Ar Bricks 21

CHAPTER 1 INTRODUCTION AAC was invented in mid-1923 in Sweden. It is also known as Autoclaved Cellular Concrete (ACC) or Autoclaved Lightweight Concrete (ALC). Production process of AAC is fairly simple. It is made with made with a mixture of fly ash, lime, cement, gypsum, an aeration agent and water. Aeration process, imparts it a cellular light-weight structure. AAC products are precast in various sizes and provide structure, insulation, and fire and mold resistance. AAC products are offered in various shapes and sizes including but not limited to blocks, wall panels, floor and roof panels, and lintels. Use of Autoclaved Aerated Concrete (AAC) blocks in construction industry in India offers interesting proposition for various segments in the society. For a project developer it means faster and lower cost construction. For environmentally conscious it means eco-friendly products and for those who occupy buildings built with AAC blocks it means better safety and lower energy costs for cooling or heating. Primary raw material for AAC is fly ash. Thousands of tonnes of fly ash is generated by thermal power plants everyday and its disposal is a cause of concern. Moreover, using fly ash does not harm the environment at all. In fact using fly ash takes care of issues related to disposal of fly ash. Therefore by using fly ash to produce AAC products provides a sustainable, economic and environment friendly option. At the end it all translates to a better world for future generations.

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Types of Aerocon bricks One interesting aspect of Aerocon brick is that it lets the user build the walls of with the thickness of his choice. Contrary to the wall made by traditional bricks, walls made with Aerocon bricks are thinner but are still sustainable. However, depending on different various needs of internal and external walls, Aerocon bricks are available in different sizes and varied thickness as follows. Aerocon bricks are currently available in three sizes: Infill, Jumbo, and Thermal blocks

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Infill blocks The size of the Infill Aerocon brick is 600X600 mm and the thickness varies in the ranges of 75,100,125,150,200 mm. The main advantage of Infill blocks is that they can easily replace 60% of the concrete in roof slabs and thus help in saving significant amounts of concrete, steel, labor, water, plaster etc. These blocks are especially suitable for building roofs in large column-free constructions.

Jumbo blocks Jumbo blocks are typically in the size of 600X300 mm, and thickness ranges from 75,100,125,150, to 200 mm. The unique large size of Jumbo Aerocon bricks results in the usage of much fewer bricks and hence less mortar is required. These bricks are more suitable for non-load bearing walls, multi-storeid buildings etc.

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Thermal blocks These blocks are also called as Aerocool thermal blocks whose size and thickness is 300X200 mm and 50 mm respectively. These blocks are ideal for roofing since they delay the transmission of heat flow and also help interiors remain warm during winters and cool during summers.

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CHAPTER 2 COMPARISION BETWEEN AEROCON BRICKS AND CLAY BRICKS Comparison between Autoclaved Aerated Concrete (AAC) blocks and clay bricks Serial

Parameter

AAC Blocks

Clay Bricks

1

Soil Consumption

One sq ft of carpet area with clay brick walling will consume 25.5 kg of top soil

2

Fuel Consumption

3

CO2 Emission

4

Labour

Uses fly ash which is a thermal power plant waste product & thus no consumption of top soil One sq ft of carpet area with AAC blocks will consume 1 kg of coal One sq ft of carpet area will emit 2.2 kg of CO2 Organized sector with proper HR practices

5

Production Facility

State-of-the-art factory facility

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Tax Contribution

7

Size

8 9 10 11

Variation in Size Compressive Strength Dry Density Fire Resistance (8" wall) Cost Benefit

Contributes to government taxes in form of Central Excise, VAT and Octroi 625 mm x 240 mm x 100-300 mm 1.5 mm (+/-) 3.5-4 N/m2 550-700 kg/m3 Up to 7 hours

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5

Reduction in dead

One sq ft of carpet area with clay bricks will consume 8 kg of coal One sq ft of carpet area will emit 17.6 kg of CO2 Unorganized sector with rampant use of child labour Unhealthy working conditions due to toxic gases Does not contribute to government exchequer

225 mm x 100 mm x 65 mm 5 mm (+/-) 2.5-3 N/m2 1800 kg/ m3 Around 2 hours None

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weight leading to savings in steel and concrete Approx.30% heating and cooling

Energy Saving

None

The advantages of Aerocon blocks over conventional clay bricks 

Aerocon Blocks are an innovative product in the green building revolution.



