Scholarly article on topic 'The Effect of Temperature and Duration of Curing on the Strength of Fly Ash Based Geopolymer Mortar'

The Effect of Temperature and Duration of Curing on the Strength of Fly Ash Based Geopolymer Mortar Academic research paper on "Materials engineering"

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Procedia Engineering
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{"Geopolymer mortar" / "Fly ash" / "Alkaline activator" / "Heat curing" / "Duration of curing"}

Abstract of research paper on Materials engineering, author of scientific article — Andi Arham Adam, X.X.X. Horianto

Abstract The optimum temperature and duration of curing is essential in geopolymerization reaction to achieve higher strength. As such, fly ash based geopolymer mortars were prepared by varying the curing temperature of 80, 100 and 120°C, for the duration of 4, 6 and 20hours. The fly ash was activated by sodium silicate and sodium hydroxide solution. The dosage of activator was 55% and the ratio between sodium silicate and alkaline activator was 1: 2. The results show that the highest compressive strength was obtained at the temperature and duration of curing of 120°C and 20hours.

Academic research paper on topic "The Effect of Temperature and Duration of Curing on the Strength of Fly Ash Based Geopolymer Mortar"

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Procedía Engineering 95 (2014) 410 - 414

Procedía Engineering

www.elsevier.com/locate/procedia

2nd International Conference on Sustainable Civil Engineering Structures and Construction

Materials 2014 (SCESCM 2014)

The effect of temperature and duration of curing on the strength of

fly ash based geopolymer mortar

Andi Arham Adam*, Horianto

Department of Civil Engineering, Tadulako University, Palu 94118, Indonesia

Abstract

The optimum temperature and duration of curing is essential in geopolymerization reaction to achieve higher strength. As such, fly ash based geopolymer mortars were prepared by varying the curing temperature of 80, 100 and 120°C, for the duration of 4, 6 and 20 hours. The fly ash was activated by sodium silicate and sodium hydroxide solution. The dosage of activator was 55% and the ratio between sodium silicate and alkaline activator was 1 : 2. The results show that the highest compressive strength was obtained at the temperature and duration of curing of 120°C and 20 hours.

© 2014TheAuthors.PublishedbyElsevierLtd.Thisisan open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).

Peer-review underresponsibility oforganizingcommittee of the 2nd International Conference on Sustainable Civil Engineering Structures and Construction Materials 2014

Keywords: Geopolymer mortar; Fly ash; Alkaline activator; Heat curing; Duration of curing

1. Introduction

The high CO2 emission contribution of cement industries has led some researchers to find solutions to minimize its impact. One of the promising alternatives is to use fly ash as part or total replacement of cement in concrete. The total replacement of cement has been possibly made since the introduction of geopolymer by Davidovits in 1979 [1]. At room temperature the geopolymeric reaction will take place very slowly as such oven curing is favourable [2]. During curing process, the geopolymer mortar and concrete will undergo polymerization reaction. At higher

* Corresponding author. Tel.: +6281387408555; fax: +62-451-422844. E-mail address:adam.arham@gmail.com

1877-7058 © 2014 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.Org/licenses/by-nc-nd/3.0/).

Peer-review under responsibility of organizing committee of the 2nd International Conference on Sustainable Civil Engineering

Structures and Construction Materials 2014

doi:10.1016/j.proeng.2014.12.199

temperature this reaction will take place faster and about 70% of the strength of geopolymer mortar and concrete will be achieved within 3 to 4 hours heat curing [3]. Khale and Chaudhary [4] concluded that 30° to 90°C was the effective range of curing temperature that ensure the geopolymeric reaction will occur effectively. The effect of heat curing on the strength of geopolymer have been reported elsewhere however the optimum temperature and duration varied among the researchers as presented in Table 1. The variations of curing temperature are manly influenced by physical and chemical characteristic of fly ash as well as the chemical composition of the activators.

Table 1. Curing regimes on fly ash based geopolymer [5].

No Range Optimum Researcher

1 30, 60, 91°C for 24 hours 60°C 24h Hardjito

2 30, 75°C for 24 hours 60°C 24h Sindhunata

3 75, 95°C for 6 and 24 hours 60°C 24h Bakharev

4 45, 65, 85°C for 24 hours 60°C 24h Fernandez-Jimenez and Palomo

2. Materials and methods

Class F fly ash (Table 2) taken from local power plant station was used as row materials. The activator consists of sodium silicate solution (Na2O = 15.4% and SiO2 = 32.33%) and 10M sodium hydroxide solution. The activator dosage (activator / fly ash) was 55% and the ratio of sodium silicate to activator was 1 : 2.

