International Journal of Scientific & Engineering Research, Volume 6, Issue 1, January-2015 414
ISSN 2229-5518
Experimental Analysis on Improving Concrete
Quality by Using – SF Micro Silica
Dr.A.S.Kanagalakshmi, A.Latha Ganesan, V.Jayashree & J.Caroline Saro
Abstract-Concrete is the most important Engineering material in construction industry because of its inherent strength properties. However the addition of some other materials may change the properties of concrete. Mineral addition which are also used as mineral admixtures have been used with cement for many years. Micro silica, is a non crystalline material also called as Silica Fumes (SF) is produced in electric arc furnace as a by production of elemental silicon or alloy containing silicon. Micro silica was initially viewed as cement replacement material and in some area it is generally used as replacement material as silica fume in pozzolanic admixtures. The silica gives protection against embedded steel in porous water. It increases the compressive strength of concrete up to 20000 psi (140 Mpa). The compressive strength of concrete cubes of grade M40, M50 grades are increased by
10% to 30% in replacement of micro silica. The Ceraplast is a strength improving admixture used for ultimate strength, workability and admixtures are used with concrete to find the compressive strength and split tensile strength for M40, M50 grade cylindrical cubes. The study of silica gives the advantages such as its increase in durability, reduces concrete permeability, and improves resistance to corrosion.
—————————— ——————————
is the main cause of inelastic deformation. Addition of
small closely spaced and uniform micro silica or silica
igh-strength and High-performance the concrete
are being widely used throughout the world and it
is necessary to produce them to reduce the water
binder ratio and increase the binder content. High- strength concrete governs good abrasion, impact
and cavitation resistance. Today High-strength concrete are used in structures since it results in economical advantages. Recently applications of high strength concrete are more in
high-rise buildings, long span bridges and some special structures. Major application of high strength concrete in tall structures have been in columns and shear walls, which resulted in decreased dead weight of the structures and increased the amount of the rental floor space in the lower stories. In future, high range water reducing admixtures (super plasticiser) will open up new possibilities for use of these materials as a part of cementing materials in concrete to produce very high strengths, as some of them are more finer than cement.
Plain cement concrete possesses a very low tensile strength, limited ductility and little resistance to cracking. Internal micro cracks, poor tensile strength eventually lead to brittle fracture of concrete. The development of such micro cracks
————————————————
• A.Latha Ganesan, Assistant Professor, Panimalar Engineering College, Chennai. India.
• V.Jayashree & J.Caroline Saro is currently pursuing bachelors degree program in civil engineering, Panimalar Engineering College, Chennai. India.
fumes with concrete would act as crack arrester and would substantially improve the static and dynamic properties. Most of the concrete has less durability properties. To remove such properties in concrete ceraplast admixtures are used in the concrete. Admixtures also give strength and workability to the concrete. Hence this experimental analysis helps for the following studies:
• To study the behaviour of silica fumes in concrete.
• To study the compressive strength of conventional and silica fumed concrete cubes of M40 and M50
Grade.
• To study the split tensile strength of conventional and silica fumed concrete cylinders of M40 and M50 Grade.
Silica fume
Ceraplast
The American Concrete Institute (ACI) defines silica fume as “very fine non-crystalline silica” produced in electric arc furnaces as a by-product in the production of elemental silicon or alloys containing silicon (ACI 116R). It is usually a gray colored powder, somewhat similar to Portland cement or some fly ashes. Silica fume is usually categorized as a supplementary cementitious material. This term refers to materials that are used in concrete in addition to Portland cement.
Increased Cohesion - Fresh concrete made with silica fume is more cohesive and therefore less prone to segregation
IJSER © 2015 http://www.ijser.org
International Journal of Scientific & Engineering Research, Volume 6, Issue 1, January-2015 415
ISSN 2229-5518
than concrete without silica fume. To offset this increased cohesion when placing, silica-fume concrete is typically placed at 40 to 50 mm greater slump than concrete without silica fume in the same placement. The main benefit from increased cohesion can be seen in shotcrete, whether it is for new construction, repair of existing structures, or ground support in tunnelling operations. Using silica fume in shotcrete allows for greater thickness of shotcrete layers, particularly when shooting overhead, and a significant reduction in rebound.
• Reduced bleeding
• Enhanced mechanical properties
Because of the very high surface area of the silica fume and very low water content of silica-fume in concrete, there will be very less bleeding. Once a silica fume content of about five percent is reached, there will be no bleeding in most concretes. Concrete bleeds as the heavier components (cement and aggregates) settle under the influence of gravity before the concrete stiffens.
Silica fume gained initial attention in the concrete market place because of its ability to produce concrete with very high compressive strength.
Ceraplast is a resin based air entraining admixture which principally improves workability and plasticity of mortars used for plastering and masonry. It is a liquid mortar plasticizer. It entrains microscopic air bubbles, which makes the mortar easier to work and spread. These pockets of air also have the effect of interrupting the formation of capillary channels so that the passage of water through the mortar is minimized. The volume of these air bubbles is also sufficient to absorb the internal stresses set up by the alternate freezing and thawing of entrapped air.
