the types.Each use a cone shaped crushing surface, and the same principal in the eccentric is employed to develop the crushing action required.

The difference between the two is first the speed that the mantle travels while crushing the ore. A primary revolves at 100-200 R.P.M. While the Secondary and the Tertiary crushers travels between 500-600 R.P.M. This difference in the speed results in a HAMMERING type crushing action over the SQUEEZING type employed by the primary.

The other most noticeable change is the crushing action of the mantle. In the Gyratory all the movement is in the bottom of the crusher mantle. This is due to the angle that the main shaft is on. The greater angle of the cone crusher puts the pivot point below the distributor plate. While the pivot point for the gyratory crusher is at the spider cap. This difference in the pattern of gyration has a purpose.

The primary crusher produces a product that is gauged by the size of the open side of the mantle. This is because the slow speed of the gyration allows a high percentage of material to fall through the larger opening without being crushed by the smaller opening. With the cone crusher however the gyration has a greater arc and an equally greater speed. If we look at a profile of the crushing surface we will see an area of the two surfaces that are parallel to one another.

This area is called the PARALLEL ZONE. Because of the speed, the primary crusher produces a product that is gauged by the size of the open side of the mantle. This is because the slow speed of the gyration allows a high percentage of material to fall through the larger opening without being crushed by the smaller opening. With the cone crusher however the gyration has a greater arc and an equally greater speed. If we look at a profile of the crushing surface we will see an area of the two surfaces that are parallel to one another that the mantle is travelling at, it is very hard for the ore to pass through this zone without being hit at least once by the crusher.

built to connect - astec

built to connect - astec

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zenith cone crusher 48 gyrasphere

zenith cone crusher 48 gyrasphere

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impact crusher - an overview | sciencedirect topics

impact crusher - an overview | sciencedirect topics

The impact crusher (typically PE series) is widely used and of high production efficiency and good safety performance. The finished product is of cube shape and the tension force and crack is avoided. Compared with hammer crusher, the impact crusher is able to fully utilize the high-speed impact energy of entire rotor. However, due to the crushing board that is easy to wear, it is also limited in the hard material crushing. The impact crusher is commonly used for the crushing of limestone, coal, calcium carbide, quartz, dolomite, iron pyrites, gypsum, and chemical raw materials of medium hardness. Effect of process conditions on the production capacity of crushed materials is listed in Table8.10.

Depending on the size of the debris, it may either be ready to enter the recycling process or need to be broken down to obtain a product with workable particle sizes, in which case hydraulic breakers mounted on tracked or wheeled excavators are used. In either case, manual sorting of large pieces of steel, wood, plastics and paper may be required, to minimise the degree of contamination of the final product.

The three types of crushers most commonly used for crushing CDW materials are the jaw crusher, the impact crusher and the gyratory crusher (Figure 4.4). A jaw crusher consists of two plates, with one oscillating back and forth against the other at a fixed angle (Figure 4.4(a)) and it is the most widely used in primary crushing stages (Behera etal., 2014). The jaw crusher can withstand large and hard-to-break pieces of reinforced concrete, which would probably cause the other crushing machines to break down. Therefore, the material is initially reduced in jaw crushers before going through any other crushing operation. The particle size reduction depends on the maximum and minimum size of the gap at the plates (Hansen, 2004).

An impact crusher breaks the CDW materials by striking them with a high-speed rotating impact, which imparts a shearing force on the debris (Figure 4.4(b)). Upon reaching the rotor, the debris is caught by steel teeth or hard blades attached to the rotor. These hurl the materials against the breaker plate, smashing them into smaller particle sizes. Impact crushers provide better grain-size distribution of RA for road construction purposes, and they are less sensitive to material that cannot be crushed, such as steel reinforcement.

Generally, jaw and impact crushers exhibit a large reduction factor, defined as the ratio of the particle size of the input to that of the output material. A jaw crusher crushes only a small proportion of the original aggregate particles but an impact crusher crushes mortar and aggregate particles alike and thus generates a higher amount of fine material (OMahony, 1990).

Gyratory crushers work on the same principle as cone crushers (Figure 4.4(c)). These have a gyratory motion driven by an eccentric wheel. These machines will not accept materials with a large particle size and therefore only jaw or impact crushers should be considered as primary crushers. Gyratory and cone crushers are likely to become jammed by fragments that are too large or too heavy. It is recommended that wood and steel be removed as much as possible before dumping CDW into these crushers. Gyratory and cone crushers have advantages such as relatively low energy consumption, a reasonable amount of control over the particle size of the material and production of low amounts of fine particles (Hansen, 2004).

For better control of the aggregate particle size distribution, it is recommended that the CDW should be processed in at least two crushing stages. First, the demolition methodologies used on-site should be able to reduce individual pieces of debris to a size that the primary crusher in the recycling plant can take. This size depends on the opening feed of the primary crusher, which is normally bigger for large stationary plants than for mobile plants. Therefore, the recycling of CDW materials requires careful planning and communication between all parties involved.

A large proportion of the product from the primary crusher can result in small granules with a particle size distribution that may not satisfy the requirements laid down by the customer after having gone through the other crushing stages. Therefore, it should be possible to adjust the opening feed size of the primary crusher, implying that the secondary crusher should have a relatively large capacity. This will allow maximisation of coarse RA production (e.g., the feed size of the primary crusher should be set to reduce material to the largest size that will fit the secondary crusher).

The choice of using multiple crushing stages mainly depends on the desired quality of the final product and the ratio of the amounts of coarse and fine fractions (Yanagi etal., 1998; Nagataki and Iida, 2001; Nagataki etal., 2004; Dosho etal., 1998; Gokce etal., 2011). When recycling concrete, a greater number of crushing processes produces a more spherical material with lower adhered mortar content (Pedro etal., 2015), thus providing a superior quality of material to work with (Lotfi etal., 2017). However, the use of several crushing stages has some negative consequences as well; in addition to costing more, the final product may contain a greater proportion of finer fractions, which may not always be a suitable material.

Reduction of the broken rock material, or oversized gravel material, to an aggregate-sized product is achieved by various types of mechanical crusher. These operations may involve primary, secondary and even sometimes tertiary phases of crushing. There are many different types of crusher, such as jaw, gyratory, cone (or disc) and impact crushers (Fig. 15.9), each of which has various advantages and disadvantages according to the properties of the material being crushed and the required shape of the aggregate particles produced.

Fig. 15.9. Diagrams to illustrate the basic actions of some types of crusher: solid shading highlights the hardened wear-resistant elements. (A) Single-toggle jaw crusher, (B) disc or gyrosphere crusher, (C) gyratory crusher and (D) impact crusher.

