ADVANTAGE OF CEMENT CONCRETE BLOCKS: ENVIRONMENTAL FRIENDLY & ECONOMICAL
CHANDIGARH (VAIBHAV BANSAL BUREAU CHIEF): The concrete block masonry unit which is also known as the concrete masonry unit (CMU) has advantages over brick and stone masonry. Concrete blocks are manufactured in the required shape and sizes and these may be solid or hollow blocks. The common size of concrete blocks is 39cm x 19cm x (30cm or 20 cm or 10cm) or 2 inch, 4 inch, 6 inch, 8 inch, 10 inch and 12-inch unit configurations.
A concrete masonry unit (CMU) is a standard size rectangular block used in building construction. CMUs are some of the most versatile building products available because of the wide variety of appearances that can be achieved using them.
Those that use cinders (fly ash or bottom ash) as an aggregate material are called cinder blocks in the United States, breeze blocks (breeze is a synonym of ash) in the United Kingdom, and hollow blocks in the Philippines. In New Zealand and Canada, they are known as concrete blocks (a name common in the United States also). In New Zealand, they are also called construction blocks.
In Australia, they are also called Besser blocks and Besser bricks, because the Besser Company was a major supplier of machines that made concrete blocks. Clinker blocks use clinker as aggregate. In non-technical usage, the terms cinder block and breeze block are often generalized to cover all of these varieties.
Cement, aggregate, water is used to prepare concrete blocks. The cement-aggregate ratio in concrete blocks is 1:6. The aggregate used is 60% fine aggregate and 40% coarse aggregate. Their Minimum strength is about 3N/mm2. ASTM C-90-91 specifies the compressive strength requirements of concrete masonry units.
Concrete blocks are made from cast concrete (e.g. Portland cement and aggregate, usually sand and fine gravel, for high-density blocks). Lower density blocks may use industrial wastes, such as fly ash or bottom ash, as an aggregate. Recycled materials, such as post-consumer glass, slag cement, or recycled aggregate, are often used in the composition of the blocks. Use of recycled materials within blocks can create different appearances in the block, such as a terrazzo finish, and may help the finished structure earn LEED certification. Lightweight blocks can also be produced using autoclaved aerated concrete.
Sizes and structure
The use of blockwork allows structures to be built in the traditional masonry style with layers (or courses) of staggered blocks. Concrete blocks may be produced with hollow centers (cores) to reduce weight, improve insulation and provide an interconnected void into which concrete can be poured to solidify the entire wall after it’s built. Blocks come in modular sizes, with the most popular typically referred to (by their thickness) as “4-inch”, “6-inch”, “8-inch”, and “12-inch”. In the US, CMU blocks are nominally 16 in (410 mm) long and 8 in (200 mm) wide. Their actual dimensions are 3⁄8 inch (9.5 mm) less than the nominal dimensions (to allow for 3⁄8-inch mortar joints between blocks in any orientation). In Ireland and the UK, blocks are usually 440 mm × 215 mm × 100 mm (17.3 in × 8.5 in × 3.9 in) excluding mortar joints. In Australia, New Zealand, and Canada, blocks are usually 390 mm × 190 mm × 190 mm (15.4 in × 7.5 in × 7.5 in) excluding mortar joints.
Block cores are typically tapered so that their top surface (as laid) has a greater surface on which to spread a mortar bed and for easier handling. Most CMUs have two cores, but three- and four-core units are also produced. A core also allows for the insertion of steel reinforcement to span courses in order to increase tensile strength. This is accomplished by grouting the voids of blocks containing rebar with concrete. Thus reinforced, CMU walls are better able to resist lateral forces such as wind load and seismic forces. Cores may also be filled with expanded-polystyrene (EPS) block foam insulation, substantially increasing the R-value of the resulting wall to be in compliance with the US national energy code.
A variety of specialized shapes exist to allow special construction features. U-shaped blocks or knockout blocks with notches to allow the construction of bond beams or lintel assemblies, using horizontal reinforcing grouted into place in the cavity. 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, allowing a filler material to be anchored between the un-mortared block ends. Other features, such as radiused corners known as “bullnoses” may be incorporated. A wide variety of decorative profiles also exist.
Concrete masonry units may be formulated with special aggregates to produce specific colors or textures for finish use. Special textures may be produced by splitting a ribbed or solid two-block unit; such factory-produced units are called “split-rib” or “split-face” blocks. Blocks may be scored by grooves the width of a mortar joint to simulate different block modules. For example, an 8-by-16-inch (200 mm × 410 mm) block may be scored in the middle to simulate 8-by-8-inch (200 mm × 200 mm) masonry, with the grooves filled with mortar and struck to match the true joints.
