Fly Ash Cement And Phosphogypsum Bricks Engineering Essay

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Abstract- In Civil Engineering traditionally, we are using different materials in the form of building units. Some of the building units which we are using for construction are bricks and concrete blocks. Especially for bricks we have to use good plastic clay as primary raw material. This clay is often obtained from prime agricultural land, causing degradation as well as economic loss due to diversion of agricultural land. Manufacturing of bricks produces harmful gases which results in significant air pollution.

This study is an attempt to use cement, flyash and waste gypsum for the manufacturing of building units so as to replace the traditional building material at least partially.

Keywords- Flyash, Phosphogypsum, Compressive strength, Low cost housing.

Introduction:

Traditionally we are using burnt clay bricks for construction. It is a clay product which proved it's importance since the dawn of civilization. For production of bricks we are using good plastic clay as primary raw material. This clay is often obtained from prime agricultural land, causing land degradation as well as economic loss due to diversion of agricultural land. Though clay is easily and abundantly available in nature, its resources has a threshold limit and utilization of clay has reached such a point in construction. Excess use of good clay caused erosion of fertile soil and soil degradation and disturbed the ecology.

The burnt clay brick industry in India produces over 60 billion clay bricks annually resulting in strong impact on soil erosion and unprocessed emissions. For production of these bricks about 160 million tones of top soil, making barren 7500 acres of fertile land. Because of all these ill effects this is proper time to search an alternative of the burnt clay bricks.

Use of Cement, Fly Ash and Phosphogypsum as AN ALTERNATIVE for burnt clay bricks:

This is new technology which works with the strength of fly ash, lime and gypsum chemistry. The slow chemistry of fly ash and lime is maneuvered by tapping ettringite phase to it's threshold limits through sufficient limit of gypsum. Therefore, it does not require heavy duty press or autoclave, which is otherwise requires in case of only fly ash and lime. The process completely eliminates the thermal treatment (Except open air drying) and does not require combustion of any fossil fuel. The ingredients of the units such as bricks and blocks, fly ash, lime (from OPC) and gypsum are well known minerals that are widely used in the industries. All these minerals are available in the form of wastages and by-products from industrial activities. In certain areas where by product lime is not available in adequate quantity, Ordinary Portland Cement (OPC) can be used as the source of lime producing the good quality of bricks and blocks. This technology is proved to be environmentally safe and sound.

Materials:

Fly ash used for the present study is obtained from the Thermal Power Plant, Eklehara, Nashik. As good quality of lime is not available in the vicinity O.P.C. is used as a source of lime and Phosphogypsum (CaSO4 2H2O) is obtained from Savil Agrovates, a Kopargaon based company producing agricultural product where phosphogypsum is available as a waste.

Mix Proportions:

As our main intention is to search an alternative material for the conventional burnt clay bricks by using the waste materials and to produce a low cost building material, emphasis is given to use the waste products to the maximum extent and hence following mix proportions are used for the present study. The mix proportions are given in the Table No.1 are in terms of dry weights of the ingredients. Shrinkage cracking is a major weakness in gypsum based blocks. Shrinkage cracking can be minimized by keeping the water content of the binder as low as possible.

Sr.

No.

Mix Designation

Constituent materials

( Percentage)

Fly Ash

Cement

P.G.

01

M-1

25

50

25

02

M-2

30

40

30

03

M-3

35

30

35

04

M-4

40

20

40

05

M-5

45

10

45

06

M-6

50

--

50

Table 1 Mix proportions

Methodology:

Mixing of raw Materials:

The weighed quantity of Phosphogypsum, Cement and fly ash were thoroughly mixed in dry state in a pan with the help of a trowel. The mixture in dry state is mixed till it attains a uniform colour. When the mixture attains uniform colour weighed quantity of water is added in the mixture of fly ash, cement and phosphogypsum. After addition of the required quantity of water the mixture is thoroughly mixed with the help of trowel in a pan. After mixing the mix initially with the trowel the mixture is again mixed thoroughly by kneading until the mass attained a uniform consistency.

