8.2. Recycling Equipment and Technologies
Typical recycling ways of construction and demolition waste are listed in Table 8.5.
8.2.1. Classified Utilization of Recycled Materials
Classified categories of recycled materials produced by concrete, bricks, and renovation construction waste are listed in Tables 8.6–8.8, respectively.
The classified utilization of recycled building materials is listed in Table 8.9. It is divided into road engineering materials and building engineering materials. The types of recycled building materials and the aggregate used are also introduced.
Table 8.5
Typical Recycling Ways of Construction and Demolition Waste
| Wall materials | Normal load-bearing and non-load-bearing building blocks |
| (190, 280, 300 series) 80 types, including single row of holes, multiple rows of holes, blind holes, lintels, and solid standard bricks | |
| Decorative building blocks | |
| 40 types, including normal single-sided splitting blocks, double-sided splitting blocks, color splitting tiles, and striped wall tiles | |
| Functional building blocks | |
| 20 types, including bearing thermal insulating blocks and sound insulating blocks | |
| Floor materials | Paving bricks |
| 50 types, including normal (bearing) paving bricks, water permeable paving bricks, and classic paving bricks | |
| Road traffic stones | |
| 10 types, including road curbstones and gardening hoarstones | |
| Lawn bricks | |
| 20 types, including normal grass-planting bricks and bearing lawn bricks | |
| Green building materials | Retaining blocks |
| Segmental retaining blocks, other gardening blocks | |
| Slope protection blocks (hydraulic block) | |
| 20 types, including interlocking revetment blocks, articulated slope protection blocks, embedded protective bricks, and grass bricks |
Table 8.6
Classified Categories of Recycled Materials Produced by Concrete
| Classified Categories | Particle Size (mm) | Stacking Density (kg/m3) |
| Recycled muck | <5 | <1200 |
| Recycled coarse aggregate | <37.5 | <1500 |
| Recycled fine aggregate | <4.75 | <1200 |
| Recycled powder material | <0.075 | <700 |
8.2.2. Crushing Equipment and Technologies for C&D Waste
Crushing equipment can be divided into impact crusher and laminated crusher based on the operating principles. They can also be classified into three groups according to the hourly production capacity (t/h) of each crushing device:
Large crusher: production capacity between 300 and 1500 t/h;
Middle crusher: production capacity between 100 and 300 t/h;
Small crusher: production capacity between 0 and 100 t/h.
There are also other classification methods depending on the rotor, for instance, crusher with single rotor and double rotors.
Three kinds of crushers are introduced in this chapter, whereas DPF specific crusher for construction and demolition waste will be introduced in detail.
DPF Specific Crusher for C&D Waste
Two-stage crushing is commonly used in C&D waste recycled fine aggregate crushing due to the physical characteristics of the material itself, and the particle size of the crushed materials is about 0–10 mm. The two-stage crushing can be replaced by three-stage crushing to improve the production amount of fine aggregate and the diameter of most crushed materials is under 10 mm. DPF crusher is designed to overcome the common problems raised in the production process including complex process arrangement, and large electricity and investment consumptions. The crusher is demonstrated in Fig. 8.1.
The raw materials entering the crusher are stacked on the middle plate inside, while the hammer operating in the gap of the plate continuously crushes and breaks the large bulks of materials. The falling small pieces of materials are finely crushed by the contact with the high-speed operating hammer and then fall to the homogenizing section and discharge. Meanwhile, grooves are set on the plate of the homogenizing section where the mixed reinforced bars are impeached out. The distance between the homogenizing plate and the hammer is adjustable. The smaller the distance is set, the smaller the outlet particle size will be obtained.
Table 8.9
Classified Utilization of Recycled Building Materials
| Utilization of Construction and Demolition Waste | Type of Recycled Building Materials | Aggregate Used |
| Road engineering materials | Pavement structure layer: subgrade cushion material | Concrete, brick, recycled coarse and fine renovation aggregate |
| Pavement structure layer: subgrade stabilization material | Concrete, brick, recycled coarse and fine aggregate | |
| Recycled concrete road blocking pier | Concrete, brick, recycled coarse and fine renovation aggregate | |
| Recycled concrete noise barrier | Concrete, brick, recycled coarse and fine renovation aggregate | |
| Recycled concrete road traffic stone | Concrete, brick, recycled coarse and fine renovation aggregate | |
| Recycled concrete water permeable brick | Concrete, brick, recycled coarse and fine renovation aggregate | |
| Recycled concrete barrier | Concrete, brick, recycled coarse and fine renovation aggregate | |
| Composite product in municipal facilities | Concrete, brick, recycled coarse and fine renovation aggregate | |
| Building engineering materials | Floor, plaster, masonry mortar | Concrete, recycled fine brick aggregate, powder material |
| Recycled concrete | Recycled coarse and fine concrete aggregate | |
| Thermal insulation recycled concrete in structure | Recycled coarse and fine brick aggregate | |
| Aerated concrete block, brick | Recycled fine brick aggregate, recycled powder material | |
| Recycled concrete cavity block | Recycled fine brick aggregate, recycled powder material | |
| Recycled concrete wallboard | Recycled fine brick aggregate, recycled powder material | |
| Recycled concrete decorative board | Recycled fine brick aggregate, recycled powder material | |
| Composite admixture | Recycled concrete powder, recycled brick powder |
The diagram of a rotor is demonstrated in Fig. 8.2, which is composed of the principle axis, belt pulley, main bearings, bearing support, hammerhead, hammer shaft, and other parts. A rotor should be equipped with a good dynamic balance, wear resistance pieces, and principle axis support of high durability to perform well in crushing and avoid frequent maintenance.
The external shell is the supporting component of the crusher, which supports the rotor and bears the crushing force task for the crusher. Plates and crushing boards with high strength are equipped in the shell the function of which is to crush and collect the materials during the hammer crushing. The crushed materials coming through the coarse and fine crushing chambers are discharged through the grate plate at the bottom.
