Aerated Autoclave Concrete

1. Noaina Hassan Khan---Tanzeel Ahmed--- Reema Khan
Nadia Ali --- Atia Khursheed

2.  Autoclaved aerated concrete (“AAC”), is one of the many
building products being touted as “green” or
“environmentally friendly.”
 Developed in Sweden in the 1920s in response to
increasing demands on timber supplies, AAC is a
lightweight manufactured building stone.
 . Comprised of all natural raw materials, AAC is used in a
wide range of commercial, industrial, and residential
applications.
 AAC now accounts for over 40% of all construction in the
United Kingdom and more than 60% of construction in
Germany.

3.  AAC is a precast product manufactured by combining silica (either in
the form of sand, or recycled fly ash), cement, lime, water, and an
expansion agent - aluminium powder, and pouring it into a mould.
 In structurally reinforced AAC products like lintels or roof panels,
steel rebar or mesh is also placed in the mould.
 Once added to the concrete, the aluminium powder reacts with the
silica, resulting in the formation of millions of microscopic hydrogen
bubbles. The hydrogen bubbles cause the concrete to expand to
roughly five times its original volume.
 The hydrogen subsequently evaporates, leaving a highly closed-cell
aerated concrete, then cut into which are further steam and
pressure cured in an autoclave.

5.  AAC products consist of load bearing, non-load
bearing and cladding applications.
 Complete load bearing applications, however, are
limited to low-rise construction.
 Cladding and large panels are available to take
advantage of AAC’s insulative, fire proofing, and
other benefits on mid- and high-rise projects.
 The large wall, floor, and roof panels, measuring up
to 20 feet long, 2 feet wide, and in various
thicknesses, are also used in load-bearing capacities
and are common in commercial and industrial
applications.
 The remainder of the AAC system consists of blocks,
also called “units” which are stacked using thin-set
mortar, as opposed to the traditional cement-based
mortar.

6. The blocks are available in a variety of sizes and types.
 STANDARD BLOCKS - typically measuring 24 inches long, 8 inches
high, and in thicknesses between 6 (non-load-bearing) and 12
inches
 CORED BLOCKS – also known as O-blocks, which are used
adjacent to corners and openings and have a centred, 4 inch
vertical core at one end of the block to form a continuous
vertical core through the wall that is then filled with rebar
and concrete.

7.  JUMBO BLOCKS - which reduce construction time.
 U-BLOCKS- which have a channel running the length of
the block that once filled with concrete, provides
structural support as headers and on the top course of
each floor (the “bond beam”). AAC lintels with
integrated structural support are also manufactured
and are an alternative to using the U-block system for
headers.

8. AAC reduces additional material use and minimizes waste and pollution.
 AAC is approximately 80% air, the finished product is up to 5 times the volume of the
raw material consumed in its production.
 AAC production raw materials are generally locally sourced and may consist of
recycled materials.
 AAC consumes approximately 50%-20% less energy than that needed to produce
CMUs.
 The manufacturing process, produces no waste or pollution and the final product is
completely recyclable.
 Due to its light weight and dimensional accuracy, AAC can be
assembled with minimal waste and a reduced need for additional
equipment.
 The product is virtually maintenance free, eliminating the need for
repair materials, pesticides, and chemical treatments, while also
lowering operating costs

9. AAC Has High Thermal Efficiency
 AAC structures result in solid wall construction with integrated
insulation, preventing thermal bridging, creating an airtight
building envelope, minimizing uncontrolled air changes.
 AAC benefits from low thermal conductivity value.
AAC Reduces Noise Pollution and Improves
Indoor Air Quality
 Its millions of independent air cells dampen sound
transmission.
 Because AAC construction has very low air
infiltration and is mold resistant, indoor air quality
of AAC structures is improved.

10. AAC Structures Are Price Competitive
 AAC buildings constructed near a supplier’s manufacturing
facilities cost approx. the same as traditional materials.
 AAC’s light weight helps lower shipping costs.
 The higher initial cost must be balanced against savings due to
lower operating and maintenance costs, the structure’s longer
lifespan.
Easily workable
 Less time consuming due to large size of blocks.
 Light weight also makes it easy to handle.
AAC Structures Are Well-Suited to Withstand Fires, Earthquakes, and
Other Natural Disasters
 It receives a 4 hr. UL fire rating and has a melting point of over 2900° F.
 AAC is also termite and mold resistant, and nearly fireproof.