It is common, but not invariable, for jaw or gyratory crushers to be utilised for primary crushing of large raw feed, and for cone crushers or impact breakers to be used for secondary reduction to the final aggregate sizes. The impact crushing machines can be particularly useful for producing acceptable particle shapes (Section 15.5.3) from difficult materials, which might otherwise produce unduly flaky or elongated particles, but they may be vulnerable to abrasive wear and have traditionally been used mostly for crushing limestone.

Reduction of the broken rock material, or oversized gravel material, to an aggregate-sized product is achieved by various types of mechanical crusher. These operations may involve primary, secondary and even sometimes tertiary phases of crushing. There are many different types of crusher, such as jaw, gyratory, cone (or disc) and impact crushers (Figure 16.8), each of which has various advantages and disadvantages according to the properties of the material being crushed and the required shape of the aggregate particles produced.

Fig. 16.8. Diagrams to illustrate the basic actions of some types of crusher: solid shading highlights the hardened wear-resistant elements (redrawn, adapted and modified from Ref. 39). (a) Single-toggle jaw crusher, (b) disc or gyrosphere crusher, (c) gyratory crusher, and (d) impact crusher.

It is common, but not invariable, for jaw or gyratory crushers to be utilised for primary crushing of large raw feed, and for cone crushers or impact breakers to be used for secondary reduction to the final aggregate sizes. The impact crushing machines can be particularly useful for producing acceptable particle shapes (section 16.5.3) from difficult materials, which might otherwise produce unduly flaky or elongated particles, but they may be vulnerable to abrasive wear and have traditionally been used mostly for crushing limestone.

The main sources of RA are either from construction and ready mixed concrete sites, demolition sites or from roads. The demolition sites produce a heterogeneous material, whereas ready mixed concrete or prefabricated concrete plants produce a more homogeneous material. RAs are mainly produced in fixed crushing plant around big cities where CDWs are available. However, for roads and to reduce transportation cost, mobile crushing installations are used.

The materiel for RA manufacturing does not differ from that of producing NA in quarries. However, it should be more robust to resist wear, and it handles large blocks of up to 1m. The main difference is that RAs need the elimination of contaminants such as wood, joint sealants, plastics, and steel which should be removed with blast of air for light materials and electro-magnets for steel. The materials are first separated from other undesired materials then treated by washing and air to take out contamination. The quality and grading of aggregates depend on the choice of the crusher type.

Jaw crusher: The material is crushed between a fixed jaw and a mobile jaw. The feed is subjected to repeated pressure as it passes downwards and is progressively reduced in size until it is small enough to pass out of the crushing chamber. This crusher produces less fines but the aggregates have a more elongated form.

Hammer (impact) crusher: The feed is fragmented by kinetic energy introduced by a rotating mass (the rotor) which projects the material against a fixed surface causing it to shatter causing further particle size reduction. This crusher produces more rounded shape.

The type of crusher and number of processing stages have considerable influence on the shape and size of RA. In general, for the same size, RAs tend to be coarser, more porous and rougher than NAs, due to the adhered mortar content (Dhir etal., 1999). After the primary crushing, which is normally performed using jaw crushers (Fong etal., 2004), it is preferable to adopt a secondary crushing stage (with cone crushers or impact crushers) (CCANZ, 2011) to further reduce the size of the CDW, producing more regularly shaped particles (Barbudo etal., 2012; Ferreira etal., 2011; Fonseca etal., 2011; Pedro etal., 2014, 2015; Gonzlez-Fonteboa and Martnez-Abella, 2008; Maultzsch and Mellmann, 1998; Dhir and Paine, 2007; Chidiroglou etal., 2008).

CDW that is subjected to a jaw crushing stage tends to result only in flatter RA (Ferreira etal., 2011; Fonseca etal., 2011; Hendriks, 1998; Tsoumani etal., 2015). It is possible to produce good-quality coarse RA within the specified size range by adjusting the crusher aperture (Hansen, 1992). In addition, the number of processing stages needs to be well thought out to ensure that the yield of coarse RA is not affected and that the quantity of fine RA is kept to the minimum (Angulo etal., 2004). This is because the finer fraction typically exhibits lower quality, as it accumulates a higher amount of pulverised old mortar (Etxeberria etal., 2007b; Meller and Winkler, 1998). Fine RA resulting from impact crushers tends to exhibit greater angularity and higher fineness modulus compared with standard natural sands (Lamond etal., 2002; Hansen, 1992; Buyle-Bodin and Hadjieva-Zaharieva, 2002).

One of the commonly known issues related to the use of RCA is its ability to generate a considerable amount of fines when the material is used (Thomas etal., 2016). As the RCA particles are moved around, they impact against one another, leading to the breakage of the friable adhered mortar, which may give rise to some technical problems such as an increase in the water demand of concrete mixes when used as an NA replacement (Thomas etal., 2013a,b; Poon etal., 2007).

The coarse fraction of RMA tends to show a higher shape index owing to the shape of the original construction material (e.g., perforated ceramic bricks) (De Brito etal., 2005). This can pose a problem in future applications as RMA may not compact as efficiently as RCA or NA (Khalaf and DeVenny, 2005). Its shape index may be reduced if the material is successively broken down to a lower particle size (De Brito etal., 2005).

Impact crushers (e.g., hammer mills and impact mills) employ sharp blows applied at high speed to free-falling rocks where comminution is by impact rather than compression. The moving parts are beaters, which transfer some of their kinetic energy to the ore particles upon contact. Internal stresses created in the particles are often large enough to cause them to shatter. These forces are increased by causing the particles to impact upon an anvil or breaker plate.

There is an important difference between the states of materials crushed by pressure and by impact. There are internal stresses in material broken by pressure that can later cause cracking. Impact causes immediate fracture with no residual stresses. This stress-free condition is particularly valuable in stone used for brick-making, building, and roadmaking, in which binding agents (e.g., tar) are subsequently added. Impact crushers, therefore, have a wider use in the quarrying industry than in the metal-mining industry. They may give trouble-free crushing on ores that tend to be plastic and pack when the crushing forces are applied slowly, as is the case in jaw and gyratory crushers. These types of ore tend to be brittle when the crushing force is applied instantaneously by impact crushers (Lewis et al., 1976).

Impact crushers are also favored in the quarry industry because of the improved product shape. Cone crushers tend to produce more elongated particles because of their ability to pass through the chamber unbroken. In an impact crusher, all particles are subjected to impact and the elongated particles, having a lower strength due to their thinner cross section, would be broken (Ramos et al., 1994; Kojovic and Bearman, 1997).

Figure 6.23(a) shows the cross section of a typical hammer mill. The hammers (Figure 6.23(b)) are made from manganese steel or nodular cast iron containing chromium carbide, which is extremely abrasion resistant. The breaker plates are made of the same material.

