Claims:1. Low density and high compressive strength Autoclave Aerated Concrete Blocks, comprising: pulverized fly ash/pond ash in weight percentage that ranges from 45% to 75%; OPC cement in weight percentage that ranges from 20% to 30%; quick lime powder mixed with water in weight percentage that ranges from 5% to 10%; gypsum or plaster of paris in weight percentage that ranges from 0.5% to 3%, aluminium paste or aluminium powder in weight percentage that ranges from 0.05% to 1%, and one or more additives, with the said additives not exceeding 1 wt%, and with the mix batch weight being 640 kg per cubic meter.

2. Low density and high compressive strength Autoclave Aerated Concrete Blocks, comprising: pulverized fly ash/pond fly ash in weight percentage that ranges from 50% to 70%; OPC cement in weight percentage that ranges from 25% to 35%; quick lime powder mixed with water in weight percentage that ranges from 5% to 10%; gypsum or plaster of paris in weight percentage that ranges from 0.5% to 3%, aluminium paste or aluminium powder in weight percentage that ranges from 0.02% to 0.8%, and one or more additives not exceeding 1 wt%, and with the mix batch weight being 700 kg per cubic meter.
3. A process of manufacturing low density and high compressive strength Autoclave Aerated Concrete Blocks, comprising the steps of: mixing 45 wt% to 75 wt% of pulverized fly ash/pond ash fly ash, 20 wt% to 30 wt% of OPC cement, 5 wt% to 10 wt% of quick lime powder mixed with water, 0.5 wt% to 3 wt% of gypsum, and not more than 1 wt% of one or more additives to form a homogeneous mixture, with the mix batch weight being 640 kg per cubic meter; adding 0.05wt% to 1 wt% of aluminum powder or aluminium paste to the homogenous mixture; pouring the slurry into moulds for setting; allowing the moulds to set; demoulding and cutting into desired sizes; autoclaving under vacuum at a pressure of 10 bar to 14 bar for 4 hours to 8 hours; and readying for dispatch after three days.

4. A process of manufacturing low density and high compressive strength Autoclave Aerated Concrete Blocks, comprising the steps of: mixing 50 wt% to 70 wt% of pulverized fly ash/pond ash, 25 wt% to 35 wt% of OPC cement, 5 wt% to 10 wt% of quick lime powder mixed with water, 1 wt% to 3 wt% of gypsum, and not more than 1 wt% of one or more additives to form a homogeneous mixture, with the mix batch weight being 700 kg per cubic meter; adding 0.02 wt% to 0.8 wt% of aluminum powder or aluminium paste to the homogenous mixture; pouring the slurry into moulds for setting; allowing the moulds to set; demoulding and cutting into desired sizes, autoclaving under vacuum at a pressure of 10 bar to 14 bar for 4 hours to 8 hours; and readying for dispatch after three days.

5. Low density and high compressive strength Autoclave Aerated Concrete Blocks as claimed in claim 1 or claim 3, wherein the one or more additives include superplasticizers, oxidizing agents, surface tension reducing agents, and fly ash dispersing agents.

6. Low density and high compressive strength Autoclave Aerated Concrete Blocks as claimed in claim 5, wherein the oxidizing agent is potassium dichromate.

7. Low density and high compressive strength Autoclave Aerated Concrete Blocks as claimed in claim 5, wherein the surface tension reducing agent is cetyltrimethylammoniumbromide (CTAB).

8. Low density and high compressive strength Autoclave Aerated Concrete Blocks as claimed in claim 5, wherein the fly ash dispersing agent is polyacrylicacid salts.

9. Low density and high compressive strength Autoclave Aerated Concrete Blocks as claimed in claim 2 or claim 4, wherein the one or more additives include superplasticizers, oxidizing agents, surface tension reducing agents, and fly ash dispersing agents.

10. Low density and high compressive strength Autoclave Aerated Concrete Blocks as claimed in claim 9, wherein the oxidizing agent is potassium dichromate.