Ceraplast 300 resin is a high performance new generation super plasticiser cum retarding admixture which lowers the surface tension of water and makes cement particles hydrophilic, resulting in excellent dispersion as well as controls the setting of concrete, depending on dosage. This increases the workability of concrete drastically and also facilitates excellent retention of workability. The workability offered at a lower water water-cement ratio eliminates chances of bleeding, increased workability, retention allows increased travel time.
• Increased cohesiveness of the fresh concrete, which can lead to improved handling characteristics
• Curing can start earlier as there is no need to wait for bleed water to dissipate.
• Lower permeability and improved durability (due to the fine particle size and reactivity of SF).
• Greater resistance to abrasion and impact than conventional concretes of similar strength grade.
• Compressive strengths in excess of 60
N/mm2 are easily achieved.
• Higher flexural strength and modulus of elasticity than conventional concretes of equal compressive strength is obtained.
The overall resistance of silica-fume concrete to attack by an aggressive chemical is not significantly different from that of conventional Portland cement concrete. However, the reduced permeability of silica-fume concrete may extend the life of a concrete structure or extend the time between repairs, simply by slowing down the rate of the attack.
SF is an extremely fine material, with an average diameter
100 times finer than cement. At a typical dosage of 8% by
weight of cement, approximately 100,000 particles for each
grain of cement will fill the water spaces in fresh concrete.
The reduced permeability of SF provides protection against intrusion of chloride ions thereby increasing the time taken for the chloride ions to reach the steel bar and initiate corrosion. In addition, SF concrete has much higher electrical resistivity compared to OPC concrete thus slowing down the corrosion rate.
SF (Silica Fume) is used in shotcrete whether produced by wet or dry process, to reduce rebound loss, to increase application thickness per pass, improve resistance to wash out in marine construction or wet areas and to improve the properties of hardened shotcrete.
By replacing cement with SF and observing the efficiency factor of SF, a lower rise maximum temperature and temperature differential will take place for concrete with the same strength.
IJSER © 2015 http://www.ijser.org
International Journal of Scientific & Engineering Research, Volume 6, Issue 1, January-2015 416
ISSN 2229-5518
Concrete mix design is an art of fixing the preparation of the various ingredient of concrete namely, fine aggregate, coarse aggregate, cement and water. It is a trial and error
Specim en
No
Grade of Concre te
Water
Ratio
Admixt ure
Ratio (Cerapl ast)
Compr essive Strengt h at 7 days in MPa
Averag e strengt h in MPa
Compr essive Strengt h at 28 days in MPa
Averag e strengt h in MPa
method of setting the various values in order to attain the
maximum strength with the given proportion. The report
C-1 M-40 0.35 0.10 36.0
44.2
has followed the Erntroy and Shacklockmethod for the mix design and the mix design has been done for M40 and M50 grades of concrete.
C-2 M-40 0.35 0.10 35.3 44.0
35.9
C-3 M-40 0.35 0.10 36.4 44.2
44.1
Table 1 M40 - Conventional Concrete Compressive
Strength
Fig.3 COMPARISON OF COMPRESSIVE STRENGTH FOR 10% TO 30% REPLACEMENT OF CEMENT BY SF FOR M40 GRADE CONCRETE
th in
50
7 DAYS
40
30
20 34.7 35.9
25.5 27.4
10
0
28 DAYS
42.4 43.6 43.8 44.1
0%
10%
20%
30%
0% 10% 20% 30% 0% 10% 20% 30%
NUMBER OF DAYS
Fig.1 Compressive strength of concrete before replacement
Table 3 M50 - Conventional concrete Compressive strength
Admixture
of cement by micro silica
Specimen
No
Grad
e of
Conc rete
Water
Ratio
Ratio
(Ceraplast)
Compressive Strength at 7 days in MPa
Average strength in MPa
Compressive Strength at 28 days in MPa
Average strength in MPa
45
40
35
30
25
20
15
25.5
10
5
42.4
7 days
28 days
C-1 M-50 0.35 0.10
38.3
51.7
0
7 days 28 days
`
C-2 M-50 0.35 0.10 38.7
0.35
38.5
51.3
51.5
Table 2 M40 - Concrete Cubes With 30% Replacement of
Cement by Micro silica
C-3 M-50
0.10 38.5
51.5
Fig.2 the compressive strength has been increased by replacing cement with SF
Table 4 M50 - Concrete Cubes With 30% Replacement of
