The present invention relates to a chemical resistant geopolymer fly ash bricks useful for construction industry. The process for manufacturing building bricks uses high volume fly ash. This invention particularly also relates to a process for development of chemical resistant geopolymer fly ash bricks with improved chemical resistant properties.
Fly ashes produced by different thermal power stations are classified into different categories namely ESP fly ash (Fly ashes collected by using electrostatic precipitators), bottom ash and pond ash. The ESP fly ashes are of superior quality when compared to the properties of pond ash / bottom ash, which are found to be inferior. The production of ESP fly ash is very less and cement manufacturers are directly utilizing the same. The bottom ash / pond ash are generated as a by-product in large quantities and pose an environmental threat and cause pollution to the environment such as air, water land etc. Hence utilization of fly ash / bottom ash is critical factor as such in the existing condition.
The use of fly ash in concrete technology has been popular throughout the world, mainly due to the consideration of cost savings, environmental protection and conservation of resources. In India at present, there are more than 72 thermal power stations, producing 60-105 million tonnes of fly ash per year.
The production of every tonne of Portland cement contributes about one tonne of CO2 to the atmosphere. Minor amounts of NO2 and CH4 are also released into atmosphere. The production of fly ash by thermal power stations may likely to exceed 170 million tonnes by 2012 and therefore will become a serious disposal problem. The safe, environment friendly disposal of the fly ash is of major concern.
The search of environmentally friendly construction material is imperative, as the world is facing serious problems due to environmental degradation. There is a significant expectation on the industry to reduce carbon dioxide (CO2)emissions to the atmosphere.

A significant advance in the usage of fly ash in construction industry is the development of high volume fly ash brick with excellent compressive strength and chemical resistant properties with enhanced durability performance.
Reference may be made to M.Singh and R.Kumar, Some aspects of a durability of a phosphogypsum - lime - fly ash binder published in construction and building Materials Vol.10, pages 273-279, wherein it is reported that the strength of the binder decreased and loss in weight increased with increases in exposure temperatures. The maximum loss in strength occurs at 60°C. In this paper, the bricks were tested at a particular temperature.
Reference may be made to M.D.Gadrin, K.K.Prasad and Amit Chatterjee, on their article manufacture of building bricks with fly ash, published in Indian Concrete Journal Vol.52, No.5 Pages 150-155, where in they have reported that the bricks develop sufficient strength when cured at room temperature for about 25 days. In this paper, the bricks were air cured for about 25 days.
Reference may be made to N.Chitharanjan, on compressed lime fly ash - gypsum blocks, published in Indian Concrete Journal Vol.57 No.6 Pages 153-156, where in it has reported that the lime fly ash gypsum blocks were suitable for load bearing masonry walls. The blocks were reported to have the density of 11000 g/m3 and compressive strength of 4.12 N/m2.
Reference may be made to T.Fatih and A.Umit, Utilization of fly ash in manufacturing by building bricks, published in fly ash library: WWW. Fly ash, info, wherein it has been reported that the addition of fly ash upto 60% at a fixing temperature of 950°C has no significant harmful effect on the brick quality. The drawback is that the bricks were fired at high temperature.
Reference may be made to US Patent number 5358760 dated 25.10.1994 by Furlong Tresea and Hearne John, wherein the process for

producing solid bricks from fly ash, bottom ash, lime, gypsum and calcium carbonate has been reported. The draw back is use of a synthetic polymeric material.
Reference may be made to US patent number 5580378 dated 3.12.1996, by Shulman David. M wherein improved lightweight cementitious product made up of an aqueous cementitious mixture. The draw backs is it needs curing.
Reference may be made to CN patent number 1072913 dated 9.6.1993 by Rongming liu; Shavgwen Ma, wherein the process for making fly ash brick using an additive of 3-5% sodium silicate as the binder has been reported. The process needs high temperature baking at 950° + 20°C.
Reference may be made to KR.Patent Number 8601755 dated 21.10.1986 by Park Byong UK, wherein a method for producing brick was reported. The process involves, moulded bricks of fly ash covered with powder of cement or lime in calcium silicate solutions. The process needs water quenching.
Reference may be made to CN Patent Number 1210057 dated 10.03.1999 by Li Xianyun, wherein a high strength fly ash bricks using powdered coal ash and cement through adding water, stirring and cured for 28 days has been reported. This process needs 28 days water curing.
The main object of the present invention is to provide a process for the development of chemical resistant geopolymer fly ash bricks using high volume fly ash.
Another object of the present invention is to provide a process for manufacturing chemical resistant bricks using high volume fly ash (pond ash / bottom ash).

