EFFECT OF SUPERPLASTICIZERS ON WORKABILITY AND STRENGTH OF CONCRETE

EFFECT OF SUPERPLASTICIZERS ON WORKABILITY AND

STRENGTH OF CONCRETE

Saeed Ahmad*, University of Engineering & Technology,Taxila, Pakistan Muhammad Nawaz, University of Engineering & Technology, Taxila, Pakistan

Ayub Elahi, University of Engineering &Technology, Taxila, Pakistan

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30th _{Conference on OUR WORLD IN CONCRETE & STRUCTURES: 23 – 24 August 2005, Singapore}

EFFECT OF SUPERPLASTICIZERS ON WORKABILITY AND

STRENGTH OF CONCRETE

Saeed Ahmad*, Universityof Engineering & Technology,Taxila, Pakistan

Muhammad Nawaz,University of Engineering & Technology, Taxila, Pakistan

Ayub Elahi,University of Engineering &Technology, Taxila, Pakistan

Abstract

It has long been a concrete technologist’s dream to discover method of making concrete at the lowest possible water/cement ratio while maintaining a high workability. To a considerable extent this dream has been fulfilled with the advent of superplasticizers. Have indeed added a new dimension to the application of admixtures with regards to production of high strength and flowing concretes. It is now possible to produce concrete with compressive strength of the order of 13000 psi (90 Mpa). In addition, these are also suitable for use with other cementations materials like fly ash and blast furnace slag.

In the wake of energy conservation policy and diminishing supplies of high quality raw materials, there is a need to use marginal quality cements and aggregates for the production of concrete. In such instances the use of superplasticizers permits the production of concrete at low water/ cement ratios. Thus many waste materials of today become the useful by products of tomorrow. It is the particular role of superplasticizers, which is very importance for us here in Pakistan, because of our poor economy and less developed industrial base. Besides, the addition of superplasticizers to produces concrete with less cement but normal strength and workability is another application, which has received more attention.

In this research programme two types of superplasticizers(Rheobuild 1100,Rheobuild561M) of synthetic polymer base confirming to ASTM C-494 type A&F and ASTM type B,D&G respectively has been used. Three nominal ratios of 1:1:2, 1:1.5:3 and 1:2:4 were used for mix proportioning of concrete constituents by weight. The water cement ratio was maintained as 0.50, 0.55 and 0.60 to study the effect of these SP on various properties of concrete. The dosage of superplasticizers was adopted as constant @ 0.80% by the weight of cement. To study the effects of superplasticizers the experiments have been divided into three series namely workability series, water reduction series and cement saving series.

The result have shown substantial improvement in the properties of concrete after use of the superplsasticizers.The Rheobuild 561M high range water reducer,superplasticizer has given more promising results as compared to Rheobuild1100.

Key words: Superplasticizers, reinforcement, pre-cast, slab, beam, slender, mixproportioning,

1. Introduction

The earliest known published reference to the use of small amounts of organic material to increase the fluidity of cement containing composition was made in 1932 [1] where polymerized naphthalene formaldehyde sulphonate salts were claimed as useful in this role. This was followed during the mids 1930s to early 1940s by numerous disclosures regarding the use of lignosulphonate and improved composition [1].In recent years, construction agencies in North America, Great Britain and other countries have evinced great intrest in the use of superplasticizers, superfluidifiers, siper water- reducers or high range water reducers [3].

The superplastisizers (SP) are refered to as high range water reducing admixture by ASTM-C494,which mainly disperses the water in concrete matrix. This property is some time called as dispersion-fluidification property of concrete admixture. The superplasticizers are classified in the following four major groups;

 Sulphonated Nephthalene Formaldehyde Condense(SNF).  Sulphonated Melamine Formaldehyde Condense (SMF).  Modified Lignosulphonates (MLS).

 Others.

Today superplasticizers are used in all important projects across the world in high raise buildings, pre-stressed concrete, slender components with congested and densely packed reinforcement, beams and slabs pre-cast elements and long slender columns.

The superplasticizer affect the various properties of concrete both in fresh and hardened forms mainly due to the following facts as commented by M.Collperdi [1] in Concrete Admixtures Hand Book;

 Reduction in interfacial tension.

 Multilayered adsorption of Organic molecule.

 Release of water trapped amongst the cement particles.  Retarding effect of cement hydration.

 Change in morphology of hydrated cement.

The workability of concrete is mainly governed by the max size, shape, texture and grading of the aggretes. For a given value of water cement ratio, there is one value of coarse/fine ratio for given material that gives the highest workability [2].Parenchio [3] developed a miniature slump test for the cement paste which requires small amount of paste and less testing time. The high workability of SP concrete is however lost in the early 30minutes due to formation of hydrates [4].