The hammers are pivoted so as to move out of the path of oversize material (or tramp metal) entering the crushing chamber. Pivoted (swing) hammers exert less force than they would if rigidly attached, so they tend to be used on smaller impact crushers or for crushing soft material. The exit from the mill is perforated, so that material that is not broken to the required size is retained and swept up again by the rotor for further impacting. There may also be an exit chute for oversize material which is swept past the screen bars. Certain design configurations include a central discharge chute (an opening in the screen) and others exclude the screen, depending on the application.

The hammer mill is designed to give the particles velocities of the order of that of the hammers. Fracture is either due to impact with the hammers or to the subsequent impact with the casing or grid. Since the particles are given high velocities, much of the size reduction is by attrition (i.e., particle on particle breakage), and this leads to little control on product size and a much higher proportion of fines than with compressive crushers.

The hammers can weigh over 100kg and can work on feed up to 20cm. The speed of the rotor varies between 500 and 3,000rpm. Due to the high rate of wear on these machines (wear can be taken up by moving the hammers on the pins) they are limited in use to relatively non-abrasive materials. They have extensive use in limestone quarrying and in the crushing of coal. A great advantage in quarrying is the fact that they produce a relatively cubic product.

A model of the swing hammer mill has been developed for coal applications (Shi et al., 2003). The model is able to predict the product size distribution and power draw for given hammer mill configurations (breaker gap, under-screen orientation, screen aperture) and operating conditions (feed rate, feed size distribution, and breakage characteristics).

For coarser crushing, the fixed hammer impact mill is often used (Figure 6.24). In these machines the material falls tangentially onto a rotor, running at 250500rpm, receiving a glancing impulse, which sends it spinning toward the impact plates. The velocity imparted is deliberately restricted to a fraction of the velocity of the rotor to avoid high stress and probable failure of the rotor bearings.

The fractured pieces that can pass between the clearances of the rotor and breaker plate enter a second chamber created by another breaker plate, where the clearance is smaller, and then into a third smaller chamber. The grinding path is designed to reduce flakiness and to produce cubic particles. The impact plates are reversible to even out wear, and can easily be removed and replaced.

The impact mill gives better control of product size than does the hammer mill, since there is less attrition. The product shape is more easily controlled and energy is saved by the removal of particles once they have reached the size required.

Large impact crushers will reduce 1.5m top size ROM ore to 20cm, at capacities of around 1500th1, although units with capacities of 3000th1 have been manufactured. Since they depend on high velocities for crushing, wear is greater than for jaw or gyratory crushers. Hence impact crushers are not recommended for use on ores containing over 15% silica (Lewis et al., 1976). However, they are a good choice for primary crushing when high reduction ratios are required (the ratio can be as high as 40:1) and the ore is relatively non-abrasive.

Developed in New Zealand in the late 1960s, over the years it has been marketed by several companies (Tidco, Svedala, Allis Engineering, and now Metso) under various names (e.g., duopactor). The crusher is finding application in the concrete industry (Rodriguez, 1990). The mill combines impact crushing, high-intensity grinding, and multi-particle pulverizing, and as such, is best suited in the tertiary crushing or primary grinding stage, producing products in the 0.0612mm size range. It can handle feeds of up to 650th1 at a top size of over 50mm. Figure 6.22 shows a Barmac in a circuit; Figure 6.25 is a cross-section and illustration of the crushing action.

The basic comminution principle employed involves acceleration of particles within a special ore-lined rotor revolving at high speed. A portion of the feed enters the rotor, while the remainder cascades to the crushing chamber. Breakage commences when rock enters the rotor, and is thrown centrifugally, achieving exit velocities up to 90ms1. The rotor continuously discharges into a highly turbulent particle cloud contained within the crushing chamber, where reduction occurs primarily by rock-on-rock impact, attrition, and abrasion.

This crusher developed by Jaques (now Terex Mineral Processing Solutions) has several internal chamber configurations available depending on the abrasiveness of the ore. Examples include the Rock on Rock, Rock on Anvil and Shoe and Anvil configurations (Figure 6.26). These units typically operate with 5 to 6 steel impellers or hammers, with a ring of thin anvils. Rock is hit or accelerated to impact on the anvils, after which the broken fragments freefall into the discharge chute and onto a product conveyor belt. This impact size reduction process was modeled by Kojovic (1996) and Djordjevic et al. (2003) using rotor dimensions and speed, and rock breakage characteristics measured in the laboratory. The model was also extended to the Barmac crushers (Napier-Munn et al., 1996).

Figure 9.1 shows common aluminum oxide-based grains. Also called corundum, alumina ore was mined as early as 2000 BC in the Greek island of Naxos. Its structure is based on -Al2O3 and various admixtures. Traces of chromium give alumina a red hue, iron makes it black, and titanium makes it blue. Its triagonal system reduces susceptibility to cleavage. Precious grades of Al2O3 are used as gemstones, and include sapphire, ruby, topaz, amethyst, and emerald.

Charles Jacobs (1900), a principal developer, fused bauxite at 2200C (4000F) before the turn of the 20th century. The resulting dense mass was crushed into abrasive particles. Presently, alumina is obtained by smelting aluminum alloys containing Al2O3 in electric furnaces at around 1260C (2300F), a temperature at which impurities separate from the solution and aluminum oxide crystallizes out. Depending upon the particular process and chemical composition there are a variety of forms of aluminum oxide. The poor thermal conductivity of alumina (33.5W/mK) is a significant factor that affects grinding performance. Alumina is available in a large range of grades because it allows substitution of other oxides in solid solution, and defect content can be readily controlled.

For grinding, lapping, and polishing bearing balls, roller races, and optical glasses, the main abrasive employed is alumina. Its abrasive characteristics are established during the furnacing and crushing operations, so very little of what is accomplished later significantly affects the features of the grains.

Aluminum oxide is tougher than SiC. There are four types of gradations for toughness. The toughest grain is not always the longest wearing. A grain that is simply too tough for an application will become dull and will rub the workpiece, increasing the friction, creating heat and vibrations. On the other hand, a grain that is too friable will wear away rapidly, shortening the life of the abrasive tool. Friability is a term used to describe the tendency for grain fractures to occur under load. There is a range of grain toughness suitable for each application. The white friable aluminum oxide is almost always bonded by vitrification. It is the main abrasive used in tool rooms because of its versatility for a wide range of materials. In general, the larger the crystals, the more friable the grain. The slower the cooling process, the larger are the crystals. To obtain very fine crystals, the charge is cooled as quickly as possible, and the abrasive grain is fused in small pigs of up to 2ton. Coarse crystalline abrasive grains are obtained from 5 to 6ton pigs allowed to cool in the furnace shell.