The kinetic energy generated by the host engine is conveyed from the cone belt to the large pulley of the crusher by the electric motor pulley. The entire rotor is driven in a circular motion by the large pulley and the continuous operation and crushing is achieved.
The function of the drive system is to transfer the kinetic energy from the host engine to the crusher. The pulley should be manufactured using high-quality cast iron to avoid deformation in long-term use. As for the structure, the wrapping angle of the small pulley should be as large as possible to increase the transmission efficiency. The diagram of the drive system is demonstrated in Fig. 8.3.
Figure 8.2 Diagram of rotors of the DPF crusher. 1-bearing, 2-bearing support, 3-hammerhead, 4-hammer shaft, 5-hammer plate, 6-key principle axis, 7-principle axis, 8-terminal cover, 9-terminal plate, 10-clamp, 11-belt pulley.
The energy generated in impact crushers is produced by the impact of hammerhead on the materials while the materials are crushed when being hit on the crushing board. The wearing pieces are the fundamental components during the crushing of materials. Enough surface and internal hardness is required for the wearing pieces to reduce crushing cost and increase the operation efficiency of the crusher.
The hydraulic system is a supporting section in a crusher which is designed for easier maintenance and operation. The hydraulic system should be fully enclosed. The diagram of the hydraulic system is demonstrated in Fig. 8.4.
Jaw Crusher
The main features of a jaw crusher are large crushing ratio, even granularity, simple structure, reliable operation, easy maintenance, and low operating costs. The jaw crusher is widely used in many fields where the breaking strength is less than 320 MPa like mining, smelting, building material production, highway, railway, water conservancy, and chemical industries, and is the preferred primary crushing equipment.
Impact Crusher
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 Table 8.10.
Table 8.10
Effect of Process Conditions on the Production Capacity of Crushed Materials
| Process Condition | Production Capacity of Limestone | Production Capacity of Chamotte | ||
| Particle Size of 85% Outlet Materials Is <25 mm | Particle Size of 85% Outlet Materials Is <75 mm | Particle Size of 85% Outlet Materials is <5 mm | Particle Size of 85% Outlet Materials Is <10 mm | |
| Large inlet particle size | Decrease | Decrease | Decrease | Decrease |
| Small inlet particle size | Increase | Increase | Increase | Increase |
| Large outlet particle size | Increase | Increase | Increase | Increase |
| Small outlet particle size | Decrease | Decrease | Decrease | Decrease |
| Large water content | Decrease | Decrease | Decrease | Decrease |
| Small water content | Increase | Increase | Increase | Increase |
| Materials easy to be crushed | Increase | Increase | Increase | Increase |
| Materials hard to be crushed | Decrease | Decrease | Decrease | Decrease |
| High rotor rotation speed | Increase | Increase | Increase | Increase |
| Low rotor rotation speed | Decrease | Decrease | Decrease | Decrease |
| Large surplus motor power | Increase | Increase | Increase | Increase |
| Small surplus motor power | Decrease | Decrease | Decrease | Decrease |
8.2.3. Screening and Auxiliary Equipment
8.2.3.1. Vibrating Screen Feeder
Vibrating screen feeder is widely used in metallurgy, mineral processing, building material production, chemistry, coal, and other industries and can be used to remove the natural fine substances, transfer, and screen for the next process. The vibrating feeder is the combination of screening and conveying and both the functions can be achieved under the vibrating motion.
The vibrating screen feeder is mainly used in the following conditions: (1) It can be used for continuous and even feeding before the coarse crushing and screening, and separate the fine substances to increase the crushing capacity. (2) The bulk and granular materials can be evenly, regularly, and continuously sent into the feeding device from the storage house during the operation. (3) It can be used for the coarse screening of materials. The double screening feeder can be used to remove the mud and other small impurities in the materials.
8.2.3.2. Belt Conveyor
Belt conveyor is necessary in the production line of gravel and construction waste, and is mainly used to connect the broken equipment of different levels, sand production facilities, and screening equipment. It is also widely used in cement, mining, metallurgy, chemical, foundry, and building materials industries. The operating condition of the belt conveyor can be in the range of −20°C to +40°C, whereas the temperature of the materials conveyed can be below 50°C. In the industrial production process, the belt conveyor can be used as a link among production facilities to achieve the continuity and automation of production processes, thus improving the productivity and reducing the labor intensity. Approximately four to eight sets of belt conveyors are involved in sand and gravel production line.
8.2.3.3. YKF Circular Vibrating Screen
This series of vibrating screen with multiple layers is in a circular motion while it is specifically designed for the screening of stone materials in a quarry. It can also be applied in product classification in coal preparation, mineral processing, building materials production, electricity, and chemical industries. The main features of circular vibrating screen are listed as follows.
(1) The flow rate can be easily and stably changed through the adjustment of the exciting force. (2) The circular vibrating screen is of stable vibration, reliable operation, and long operating life. (3) The structure is simple while operation is reliable. The relative light weight and small volume makes maintenance much easier. (4) The enclosed structure of screen body effectively prevents dust pollution. (5) Low noise intensity and small electricity consumption is produced during the operation of the vibrating screen.
8.2.3.4. Dust Catcher
The dust collection devices mainly include bag filter, pulse bag filter, and electrostatic precipitator. The main purpose of the dust collector is to remove the dust in the air. thus improving the environment and reducing pollution. Another function of dust catcher is to screen and collect the powder products such as the collection of finished cement products.
8.2.3.5. XS Sand Washing Machine With Wheel Type, Spiral Sand Washing Machine
XS Sand Washing Machine With Wheel Type
This kind of sand washing machine is mainly used for washing of mixed soil and dust, along with the sand lifting in mining. The transmission parts of this machine are isolated from the water and sand, which largely reduce the failure rate during the operation process. The main features of this kind of machine are listed as follows.