The compressive strengths of SP concrete are usually higher than the corresponding strengths of the reference mixes. When SP is used, a water reducer up to 32-33% can be achieved [5].This fact leads to the increase in the compressive strength of SP concrete. Most recently new generations of SP have been developed to give ultra high strength concrete producing concrete with compressive strength of 15000 psi and more [6] and very high early strength at 2 to 4 hours.

In water reduced SP concrete no undue segregation and bleeding of concrete occurs due to decrease in water cement ratio. if there are sufficient fine aggregates in the concrete, the segregation in high workability sp concrete can also be controlled [7]

There are three possible ways in which superplasticized concrete can be produced [19] High workability concrete, Concrete with low water/ cement ratio ,Concrete with reduced cement content.

2. Experimental Details

2.1 Material:

 Fine Aggregates: Fine aggregates confirming to the gradation of ASTM-136 were used.  Coarse Aggregates: Lime stone crushed stones of size1/2 in and below were used. Series No 1

To investigate the effect of SP on workability slump tests were carried out and to check the effect on compressive strength cubes [6*6*6] were tested at the ages of 3,7,28 days. The results are shown in Table1 to 3.

For Tensile strength of SP added concrete cylinders (6*12”) was tested by splitting tests at the age of 28days,the results are shown in Table 4.

To check the modulus rupture of SP added concrete, the standard plain concrete beams were tested at third point load after 28days of pouring. The results are shown in Table 5.

Series No 2

To check the effect of water reduction on SP added concrete the water content was gradually increased, at constant workability, keeping all other ingredients of the mix costant,.increasing the dosages of the SP to compensate for the lost in workability. Workability was kept constant by the method of successive trials; the results are shown in the Table 6&7.

Series No 3

In this test workability was kept constant both; cement content and water content were reduced keeping water/cement ratio and workability as constant. The results are shown in the Table 6&9.

Table 1 TEST RESULTS SHOWING EFFECT OF SUPERPLASTICIZERS ON COMPRESSIVE STREGNTH AND WORK ABILITY AT CONSTANT W/C RATIO (SERIES-1) MIX RATIO (1:2:4)

Superplasticizer Used W/C Ratio

Slump (mm)

Compressive Strength (Psi) 3 Days 7 Days 28 Days

Nil 0.55 8 2685 2940 4270 [email protected]% 0.55 12 2705 3005 4290 Rheobuild-561 [email protected]% 0.55 15 2715 3035 4345

EFFECT OF S.P ON COMPRESSIVE STRENGTH AT CONSTANT W/C RATIO

Ages of testing 3 Days 7 Days 28 Days

Nil 2685 2940 4270

Rheobuild-1100 2705 3005 4290

Rheobuild-561 M 2715 3035 4345

EFFECT OF SUPPER PLASTICIZER ON COMPRESSIVE WORKABILITY AT CONSTANT W/C RATIO

Superplasticizer

Comp

re

ss

iv

e St

reng

th

i(

P

i)

4500

4000

3500

3000

2500

5000

Nil

Rheobuild-1100

Rheobuild-561M

30

15

20

0

10

5

25

Slum

p

(

mm

)

Table 2 TEST RESULTS SHOWING EFFECT OF SUPERPLASTICIZERS ON COMPRESSIVE STREGNTH AND WORK ABILITY AT CONSTANT W/C RATIO

(SERIES-1) MIX RATIO (1:1:5:3) Superplasticizer Used W/C

Ratio

Slump (mm)

Compressive Strength (Psi) 3 Days 7 Days 28 Days

Nil 0.55 15 2935 4135 6070 [email protected]% 0.55 30 2980 4240 6125 Rheobuild-561 [email protected]% 0.55 45 3035 4380 6230

EFFECT OF S.P ON COMPRESSIVE STRENGTH AT CONSTANT W/C RATIO

Ages of testing 3 Days 7 Days 28 Days

Nil 2935 4135 6070

Rheobuild-1100 2980 4240 6125

Rheobuild-561 M 3035 4380 6230

EFFECT OF SUPPER PLASTICIZER ON COMPRESSIVE WORKABILITY AT CONSTANT W/C RATIO

Superplasticizer

Compressi

v

e Streng

th

i(

P

i)

Nil

Rheobuild-1100

Rheobuild-561M

60

30

40

0

20

10

50

Sl

u

m

p

(

mm

)

