IMPROVEMENT IN DURABILITY OF FERROCEMENT USING FLY ASH AND SILICA FUME MODIFIED MORTAR

8/20/2019 IMPROVEMENT IN DURABILITY OF FERROCEMENT USING FLY ASH AND SILICA FUME MODIFIED MORTAR

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International Journal of Scientific Research Engineering & Technology (IJSRET), ISSN 2278 – 0882

Volume 3, Issue 6, September 2014

IMPROVEMENT IN DURABILITY OF FERROCEMENT USING FLY ASH

AND SILICA FUME MODIFIED MORTAR

Sabih Akhtar

Associate Professor, Department of Civil Engineering, AMU, Aligarh, U.P.-202002

e-mail: [email protected]; Mobile No. +91 412596531

AbstractFerrocement has proven itself as an excellent materialfor low cost housing. It has high degree of ductility andenergy absorbing capacity and has been increasinglyused both in terrestrial and marine environments as a

structural grade material system, which competesfavourably with reinforced concrete and other buildingmaterials. Success of ferrocement, as with other

materials, depends largely upon its durability.Reinforcement corrosion is one of the most important

criteria governing durability of the ferrocement since thediameter of the wire meshes used in ferrocement are

much smaller as compared to the conventionalreinforced cement concrete. In the present investigationan attempt has been made to modify the conventional

mortar using fly ash and silica fume so that the densematrix can be achieved. The strength properties as well

as protection of the steel wire mesh against corrosionhave been investigated.

Key Words: Ferrocement, fly ash, silica fume, partialreplacement of cement, compressive strength, corrosion

control.

1. INTRODUCTION

Providing low cost housing especially to middle and lowincome group both in rural and urban areas is a serious

national problem. The magnitude and acuteness of the problems is obviously more pronounced in urban areas.Also the conventional construction materials are

becoming excessively costly day by day. Innovative andlow cost construction materials and techniques thereby

become urgent need. Ferrocement may serve as one suchalternative. It has proven itself as an excellent materialfor low cost housing. It has high degree of ductility andenergy absorbing capacity and has been increasinglyused both in terrestrial and marine environments as a

structural grade material system, which competesfavourably with reinforced concrete and other building

materials (Hermosura, and Austriaco, 1994; Ramli andWahab, 1994; Arif et al.1994; Naaman, 2006).

Investigations on the use of pre-cast ferrocement

elements in low cost housing have proved theeffectiveness of the material system under staticconditions. The prefabricated ferrocement elements havealso been used successfully in both residential andindustrial buildings. It has been established in the studies

reported that the ferrocement has performed well underalmost all the loading conditions, whether it is tension

compression, flexure, shear, torsion, fatigue, impact orthe dynamic loading. A large number of experimental

and analytical studies dealing with ferrocemenstructural elements, having various shapes and sizessubjected to different loading conditions are reported in

literature. These studies have established the materiaworthiness for use in diversified applications and prove

it to be a strong alternative to conventional constructionmaterial. Improvement in strength of ferrocement hasalso been suggested through the use of different types of

wire meshes and modified mortar (Desai and Desai1988; Mathews et al. 1994; Rivas, 1994; Pande et al.1997; Olvera, et al., 1998; Osorio and Rivas, 1998; Lauet al., 2001).

Ferrocement is an excellent material for use in houseconstruction mainly for roofing because of its relativelylow cost. Its ease in manufacture and fabrication bysupervised local labourer using mainly indigenousmaterials further makes it an extremely good choice in

pre-fabricated housing. If modified mortar has beenused, the cost of the ferrocement elements can bereduced further (Pama, 1990; Arif et al., 2001). In the

present study it has been attempted to address the

problem of durable low cost housing in conjunction with

the waste management. In the first part of investigationthe compressive strength of mortar cubes prepared from

cement replacement with the fly ash and silica fumewere studied. In the later part of the investigation

ferrocement cuboids were cast and tested for estimatingcorrosion resistance provided by the dense mortar.

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2. EXPERIMENTAL PROGRAMME

Mortar mix ratios (cement:sand : 1:3.0) was chosen for

the preparation of mortar cubes. In each mix cement wasreplaced with 5, 10, 15, 20 and 25% fly ash and silicafume. The water cement ratio was varied as 0.30, 0.35

and 0.40.

