※Building☆Material☆World※: ※Bricks and Blocks※

Introduction

       Brick is small building unit in the form of a rectangular block, first produce in a sun-dired form at least 6,000 year ago. Besides that, it also is a block of ceramic material used in masonry construction. Moreover, it also considered as one of the strongest building material and longest lasting building material.

         Main body of brick made up by natural clay mineral, include kaolin and shale. Small amounts of manganese, barium, and other additive are blended with the clay to produce different shades, and barium carbonate was use to omprove brick's chemical resistance to the elements. Besides that, many other additives are used in brick. A wide vaity of coating material and methos are used to produce brick of a certain colour or surface texture.

       The oldest discovered bricks, originally made from shaped mud and dating to before 7500B.C. were found at Tell Aswad the later in the upper Tigris region and in southeast Anatolia close to Diyarbakir. But the first brick made was probably in Middle East. In pre-modern China, making a brick was a job of an unskilled artisan. The brick founding case was different in Europe. The oldest domestic brick were fond in Greece.

GENERAL PROPERTIES (bricks)

Building bricks used for building exterior and interior walls. Facing bricks outer surface has an excellent quality, which allows withstanding various influences. Bricks should have sufficient strength, the lowest requirement is able to take the self-imposed load. Besides that, durability of bricks is important too. Bricks need able to withstand weathering and exposure to the elements. For the appearance, facing brickwork should have quality and good appearance. The bricks size and shape are important to facilitate bonding. The size of bricks can divided into four types which are single, one and a half, double and non standard. The strength of bricks is determined by the ability of a construction material doesn’t collapse under influence of external forces that can causes internal stresses.

GENERAL PROPERTIES OF CLAY

BRICKS

(A) Sound insulation

Good clay brickwork provides good insulation against air borne sound in proportionate ratio to its density and thickness. But, a bad brick-laying leaves small gap for sound to pass through a wall.

(B) Appearance

Actually the clay bricks appearance is not so important. This is because masonry works constructed from them are plastered. But for facing bricks, appearance need to be good in terms of colours or textures.

(C) Crushing strength

The basic requirement for clay bricks is to have high compressive strength. If bricks want to the ability to withstand highly compressive strength, it needs to be fired and made by modern de-aerated extruder. This makes clay bricks suitable for load-bearing structures.

(D) Porosity or water absorption

The porosity of clay bricks is attributed to its fine capillaries. Moisture is released at day time and reabsorbed during night time. Clay bricks have the ability to release and reabsorb moisture by capillary effect. This helps clay bricks to regulate the temperature and humidity of atmosphere in a building. Thus, clay bricks are proof to be a suitable material for building houses.

(E) Durability

The durability of clay bricks same as normal bricks. It depends on the amount of soluble salts in the bricks. Besides that, those clay bricks which well burnt always are durable.

So dependently, the firing temperature of clay bricks is related to durability.

(F) Fire resistance

Fire resistance of clay bricks is and inherent property. Maybe a lot people will confuse about it. Here some knowledge, a 100mm thick clay brick with 12.5mm thick plastering can provide a fire resistance of 2 hours and a 200mm thick similar wall non-plastered can give a maximum fire rating of 6 hours.

(G) Efflorescence

We should know that all clay bricks some soluble salts. Where do these soluble salts come from? They come from the original clay. Besides that, the reaction of clay bricks with sulphur compounds from the fuel is the source of soluble salts in clay bricks.

(H) Flexibility

Clay bricks can be used for variety applications in building structures. Clay bricks can used as load bearing wall, earth retaining wall, fencing, manholes, drain sumps, partition walls and decorative walls. The flexibility of clay bricks made into convenient size and shape makes its wide range of usage in our daily life.

(I) Thermal insulation or conductivity

The thermal insulation of clay bricks is considered very good when compared to other building materials. We can improve thermal insulation of bricks by perforations. Thermal conductivity is highly related to density and moisture content of clay bricks. 0

MANUFACTURE OF CLAY BRICKS

Before we understand the manufacture process of clay bricks, let us enjoy a video of clay bricks manufacturing process first.

In brick making terms, clay covers a range of naturally occurring raw materials which are used to make a product. They have the ability to be crushed and mix with water to form a plastic material which can be mould into various shapes. The main process for the manufacture of clay bricks includes preparation, forming, drying and firing.

