There are an almost infinite number of CMU shapes available. Prefaced Concrete and Calcium Silicate Masonry Units ASTM DESIGNATIONĬMUs for construction of Catch Basins and Manholes ASTM C90 covers most conventional CMU construction and is the standard referenced by the ICC codes. The following table provides the ASTM standards that apply to concrete masonry units. Architects must specify the CMU weight if a particular weight is required. Heavier units tend to reduce sound transmission, have much higher compressive strengths, and have greater thermal storage capacity however, they are more expensive and cost more to install. Lighter CMUs are less expensive, require less labor to install, and tend to have better fire resistance properties. There are three classifications of CMU: lightweight (less than 105 lb/ft 3), medium weight (between 105 lb/ft 3 and 125 lb/ft, and normal weight (more than 125 lb/ft 3. The weight of concrete masonry units varies depending on the density of concrete mix used. The standards identify appropriate materials, compressive strength, dimensional tolerance, moisture absorption, and other performance characteristics.Ĭoncrete brick is made from concrete similar to concrete block, but concrete bricks are fabricated in sizes that match traditional clay bricks (i.e. CMU SIZEĬoncrete Masonry Unit (CMU) SpecificationsĬMU manufacturers must conform to ASTM standards when fabricating concrete blocks. While 4", 6", 8", 10", and 12" are the standard sizes, some manufacturers offer other sizes not listed below. The following table provides concrete block sizes in both nominal and actual dimensions. The architect should always attempt to design buildings using the nominal dimensions to the nearest half-block size to reduce waste and labor due to cut blocks. For instance, a 6" CMU is nominally 6" deep while a 10" CMU is nominally 10" deep.Ĭoncrete blocks also come in half-sizes, which are helpful in reducing the need to cut blocks in the field at corners or the end of walls. They are identified by their depth – i.e. For high quality concrete hollow blocks from premium brands that provide assurance of durability and reliability, the average cost is Rs 86 for a 4 inch wide block and Rs 100 for a 6 inch wide block without delivery charge.Concrete Block - Nominal vs Actual Dimensions Concrete Block (CMU) SizesĬoncrete Masonry Units (CMUs) are manufactured in a variety of sizes. The cheapest blocks are in Makwanpur where the average cost per block is Rs 33 which is below the overall average. The average price in Kathmandu for a 6 inch wide block is Rs 75 and for a 4 inch wide block is Rs 65. The price also varies with the ratio of cement used, the cost of cement in the manufacturing place and the delivery charge. The average price in different districts in Nepal is Rs 58 per block. The prices of concrete hollow blocks in Nepal depends upon the manufacturers, quality of products, competition in the market and the district where the manufacturing is done. The required density for Grade A concrete blocks is more than 1500 kg/m3 while for Grade B, it is between 1100 to 1500 kg/m3. Grade A concrete blocks have strength between 5 to 15 N/mm2 while Grade B blocks have strength between 3.5 to 5 N/mm2. The minimum compressive strength required for a concrete block is 3 N/mm2. For a 100 meter square wall, we need 1350 units of hollow blocks. The standard side surface area of a concrete hollow block in Nepal is 0.0741 meter square. The standard size of concrete hollow blocks in Nepal is 390X200X190 mm3 (15.35X8X7.5 inches). Dimension and Specification of Concrete Blocks Other additives that can be used are volcanic ash, granite rubble, sand, broken glass, brick, concrete, hardened cement, expanded clay, river gravel, crushed stone, sawdust etc. Aggregate used is of 60% fine aggregate and 40% coarse aggregate. The cement-aggregate ratio in concrete blocks is 1:6. Raw materials used in concrete blocksĬement, aggregate, and water are used to prepare concrete blocks. This composition makes the structure lightweight and equally durable, strong and long lasting. The solid area of hollow bricks should be greater than 50%. The void area of hollow concrete blocks is greater than 25% of the total area. They are lightweight and are easy to put together. Also called cement blocks, they are used for constructing exterior and interior load bearing walls, partition walls, fire-safe walls, piers, columns and retaining walls. Concrete blocks are one of the most popular construction materials in Nepal which are used in the construction industry almost everywhere.
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