Concrete Blocks

Blocks are larger than bricks. For this reason a block usually requires both hands to lift it for laying. However, because they are larger, they can be laid more quickly than bricks, but the bigger size also means less versatility in laying especially when building up ends or corners and also laying to curves.

Generally blocks are intended to be plastered.

A concrete block is one of several precast concrete products used in construction. 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.

 Concrete blocks are termed either dense or lightweight. Lightweight concrete blocks can be one-third the weight of dense blocks. Lightweight blocks have the following advantages;

 - easier to handle and quicker to lay,

 - the air in lightweight block provide better sound and thermal insulation,

 - the lighter weight results in lighter foundations and structural members, and

 - they can be cut and chased with hand tools and hold nails and screws without plugs.

Types of  concrete blocks

Solid blocks – no formed holes or  slots.

Cellular blocks – with cavities (holes) which do not pass through.

Hollow blocks – with cavities which pass through.

Hollow Blocks

Solid Block

 Strength

The minimum crushing strength of concrete blocks are given below:

	Concrete density1 kg/mm3	Strength N/mm2
Dense aggregate	1500-2000	2.8-3.5
Lightweight aggregate	700-1500	2.8-10.5
Autoclaved aerated	400-900	2.8-7.0

Thermal and sound insulation

Thermal conductivity of blocks varies with density. Lightweight concrete blocks have better thermal insulation compared to denser blocks.

Fire resistance

Fire resistance of concrete blocks is good.

 Durability

Durability of facory-made blocks is generally good. Blocks made with dense aggregate and having a compressive strength of at least 7 N/mm²  can be used for external walls and below ground level as damp-proof courses.

Ease of construction

The speed for constructing a masonry wall using concrete blocks is faster that usual bricks-made wall. This is because the sizing of blocks is more massive then bricks.T. Furthermore, cinder and concrete blocks typically have much lower water absorption rates than brick. 

Construction of masonry wall using concrete blocks

Before filling in corefill

The various types of concrete blocks that had been appeared in the market now.

Easy, how to build a concrete block wall, a 6" block is used, by Rahgsa

Difference between clay bricks and concrete bricks

Concrete bricks	Clay bricks
Concrete bricks are far simpler to manufacture: Suitable sands, stone and cement are proportionately mixed together with water, vibrated in a press, allowed to cure for about 14 – 28 days and are then ready for use. Total process time 15 to 30 days. Energy costs are quite low and there is minimal pollution.          Concrete brick are formed in a mold and then allowed to cure (preferably for about 28 days).	Clay bricks are made in a process that starts with a suitable blend of clays that have to be mined, aged, then milled/mixed to even consistency. The clay is then extruded through a special press and sliced to size. These unburnt bricks are dried out before being placed in a kiln that is heated to between 700c and 1100c. Thereafter, when the firing is complete, the bricks need to be cooled and classified as to color and strength. The process is very energy intensive, generates large amounts of carbon dioxide, is quite difficult to control and takes up to 3 months to complete. If that was not all, the set-up cost of a reasonable factory is about 10 times that of concrete for the same output.
Concrete brick are mainly used for walkways, patios and fill-ins on concrete walls. Clay brick are used for building veneers, patios, walkways, retaining walls and more.	Clay brick have lower water absorption rates, higher strength (up to 5,000psi vs 1,200-1,800psi), have higher heat resistance, weather better, and hold their color better
Concrete bricks on the other hand tend to shrink about the same amount (partly curing and partly drying out) usually in the first 6 months after construction. So concrete masonry walls need contraction joints.	Clay bricks tend to expand after manufacture in the first few years of their life – about 3mm to 5mm over 10 meters of wall length. So expansion joints need to be provided.
Concrete bricks accept paint relatively well.	Clay bricks often exude metallic salts in their early years which cause paint to peel off.

Concrete Brick

Concrete brick is made from solid concrete. These bricks are used to cover the facade of a home, build fences, and enhance the overall beauty of a home's exterior. Bricks that are made from concrete come in a number of styles and colors making them extremely popular amongst homeowners. Aside from aesthetics, concrete bricks also have many other appealing attributes.

While regular brick does a fine job of insulating a home, concrete brick tends to be a better insulation option. Traffic, airplanes, and other outside noises are effectively muted, thanks to the solid concrete that these bricks are made from. Other benefits of concrete brick include better fire protection, less exterior home maintenance, and lower energy bills.

Bricks that are fashioned from concrete are available in a number of different styles. Consumers can select from a smooth, rough, textured, glossy, sandblasted, or stone finish. Various manufacturers may also offer customized bricks according to a consumer's specifications. In addition, hundreds of different color options are available -- most manufacturers will customize bricks to meet a homeowner's needs.

Admixtures for Portland cement

Plasticizers

Plasticizers or water reducers, and superplasticizer or high range water reducers, are chemical admixtures that can be added to concretemixtures to improve workability. Unless the mix is "starved" of water, the strength of concrete is inversely proportional to the amount of water added or water-cement ratio. In order to produce stronger concrete, less water is added, which makes the concrete mixture less workable and difficult to mix, necessitating the use of plasticizers, water reducers, superplasticizers or dispersants. 

Adding 1-2% plasticizer per unit weight of cement is usually sufficient. Adding an excessive amount of plasticizer will result in excessive segregation of concrete and is not advisable. Depending on the particular chemical used, use of too much plasticizer may result in a retarding effect.

 

 

 

Superplasticizers

superplasticizers, also known as high range water reducers. These polymers are used as dispersants to avoid particle aggregation, and to improve the flow characteristics of suspensions such as in concrete applications. Their addition to concrete or mortar allows the reduction of the water to cement ratio, not affecting the workability of the mixture, and enables the production of self-consolidating concrete and high performance concrete. This effect drastically improves the performance of the hardening fresh paste.