AAC blocks and adhesive for installation

This blog explains about the AAC blocks and the adhesive to be used for the installation of AAC block as wall:

AAC is also known as AUTOCLAVED CELLULAR CONCRETE (ACC), AUTOCLAVED LIGHTWEIGHT CONCRETE (ALC), AUTOCLAVED CONCRETE, CELLULAR CONCRETE, POROUS CONCRETE, AIRCRETE, HEBEL BLOCK, AND YTONG. It is a lightweight, precast, foam concrete building material invented in the mid-1920s that simultaneously provides structure, insulation, and fire- and mold-resistance. AAC products include blocks, wall panels, floor and roof panels, cladding (façade) panels and lintels.

AAC is produced from the common materials lime, sand, cement, water, gypsum and a small amount of rising agent. After mixing and molding, it is then autoclaved under heat and pressure to create its unique properties.

At the point when AAC is blended and cast in structures, a few compound responses occur that give AAC its light weight (20% of the heaviness of cement) and warm properties. Aluminum powder responds with calcium hydroxide and water to frame hydrogen. The hydrogen gas froths and copies the volume of the crude blend making gas rises to 3mm in distance across. Toward the end of the frothing procedure, the hydrogen escapes into the air and is supplanted via air.

The chemical reaction due to the aluminum paste provides AAC its distinct porous structure, lightness, and insulation properties, completely different compared to other lightweight concrete materials.

When the forms are removed from the material, it is solid but still soft. It is then cut into either blocks or panels, and placed in an autoclave chamber for 12 hours. During this steam pressure hardening process, when the temperature reaches 190 Deg C and the pressure reaches 8 to 12 bars, quartz sand reacts with calcium hydroxide to form calcium silicate hydrate, which gives AAC its high strength and other unique properties. Because of the relatively low temperature used AAC blocks are not considered fired brick but a lightweight concrete masonry unit. After the autoclaving process, the material is ready for immediate use on the construction site. Depending on its density, up to 80% of the volume of an AAC block is air. AAC's low density also accounts for its low structural compression strength. It can carry loads of up to 8 MPa, approximately 50% of the compressive strength of regular concrete.

AAC is produced out of a mix of quartz sand and/or pulverized fly ash (PFA), lime, cement, gypsum, water and aluminum and is hardened by steam-curing in autoclaves. As a result of its excellent properties, AAC is used in many building constructions, for example in residential homes, commercial and industrial buildings, schools, hospitals, hotels and many other applications.

Advantages or benefits of AAC Blocks:

1.    AAC Block is relatively uniform when compared to other wall unit and does not contain coarse aggregate phase.

2.    It is made from the mixture of fly ash, cement, lime, gypsum and an aeration agent.

3.    The Problem of fly ash utilisation is solved by the use of fly-ash in AAC Block. This was a major problem till day.

4.    AAC Block can be used to build internal and external walls.

5.    It can also be used as load bearing and non-load bearing walls.

6.    AAC blocks are very easy to handle and ordinary tools are used for cutting.

7.    AAC blocks are available in large sizes and hence less no of joints. This ultimately results in faster construction on site and less consumption of cement.

8.    Earthquake forces are proportional to the weight of the building and it ultimately reduces the load on buildings and hence less steel in case of RCC structure.

9.    AAC blocks are made from an inorganic material which helps to avoid termites, damages or losses.

10.Saves steel and concrete due to the reduction in dead weight.

11.Increase in floor area due to a reduction in the size of columns and thickness of the wall.

12.Easy to transport on upper floors.

13.Time-saving in construction

14.AAC blocks have a very low thermal conductivity which keeps interior remain cool in summer and warm in winter.

15.AAC blocks reduce interior temperature variation maintaining pleasant and healthy temperature for habitant.

16.AAC blocks reduce the energy cost of air-conditioning to a great extent due to its thermal property.

17.AAC blocks are appropriate for fire rated application for desired safety.

18.One AAC block of size (600 x 200 x 100 mm) is equivalent to 6 bricks hence it reduces 50% of joints resulting in saving of mortar up to 48%. In the case of 150 mm or thicker block masonry, the mortar saving is even more due to avoidance of vertical joint in conventional brick masonry.

19.Minimal wastage of AAC blocks.

20.It is environment-friendly and also saves water. Hence it is popularly used as a green product.

21.The production cost of AAC Blocks is expensive but on the whole project cost decrease.

22.Colour of AAC Block is Grey.

23.Available sizes of blocks, 400-600 x 100-200 x 100-300 mm However, it defers from manufacturer to manufacturer.

24.The AAC Blocks are accurate in size because it is produced by wire cut technology and is a factory product. Variation in Size 1.5mm(+/-).

25.AAC Blocks is a unique and excellent type of building material due to its super heat, fire and sound resistance.

26.Water Absorption of this block should not be 10 % its weight.

27.The thermal conductivity of block is lower and less heat transfer from the block.

28.Moisture resistance of AAC block is better than the Red Brick.

29.AAC block consists of unconnected micropores which prevent the capillary transport of moisture over a long distance.

30.The AAC block has good sound transmission property due to the presence of air voids. 40-45 db sound is reduced for 200 mm thick.