6000

5000

4000

3000

2000

7000

Table 3 EFFECT OF SUPERPLASTICIZERS ON COMPRESSIVE STREGNTH AND WORK ABILITY AT CONSTANT W/C RATIO

(SERIES-1) MIX RATIO (1:1:2) Superplasticizer Used

W/C Ratio

Slump (mm)

Compressive Strength (Psi) 3 Days 7 Days 28 Days Nil 0.55 35 4280 5515 6135 [email protected]% 0.55 75 4345 5530 6205 Rheobuild-561 [email protected]% 0.55 115 4395 5540 6315

EFFECTS OF S.P ON COMPRESSIVE STRENGTH AT CONSTANT W/C RATIO

Ages of testing 3 Days 7 Days 28 Days

Nil 4280 5515 6135

Rheobuild-1100 4345 5530 6205

Rheobuild-561 M 4395 5540 6315

EFFECT OF SUPPER PLASTICIZER ON COMPRESSIVE WORKABILITY AT CONSTANT W/C RATIO

Superplasticizer

C

o

mpressive

Strength

psi

(Psi)

Nil

Rheobuild-1100

Rheobuild-561M

6000

5500

5000

4500

4000

6500

120

60

80

0

40

20

100

Slum

p

(

mm

)

Table 4 TEST RESULTS SHOWING EFFECT OF SUPERPLASTICIZERS ON SPLITTING TENSILE STREGNTH OF CONCRETE AT CONSTANT W/C RATIO

(SERIES-1) MIX RATIO (1:2:4)

Superplasticizer Used W/C Ratio Slump (mm)

28 Days Splitting Tensile Strength (Psi) Nil 0.55 8 405 [email protected]% 0.55 13 415 Rheobuild-561 [email protected]% 0.55 15 430

Superplasticizer Used W/C Ratio Slump (mm)

28 Days Splitting Tensile Strength (Psi)

Nil 0.55 15 460

[email protected]% 0.55 30 485

Rheobuild-561 [email protected]% 0.55 45 500

(SERIES-1) MIX RATIO (1:1:2)

Superplasticizer Used

W/C Ratio

Slump

(mm)

28 Days Splitting

Tensile Strength (Psi)

Nil 0.55

35

560

[email protected]% 0.55 75

575

Table 5 TEST RESUTS SHOWING EFFECT OF SUPERPLASTICIZERS ON MODULUS OF RUPTURE (FLEXURAL STRENGTH) OF CONCRETE AT CONSTANT W/C RATIO

(SERIES-1)

MIX RATIO (1:2:4)

Superplasticizer Used W/C Ratio Slump (mm) 28 Days Tensile Strength (Psi) Nil 0.55 9 655 [email protected]% 0.55 12 680 Rheobuild-561 [email protected]% 0.55 16 710 MIX RATIO (1:1.5:3)

Superplasticizer Used W/C Ratio Slump (mm) 28 Days Tensile Strength (Psi) Nil 0.55 15 810 [email protected]% 0.55 30 845 Rheobuild-561 [email protected]% 0.55 45 875

MIX RATIO (1:1:2)

Superplasticizer Used

W/C Ratio

Slump

(mm)

28 Days Tensile

Strength (Psi)

Nil 0.55

35

965

[email protected]% 0.55

75

980

Rheobuild-561 [email protected]%

0.55

118

1005

Table 6 TEST RESULTS SHOWING EFFECT OF SUPERPLASTICIZER ON WATER REDUCTION AND COMPRESSIVE STREGNTH AT CONSTANT WORK ABILITY

(SERIES-2) MIX RATIO (1:1.5:3) Superplasticizer Used Rheobuild 1100 W/C Ratio (%)Water Reduction Slump (mm)

Compressive Strength (Psi) 3 Days 7 Days 28 Days

0.0% 0.60 - 18 2735 3925 5870 0.40% 0.58 3.33% 20 2815 3995 5935 0.50% 0.57 5% 19 2870 4060 5995 0.60% 0.56 6.66% 16 2910 4130 6070 0.70% 0.54 10% 18 2965 4215 6095 0.80% 0.53 11.66% 19 3025 4285 6140

EFFECTS OF SUPERPLASTICIZER ON COMPRESSIVE STRENGTH AT CONSTANT WORKABILITY

Ages of testing 3 Days 7 Days 28 Days

Nil 2735 3925 5870 Rheobuild-1100 3025 4285 6140

Comp

re

ss

iv

e St

reng

th

i(

P

i)

4500

4000

3500

3000

2500

5500

5000

6000

6500

Table 7 TEST RESULTS SHOWING EFFECT OF SUPERPLASTICIZERS ON WATER REDUCTION AND COMPRESSIVE STREGNTH AT CONSTANT WORK ABILITY

