Block

BLOCK
Blocks are larger than bricks and it is usually requires two hands to lift. Blocks can be laid more quicky than brickks Generally, blocks are intended to be plastered or rendered but many products particularly concrete blocks are sufficiently regular in shape and size and otherwise of good appearance without plaster for wailing.


Density & Strength
Concrete blocks are range in compressive strength from 2.8MPa to 30MPa witth associated densities of 420 to 2,200kg/m³. Thermal conductivity from 0.1 to1.5 W/mK at 3% moisture content . Drying shrinkage are typically in the range if 0.03to 0.05%.

Typical relationship between density & thermal conductivity

Nominal density, kg/m³	2200	1600	1000	700	420
Typical thermal conductivity, W/mK	1.5	0.63	0.27	0.17	0.1

Durability

Concrete blocks are made from Portland Cement, water, sand and gravel. This combination makes the concrete block durable and long lasting. Some concrete blocks may include other ingredients such as color pigment, air-entraining, or water repellent. Air-entraining is, according to the Federal Highway Administration, "the process whereby many small air bubbles are incorporated into concrete and become part of the matrix that binds the aggregate together." Dense concrete blocks and certain aerated lightweight blocks are resistant to freeze/ thaw conditions below damp-proof course (DPC) level. However, some lightweight concrete blocks with less than 7MPa crushing strength, should not be used below DPC level except for the inner skin of cavity construction.

Fixability

Aerated and lightweight concrete blocks offer a good background for fixing. For light load, nails to a depth of 50mm are sufficient. For a heavier loads, wall plugs and proprietary fixings are necessary. Fixing should avoids the edges of the blocks.

Fire resistance

Concrete blocks construction offers fire resistance. Solid unplastered 90mm blocks can give up to 60 minutes fire protection when used as load-bearing walls. Certain 150mm and most 215mm solids can achieve 360 minutes protection.

Sound insulation

Building regulations require minimum sound insulation of 45dB for seperating walls and 40dB for internal bedroom or WC walls. The passage airborne sound depends upon the density and porosity of the materials.

Sound absorption

Majority of concrete blocks with hard surfaces are highly reflective to sound thus creating long reverberation times within building enclosures. Acoustically  absorbing concrete blocks are manufactured with a slot on exposed face which admits sound into the central cavity . The void space is lined with sound-absorbing fibrous filler thus reducing reverberation effects.

Thermal insulation

New buildings to be compliant with an overall energy energy and carbon performance, the Target Emission Rate (TER) based on the  whole building. The limiting area - weighted U-value standard for wall elements in new buildings is 0.35W/m²K. But to achieve TER overall, most buildings will require wall U-values within the range of 0.27-0.30W/m²K.

Concrete Block 

The concrete block is used in the construction wall. It is one of building materials. The concrete block also known as concrete masonry unit(CMU). The concrete block is one of the precast concrete. The term precast refers to the fact that the blocks are formed and hardened before they are brought to the job site. Most concrete blocks have one or more hollow cavities, and their sides may be cast smooth or with a design. In use, concrete blocks are stacked one at a time and held together with fresh concrete mortar to form the desired length and height of the wall. The concrete blocks are faster to build than with bricks. Furthermore, amounts of mortar are reduced to less than half by using the concrete block.

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.

The concrete block can be made by using a simple block- making machine. It can be operated by an engine or by the hand. Furthermore, the blocks also can be made by using simple wooden moulds on a floor. For the block which made by the wooden moulds, the moulds need to be lined with net steel plates to prevent damage during tamping. It also uses to reduce wear on the mounds.

   

Besides produce the concrete blocks by wooden moulds, there are another way to manufacture it. The production of concrete blocks consist of four processes, which is mixing, molding, curing and lastly is cubing.

The first process is mixing. The required amounts of sand, gravel, and cement are transferred by gravity or by mechanical. The dry material will then flow to stationary mixer where they are blended together for few minutes. After that, small amounts of water are added to the mixer. , the coloring pigment or admixture chemicals may be added at this time. Then, the concrete is mixed for 6 to 8 minutes.

The second step is molding. When the concrete is mixed thoroughly, it will be dumped into an inclined bucket conveyor and then transport to elevated hopper and finally conveyed to another hopper which is on top of the block machine. The concrete is forced downward into mould from the block machine. The liner of mould will determine outer and inner shape of the block. When the molds are full with concrete, it will be compacted by the weight of the upper mold head coming down on the mold cavities. Next, the rotating brush will remove loose material from the top of compacted block.