PREPARATION:

How to prepare the clay bricks? Firstly, we need to remove the stones and other undesirable particles. The burning of the organic material during firing contributes to the heat and save fuel. The burning out of these materials leave a less density structure in the bricks.

FORMING:

There are four processes to form clay bricks. The four ways are soft mud process, stiff plastic process, wire cut process and pressing.

SOFT MUD PROCESS:

The clay is blended with approximately 25% of water using mixers. Then, the mud is formed into lumps of size of one brick. The lump will then dipped in sand to reduce the stickiness of surface. After that, the lumps formed in moulds. The excess mud will cut off by wire. The shape and size of bricks are variable, this is because the plasticity of green brick the high drying shrinkage of such wet mixes.

STIFF PLASTIC PROCESS:

For this process, the clay is blended with approximately 15% of water. This is to make a very stiff but plastic compound. The clay extruded from the mixer and cut into brick shape. After that, it let dry for a moment before press into mould. The clay retains the same shape of the mould when ejected from mould. This shows that the clay is very stiff. This process gives some advantages which are short drying time, size of bricks easier to control, shrinkage of firing bricks is low.

WIRE CUT PROCESS:

Clay with moisture content around 25% extrudes from a rectangular die. We used wire to cut the ‘column’ of clay into bricks. This process is fully continuous. Perforations are made along the length of the ‘column’ to produce perforated bricks. This perforation process gives some advantages. As examples, a reduction in environmental impact by reducing the rate of use of clay deposites. The lighter units of bricks are less tiring to lay.

PRESSING:

Pressing which is also called mechanical pressure form the stiff clay without addition of water into bricks. This avoids the need for drying the green bricks in separate drier.

DRYING AND FIRING:

Before the ‘green’ bricks are fired, they need to be dried. Drying is usually done in separate drier or in the drying zone of a continuously fired kiln. That’s a very efficient way of mass producing bricks is to use tunnel kilns, in which the bricks are moved though a stationary fire.

Calcium Silicate Bricks

Manufacture of calcium silicate bricks

§ Mixing quicklime/ hydrated lime with silica sand together with enough water

§ Mixture is left until the lime is completely hydrated and it is pressed into moulds and cured in a high-pressure autoclave for 2-3 hours

§ Hydrated calcium silicated formed by reaction between lime and silica

§ Durable strong brick is produced and finished bricks are very accurate and uniform

Properties of calcium silicate bricks

A) Insulation

Ø Highest heat insulator

Ø Reduce heat & humidity in summer & retain heat in winter

Ø Reduction of noise at least 50% by independent testing

Ø Calcium silicate brickwork required to be thicker to achieve 3-4 hours fire resistance

B) Strength and durability

Ø Non-toxic, free from efflorescence & have consistent size & surface

Ø Extremely hard and can support heavy loads until 10-18MPa

Ø CO₂ improved strength of the bricks which making them last longer

Ø Strength of calcium brick is more uniform

C) Colour

Ø Natural colours are white/ off-white depending on the aggregates used

Ø Colour can be get also by adding pigments to the mixture before pressing by steaming

Ø Can even be unplastered for projects such as sheds

D) Value for money

Ø Low price

Ø Save cost of sand and cement due to multi-lock system

Type : Multilock (4 core)

Type : Split

E) Moisture movement

Ø Moisture movement increase in order : clay bricks, calcium silica bricks and concrete bricks

Ø Reversible moisture movement % is ± (0.01 - 0.05) and irreversible moisture movement % is – (0.01 – 0.04)

Ø Wet silica bricks built into large panel wall can cause cracking

v Often result in stepped diagonal cracking

Ø Use mortar without cement to give a weaker mortar to accommodate the moisture movement

F) Sound and thermal insulation

Ø Same with those clay bricks of same density

Batamas Sdn Bhd – 1st producer of calcium silicate brick in Malaysia

ü Incorporated in December 1983

ü Brand name “KALSA” used in marketing of the product in Malaysia

ü Construction projects by using KALSA

v Selangor Turf Club

v University Islamic Antarabangsa, Selangor

v Government Office Complex, Putrajaya

v Pusat Sukan Negara, Kuala Lumpur

Concrete Bricks

Ø Manufactured in various colour and patterns

Ø Made from Portland cement, water, & aggregates with/ without inclusion of of other materials

Ø Harder, more difficult to cut and less pleasant to handle than clay/ calcium silica bricks

Ø Reversible moisture movement and is greater than both calcium silica and clay bricks

Ø Average compressive strength typically range from 3000 – 4000 psi

Ø Rate of absorption (IRA) – 40 & 80 grams per minute per 30 sq. in.