11. Low density and high compressive strength Autoclave Aerated Concrete Blocks as claimed in claim 9, wherein the surface tension reducing agent is cetyltrimethylammoniumbromide (CTAB).`

12. Low density and high compressive strength Autoclave Aerated Concrete Blocks as claimed in claim 9, wherein the fly ash dispersing agent is polyacrylicacid salts. , Description:FIELD OF THE INVENTION
The present disclosure is generally related to high compressive strength autoclave aerated concrete blocks and a method for manufacturing the high compressive strength autoclave aerated concrete blocks.
BACKGROUND OF THE INVENTION
Conventionally, autoclave aerated concrete (“AAC”) blocks have been prepared by mixing cement, lime, and siliceous materials with water to make a slurry. Aerating agents such as aluminum powder/paste are added to the slurry so prepared. The addition of aerating agents in the slurry results in release of hydrogen gas and, hence, the mass of slurry in the tank rises as the gas produced exerts pressure to extend the mass and these air bubbles generated are trapped in great numbers to form cellular structure.
AAC is well suited for high-rise buildings and those with high temperature variations. Due to its lower density, high-rise buildings constructed using AAC require less steel and concrete for structural members. Further, the mortar needed for the laying of AAC blocks is also reduced due to the lower number of joints. Similarly, the material required for rendering is also lower due to the dimensional accuracy of AAC. The increased thermal efficiency of AAC makes it suitable for use in areas with extreme temperatures, as it eliminates the need for separate materials for construction and insulation, leading to faster construction and cost savings. In India, AAC blocks are generally manufactured as per IS 2185 Part 3, Serial No. 2
Even though AAC blocks are used for construction, sometimes cracks get formed on the wall, which tear the wall vertically resulting in a crack at the center of the length of the wall. The reasons for the crack development are drying shrinkage, low compressive strength, and the strength of plaster used.
The strength of the blocks need to be a minimum of 4Mpa, which brings down the drying shrinkage value to less than 0.05%, otherwise cracks develop after construction due to plastering.
With an increase the compressive strength, the density of AAC blocks also increases, which, in turn reduces the thermal insulation of the wall. Further, this also increases the load of the wall, hence more support structures are required for high-rise buildings.
Chinese patent application number CN101891434A attempts to increase the compressive strength of AAC blocks without increasing the density, in which river sand and quicklime are used in the range of 25-30 parts and 13-18 parts respectively.
However, when the quicklime % is increased in the slurry, it results in micro cracks due to high reactivity of lime, which results in an increased rejection rate due to the cakes becoming difficult to cut and increased corner damages to the blocks. Due to environmental impacts, the availability of river sand is also restricted.
There is, therefore, a need in the art for low density AAC blocks with low percentage of quick lime, with density as per IS 2185 Part 3, Serial No. 2, but compressive strength of the next grades as per IS 2185 Part 3, Serial No 3 or 4 that overcomes the aforementioned drawbacks and shortcomings.
SUMMARY OF THE INVENTION
Low density and high compressive strength Autoclave Aerated Concrete Blocks are disclosed. In an embodiment, the low density AAC blocks are of compressive strength 5 MPa, and comprise: pulverized fly ash/pond ash in weight percentage that ranges from 45% to 75%; OPC cement in weight percentage that ranges from 20% to 30%; quick lime powder mixed with water in weight percentage that ranges from 5% to 10%; gypsum or plaster of paris in weight percentage that ranges from 0.5% to 3%, aluminium paste or aluminium powder in weight percentage that ranges from 0.05% to 1%, and one or more additives, with the said additives not exceeding 1 wt%, with the mix batch weight being 640 kg per cubic meter.
In another embodiment, the low density AAC blocks are of compressive strength 6 MPa, and comprise: pulverized fly ash/pond fly ash in weight percentage that ranges from 50% to 70%; OPC cement in weight percentage that ranges from 25% to 35%; quick lime powder mixed with water in weight percentage that ranges from 5% to 10%; gypsum or plaster of paris in weight percentage that ranges from 0.5% to 3%, aluminium paste or aluminium powder in weight percentage that ranges from 0.02% to 0.8%, and one or more additives, with the said additives not exceeding 1 wt%, with the mix batch weight being 700 kg per cubic meter.
Methods of manufacturing the 5 MPa and the 6 MPa AAC blocks are also disclosed.
The disclosed AAC blocks have a low density as per IS 2185 Part 3, Serial No. 2, while their compressive strength and other properties are comparable to AAC blocks of the next grade.
DETAILED DESCRIPTION OF THE INVENTION
