Strength & Development of Fly ash and GGBS Based Geopolymer Mortar

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International Journal of Recent Advances in Engineering & Technology (IJRAET)

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ISSN (Online): 2347 - 2812, Volume-3, Issue -1, 2015 42

Strength & Development of Fly ash and GGBS Based Geopolymer Mortar

1Banda Rohit Rajan, ²K.Ramujee

1Department of Civil Engineering VNRVJIET Hyderabad, Telangana, India

2Associate professor M.Tech (PhD) Department of Civil Engineering VNRVJIET Hyderabad, Telangana, India E-mail: ¹[email protected]

Abstract — In this paper, the properties of geopolymeric binder prepared using the source materials such as Fly Ash and Ground Granulated Blast Furnace Slag (GGBS) without using any conventional cement have been investigated. The individual properties of the mortar such as setting time, normal consistency, slump test, compressive strength, were determined as per relevant Indian and ASTM standards. The different parameters considered in this study are the proportion of binder components, the ratio of Na2SiO3 / NaOH and the alkaline liquid to binder ratio. The various combinations of fly ash and GGBS considered are 90% & 10%, 80% & 20%, 70% & 30%.

The ratio of Na2SiO3 /NaOH is taken as 2 and 2.5 and the alkaline liquid to binder ratio as 0.45. The test results reveal that the geopolymer mortar develops the strength even at ambient conditions. Compressive strength increases with an increase in the quantity of GGBS. It was also found that geopolymer mortars made with Na2SiO3 /NaOH ratio as 2.5 & alkaline liquid to binder ratio as 0.45 produces higher strength. It can be concluded that the results of geopolymer mortars are high when compared with conventional mortars in terms of strength.

Keywords — Geopolymer Mortar, Fly ash, GGBS, Binder, Alkaline liquid, Strength

I. INTRODUCTION

Geopolymers are inorganic polymeric binding materials, firstly developed by Joseph Davidovits in 1970s.

Geopolymerisation involves a chemical reaction between solid alumino-silicate oxides and alkali metal silicate solutions under highly alkaline conditions yielding amorphous to semi-crystalline three-dimensional polymeric structures, which consist of Si-O-Al bonds. The geopolymerisation reaction is exothermic and takes place under atmospheric pressure at temperatures below 100°C.

Fly ash, which is rich in silica and alumina, has full potential to use as one of the source material for Geopolymer binder. It is the main solid waste generated from the coal combustion in the power stations. Since the worldwide electric power industry relies heavily on the use of coal as a primary energy source, enormous quantities of fly ash are generated every year. Presently, as per the Indian Ministry of Environment

and Forest figures, only 20% to 30% of fly ash is used in manufacturing cements, construction, concrete, block and tiles and some disposed off in landfills and embankments, but a huge amount of fly ash is unutilized which causes several environmental problems of the air, soils and surface and ground-water pollution.

Recent works on the Geopolymerisation of fly ash, reported production of geopolymeric materials with high mechanical strength, low density, less water absorption, negligible shrinkage and significant fire and chemical resistance. Due to these properties, Geopolymeric materials are viewed as an alternative to Portland cement for certain industrial applications in the areas of construction, transportation, road building, aerospace, mining and metallurgy. Significant research work on geopolymer concrete manufactured from fly ash in combination with sodium silicate and sodium hydroxide solution has been carried out by Rangan B.V. et al., [9]. The authors have reported higher strength and better durability of geopolymer concrete than Portland cement concrete.

II. LITERATURE REVIEW

According to the American Concrete Institute (ACI) Committee 116R, fly ash is defined as ‘the finely divided residue that results from the combustion of ground or powdered coal and that is transported by flue gasses from the combustion zone to the particle removal system’ (ACI Committee 232 2004).

It is generally known that GGBS can improve the durability of a concrete structure by reducing the water permeability, increasing the corrosion resistance and increasing the sulphate resistance. The improved properties can extend the service life of structures and reduce the overall maintenance costs. Based on a life cycle prediction model, the service life of a Maryland bridge deck was estimated to have increased from 38 years to 75 years with the use of concrete incorporating 40% GGBS replacement (Slag Cement Association, 2005).

