STRENGTH AND DURABILITY PERFORMANCE OF OPEN AIR ...

Journal of Civil Engineering Technology and Research Volume 2, Number 1 (2014), pp.147-157 © Delton Books http://www.deltonbooks.com

Strength and Durability Performance of Open Air Cured Alkali Activated Concrete Manjunatha G. S., Radhakrishna, Varuna Koti & Venugopala K 1 Prof. & Head, Department Civil Engg., Gogte Institute of Technology, Belgaum-590 008. 2 Associate Dean, Department Civil Engg., R.V. College of Engineering, Bangalore. 3 Lecturer, Department Civil Engg., Gogte Institute of Technology, Belgaum-590 008. 4 Head, Department Civil Engg., SEA College of Engineering, Bangalore. *Corresponding Author’s Email: [email protected] Abstract: The article presented herein deals with synthesis and performance evaluation of alkali activated, Fly ash and Ground granulated blast furnace slag based ambient cured geopolymer concrete without any Portland cement. The compressive and split tensile strengths of the concrete were determined. The durability performance studies included resistance to alternate wetting and drying cycles and elevated temperature. Concomitantly, for comparison purpose, Portland cement concrete control specimens were also evaluated for strength and durability performance following the same techniques. Durability response of geopolymer and control concrete was ascertained using degree of deterioration in terms of compressive strength. It was established that open air cured alkali activated fly ash-GGBS based geopolymer concrete performs superior compared to portland cement based conventional concrete both in terms of strength and durability. Key words: Geopolymer, ambient, alkaline solution, quarry dust, durability.

1. Introduction Unarguably, OPC based concrete has been the most adaptable, widely accepted and comprehensively used construction material ever since its inception whose global usage is estimated to be around one cubic metre for every person on earth [01] and surpassed only by water. The increased demand for concrete due to unprecedented growth in the infrastructure development has resulted in an increased production of cement [01, 02, 03]. However, the manufacture of cement is plagued by high energy intensiveness, consumption of considerable amount of natural resources and emission of approximately an equal amount of CO 2 [04]. Efforts are on, across the world, to minimize the use of Portland cement to mitigate the undesirable attributes associated with it through the use of several alternatives to Portland cement. The use of supplementary cementitious materials (SCM) and the introduction of blended cements are definitely considered to be important developments in this direction. The

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Manjunatha G. S., Radhakrishna, Varuna Koti & Venugopala K.

concept of high volume fly ash (HVFA) cement, which enabled the OPC replacement upto around 60% by weight of cement and yet still exhibiting excellent strength and durability performance [05, 06] is a significant development [07, 08, 09]. However, these measures have yielded limited results in mitigating the adverse impacts of heavy use of OPC. Geopolymer is considered to be one among the many alternative binder materials having great potential to replace OPC completely in synthesizing concrete. Geopolymers could be produced by a polymeric reaction of alkaline liquids with silica and alumina in source materials of geological origin such as kaolin, volcanic ash etc or byproduct materials such as fly ash, GGBS, silica fume, rice husk ash, etc. Hydroxides or silicates of sodium or potassium or their combinations are generally used as alkaline solutions to activate the source materials in synthesizing geopolymers. 'Geopolymer' developed by Davidovits [10] had geopolymeric aluminosilicate gel, performing the role of binder. He utilised silica (SiO 2) and alumina (Al2O3) in metakaolin to get inorganic polymeric system of alumino-silicates. Rangan and Hardijto [11] also exploited silica and alumina of fly ash to produce geopolymeric binder suitable for making structural grade concretes. Literature [11, 12] reveal that thermally cured geopolymer composites exhibit excellent mechanical properties, good thermal stability, better resistance to fire and acids. Geopolymer composites possess low shrinkage, low creep and excellent resistance to sulphate attack [08, 13]. Xiaolu Guo et. al. [14] synthesized class C fly ash based geopolymer pastes and realized a compressive strength of 63.4 MPa when cured at 75 0C for 8hours followed by curing at 230C for 28 days. Results of the investigation [15] on inorganic polymeric binder prepared from natural pozzolan reveal that any increase in both duration and temperature of curing increases the compressive strength. Rangan et. al. [08, 16] have presented a detailed discussions on the performance of a wide range of fly ash based thermally cured geopolymer concrete. They concluded that higher the curing temperature higher will be the compressive strength and that heat cured geopolymer concrete exhibit similar properties compared to OPC based concrete. Radhakrishna et.al. [17, 18, 19 ] have reported that the strength development of temperature cured fly ash based geopolymer concrete follows Abrams and Bolomey laws. An investigation undertaken by Bakharev [20] to assess the durability of fly ash based geopolymer materials when exposed to acetic and sulphuric acids revealed their superiority over ordinary portland cement paste. Again, according to Bakharev [21], fly ash based geopolymer materials exhibited high shrinkage and large changes in compressive strength with increasing fired temperature in range of 800-12000C. According to Zongjin et.al. [22], thermal-cured low-calcium fly ash-based geopolymer concrete offers several economic benefits over Portland cement concrete. Davidovits [23] reports that in the production of geopolymer, about less than 3/5 of energy is required and 80–90% less CO2 is generated than in the production of OPC. The investigation by