Throughout this specification, the use of the word "comprise" and “include”, and variations such as "comprises" "comprising", “includes”, and “including” may imply the inclusion of an element or elements not specifically recited.
Throughout this specification, the disclosure of a range is to be construed as being inclusive of the lower limit of the range and the upper limit of the range.
Low density AAC blocks are disclosed. In an embodiment of the present disclosure, the low density AAC blocks are of compressive strength 5 MPa, possess a dry density of 551 kg/m3 to 650 kg/m3, with a drying shrinkage of 0.05%, and comprise: pulverized fly ash/pond ash in weight percentage that ranges from 45% to 75%; OPC cement in weight percentage that ranges from 20% to 30%; quick lime powder mixed with water in weight percentage that ranges from 5% to 10%; gypsum or plaster of paris in weight percentage that ranges from 0.5% to 3%, aluminium paste or aluminium powder in weight percentage that ranges from 0.05% to 1%, and one or more additives, with the said additives not exceeding 1 wt%, with the mix batch weight being 640 kg per cubic meter.
In another embodiment of the present disclosure, the low density AAC blocks are of compressive strength 6 MPa, possess a dry density of 551 kg/m3 to 650 kg/m3, with a drying shrinkage of 0.05%, and comprise: pulverized fly ash/pond fly ash in weight percentage that ranges from 50% to 70%; OPC cement in weight percentage that ranges from 25% to 35%; quick lime powder mixed with water in weight percentage that ranges from 5% to 10%; gypsum or plaster of paris in weight percentage that ranges from 0.5% to 3%, aluminium paste or aluminium powder in weight percentage that ranges from 0.02% to 0.8%, and one or more additives, with the said additives not exceeding 1 wt%, with the mix batch weight being 700 kg per cubic meter.
The significance of increasing the mix batch weight is to maintain the volume of cellular structure.
In yet another embodiment of the present disclosure, the low density AAC blocks are of compressive strength 5 MPa, possess a dry density of 551 kg/m3 to 650 kg/m3, with a drying shrinkage of 0.05%, and are manufactured by: mixing 45 wt% to 75 wt% of pulverized fly ash/pond ash fly ash, 20 wt% to 30 wt% of OPC cement, 5 wt% to 10 wt% of quick lime powder mixed with water, 0.5 wt% to 3 wt% of gypsum, and not more than 1 wt% of one or more additives to form a homogeneous mixture, with the mix batch weight being 640 kg per cubic meter; adding 0.05 wt% to 1 wt% of aluminum powder or aluminium paste to the homogenous mixture; pouring the slurry into moulds for setting; allowing the moulds to set; demoulding and cutting into desired sizes; autoclaving under vacuum at a pressure of 10 bar to 14 bar for 4 hours to 8 hours; and readying for dispatch after three days.
In yet another embodiment of the present disclosure, the low density AAC blocks are of compressive strength 6 MPa, possess a dry density of 551 kg/m3 to 650 kg/m3, with a drying shrinkage of 0.05%, and are manufactured by: mixing 50 wt% to 70 wt% of pulverized fly ash/pond ash, 25 wt% to 35 wt% of OPC cement, 5 wt% to 10 wt% of quick lime powder mixed with water, 0.5 wt% to 3 wt% of gypsum/plaster of Paris either alone or in combination, and not more than 1 wt% of one or more additives to form a homogeneous mixture, with the mix batch weight being 700 kg per cubic meter; adding 0.02 wt% to 0.8 wt% of aluminum powder or aluminium paste to the homogenous mixture; pouring the slurry into moulds for setting; allowing the moulds to set; demoulding and cutting into desired sizes, autoclaving under vacuum at a pressure of 10 bar to 14 bar for 4 hours to 8 hours; and readying for dispatch after three days.
It is necessary for quicklime to be slaked in a controlled environment because it can create heat that reaches up to 49°C. Use of quicklime during summer for the manufacturing of AAC blocks increases the formation of cracks in the cakes due to its violent reaction with water. Decrease in quicklime reduces the formation of the cellular structures, resulting in an increase in density.
In yet another embodiment of the present disclosure, the one or more additives are superplasticizers.
In yet another embodiment of the present disclosure, the one or more additives include quaternary ammonium salts, surface tension reducing agents like cetyltrimethylammoniumbromide (CTAB), sodium poly carboxylates, oxidizing agents like potassium dichromate, and fly ash dispersing agents like polyacrylicacid salts.
The disclosed AAC blocks have a low density as per IS 2185 Part 3, Serial No. 2, while their compressive strength and other properties are comparable to AAC blocks of the next grade. This is achieved by obtaining the desired cellular structure by means of controlling the aeration process. Aeration process is controlled by modifying batch weight, controlling cake raise, and mixing time. In addition to that, the quantity of quick lime is also reduced to control the reaction rate.
The efficiency of the disclosed AAC blocks shall now be illustrated with examples.