Ø Special care required to be taken to prevent cracking of brickwork after laying

Ø Joint reinforcing steel with concrete units is required to help minimize cracking due to shrinkage

Ø Difficult to cut cleanly using a trowel or brick hammer and required saw-cutting units

Ø Quality control is poor

Blocks

Clay Blocks

Properties of clay blocks

§ Foremost method in most of the European country

§ Suitable for single/double storey application

§ Minimum average compressive strengths for clay blocks are :

§ Non-loadbearing walls/ partitions 1.4 N/mm²

§ Facing and common blocks 2.8 N/mm²

§ Blocks for loadbearing internal walls 2.8 N/mm²

Ø Modern clay blocks are made up of sand, straw or recycled material, extruded, dried and fired

Ø These materials creates a special properties as they are burned off during firing leaving behind uncountable small holes and connecting pores

§ Retain heat and reduce sound transmission

Ø Does not rust & resistant to fire & attack from insects

§ Require very little immediate/ on-going maintenance & lend themselves to an array of final surface finishes

§ Traditional clay blocks are best finished with lime render

v To allow the building to “breathe”

Ø Modern clay blocks are more costly than traditional brick and block cavity walls but is more attractive, cost effective and realistic

Ø Highly eco-friendly

§ Less environmental impact during manufacture process

§ Finished building gives very high insulation values

The walls of 20 X 20 X 50 cm fired clay blocks with “glued” joints like the “monomer” walls go up rapidly.

Concrete Blocks

Ø Also known as concrete masonry unit (CMU)

Ø Mixture of powdered portland cement, water, sand and gravel

Ø High compressive strength

Ø Precast products used in construction

Ø Have at least one hollow cavities

Ø Stacked one at a time & held together with fresh concrete mortar to form desired length & height of the wall

Ø A typical concrete block weight is 17.2-19.5kg

Ø Divided into

ü Dense concrete blocks

ü Lightweight concrete blocks

Lightweight concrete blocks

Ø 1/3 weight of dense blocks

Ø Easier to handle and quicker to lay

Ø Air in lightweight block provide better sound &thermal insulation

Ø Lighter weight results in lighter foundations and structural members

Ø Cut & chased with hand tools & hold nails & screws without plugs

Ø Used mostly in internal wall partitions

Ø Better thermal insulation than denser blocks

Ø Good fire resistant

§ test to ASTM standard show that a loadbearing foam concrete slab wall 15mm thick has a fire resistance exceeding 7 hours

Ø Density requirement of range 700 kg/m³ – 1600 kg/m³

Ø Effective sound barrier

§ Coefficient of sound absorption of unplastered foam concrete of 800 kg/mdensity

Manufacturing process of concrete blocks

Mixing

1) Sand & 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 measuring 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. First type is known as a planetary/ 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 colouring pigments may also be added at this time. The concrete is then mixed for 6 – 8 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 comveyed to another hopper on top of the block machine at a measured flow rate. In the block machine, the concrete is forced downard into molds. The molds consist of an outer mold box contaning several mold liners. The liners determine the outershape of the block and the inner shape of the block cavities. As many 15 blocks may be molded at 1 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 orhydraulic 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 then pushed out of the machine and onto a chain conveyor. In some operations the blocks then pass under a rotating bursh which removes loose material from the top of the blocks.

Curing

Concrete block curing chamber.

9) The pallets of blocks are conveyed to an automated stacker or loader which places them in 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 1-3 hours at room temperature o allow them to harden slightly. Steam is then gradually introduced to raise the temperature at a conctrolled rate of not more then 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 cured at 170-185°F (77-85°C).

When the curing temperature has been reached, the steam is shut off, and the blocks are soak in the hot, moist ai 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. Intthis 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 5-10 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 blacks in a less time.

Concrete block cured under the sun in Haiti.

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 bloack, they are first molded as 2 block joined together. Once these double blocks are cured, they pass through a splitter, which strikes them the doubleblock 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 ino a cube 3 blocks across by6 blocks deep by 3/4 blocks high. These cubes are carried outside with a forklift and placed in a storage.

Concrete block cubing system.

Full automatic concrete block production line.