For the tests undertaken Ordinary Portland cement (43grade) was used. The initial and final setting time wasfound to be 43 and 460 minutes. Locally available coarse

sand has been used as fine aggregate. Fineness modulusof the sand was found to be 2.25. The properties of flyand silica fume are given in Tables 1-2. Potable waterhas been used for mixing and curing. Welded squarewire mesh having average diameter of 1.42 mm and

opening size 25.4mm were used for the preparation offerrocement cuboids. Yield strength of the wire mesh

was found to be 300 N/mm2.

3. TESTING OF MORTAR CUBES AND

FERROCEMENT CUBOIDS

Mortar cubes of 100100100 mm size were cast intriplicate with varying proportions of cement, fine

aggregate, fly ash and silica fume. The water cement ratiowas varied as 0.30, 0.35 and 0.40. These mortar cubeswere tested for compressive strength. The details of the

mix and the test results are given in Tables 3. For thecorrosion tests ferrocement cuboid specimens of size 35 ×

35 × 24 mm were prepared using best performing mortarmix in compressive strength test in both the categories.For the comparison cuboids without any additive (0%

replacement of cement) were also prepared to serve ascontrol specimen. Welded steel meshes were used asreinforcement in the cuboid specimens (Figs 1-2). Thesespecimens were exposed to alternate drying and wetting

cycle in accelerated corrosion testing simulator in the presence of 3.5% NaCl solution. After undergoing 60 wetand dry cycles of 24 hrs each the specimens were testedusing AC Gill potentiostat (Fig.3). After the test the wiremesh was taken out by splitting the specimen for visual

observation.

Table-1 Properties of Fly ash

Characteristics Values

Colour

Specific Gravity

% Retained on 90µ IS Sieve

% Retained on 75µ IS Sieve

Light grey

2.40

47

68

Table-2 Properties of silica Fume

Characteristics Values

Colour

Specific Gravity

Grey

2.25

Table-3 Compressive Strength of Mortar Cubes withFly ash and Silica Fume

S.

No.

Mix

Proportions

(C:FA/SF:FA)*

W/C

ratio

Compressive strength of

cubes at 28 days (MPa)

Fly ash Silica Fum

1. 1.0:0.0:3.0 0.30

0.35

0.40

38.0

43.5

43.1

38.0

44.5

44.1

2. 0.95:0.05:3.0 0.30

0.35

0.40

32.5

45.3

45.2

36.5

40.5

41.0

3. 0.90:0.1:3.0 0.30

0.35

0.40

27.0

46.5

46.2

26.8

47.1

52.5

4. 0.85:0.15:3.0 0.30

0.35

0.40

20.5

46.8

47.3

23.5

48.3

56.0

5. 0.80:0.20:3.0 0.30

0.35

0.40

20.0

48.7

47.0

18.5

31.5

33.0

6. 0.75:0.25:3.0 0.30

0.35

0.40

14.0

36.5

35.1

16.5

30.2

30.5

C: Cement; FA: Fly ash; SF: Silica fume; FA: Fineaggregate

Fig.1 Specimen under preparation



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Fig.2: Prepared Specimen

Fig.3: Electrochemical workstation and test set-up

4. DISCUSSION ON TEST RESULTS

An increase in compressive strength values as comparedto the corresponding control has been observed in fly ashmodified mortar for the w/c ratios 0.35 and 0.4. This

increase is observed for cement replacement up to 20%.However with the w/c ratio 0.3 in the entire six mixratios, the values are less than the control specimen.Also for the 25% replacement the values of thecompressive strength has been observed to be lower than

the control values.

Similar trend has been observed for the silica fumemodified mortar for the cement replacement up to 15%.However the compressive strength values are

substantially higher in case of silica fume modifiedmortar than the control as well as the fly ash modified

mix. The increase in the compressive strength values forthe most of the mixes may be attributed to the improved

packing of the entire mass thereby providing a relativelydense matrix. However for other mixes where the valuesare lower than the control reason appears to be increased

water demand due to increased surface area of theingredients of the matrix.

It is evident from Tafel plot (Fig.4) that the substantial protection of reinforcement from corrosion has beenachieved in modified mortar specimens. In both thespecimen reduced corrosion current values as comparedto the control specimen is suggestive protection of steel

wire mesh embedded inside the modified mortarspecimens. Visual inspection of the welded steel wire

mesh used in the specimens and taken out by splittingthe tested specimen, clearly indicates the onset ofcorrosion in control (Fig.5). A little stain mark can be

observed in fly as modified mortar specimen’s meshwhereas silica fume modified matrix mesh is completely

free of corrosion. This could be attributed to the densemortar not allowing much ingress of chloride ion into

the matrix which is responsible for the corrosion of theembedded steel.