Strength and Durability Performance of Open Air Cured Alkali Activated Concrete

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Thokchom et.al. [24] confirms that fly ash based, thermally cured geopolymer mortar shows excellent durability interms of extremely low weight loss and high retention of compressive strength when exposed to nitric acid. Mandal et. al. [25] observed volumetric shrinkage, rapid loss of weight upto 3000C and disrupted microstructure when fly ash based geopolymer paste was exposed to elevated temperature. Geopolymers have attracted more attention due to their low energy cost, environmental friendly nature due to almost exclusive usage of secondary raw materials and preservation of precious virgin natural resources. Geopolymer technology is generating considerable interest in the construction industry in light of the ongoing emphasis on sustainability.

2. Research Significance And Objectives One of the important steps of geopolymer synthesis is curing between 40 and 100 0C for 4 to 48h in dry or steam conditions and thus till recently, the research emphasis was on thermally cured geopolymer composites synthesized normally with one source material. Most research articles deal only with alkali activated slag or fly ash; literature is either scant or silent in respect of geopolymer synthesis with the combined use of both fly ash and GGBS as bender components [26, 27, 28]. Further, being able to cure and develop strength at ambient temperature conditions is very important in terms of practical application. Further, hardly there is any research reported on the development of ambient cured fly ash-GGBS based geopolymer concrete with quarry dust as fine aggregate. In view of the above discussion, the present research article assumes significance. The paper presents a brief outcome of an experimental study of using fly ash and GGBS as binder components and quarry dust as fine aggregate in producing ambient cured geopolymer concrete without any conventional cement and evaluation of it’s fundamental properties, considered important for structural applications. The objective of this research is to significantly increase the use of fly ash and GGBS in construction.

3. Experimental Program 3.1. Materials And Methods Combinations of class F fly ash sourced from Raichur Thermal Power Station, India and GGBS from J.S.W. Steel, Bellary, India, activated by alkaline solution perform the function of binder in the development of ambient cured geopolymer concrete. Quarry dust (specific gravity of 2.85 and fineness modulus 3.15) and crushed stone (specific gravity 2.9 and fineness modulus 6.1), both of basaltic origin and sourced from local quarry/crusher industry are used as fine aggregate and coarse aggregates. The alkaline solution used is a mixture of sodium silicate and 10 M sodium hydroxide (pellets, 96-98% purity, specific gravity 2.13) solutions in the ratio of 2:1 by weight. Both are of commercial grades, procured from local supplier. Tap water was used to prepare alkaline solution. The fluid shall be prepared at least one day prior to use.

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Table 1 gives the composition of fly ash and ground granulated blast furnace slag and table 2 gives the composition of Sodium Silicate. Table 1. Composition of fly ash and ground granulated blast furnace slag. Binder Fly Ash GGBS

Sp. Gr.