The raw material, bauxite, containing 8590% alumina, 25% TiO2, up to 10% iron oxide (Fe2O3), silica, and basic oxides, is fused in an electric-arc furnace at 2600C (4700F). The bed of crushed and calcined bauxite, mixed with coke and iron to remove impurities, is poured into the bottom of the furnace where a carbon starter rod is laid down. A couple of large vertical carbon rods are then brought down to touch and a heavy current applied. The starter rod is rapidly consumed, by which time the heat melts the bauxite, which then becomes an electrolyte. Bauxite is added over several hours to build up the volume of melt. Current is controlled by adjusting the height of the electrodes, which are eventually consumed in the process.

After cooling, the alumina is broken up and passed through a series of hammer, beater, crush, roller, and/or ball mills to reduce it to the required grain size and shape, producing either blocky or thin splintered grains. After milling, the product is sieved to the appropriate sizes down to about 40 m (#400). The result is brown alumina containing typically 3% TiO2. Increased TiO2 content increases toughness while reducing hardness. Brown alumina has a Knoop hardness of 2090 and a medium friability.

Electrofused alumina is also made using low-soda Bayer process alumina that is more than 99% pure. The resulting alumina grain is one of the hardest, but also the most friable, of the alumina family providing a cool cutting action. This abrasive in a vitrified bond is, therefore, suitable for precision grinding.

White aluminum oxide is one of the most popular grades for micron-size abrasive. To produce micron sizes, alumina is ball-milled or vibro-milled after crushing and then traditionally separated into different sizes using an elutriation process. This consists of passing abrasive slurry and water through a series of vertical columns. The width of the columns is adjusted to produce a progressively slower vertical flow velocity from column to column. Heavier abrasive settles out in the faster flowing columns while lighter particles are carried over to the next. The process is effective down to about 5 m and is also used for micron sizing of SiC. Air classification has also been employed.

White 99% pure aluminum oxide, called mono-corundum, is obtained by sulfidation of bauxite, which outputs different sizes of isometric corundum grains without the need for crushing. The crystals are hard, sharp, and have better cleavage than other forms of aluminum oxides, which qualifies it for grinding hardened steels and other tough and ductile materials. Fine-grained aluminum oxide with a good self-sharpening effect is used for finishing hardened and high-speed steels, and for internal grinding.

Not surprisingly, since electrofusion technology has been available for the last one hundred years, many variations in the process exist both in terms of starting compositions and processing routes. For example:

Red-brown or gray regular alumina. Contains 9193% Al2O3 and has poor cleavage. This abrasive is used in resinoid and vitrified bonds and coated abrasives for rough grinding when the risk of rapid wheel wear is low.

Chrome addition. Semi-fine aloxite, pink with 0.5% chromium oxide (Cr2O3), and red with 15% Cr2O3, lies between common aloxite, having less than 95% Al2O3 and more than 2% TiO2, and fine aloxite, which has more than 95% Al2O3 and less than 2% TiO2. The pink grain is slightly harder than white alumina, while the addition of a small amount of TiO2 increases its toughness. The resultant product is a medium-sized grain available in elongated, or blocky but sharp, shapes. Ruby alumina has a higher chrome oxide content of 3% and is more friable than pink alumina. The grains are blocky, sharp edged, and cool cutting, making them popular for tool room and dry grinding of steels, e.g., ice skate sharpening. Vanadium oxide has also been used as an additive giving a distinctive green hue.

Zirconia addition. Aluminazirconia is obtained during the production process by adding 1040% ZrO2 to the alumina. There are at least three different aluminazirconia compositions used in grinding wheels: 75% Al2O3 and 25% ZrO2, 60% Al2O3 and 40% ZrO2, and finally, 65% Al2O3, 30% ZrO2, and 5% TiO2. The manufacture usually includes rapid solidification to produce a fine grain and tough structure. The resulting abrasives are fine grain, tough, highly ductile, and give excellent life in medium to heavy stock removal applications and grinding with high pressures, such as billet grinding in foundries.

Titania addition. Titaniaaloxite, containing 95% Al2O3 and approximately 3% Ti2O3, has better cutting ability and improved ductility than high-grade bauxite common alumina. It is recommended when large and variable mechanical loads are involved.

Single crystal white alumina. The grain growth is carefully controlled in a sulfide matrix and is separated by acid leaching without crushing. The grain shape is nodular which aids bond retention, avoiding the need for crushing and reducing mechanical defects from processing.

Post-fusion processing methods. This type of particle reduction method can greatly affect grain shape. Impact crushers such as hammer mills create a blocky shape while roll crushers cause splintering. It is possible, using electrostatic forces to separate sharp shapes from blocky grains, to provide grades of the same composition but with very different cutting actions.

The performance of the abrasive can also be altered by heat treatment, particularly for brown alumina. The grit is heated to 11001300 C (20152375 F), depending on the grit size, in order to anneal cracks and flaws created by the crushing process. This can enhance toughness by 2540%.

Finally, several coating processes exist to improve bonding of the grains in the grinding wheel. Red Fe2O3 is applied at high temperatures to increase the surface area for better bonding in resin cut-off wheels. Silane is applied for some resin bond wheel applications to repel coolant infiltration between the bond and abrasive grit, and thus protect the resin bond.

A limitation of electrofusion is that the resulting abrasive crystal structure is very large; an abrasive grain may consist of only one to three crystals. Consequently, when grain fracture occurs, the resulting particle loss may be a large proportion of the whole grain. This results in inefficient grit use. One way to avoid this is to dramatically reduce the crystal size.

The earliest grades of microcrystalline grits were produced as early as 1963 (Ueltz, 1963) by compacting a fine-grain bauxite slurry, granulating to the desired grit size, and sintering at 1500C (2735F). The grain shape and aspect ratio could be controlled by extruding the slurry.

One of the most significant developments since the invention of the Higgins furnace was the release in 1986, by the Norton Company, of seeded gel (SG) abrasive (Leitheiser and Sowman, 1982; Cottringer et al., 1986). This abrasive was a natural outcome of the wave of technology sweeping the ceramics industry at that time to develop high strength engineering ceramics using chemical precipitation methods. This class of abrasives is often termed ceramic. SG is produced by a chemical process. In a precursor of boehmite, MgO is first precipitated to create 50-m-sized aluminamagnesia spinel seed crystals. The resulting gel is dried, granulated to size, and sintered at 1200C (2200F). The resulting grains are composed of a single-phase -alumina structure with a crystalline size of about 0.2m. Defects from crushing are avoided; the resulting abrasive is unusually tough but self-sharpening because fracture now occurs at the micron level.

With all the latest technologies, it took significant time and application knowledge to understand how to apply SG. The abrasive was so tough that it had to be blended with regular fused abrasives at levels as low as 5% to avoid excessive grinding forces. Typical blends are now five SGs (50%), three SGs (30%), and one SG (10%). These blended abrasive grades can increase wheel life by up to a factor of 10 over regular fused abrasives, although manufacturing costs are higher.