Yet another object of the present invention is to provide a process for the development of chemical resistant geopolymer fly ash bricks with improved chemical resistant properties, which obviates the drawbacks as detailed in the description of prior art.
Still another object of the present invention is that it completely eliminates autoclave curing.
Still yet, another object of the invention is that it eliminates water curing.
Still yet, another object of the invention is that it attains it strength at room temperature within 72 hrs.
Still yet, another object of the invention is that the water absorption is very less.
A further object of the present invention is to provide a process for the development of chemical resistant geopolymer fly ash bricks with improved chemical resistance properties.
In the present invention there is provided a process for the development of chemical resistant geolpolymer fly ash bricks from as received, un activated pond ash / bottom with improved chemical resistance properties. The novel process of the present invention involves, that the chemical resistant geopolymer fly ash bricks attains its maximum compressive strength at room temperature.
Accordingly a chemical resistant geoploymer fly ash brick or like building material, which comprises
a) fly ash,Pond ash or bottom ash - 1 part ,Sand - 3 parts
b) an activator selected from Sodium hydroxide, Potassium hydroxide and Calcium hydroxide of 0.5% by weight of cement at molar

concentration ranging between 0.5 to 4 and a hardeners selected from Sodium silicate , Calcium silicate and Potassium silicate of 0.5% by weight of cement at molar concentration ranging between 0.5 to 4.
In an embodiment of the present invention, the sodium hydroxide, potassium hydroxide, calcium hydroxide and sodium silicate, calcium silicate, potassium silicate are of commercially available grade.
In another embodiment of the present invention, wherein fly ash, bottom ash and pond ash are locally available materials.
In further embodiment of the present invention, wherein hardner and activator used in equal proportion .
In one more embodiment of the present invention, a chemical resistant geoployrner fly ash brick having felling characterities : Table 1,2,3,4
In another embodiment of the present invention, the activators and hardeners used is of pollution free/eco friendly chemicals.
In still another embodiment of the present invention, the chemical resistant geopolymer fly ash bricks capable of increasing the compressive strength of the bricks.
In a further embodiment of the present invention, the chemical resistant geopolymer fly ash brick is having very low water absorption.
The chemical resistant geopolymer fly ash bricks of the present invention for the construction industries eliminates high temperature curing.
In normal fly ash lime fly ash cement bricks it is possible to develop the compressive strength 10-12 N/mm2 by autodaving or by rotary pressing, but in the present invention it is possible to develop a compressive strength of 10-15 N/mm2 by simple hand moulding.

The chemical resistant geopolymer fly ash bricks of the present invention useful for the construction industries not only increased the compressive strength but also reduced the percentage of water absorption.
Accordingly a chemical resistant geoploymer fly ash brick or like building material comprising
a) preparing a dry mix of Pond ash, fly ash or bottom ash and Sand in the ratio of 1:3.
b) preparing an aquieous solution of a hardner selected form group consisting of Sodium silicate , Calcium silicate and Potassium silicate and an activator selected from Sodium hydroxide, Potassium hydroxide and Calcium hydroxide,
c) adding the solution obtain in step (b) to dry mix at a temperature ranging between 20 to 40°C followed by through mixing
d) transfering the mix used desird would follwed by demoulding after 24 hrs and keeping the demoulded bricks in open for a period of about 3 days.
The non-obvious inventive step enabling achievement of the novelty of the present invention lies in providing an activators like sodium hydroxide potassium hydroxide, calcium hydroxide, potassium silicate (0.5-4M) & sodium silicate, calcium silicate, potassium silicate (0.5-4M).
In chemical resistant geopolymer fly ash brick of the present invention useful for construction industries is made use of the activators such as sodium hydroxide, potassium hydroxide (0.5-4M) and hardeners such as sodium silicate, calcium silicate, potassium silicate (0.5-4M) are responsible for strength formation.