To calculate the quantity of water to be added Standard normal consistency test was performed and the water content for the normal consistency was determined. The water content used in the mix for strength tests was 90% of that required to produce the standard normal consistency.

Preparation of mortar blocks:

Standard cement mortar cube moulds of size 70.7mm x70.7mm x 70.7mm were used for preparation of blocks. The mixed binder was placed in the cube mould and was compacted properly by rod. Excess paste was hand finished. The mould was filled in three layers and each layer was compacted properly.

Method of curing:-

The blocks were taken out from the moulds after 24 hours. After removal from the moulds the blocks were kept for air drying for 2 days. After sufficient strength was gained these blocks were transferred to water filled curing tanks.

Experimental Work:-

To check the feasibility of Cement, F.A. and P.G. binder as an alternative material for traditional burnt clay bricks following tests are performed on the binder

1) Compression Strength Test

2) Water Absorption Test

Above tests were performed as per Indian Standards .

During testing it has been observed that the cubes prepared with M-6 are difficult to handle as they breaks easily during handling.

After testing number of cubes of the above mix proportions M-5 is found suitable for use as a material for bricks.

Table 2 shows test results for compressive strength, water absorption test and density for all trial mix.

Mix

Age

Compressive

Strength (MPa)

Water Absorption

%

Dry Density

KN/m3

M-1

28

23.56

29.29

14.46

M-2

28

20.67

30.37

14.04

M-3

28

18.13

24.91

14.58

M-4

28

17.46

20.25

14.68

M-5

28

12.00

28.22

13.53

M-6

28

--

--

--

Table 2 Test Results

Note: For M-5 -07 days compressive strength is equal to 3.16 MPa

14 days compressive strength is equal to 7.96 MPa

Testing of Bricks:

After carrying above investigation mix designated as M-5 is selected for moulding of bricks.

For moulding of bricks a wooden mould of size 113x83x235 mm was used. This size of mould was selected considering the size of traditional bricks available in the local market.

Compression test on the bricks was performed to calculate the compressive strength of the bricks. The test was performed as per I.S. codes.

The bricks were also testes for water absorption and density.

Table 3 gives the test results for the bricks when tested for different tests.

Sr.

No.

Age

Compressive

Strength (MPa)

Water Absorption

%

Dry Density

KN/m3

01

07

2.254

--

--

02

14

6.360

--

--

03

28

9.420

28.44

12.854

Table 3 Test Results For bricks

Figure 1. Compressive Strength of Bricks

Test Results and Discussions:-

The test results show that the compressive strength of the mix increases with age the bricks have sufficient strength even at the age of 14 days. At the age of 28 days the bricks show sufficient strength, while the water absorption is on higher side. The Dry density of the bricks is less than the conventional burnt clay bricks.

Conclusions:-

From the above tests results and test results for cubes it has been observed that mixture of Cement, Fly Ash and Phosphogypsum can be used for bricks. Bricks prepared with the proportion M-5 have sufficient strength to be used as an alternative for the conventional burnt clay bricks.

Even though the bricks prepared with M-5 are having more water absorption than the normally used conventional bricks i.e. more than 20% such bricks can be used for internal walls of a building where water absorption is not a measure issue.

Unique possibility exists for the bulk utilization of fly ash in producing bricks from Cement, F.A. and P.G. in the proximity of thermal power plants, phosphoric acid and fertilizer industries.

Being lighter in weight, Cement,F.A. and P.G. mix will reduce the dead weight and material handling cost in multi storied constructions.

The utilization of wastes in making cementitious binder will help in solving the disposal and health hazard problems. It is further needed to develop awareness among users, professionals and financial supporters for using these waste materials for techno-economic reasons in addition to balance economy and achieve energy conservation. The use of these wastes for building industries will definitely reduce the environmental pollution which will be there because of use of burnt clay bricks. Such products can be used for low cost construction practices.

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