Cement by Micro silica
IJSER © 2015 http://www.ijser.org
60
40
International Journal of Scientific & Engineering Research, Volume 6, Issue 1, January-2015 417
ISSN 2229-5518
Fig.4 COMPARISON OF COMPRESSIVE STRENGTH FOR 10% TO 30% REPLACEMENT OF CEMENT BY SF
FOR M50 GRADE CONCRETE
Fig.5 M40 Grade Concrete Split Tensile Strength
6
4
2 3.5
0
5.4
7 days
28 days
7 days 28 days
NUMBER OF DAYS
Fig.6 M40 Grade -30% Replacement of Cement by Micro silica
7
6
5
4
6.3
3 5
2
1
0
7 days
28 days
Table 5 M40 - Concrete Split Tensile Strength
7 days 28 days
NUMBER OF DAYS
Fig.7 COMPARISON OF SPLIT TENSILE STRENGTH FOR 10% TO 30% REPLACEMENT OF CEMENT BY SF FOR M40 GRADE CONCRETE
7
6
5 7 DAYS
4
3
2 3.5 4.2 4.3 5
1
0
28 DAYS
5.4 5.7 6.1 6.3
0%
10%
20%
30%
0% 10% 20% 30% 0% 10% 20% 30%
REPLACEMENT OF CEMENT BY MICROSILICA
Table 6 M40 - Concrete Cylinders With 30% Replacement of Cement by Micro silica
Table 7 M50 - Conventional split tensile strength
IJSER © 2015 http://www.ijser.org
International Journal of Scientific & Engineering Research, Volume 6, Issue 1, January-2015 418
ISSN 2229-5518
Specime n No | Grade of Concret e | Wate r Rati o | Admixtur e Ratio (Ceraplas t) | Split Tensile Strengt h at 7 days in MPa | Averag e strengt h in MPa | Split Tensile Strengt h at 28 days in MPa | Averag e strengt h in MPa |
C-1 | M-50 | 0.35 | 0.10 | 5.57 | 5.59 | 5.90 | 5.87 |
C-2 | M-50 | 0.35 | 0.10 | 5.60 | 5.59 | 5.85 | 5.87 |
Table 8 M50 - Concrete Cylinders With 30% Replacement of Cement by Micro silica
Specime n No | Grade of Concret e | Wate r Rati o | Admixtur e Ratio (Ceraplas t) | Split Tensile Strengt h at 7 days in MPa | Averag e strengt h in MPa | Split Tensile Strengt h at 28 days in MPa | Averag e strengt h in MPa |
C-1 | M-50 | 0.35 | 0.10 | 6.20 | 6.34 | 7.90 | 7.98 |
C-2 | M-50 | 0.35 | 0.10 | 6.47 | 6.34 | 8.05 | 7.98 |
Fig.8 M50- Grade Combined Split Tensile Strength
Fig.9 Comparison of M40 and M50 Grade Compressive
Strength for 7 Days
Fig.10 Comparison of M40 and M50 Grade Compressive
Strength for 28 days
Fig.11 Comparison of M40 and M50 Grade Concrete Split
Tensile Strength for 7 Days
Fig.12 Comparison of M40 and M50 Grade Concrete Split
Tensile Strength for 28 Days
IJSER © 2015 http://www.ijser.org
International Journal of Scientific & Engineering Research, Volume 6, Issue 1, January-2015 419
ISSN 2229-5518
Silica fume increases the strength of concrete more by 25%. Silica fume is much cheaper than cement therefore it is very important from economical point of view. It is a material which may be a violent of air pollution, as this is a byproduct of some Industries. Use of micro silica with concrete decreases the air pollution. Silica fume also decreases the voids in concrete. Addition of silica fume reduces capillarity, absorption and porosity because fine particles of silica fume reacts with lime present in cement.
1. Krishna M.V., Rao P., Kumar Ratish and Khan Azhar M., A study on the influence of curing on the strength of a standard grade concrete mix, Architecture and Civil Engineering, 8(1), 23–34 (2010)
2. Bhanjaa S. and Sengupta B., Influence of silica fume on the
tensile strength of concrete, Cement and Concrete Research,
35, 743–747 (2005)
3. IS 10262 -2009 Indian Standard recommended guide lines for
concrete mix design (2009)
4. IS 383-1970 code for properties of aggregates (1970)
5. ACI report 234R-96
6. Abdullah K. M, Hussin W, Zakaria F, Muhamad R, Abdul
Hamid Z. (2006) “POFA: A Pontential Partial Cement
Replacement in Aerated Concrete” Proceedings of the 6th Asia- Pacific Structural Engineering and Construction Conference (APSEC 2006), 5-6 September 2006, Kuala Lumpur, Malaysia.
7. Adepegba D. (1989) “ Pozzolanin Activity of Palm Bunch
Wastes, Materials and Structures” Riaux et Constructions,
1989, 22,220-224.
8. Bentur A. (2002), Cementitious Materials – Nine Millennia and A New Century: Past, Present and future. Journal of Materials in Civil Engineering 2002: 14(1): 1-22.
9. Bhanja S, Sengupta B. Optimum silica fume content and its
mode of action on concrete, ACI Materials Journal,
September – October 2003, pp. 407 – 712.
10. Coutinho SJ. (2003), The combine benefit of CPF and RHA in
improving the durability of concrete structures. Cement and Concrete Composites 2003: 25(1):5159. Gastaldine ALG, Isaia GC, Gomes NS.
IJSER © 2015 http://www.ijser.org