Local sand was used as fine aggregate. The specific gravity and fineness modulus of sand were 2.6 and 2.75 respectively.

The geopolymer mortar was prepared using water to solid ratio (w/s) 0.35. The water content is the total water in activator and additional water whilst the solid is the fly ash and solid part of the activator. The ratio of fly ash to sand was 1 : 2.75

Table 2. Oxide composition of fly ash.

Oxides Mass (%)

SiO2 55.540

Fe2O3 23.760

AI2O3 14.020

CaO 2.020

K2O 1.580

SO3 1.300

TiO2 0.920

MnO 0.291

SiO2 55.540

Fe2O3 23.760

Al2O3 14.020

The mix design of mortar (Table 3) was adopted from Adam et al. [6], with some modification due to the difference in molarity of NaOH.

The mix was prepared using a 5-liter Hobart mixer. The mix was cast in 50 mm cube, in accordance with SNI 066825-2002. The mortar samples were sealed with cling wrap and left at room temperature for 3 hours before subjected to oven curing at 80°C, 100°C and 120°C for 4, 6, and 20 hours. Another set of samples were exposed to outside weather (air cured). In Addition, OPC mortar with 0.5 w/c ratio and sand-cement ratio (S/C) of 2.75 was

also cast for comparison. Compressive strength test was conducted at the age 3, 7, 14, and 28 days. The average strength of five samples was obtained for each curing regime.

Table 3. Mix composition .

Fly ash 2.1.1. S and (kg) Activator (kg) 2.1.2. Added

(kg) Na2SiÜ3 (liquid) NaOH (10M) water (kg)

0.516 1.420 0.142 0.142 0.046

3. Results and discussions

3.1. The effect of heat curing on strength

Strength of geopolymer mortar cured at 80°C for 4 hours at the age of 3, 7, 14 and 28 days as presented in Fig. 1 were 1.16, 3.16, 6.28, and 11.75 MPa respectively. For duration of 6 hours, the strengths were 5.04, 6.56, 8.64, and 12.50 MPa and for duration of 20 hours, the strengths were 17.12, 19.20, 19.36, and 19.40 MPa.

Specimens cured at 80°C for 4 and 6 hours exhibited lower compressive strength compared to the one cured for 20 hours, however there was a linear increase in strength of the 4 and 6 hours cured specimens compared to the 20 hours cured specimens which was constant at 7 days age. Moreover the 4 and 6 hours cured specimens behaved similarly with air cured specimens. This suggests that at 4 and 6 hours duration, the geopolymer mortar did not get enough heat to complete the geopolymer reaction at earlier age therefore the reaction took place at later age at slower rate. For the specimens cured for 20 hours, the reaction was completed at 7 days and reach maximum strength.

80°C for 4 hrs -*-80°C for 6 hrs

-• 80°C for 20 hrs —♦—Air cured

0 7 14 21 28

Age (days)

Fig. 1. Compressive strength of geopolymer mortar cured at 80° for 4, 6, and 20 hours.

Significant increase in strength was found on geopolymer mortar cured at 100°C as presented in Fig. 2. At the age of 3, 7, 14 and 28 days, the strengths of 4-hours curing specimens were 11.68, 12.88, 13.24, and 13.45 MPa respectively. For duration of 6 hours, the strengths were 16.28, 16.68, 17.80, and 18.50 and for duration of 20 hours, the strengths were 20.68, 21.16, 21.36, and 21.90 MPa.

Regardless of curing duration, all the specimens cured at 100°C, have reached their maximum strength which can be observed by almost constant strength at the age of 3 days and beyond. However, there was a significant gain in strength as the duration increased from 4 to 20 hours.

The strengths of geopolymer mortar cured at 120°C for 4 hours at the age of 3, 7, 14 and 28 days as presented in Fig. 3 were 11.68, 13.20, 13.52, and 14.30 MPa respectively. For duration of 6 hours, the strengths were 16.28, 17.80, 17.92, and 19.60 MPa and for duration of 20 hours, the strengths were 27.68, 32.16, 33.04, and 33.10 MPa. