Material Blockwork

Faculty of Architecture, Planning and Surveying

QSD 132 – Construction of Technology (Material)

Report of Block

Name : Dahlia Binti Ab Aziz

Class : AP1141FC

Student ID : 2012611132

Lecturer’s Name : En. Abdul Muhaimin Ab Wahid

Date of Submission : 05.09.2012

Index

Acknowledgement 2

Introduction 3

History 4

General Types of Blocks 5

Dense Concrete Blocks 5 Lightweight Concrete Blocks 5 Aerated Concrete Blocks – Aircrete 6

Types Of Blocks 7

The Manufacturing Process of Concrete Masonry Blocks 9

Raw Material and Design 9

The Process 10

Step by Step Manufacturing Process 13

Conclusion 15

Reference 16

Appendixes 17

Types Of Block and Manufacturing Process | 1

Acknowledgement

This assignment would only be achieved by the support from my lovely and spirited parents and from my darling yet straightforward sisters. I hereby wish them all the thanks in the world to show on how grateful I am from their effortless moral support and ideas on the proceedings for assignment.

While searching for information, there were few other scholars that were such a help on my findings, making me feel the need to bid them lots of thanks here to show my appreciation on their time and energy spent. To my bashful friends that refused to be name, may my gratefulness has been conveyed.

Last but would never be least in fact the biggest thanks should be given to my charming lecturer, En. Abdul Muhaimin on his understanding and ambiance towards his students including me, who is still trying to grasp the idea that I am a scholar now. Thank you, En. Abdul Muhaimin for teaching me new knowledge


Introduction

A cement block may also be called a concrete block, a foundation block, or a concrete masonryunit (CMU). It is also known as a breeze block, a cinder block, or a clinker block. These blocks are made with a mixture of Portland cement, aggregate, and water. The standard size is listed as 8 inches x 8 inches x 16 inches (20 cm x 20 cm x 41 cm) in the US and 44 cm x 21.5 cm x 10 cm (17.3 inches x 8.5 inches x 3.9 inches) in the UK, although the blocks are actually a bit smaller to allow room for mortar joints. Some cement block companies will make other sizes upon request.

The most common aggregate for cement blocks is a mixture of sand and gravel. This is mixed as a rather dry, low-slump mix that results in a hard, durable cement block. Aerated concrete can be used to make blocks that are lighter in weight but still very strong. coats sand/cement render. Insulation is in the form of cavity boards and a lightweight block inner leaf. Blocks (dense and lightweight) are also used for internal loadbearing walls and partitions

Industrial wastes are sometimes used as aggregate, but the cement blocks will be lower in density and therefore less durable. Cinder blocks, called breeze blocks in the UK, have cinders in the aggregate, and clinker blocks have clinkers. These blocks are made from lightweight, aerated concrete. They form the internal leaf of a cavity wall and will be finished with plasterboard fixed on plaster dabs. These blocks are also suitable for plastering. But sadly, these blocks have less compressive strengthand are not suitable for foundation work.

Concrete masonry units have become a standard building material due to the structural advantages, energy efficiency, durability, fire-resistant quality, economics, and minimal maintenance. Concrete masonry also allows architectural freedom and versatility. Due to its durable attributes CMU is a prudent material for both hot and cold weather environments, hurricane or high wind areas, or fire prone areas. Concrete masonry units can be a value in achieving LEED rating points.

The concrete mixture may also contain ingredients such as air-entraining agents, coloring pigment, and water repellent. Recycled aggregate products are also being used in making CMU. There are many different applications for CMU which are derived from its manufacturing process. Concrete masonry units can be manufactured into a variety of shapes and sizes for a variety of applications. During the manufacturing process, a machine molds moist, low-slump concrete into the desired shapes for their specific use such as residential building, commercial and industrial building needs, permeable concrete pavers, and segmental retaining wall usage. Other uses for concrete masonry units include retaining walls, hurricane safe enclosures (Safe Rooms) and exterior décor hardscape applications such as patios, walkways, chimneys and fireplaces.

In addition to its many uses, concrete masonry units can be manufactured for virtually any architectural or structural function. Split-face block units have been fractured lengthwise or crosswise by machine to produce a rough stone-like texture. A patented slotted concrete block provides high sound absorption, making it ideal for use in residential home construction and commercial construction including gymnasiums, factories, bowling alleys, or other places where noise generation is high. Concrete masonry applications are used to construct small to large residential homes and commercial and industrial buildings.


History

Concrete mortar was used by the Romans as early as 200 B.C. to bind shaped stones together in the construction of buildings. During the reign of the Roman emperor Caligula, in 37-41 A.D. , small blocks of precast concrete were used as a construction material in the region around present-day Naples, Italy. Much of the concrete technology developed by the Romans was lost after the fall of the Roman Empire in the fifth century. It was not until 1824 that the English stonemason Joseph Aspdin developed portland cement, which became one of the key components of modern concrete.

The first hollow concrete block was designed in 1890 by Harmon S. Palmer in the United States. After 10 years of experimenting, Palmer patented the design in 1900. Palmer's blocks were 8 in (20.3 cm) by 10 in (25.4 cm) by 30 in (76.2 cm), and they were so heavy they had to be lifted into place with a small crane. By 1905, an estimated 1,500 companies were manufacturing concrete blocks in the United States.

These early blocks were usually cast by hand, and the average output was about 10 blocks per person per hour. Today, concrete block manufacturing is a highly automated process that can produce up to 2,000 blocks per hour.Concrete blocks have been in common use since the 1930s. Early blocks were often made from local aggregates, most of which are no longer available. Concrete blocks have been used since the 1930s although it was not until the 1950s and early 1960s that they completely replaced bricks as the internal leaf in cavity walls. In their early years (30s and 40s) they tended to be used for internal partitions, both loadbearing and non-loadbearing.

Concrete blocks were first used in the United States as a substitute for stone or wood in the building of homes. The earliest known example of a house built in this country entirely of concrete block was in 1837 on Staten Island, New York. The homes built of concrete blocks showed a creative use of common inexpensive materials made to look like the more expensive and traditional wood-framed stone masonry building.

This new type of construction became a popular form of house building in the early 1900s through the 1920s. House styles, often referred to as "modern" at the time, ranged from Tudor to Foursquare, Colonial Revival to Bungalow. While many houses used the concrete blocks as the structure as well as the outer wall surface, other houses used stucco or other coatings over the block structure. Hundreds of thousands of these houses were built especially in the midwestern states, probably because the raw materials needed to make concrete blocks were in abundant supply in sand banks and gravel pits throughout this region.

The concrete blocks were made with face designs to simulate stone textures: rock-faced, granite-faced, or rusticated. At first considered an experimental material, houses built of concrete blocks were advertised in many portland cement manufacturers' catalogs as "fireproof, vermin proof, and weatherproof" and as an inexpensive replacement for the ever-scarcer supply of wood. Many other types of buildings such as garages, silos, and post offices were built and continue to be built today using this construction method because of these qualities.


General Types of Block

Dense Concrete Blocks

Dense concrete blocks have barely changed in the last 60 years or so. They are usually made from cement, fine aggregate and coarse aggregate. They can be produced in a range of crushing strengths and, nowadays, tend to be used for loadbearing partitions, foundations and, possibly, party walls. They generally have poor thermal insulation and readily absorb water. However, 20 years ago they were common in the internal leaf of cavity walls (when insulation requirements were less onerous) and nowadays they can also be used to form the external leaf providing some form of cladding or render is provided. Dense blocks should be laid in mortars of average strength; 1:1:6 or 1:2:9 (or their equivalent). Stronger mortars may limit movement and may cause cracking in the blocks rather than the joints. Weaker mixes may compress under loading. Stronger mortars are sometimes specified below ground level. Both these picture show dense blocks forming part of the substructure.

A standard block is the equivalent of three bricks high and two bricks long. They are available in a range of widths from about 50mm to 300mm. Dense blocks provide a good key for most plasters and renders. However they should be allowed to dry properly before plastering as the blocks absorb rainwater and will shrink on drying. This can cause cracking. During the last 50 years or so there have been several other types of block used in the UK. The ones featured here are no longer available but will be found in older buildings during rehab works etc. Both these blocks had disappeared by the early 1980s The left hand block is made from clay. These provided good fire resistance but were difficult to cut on site. The right hand block, formed from concrete, sometimes had the voids filled with polystyrene insulation. They shattered easily when cut or chased (for wiring etc). The polystyrene beads littered many sites in the 1970s and 1980s.