31.AAC blocks are insect resistant, inorganic and solid wall construction material.

32.AC block does not allow spread of  termites and pests and hence increase the life of wall.

33.The Speed of work will be double than that of clay brick work.

34.More carpet area available due to less thickness of the block.

35.AAC Blocks are recommended for high-rise buildings because it substantially reduces the total dead load of the building.

36.Requires less mortar due to flat and even surface & less number of joints.

37.Speedy construction of wall due to the bigger block size, light in weight and less number of joint.

38.Block is cured by steam and block masonry also requires less curing hence less water is used and there is saving in electricity bill.

39.Negligible breakage almost 100 % utilisation is possible.

40.Readily available at any time & in any season at a short notice, so no storage required.

41.Efflorescence occurs through mortar and water, but not through blocks.

42.K value for AAC Blocks is around 0.21 to 0.42W/Mk and this results in strong thermal insulation of walls with energy saving upto 20%.

 See what IS 2185 Part 3 - says about the AAC blocks

See what ASTM C 1386 - says about the AAC blocks

See what IS 2250 - says about the mortar to be used for the installation of AAC blocks

Also see what IS 6041 - says about the mortar to be used for the installation of AAC blocks

See what ASTM C 1660 - says about the compressive strength of AAC block adhesive

Cure the specimens in air at a temperature of 75 ±6 15°F (24 6 8°C) and a relative humidity of less than 80 % for at least 28 days, or for a time prescribed by the mortar manufacturer, in a stacked position.

AAC are available in block shapes and in larger pre-casted panels suitable for both wall and floor applications. As a lightweight construction material, it has excellent heat and sound insulation properties, is easy to shift, cut, handling, placing, do not add much load to structure. This lightweight concrete has some different properties compared to a conventional concrete. They will have relatively low compressive strength and shear strength, very porous but have excellent insulation property compared to normal concrete or concrete blocks.

Consideration are necessary when it comes for the subsequent application on these AAC blocks or panels are as follows:

1. Control joints movement joints shall be provided in wall and floor systems to relieve stresses due to movement of the structural system and to control the locations where movement can occur without detrimental effects on the finishes. These joints shall be applied with waterproofing membrane system along with the coving bandage.

2. Cementitious putty material shall be applied over AAC which will seal all holes and make the surface and joints in line, level, etc followed by priming coat is required prior to the application of any coatings such as waterproofing or any decorative finish.

3.These walls must be sealed on one side only to allow the Hebel material to ‘breathe’ and expand/contract with changes in the temperature and moisture content in the atmosphere, specially wall at exterior walls.

4. At wet area, waterproofing coating is must for wall and floor with protection like tiling or sloping screed.

5. Internal wall shall be covered by sheet linings say plasterboard / fiber cement boards and then install tiling.

6. Heavy tile finishes may adhere to AAC blocks, but failure may occur due to the low cohesive strength of surface of AAC. Tiles can be installed on the AAC with cementitious putty material which will seal all holes and make the surface and joints in line, level, etc.

7. Tiling is not recommended on to the external surfaces of AAC walls or panels.

8. At floor area, due to low compressive strength, point load will damage the panel. Hard floor finishes such as tiles can spread the load over a wider area, but tile shall be installed with 100% adhesive spread.

9. Vinyl or carpet can be installed over the AAC floor panel by priming and then by installed self leveling compound. All panel joints, gaps, holes shall be sealed using cementitious rapid drying and hardening internal repair mortar prior to the installation of SLC. This is recommended only at internal dry areas.
10. ARCHITECTURE CIVILENGINEERING ENVIRONMENT - (ACE) from The Silesian University of Technology: MORTAR SELECTION IN DESIGN PRACTICE – DESCRIPTION OF THE PROBLEMS, SOLUTIONS AND REQUIREMENTS says: about how should be the mortar / adhesive used for AAC / clay brick:

In market there are many manufacturer who produces adheisve for the installation of AAC block, one best product among them is M15. The below is the snap of the certificate of test report of M15 which passes IS 2250 with two very important parameters with the compressive strength of Approx 19 N/Sqmm:

https://themasonrychandrastore.com/blogs/cold-hard-tuckin-faqs/choosing-the-proper-mortar-for-any-masonry-chandraapplication-and-then-where-tochandra-buy-it

WALL HEIGHT & LINTEL in the construction of AAC block:

1. There should be a coping beam to be placed after every 1.2 meter of height of wall with minimum reinforcement of 2 nos of 8 mm bar. 

2. It is advisable to perform masonry work of maximum six layers of blocks in a one day. 

3. Door and Window Lintel should be rest on full block on the both sides of opening for proper load distribution. 

4. Use proper wire mesh and mortar at Beam & Column Junctions to avoid weak joints.

https://themasonrychandrastore.com/blogs/cold-hard-tuckin-faqs/choosing-the-proper-mortar-for-any-masonry-chandraapplication-and-then-where-tochandra-buy-it

For answer to : Mortar to be used to bond the AAC shall have less or more compression strength? refer to:https://annayyachandrashekar.blogspot.com/2018/12/mortar-to-be-used-to-bond-aac-shall.html


Many thanks to Google.com and doc88.com from where the images and details were took.