LOI

Al2O3

Fe2O3

SiO2

MgO

SO3

Na2O

Chloride s

CaO

2.4

0.9 0

31.23

1.50

61.12

0.75

0.5 3

1.35

0.06

3.2

2.9

0.1 9

13.24

0.65

37.21

8.46

2.2 3

----

0.003

37.2

Table 2. Composition of Sodium Silicate. Sp. Gravity

Viscosity

Na2O %

SiO2 %

Water %

pH

1.385

68 Seconds

8.35

28.12

63.53

10.4

3.2. Specimen Preperation, Casting And Curing Geopolymer concrete is prepared by mixing fly ash, GGBS, quarry dust and coarse aggregate in the pre-determined proportions in a pan mixer to get dry uniform mixture. Then, the activator solution of required fluid binder ratio for a specified workability is added and mixed to get a homogeneous mix. After ascertaining the workability by slump test, fresh concrete is filled into moulds (cubes of 100mm sides for compressive strength and durability tests and cylinders of 100mm diameter and 200mm height for split tensile tests), with manual compaction followed by vibration. On de-moulding after 24 hours, triplicate sets of geopolymer concrete specimens were stored in room temperature for ambient curing until tested, without any special curing regime. An equivalent number of OPC based conventional concrete specimens were also cast as reference concrete for comparing with geopolymer concrete, adopting the conventional methods. After de-moulding, triplicate sets of reference concrete specimens are kept in water for 28 days for curing or until tested whichever is earlier. F/B ratio for geopolymer concrete and W/C ratio for reference concrete are maintained such that the resulting concretes possess a slump in the range of (100±10) mm. Regarding the mix design, geopolymer concrete is proportioned following the procedure proposed (for the design of steam cured fly ash based geopolymer concrete) by Rangan [29] and maintaining the same proportion for reference concrete. The mix proportion of 1:1.5:3.0 was arrived, requiring 400kg of binder, 600kg of fine aggregate and 1200kg of course aggregate for one cubic metre of concrete with 280kg of alkaline fluid and 240 kg of water for geopolymer and normal concrete respectively. The binder (FA:GGBS) proportion was taken as 70:30 based on authors’ previous works.


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Table 3 gives the series designation of geopolymer concrete and reference concrete along with the other related parameters considered in the study. study Table 3: Series Designations of the geopolymer and reference concrete Mix Proportion 1 : 1.5 : 3.0 Particulars Geopolymer Concrete Reference Concrete

Series Designation GPC NC

Slump : (100±10) mm. Binder Composition % Fly ash : GGBS 70 : 30 OPC 100

F/B ratio F/B = 0.70 W/C = 0.60

4. Results And Discussions The experimental studies involve evaluation of compressive and split tensile strength development upto 90 days and durability assessment when exposed to alternate wetting and drying cycles upto 90 days, elevated temperature upto 8000C for a constant duration of 4 hours. Experimental results are presented in the form of grap graphs hs facilitating the discussions, considering the he average results of 3 specimens. specimens 4.1. Strength Studies 4.1.1. Variation of Compressive strength with age Figure 1 represents the variation of compressive strength of geopolymer concrete and reference concrete with age.

Compressive strength (MPa)

Compressive Strength test results 50.00 45.00 40.00 35.00 30.00 25.00 20.00 15.00 10.00 5.00 0.00

3 days

7 days

28 days

56 days

90 days

GPC

18.00

21.33

34.64

46.54

47.19

NC

10.48

18.43

25.48

34.86

39.72

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Manjunatha G. S., Radhakrishna, Varuna Koti & Venugopala K. Figure 1. Variation of Compressive strength with age

The compressive strength steadily increases with age for both geopolymer concrete and reference concrete as seen from Fig Figure 1. The objective was to achieve a 28 days compressive strength of 20N/mm 2 for geopolymer concrete corresponding to a mix of 1:1.5:3 which represents nominal mix for conventional concrete of grade M 20. The geopolymer concrete attained the required compressive strength of 20N/mm 2 at the age of 7 days itself. Thus, it is possible to optimize timize the proportion for the required strength at the required age. It was observed that the percentage increase in strength of geopolymer concrete compared to reference concrete was 13.59%, 26.44%, 25.09% and 15.82% for 7 days, 28 days, 56 days, and 90 days respectively.. It was also observed that the 3 day strength of geopolymer concrete is equivalent to 7 days strength of reference concrete and the strength attained by conventional concrete in 56 days has been achieved by geopolymer concrete in 28 days. The strength development of geopolymer concrete at 7 days with respect to it’s 28 days strength was 61.58%, at 28 days with respect to 56 days strength was 74.43% and at 56 days with respect to 90 days strength was 98.62%. Therefore Therefore, the compressive strength of geopolymer concrete at all ages is greater than that for conventional concrete. 4.1.2.

Variation of Split tensile strength with age

Figure 2 represents the variation of split tensile strength of GPC and NC with age.

Split tensile strength (MPa)

Split Tensile strength test results 4 3.5 3 2.5 2 1.5 1 0.5 0

3 days

7 days

28 days

56 days

90 days

GPC

1.53

1.89

2.71

2.98

3.42

NC

1.15

1.58

2.22

2.60

2.90

Figure 2. Variation of split tensile strength with respect to age

It can be observed that the split tensile strength of geopolymer concrete and normal concrete (conventional concrete) increases with increase in age. The test results show that the spilt tensile strength of geopolymer concrete is only a fraction of the compressive strength, as in the case of Portland cement concrete; it’s 28 days split tensile strength is about 7.1% of its corresponding compressive strength. h. Split tensile strength of geopolymer concrete at all ages


153

is greater than that for reference concrete. However However, the trend of strength development for geopolymer concrete and normal concrete is similar.