Lightweight Concrete Blocks

Since the 1930s a wide range of lightweight blocks have been produced. In many cases the early blocks were meant to be light, not because of their insulation properties, but because they were light and easy to handle. However, as fuel prices rose in the late 1960s more emphasis was placed on thermal insulation. Nowadays, the big advantage of lightweight blocks is their thermal insulation characteristics.

During the last 80 years or so a variety of aggregates have been used to make lightweight blocks. These would often depend on the availability of local industrial wastes. Breeze blocks (no longer available) for example, were made from coke. Clinker blocks were made from furnace clinker (8 parts clinker to 1 part cement was typical). Blast furnace slag (from the iron and steel industry) was also a common aggregate. These slags contained hydraulic limes and so only small amounts of cement were required to make the blocks. Some blocks have been made from naturally occurring lightweight aggregates. Pumice, for example, is a lightweight volcanic material. These are fairly rare in modern construction.

In the 1970s and early 1980s there were a number of blocks available which, although made from dense concrete, incorporated thermal insulation. Two are shown here; the one on the left had two or more cells filled with polystyrene beads. On site these were a bit of a nuisance. They were difficult to cut, eg, to make a three quarter block, and the pellets often escaped and drifted over the site. They were also difficult to chase for wiring and sockets. The one on the right had a foamed insulation bonded to the inner face, ie the cavity side. Both these blocks have been generally superseded by aerated concrete blocks. These were introduced in the early 1950s when they were known as cellular concrete or gas concrete blocks. They are now often referred to as aircrete blocks


Aerated Concrete Blocks – Aircrete

Aerated blocks are made from cement, lime, sand, pulverised fuel ash (from power stations) and water. First the PFA sand and water are mixed to form a slurry. This is then heated and mixed with cement and lime and finally a small amount of aluminium powder is evenly dispersed through the mixture before it is poured into moulds. The aluminium powder reacts with the mix to form millions of tiny pockets of hydrogen. These subsequently diffuse from the material to be replaced by air (see photo right). When the mixture has partially set the long strips of aerated concrete are wire cut into blocks of the right size and the cut blocks are transferred to an autoclave for high pressure steam-curing. During this process calcium silicates are formed which bind all the ingredients together.

Different manufacturers produce blocks with slightly different characteristics. Celcon, for example, produce a range of blocks, some of which are described below.

Standard blocks are available in a range of thicknesses from 75m to 230mm. Thermal conductivity is 0.15W/mK and compressive strength is 3.5N/mm2. When used in modern cavity walls with a brick external leaf they will usually require additional insulation to achieve the requirements of the Building Regulations. These blocks can be used in internal and external leaves of cavity walls, solid walls, party walls, partitions, beam and block floors, and foundations.

Types of Aerated Concrete Blocks

A Solar block is also available in thicknesses of 100 to 250mm. Its strengths is 2.8N/mm2 and its thermal conductivity is 0.11 W/mK. Both these blocks are available in face sizes of 440x215, 610x215, 610x140, and 610x270mm. These blocks are suitable for cavity walls, solid walls, partitions and foundations

Hi-seven blocks are 75 to 230mm thick, thermal conductivity is 0.19W/mK and strength is 7.0N/mm2. There is a black stripe on one end to facilitate recognition on site. They are suitable in the same situations as Standard blocks.

Hi-ten blocks are 100 to 200mm thick, thermal conductivity is 0.19W/mK and strength is 8.4N/mm2. There is a red stripe on one end to facilitate recognition on site. Both these blocks are used where greater strength is required, for example in houses of 3 storeys or more.

Most aircrete manufacturers make blocks suitable for solid foundations. These blocks are quick to lay and don't require the rather slow and expensive cavity fill normally needed to stop two separate leaves being squashed together during backfill. Celcon's blocks are available in strengths of 3.5N/mm2, 7 N/mm2 and 8.4N/mm2. They are resistant to frost attack and will also resist most sulfates.