In 1981, prior to the introduction of SG, the 3M Co. introduced a solgel abrasive material called Cubitron for use in coated abrasive fiber discs (Bange and Orf, 1998). This was a submicron chemically precipitated and sintered material but, unlike SG, had a multiphase composite structure that did not use seed grains to control crystalline size. The value of the material for grinding wheel applications was not recognized until after the introduction of SG. In the manufacture of Cubitron, alumina is co-precipitated with various modifiers such as magnesia, yttria, lanthana, and neodymia to control microstructural strength and surface morphology upon subsequent sintering. For example, one of the most popular materials, Cubitron 321, has a microstructure containing submicron platelet inclusions which act as reinforcements somewhat similar to a whisker-reinforced ceramic (Bange and Orf, 1998).

Direct comparison of the performance of SG and Cubitron is difficult because the grain is merely one component of the grinding wheel. SG is harder (21GPa) than Cubitron (19GPa). Experimental evidence suggests that wheels made from SG have longer life, but Cubitron is freer cutting. Cubitron is the preferred grain in some applications from a cost/performance viewpoint. Advanced grain types are prone to challenge from a well-engineered, i.e., shape selected, fused grain that is the product of a lower cost, mature technology. However, it is important to realize that the wheel cost is often insignificant compared to other grinding process costs in the total cost per part.

The SG grain shape can be controlled by extrusion. Norton has taken this concept to an extreme and in 1999 introduced TG2 (extruded SG) grain in a product called ALTOS. The TG2 grains have the appearance of rods with very long aspect ratios. The resulting packing characteristics of these shapes in a grinding wheel create a high strength, lightweight structure with porosity levels as high as 70% or even greater. The grains touch each other at only a few points, where a bond also concentrates in the same way as a spot weld. The product offers potential for higher stock removal rates and higher wheelspeeds due to the strength and density of the resulting wheel body (Klocke and Muckli, 2000).

Recycling of concrete involves several steps to generate usable RCA. Screening and sorting of demolished concrete from C&D debris is the first step of recycling process. Demolished concrete goes through different crushing processes to acquire desirable grading of recycled aggregate. Impact crusher, jaw crusher, cone crusher or sometimes manual crushing by hammer are preferred during primary and secondary crushing stage of parent concrete to produce RA. Based on the available literature step by step flowchart for recycling of aggregate is represented in Fig. 1. Some researchers have also developed methods like autogenous cleaning process [46], pre-soaking treatment in water [47], chemical treatment, thermal treatment [48], microwave heating method [49] and mechanical grinding method for removing adhered mortar to obtain high quality of RA. Depending upon the amount of attached mortar, recycled aggregate has been classified into different categories as shown in Fig. 2.

Upon arrival at the recycling plant, CDW may either enter directly into the processing operation or need to be broken down to obtain materials with workable particle sizes, in which case hydraulic breakers mounted on tracked or wheeled excavators are used. In either case, manual sorting of large pieces of steel, wood, plastics and paper may be required, to minimize the degree of contamination.

The three types of crushers most used for crushing CDW are jaw, impact, and gyratory crushers (Fig.8). A jaw crusher consists of two plates fixed at an angle (Fig.8a); one plate remains stationary while the other oscillates back and forth relative to it, crushing the material passing between them. This crusher can withstand large pieces of reinforced concrete, which would probably cause other types of crushers to break down. Therefore, the material is initially reduced in jaw crushers before going through other types. The particle size reduction depends on the maximum and minimum size of the gap at the plates. Jaw crushers were found to produce RA with the most suitable grain-size distribution for concrete production (Molin etal., 2004).

An impact crusher breaks CDW by striking them with a high speed rotating impact, which imparts a shearing force on the debris (Fig.8b). Materials fall onto the rotor and are caught by teeth or hard steel blades fastened to the rotor, which hurl them against the breaker plate, smashing them to smaller-sized particles. Impact crushers provide better grain-size distribution of RA for road construction purposes and are less sensitive to material that cannot be crushed (i.e. steel reinforcement).

Gyratory crushers, which work on the same principle as cone crushers (Fig.8c), exhibit a gyratory motion driven by an eccentric wheel and will not accept materials with large particle sizes as they are likely to become jammed. However, gyratory and cone crushers have advantages such as relatively low energy consumption, reasonable amount of control over particle size and production of low amount of fine particles.

Generally, jaw and impact crushers have a large reduction factor, defined as the relationship between the input's particle size and that of the output. A jaw crusher crushes only a small proportion of the original aggregate particles but an impact crusher crushes mortar and aggregate particles alike, and thus may generate twice the amount of fines for the same maximum size of particle (O'Mahony, 1990).

In order to produce RA with predictable grading curve, it is better to process debris in two crushing stages, at least. It may be possible to consider a tertiary crushing stage and further, which would undoubtedly produce better quality coarse RA (i.e. less adhered mortar and with a rounder shape). However, concrete produced with RA subjected to a tertiary crushing stage may show only slightly better performance than that made with RA from a secondary crushing stage (Gokce etal., 2011; Nagataki etal., 2004). Furthermore, more crushing stages would yield products with decreasing particle sizes, which contradicts the mainstream use of RA (i.e. coarser RA fractions are preferred, regardless of the application). These factors should be taken into account when producing RA as, from an economical and environmental point of view, it means that relatively good quality materials can be produced with lower energy consumption and with a higher proportion of coarse aggregates, if the number of crushing stages is prudently reduced.

aggregate concrete - an overview | sciencedirect topics

aggregate concrete - an overview | sciencedirect topics

The objective of any concrete aggregate processing operation should be the production of good-quality, clean coarse and fine materials in the normal range of sizes. The types of equipment used and the flow design of the plant are more or less completely dependent upon the nature and properties of the source raw material. Even after basic design, any plant will require commissioning trials, after which the experience gained will dictate both major and minor modifications to the process. The technology of aggregate processing is complicated and continually developing and is more comprehensively covered elsewhere.25,26,40,41 In general terms, however, processing consists of a reduction stage (always with crushed rock and sometimes with sand a gravel), a washing and beneficiation stage (as required) and a sizing stage.

Reduction of the broken rock material, or oversized gravel material, to an aggregate-sized product is achieved by various types of mechanical crusher. These operations may involve primary, secondary and even sometimes tertiary phases of crushing. There are many different types of crusher, such as jaw, gyratory, cone (or disc) and impact crushers (Fig. 15.9), each of which has various advantages and disadvantages according to the properties of the material being crushed and the required shape of the aggregate particles produced.