The following step is curing. The block will be moved in to a curing kiln. There are two type of curing kiln, which is low-pressure steam kiln and high pressure kiln (autoclave). The common type is low-pressure curing kiln. In this type, the blocks are held in kiln fro 1-3 hours to harden slightly. The standard weight blocks are cured at a temperature of 66-74 degree Celsius. When the temperature had been reached, the steam will shut off and the blocks are allowed to soak in the hot air for 12-18 hours. After soaking, the blocks will dry by exhausting the moist air and rising the temperature in the kiln. Another type is high –pressure steam kiln. The temperature will rise to 149-199 degree Celsius. The block is soaking for 5-10 hours. The pressure is then rapidly vented and cause the blocks to quickly release the trapped moisture. This curing process is high cost and high energy but it can produce block in less time.

The last step is cubing. For the split-face blocks, they will be molded as two blocks joined together, cured together and pass through splitter. This causes the double block to fracture and form a rough on the one face of each piece. These cubes are carried outside with forklift and placed in storage.  

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.

The variety of concrete blocks is extensive, ranging from dense through lightweight, offering load-bearing strength, sound, and thermal insulation properties. Dense concrete blocks (solid, cellular or hollow) are manufactured from natural dense aggregates including crushed granite, limestone and gravel. Light concrete blocks are manufactured incorporating a wide range of aggregates including expanded blast furnace slag, sintered ash and pumice. Lightweight blocks may be less than one-third of the weight of the dense blocks and can be laid more quickly than bricks. Lightweight blocks have been widely used for the inner leaves of cavity walls, internal walls and non-loadbearing wall. Thermal insulation provided by air in lightweight aggregates, aerated mortars and in voids in blocks. Filling voids with polyurethane foam substantially improves thermal resistance of blocks. Typical lightweight blocks can be cut with hand tools and hold nails and screw without plugs. However drying shrinkage is significant and cracking of blockwork is paticularly likely to occur in panels where distance between contraction joints exceeds 6m or twice their height. 

Concrete Paving blocks are widely used for town pedestrian precincts and house driveways. Concrete block paving units are manufactured to a wide range of designs Blocks may be of standard brick form 200mm x 100mm, to thickness of 60, 80 or 100mm. Concrete paving blocks  are usually laid on a compacted sub-basewith 50mm of sand.

Earth-retaining blockwork is a range of precast-cellular concrete-interlocking blocks is manufactured for the construction of dry-bed retaining walls. Soil is placed in the pockets of each successive course to allow for planting. The rear is backfilled with granular material to allow for drainage. The size of the block determines the maximum construction height but over 20m can be achieved with very deep units. A face angle of 15° to 22° is typical to ensure stability but other gradients are possible. Concrete interlocking blocks with planting are used to create environment walls.

Where visual blockwork is requires, fair faced blocks offer a selection of textures and colours at a different visual scale compared to that associated with traditional brickwork. Fairfaced blocks are available in a wide range of colours from white through buff (pale yellow-brown) and stone, yellow to pink, blue, green and black. Frequently, the colour is all through although some blocks have an applied surface colour. Texture range from polished, smooth and weathered (sand or short-blastered) to split face.

   

Fair Faced blocks                        Lightweight blocks     

 

Concrete Pving blocks                 Concrete Interlocking blocks

 Clay Block

   

Clay blocks are generally ectruded hollow units. The material used in manufacture of clay block is the same as clay bricks. After firing, clay blocks are dense, hard and brittle which make them difficult to cut and fix.

Clay block construction is an extremely versatile and efficient way to build. Its excellent energy saving characteristics combined with the build quality and speed will outperform most other traditional aggregate blocks. The benefits are such that building with clay blocks has become the foremost method of construction in many European countries. Utilised on many commercial and domestic projects, clay blocks are suitable for single and multi storey applications.

Modern clay blocks are precision engineered walling units designed to be thermally and acoustically efficient. During manufacture clay is prepared with sand, straw or recycled materials, extruded, dried and fired. The addition of these other materials helps enhance their unique properties as they are burned off during firing leaving behind innumerable small holes and connecting pores. The air trapped within these pores helps retain heat and reduce sound transmission. After firing the blocks are precision ground within +/- 0.5mm allowing for the construction of highly accurate and precise walls.