Thin joint systems are starting to become a more common sight on UK building projects. The blocks are typically 610mm long by 215mm or 270mm high. They can be laid with normal sand/cement mortar joints. When laid with thin joints (using special quick setting mortar) considerable heights can be achieved in one day. The system is designed for cavity walls, solid walls, party walls, partitions, and foundations.


Types Of Block

Standard Concrete Masonry Unit

The standard concrete masonry unit (CMU) is the basic concrete block used for most masonry construction. This block has unfinished surfaces and is usually coated with a number of different finishes including paint, stucco, stone, brick and even wood veneers. The standard CMU is designed for use in structural areas that are commonly unseen, and it is this reason that they are made with plain faces.

Split-Face Block

Split-face block is used similarly to standard concrete block; the only difference is the natural stone-like texture and appearance of the split face. This is accomplished by molding two blocks face to face instead of separately. These blocks are then split apart, creating the coarse surface. This is a popular block to use on exterior walls as it is aesthetically pleasing, and does not need further veneers.

Scored Block

The scored block is made with one or more vertical scores on its face to give the appearance of multiple mortar joints. These scores are molded on the face of the block during the manufacturing process. The scored face block is most commonly seen with one vertical score, but two to seven scores are possible.

Ribbed Block

Ribbed blocks are similar to scored block, as both of them have vertical features. These ribs (or flutes) are molded in a circular or rectangular profile, and often have a split type surface. This effect creates continuous vertical elements on a given wall, as the multiple courses of block line up with each other.

Honed Block

Honed blocks are polished after the manufacturing process to create a smooth finish that can resemble polished stone. This finished look can be changed by altering the aggregate type and proportions. These blocks are not typically used in residential applications; they are instead seen in commercial structures like office building and school type exteriors.

Glazed Block

Glazed blocks are manufactured with a permanent colored face, creating an appearance similar to that of a ceramic tile finish. This is achieved in a similar way; once the bare block has cured, it is then coated with the glaze layer just like ceramics would be. This surface is waterproof and resistant to vandalism, and is therefore commonly used in educational and health care settings.


Offset Block

Offset block creates a highly textured wall rich with different patterns of light and shadow. The faces of these blocks consist of two square surfaces at different depths that create a staggered effect. The offsets can be controlled by request to create a number of different effects

Standard Core-Fill Block

The standard, core-fill block, also called a "stretcher" block or "cinder" block, is the most common type of block used to make partition, retaining and structural walls. The standard block is a rectangle measuring 8 inches by 8 inches by 16 inches. Viewed from above, the rectangle reveals a set of two portioned cells. After stacking and mortaring layers of standard block, a mason fills the hollow cells with concrete.

Column Block

The square-shaped concrete column block is specially designed to form the exterior casing of a cast concrete column. Like the standard core-fill block, the column block's interior is hollow. Column blocks typically measure 12 inches square and 8 inches tall. Although standard blocks may be used to construct block columns, the large interior cell of the column block generally accommodates more reinforcing steel and results in stronger load-bearing capacity. To build with column block, a mason stacks and mortars the block, inserts reinforcement bars into the block's cell and pours concrete into the hollow

Slump Block

Slump block is a decorative variation of the standard core-fill concrete block. The concrete mixture used to create slump blocks intentionally sags during curing. Contoured lumps cover the exterior surface of slump block; the appearance of this block resembles the look of old adobe buildings. Slump block, like standard core-fill block, has two interior cells. A mason stacks, mortars and fills the block as usual. Slump block is usually available in grey and tan.

Retaining-Wall Block

Although many types of block are used to construct retaining walls, the term "retaining-wall block" generally refers to a specific type of solid, interlocking concrete blocks. Retaining-wall block is easy to install and requires no mortaring or core-filling. Viewed from above, retaining-wall block has a roughly trapezoidal shape; a short flat back faces the retained dirt and two angled sides connect to a rough front. A lip on the top of the block helps the builder to align blocks during stacking. Retaining-wall block is available in a variety of colors and sizes.


