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.