(1) The loss of fine sand and stone powder in sand washing process is small. The washed sand is of good gradation, the fineness modulus can easily meet the requirements of relevant standards. (2) The structure is simple. The bearing device of impeller driving is isolated from the washing water and sand thus largely decreasing the failure rate. (3) The washed sand is of high degree of cleanliness. Meanwhile, large operation capacity, low power consumption, and long service life can also be obtained.
Spiral Sand Washing Machine
The spiral sand washing machine (XL series, for example) is able to wash and separate the soil and other impurities in sand and gravel aggregate. The enclosed structure, adjustable overflow weir plate, and reliable transmission parts increase the cleaning and dehydration effect, which can be applied to road, hydraulic, and construction industries. The main features are listed below.
(1) The structure is simple. The bearing device of impeller driving is isolated from the washing water and sand thus largely decreasing the failure rate. (2) The loss of fine sand and stone powder in sand washing process is small. The washed sand is of good gradation; the fineness modulus can easily meet the requirements of relevant standards. (3) Almost no components of the machine are vulnerable to wearing and breaking down except the screen.
8.2.4. In Situ or Mobile Crushing and Regeneration Device
8.2.4.1. General Introduction
Building garbage recycling equipment in Western developed countries is generally mobile crushing station and mobile screen station, which can be divided into two categories, i.e., wheeled and tracked, shown in Figs 8.5 and 8.6. They can be used either alone or in combination with multiple devices. Characteristics of rubber-tired mobile crushing plant are as follows:
1. strong mobility;
2. integrated complete sets of equipment;
3. reduced cost of material handling;
4. flexible combination and strong adaptability;
5. work directly and effectively; and
6. the installation form of integrated complete sets of equipment eliminates complex installation work caused by site and infrastructure of fission components, thus cutting down the consumption of the material and working hours.
Characteristics of crawler-type mobile crushing plant:
1. Low noise and low fuel consumption has realized the real economic and environmental protection.
2. The machine adopts all-wheel drive and it can realize spin in situ. Standard configuration and quick change device with perfect function of security protection is especially suitable for narrow space and complex area.
4. Typical multifunction engineering machinery products integrated machine, electricity, and liquid have compact structure and different models of complete machine dimension.
5. Convenient transportation, crawler walking, no damage to the road surface, equipped with multifunction apparels, and wide adaptation.
Compared with the traditional crushing screening equipment, the mobile crushing station has characteristics of mobility, reconfigurability, and automation. The crushing, screening, and debris sorting of construction waste can be realized if these features are applied to the recycling of construction waste, which can completely meet the requirements of comprehensive treatment of construction waste. In addition, the combination of different types of mobile crushing station screened by the mobile screen substation, which manage the primary and secondary crushing of construction waste, cannot only improve the performance of recycled aggregates, but also get the recycled aggregates piled up in accordance with the aggregate graded, facilitating the recycle of recycled aggregates.
In the process of construction waste treatment with mobile crushing station, the interaction of the waste concrete with itself contains a mix of collision and friction with each other using vibrating equipment, such as vibrating feeder and the original vibrating screen, which can reduce relatively loose waste mortar on its surface. Compared with the mechanical rub method, there is an effect gap between the two, but it plays the same role as well, which improves the performance of the recycled aggregates to some extent.
New renewable equipment can not only break, but also sieve. Mobile crushing screening equipment produced by Atlas Copco, take PC1375 type I crusher, for example, its high efficiency and flexibility, simplicity of operation, product design for easier transportation make it very suitable for field use in harsh environment, and most important of all, products broken by this device is of high capacity and good quality. PC1375 type I crusher is equipped with a special design of 19-mm-thick conveyor belt with high-strength steel wire, which effectively prolongs its service life. Its standard configuration is high-intensity magnetic belt, which can separate all the metal materials out before conveying crushing material to the dump, producing clean broken end products and the separated metal materials can earn extra income. The discharging mouth of the crusher is equipped with rollers, the impact absorption plate with special design is composed of replaceable rubber and steel, and the conveyor belt is removable, which makes obstruction cleaning and equipment maintenance very convenient.
8.2.4.2. Introduction of the Rockster Mobile Crushing Station
The design of the overall structure is demonstrated in Fig. 8.7. Features of the five main functional components, the feeding device, crushing section, presieving, drive system, and unloading parts, are highlighted in the figure.
The partial enlarged drawing of the impact crusher is shown in Fig. 8.8. The main features including the swing rollers, rotor, bearing and bearing shaft, impact plate, and unloading part are listed on the left.
The partial enlarged drawing of the jaw crusher is shown in Fig. 8.9. The main features including the crushing gap, bearing, and bearing shaft are listed on the left.
Hydrostatic Transmission Drive System of the Crushing Device
1. No clutch and energy and material loss.
2. The speed of crusher can be continuously variable between 0 and 850 rpm.
4. Best adapted adjustment between the performance of the engine and the requirement of the power of the crusher.
Accessories of the Rockster Mobile Crushing Station
1. Main unloading belts—wear resistance protection
The adjustable wear-resistance plate installed at the outlet of the crushing chamber provides protection for the main unloading belts.
2. Lubrication—central lubrication
Automatic lubrication measures can be performed on all the parts required in the crushing station.
3. Other accessories
a. Air compressor: used for device cleaning (the cooler, for example) and is connected to the hydraulic system.
b. Replace device of hammers: equipped on the lifting bracket of the crushing chamber.
c. Water pump: used for the external water supply of the dust removal system.
A high production capacity of the Rockster impact crusher can be obtained and maintained even under the condition of high crushing ratio. The dual swing rollers are based on the hydraulic adjustment and the easily controlled rotors, and the size of the finished products can be optimally adjusted. The wear-resistance materials effectively reduced the operation loss.
8.2.5. Crushing and Grinding Technologies of C&D Waste
Lamination of construction waste is the extrusion and regeneration process of the groups of material layers and is of high crushing power utilization. In traditional sand and gravel crushing line process, little kinetic energy is produced during the hit motion, whereas most crushing power is transferred into sound energy (large noise generation) and heat energy.