The Manufacturing Process of Concrete Masonry Blocks

Raw Materials

The concrete commonly used to make concrete blocks is a mixture of powdered portland cement, water, sand, and gravel. This produces a light gray block with a fine surface texture and a high compressive strength. A typical concrete block weighs 38-43 lb (17.2-19.5 kg). In general, the concrete mixture used for blocks has a higher percentage of sand and a lower percentage of gravel and water than the concrete mixtures used for general construction purposes. This produces a very dry, stiff mixture that holds its shape when it is removed from the block mold.

If granulated coal or volcanic cinders are used instead of sand and gravel, the resulting block is commonly called a cinder block. This produces a dark gray block with a medium-to-coarse surface texture, good strength, good sound-deadening properties, and a higher thermal insulating value than a concrete block. A typical cinder block weighs 26-33 lb (11.8-15.0 kg).

Lightweight concrete blocks are made by replacing the sand and gravel with expanded clay, shale, or slate. Expanded clay, shale, and slate are produced by crushing the raw materials and heating them to about 2000°F (1093°C). At this temperature the material bloats, or puffs up, because of the rapid generation of gases caused by the combustion of small quantities of organic material trapped inside. A typical light-weight block weighs 22-28 lb (10.0-12.7 kg) and is used to build non-load-bearing walls and partitions. Expanded blast furnace slag, as well as natural volcanic materials such as pumice and scoria, are also used to make lightweight blocks.

In addition to the basic components, the concrete mixture used to make blocks may also contain various chemicals, called admixtures, to alter curing time, increase compressive strength, or improve workability. The mixture may have pigments added to give the blocks a uniform color throughout, or the surface of the blocks may be coated with a baked-on glaze to give a decorative effect or to provide protection against chemical attack. The glazes are usually made with a thermosetting resinous binder, silica sand, and color pigments.

Design

The shapes and sizes of most common concrete blocks have been standardized to ensure uniform building construction. The most common block size in the United States is referred to as an 8-by-8-by-16 block, with the nominal measurements of 8 in (20.3 cm) high by 8 in (20.3 cm) deep by 16 in (40.6 cm) wide. This nominal measurement includes room for a bead of mortar, and the block itself actually measures 7.63 in (19.4 cm) high by 7.63 in (19.4 cm) deep by 15.63 in (38.8 cm) wide.

Many progressive block manufacturers offer variations on the basic block to achieve unique visual effects or to provide desirable structural features for specialized applications. For example, one manufacturer offers a block specifically designed to resist water leakage through exterior walls. The block incorporates a water repellent admixture to reduce the concrete's absorption and permeability, a beveled upper edge to shed water away from the horizontal mortar joint, and a series of internal grooves and channels to direct the flow of any crack-induced leakage away from the interior surface.


Another block design, called a split-faced block, includes a rough, stone-like texture on one face of the block instead of a smooth face. This gives the block the architectural appearance of a cut and dressed stone

The Process

Concrete Masonry Blocks are made by blending different materials together at a predetermined ratio through the following procedures.

1. Raw materials preparation There are two major types of materials in the composition of concrete blocks. Namely, aggregates

and cements: The function of aggregates is to form the main structure of a masonry block. Different materials can be used for aggregates. Sands and crashed stones are typical examples of natural aggregates. Cinder, slag and fly ash are typical examples of industrial waste aggregates. The function of cement is to combine the aggregates together. The procedure to prepare raw materials is not a continuous process. It is done in batches.

a) Aggregate material preparation:

Aggregates come in different types and sizes. Usually, different materials are delivered by big trucks into the raw materials yard. Different materials must not be blended in the yard. The size and purity of different materials should be consistent. They are transferred to large bins by a loader to be stored for production. To get good physical and chemical performance from the block, in each batch, the ratio of different aggregates must be determined. Each aggregate is weighed according to the design by a weight belt underneath the bins and then dumped in a large mixer waiting to be blended.

b) Cement preparation

Different types of Cement are delivered in bulk by cement trucks to the plant, and then blown into cement silos. Different cement types or even the same type of cement from different manufacturers must not be blown into the same silo. When in production, cement is weighed according to the design by a weighing system and then dumped in the same mixer as the aggregate.

2. Concrete preparation

After the preparation of all the raw materials, one batch of different materials is put into the large mixer. The mixing procedure starts, all the materials are blended together by big blades in the mixer and water is added to the mixture. The function of water is to hydrate (harden) cement. In this procedure the materials must be completely blended to guarantee the consistency of the mixture; which is now called concrete. In the block business, concrete is not prepared wet (ready top flow) or too dry. Water content is controlled precisely between a certain ranges.