EXAMPLE 1 CONVENTIONAL AAC BLOCKS
Raw Material Weight %
Ordinary Portland Cement 18 to 22
Pulverized Fly Ash 50 to 75
Lime Powder 4 to 6
Gypsum 0 to 3
Aluminum Paste 0.05 to 0.5
Additives 0.01 to 0.25
Total 100
Mixing time (Minutes) 7 - 8

RESULTS
Specification as per IS 2185 Part.3 S. No.2, Grade 2
Property Units Results Specification
Density Kg/M3 560 551 to 650
Compressive strength MPa 3.5 >3MPa
Thermal conductivity W/m.K 0.15 0.24
Drying shrinkage % 0.1 0.1

EXAMPLE 2: DISCLOSED AAC BLOCKS (5 MPa)
Raw Material Weight %
Pulverized Fly Ash/Pond Ash 68
OPC cement 24.85
Quick Lime Powder 6.41
Plaster of Paris 0.6
Aluminum paste 0.09
Additives 0.05
Total 100
Mixing time (min) 11 - 12

RESULTS
Specification as per IS 2185 Part.3
Property Units Results Specification – S. No. 2, Grade 2 Specification – S. No. 3, Grade 2
Density Kg/M3 600 551 to 650 651 to 750
Compressive Strength MPa 5.2 >3MPa >4MPa
Thermal conductivity W/m.K 0.18 0.24 0.30
Drying shrinkage % 0.05 0.1 0.1

EXAMPLE 3: DISCLOSED AAC BLOCKS (5MPa)
Raw Material Weight %
Pulverized Fly Ash/Pond Ash 66.5
OPC Cement 26.3
Quick Lime Powder 6.2
Plaster of Paris 0.89
Aluminum Paste 0.1
Additives 0.01
Total 100
Mixing time (min) 11 - 12

RESULTS
Specification as per IS 2185 Part.3
Property Units Results Specification – S. No. 2, Grade 2 Specification – S. No. 3, Grade 2
Density Kg/M3 619 551 to 650 651 to 750
Compressive Strength MPa 5.4 >3MPa >4MPa
Thermal conductivity W/m.K 0.19 0.24 0.30
Drying shrinkage % 0.05 0.1 0.1

EXAMPLE 4: DISCLOSED AAC BLOCKS (6MPa)
Raw Material Weight %
Pulverized Fly ash/Pond Ash 62.35
OPC Cement 29.6
Quick Lime Powder 7.2
Plaster of Paris 0.7
Aluminum Paste 0.12
Additives 0.03
Total 100
Mixing time (min) 11-12

RESULTS
Specification as per IS 2185 Part.3
Property Units Results Specification – S. No. 2, Grade 2 Specification – S. No. 4, Grade 2
Density Kg/M3 648 551 to 650 751 to 850
Compressive Strength MPa 6.2 >3MPa >5MPa
Thermal conductivity W/m.K 0.21 0.24 0.37
Drying shrinkage % 0.05 0.1 0.1

It will be apparent to a person skilled in the art that the above description is for illustrative purposes only and should not be considered as limiting. Various modifications, additions, alterations and improvements without deviating from the spirit and the scope of the disclosure may be made by a person skilled in the art. Such modifications, additions, alterations and improvements should be construed as being within the scope of this disclosure.