Effect of Blended Fly ash and Superplasticizer on Pozzolanic Activity and Compressive Strength of Cement Paste

Preeti Sharma, Research Scholar, Devendra Tyagi, Associate Professor, Department of Chemistry, D.A.V College Dehradun, H.N.B Garhwal University, Srinagar. S.K Agarwal, Scientist, C.B.R.I, Roorkee

It is a very well known fact that the use of fly ash in masonry and concrete enhances the durability of structure hence use of fly ash is gaining momentum in the cement/ concrete Industry. But due to lack of awareness, utilization of flyash is still too low in India.

Present study covers the factors affecting the pozzolanic activity of flyash
  1. Effect of blending of flyash from different sources such as Silo1 (Hopper 1 & Hopper 2 mixture), Silo 2 (Hopper 3, Hopper 4 & Hopper 5 mixture).
  2. Effect of superplasticizer.
The main properties that influence the pozzolanic activity of Flyash are Loss on ignition and Fineness.

In this paper, the effect of fly ash percentage of different fields on the compressive strength of cement paste with and without superplasticizer has been studied

Fly ash of Silo-1 is very coarse in nature where as flyash of Silo-2 is fine. Hence flyash from Silo1 and Silo 2 were blended in varying proportion to study the effect on pozzolanic activity. Since Silo 1 flyash account for 80 % of total flyash generated hence efforts have been made to maximize the utilization of Silo 1 flyash with addition of superplasticizer.

The pozzolanic activity increases from field I to V as expected, the noticeable observation is that with the use of superplasticizer, the pozzolanic activity of Silo-1 is comparable to control value of 358 kg/cm2.

Introduction

Fly ash is a byproduct of the combustion of the pulverized coal in thermal power plants. Fly ash collected from each hopper in the ESP system are transported and stored in the silo. It is known that the properties of fly ashes collected from each hopper in an ESP system varies as we move from the boiler (Hemming et al., 1994; Itskos et al., 2009; Monzo et al., 1994; Erdogdu et al., 1998; Lee et al., 1999). Fly ash consists of inorganic matter present in the coal that has been fused during coal combustion. The particle diameter of fly ash ranges from <1 to 150 µm. Specific surface area is extremely variable ranging from <200 m2/kg to 800 m2/kg.

It is a most common artificial pozzolana, which is defined as a chemically inert silicious and aluminous material that possesse little or no cementitious value. But when it is in finely divided form and in the presence of water, it reacts with calcium hydroxide at ordinary temperature to form compounds possessing cementitious properties.

Pozzolanic activity is indicative of lime pozzolana reaction, it is mostly related to the reaction between reactive silica and alumina in fly ash with Ca(OH)2 librated during the hydration of portland cement to form CSH and calcium aluminate hydrate. Fly ash is suitable for massive concrete structures because its addition as a partial substitute for cement reduces the heat of hydration, thereby improving the overall durability of the concrete.

Researchers have given various factors for measuring or assessment of pozzolanic activity:
  1. Quantity of reactive silica
  2. Composition of SiO2 + Al2O3 + Fe2O3
  3. Fineness / surface area of the fly ash particles
  4. Measurement of compressive strength/ strength activity index
  5. Lime reactivity test specified in Indian Standard IS 3812
Fineness of fly ash is very important property affecting pozzolanic reactivity. Different techniques used for measurement of fineness have shown different pozzolanic activity. Fineness of fly ashes plays an important role in strength development. Some researchers give more emphasis on % retained on sieve while some have shown correlation between blain’s fineness and compressive strength.

The sum of Silica + Alumina + Iron oxide is stipulated in most of the standards as a major requirement. It is also observed that silica and alumina in amorphous form contribute to pozzolanic reactivity. Small quantity of iron present in glass phase is reported to have deleterious effect on pozzolanic activity.

Measurement of compressive strength is rated as the best technique for measurement of pozzolanic reactivity. There are incidences where low lime reactivity fly ash has shown more compressive strength while fly ash having higher lime reactivity shown less compressive strength.

It is generally accepted that the fly ash collected at various Sillo/ESP exhibit no greater difference in their chemical composition, but the glassy content of the higher fields is greater [5-7]. Due to this reason cement/ concrete industry is hesitant to use it in concrete. First and second field fly ashes is coarser than other fields and the quantity generated by these fields are nearly 70-80% of the total generation, so it is very important to enhance its reactivity.

There are different ways to enhance the reactivity like
  1. Grinding of fly ash
  2. Use of chemical admixtures
  3. Blending of fly ash of different fields
In the present study blending of Silo one fly ash with subsequent fields has been evaluated for pozzolanic activity. Effect of superplasticizer on the pozzolanic activity has also been studied. This paper reports the effect of fly ash collected from different fields with different percentages on the compressive strength of cement paste.

Material Used

Fly Ash: Fly ash of different fields from thermal power stations (Near Delhi) was collected. The flyash was analyzed and their physical and chemical properties are given in Table 1 & 2.

Table 1: Physical characteristics of fly ash sample of different field
S.No Fly ash Fields LOI Specific Gravity Surface Area (m2/Kg)
1. S-1 1.10 2.25 398
2. S-2 0.67 2.37 500

Table 2: Chemical Characteristics of Fly ash of Different Fields
S.No Sample Details (Fly ash) SiO2 R2O3 CaO SO3
1. S-1 60.27 31.48 3.68 0.12
2. S-2 61.82 29.54 3.74 0.11

Table 3: Physical and Chemical Properties Of Portland Cement
Compressive Strength    
3 Day 260 kg/cm2 ≤230
7 Day 370 kg/cm2 ≤330
28 Days 450 kg/cm2 ≤430
Fineness 334 m2/kg ≤300 m2/kg
Setting Time    
Initial 185 mins ≤ 30 mins
Final 230 mins ≤ 600 mins
Insoluble Residue 1.2  
Magnesia 3.2  
Alkalies 0.40  
SO3 2.5  
Silica Content 20.5  
CaO 60.5  
Specific Gravity 3.14  

Cement: Ordinary Portland cement 43 grade confirming to BIS 8112/1989 had been used in present study. The cement was analyzed and its physical and chemical properties are given in Table 4.

Table 4: Pozzolanic Activity Index Of Fly Ash Of Different Fields With and Without Superplasticizer
System CASE-1
Without Superplasticizer c.s (kg/cm2)
CASE- 2
With Superplasticizer
c.s (kg/cm2)
Control 340.0 420.0
S-1 307 358.0
S-2 370 421.0

Superplasticizer: Sulphonated Naphthalene Formaldehyde Condensate (SNF) conforming to BIS 9103 (2004) was used in the present study Binder had been used as 1% dose by weight in all the test mixture.

Sand: Standard sand (annore) had been used in the present study.

Experimental Procedure

Pozzolanic Activity

Control Mixture:- The control was prepared with 250 gm of portland cement, 687.5 gm ( 229 fraction I + 229 fraction II + 229 fraction III) of graded sand and 121 ml of water.

Test Mixture: The test mixture was prepared with 225 gm of cement and 25 gm of pozzolana. The flyash was blended in the following proportions :
  • SET 1: Silo 1 (90%) + Silo 2 (10%)
  • SET 2: Silo 1 (70%) + Silo 2 (30%)
  • SET 3: Silo 1 (50%) + Silo 2 (50%)
The above set of experiments was repeated with 1% superplasticizer addition.

Mixing Procedure: The mortar mixture was prepared using ELE (UK) Automatic mixture. 50 mm cubes were casted for the present study.

Storage of Specimens: After 24 hours of initial curing in a moist room (25 ± 2ºC) with relative humidity not less show 95%. The cubes were placed in air tight glass containers and stored at (65 ± 2ºC) for 6 days.

Determination of Compressive Strength: The compressive strength of mortar cubes was determined after 7 days of demoulding of control and test mixture and average of the three samples has been reported in Table 5

Table 5: Pozzolanic Activity Index Of Fly Ash Of Different Fields With and Without Superplasticizer
System Without Superplasticizer c.s (kg/cm2) With Superplasticizer
c.s (kg/cm2)
Control 340.0 420.0
SET 1: Field I + Field II
(90% + 10%)
325.0 360.0
     
SET 2 : Field I + Field II
(70% + 30%)
350.0 393.0
     
SET 3 : Field I + Field II
(50% + 50%)
410.0 440.0

Paste Studies

Cement cubes of 25mm were cast with various percentages (10, 30 and 50%) of fly ash of different Silo with and without superplasticizer at the same consistency level. The compressive strength of these cubes was determined at different time interval of 1,3,7,28,90 and 360 days.

Results and Discussion: In the present study compressive strength method had been used to evaluate pozzolanic activity.

Table 1 clearly indicates that the surface area of fly ash increases as we move from Silo 1 to 2.

The pozzolanic activity of fly ash of Silo 1 & 2 with and without superplasticizer has been reported in Table-5. It was observed in both the cases (Case 1 & Case 2) that the pozzolanic activity increases as we move from Silo-1 to Silo-2.