Alkali activation of aluminosilicates can produce amorphous aluminosilicate gels or geopolymers with excellent mechanical and chemical resistant properties. These aluminosilicate gels consisting of three dimensional framework of SiO4 and AIO4 tetrahedra are interlinked by shared O atoms. The negatively charged and coordinated Al(lll) atoms inside the network are charge balanced by alkali metal cations such as Na, K and Ca. These gels can be used to bind fine aggregates, such as sand to produce mortars.
The present invention provides a process for the development of chemical resistant geopolymer fly ash bricks for construction industries, which comprises an activator of sodium hydroxide, calcium hydroxide, potassium hydroxide (0.5 - 4M concentration) and sodium silicate, calcium silicate, potassium silicate (0.5 - 4M concentration).
The process stipulates mixing of fly ash and sand in (1:3 ratio) in dry condition and the chemical accelerators used are.
Sodium hydroxide or —, - activators
Potassium hydroxide or — - (0.5-4Molar concentration)

Calcium hydroxide and _ Sodium silicate or Calcium silicate or Potassium silicate

hardeners
(0.5-4Molar concentration)

Each ingredient added was 0.5% by wt of total matrix. All the ingredients used were of commercially available grade.
Bricks of size 22.5 x 11.5 x 7.0 cm were cast with 1:3 ratio with required quantity of aqueous solutions. After 72 hours the specimens were demoulded and subjected to compressive strength measurements.

The following examples are given by way of illustration of the working of the invention in actual practice and therefore should not be construded to limit the scope of the present invention.
Example -1 The composition of the fly ash used was as given below.
(Table Removed)

Compressive Strength : (IS3102-1992)
The compressive strength of the chemical resistant geopolymer fly ash bricks are tested as per BIS 3495 -1992 and the results are compared with the burnt clay bricks.
The following are the materials used for making fly ash bricks.

Fly ash - 1 part Sand - 3 parts Sodium hydroxide — Potassium hydroxide
Calcium hydroxide
Sodium silicate —, Calcium silicate Potassium silicate _

activators, 0.5% by weight of cement (0.5-4Molar concentration)
hardeners, 0.5% by weight of cement (0.5-4Molar concentration)

Initially fly ash and sand in the proportion 1:3 was taken and mixed thoroughly in a dry condition. Both activators and hardeners were mixed together in equal proportion and taken in required quantity and stirred well. Then the aqueous solution is added to the dry mix and the mixture is uniformly mixed to get a homogeneous mixture. Then the wet mix was transformed into the brick moulds of size 22.5 x 11.3 x 7.5 cm. The mould is vibrated using the table vibrator. After 24 hrs the bricks were demoulded and kept in open air

atmosphere for 3 days. After 72 hours drying the brick is placed in compression testing machine with flat face horizontal, the bricks were subjected to compression test using the AIMIL compression testing machine at a rate of loading of 14 N/mm2 min. till the brick specimen fails. The following table shows the compressive strength of fly ash bricks after 3 days drying in open atmosphere.
Table -1
(Table Removed)

It is seen from the above table that, all the chemical resistant brick shows higher compressive strength than the conventional burnt clay bricks. Most of the brick systems are lying in the the category of second class bricks.
Example - 2 Water absorption test: (ASTM C 67-00)
The bricks were dried in an oven at 110°C for 24 hours. After 24 hours, the bricks were taken out and kept at room temperature for a period of 4 hours. Then the initial wt. of the brick is taken using the top pan balance. The dry weight of the brick taken is Wd. Immediately after taking the initial weight to the dry bricks, the bricks were immersed in water over a period of 24-48 hrs. At the end of 48 hours the immersed bricks were taken out and the

surface is wiped out with a clean cloth and the wet weight is taken (Ws) using the top pan balance. Each weight of the brick is completed within 1 or 2 minutes after removing the specimen from the water bath. The percentage of water absorption is calculated from the above two weights as follows.
Ws-Wd
Water absorption (%) = x 100
Wd The following table shows the water absorption of different systems of fly ash bricks.
Table – 2
(Table Removed)