Types of Concrete Blocks or Concrete Masonry Units
Depending upon the structure, shape, size, and manufacturing processes concrete blocks are mainly classified into 2 types and they are
Solid concrete blocks
Hollow Concrete Blocks
Solid Concrete Blocks
Solid concrete blocks are commonly used, which are heavy in weight and manufactured from the dense aggregate. They are very strong and provides good stability to the structures. So for large work of masonry like for load-bearing walls these solid blocks are preferable. They are available in large sizes compared to bricks. So, it takes less time to construct concrete masonry than brick masonry.
Hollow Concrete Blocks
Hollow concrete blocks contain void area greater than 25% of gross area. The solid area of hollow bricks should be more than 50%. The hollow part may be divided into several components based on our requirements. They are manufactured from lightweight aggregates. They are lightweight blocks and easy to install.
Types of Hollow Concrete Blocks:
Frogged brick block
Concrete Stretcher Blocks
Concrete stretcher blocks are used to join the corner in the masonry. Stretcher blocks are widely used concrete hollow blocks in construction. They are laid with their length parallel to the face of the wall.
Concrete Corner Blocks
Corner blocks are used at the ends or corners of masonry. The ends may be window or door openings etc. they are arranged in a manner that their plane end visible to the outside and the other end is locked with the stretcher block.
Concrete Pillar Blocks
A pillar block is also called a double corner block. Generally, these are used when two ends of the corner are visible. In the case of piers or pillars, these blocks are widely used.
Jamb Concrete Blocks
Jamb blocks are used when there is an elaborated window opening in the wall. They are connected to stretchers and corner blocks. For the provision of double-hung windows, jamb blocks are very useful to provide space for the casing members of the window.
Partition Concrete Block
Partition concrete blocks are generally used to build partition walls. Partition blocks have a larger height than their breadth. The hollow part is divided into two to three components in the case of partition blocks.
Lintel block or beam block is used for the purpose of provision of beam or lintel beam. Lintel beam is generally provided on the top portion of doors and windows, which bears the load coming from the top. Concrete lintel blocks have a deep groove along the length of the block as shown in the figure. After placing the blocks, this groove is filled with concrete along with reinforcement.
Frogged Brick Blocks
Frogged brick block contains a frog on its top along with a header and stretcher like a frogged brick. This frog will help the block to hold the mortar and to develop a strong bond with the top laying block.
Bullnose Concrete Block
Bullnose blocks are similar to corner blocks. Their duties also the same but when we want rounded edges at the corner bullnose bricks are preferred.
Concrete block, when built with integral steel reinforcement, is a very common building material for the load-bearing walls of buildings, in what is termed concrete block structure (CBS) construction. One of the common foundation types for American suburban houses is the “crawl space foundation” which consists of a concrete block wall around the perimeter on which dimensional lumber floor joists are supported. Retaining walls, which also be constructed of concrete blocks, either using blocks designed to be set back each course and used with a sand base and without mortar or reinforcing (gravity wall), or using blocks (typically an architectural style of block or clad with a veneer such as brick) with a concrete base, steel reinforcing and mortar (piling wall). Other very common, non-structural uses for concrete block walls (especially in American schools) are as interior fire-rated and extremely durable partition walls, and as exterior backup curtain walls for attachment of building envelope systems (rigid foam insulation and an air/vapor barrier) and veneers (stucco, steel, brick, or split-face concrete block).
Concrete masonry walls may be ungrouted, partially grouted, or fully grouted, the latter two enhancing their structural strength. Additionally, steel reinforcement bars (rebar) can be used both vertically and horizontally inside a CMU wall to maximize its structural performance. The cells in which the rebar is placed must be grouted for the bars to bond to the wall. For this reason, high seismic zones typically only allow fully grouted walls in their building codes. The American design code that guides design engineers in using CMU as a structural system is the Masonry Standards Joint Committee’s Building Code Requirements & Specification for Masonry Structures (TMS 402/ACI 530/ASCE 5). The compressive strength of concrete masonry units and masonry walls varies from approximately 1,000 psi (7 MPa) to 5,000 psi (34 MPa) based on the type of concrete used to manufacture the unit, stacking orientation, the type of mortar used to build the wall, and other factors.
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