It can be depicted for Table 5 that with the use of superplasticizer it is possible to enhance the pozzolanic activity of flyash.

Table 5 indicates the effect of blending of flyash from different fields in varying proportions. SET 1 pozzolanic activity was comparable to control value i.e. 340 kg/cm2, whereas in case of SET 3 the pozzolanic activity was approximately 20 % more than control, thus indicating that the pozzolanic activity was enhanced from SET 1 to SET 3. Hence it was observed that the activity increased with the increasing proportion of Silo 2 flyash thus indicating that fly ash particles with larger medium size particle are more reactive. Enhancement of pozzolanic activity of fly ash through blending helps reduce the cost of superplasticizer.

Table 6: Compressive Strength of Cement Paste with Fly Ash (10%) of Different Fields
System 1day 3days 7days 28days 90days 360days
Control 180 280 390 515 535 560
S-1 168 265 368 515 540 570
S-2 210 305 425 580 597 616

Table 7: Compressive Strength of Cement Paste with Fly Ash (10%) Of Different Fields with Superplasticizer
System 1day 3days 7days 28days 90days 360days
Control 225 340 450 523 550 600
S-1 215 365 450 528 562 590
S-2 242 420 480 585 604 620

The results of the compressive strength of cement paste with different percentages (10, 30 and 50%) of fly ash of Silo-1&2 with and without superplasticizer up to 360 days are given in tables 6-11.

It is clear from the Table 6-11 that the compressive strength of cement paste increases from S-1 to S-2. Since the fineness of fly ash increases from S-1 to S-2, this indicates that the fine fly ash is very reactive and has larger influence on the strength.

Table 8: Compressive Strength of Cement Paste with Fly Ash(30%) of Different Fields
System 1day 3days 7days 28days 90days 360days
Control 180 280 390 515 535 560
S-1 95 170 280 350 425 472
S-2 117 205 360 465 520 548

Table 9: Compressive Strength of Cement Paste with Fly Ash (30%) Of Different Fields with Superplasticizer
System 1day 3days 7days 28days 90days 360days
Control 225 340 450 523 550 600
S-1 150 208 298 440 479 545
S-2 167 280 440 520 590 625

Table 6 and 7 gives strength data of cement paste with 10% fly ash of different fields with and without superplasticizer up to 360 days. The high pozzolanic activity of fly ash of Silo-2 the strength is 10-15% more at one day. The trend is similar up to one year. However, for Silo-1 the strength is slightly less compare to control up-to 7days but beyond that it is comparable to control.

With the use of superplasticizer the 1&3 day strength is more than the control and the gain in strength is observed up to one year.

The results of 30% replacement of fly ash of different fields are given in table 8 and 9. Compressive strength of cement paste without superplasticizer exhibits lower values for Silo-1 upto 360 days. However in case of field Silo-2 strength at 90 days are comparable to control. With the use of superplasticizer Silo-1 show comparable strength at 360 days and Silo-2 show comparable strength at 28 days and at 90 and 360 days the strength is approx. 7 % higher than control. This gain in strength is due to reduction in w/b as we move from field Silo 1-2.

Table 10: Compressive Strength of Cement Paste with Fly Ash (50%) of Different Fields
System 1day 3days 7days 28days 90days 360days
Control 180 280 390 515 535 560
S-1 70 62 100 197 234 415
S-2 115 80 120 225 275 480

Table 11: Compressive Strength of Cement Paste with Fly Ash (50%) Of Different Fields with Superplasticizer
System 1day 3days 7days 28days 90days 360days
Control 225 340 450 523 550 600
S-1 87 101 160 235 390 520
S-2 140 160 205 400 495 575

The strength data of 50% replacement of fly ash is given in table 10 and 11. The strength is less compare to control upto 28 days with and without superplasticizer for fly ash of different fields. At 90 days compressive strength for this is comparable to control when superplasticizer has been used. Beyond 90 days the compressive strength is either equivalent or more compare to control for Silo-2. The use of fine fly ash also has a packing effect and the filling of the small voids and this helps in the strength development (Chindaprasirt et al., 2004).