From the table it is observed that, the water absorption for the conventional burnt clay brick is 3-4 times greater than the fly ash bricks. All the four types of chemical resistant geopolymer fly ash bricks were found to have very less water absorption than conventional burnt clay bricks,
Example 3 Dry Density Test:( ASTM C67)
The dry density of various types of chemical resistant geopolymer bricks are shown in the following table.
Table – 3
(Table Removed)

From the table it is observed the fly ash bricks have the density ranging from 1800-2000 kg/m3, whereas for the conventional burnt clay bricks have the density of 1700-1800 kg/m3. The chemical resistant geopolymer fly ash bricks have higher density than the conventional burnt clay bricks.
Example - 4 Alkali / Sulphate / Acid resistance test:
The brick specimens were immersed in 1 (NH4)2S04, 1N HCI and 1 %
H2SO4 solution for 45 days. After that the bricks were tested for its
compressive strength. The loss in compressive strength is calculated as
follows.
Loss in comp. Str. =
Strength of brick with out exposure - Strength of brick after 45 days
immersion in acid
x100
Strength of brick with out exposure
Table- 4: Loss of compressive strength in 1% H2SO4 medium
(Table Removed)

Table - 4a: Loss of compressive strength in 1% HCI medium
(Table Removed)

Table- 4b: Loss of compressive strength in 1% NH2S04 medium
(Table Removed)

From the tables it is observed that, after 45 days immersion in aggressive acids like HCI, H2SO4, (NH4)2SO4 the loss in compressive strength is found to be very less, when compared to the conventional burnt clay bricks. So the developed geopolymer fly ash bricks are highly chemical resistant.
Example - 5 Soundness test:
In this test, two bricks were taken and struck with each other. They should not break and a clear ringing sound shoul emerge. These developed bricks when struck with each other gave clear ringing sound.
The main advantages of the chemical resistant geoploymer fly ash bricks of the present invention especially for the construction sectors are:
1. Economical & eco friendly technology
2. A non - cement based brick
3. Increase in compressive strength
4. Water absorption is very less
5. Excellent chemical resistance properties
6. No emission of green house gases
7. More durable
8. Completely eliminates autoclave curing
9. Completely eliminates water curing

We claim :
1. A chemical resistant geoploymer fly ash brick useful for construction sectors, which comprises; fly ash selected from Pond ash / bottom ash- 1 part, sand -3 parts, activators 0.5 wt % of cement of 0.5 -4 molar concentration selected from sodium hydroxide, potassium hydroxide or calcium hydroxide, hardners 0.5 wt% of cement of 0.5-4 molar concentration selected from sodium silicate, calcium silicate or potassium silicate.
2. A chemical resistant geoploymer fly ash brick as claimed in claim 1, where in sodium hydroxide, potassium hydroxide and sodium silicate are of commercially available grade.
3. A chemical resistant geoploymer fly ash brick as claimed in claim 1, wherein fly ash / bottom ash and river sand are locally available materials.
4. A chemical resistant geoploymer fly ash brick as claimed in claims 1-3, it is a non-cement based brick.
5. A chemical resistant geoploymer fly ash brick as claimed in claim 1, wherein the brick has increased compressive strength, low water absorption capacity, high density and high chemical resistant.
6. A process for production of chemical resistant geopolymer fly ash brick as claimed in claim 1, comprises; i) mixing fly fly ash selected from Pond ash / bottom ash and sand in a ratio of 1:3 on dry basis, adding to the mixture of step i) activators 0.5 wt % of cement of 0.5 -4 molar concentration selected from sodium hydroxide, potassium hydroxide or calcium hydroxide, and hardners 0.5 wt% of cement of 0.5-4 molar concentration selected from sodium silicate, calcium silicate or potassium silicate, iii) adding aqueous solution to this dry mix and
mixing uniformly to get a homogeneous mixture useful for moulding bricks. 7. A chemical resistant geoploymer fly ash brick and process thereof useful for the construction sectors, substantially as herein described with reference to the examples.