The energy consumption of the three main recycled materials, namely, recycled coarse aggregate, recycled sand powder, and recycled ultrafine powder is 2, 5, and 50 kWh/t (half of that of cement production), respectively.
Jaw crushing is a kind of intermittent crushing by jaw squeezing, which will cause the wrapping of concrete around the reinforced bars. However, the concrete and reinforced bars of prestressed reinforced concrete floor board can be separated in composite lamination and crushing. The selective regenerated lamination of construction waste can be especially applied for the crushing of mixed construction waste, brittle waste bricks, and waste concrete, along with the compression of tough materials like wood and fabric, etc.
A small amount of dust and noise is generated in C&D waste lamination and regeneration. The applicability analysis of this treatment in different sections is discussed below in detail.
8.2.5.1. Applicability Analysis of C&D Waste Lamination
1. Coarse Composite Crushing in the Cut Roll Crusher
The composite crushing, which consists of the sheer force produced by bite of gears on the coarse roller, and the roll crushing increases the crushing capacity. When it is used for the crushing of brick and concrete C&D waste, the reinforced bars in the prestressed concrete floor can be easily peeled and separated. When it is used for the crushing of renovation C&D waste, the packed bags can be easily broken.
2. Intermediate Selective Crushing in the Cut Roll Crusher
The intermediate crushing in the cut roll crusher is mainly used for the crushing of brittle materials like concrete and clay sintered bricks, along with the compression of rough materials like wood and fabric (to avoid being too small in size) after the coarse (primary) crushing. The selective crushing in this process is good for the separation of impurities. Impact crushers are commonly applied in intermediate crushing. However, when used in crushing of mixed C&D waste, the wood and fabric materials will be broken and mixed in recycled aggregate materials by the high-speed operating rotors and are difficult to be separated.
3. Fine Crushing in the Cut Roll Crusher and Recycled Sand Production
The C&D waste debris after the intermediate (secondary) crushing is further crushed in which the sand and gravel can also be the grinding media for the extrusion and crushing of brick particles. Those bricks of low strength will be crushed to recycled powder materials while the sand and gravel will become coarse and fine sand materials. The raw materials (sand and gravel) and chamotte (clay sintered brick, cement paste) are classified and regenerated.
4. Hoop-Roller Grinding and Ultrafine Powder Material Production
The particle size of recycled powder materials after hoop-roller grinding can be adjusted from 1 to 80 μm (300–3000 mesh), and the market adaption capacity of recycled powder material can be greatly enhanced. Particles of size less than 30 μm are called ultrafine powder.
The recycled hoop-roller grinder can be applied as the corollary equipment in C&D waste disposing companies due to the small volume, negative pressure operation, and mediate production capacity.
The building materials made up of silicon aluminum powder have been developed to a major category of building materials, such as aerated concrete blocks, aerated concrete panels, foam concrete plates, and powder concrete. Powder material production technology will be widely applied in the near future.
5. Separation of Lightweight Substances
The drum-type lightweight combustible separator is particularly suitable for the separation of lightweight material and construction waste. The particle size of most brittle materials in the mixed crushed C&D waste after intermediate (secondary) crushing is below 30 mm, whereas that of rough materials is above 30 mm. The lightweight materials larger than 30 mm in diameter like wood and fabric are attached on the screen and lifted so that the screen mesh blinding is avoided and the 30 mm size of particles are successfully separated.
The construction waste recycled coarse aggregate below 30 mm in size falls down through the sieve drum. The mixed construction waste materials, which are mostly brittle and 5 mm or less, between 5 and 30 mm, are finely cut and roll. The particle size of the brittle materials in mixed C&D waste debris after being finely crushed is mostly above 5 mm, whereas that of rough materials is between 5 mm and 30 mm. They can be separated similarly.
The vibrating screen used in traditional sand and gravel industry is suitable for sand grading but not for the separation of mixtures due to the flat screen machine. Lightweight substances are absorbed on the flat screen and easily cause mesh blinding, which will severely affect the screen efficiency. Meanwhile, this process must be performed under the dry weather.
8.2.5.2. Applicability Analysis of Three Processes Involved in the C&D Waste Lamination
One-Stage Composite Impact Crushing Pretreatment Process
As the strength of C&D waste is relatively low, the impact crusher can basically meet the demand for coarse crushing and the particle size of 70% crushed waste can be below 50 mm after primary crushing (once). The peeling efficiency of cement paste from concrete blocks, reinforced bars from prestressed floor boards, and the package breaking is lower for traditional impact crushing. The composite impact crusher is equipped with gears capable of shearing and impact crushing. The rotors with gears can easily peel the cement paste or reinforced bars mentioned earlier in the corresponding processes.
Roll Crushing + Roll Grinding Combined Recycling Process
The rolling machine along with the hoop-roller grinder can be used in C&D waste debris grinding and the recycled fine aggregate and recycled powder can be recycled, respectively. The crushing ratio and energy consumption of both facilities are high and low, respectively.
Fine crushing of brick and concrete waste can be easily achieved using the high-pressure rolling machine, the particle size of about 90% of which will be below 5 mm when crushed once. Peeling of concrete from the prestressed reinforced bars can also be achieved.
Single-stage or multiple-stage hoop-roller grinder should be selected depending on the powder specification and energy production demands. The multiple-stage hoop-roller grinder is widely used in the production of inorganic powder and mineral powder.
Rolling + Rolling Combined With Extrusion Treatment Process
The main task of renovation construction waste handling is the separation of lightweight impurities and construction waste. The rolling crusher with opposite rollers is capable of crushing the brittle debris and compressing the lightweight materials by the low-speed and high-pressure extrusion of the two opposite rollers. As the gap between the opposite rollers, rotation speed, and pressure are all adjustable, materials of different scales in renovation construction waste can be handled.