Aerocon blocks are the new blocks in walling materials, substituting conventional and environmentally unsustainable materials like clay bricks, concrete and hollow blocks.



The raw materials used in the manufacture of these blocks are environmentally friendly and are certified green products. The basic raw materials used in production of Aerocon blocks are Cement, Fly ash, lime and water.



Aerocon blocks can be plastered, painted, and dry lined or tiled.

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Aerocon block is extremely light, just one-third the weight of clay bricks or onefourth the density of R.C.C. They are much easier to handle on the site.



They are easy to install and can complete the construction procedure in a shorter span in case of scarcity of labour and in the usage of mortars. The required time to complete a building with aerocon blocks is 1/3 lesser than that of the conventional building materials.



The edges of the blocks are such that they allow easy workability and accurate dimensioning and are easy to cut, drill, nail, shape and chase using ordinary wood working tools. Power tools can be used for rapid chasing for embedding service lines. 6

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Aerocon blocks can be cut virtually in any shape or angle making them extremely adaptable.

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Aerocon block covers the same area as that 14 clay bricks do enabling a faster construction results in saving of labour, time and material.

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Aerated concrete is perfect building material for any climate. It is used to build all kinds of walls: exterior and interior bearing and non-bearing walls, foundation walls, partition walls as filling agent in framework structures, wall partitions, fire division walls, etc.



Aerocon excellent thermal properties helps in saving recurring energy costs of heating and cooling. The thermal resistance combined with the benefits of thermal mass inertia and whole wall coverage eliminates the need for additional insulation.



Aerocon blocks are available in various sizes and shapes.They are available in three types; Infill blocks, Jumbo blocks and Thermal blocks. They are included into the category of Green Building materials because they don‟t emit VOC (Volatile Organic Compounds) which cause environmental pollution.



Apart from being eco-friendly these blocks are also light weight with high thermal insulation, fire resistance, sound insulation, have strength and durability, have consistent quality control and gives a perfect finish with dimensional stability. Buildings constructed out of these blocks ensure long term sustainability and save a lot of water during the construction.



Excluding the eco-friendly characteristics of these blocks, they are also used in construction for various other reasons. There are a number of problems involved in acquiring the sand and bricks and also the prices of these basic materials are hiking up. As the traditional construction materials have a higher price the initiation of Aerocon blocks acts as better substitutes with affordable prices. Due to these reasons the Aerocon blocks are in great demand.

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

Hence, it is one of the revolutionary materials that can be used to make the world a better, greener and cleaner place to live in. It is a revolutionary material that combines the unique properties such as durability and strength, low weight, very simple construction technology and excellent environmental performance.

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CHAPTER 3 DESIGN CONSIDERATIONS

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.

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”

Cutting blocks (adjustments and chases) 

A hand saw or band saw to cut the blocks to specific lengths.

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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. 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. 10

•

After installation, the chase are filled with repair mortar or cement sand mortar.

Renders • • • •

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.

Raw Material Fly Ash or Sand Key ingredient for manufacturing AAC blocks is silica rich material like fly ash or sand. Most of the AAC companies in India use fly ash to manufacture AAC blocks. 11

Fly ash is mixed with water to form fly ash slurry. Slurry thus formed is mixed with other ingredients like lime powder, cement, gypsum and Aluminum powder in quantities consistent with the recipe. Alternately sand can also be used to manufacture AAC blocks. A „wet‟ ball mill finely grinds sand with water converting it into sand slurry. Sand slurry is mixed with other ingredients just like fly ash slurry.

Lime Powder Lime powder required for AAC production is obtained either by crushing limestone to fine powder at AAC factory or by directly purchasing it in powder form. Although purchasing lime powder might be little costly, many manufacturers opt for it rather than investing in lime crushing equipment like ball mill, jaw crusher, bucket elevators, etc. Lime powder is stored in silos fabricated from mild steel (MS) or built using brick and mortar depending of individual preferences.