3. Concrete transferring and block forming

This is the most important procedure in the process of block manufacturing. The concrete is transferred to a block forming machine by belt, and dumped into the block forming mold on pallets. Then the concrete is compressed and vibrated into certain forms; stripped from the mold but still on pallets and delivered to be loaded on racks. Now the product is called green block. The green block is not hard yet as cement needs time to become hard. The block forming machine is ready for another cycle. Different quantities of blocks can be made on different block machines. Bigger machine can make more blocks each time. Different molds can be placed in the block machine to make different shape blocks. As this process is very important too for the strength and form of the block, much attention must


be paid the procedure. Materials must be fed evenly, and completely. The vibration time and force must be controlled properly to guarantee the height and strength of the block.

4. Stacking and Curing

After green block is stacked on the rack, they are transferred to the kilns. There they are kept on the rack for about 24 hours to become hard (curing) enough for handling. In the kiln, high temperatures (still durable for human beings) and humidity needs to be kept for the fast curing of the block.

5. Depalletizing and Cubing

After they stay in the kiln for about one day, the green blocks become hard enough (finished products) for handling. They are transferred out to be removed from racks and then removed from pallets. After that, the blocks are transferred for stacking into cubes on wood or plastic pallets, packaging and removal by forklift to the yard.

6. Yard Storage

Concrete blocks are stored in the yard for further curing because cement needs about 28 for complete hydration (hardening). Different products are stored in their designated areas for good yard management. They are stored according to types, strengths, colors and so on. Good storage management is also very important for good customer service.

Quality Assurance Tests are carried out throughout the whole process; incoming materials must be tested for weight, quantity, size, water and purity consistency. Accuracy of batching system must be observed; water content in the concrete must be tested and controlled. The green block needs to be checked for the height and density constantly. Temperature and humidity must be maintained for right curing of blocks. Finished blocks are tested for

.


Step by Step Manufacturing Process

The production of concrete blocks consists of four basic processes: mixing, molding, curing, and cubing. Some manufacturing plants produce only concrete blocks, while others may produce a wide variety of precast concrete products including blocks, flat paver stones, and decorative landscaping pieces such as lawn edging. Some plants are capable of producing 2,000 or more blocks per hour.

The following steps are commonly used to manufacture concrete blocks.

Mixing

1 The sand and gravel are stored outside in piles and are transferred into storage bins in the plant by a conveyor belt as they are needed. The portland cement is stored outside in large vertical silos to protect it from moisture.

2 As a production run starts, the required amounts of sand, gravel, and cement are transferred by gravity or by mechanical means to a weigh batcher which measures the proper amounts of each material.

3 The dry materials then flow into a stationary mixer where they are blended together for several minutes. There are two types of mixers commonly used. One type, called a planetary or pan mixer, resembles a shallow pan with a lid. Mixing blades are attached to a vertical rotating shaft inside the mixer. The other type is called a horizontal drum mixer. It resembles a coffee can turned on its side and has mixing blades attached to a horizontal rotating shaft inside the mixer.

4 After the dry materials are blended, a small amount of water is added to the mixer. If the plant is located in a climate subject to temperature extremes, the water may first pass through a heater or chiller to regulate its temperature. Admixture chemicals and coloring pigments may also be added at this time. The concrete is then mixed for six to eight minutes.

Molding

5 Once the load of concrete is thoroughly mixed, it is dumped into an inclined

bucket conveyor and transported to an elevated hopper. The mixing cycle begins again for the next load.

6 From the hopper the concrete is conveyed to another hopper on top of the block machine at a measured flow rate. In the block machine, the concrete is forced downward into molds. The molds consist of an outer mold box containing several mold liners. The liners determine the outer shape of the block and the inner shape of the block cavities. As many as 15 blocks may be molded at one time.

7 When the molds are full, the concrete is compacted by the weight of the upper mold head coming down on the mold cavities. This compaction may be supplemented by air or hydraulic pressure cylinders acting on the mold head. Most block machines also use a short burst of mechanical vibration to further aid compaction.