Fig. 15.9. Diagrams to illustrate the basic actions of some types of crusher: solid shading highlights the hardened wear-resistant elements. (A) Single-toggle jaw crusher, (B) disc or gyrosphere crusher, (C) gyratory crusher and (D) impact crusher.

It is common, but not invariable, for jaw or gyratory crushers to be utilised for primary crushing of large raw feed, and for cone crushers or impact breakers to be used for secondary reduction to the final aggregate sizes. The impact crushing machines can be particularly useful for producing acceptable particle shapes (Section 15.5.3) from difficult materials, which might otherwise produce unduly flaky or elongated particles, but they may be vulnerable to abrasive wear and have traditionally been used mostly for crushing limestone.

In any crushing operation, the raw material flow rate and the reduction ratio (ratio of feed size to product size) have obvious influences on the wear of crushing equipment. However, the hardness and fracture toughness of the rocks being crushed are unavoidable parameters in allowing for the wear of crushing plant. Traditionally, the assessment of hardness has been used as a crude guide to abrasiveness, although hardness alone is not in fact a reliable wear criterion.42 Of the common rock-forming minerals, quartz alone is harder than normal steel so that the average content of quartz (or free-silica) in the raw feed is some guide to the sliding abrasiveness to be expected (fracture toughness is important to the impact abrasiveness).

Quantitative criteria for the relationship between quartz and wear are not easily available, but obviously the liability to high wear rates tends to increase with quartz content. Orchard42a has suggested that free silica contents of <5% will not cause trouble, whereas amounts above 20% might become a problem. At a quarry in western Kenya, a secondary impact crusher was included in the aggregate processing design on the basis of the incorrect information that the raw material was a quartz andesite, perhaps with a maximum quartz content of 10%. In fact, the material was mostly a dacite with quartz contents of up to 70% and the machines blow bars had to be replaced every third day during production, with obvious financial and contractual implications (in the limestone industry a set of blow bars will last for several months).

Sand and gravel materials, and more rarely crushed rock materials, are washed to remove clay or excessive proportions of silt. In more recent years, concrete aggregates have also been washed specifically to remove soluble salts (especially sodium chloride) which otherwise might induce or exacerbate the corrosion of steel reinforcement and other embedded metal or increase the risk of ASR.

Washing may be carried out by water jets during screening or by passing the raw feed through a washer barrel.25 If the material contains less dispersive clay or more resistant clay lumps, it may be necessary to employ more vigorous washing using a scrubber or log washer. Where it is important to minimise the sodium chloride content as well as removing fines, washing must be done using, and regularly replenishing, fresh water. Simple dewatering of marine aggregates or other aggregates washed using sea water will appreciably reduce the level of salt contamination, though not necessarily to a level which will avoid the need for any further washing.

Additional processing to improve the quality of a product by selective removal of less desirable constituents is termed beneficiation and is quite common in the metallic minerals industry. Beneficiation is employed only on a limited basis in the production of aggregates because of the relatively high plant and operating costs. Gravity and centrifugal separation plants are capable of successfully removing notably lightweight materials, such as coal, or notably heavyweight materials, such as iron ore particles. Some success has been claimed for the removal of unsound low-density chert from a crushed gravel aggregate.43

Discrete flakes of mica are frequently detrimental in fine aggregates for concrete (Section 15.4.4) and could usefully be removed by beneficiation where uncontaminated sands are not available. Mica was formerly removed from some Cornish China clay sands but principally to recover the mica for commercial sale rather than deliberately to beneficiate the sand aggregate.44 Fookes and Marsh45 have described some modified washing procedures for the reduction of mica content in Nepalese fine aggregates.

The separation of crushed aggregates, or sand and gravel, into different sizes is achieved by large sieves or industrial screens. Coarse screens known as grizzlies or scalpers are used to separate oversized or undersized materials from the raw feed as part of the crushing operation. Static, horizontal and cylindrical screens have been used, but today most plants are designed with inclined vibrating screens (Fig. 15.10), some of which are primarily intended to discard undersized material and others of which are primarily intended to discard oversized material. A good overall design of a screening plant achieves clear and reliable separation of sizes (Fig. 15.11). The further sizing of sand material, with particle sizes of 4mm or less, is achieved by a process of classification which is based upon the principle that coarse particles settle out from a watersand slurry at a faster rate than fine particles.46 Sand classification is more inefficient than coarse aggregate screening and differently graded products result which can be used for different purposes.

Preplaced-aggregate concrete is more resistive to shrinkage and creep than conventional concrete is. This is due to the aggregate. The net result is more protection against cracking. This type of concrete can be used on numerous types of structures. The cost involved with using preplaced-aggregate concrete is likely to be more, but it may be worth it in the long run.

In comparison to conventional NAC, self-compacting concrete (SCC) concrete contains a higher binder content, various chemical admixtures, and supplementary cementitious materials (SCMs). SCC concrete is renowned for its ease of flow through congested reinforcement and its self-compacting (under its own weight) abilities with little to no mechanical vibration required (Aslani and Maia, 2013).

The quality of the parent crushed concrete in the RCA is noted to have a great influence on the SCC. As the RCA used in the experiment had similar quality to the SCC being produced, minor losses in strength were observed. The experiment concluded that using RCA in SCC is justified, and provided that the quality of the RCA is substantially high, then HPCs can be obtained (Grdic et al., 2010).

Fakitsas et al. (2012) studied the effectiveness of internal curing using saturated RAs in SCC. The aggregates were submerged in water for 3 days and then surfaced dried for 12h before being used in the concrete mixture. It was found that these soaked aggregates achieved an 80%90% degree point of saturation. A comparative study between the behavior of RAs and natural aggregates employed in SCC has determined that the RAs concrete has a higher compressive strength at 28 days which is even greater at 90 days. This is attributed to internal curing due to the water absorption and retention of the RA.

According to Aslani et al. (2018), an increase in the percentage of RA replacement results in a decrease of the flowability and passing ability decreases. Moreover, the use of fine RA in SCC mixtures showed improvements in mechanical strength when the fine recycles aggregates were sourced from a high-strength concrete.

A deterministic calculation following Eurocode 2s formulae and the characteristic values of the parameters involved in Eurocodes 2 limit-state functionthis step will be used to design the structural element.

A reliability assessment of the design, using the probabilistic distribution and statistics of each RV of a probabilistic calculation accounting for the variability in modelling, material strength, actions, load-effects and geometry.

The effect of RCA incorporation on the reliability will be analysed for ultimate limit-states (flexural strength verifications) and serviceability limit-states (cracking moment). A beam with varying reinforcement ratio (within a common range) will be analysed. Since this calibration will not be exhaustive, the conclusions of this chapter are, at this stage, preliminary. In the short future, a more definite analysis will be performed.

