Autoclaved aerated concrete (AAC block) is a lightweight, precast, foam concrete building material suitable for producing concrete masonry unit (CMU) like blocks. Composed of quartz sand, calcined gypsum, lime, cement, water, and aluminum powder, AAC products are cured under heat and pressure in an autoclave. (Reference Wikipedia). Due to its incredible stability and other constructive properties, AAC blockwork is more common with not only builders but acceptable to architects also as they have much more freedom than other conventional methods. This post explains the method of construction to be followed in the site for AAC Blockwork.
The purpose of this document is to detail the Procedure for AAC blockwork as per the approved details. The documentation will apply to all Engineers, Workmen, QC personnel, and other concerned persons associated with the work.
2. Scope of work
This Procedure covers plant and tools, manpower requirements erection/installation works of formworks, and quality control to be followed for AAC blockwork construction.
The scope of work consists of:
- Storage of materials
- Setting out and Survey works
- Brickwork construction and lintel works.
- Drawings and any other relevant/applicable documents.
- Project technical specifications
- Respective Indian standards
- Inspection and test plan for Block work
- AAC blocks (light weight) shall generally conform to IS: 2185 (Part-3). Blocks shall be regular in size & shape and shall be of specified strength & quality conforming to IS: 2185 (Part-3). Half or three-quarter size blocks are to be used wherever required to make up length of wall and broken blocks shall not be used.
- Water: Water used for masonry shall be clean and free from injurious amount of deleterious materials conforming to IS 456.
- Jointing Mortar: A pre-mixed, easy to apply high-quality mortar comprising of cement, graded sand and admixtures which replaces conventional jointing mortar of 12-18 mm thickness with highly versatile 3-5 mm thickness shall be used. Mortar application must be as per manufacturer recommendation.
5. Material delivery and storage
- Transport the blocks in such a manner that the units are adequately protected during its movement. The units shall be handled in a manner, which will prevent soiling, chipping or damage of any kind. Broken, chipped or otherwise damaged units will be rejected and shall not be used in the work.
- A sample of 24 blocks shall be taken from every consignment of 10000 blocks of the same size, batch and manufacturer for conducting tests as per IS 2185 Part 3 Clause 10.
7. Tolerances in Blocks
- Maximum variation in the dimensions of AAC block work construction shall be +/- 5% in length and +/- 3% in width and height as per IS 2185 Part 3. The number of blocks with dimensions outside the tolerance limit and or with visual defects, among those inspected, shall not be more than two.
Project Engineer, Site Engineers, Supervisors, Foremen, and helpers.
9. Safety Precautions
- Safety of the personnel and properties is to be given prime importance and all works to be carried out without causing any accidents or property damages.
- Blocks shall be stacked properly near the place of work (Do not stack too large quantity near the work area thereby causing safety hazard).
- Height of the stack should not be more than one and half meter.
- Scaffolding to be braced adequately.
- Working space to be clear of rubbish, waste mortar etc so that easy access and cleanliness is ensured.
- Scaffolding to be checked for the load carrying capacity and ensure no overloading.
- Lifting, manual transporting of blocks etc must be carried out by workers who are properly trained. Otherwise, this may cause serious injuries to workers.
- Chasing in the block work must be carried using appropriate cutting tools only. While doing chasing on the walls the worker must wear proper safety appliances like shoes, goggles, helmets etc.
- Throwing of debris from height strictly prohibited.
- Before commencement of block work in front of lift shaft safety permit should be taken.
- CT props to be fixed in front of lift shaft to tie the safety belt.
- Hard barricading to be cut only by gas cutting (If any anchored in concrete along the openings and edges of the building).
The Project Manager/Construction Manager shall be responsible for the overall implementation of this procedure.
- Shop drawings: Shop drawings for AAC Block work shall be approved, stamped for GFC by all the concerned parties for architectural floor plans, Doors and windows schedule, MEP services and typical details must be available before proceeding with the construction.
11. Equipment and Tools Used
Plumb Bob, Spirit Level, Straight Edge, Measuring Tape, Tube Level, Try Square Usage Tools, Mason Trowel & Adhesive Trowel, 12mm thick Ply piece, Block Cutting Machine, Wooden Float, Hammer & Chisel, Spade / Shovel, Wire Brush, Ghamela / Tray
12. Mortar for Construction
The recommended mortar mix for AAC Blockwork construction (proportion by volume) is 1:1:6 Cement, Lime, and Sand or 1:6 Cement, Sand. Preferably use PPC/PSC cement for best results. The mortar shall not be spread so much ahead of the actual laying of the blocks as it tends to stiffen and lose its plasticity thereby resulting in poor adhesion and bond. Mortar consistency to be maintained at the time of laying block masonry. Likewise ready mixed mortar as per the manufacture’s recommendation can replace the traditional mortar.
13. Control Joints
They are used to reduce restraint by accommodating movement of the AAC Blockwork , or movement of structural elements adjacent to the wall, and thus to control cracking. They are vertical separations built into the wall at locations where cracking is likely due to excessive horizontal stresses. It shall be provided as shown in the drawings.
14. Work procedure; – Preparatory Work & First Layer Installation.
- Mark the wall lines on floor to get proper layout of blockwork. Scrub & clean with proper tool, Hack the concrete surface where new block work is to be done.
- All binding wires, nails, masking tapes and stuck shuttering material is removed. Patching of honeycomb if any to be completed and curing of it monitored.
- When the blocks are set in proper position, the two corner blocks shall be removed, a mortar bed spread, and these blocks laid back in place truly level and plumb. After completing this procedure for a section of work Inspection for approval of this first layer shall be done and get it approved.
- The base layer of the AAC block work shall be done with cement mortar of mix 1: 6 to align the undulations & to maintain the top-level uniform.