Cement 53-grade Ordinary Portland Cement (OPC) from reputed manufacturer is required for manufacturing AAC blocks. Cement supplied by „mini plants‟ is not recommended due to drastic variations in quality over different batches. Some AAC factories might plan their captive cement processing units as such an unit can produce cement as well as process lime. Such factories can opt for „major plant‟ clinker and manufacture their own cement for AAC production. Cement is usually stored in silos.

Gypsum Gypsum is easily available in the market and is used in powder form. It is stored in silos.

Aluminum Powder/Paste Aluminum powder/paste is easily available from various manufacturers. As very small quantity of Aluminum powder/paste is required to be added to the mixture, it is usually weighed manually and added to the mixing unit. 12

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CHAPTER 4 PRODUCTION PROCESS

Raw Material Preparation and Storage The first step of AAC production is grinding of silica rich material (sand, fly ash, etc) in ball mills. For different materials, different processing is adopted, such as dry grinding (into powder), wet grinding (into slurry) or mixed grinding with quicklime (CaO). There are two methods for mixed milling. One is dry mixing to produce binding material, and the other method is wet mixing. Since most quicklime is agglomerate, it should be crushed and then grinded. Gypsum is normally not ball milled separately. It is grinded with fly ash or with quicklime, or it could be grinded with the same miller for quicklime in turn. Other supplementary and chemicals are also have to be prepared. Raw material storage assures the continuous production and material stability. The continuous production guarantees the non-stop & on-time supply, and the material stability guarantees the quality of products, since the raw material might come from different sources, with different qualities. Raw material preparation & storage is the pre-step for proportioning batching. This pre-step guarantees the raw material meet the standard for AAC production, and it is also finishes the storage, homogenization and aging process. It is the basic process that assures the smooth production and production quality.

Dosing and mixing Maintaining ratio of all ingredients as per the selected recipe is critical to ensure consistent quality of production. This is accomplished by using various control systems to measure and release the required quantity of various raw materials. A dosing and mixing unit is used to form the correct mix to produce Autoclaved Aerated Concrete (AAC) blocks. Fly ash/sand slurry is pumped into a separate container. Once the desired weight is poured in, pumping is stopped. Similarly lime powder, cement and gypsum are 14

poured into individual containers using screw conveyers. Once required amount of each ingredient is filled into their individual containers control system releases all ingredients into mixing drum. Mixing drum is like a giant bowl with a stirrer rotating inside to ensure proper mixing of ingredients. Steam might also be fed to the unit to maintain temperature in range of 40-42o C. A smaller bowl type structure used for feeding Aluminium powder is also attached as a part of mixing unit. Once the mixture has been churned for set time, it is ready to be poured into molds using dosing unit. Dosing unit releases this mixture as per set quantities into molds for foaming. Dosing and mixing process is carried out continuously because if there is a long gap between charging and discharging of ingredients, residual mixture might start hardening and choke up the entire unit. In modern plants, entire dosing and mixing operation is completely automated and requires minimum human intervention. This entire operation is monitored using control systems integrated with computer and CCTV cameras. As with any industrial operation, there is provision for human intervention and emergency actions integrated inside the control system.

Casting, Foaming and Pre-curing Once the desired mix is ready, it is poured into moulds. These moulds can be of various sizes depending on the production capacity of a manufacturing unit. Once mix is poured into moulds, it is ready for pre-curing. After casting, the slurry in molds will be in the pre-curing chamber to finish foaming and hardening. Foaming and hardening actually starts when the slurry is fed into molds, which includes gas-forming expansion and perform, curing to achieve certain strength, which is enough for cutting. Pre-curing is always done under set temperature. Hence it is also called as “Heating-room-pre-curing.” Pre-curing as not a complicated process, but should avoid vibration. Operations must keep eyes to monitory the slury change during foaming and provide feedback to dosing, mixing and casting process. Pre-form defects (cracking, sinking, etc.,) mainly occur during the process.

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Cutting During this process, the pre-cured block goes through cutting and shaping, into different size & shapes as per requirements. The high workability and large variety of sizes make AAC production more suitable for massive production with higher mechanization. Cutting can be done mechanically or manually. With a cutting machine, the production efficiency and dimensional accuracy is easily achieved.