The concrete C&D waste recycling process of “impact crusher + cone crusher + hoop-roller grinder” is also capable of handling brick waste. In general, the secondary crushing using the cone crusher in this process with an enclosed crusher is a process of multicrushing, and the water content of waste will become an important affecting factor. The wet waste will be adhered on the wall of the grinding chamber, and the crushing efficiency and waste discharging will be affected. When the climate is humid, only coarse impact crushing is performed and in this case the crushed materials are used for roadbase materials. Otherwise, three consecutive crushings are performed and the recycled coarse aggregate, fine aggregate, and powder materials are collected, respectively.
The brick and concrete C&D waste recycling process of “impact crusher + rolling crusher + hoop-roller grinder” is also capable of handling the concrete waste. In this case, the water content of waste will not be an important affecting factor. This process is suitable in the regions with wet climates.
The renovation C&D waste recycling process of “rolling crusher (coarse/primary crushing) + rolling crusher (intermediate/secondary crushing) + rolling crusher (fine/tertiary crushing)” is also capable of handling the two kinds of waste discussed earlier. The particle size of debris is crushed less than 20 mm and the lightweight materials are compressed, and they are separated using the drum sieve. The energy consumption is low in this process; however, the shape of products is not good (usually flat and with cracks). There is no problem in roadbase material and raw materials of prefabricated product production. But molders (the rotation of rotors in crusher is used to polish the edge and corner) should be used for premixed concrete and mortar production.
8.2.6. Manufacturing System of Sand and Gravel Aggregate
8.2.6.1. General Information
Sand and gravel aggregate includes sand, gravel, detritus, pebble, stone, rock, and other materials and is the main construction material used in concrete and other piling structures. Particle size of this kind of aggregate is usually larger than 4.75 mm and is called coarse aggregate in concrete application. It is commonly composed of two kinds, gravel and pebbles. Gravel is a kind of rock particle produced by mechanical crushing and sieving of natural rock, whereas pebble is the rock particle generated from natural weathering, water transportation, and sorting, and the particle size of both is above 4.75 mm.
Sand generally refers to particles of size less than 4.75 mm, and it belongs to fine aggregate in concrete application. Sand generally includes river sand, artificial sand, mountain sand, dilute sand, and lake sand. It can be classified into four grades according to fineness modulus:
Coarse sand: fineness modulus of 3.7–3.1, with an average particle diameter of 0.5 mm or more;
Medium sand: fineness modulus of 3.0–2.3, with an average particle size of 0.5–0.35 mm;
Fine sand: fineness modulus of 2.2–1.6, with an average particle diameter 0 35–0 25 mm;
Special fine sand: fineness modulus of 1.5–0.7, with an average particle diameter of 0.25 mm or less.
The larger the fineness modulus is, the coarser the sand will be. The appropriate range of fineness modulus of the sand aggregate used in normal concrete is 3.7–1.6. Both medium sand and coarse sand spiked with some fine sand (coarse:fine = 4:1) are applicable.
Sand aggregate plays a significant role as a skeleton and in passing the stress in concrete. Aggregates can also bear the load even without grout while suppressing the shrinkage and prevent cracking. The cement mortar produced from sand and cement is able to improve the workability and flowability of concrete.
The coarse aggregate can be classified as follows according to the particle diameter:
One-graded 5–20 mm
Two-graded 5–20, 20–40 mm
Three-graded 5–20, 20–40, 40–80 mm
Four-graded 5–20, 20–40, 40–80, 80–120 (150) mm
The fine aggregate should meet the requirement regulated in Table 8.11.
Traditional aggregates production process includes the following procedures: primarily crushing by jaw crusher after blasting of rocks, then use impact crusher or cone crusher for further crushing according to the fineness of stone and production demands. Standard sand and gravel aggregate particles are subsequently produced by sand production machines. For wet sand process, cleaning is also required for sand production machines.
Table 8.11
Quality Requirement Regulated for Fine Aggregate
| Item | Index | Note |
| Mud content in natural sand (%) | <3 | (1) Mud content is the total amount of the silt, clay the size of which is less than 0.08 mm |
| Clay content (%) | <1 | (2) Should not contain clay cluster |
| Rock powder in artificial sand (%) | 6–12 | Particle size less than 0.15 mm |
| Consistency (%) | <10 | Loss amount after five circulations of sodium sulfate solution method |
| Mica content (%) | <2 | |
| Lightweight material content (%) | <1 | Density less than 2.0 g/cm3 |
| Density (%) | >2.5 | |
| Sulfide and sulfosalt content (%) | <1 | By weight (SO3) |
| Organic matter content (%) | Lighter than standard color | If darker, mortar should be prepared for strength comparison |
Cited from Chinese standard quality control of sand and gravel production.
8.2.6.2. Production Process
1. Classification of sand and gravel aggregate production process:
a. Single-stage aggregate production process;
b. Multistage aggregate production process;
c. Manufactured-sand production line process;
d. Fixed production line process;
e. Mobile production line process.
2. Selection of regular construction stone aggregate line
Factors affecting the selection of sand and gravel production line equipment:
a. fragility of materials
b. feeding particle size of materials
c. output particle size of finished materials
d. geographical limitations of the production site
e. shape requirements for finished products
3. Case analysis of aggregate production line
Type selection of common facilities used during aggregate process line is listed in Table 8.12.
Selection of crushers under specific application cases is listed in Table 8.13.