5. CONCLUSIONS

It has been concluded from this study that if the matrix is properly modified not only the strength of the matrix isimproved but the reinforcement used in the form of the

wire mesh can also be protected from corrosion. Thiswill definitely lead to improvement in durability therebyadding prolonged life to the ferrocement structuralelements.

Fig.4 Tafel plot for specimens having control and

modified mortars

3 - Silica fume modified

matrix

2 - Fly ash modified matrix specimen

1 - Control specimen

1

23



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Blank Flyashmodified

Silica fumemodified

Fig. 5 State of welded mesh at the end of theinvestigation

REFERENCES

1. Arif, M., Pankaj and Kaushik S.K. “Mechanical

Behaviour of Ferrocement Composites: An

Experimental Investigation”, Cement and Concrete

Composites, 21, 301-312, 1999. 2. A

rif, M., Akhtar, S., Masood, A., Garg, M. and Basit,

F., “Flexural behaviour of fly ash mortar

ferrocement panels for low cost housing” Journal of

Ferrocement, 31(4):125-135, 2001.

3. Desai, J.A. and Desai, M.D. “Ferrocement Roofing

Element for Low Cost Housing”, Proceedings 3 rd

International Symposium on Ferrocement,

University of Roorkee, Roorkee, India, 422-429,

1988.

4. Hermosura, N.K. and Austriaco, L.R. “Research on

Ferrocement Housing- Global Perspective”, Journal

of Ferrocement, 24(1), 1-6, 1994.

5. IS: 8112-1989, “Specification for 43 Grade Ordinary

Portland Cement”, BIS, New Delhi.

6. IS: 8112-1989, “Specification for 43 Grade Ordinary

Portland Cement”, BIS, New Delhi.

7. Lau, J.M., Tay, L., Koh, C.K. and Lee, S.H. ,

“Development of Ferrocement Products for Public

Housing Construction-The HDB Experience”,

Proceedings of 7th International Symposium on

Ferrocement and Thin Reinforced Cement

Composites, National University of Singapore,

Singapore, 271-286, 2001.

8. Mathews, M.S., Prakash, V.S. and Shaji, T.L.

“Ribbed Ferrocement Elements for Low Cost

Housing, Journal of Ferrocement”, 24(1), 35-49,

1994.

9. Naaman, A.E. “Ferrocement and Thin Reinforced

Cement Composites: Four Decades of Progress”,

Proceedings 8th International Symposium and

Workshop on Ferrocement and Thin Reinforced

Cement Composite, Bangkok, Thailand, 3-21, 2006.

10. Olvera, L.A. et al. “Applications of Prefabricated

Ferrocement Housing in Mexico”, Proceedings o

6th International Symposium on Ferrocement

University of Michigan, Michigan, U.S.A., 95-108

1998.

11. Osorio, S.M. and Rivas, H.W. “Technology for

Prefabrication and Assembling of Ligh

Ferrocement Panels”, Proceedings of 6t

International Symposium on Ferrocement

University of Michigan, Michigan, U.S.A., 119-

128, 1998.

12. Pama, R.P.,“Research on ferrocement - Globa

perspective”, Journal of Ferrocement, 20(4):385

410, 1990.

13. Pande, A.M., Patil, A.B. and Waghe U.P

“Performance of Pre Cast Ferrocement Elements in

Low Cost Housing, International Conference on

Habitat and Sustainable Development”, Institution

of Engineers (I), New Delhi, India, I/96 - I/101

1997.

14. Ramli, M. and Wahab, I. “Ferrocement in AffordableHousing Construction: The Malaysian Experience”

Journal of Ferrocement, 24(1), 17-21, 1994.

15. Rivas, H.W. “Low Cost Housing Built with

Ferrocement Pre-cast Elements, Journal of

Ferrocement”, 24(1), 29-34, 1994.

Dr. Sabih Akhtar is Associate Professor in the Department of

Civil Engineering, Aligarh Muslim University (AMU)

Aligarh, India. He has obtained his bachelor’s degree from

B.U. in the year 1991, Masters in 1994 and Ph. D. in 2008

from A.M.U in the area of structural engineering.

He has teaching and research experience of about 20 years. He

has authored more than 34 research papers in various

international and national journals and conferences. He hassupervised 30 M. Tech dissertations.

His areas of interest include cementitious composites

corrosion control in structures, low cost housing and

innovative construction materials.

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IMPROVEMENT IN DURABILITY OF FERROCEMENT USING FLY ASH AND SILICA FUME MODIFIED MORTAR