Ultimate limit-state: all beams had the same cross-section. The permanent load (G) was kept constant and three different live loads were defined, in order to analyse the reliability of beams with different reinforcement ratios. To make a fair reliability comparison between mixes, the tensile reinforcement ratio was changed from composition to composition, since the average compressive strengths properties are different.

Since it was intended to make a safe-side estimation of the effects of RCA incorporation on the reliability of the beams, the compressive reinforcement was not considered in the design for the ultimate limit-state verification. Similarly, the influence of the statistics of the concretes tensile strength on the reliability was overestimated by disregarding the tensile and compressive reinforcements.

A case study on environmental assessment of four concrete types with different natural and recycled concrete aggregate was performed using the LCA methodology. The results of this specific study, along with other researchers results, showed that the contribution of the aggregate production phase to total impacts of concrete is rather small about 5% at maximum, depending on impact category. Although the production of recycled concrete aggregate is more energy intensive than natural aggregate production, it does not affect the results significantly.

the increase in cement content of recycled aggregate concrete compared to natural aggregate concrete is small, up to a few percent at most; this is possible in RAC with 100% coarse aggregate replacement if the RCA is of good quality, and certainly achievable in RAC with 50% coarse aggregate replacement.

the transport distance of RCA is smaller than the transport distance of NA; for example, in this study the ratio of transport distances of RCA to NA was assumed to be 15km:100km, which means that the recycling plant must be located much closer to the concrete plant than the place of NA extRACtion, if similar environmental impacts are expected.

The importance of the cement content and transport distance and type is best seen with the example of natural aggregate concrete with crushed aggregates in this case study. This type of concrete had the largest impacts, due to the increased cement content and assumed transport distance and type. The influence of the transport phase was analyzed and the limit transport distance of gravel aggregate was calculated for different category indicators.

However, utilization of RAC brings environmental benefits through saving of natural aggregate resources and landfill space. These benefits cannot be expressed with specific category indicators, since most of the proposed methodologies do not include solid waste production/landfill capacity as an impact category, or consider sand and stone as abiotic resources that can be depleted.

Another benefit that can be gained with recycling is CO2 reabsorption of concrete during the secondary life of a structure. Results of published research show that CO2 uptake in this phase can be significant, depending on the post-use of the concrete structure. If demolished concrete is crushed into RCA and applied in new construction in unbound form for another 30 years, CO2 uptake can reach 40% of total CO2 emissions from cement manufacture.

Future research should be aimed towards development of special indicators for natural bulk resources depletion and landfill space depletion. Also, CO2 uptake of concrete over the structures primary and secondary life should be included in LCA models of concrete. Further, more detailed research is needed in this area.

Design criteria for both concrete mixes NAC and RAC were adopted according to Eurocode 2 Part 1 and EN 1992-1-2 (CEN/TC250, 2004b). In the following, EN 1992-1-2 is referred to as Eurocode 2 Part 2.

All the properties and equations used in the design of floor slabs are summarised in Table 10.5. Designations and meaning of parameters in Table 10.5 completely follow notations and equations used in Eurocode 2 Parts 1 and 2.

The measured concrete strength in selected tests was considered as mean concrete compressive strength fcm. For NAC mixes, the 28-day characteristic compressive strength fck, tensile strength fctm, modulus of elasticity Ecm and creep coefficient (t,t0) were calculated according to Eurocode 2 Part 1 provisions, Table 10.5. For RAC mixes, the 28-day characteristic compressive strength fck and tensile strength fctm were also calculated according to Eurocode 2 Part 1 provisions. It has been shown in previous extensive research that the relationship between compressive and tensile strength given in this standard is valid, with the same reliability level, for RAC mixes (Silva et al., 2015).

However, it is now well-known that RAC mixes have a lower modulus of elasticity and exhibit larger creep compared to companion NAC mixes. Various proposals for prediction models were published in literature and prediction models presented in Lye et al. (2016) for RAC modulus of elasticity and for RAC creep coefficient were selected in this work. So, for modulus of elasticity following relationship was obtained (Lye et al. 2016):

Based on the statistical analysis of a comprehensive database of RAC and companion NAC beams flexural and shear strength (Toi et al., 2016), it was concluded that flexural and shear strength (without stirrups) of RAC beams can be calculated using the existing provisions of Eurocode 2 Part 1 without any alterations. The same assumption was adopted for RAC slabs design in this work, Table 10.5.

For crack width and long-term deflection calculations the Eurocode 2 Part 1 provisions were used for both NAC and RAC mixes, taking into account their different properties, Table 10.5. In other words, it was assumed that same prediction models can be used, that is, different NAC and RAC slab serviceability behaviour was caused only by different concrete properties, and not by different structural behaviour. This assumption was justified by the experimental results on bond strength and tension stiffening of RAC mixes published in the literature. Most of the research performed on the RAC bond strength showed that relative bond strength (ratio of bond and compressive strength) of RAC with 100% course RCA was larger or, at least, very similar as in NAC (Xiao and Falkner, 2007; Maleev et al., 2010; Kim and Yun, 2013; Prince and Singh, 2013). However, there was also research which reported lower RAC relative bond strength, as for instance in Butler et al. (2011). Recent experimental research on tension stiffening behaviour of RAC, although with 50% course RCA, showed that the use of RCA did not affect the resulting concrete performance, resulting tensile behaviour and steel-to-concrete interaction (Rangel et al., 2017).

Regarding durability, two XCs for concrete inside buildings were analysed: XC1 and XC3. The slabs of the 1st4th floor were designed for XC1 class (dwellings, low-air humidity), while the slab of the ground floor was designed for XC3 class (moderate or high-air humidity as parking space was located beneath the ground floor). Both XCs are related to the carbonation-induced reinforcement corrosion.

The carbonation resistance of RAC has been widely investigated. The results of studies (Silva et al., 2015) showed that it was possible to correlate the carbonation resistance with the compressive strength and that this relationship was marginally affected by the replacement level, type and size of recycled aggregates. The relationship between the carbonation depth of RAC and NAC with similar mix designs may be calculated using the following equation (Silva et al., 2016):

where xc, RAC and xc, NAC are carbonation depths of RAC and NAC, respectively. The relationship [Eq. (10.10)] is valid only for concrete mixes with CEM I cement, which was the case in this work. This relationship was used to correlate the required cover depth of RAC to that of the NAC mix in order to provide equal durability, Table 10.5.

As for the fire resistance, previous research showed that concrete with aggregate both fully and partially replaced with coarse RCA exhibited good performance under elevated temperatures and post-fire mechanical and durability properties, which was comparable or even better than conventional concrete performance (Vieira et al., 2011; Sarhat and Sherwood, 2013; Xiao et al., 2013; Kou et al., 2014). Therefore, there should be no differences in the structural fire design between RAC and NAC mixes, and same requirements of Eurocode 2 Part 2 were applied to both concrete mixes, Table 10.5.