A clay block does not rust or warp and is resistant to fire and attack from insects. They require very little immediate or on-going maintenance and lend themselves to an array of final surface finishes. Although facing bricks or a modern wall cladding system are options, traditionally clay blocks are best finished with lime render to allow the building to 'breathe'.

Although on first appearance the price of each unit can be a little higher than other construction methods, when costs for materials and laying are taken into account clay blocks become an attractive, cost effective and realistic alternative to traditional brick and block cavity walls. In some cases using a clay block construction system can also help increase the overall value of the project in question.

Clay block construction projects are highly eco-friendly. The blocks themselves have less environmental impact during their manufacture than most other building materials, and the finished building offers very high insulation values.

Why it suitable to use in construction of buiding???? 

The clay block wall provides a unique combination of thermal insulation and heat storage.

 It is pleasantly cool in summer!! Clay blocks are unique in offering high thermal insulation with equally high heat retention properties. This natural air conditioner ensures a relatively constant indoor temperature as well as protection from the heat in summer. No other building material is capable of the same.

 Lowest moisture content of all comparable building materials 

Clay blocks are dried and then fired during the manufacturing process. They have the shortest drying time and the lowest residual moisture of all comparable building materials. This is particularly true when comparing them with blocks containing binding agents (cast stone, lightweight concrete), the final drying of which takes up to 3 years or more. Clay blocks thus provide thermal insulation from the very beginning.

concrete

concrete:

    concrete is a mixture of cement water and aggregate which takes the shape and texture of its mould or formwork on site.when it cured at a suitable temperature and humidity,it will become harden. Concrete is a strong hard building material composed of sand and gravel and cement and water. It is used for making buildings, roads, bridges, vessels pipes etc etc etc.   As the concrete formulations develop concrete is increasing its range of applications such that it is making inroads into those presently monopolised by metals.To enable concrete to withstand tensile loads it is often reinforced with steel rebars or with natural or artificial fibres...
    there are some different type of concrete,such as dense concrete and less dense concrete.dense concrete has a density over 2000kg/m3.less dense concrete is made by aerating the mix,by using lightweight aggregrate or by omitting the fine aggregate are classified as 'lightweight concrete'.tensile strength is given to concrete by reinforcement steel bars. 

    The Properties of concrete are its characteristics or basic qualities.The four main properties of concrete are workability,cohesiveness,strength and durability.Concrete has three different states,that is plastic,setting and hardening.In each state it has different properties.

At plastic state, the concrete is first mixed it is like 'bread dough'.It is soft and can be worked or moulded into different shapes. In this state concrete is called plastic. Concrete is plastic during placing and compaction.The most important properties of plastic concrete are workability and cohesiveness.A worker will sink into plastic concrete.

At setting state, concrete then begins to stiffen. The stiffening of concrete, when it is no longer soft, is called setting.Setting takes place after compaction and during finishing.Concrete that is sloppy or wet may be easy to place but will be more difficult to finish.A worker leaves footprints in setting concrete.

At hardening state, after concrete has set it begins to gain strength and harden. The properties of hardened concrete are strength and durability.Hardened concrete will have no footprints on it if walked on.

     Workability means how easy it is to place,handle,compact and fi nish a concrete mix.
Concrete that is stiff or dry may be difficult to handle, place, compact, and finish and, if concrete is
not constructed properly, concrete will not be as strong or durable when finally hardened. A slump
test can be used to measure the workability of concrete.Workability is affected by the amount of cement paste.The cement paste is the soft or liquid part of the concrete mix. The more paste
mixed with the coarse and fine aggregates, the more workable a mix.beside,it also can affected by the aggregate grading.Well-graded, smooth, rounded aggregates improve the workability of a mix.To make a more workable mix,we can add more cement paste,use well graded aggregates and use an admixture.Never try to make a mixture more workable by just adding more water because this lowers the strength and durability of concrete.
     Well made concrete is a naturally strong and durable material.It is dense, reasonably watertight, and able to resist changes in temperature, as well as wear and tear from weathering.Strength and Durability are affected by the density of the concrete. Denser concrete is more watertight (or less permeable).Concrete durability increase with strength.Well made concrete is very important to protect the steel in reinforced concrete.Strength of concrete in the hardened state is usually measured by the compressive strength by using the compression test.Strength and Durability of concrete are affected by fews factors.First,compaction. Compaction is removing the air from concrete. Proper compaction results in concrete with an increased density which is stronger and more durable. second,curing.Curing is keeping concrete damp for a period, to allow it to reach maximum strength. Longer curing will give more durable concrete.third,weather. Warmer weather will cause concrete to have a higher early strength.forth,type of cement.Different types of cement will affect concrete properties.for example, how
quickly or slowly concrete gains strength.fifth,water to cement ratio.Too much water and not enough cement means concrete will be weaker and less durable.
The water to cement ratio (W/C) is the weight of the water divided by the weight of cement.The lower the ratio, the stronger
the concrete.