(SERIES-2) MIX RATIO (1:1.5:3)

Superplasticizer Used Rheobuild 561 M W/C Ratio (%)Water Reduction Slump (mm)

Compressive Strength (Psi) 3 Days 7 Days 28 Days

0.0% 0.60 - 18 2738 3925 5875 0.40% 0.57 5% 19 2825 4010 5945 0.50% 0.56 6.66% 20 2885 4085 6005 0.60% 0.54 10% 17 2920 4135 6085 0.70% 0.53 11.66% 18 2970 4225 6195 0.80% 0.52 13.33% 19 3055 4390 6255

EFFECTS OF SUPERPLASTICIZER ON COMPRESSIVE STRENGTH AT CONSTANT WORKABILITY

Ages of testing 3 Days 7 Days 28 Days

Nil 2738 3925 5875 Rheobuild-1100 3055 4390 6255

Comp

ressive

Streng

th

i(

P

i)

4500

4000

3500

3000

2500

5500

5000

6000

6500

Table 8 TEST RESULTS SHOWING EFFECT OF SUPERPLASTICIZER ON CEMENT SAVING AT CONSTANT WORK ABILITY AND CONSTANT W/C RATIO

(SERIES-3) TRIAL MIX RATIO (1:1.5:(SERIES-3)

Superplasticizer

Used

Rheobuild-1100

W/C

Ratio

Cement

saving

(%)

Slump

(mm)

Compressive Strength (Psi)

3 Days

7 Days

28 Days

0.0% 058

-

22

-

4070

6005

0.40% 0.58

3.08%

21

-

4095

6065

0.50% 0.58

4.18%

19

-

4120

6082

0.60% 0.58

5.62%

22

-

4168

6098

0.70% 0.58

7.15%

23

-

4192

6105

0.80% 0.58

8.30%

24

-

3845

5430

Table 9 TEST RESULTS SHOWING EFFECT OF SUPERPLASTICIZER ON CEMENT SAVING AT CONSTANT WORK ABILITY AND CONSTANT W/C RATIO

(SERIES-3) TRIAL MIX RATIO (1:1.5:(SERIES-3)

Superplasticizer

Used

Rheobuild-561 M

W/C

Ratio

Cement

saving

(%)

Slump

(mm)

Compressive Strength (Psi)

3 Days

7 Days

28 Days

0.0% 0.58

-

21

-

4064

6018

0.40% 0.58

3.21%

19

-

4136

6082

0.50% 0.58

4.58%

21

-

4172

6115

0.60% 0.58

5.82%

23

-

4196

6158

0.70% 0.58

7.96%

22

4230

6194

0.80% 0.58

8.85%

23

-

3995

5545

On the basis of observation on test result it can be stated that properties of concrete in fresh and hardened stages have been improved with the addition of both types of superplasticizer for all nominal mixes of concrete the rheobuild561M have shown however more pronounced in terms of increase in the compressive strength, workability, water reduction, cement saving requirements of concretes.

4. References

[1] RIXOM, M.R and MAILVGANAM, N.P. Chemical admixtures for concrete, [Second edition],Publisher E.and F.N. Spon[London],pp 1-91 and 195-236

[2] RAMACHANDRANV.S, FELDMANR.F, BEAUDOIN J.J Concrete Science-Treatise on current research, pp. 91-110 and 145-166 Heyden and sons Limited, Philadelphia, 1981.

[3] Collepradi, M,”Concrete Admixtures Hand Book”2nd Edition Noys Publisher, 1995 pp.359

[4] Hewiett, P.C. “Superplasticizing admixtures in concrete” Cement and Concrete Association Publication, Vol.45, NO. 30, 1976

[5] Basile et. Al “Influence of different sulfonated Polymers on the fluidity of cement paste” Proceeding of third International Conference CANMET/ACI Ottawa, 1989 pp 209-220. [6] Glanville, W.H., Collins, A>R and Mathews “The grading of aggregates and workability

of concrete. Road Research Technology paper London.

[7] Aignesberger, A, and Kern, A “Use of melamine based superplasticizers as water reducers”. ACI Special Publication 1981, pp 061-80.

[8] Kinoshita,M, et.al “application of new superplacticizer fro Ultra high strength concrete”. Proceedings of Japan cement association Japan 1990.

[9] Rivera, R, Davila., and Durn. A “High performance concrete using fly ash and superplasticizers” Proceeding of International Symposium on High Performance and Reactive Powders concretes Sherbrook 1998.

[10] New Types of concrete. Concrete in developing countries material design and construction, Vol-1. Proceeding of International colloquium, Lahore (Pakistan) 1985, pp 14-25.