4. Flow sheet of various processing lines
a. Typical sand and gravel aggregate processing line flow sheet with secondary crushing with 500 t/h
Table 8.12
Type Selection of Common Facilities Used for Aggregate Process Line
| No. | Production Capacity (t/h) | Primary Crushing Facilities | Secondary Crushing Facilities (Normal Material) | Secondary Crushing Facilities (Material of High Silica Content) |
| 1 | 50–130 | PE600 × 900 | PF1214 | PYS-B0917 |
| 2 | 110–250 | PE750 × 1060 | PF1315 | PYSB-1321 |
| 3 | 160–380 | PE900 × 1200 | PF1416 | PYS-B1624 |
| 4 | 310–550 | PE1000 × 1200 | PF1520 | PYS-B1626 |
| 5 | 400–800 | PE1200 × 1500 | PF1620 | PYS-B2133 |
Table 8.13
Selection of Crushers Under Specific Application Cases
Typical sand and gravel aggregate processing line flow sheet with secondary crushing at 500 t/h is demonstrated in Fig. 8.10. Material being sent into the stock bin by forklift is divided into two groups: materials of size 0–100 mm and >100 mm through the outlet of feeder ZSW500. Those materials of size 0–100 mm are sent to the vibrating sieve 2YK1848 by belt conveyor, whereas those >100 mm are to be broken by jaw crusher PE1000 × 1200. Two kinds of materials (0–10 and >10 mm of size) are obtained after 2YK1848; the former materials are sent by conveyor to the stockage piles of finished materials, whereas the latter materials along with those being crushed by PE1000 × 1200 are sent together to the impact crusher [PF2024] for further crushing. The crushed materials are then sent to No. 1 vibrating sieve 2YK3070 through the conveyor, the materials obtained here are classified as particle size of >30, 20–30, and <20 mm. Particles with sizes larger than 30 mm are sent back to the impact crusher [PF2024], those with sizes between 20 and 30 mm are conveyed to stockage piles of finished materials, and those with sizes smaller than 20 mm are transported to No. 2 vibrating sieve 2YK3070. Three classified groups of materials based on their sizes are gained after this sieve, namely, 10–20, 5–10, and <5 mm, all of which are conveyed to stockage piles of finished materials separately. Dust removal equipment can be added to each device in accordance with local environmental regulations.
b. Limestone processing line flow sheet with single crushing stage with 500 t/d
Limestone processing line flow sheet with single crushing stage with 500 t/d is demonstrated in Fig. 8.11. Material being sent into the stock bin by forklift is divided into two groups: materials of size 0–80 and >80 mm through the outlet of feeder ZSW630. Materials of size 0–80 mm are sent to the vibrating sieve 2YK1848 by belt conveyor, whereas those >80 mm are to be broken by hammer crusher ZPC1620. Two kinds of materials (0–10 and >10 mm of size) are obtained after 2YK1848 like the process (a) discussed earlier, the former materials are sent by conveyor to the stockage piles of finished materials, whereas the latter materials are sent back to the hammer crusher ZPC1620 for further crushing. The crushed materials are then sent to No. 1 vibrating sieve 2YK3070 through the conveyor, the materials obtained here are classified as particle size of >30, 20–30, and <20 mm. Particles with sizes larger than 30 mm are sent back to hammer crusher ZPC1620, those with sizes between 20 and 30 mm are conveyed to stockage piles of finished materials, and those with sizes smaller than 20 mm are transported to No. 2 vibrating sieve 2YK3070. Three classified groups of materials based on their size are gained after these sieves, namely, 10–20, 5–10, and <5 mm, all of which are conveyed to stockage piles of finished materials separately. Dust removal equipment can be added to each device in accordance with local environmental regulations.
c. Typical flow sheet of stone processing line: normal raw material (project of hourly production of 400 t sand and gravel processing line in Henyang City)
The typical flow sheet of stone processing line is demonstrated in Fig. 8.12. Material being sent into the stock bin by forklift is crushed by jaw crusher PE1000 × 1200 after the loader ZSW500, and then is further crushed by impact crusher PF1620. Those materials are sent to the vibrating sieve YKF2460 for screening and two classified materials (of size >60 and 0–60 mm) are obtained. The former materials are sent by conveyor back to the impact crusher PF1620, whereas the latter materials are conveyed to the transit storage bin and separated to two processing lines with the same production capacity for crushing. These materials are transferred from electromagnetic vibrating feeder to the German sand producing machine GZD 130-5. The crushed materials are then sent to the vibrating sieve 2YKF2865 and two classified materials (of size 0–5 and >5 mm) are thus produced. Those materials (0–5 mm) are lifted by the bucket elevator NE200 to the separator YND1000, whereas the other materials are sent back to BHS 1222 for further crushing. Two classified materials (of size 0–0.075 and 0.075–5 mm) are produced from YND1000 and are sent separately to the finished product stockpiles.
d. Hard raw materials (350–400 t/h granite processing project)
Hard raw materials processing project (350–400 t/h granite processing project) is demonstrated in Fig. 8.13. Material being sent into the stock bin by forklift is crushed by jaw crusher PE1000 × 1200 after the loader ZSW500, and then is further crushed by cone crusher PYS-1626 through the transit storage bin and the electromagnetic vibrating feeder GZD110-4. Two kinds of materials (of size >35 and 0–35 mm) are obtained after the crushed materials are sent to the vibrating sieve 2YK1848. Those >30 mm are sent for further crushing by PYT-1200 and then screened by YK2460, whereas the other materials are conveyed to the impact sand producing facility PCX1400 and the materials obtained are screened by 2YK2460. The materials obtained here are classified as particle size of >30, 20–30, and <20 mm. The subsequent process is similar to the project discussed earlier. Three classified groups of materials based on their size are gained after another crushing and screening, which are 10–20, 5–10, and <5 mm, respectively. All of them are conveyed to stockage piles of finished materials separately. Dust removal equipment can be added to each device in accordance with local environmental regulations.
8.2.7. System of Sand Processing Line
Sand and gravel industry provides the basic raw materials of construction engineering and has largely contributed to the rapid development of construction and traffic industry. With the gradual decrease of natural sand resources, production of sand and gravel aggregate using low-grade limestone mines or other waste mineral for the replacement of natural resources should be encouraged.
8.2.7.1. Division of Sand and Gravel Materials
1. Natural Sand
It is naturally generated, and the particle size is less than 4.75 mm after artificially mining and sieving, including river sand, lake sand, mountain sand, and sea sand, not including soft and weathered rock particles.
2. Manufactured Sand
Manufactured sand is produced by mechanic crushing and screening and the particle size is less than 4.75 mm. Most manufactured sand is rock, mine tailings, or industrial waste particles, not including soft and weathered rock particles.
3. Category of Sand
Sand can be divided into class I, II, and III according to the technical requirements.