      Cohesiveness is how well concrete holds together when plastic.Cohesiveness is affected by the aggregrate grading.Graded Aggregate means that there is a range of size of aggregates, from large
rocks to small sands.Well-graded aggregates give a more cohesive mix, too much
coarse aggregate gives a boney mix.A mix that has too much water will not be cohesive and may separate and bleed.

      There are two main tests to be done on concrete,first,the slumping test.
The slump test shows the workability of concrete.Workability measures how easy the concrete is to place, handleand compact.

Second,the compression test.The compression test shows the best possible strength concrete can reach in perfect conditions.The compression test measures concrete strength in the hardened state.Testing should always be done carefully. Wrong test results can be costly.sampling is  the first step is to take a test sample from the large batch of concrete. This should be done as soon as discharge of the concrete commences. The sample should be representative of the concrete supplied.The sample is taken in one of two ways.first,for purposes of accepting or rejecting the load.Sampling after 0.2 m3 of the load has been poured.For routine quality checks: Sampling from three places in the load.

     A concrete mix is designed to produce concrete that can be easily placed at the lowest cost.
The concrete must be workable and cohesive when plastic, then set and harden to give strong and
durable concrete.The mix design must consider the environment that the concrete will be in; ie exposure to sea water,trucks, cars, forklifts, foot traffic or extremes of hot
and cold.Concrete is a mixture of cement, water, coarse and fine aggregates and admixtures.
The proportions of each material in the mixture affects the properties of the final hardened
concrete. These proportions are best measured by weight. Measurement by volume is not
as accurate, but is suitable for minor projects.As the cement content increases, so does strength and durability.Therefore to increase the strength, increase the cement content of a mix. Adding more water to a mix gives a weaker hardened concrete.Always use as little water as possible, only
enough to make the mix workable.As the Water to Cement ratio increase, the strength and
durability of hardened concrete decrease.To increase the strength and durability of
concrete, decrease the Water-Cement ratio.

     In modern times, researchers have experimented with the addition of other materials to create concrete with improved properties, such as higher strength or electrical conductivity.

There are many types of concrete available, created by varying the proportions of the main ingredients below. In this way or by substitution for the cemetitious and aggregate phases, the finished product can be tailored to its application with varying strength, density, or chemical and thermal resistance properties.Recently the use of recycled materials as concrete ingredients has been gaining popularity because of increasingly stringent environmental legislation. The most conspicuous of these is fly ash, a by-product of coal-fired power plants. This use reduces the amount of quarrying and landfill space required as the ash acts as a cement replacement thus reducing the amount of cement required.

      The mix design depends on the type of structure being built, how the concrete will be mixed and delivered and how it will be placed to form this structure.first,cement.Portland cement is the most common type of cement in general usage. It is a basic ingredient of concrete, mortar and plaster.It consists of a mixture of oxides of calcium, silicon and aluminium. Portland cement and similar materials are made by heating limestone (a source of calcium) with clay and grinding this product (called clinker) with a source of sulfate (most commonly gypsum).

      second,water. Combining water with a cementitious material forms a cement paste by the process of hydration. The cement paste glues the aggregate together, fills voids within it and allows it to flow more freely.Less water in the cement paste will yield a stronger, more durable concrete; more water will give a freer-flowing concrete with a higher slump. Impure water used to make concrete can cause problems when setting or in causing premature failure of the structure.Hydration involves many different reactions, often occurring at the same time. As the reactions proceed, the products of the cement hydration process gradually bond together the individual sand and gravel particles and other components of the concrete, to form a solid mass.