Conclusions

  • Pozzolanic activity of fly ash of Silo-1 is less than control.
  • Pozzolanic activity of Silo 2 is 5-8 % more than control.
  • Pozzolanic activity of Silo-1 fly ash with 1% superplasticizer is comparable to control value.
  • Blending of fly ash Silo-1 (90%, 70% as 50%) with Silo-2 has comparable pozzolanic activity to control. However, use of superplasticizer with blended fly ash shows enhanced pozzolanic activity
  • This study may help in identifying the optimized blend of fly ash from different fields with/without addition of superplasticizer, to be used in cement / concrete industry.
  • With 30% replacement of cement with fly ash the compressive strength of cement paste from Silo-1 to Silo-2 is comparable to control in case of Silo-1, where as for Silo-2; the strength is more at 360 days in the presence of superplasticizer. However compressive strength of cement paste with 50% replacement for Silo-2 in the presence of superplasticizer beyond 90 days is either comparable or more than control.
  • Test results indicate that fly ash of different fields have noticeable effect on the compressive strength due to different fineness. The fine fly ash (Silo-2) with high surface area is more reactive and thus results in increase in strength.

References

  • Hemming, R.T., and Berry, E.E., On the glass in coal fly ashes: recent advances, Mater. Res. Soc. Symp. Proc. 113, p3-38 (1998)
  • Lee, S.H., Sakai, E., Daimon, M., and Bang, W.K. Characterization of fly ash directly collected Research, Vol. 29 p1791-1797 (1999)
  • Lee, S.H., Sakai, E., Watanbe, K., Yanagizawa, T., and Daimon, M., Properties of classified fly ashes by using electrostatic precipitator and the modification of fly ashes by removal of carbon, J.Soc. Mater. Sci. Jpn. 48, p837-842 (1999).
  • Ranganath, R.V., Sharma, R.C., and Krishnamorthy, S., Proceeding of fifth CANMET/ACI international conference on fly Ash, Silica fume, slag and natural pozzolana in concrete, Miwauke, SP-153, vol. I p 355-366, ACI Detroit (1995)
  • Stanica, S., Cement and concrete, Research, p21 p285 (1991)
  • Mora, E., Paya, J., and Monzo, J., Cement and concrete Research Vol. 41, p29 (1991)
  • Dodson, V., Concrete Admixtures, Structural Engineering Series P 162-164. Van Norsland Rein hold, N.Y.1994.
  • Dongxu, Li., Yimin, C., Jinlin, S., jiashna, S., and Xuequan, W., Cem. Concr. Res. Vol. 30, p 881-886(2000)
  • Yueming, F., Suhong, Y., Zhiyum, W., and jingyn, Z., Activation of fly ash and its effect on cement properties, Cement and Concrete Research, Vol. 29 p 407-472 (1999)
  • Antiohos., S., and Tsiman, S., Activation of fly ash cementitious systems in the presence of quicklime. Part I Compressive strength and Pozzolanic reaction rate Cement and Concrete Research, p 769-779 (2004);
  • IS 1727-1967, methods of test of Pozzolanic Materials, BIS Manak Bhavan, New Delhi (1999)
  • American Society for Testing and materials 1990 Standard test methods for sampling and testing fly ash or natural Pozzolanas for use as mineral admixture in Portland cement concrete ASTM, Pliladelphia PA, ASTM-C311
  • Throne, D.J., and Watt, J.D., Composition and Pozzolanic properties of pulverized ashes II Pozzolanic properties of fly ashes as determined by crushing strength tests on lime mortars, J. Appl. Chem. 15(1965) p 595-604.
  • Watt. J.D., and Throne, J.D., The composition and pozzolanic properties of pulverized ashes. III Pozzolanic properties of fly ashes on determined by chemical methods, J. Appl. Chem 16(1996) p 33-39
  • Aggarwal, S.K. Pozzolanic activity of various siliceous material’, Cement and Concrete Research, Vol. 36 p 1735-39 (2006)
  • Aggarwal, S.K.,Pozzolanic activity of Blended Fly ash, Cement and Concrete Research, Vol. 36 p 1735-39 (2006)
  • A.M Pande, L.M Gupta , Properties of fly ash & Pozzolanic activity, Fly ash Utilization Programme (FAUP), TIFAC
  • Erdogdu K, and Turker P (1998) Effects of fly ash particle size on strength of Portland cement fly ash mortars. Cem. Concr. Res. 29:1217
  • Lee SH, Sakai E, Diamond M and Bang WK (1999) Characterization of fly ash directly from the electrostatic precipitators. Cem. Concr. Res. 29: 1791.
  • Agarwal S.K, and Sharma P, (2009) Role of additives in optimization of flyash in cement. NBM &CW March , p-132, 2009
  • Nagataki S, Sakai E, and Takeuchi T (1984) The fluidity of fly ash cement paste with superplasticizer. Cem. Concr. Res. 14: 631.