4. Clay Content
Clay content refers to the particle content of size less than 75 μm in natural sand. Clay content of natural sand class I is ≤1.0%.
5. Powder Content
Powder content is the particle content of size less than 75 μm in manufactured sand. Powder content of sand class I is ≤10.0%.
6. Specification of Sand
Sand can be classified into three specifications according to the fineness modulus.
• Coarse: 3.7–3.1
• Medium: 3.0–2.3
• Fine: 2.2–1.6
Sand production process can be divided into dry production and wet production.
8.2.7.2. Dry Production Line
The dry production process is established later than wet production process, and is further developed on the basis of the traditional wet production. Main facilities involved in this process include hoppers, vibrating loaders, belt conveyors, impact sand producing machines, SZZ vibrating sieves, elevators, high-efficiency separators, and storage bins. During this process, no water is needed and added in the cleaning of clay powder from the sand.
The key components of shortened dry sand processing system is German BHS sand producing machine and the air mesh, the closed-loop controlling system is made up of the feeder, regulatory panel, recycled filter, and dust collector. Automatic control of fineness modulus is the key technology in this process. Typical features are listed below in detail.
1. German BHS sand producing host machines are equipped and of low energy consumption, low cost, good particle shape, and stable grading. The impact rotors in two cavities largely increase the crushing effect and reduce the power.
2. The sorting technology using air mesh is able to simultaneously separate the qualified and unqualified products in the crushed materials. The classification process is even more accurate. Those dusts of particle size below 0.075 mm will be removed by the dust catcher. Grading adjustment can be performed by regulation, while unqualified products will be sent back to the crusher.
3. Target products of particle size between 0.7 and 1.5 mm used to be difficult to produce and can be largely increased by the application of the backward closed system. The particle shape of products can be as good as that of natural sand (solid content 57–59%). Appropriate moisture content can also be obtained using spraying devices.
4. High energy performance in the system and high sand production ratio (60–70%) is found. Low electricity consumption of less than 2.3 kWh for a ton of sand production can also be achieved.
5. The frame structure requires small land occupation, short construction time period, and low civil engineering investment. The enclosed structure largely decreases the dust emission, which is far lower than the regulated value 30 mg/Nm3.
A shortened dry sand processing line is demonstrated in Fig. 8.14.
The raw materials coming out of the electromagnetic vibrating feeder GZG850-4 are lifted by the elevator NE300 to HBS1222 sand producing machine for crushing. The crushed materials are transported to the winnower screening 4FX2460 and separated into four groups. The large particles on the top layer are sent back to sand producing machine for crushing, whereas the other three groups of materials are conveyed to the product stockpiles. The bag filter SLQM96-10B is also equipped for dust removal and the small particles collected are elevated to the powder storage bin.
The distribution control system of the dry sand processing line involved is demonstrated in Fig. 8.15.
8.2.7.3. Wet Production Line
Wet artificial sand aggregates production process is more suitable in regions rich in water resources. Typical flow sheet of process line is demonstrated in Fig. 8.16.
The crushed materials coming from the jaw crusher PE1200 × 1500 through the vibrating feeder ZSW630 are then conveyed to the transit storage bin, where these materials are separated and, respectively, sent to the impact crusher PFG1822 and two cone crusher (for coarse crushing) PYS-B1636. The crushed materials are transported to the vibrating sieve No. 1 2YK3270, where three classified grades of materials (of particle size >30, 20–30, and <20 mm) are obtained. Particles of size larger than 30 mm are conveyed to PYS-B1626 cone crusher (for fine crushing) and then sent back to the vibrating sieve. Particles of size between 20 and 30 mm are transported to the finished product stockpiles. The rest of the materials are conveyed to the vibrating sieve No. 2 2YK3270 where three other classified grades of materials are got (size 10–20, 5–10, and 0–5 mm). Those materials of particle size smaller than 5 mm are sent to the spiral sand washing machine for clay and mud removal before entering the finished product stockpiles.
Wet artificial sand aggregate processing has the following advantages:
1. The aggregates produced are clean on the surface and the quality is better.
2. No dust pollution is caused due to the water washing procedure.
8.2.8. Integration Technology of Renewable Wall Materials
At present, most infilled walls of residential construction buildings of frame structure in big cities are composed of small pieces of materials and are built piece by piece, followed by huge amount of leveling, painting, and other wet work like brick structure. In this case, wet wall painting and plastering accounts for over 50% of the total wall construction work. The cost of wet wall construction work is more than twice that of wall materials. Meanwhile, the wet wall construction work may also result in slow construction work, low efficiency, and large resource consumption.
8.2.8.1. Eco-Friendly Ecological Wall Board
It refers to the ecological environment construction materials. The production amount of building materials is the largest while the resource consumption and pollution level are also the highest among all kinds of materials. Human health is also closely related to the pollution level of building materials. On the other hand, it is most likely to use other solid wastes as raw materials to produce building materials to improve the ecological environment. Ecological building materials is a class of new building materials, which might meet the following principles: (1) low resource and energy consumption and environmental pollution level in their production and usage; (2) recycling and utilization of waste; (3) capable of improving living environment and health condition; (4) of good feature and performance, capable of meeting the requirements of various construction projects.
Technical Route of EF Ecological Wall Board Processing
1. Recycled aggregate production process
2. Ecological wallboard manufacturing process
Mixing of cementitious materials, recycled aggregates, modified materials, additives, conveying, extrusion molding, cutting, packaging, steam curing, storage.
3. Ecological wallboard assembly construction process
The first layer, setting out, adhesive plastering on wallboard joints, wallboard installing, correction, construction of the second block is similar. The construction of the second and third layers is the same as that of the first layer. The vertical joint of layers should be stagger-jointed to avoid the crack resulting from stress concentration. Assembly of the entire wall completed—direct scraping of 2 mm putty once or twice—painting of coatings.