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The most common alkaline liquid used in geo polymerisation is a combination of sodium hydroxide (NaOH) or potassium hydroxide (KOH) and sodium silicate or potassium silicate (Davidovits 1999; Palomo. 1999; Barbosa. 2000; Xu and van Deventer 2000; Swanepoel and Strydom 2002; Xu and van Deventer 2002). The use of a single alkaline activator has been reported (Palomo. 1999; Teixeira-Pinto. 2002),

Palomo (1999) concluded that the type of alkaline liquid plays an important role in the polymerisation process.

Reactions occur at a high rate when the alkaline liquid contains soluble silicate, either sodium or potassium silicate, compared to the use of only alkaline hydroxides.

Xu and van Deventer (2000) confirmed that the addition of sodium silicate solution to the sodium hydroxide solution as the alkaline liquid enhanced the reaction between the source material and the solution. Furthermore, after a study of the geo polymerisation of sixteen natural Al-Si minerals, they found that generally the NaOH solution caused a higher extent of dissolution of minerals than the KOH solution.

III. EXPERIMENTAL WORK

1.1 Materials 2.1.1 Fly ash

The In the present experimental work, low calcium, Class F (American Society for Testing and Materials 2001) dry fly ash obtained from the silos of Ramagundam thermal power station, Telangana, which was used as the base material.

Oxide Mass (%) SiO2 56.01 Al2O3 29.80 Fe2O3 3.58 TiO2 1.75 CaO 2.36 MgO 0.30 K2O 0.73 Na2O 0.61 SO3 NIL P2O5 0.44 LOSS ON IGNITION 0.40

2.1.2 Alkaline activator

The alkaline activator liquid used was a combination of sodium silicate solution and sodium hydroxide. The sodium silicate solution (Na2O = 14.7%, SiO2 =29.4% and 55.9%

water) with silicate modulus of 2.0 and a bulk density of 1390 kg/m3 P and an analytical grade sodium hydroxide in pellets form (Prince Chemicals Ltd., NaOH with 98% purity) was used to adjust the composition of activating solution. The

activator solution was prepared at least one day prior to its use in specimen casting.

2.1.3 Fine aggregate

The fine aggregate was river sand obtained from local source.

The specific gravity of sand was 2.54 and fineness modulus of the sand was 2.65. As per IS 383- 1976, the particle size distribution of sand shows that it is in zone II.

1.2 Preparation of geopolymer specimens 1.2.1 Mix proportions

MORTAR SAMPLES

a) We are done by the 3 ratios of mortar samples:

b) Ratios =1:1,1:1.5,1:2

c) For a cube of size 100 x 100 x 100 mm:

FOR 1:1 RATIO CALCULATION

Weight= 0.1×0.1×0.1×2200×1.2×3 Total weight of material=7.92kg/m³ Weight of cement=7.92/2

Weight of cement=3.96kg

Weight of fine aggregate = (total weight of material) – (weight of cement) = 7.92 - 3.96 =3.96kg

And W/c= 0.38 Water= cement×0.38

Water=3.96×0.38=1.504kgs

TOTAL CASTING CUBES =171 Unit weight of Geopolymer mortar = 2200kg/m³

Aggregate to Binder ratio = 1:1

Mass of Fine Aggregates = 50% of 2200 = 1100 kg/m³ Mass of Binder = 2200-1100 = 1100 kg/m³ Assume,

Alkaline liquid/ Binder Ratio = 0.45 Mass of alkaline liquid = 495kg/m3 Assume,

Sodium silicate/sodium hydroxide = 2.5 Mass of sodium hydroxide = 495/3.5

= 150 kg/m³ For 8 Molar,

Sodium hydroxide solid = 26.23% of 150

= 39.345 kg/m³

Water = 110.655 kg/m³

Mass of sodium silicate = 495-150 = 345kg/m³ Mass of sodium silicate gel = 44.1% of 345

= 153.18 kg/m³ Mass of water = 188.82 kg/m³

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Table 1.1- Percentage of Sodium Hydroxide Flakes in Various Molarity

SODIUM HYDROXIDE SOLUTION %

NaOH 6M 21.21

NaOH 8M 26.23

NaOH 10M 31.37

NaOH 12M 36.0

NOTES:

Molarity = moles of solute/liter of solution Alkaline liquid-to-Fly Ash ratio: 0.45