11. Familiarity with Product
 Few contractors are a currently familiar with the product, and trained
masons must adjust to using thin-set mortar as opposed to traditional
cement-based mortar, which requires less precision in its application.
Scarcity of Manufacturing Plants.
 Projects far from manufacturing facilities will suffer
from higher initial costs.

12. General considerations
AAC masonry components(block units) can be used to build
load bearing or non load bearing walls.
 O-block units used to build pilasters.
 U-block units used to build bond beams and lintels.
 Control joints on AAC reinforced walls must be placed at
maximum 16 ft. o.c.
Installation Guide
 Check foundation.
 Receiving and distribution of AAC
wall units.

13.  Installation requirements.
 Tools
 Equipment
 Other materials
 Installing O-block for pilasters in first
course.
 Laying the first course (levelling course).
 Lay the first course over a semi-dry cement
mortar levelling bed- ½” to 2” thick.
 Corner blocks are laid first and the first
course should be completed before second
course installation.
 Once corner blocks are placed apply thin bed
mortar, to the vertical joints for other blocks.
 Thin bed mortar 1/16” inch to 1/8”
Anchoring vertical
reinforcement to foundation

14.  Cutting blocks (adjustments and chases)
 A hand saw or band saw to cut the blocks to specific lengths.
 Placing control joints in first course
 These are vertical joints taken through the full wall thickness, and from
bottom to top.
 3/8” to ½” thick.
 Maximum spacing between control joints should be 15 ft.
 Laying the subsequent courses
 For subsequent courses use only thin bed mortaring on all joints between
AAC blocks.
 Minimum overlapping of vertical joints between layers should be 4”.
 Metal strip ties should be placed every two courses at – 1) connection of
secondary walls to main walls – 2) connection of walls to concrete
columns.
 Control joints in subsequent layers.
 V-shaped metal strips should be set at every two courses
unless there are two pilasters on both sides of control joints
and less than 2” from the joint.
 Once the wall is built fill the gap using backer rod and seal
with caulking.

15.  Fill up pilasters by pouring concrete.
 Building on site lintels using U-blocks.
 Install temporary supports before putting U-blocks in place apply
thin bed mortar to the vertical joints.
 Once U-block are set, place rebars according to construction
drawings and with concrete.
 Installing U-blocks to build bond beams.
 Lay U-block course applying thin bed mortar on all joints.
 At each pilaster location, drill a hole in the bottom side so the
vertical bars can be attached in the bond beam.
 Before pouring concrete place rebar and anchor bolts according to
construction drawings.
 Utilities installation after the walls are built:
 For electrical conduits and piping installation, a chase is cut using
an electrical router or a chasing tool.
 When required depth of chase is bigger than maximum depth
recommended, additional O-blocks are used to lodge the pipes or
interrupt wall continuity.
 After installation, the chase are filled with repair mortar or cement
sand mortar.
Bond beam and pilaster
connection

17.  Renders and finishes
 Surface patching: rasp block joints and other areas where AAC
surface is out of plane.
 Surface must be cleaned using a scrub brush and any loose or
damaged material be removed.
 A rubber float is commonly used to smooth the wall surface.
 Fiber glass mesh: This should be installed directly over one layer of
render in all control joints, around windows, doors and utility
locations.
 Finishes:
 AAC masonry walls can be finished with stucco , acrylic texture
coats, or a combination of both, also laminated stones, ceramic or
clay tiles, concrete pieces and ornamental products.

18.  Anchoring to AAC:
 Fasteners: Anchors used with AAC shall be made of plastic or nylon. Wood, fiber,
lead, metal or expansion anchors are not recommended.
 Use power drills to make holes for fasteners. Percussion drilling or inverting the
rotation direction when drilling shall be avoided.
 The anchor shall penetrate tightly to avoid rotation when placing the screw.
 Hebel AAC nail: Galvanized nails are designed specifically to provide definitive
anchorage in the AAC, and are directly hammered into it.
 Screws: minimum length of screw is defined by anchor length plus thickness of
the finish layer and the element to be fixed.