8 The compacted blocks are pushed down and out of the molds onto a flat steel pallet. The pallet and blocks are pushed out of the machine and onto a chain conveyor. In some operations the blocks then pass under a rotating brush which removes loose material from the top of the blocks.


Curing

9 The pallets of blocks are conveyed to an automated stacker or loader which places them in a curing rack. Each rack holds several hundred blocks. When a rack is full, it is rolled onto a set of rails and moved into a curing kiln.

10 The kiln is an enclosed room with the capacity to hold several racks of blocks at a time. There are two basic types of curing kilns. The most common type is a low-pressure steam kiln. In this type, the blocks are held in the kiln for one to three hours at room temperature to allow them to harden slightly. Steam is then gradually introduced to raise the temperature at a controlled rate of not more than 60°F per hour (16°C per hour). Standard weight blocks are usually cured at a temperature of 150-165°F (66-74°C), while lightweight blocks are cured at 170-185°F (77-85°C). When the curing temperature has been reached, the steam is shut off, and the blocks are allowed to soak in the hot, moist air for 12-18 hours. After soaking, the blocks are dried by exhausting the moist air and further raising the temperature in the kiln. The whole curing cycle takes about 24 hours.

Another type of kiln is the high-pressure steam kiln, sometimes called an autoclave. In this type, the temperature is raised to 300-375°F (149-191°C), and the pressure is raised to 80-185 psi (5.5-12.8 bar). The blocks are allowed to soak for five to 10 hours. The pressure is then rapidly vented, which causes the blocks to quickly release their trapped moisture. The autoclave curing process requires more energy and a more expensive kiln, but it can produce blocks in less time.

Cubing

11 The racks of cured blocks are rolled out of the kiln, and the pallets of blocks are unstacked and placed on a chain conveyor. The blocks are pushed off the steel pallets, and the empty pallets are fed back into the block machine to receive a new set of molded blocks.

12 If the blocks are to be made into split-face blocks, they are first molded as two blocks joined together. Once these double blocks are cured, they pass through a splitter, which strikes them with a heavy blade along the section between the two halves. This causes the double block to fracture and form a rough, stone-like texture on one face of each piece.

13 The blocks pass through a cuber which aligns each block and then stacks them into a cube three blocks across by six blocks deep by three or four blocks high. These cubes are carried outside with a forklift and placed in storage.

Quality Control

The manufacture of concrete blocks requires constant monitoring to produce blocks that have the required properties. The raw materials are weighed electronically before they are placed in the mixer. The trapped water content in the sand and gravel may be measured with ultrasonic sensors, and the amount of water to be added to the mix is automatically adjusted to compensate. In areas with harsh temperature extremes, the water may pass through a chiller or heater before it is used.

As the blocks emerge from the block machine, their height may be checked with laser beam sensors. In the curing kiln, the temperatures, pressures, and cycle times are all controlled and recorded automatically to ensure that the blocks are cured properly, in order to achieve their required strength.



Conclusion

A specific topic was given and expected to be elaborate and present the findings to the class. Thus, to explain and support my findings on the subject, I strategize by stating and explaining the specific subject with details and accuracy. It is concluded that concrete blocks are brilliant technology that continuously develops over the decade.

With the technology provided it is safe to assume that buildings with blocks varies more than what it looks from outside. The manufacturing process helps us to better understanding towards material and the science behind the hard though light blocks. The building industries would always use blocks as it is much practical. Type of blocks gives various choices when building a partitions that adapts to the environment and surroundings. Manufacturing process gives the opportunities to innovate and increase the quality of product.

All these technology and science helps to build the concrete jungle that is growing from city to city. As long as the human race continues the need for better technology amongst us would strive and develops twice as functional and quality material made. Is it been my pleasure to the one that research, present and report on the specific subject.


Reference

http://www.penningtonblockco.com/types.html

http://www.ehow.com/list_7412340_different-types-concrete-block.html

http://www.ehow.com/about_5516128_types-concrete-blocks.html

http://www.cement.org/masonry/block.asp

https://environment7.uwe.ac.uk/resources/constructionsample/Conweb/walls/blocks/print.htm


Appendixes


Documents

Material Blockwork