In determining the depth of the concrete cover it was assumed that the carbonation rate coefficient (k-factor) is equal to 0 on the top surface of the slab, according to recommendations in CEN/TC229/WG5-N012 (2016) for elements inside buildings in dry climate and covered with tiles, parquet and laminate. So, the minimum top cover was determined to satisfy bond (cmin,b) and fire-resistance requirements, which were assumed to be same for both NAC and RAC. The bottom surface of the slab was assumed to have no extra cover, so the minimum bottom cover was determined to satisfy bond (cmin,b), durability (cmin,dur) and fire-resistance requirements, see Table 10.5. The value of cmin,dur for RAC was calculated on the basis of cmin,dur for NAC according to Eurocode 2 Part 1 requirements and equation [Eq. (10.10)]. In all cases, minimum cover was increased to allow for the deviation with a value cdev=10mm.

According to Eurocode 2 Part 1, minimum 28-day characteristic compressive strength for XC1 and XC3 class is 25 and 30MPa, respectively. The requirement for XC3 was not satisfied in the NAC1 and RAC2 cases. The slightly lower characteristic strength (less than 10%) in these cases was considered to have a minor effect.

Results of the design values are presented in Table 10.6 where designation of a particular slab (S) includes the type of concrete mix and aggregate quality (NAC or RAC; 1 for high RCA quality and 2 for low RCA quality) and the XC (XC1 or XC3). All slabs, whether made with NA, high- or low-quality RCA and whether exposed to XC1 or XC3, fulfil Eurocodes requirements for strength, serviceability, durability and fire resistance. So, full functional equivalence was achieved. The component material amounts in Table 10.6 present reference flows and input data for comparative LCA.

The use of superplasticising chemical admixtures in RAC mixes with total w/c ratio equivalent to that of NAC mixes has shown encouraging outcomes, from a mechanical performance point of view (Dapena etal., 2011; Domingo etal., 2010; Domingo-Cabo etal., 2009; Amer etal., 2016). However, the comparable slump levels can be observed only at the initial phase since the superplasticisers eventually lose their effectiveness because of the considerable water absorption by the RA over time.

This phenomenon can be better explained with the use of Figure 7.2, which presents the dynamics of the effective water content in concrete over time. As the (partly) dry aggregates are placed in water, these will absorb part of the water depending on the duration and the water absorption capacity of the aggregate. Therefore, even though NAC and RAC may present equivalent total w/c ratios, the incorporation of dry RA (or semi-dry RA) leads to gradual reduction of the effective w/c ratio over time, as well as a reduction in the consistence of the concrete. The addition of extra water, on the other hand, even though it increases the total w/c ratio, assuming that every other criterion is equal, will allow maintaining the same amount of effective water, thereby resulting in comparable consistence (workability) at the time of measuring the mixs slump (Dosho, 2007).

From a microscopic perspective, this method, in comparison with the previous two, produces RAC with a significantly different microstructure, with a lower amount of effective water available for the consistence and hydration of the mix. Naturally, this leads to lower levels of porosity of the concrete and possibly improved mechanical behaviour of the concrete in the hardened state.

Outcomes of slump test of waste cover plastic aggregate (CPA) concrete mixtures are shown in Fig.5.14. The results show that CPA mix slump reduces slightly from reference mix slump. The percentage decreases of slump were: 29.5%, 40.8%, 50.0%, and 64.3% for 5%, 10%, 15% and 20%, respectively. As shown from these results, the slump of CPA mixes is lower than for reference mix. As shown from these results, the slump of CAP mixes and reference mix are nearly close. This may be due to similarity between shape of CPA and naturally crushed coarse aggregate. Both aggregate have sharp angular ends.

Results of slump test of waste compact disk plastic coarse aggregate concrete (CDPCA) mixtures are shown in Fig.5.15. The results show that CDPCA mixes slump reduce sharply when compared to reference mix slump. The percentage decreases of slump were: 31.7%, 43.5%, 64.7%, 74.1%, and 82.3% for 5.0%, 10%, 15%, 20%, and 25%, respectively.

In total, 29 case studies with 34 RA concrete mixes altogether used in structural applications have been recorded as of this writing. The type and size of RA used for each concrete mix are shown in Figure 13.3. RCA was commonly used as a replacement for NA because of its relatively higher quality and availability compared with other types of RA. Only one case reported that 20% MRA was included in the construction of a 0.5-m-thick heavily reinforced slab for BRE Cardington Laboratory in the United Kingdom (Collins, 2003). There are some cases in which the information on the type of RA was unclear, although it was likely to be RCA (Xiao and Ding, 2013; Henson, 2011).

The use of fine RA alone in structural concrete has been limited. However, its use in conjunction with coarse RA, known as all-in aggregate as defined by BS EN 12620 (2008), for up to 100% total NA replacement, has been found in a few case studies (Grubl and Nealan, 1998; Koster and Ruhl, 2001; Yoda and Shintani, 2014; Kasai, 1998). However, the information therein suggests that the use of all-in RA gave rise to some negative effects in both fresh and hardened properties of concrete.

It is apparent that the ratio of masonry modulus/block strength ratio varies considerably. The recorded secant modulus of elasticity is mostly that corresponding to strain at the first application of stress in creep tests so that likely sources of variability are rate of loading or time to apply the load, the level of stress (high stress/strength ratios above 0.3 can cause nonlinear strain), type of mortar, and age at test.

In Ameny etal.'s tests [45], the average ratio of concrete blockwork modulus to concrete blockwork strength was 0.70, whereas in Brooks and Amjad's tests [36], the average concrete blockwork modulus of elasticity (GPa) was numerically equal to the average concrete blockwork strength (MPa); like clay and calcium silicate brickwork, both modulus and strength were independent of height/least lateral width ratio.

In the report by CERAM Building Technology [42], tests of autoclaved aerated concrete (AAC) or aircrete masonry indicated that moduli of elasticity given by the BRE digest [44] were higher than measured ones. Table 5.5 shows that, for a range of AAC block strengths of 3.27.5MPa, the modulus of elasticity of masonry was 1.62.7GPa and, generally, BRE suggest that the modulus (GPa) can be taken as 0.6block strength (MPa). However, for low-strength AAC blocks, CERAM Building Technology found a lower average masonry modulus of 0.4block strength.

When the modulus of block is low, the modulus of masonry is approximately equal to the block modulus because the influence of the mortar is negligible, as indicated by Eq. (3.40), since the modulus of blockwork is dominated by the block modulus term. Hence, for AAC blockwork, Ewy=Eby and from the average results of the BRE Digest and CERAM Building Technology shown in Table 5.5:

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