Autoclaved Curing After cutting into the desired sizes & shapes, „green‟ AAC blocks are transferred into autoclaves. Autoclaves are used for steam curing under pressure. AAC must be pre-cured and steam cured to finish the physical and chemical changes, and then to achieve enough strength for desired usage. A batch of AAC blocks is steam cured for 10-12 hours at a pressure of 12 bar and temperature of 190°C. In hot and humid conditions, AAC blocks undergo last stages of hydro-thermal synthesis reaction to transform into a new product with required strength and various physical performances. Autoclaved curing imparts inherent properties and performance of AAC.

Grouping Grouping could be the last step of AAC production (in some AAC plant, the AAC will be further processed into panels after leaving autoclaves). After the cured AAC leaves the autoclaves, inspection and packaging is done.

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Process Flow Chart. Main Fly Ash

Gypsum

Lime

OPC

Raw material

Water Flyash

Weight

Slurry

Batched

Weight Batched Quantity

Batched

Pouring Mixture to mix ingredients

Bricks Casting on Mould

De-molding and Wire Cutting

Hi Pressure Steam Curing for 817 Hours

Eco-Bricks Ready for Sale

Aluminum Aluminum

CHAPTER 5 ANALYSIS

Market Shelter is third skin, according to a German Concept, which implies its importance next to human Skin and Clothing. This also shows the attachment of human race to this fundamental requirement. Building Material accounts for major component of the construction cost. Depending on the location they can contribute to 60 - 70 % of the cost of construction. With the ever increasing population, the demand for housing increases. This directly creates demand for this prime commodity of building. Add to the above fact the nearby area of this project site is undergoing a major infrastructure revolution. As Residential, Commercial, IT companies, and Industrial establishments are coming in, we can conclude that the Blocks unit will prosper and flourish in this environment. There is a central government gadget notification mandating government departments and CPWD to use 100% Fly Ash based Bricks in their all constructionsdirectly of through contractors. This factor will help the marketability of this product immensely. Fly Ash policy of the Government also mandates that 20% of Fly ash Generated by a power plant must be given free of cost to SME sector on a priority basis.

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Carbon Credits Estimates AAC blocks are being seriously considered for CDM projects in India for earning Carbon Credits. As the CER Generated is also relatively less, four or five such units can be bundled together to make a Group CDM in the same sactors. This project is likely to generate 1 CER per each 7 or 8 Cubic Meter of Blocks production, depending on, and subject to the CDM methodology adopted, and the interpretation of additionality and baseline parameters by the validating authority. Just for a rough estimate of CERS, for an annual production of average size AAC plant, that is 100000CM/Annum, we are likely to get around 12500 CERs on full capacity Production. At present market rate of 11.5 Euros per CER and @ Rs. 60 per Euro, we can expect to get additional revenue on CER. But we must expect to take a cut of around 20 to 30% of CERs, if we want to forward sell the CERs and get the CDM part sponsored by the buyer

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Raw Material Suitability Almost 95% of the raw materials can be made suitable for AAC line through proper mix design. Also we can have many different mix designs for the same denicity…same strength of Blocks. We will help you to get the Best quality blocks at optimal cost by means of designing proper Mix as per your input raw materials. The following are basic guidelines (certainly not the final call) on the suitability of basic raw materials for AAC. 1. Fly ash (65-70%) Index Item

Grade (%) Gr-I

Gr-II

≤

30

45

≤

15

25

≤

5.0

10.0

SiO2

≥

45-55

40

SO3

≤

1

2

(0.045 square hole sieve left Degree of

amount) (0.080 square hole sieve left

fineness Ignition loss

amount)

Reference : The fineness can be 0.045 or 0.080 square sieve left amount.

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2. Lime (8-25%) Item

Grade Super Gr.

1st Gr.

2nd Gr

A(CaO+MgO)Quality Fraction %

≥

90

75

65

MgO

Quality Fraction %

≤

2

5

8

SiO2

Quality Fraction %

≤

2

5

8

Digestion speed

5-15

≤

,min

Digestion temperature ,℃

≥

Undigested residue quality fraction ,%

≤

5

10

15

Fineness (0.080 square hole sieve left amount) %

≤

10

15

20

CO2

≤

2

5

7

Quality Fraction %

60-90

3. Cement (6-15%)

SiO2 21-23

Al2O3 5-7

Fe2O3 3-5

CaO

MgO

64-48

4-5

C3 S

C2 S

C3A

C4AF

44-59

18-30

5-12

10-18

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4. Gypsum/Plaster (3-5%)

CaSO4

＞

70%

MgO

＜

2%

Chloride

＜

0.05%

Preferably ground residue 90µm

＜

10-15%

5. Aluminum Power (about 0.08%)

Type and recommendation for supply depend on raw materials and mix formula Metal Content

Approx.