4.2.

Durability Studies


4.2.1. Exposure to alternate wetting and drying Tests were performed to study the resistance of geopolymer concrete and normal concrete when exposed to alternate nate wetting and drying cycles for a period of upto 90 days (45 cycles). cycles) The unexposed specimens were leftt undisturbed at the room temperature. At the end of 30, 60 and 90 days, exposed and unexposed geopolymer and reference concrete specimens were tested for compressive strength for evaluating the strength loss. Figures 3 and 4 give the compressive strengths of exposed and unexposed GPC and NC specimens and percentage loss of strength when exposed to alternate wetting and drying cycles. Alternate wetting and drying cycles 60 50 40 30 20 10 0

Unexposed (GPC)

Unexposed (NC)

Exposed (GPC)

Exposed (NC)

1 month

32.68

30.54

29.70

22.81

2 month

37.21

38.08

31.87

26.52

3 month

53.10

42.22

44.14

28.18

Figure 3. Compressive ompressive strength of GPC and NC unexposed and exposed to alternate wetting and drying conditions.

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% loss of strength

Loss of strength of GPC and NC under alternate wetting and drying cycles 35 30 25 20 15 10 5 0

1 month

2 month

3 month

Percentage loss of strength (GPC)

10.03

16.76

20.30

Percentage loss of strength (NC)

25.31

30.35

33.25

Figure 4. Loss of strength of GPC and NC under alternate wetting and drying cycles

Figure 3 represents the compressive strengths strength of geopolymer concrete and normal concrete concrete, unexposed and exposed to alternate wetting and drying cycles. It can be observed from figure 4 that the percentage loss of strength increases with the increase in duration of exposure for both GPC and NC. The percentage loss of strength in geopolymer concrete is found to be less than that for normal concrete at the eend nd of 1, 2 and 3 months. Thus, geopolymer concrete fares much better than normal concrete when exposed to alternate wetting and drying conditions. 4.2.2. Exposure to elevated temperature


The geopolymer and reference concrete specimens were subjected to temperatures res of 2000C, 4000C, 6000C and 8000C for a constant duration of 4 hours to assess their resistance to elevated temperature. Compressive strength strengths of unexposed specimens were also ascertained to evaluate loss of strength. Figures 5 and 6 show the variations of compressive strength and percentage loss of strength in relation to unexposed specimens for both GPC and NC respectively. Elevated temperature (4 hours) [GPC & NC] 35.00 30.00 25.00 20.00 15.00 10.00 5.00 0.00

200°° C

400° C

600° C

800° C

Geopolymer concrete

31.00

28.20

25.46

23.09

Normal concrete

24.05

22.79

19.49

9.55

Figure 5. Compressive ompressive strength of GPC and NC subjected to elevated temperature.


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% loss of strength

Loss of strength under elevated temperature 70 60 50 40 30 20 10 0

200° C

400° C

600° C

800° C

Percentage loss of strength (GPC)

10.51

18.59

26.50

33.34

Percentage loss of strength (NC)

14.56

19.04

30.76

66.07

Figure 6: Loss of strength of GPC and NC exposed to elevated temperature. It is noticed from figure 5 that the geopolymer concrete possess higher strength retention capacity compared to reference concrete when exposed to varying elevated temperatures from 2000C to 8000C for a constant duration of 4 hours. Further, figure 6 reveals that the percentage loss of strength of geopolymer concrete and normal concrete increases with increase in temperature. It is also observed from figure 6 that GPC suffers much lesser deterioration compared to conventional concrete under elevated temperature. Thus, GPC performs much superior to OPC concrete when exposed to elevated temperature. 5. Conclusions Based on the test results the following broad conclusions can be drawn: Ø Ambient cured fly ash–ground granulated blast furnace slag (GGBS) based geopolymer concrete develops the required compressive strength at the specified age and hence can be used for structural application. Ø Compressive strength of Geopolymer concrete at any particular age up to 90 days was found to be more than the corresponding strength of conventional concrete for same proportion. Ø Split tensile strength of geopolymer concrete bears almost the same ratio with it’s compressive strength as for OPC concrete. Ø Geopolymer concrete attained the required compressive strength of 20N/mm 2 at the age of 7 days itself. Ø Geopolymer concrete performs superior to it’s OPC counterpart when exposed to alternate wetting and drying conditions and elevated temperature. Acknowledgement The authors gratefully acknowledge the support extended by the respective institutes in bringing out this article.

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