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Building Green with Concrete Masonry

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A concrete block is referred to as a concrete masonry unit or CMU, in the construction industry. Concrete blocks can be solid or hollow with two or three cores or voids. The blocks also come in a range of standard shapes and are lightweight, durable and fireproof, making them an efficient, affordable and eco-friendly building material. In case of reinforced concrete blocks (RCB), their cores or voids are filled with steel reinforcing rods and concrete for additional strength. These blocks are most suitable for foundations and basement walls and partition walls as they are unaffected by termites or extreme temperatures and are virtually soundproof Concrete blocks also provide insulation against cold & heat and can help reduce a building’s energy usage.

Method of Construction

Concrete blocks of 8”X8”X16” with two holes are laid one upon another by staggered joint. Vertical reinforcement is placed through these holes which are then grouted. No RCC column and beam structure are required except shear wall & slab staircase in RCC and foundation as simple RCC.wall footing.

In RCB construction system, structurally, each wall and slab behaves as a shear wall and a diaphragm respectively reducing the vulnerability of the building to damages during natural hazards. Also, the uniform distribution of reinforcement in both vertical and horizontal directions, through each masonry element, increases tensile resistance and ductile behaviour of building elements.

The system can safely resist lateral or cyclic loading and has proved to offer better resistance under dynamic loading when compared to other conventional systems of construction.

Aesthetics

A major architectural benefit of RCB is the modular masonry system which allows for efficient design co-ordination of sizes of building components, such as door and window frames. Ancient/ traditional type of architectural elevation is also possible by RCB type of construction.

The concrete masonry is probably the most versatile masonry product available as it offers a variety of dimensions, aspect ratios, textures, colours and profiles. A limitless palette of colours and textures is possible and the size and shape of units available is only limited by having the correct mould. It can be made to have special textures.

Eco-friendly & Affordable Construction

RCB construction saves 50% steel + shuttering material, 40% concrete and 25% on utility bills. The use of concrete masonry also benefits the environment as not only is concrete masonry fully recyclable, but manufacturers are using recycled crushed aggregate in the production of new blocks. This has major advantages in terms of lessening environmental impact and gives rise to a truly green building product. The simplicity of assembly almost halves the requirement of steel, cement, shuttering, concrete and skilled labour thereby bringing down the cost of construction by 20%.

Concrete masonry is energy efficient because the thermal mass of concrete slows down the passage of heat moving through a wall and allows the masonry structure to absorb heat instead of passing it through the inside of the building, keeping the inside cool. As the wall is cooled by nightfall, the absorbed heat is released, gradually warming the inside. Likewise, this thermal barrier helps keep a concrete masonry structure warmer in the winter months. This lessens the need for artificial climate control and therefore wasted energy.

Structural Advantages

• Earthquake: Load bearing concrete blocks can be designed to be wind/hurricane and earthquake resistant.

• Fire Proof: Due to concrete block and 3” cover to steel, rusting is minimized and such buildings are fire & bomb blast proof.

• Durable: The concrete compacted by high pressure and vibration gives substantial strength and proper curing increase compressive strength of the blocks.

• Acoustic insulation – Concrete masonry is a highly suitable material for attenuating noise as it is an extremely dense material which reduces the transmission of airborne sound.

• Speed: No heavy equipment is needed on site and with less form-work and steel used, the construction is simple and speedier.

R.C.B. is the technology backed by uniform building code and is suitable not only for three and four storied construction but also for structures up to sixteen storeys in height or more. R.C.B. is well-suited for buildings like hotels, schools, hospitals, industries, residential buildings and low cost projects like transit camps and slum redevelopment projects. Over the life cycle of a building, concrete masonry is arguably one of the most effective materials used in construction. It is completely cost effective taking into account the reduced maintenance cost, the cost of heating and cooling the building, increased resistance to natural calamities as well as the recycling of the building material at the end of the building’s life cycle.

Concrete Blocks Structural Properties

Concrete blocks are produced with hollow centres to reduce weight and improve insulation. Blocks come in many sizes. The most common nominal size is 16×8×8 in (410×200×200mm).

The presence of a core allows steel reinforcing to be inserted into the assembly, greatly increasing its strength. There may be two, three or four cores, although two cores are the most common configuration.

Reinforced cores are filled with grout to secure the reinforcing in proper relationship to the structure and to bond the block and reinforcing. The reinforcing imparts greater tensile strength to the assembly, improving its ability to resist lateral forces such as wind load and seismic forces.

Reinforcement bars can be used both vertically and horizontally inside the concrete masonry unit to strengthen the wall for better structural performance. High seismic zones typically only allow fully grouted walls in their building codes.

The compressive strength of concrete masonry units and masonry walls varies from approximately 1,000psi (7MPa) to 5,000psi (34MPa) based on mainly the type of concrete used to manufacture the unit, stacking orientation, and the type of mortar used to build the wall.

Concrete Blocks as an Architectural Element

A variety of specialized shapes exist to allow special construction features. U-shaped blocks or notches allow the construction of bond beams or lintel assemblies. Blocks with a channel on the end known as “jamb blocks”, allow doors to be secured to wall assemblies. Blocks with grooved ends permit the construction of control joints. Other features, such as radiused corners known as “bullnoses” and a wide variety of decorative profiles also exist.

Concrete masonry units may be formulated with special aggregates to produce specific colors or textures and may be scored by grooves the width of a mortar joint to simulate different masonry modules for a external finishing.

 

 

Ganesh N.Kamat

B.E. (CIVIL) Mumbai, M.S. (U.S.A)

Ganaka Engineers & Architects

Dr. Anuja Kamat

B.E. (Mumbai), M.S. (U.I.U.C),

Ph.D. (U.S.A)

 

 

 

 

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