      Third,aggregate.Fine and coarse aggregates make up the bulk of a concrete mixture. Sand, natural gravel and crushed stone are used mainly for this purpose. Recycled aggregates (from construction, demolition and excavation waste) are increasingly used as partial replacements of natural aggregates, while a number of manufactured aggregates, including air-cooled blast furnace slag and bottom ash are also permitted.Decorative stones such as quartzite, small river stones or crushed glass are sometimes added to the surface of concrete for a decorative "exposed aggregate" finish, popular among landscape designers.

The presence of aggregate greatly increases the robustness of concrete above that of cement, which otherwise is a brittle material and thus concrete is a true composite material.

Redistribution of aggregates after compaction often creates inhomogeneity due to the influence of vibration. This can lead to strength gradients.

        Forth,reinforcement concrete .Installing rebar in a floor slab during a concrete pour.

Concrete is strong in compression, as the aggregate efficiently carries the compression load. However, it is weak in tension as the cement holding the aggregate in place can crack, allowing the structure to fail. Reinforced concrete solves these problems by adding either steel reinforcing bars, steel fibers, glass fiber, or plastic fiber to carry tensile loads. Thereafter the concrete is reinforced to withstand the tensile loads upon it.

 

     Fifth, chemical admixtures are materials in the form of powder or fluids that are added to the concrete to give it certain characteristics not obtainable with plain concrete mixes. In normal use, admixture dosages are less than 5% by mass of cement and are added to the concrete at the time of batching/mixing^. The common types of admixtures are as follows.

• Accelerators speed up the hydration (hardening) of the concrete. Typical materials used are CaCl₂, Ca(NO₃)₂ and NaNO₃. However, use of chlorides may cause corrosion in steel reinforcing and is prohibited in some countries, so that nitrates may be favored.
• Retarders slow the hydration of concrete and are used in large or difficult pours where partial setting before the pour is complete is undesirable. Typical polyol retarders are sugar, sucrose, sodium gluconate, glucose, citric acid, and tartaric acid.
• Air entrainments add and entrain tiny air bubbles in the concrete, which will reduce damage during freeze-thaw cycles, thereby increasing the concrete's durability. However, entrained air entails a trade off with strength, as each 1% of air may result in 5% decrease in compressive strength.
• Plasticizers increase the workability of plastic or "fresh" concrete, allowing it be placed more easily, with less consolidating effort. A typical plasticizer is lignosulfonate. Plasticizers can be used to reduce the water content of a concrete while maintaining workability and are sometimes called water-reducers due to this use. Such treatment improves its strength and durability characteristics. Superplasticizers (also called high-range water-reducers) are a class of plasticizers that have fewer deleterious effects and can be used to increase workability more than is practical with traditional plasticizers. Compounds used as superplasticizers include sulfonated naphthalene formaldehyde condensate, sulfonated melamine formaldehyde condensate, acetone formaldehyde condensate and polycarboxylate ethers.
• Pigments can be used to change the color of concrete, for aesthetics.
• Corrosion inhibitors are used to minimize the corrosion of steel and steel bars in concrete.
• Bonding agents are used to create a bond between old and new concrete (typically a type of polymer) .
• Pumping aids improve pumpability, thicken the paste and reduce separation and bleeding.

     Sixth,mineral admixtures and blended cements.There are inorganic materials that also have pozzolanic or latent hydraulic properties. These very fine-grained materials are added to the concrete mix to improve the properties of concrete (mineral admixtures), or as a replacement for Portland cement (blended cements).

• Fly ash: A by-product of coal-fired electric generating plants, it is used to partially replace Portland cement (by up to 60% by mass). The properties of fly ash depend on the type of coal burnt. In general, siliceous fly ash is pozzolanic, while calcareous fly ash has latent hydraulic properties.
• Ground granulated blast furnace slag (GGBFS or GGBS): A by-product of steel production is used to partially replace Portland cement (by up to 80% by mass). It has latent hydraulic properties.
• Silica fume: A by-product of the production of silicon and ferrosilicon alloys. Silica fume is similar to fly ash, but has a particle size 100 times smaller. This results in a higher surface to volume ratio and a much faster pozzolanic reaction. Silica fume is used to increase strength and durability of concrete, but generally requires the use of superplasticizers for workability.
• High reactivity Metakaolin (HRM): Metakaolin produces concrete with strength and durability similar to concrete made with silica fume. While silica fume is usually dark gray or black in color, high-reactivity metakaolin is usually bright white in color, making it the preferred choice for architectural concrete where appearance is important.