>=65%

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Powder

CHAPTER 6 Indian Standard for AAC blocks Bureau of Indian Standard Code no- 2185(Part-3):1984 discusses in details regarding the AAC blocks specifications in India. The prime requirements for AAC blocks (of ISI standards) in India as per the above said code are as follows.

A.ON PHISICAL SIZES OF AAC BLOCKS

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B. ON TOLERANCES OF AAC BLOCK SIZES

C. ON DENCITY, STRENGTH & THERMAL CONDUCTIVITY

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CHAPTER 7 ADVANTAGES AND DISADVANTAGES

Advantages of using Autoclaved Aerated Concrete Lightweight AAC blocks are about 50% lighter than clay bricks of equivalent size. This translates into less dead weight of buildings and allows entire structure to be lighter therefore reducing amount of steel and concrete used in structural components like beams, columns and roof/floor slabs.

Single product solution Buildings constructed with AAC do not require separate insulation products reducing construction cost, energy footprint and environmental impact of buildings.

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Easy workability AAC is very easy to work with and can be cut accurately reducing the amount of waste generated.

Environmental impact Manufacturing of AAC does not have high energy requirements. Moreover since AAC is light weight, it also saves energy required for transportation and leads to reduced CO2 emissions by transport vehicles. Since AAC is made from fly ash – an industrial waste product – generated by thermal power plants, it offers a low cost and sustainable solution for today and tomorrow. AAC is a requisite for green buildings.

Easy transportation It is easy to transport AAC as it does not suffer from high transit breakage usually associated with clay bricks.

Longevity AAC does not lose strength or deteriorate over time. Buildings constructed with AAC do not require routine repairs that are required for buildings using clay bricks.

Shorter Project Duration Buildings can be built with AAC 50% faster compared to clay bricks. This translates to lower project completion times benefiting project developers.

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Thermal Insulation AAC offers excellent thermal insulation. This reduces recurring cost of energy required for heating and cooling. Better thermal insulation also allows usage of smaller HVAC than required conventionally.

High survivability Millions of air pockets in AAC cushion structure from major force and prevents progressive collapse of a building. AAC structures are known to maintain structural integrity despite of heavy rains, extremely low temperature and salty air.

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Fire Resistance Due to high fire resistance offered by AAC, structures made from AAC have higher rate of survivability in case of fire.

Sound Insulation Sound absorption properties of AAC make it ideal material for reducing ambient noi se.AAC is well-suited for establishments like hospitals and offices situated in noisy areas.

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Contribution to Nation AAC factories create many jobs directly and indirectly creating a social impact. Along with that they pa

Weather Resistance AAC does not decay, rust, deteriorate or burn. AAC has been found to be earthquake resistant. AAC structures are known to maintain structural integrity in heavy rains, extremely low temperature and salty air.

Pest Resistance Primary raw material used to manufacture AAC is fly ash. Fly ash (or pond ash) is an inert material and does not allow termites or other pests to survive. Excise Duty and VAT contributing to national economy

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Product Disadvantages The major disadvantages of autoclaved aerated concrete are listed below. 

The production cost per unit for ACC is higher than other ordinary concrete.



Number of manufacturer is limited. So, cost will drastically increase in places far from the manufacturer and need to travel a long distance.



It is not as strong as conventional concrete.



Very few contractors who are familiar with ACC.



Construction with autoclaved aerated concrete may will need special permission.



Environmentally friendly

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CHAPTER 8 CONCLUSION As a construction system, AAC provide significant environment and other benefits for the building owner. The short and long term effect of using AAC compared to many other materials results in lower energy consumption, reduced operating costs, greater safety and comfort, and a healthier and more trouble – free building. These features provide a better investment for building owner and for environment.

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REFERNCES

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