13.1
Design Example: Dimensioning of Concrete Masonry Construction
For the construction of a storeroom using concrete masonry units, it's essential to align the dimensions of the structure with the actual sizes of the…
Consider a construction site that needs a storeroom to be constructed.
The site has a stack of concrete masonry blocks with nominal dimensions of 8 inches in width and depth and 16 inches in length used for the storeroom construction.
The site engineer has to design the storeroom to have the 16-inch length blocks placed precisely in the walls without having to cut the blocks.
The room's dimensions in the plan are 12 feet in length and 8 feet in width, measured from the outer corners.
The actual dimensions of the block are slightly less than the nominal dimensions. The block dimensions and mortar thickness together give a length of 16 inches.
Now, precisely 9 blocks are needed for the longer dimension of the wall and 6 for the shorter.
With this arrangement, the inner dimensions of the room become 10 feet 8 inches in the longer direction and 6 feet 8 inches in the shorter direction.
This practice avoids cutting the blocks and assures faster construction and a perfect finish.
View the full transcript and gain access to JoVE Core videos
Q1: Why should concrete masonry block dimensions align with wall layout in construction?
Aligning block dimensions with wall layout eliminates the need to cut blocks, which accelerates construction and ensures a professional finish. When blocks and mortar joints are coordinated with planned wall lengths, materials fit precisely without waste. This systematic approach improves efficiency and reduces labor time on site.
Q2: How do nominal and actual block dimensions differ in concrete masonry?
Nominal dimensions represent the stated size, such as 8 by 8 by 16 inches, but actual block dimensions are slightly smaller—typically 7 5/8 by 7 5/8 by 15 5/8 inches. The difference accounts for mortar joint thickness, usually 3/8 inch. Combined, the actual block and mortar joint equal the nominal dimension, enabling precise wall planning.
Q3: What role does mortar joint thickness play in block dimensioning?
Mortar joint thickness bridges the gap between actual and nominal block dimensions. A 3/8-inch mortar allowance, when added to the actual block length of 15 5/8 inches, produces an effective block length of 16 inches. This standardized calculation ensures blocks align perfectly with planned wall dimensions without cutting.
Q4: How many blocks are needed to fill a 12-foot wall without cutting?
For a 12-foot wall using 16-inch blocks with mortar, exactly 9 blocks are required. Nine blocks multiplied by 16 inches (actual block plus mortar) equals 144 inches or 12 feet. This calculation ensures the wall fills the planned dimension precisely, avoiding material waste and construction delays.
Q5: What are the internal dimensions of a storeroom with 12-foot by 8-foot external dimensions?
When a storeroom with 12-foot by 8-foot external dimensions is constructed using 9 blocks for length and 6 blocks for width, the internal dimensions become 10 feet 8 inches by 6 feet 8 inches. This reduction accounts for the thickness of the masonry walls on both sides of the structure.
Q6: How does block coordination improve construction efficiency on site?
Coordinating block dimensions with wall layout eliminates cutting, reducing labor time and material waste. When 9 blocks fit a 12-foot wall and 6 blocks fit an 8-foot wall without modification, construction proceeds faster and achieves a cleaner aesthetic. This planning approach also reduces costs and ensures consistent quality throughout the project.
Q7: What is the effective length of a concrete masonry block including mortar?
The effective length of a concrete masonry block is 16 inches when the actual block length of 15 5/8 inches is combined with a 3/8-inch mortar joint. This combined dimension allows blocks to be laid end to end in precise multiples that match planned wall dimensions, supporting design example distributing reinforcements in concrete sections and other structural planning.