Sodium Silicate-to-Sodium Hydroxide ratio: 2.5

Table-1.2 showing proportions for different molarities of NaOH solution

Mo la rity

Na2Si O3

/Nao H

Alk Liq /Flyas h

Fine Agg kg/m³

Binde r (kg/m

3)

Alkali Liq

Sodium Silicate

Noah + water

Noah flakes

8 2.5 0.45 1100 1100 495 345 150 39.54

12 2.5 0.45 1100 1100 495 345 150 39.54

2.2.2 Mixing, curing and testing procedure

For making geopolymer mortar specimens of various test series, fly ash and alkaline activating solution in desired proportion were first mixed together in Hobart mixer for five minutes. The sand was then slowly added and mixed for another five minutes. The fresh mortar mix had good consistency and glossy appearance. The fresh mortar was then filled in 100mmx100mmx100mm steel moulds and vibrated for two minutes on vibration table to remove entrapped air. The specimens were left undisturbed to room temperature for 120 minutes before curing in an oven at 85°C for 48 hours under atmospheric pressure and uncontrolled humidity conditions. The samples were demoulded after cooling down to room temperature and left to air curing (drying) until tested for direct compression in a digital compression testing machine at the age of 3, 7 and 28 days.

The reported compressive strength is average strength of three specimens.

IV. RESULTS AND DISCUSSIONS

Table 1.3: Compressive strength results for Geopolymer Mortar at 3 days Sun & Oven Curing

S.

NO

w/c Calcined Source material combination

COMPRESSIVE STRENGTH N/mm²

Fly ash GG

BS

Sun curing Oven curing

8 Molarity 12 Molarity

8 Molarity

12 Molarity

1 0.45 100 0 41 45 52 53

2. 0.45 90 10 43.5 47 54.5 45

3. 0.46 50 50 48 55 56 56

4. 0.47 10 90 72 85 91 90

5. 0.47 0 10 78 88 95 96

Fig 1. Variation of Compressive Strength in 8M, 12M for 3- days curing in sun and oven

Table 1.4: Compressive strength results for Geopolymer Mortar at 7 days Sun & Oven Curing

Fig 2. Variation of Compressive Strength in 8M, 12M for 7- days curing in sun and oven

S.

No

ratio w/c Calcined Source material combination

AVG compressive strength N/mm²

sun curing oven curing Fly

ash

%

GGB S%

8M 12

M

8M 12M

1 1:1 0.46 100 0 14.5 23.5 18.8 27.8

0 100 57.3 66.5 62.6 69.8

2 1:1.5 0.48 100 0 13.3 27 13 25.5

0 100 42.6 79.3 44.6 69.3

3 1:2 0.50 100 0 16.3 23.1 19.8 12.1

0 100 57.3 58.8 50.8 70.3

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IV CONCLUSIONS

1. It is observed that geopolymer mortar in ambient curing conditions can obtain good strength in 28 days.

2. Compressive strength increases around 40% to 50%

from 7 days to 28 days.

3. Higher concentration (in terms of molarity) of sodium hydroxide solution results in higher compressive strength of fly ash-based geopolymer mortar.

4. Workability of geopolymer mortar decreases with the increase in concentration of sodium hydroxide.

5. Lesser sorptivity has been recorded for the cubes prepared with 12 molar sodium hydroxide when compared to the cubes prepared with 10 and 8 molar sodium hydroxide.

6. 18% to 30% economy is achieved in geopolymer mortar when compared to cement mortar.

V REFERENCES

[1] In Concrete. Farmington Hills, Michigan, ACI Committee 232 (2004). Use of Fly Ash USA, American Concrete Institute: 41.

[2] Bakharev, T. (2005b). Geopolymeric materials prepared using Class F fly ash and elevated temperature curing. Cement and Concrete Research [3] Geopolymer Chemistry and Properties. Paper

presented at the Davidovits, J. (1988b). First European Conference on Soft Mineralurgy, Compiegne, France.

[4] Hardjito, D. and Rangan, B. V. (2005) Development and Properties of Low-Calcium Fly Ash-based Geopolymer Concrete, Research Report GC1, Faculty of Engineering, Curtin University of Technology, Perth.

[5] Hardjito, D., Wallah, S. E., & Rangan, B. V. (2002a).

Research into Engineering Properties of Geopolymer Concrete. Paper presented at the Geopolymer 2002 International

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