Dry-Stacked Interlocking Masonry System (Mortarless)
The system of dry-stacked interlocked masonry enables affordable building construction, speedier construction of high quality in stretcher bond as well as aesthetics. The walls constructed using this system may be left exposed, plastered or finished with cement paint.
It is a mortarless masonry system using block that interlock to provide leveling and alignment. Though still uncommon, these systems could be used to construct strong, durable, and cost-effective buildings. In this method of masonry construction blocks are not laid on mortar except first two block layers above DPC and top two courses leading to roof band . As per the requirement of IS 4326:1993 (Indian Standard on Earthquake Resistant Design and Construction of Building – Code of Practice), a thin mortar of the specified type can be used even in these Interlocking types of the blocks.
This type of masonry system relies on self weight to resist external forces through interlocking mechanisms of shear keys.
Types of Dry Packed Interlocking Masonry Construction:
Depending on the type of occupancy of the building, the assembly of dry packed masonry can be completed in one of three ways: plain, surface bonded, and grouted (Ref. – P. J. Mancini & Associates. Structural Engineers, “Design Methodology—The Haener Interlocking Mortarless Block System” August 1989)
Plain dry-stacked units can be used for retaining walls, foundation walls, partitions, and load-bearing walls up to about 9 feet tall in structures not intended for human occupancy.
For surface-bonded walls, dry stacked units can be finished on both sides with a cementitious or acrylic bonding matrix reinforced with fiberglass mesh or plastic fibers as a rain and air barrier, as well as providing the final surface finish and color. Height limits can be as high as 21 feet 8 inches for two-story load bearing walls.
In grouted construction, dry-stacked units have their cores partially or fully filled with grout, including horizontal and vertical reinforcement. Reinforced, grouted walls provide masonry assemblies with properties and load capacities similar to conventional reinforced masonry systems. Height limits can approach 36 feet for three-storied load bearing walls.
Consideration For Dry Packed Interlocking Masonry Construction:
a) Corners: Dry-packed interlocking masonry construction should be started at the corners. One must start the first course with a shaved ½ block. It must be remembered to shave off the ridge and male face of the corner block, and further ensuring that the shaved ridge points upward and the shaved male face point’s outwards. The aim is to make the corner an integral part of the structure.
b) T – Junctions: For a T – Junction of n courses, shaved ½ blocks and shaved full blocks are required to start the first course having shaved faces pointing upwards.
c) Cross Junctions: For a cross junction that is an integral part of both the walls, only full blocks with ridges shaved off are required, ensuring that there are no straight joints.
d) Joints and Angles: Each course will have to be connected at the corner with a brick force that should be always nailed in the centre of the block and not near the edge.
Benefits of Dry-Stacked Interlocking Masonry System
. Reduction in construction time. Due to this, building construction costs also reduces.
. Reduced requirement for skilled labor.
. Reduction in usage of costly cement.
. Interlocked masonry units can be dismantled easily and can be reused.
. Blocks are water cured and do not require burning of Fuel.
. Wall face surfaces are even. Plastering not required but can be done as an option.
. The requirement for un-skilled labor makes dry stacking particularly attractive against labor based work.
.Self-aligning masonry system that uses minimal amounts of mortar (or no mortar).
. Reduction is quality control problems as in the case of mortar construction such as mortared joints e.g. inadequate bond and mortar cracking that provide an obvious path for water penetration would no longer be factors in dry-stacked assembly’s performance.
. Good quality control over manufacturing of blocks and assembly as it is done at the manufacturing factory. Quality control of the assembly would lie with the manufacturer of the interlocking block, substantially reducing responsibility at the job-site.
. Faster construction compared to masonry units, as the mixing and placing of mortar is avoided. Using interlocking units without mortar, the mason could put more units in the wall in a given period of time. Output has been as much as 900 to 1,200 units a day per crew.
. The combined effect of less skilled labor and increased output has been estimated to reduce labor cost by as much as 80%.
. Interlocking block provide stability during construction, floor and roof loads could be placed on wall assemblies without waiting for mortar to cure, thus further speeding construction.
. The blocks have an extremely appealing face-brick finish and provide a pre-pointed straight masonry that uses minimal or no mortar. The thickness of the masonry can be controlled giving more carpet area and less cubic contents of the blocks.
Suitability of Dry-Packed Interlocking Block Construction:
. In Load Bearing Masonry: Since blocks are on 220 mm width and can be made of block strength > 75 N/mm2, same can be safely used for Load Bearing construction. In terms of IS 1905, masonry can be done with thin mortar slurry of 1:3.
. In Framed Structure Masonry: Brick/ block work is to be used as an infill only. Dry -stacked block work can be used in out-walls of +/- 220 mm thickness. For block work of lesser width it is recommended to use mortar slurry.
. In Reinforced Masonry: Interlocking blocks with horizontal and vertical cavity provide an ideal solution for using reinforcements to suit the structural design requirements, of reinforced masonry.
In Boundary Walls: Dry stacked block work is well suited for this application and is very fast, aesthetic and cost effective.
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