Structure–Function Integration of EF Ecological Wallboard
EF ecological wallboards, as assembled wallboards, are not identical to sheets, strip boards, and blocks in specification and structure. “Slabs” and “ribs” (the joint portions among holes), as components of EF wallboards, are manufactured through a composite extrusion in the factory, thus avoiding the combination of flat boards (slabs) and channels (ribs) and improving the efficiency of construction. Functions of EF boards are as follows. The thickness, density, strength, etc. of EF boards meet the sound insulation, hanging force, and other functional requirements of frame structured residential infilled walls. The holes of ecological wallboards both successfully reduce the weight and save materials. The good mechanical properties of the round holes improve the flexural strength of the boards. Pipelines are easy to be arranged and can run through the holes. The “slabs” of EF ecological boards molded by machines are highly flat and can reduce the cement mortar wet paint work on construction sites.
Specifications of EF ecological wallboards can be classified into two series: 6, 8, 10 series and 6, 9, 12 series (which means the length is 60, 80, 100 mm and 60, 90, 120 mm, respectively). The main specification size is 1000 × 500 × 100–150 mm (L × H × D), 1200 × 600 × 100–150 mm (L × H × D), respectively, which corresponds with the construction module. The thickness of EF wallboards correspond with that module required by frame-structured residential infilled walls. The height of EF wallboards correspond with the connecting bars module of wall columns in reinforced concrete-structured residential buildings. The length of EF boards corresponds with the physical efficiency of manual construction (the length is correlated with board weight). EF ecological wall structure meets the demand of frame-structured residential buildings and thus can be the structure–function integration of infilled wall materials.
Modular Assembly Construction
Construction method of EF ecological wallboards is modular staggered joint and assembly combined. Thirty-six pieces of ecological wallboards are needed for the construction of a chamber wall (3 × 6 m) and the construction time is about 2 h for workers in pairs. For clay hollow bricks (240 × 115 × 90), the amount required is 720 blocks and the construction time is about 2 days. For small concrete blocks (390 × 390 × 190), 225 blocks and 1 day are needed, respectively.
8.2.8.2. Green Building Materials: High-Efficiency Self-Insulation Wall Material
The substances used in the raw material application, product manufacturing, usage, recycling process, and waste disposal of green building materials should be of no harm to human health and have low environmental burdens. It is also regulated in “Evaluation standard for green building” (GB/T 50378-2006) that: (1) The building materials used should be reusable and recycled. (2) For the building materials produced using solid waste as raw materials, the waste amount added should not be less than 30%, the usage amount among the same kind of building materials should not be less than 30%.
The self-insulation wall materials and products not only have good insulation effect, but are also long in their service life, which belong to green building materials. Take the hollow blocks with high insulation properties produced in France, for example, the heat transfer coefficient of 300-mm-thick brick wall can be reduced to 0.75–1.0 W/m2·K.
At present, self-insulation wall production can mainly refer to the wall insulation technology using composite insulation block, lightweight sand aerated concrete block, aerated concrete plate, porous brick shale modulus, etc.
Composite Insulation Block
The production process of composite insulation block is introduced as follows. The lightweight concrete aggregate or common concrete hollow block is used as the basic material. High-efficiency insulation materials (such as polystyrene material, slag, rice husk, perlite, and foam insulation materials) are used as filling materials in the holes of hollow blocks. The automatic process line is applied in which the block shells and insulation materials are molded together as the composite insulation block. The composite blocks with good insulation properties and economic value can be divided into three types: non-load-bearing, load-bearing, and interior wall blocks. The main features are high strength, low weight, low structure loading, low investment of manufacturing plant, various strength grades, feasible construction method, easy waste utilization, etc. Those hollow blocks with double or triple rows of holes are generally used of which the porosity is ≥40%. The main performance index is listed in Table 8.14.
Lightweight Sand Aerated Concrete Block
This self-insulation system of sand aerated concrete block is composed of reinforced concrete frame and sand aerated concrete block. The external side of the insulation part is mainly waterproof interface agent, paint layer (partially with alkali-resistant fiberglass mesh), and surface layer. The internal side is mainly the putty layer (partially with alkali-resistant fiberglass mesh) and the surface layer.
The main features of sand aerated concrete block are listed as follows.
1. Low density. The density of this building block is only 1/5–1/3 of that of common building materials like concrete and clay brick. The weight of constructed building can be largely reduced thereby reducing the construction costs.
2. Strong fire resistance. This building material is mainly made up of inorganic noncombustible substances of strong fire resistance. The duration of fire resistance can be longer than 4 h. No harmful gas will be emitted at high temperature.
3. Good temperature, heat, and sound insulation performance. Many small open or closed gas pores will generate inside the block in the production process. In this case, static air layers will be formed inside the block and cause the decrease of thermal conductivity. The materials used are also low in thermal conductivity (1/3 of that of clay brick).
4. Strong antipermeability. The large number of open and closed pores lengthens the time required for water absorption and temperature conductivity. It would take four more times longer to its water saturation than the clay brick.
Table 8.14
Main Performance Index of Composite Insulation Blocks
| Item | Requirement | Test Result | ||
| Polystyrene board | Dimensional stability (%) | ≤3.0 | 1.71 | |
| Water absorption ratio (in volume) (%) | ≤4.0 | 2.10 | ||
| Foam concrete | Compressive strength (MPa) | ≥0.50 | 0.64 | |
| Drying shrinkage value (mm/m) | ≤1.0 | 0.72 | ||
| Water absorption ratio (in volume) (%) | ≤12.0 | 7.3 | ||
| Composite insulation block | Compressive strength (MPa) | ≥5.0 | 6.0 | |
| Drying shrinkage value (mm/m) | ≤0.20 | 0.16 | ||
| Relative water content (%) | ≤40 | 29 | ||
| Frost resistance (D15) | Mass loss (%) | ≤5 | 0.2 | |
| Strength loss (%) | ≤25 | 6 | ||
| Thermal resistance (m2·K/W) | ≥2.5 | 3.06 | ||
| Carbonation coefficient | ≥0.8 | 0.91 | ||
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