NBMCW April 2011

Click Here
To Know More / Contact The Manufacturer
Please provide your details we will contact you as soon as possible
Please let us know your name.
Invalid Input
Please let us know your Designation.
Invalid Input
Please let us know your City.
Please let us know your State.
Please let us know your Country.
Please let us know your Contact Number.
Please let us know your email address.
Please brief your query.

Strength behaviour of M25 and M45 concrete incorporating accelerators and stone waste

Accelerators are used to accelerate the setting and development of concrete at early age, and also speed up the construction work for early removal of formwork. Due to depletion of natural resources, and emission of carbon dioxide during Read More ...

Durability of Concrete made with Marble Dust as partial replacement of Cement subjected to Sulphate attack

This experimental study presents the feasibility of the production of more durable concrete with marble dust as partial replacement of cement by 5%, 10%, 15% and 20% by weight. Standard concrete cube specimens of size Read More ...

Effect of Aggregate-Cement Ratio on Engineering Properties of Pervious Concrete

Pervious concrete is a composite type of material containing coarse aggregate, little or no fine aggregate, cement and water. In pervious concrete, carefully controlled amount of water and cementitious materials are used to Read More ...

Recent Advances in - Self-Compacting Concrete

In line of advanced concrete technology and research self-compacting concrete (SCC) contribute an innovative role for the development and its implementations worldwide. SCC, also known as self-leveling concrete Read More ...

Life-Cycle Management of Concrete Structures

A concrete structure is required to maintain its functions and performance during its design service life. However, serious damages have been sometimes found, which may be caused by physical and chemical actions. Read More ...

Green, Sustainable Construction: Solutions for Affordable Housing

Concrete is the second most consumed material in the world after water and it is used most widely in the construction industry due to its high compressive strength and other properties.[1] Therefore, the basis of Read More ...

Aesthetical Integration in High Performance Concrete for Infra Construction

Concrete, the wonder material that has shaped our surroundings, was invented in the mid-18th century, and continues to be the most widely used construction material. Concrete came to architects and designers as a boon Read More ...

Comparative Study of concrete mix design using IS and ACI methods with and without super-plasticizer

Concrete is a composite material consisting of cement, water, and aggregates. These ingredients can be mixed in different ratios to attain desired strengths. Though rough mix ratios for different strengths Read More ...

Non destructive testing for determining the strength of concrete

Civil engineering infrastructures are designed to operate for long periods of time, such as 50 to 100 years. However, several unpredictable and uncontrollable factors reduce their expected performance and life Read More ...

An Experimental investigation on utilizations of Marble Dust as partial replacement of Cement in Concrete

Marble dust is an industrial by-product obtained during sawing, shaping, and polishing of marble and causes a serious problem to the environment. Research indicate that the effect of mixing marble dust on the Read More ...

Use of Ferrocement for Construction of Mini Check Dams and Diversion Structures

Diversion structures and check dams are constructed for diverting/ storing the water, flowing in shallow rivers/ streams for various purposes. The present practice is to use brick / stone / stone block masonry Read More ...

Sustainable Concrete - An Inevitable Need for Present & Future

Concrete has become, by far, the most widely used construction material in the world. It is surpassed only by water as the most used material on earth. Concrete is perceived and identified as the provider Read More ...

Structural Behaviour of High Performance Fiber Reinforced Concrete Beam Column Joints Under Cyclic Loading

The strength & ductility of structures primarily depend on proper detailing of reinforcement in beam column joints. Under seismic excitations, beam-column joint region is subjected to high horizontal & vertical Read More ...

Translucent Concrete by Using Optical Fibers and Glass Rods

Translucent Concrete
Concrete is traditionally a solid, substantial building material. It needs a makeover. Small buildings are replaced by high-rise buildings and skyscrapers. There arises one of the major problem in deriving natural Read More ...

Practical applications of UHPC & HPC concrete by generative development...

Fiber Reinforced UHPC
Ultra High Performance Concrete (UPHC) is one of the most modern concretes developed during the last decade. It's a material generally characterized by (although not limited to the one) having Read More ...

High Performance Concrete for High-rise Construction

Self Compacting Concrete
Concrete is ubiquitous in our built environment - be it in buildings, roads, bridges, railways, or dams. Global growth in concrete consumption is partly due to the rapid industrialization of developing Read More ...
NBM&CW

New Building Material & Construction World

New Building Material & Construction World
MGS Architecture

Modern Green Structures & Architecture

Modern Green Structures & Architecture
L&ST

Lifting & Specialized Transport

Lifting & Specialized Transport
II&TW

Indian Infrastructure & Tenders Week

Indian Infrastructure & Tenders Week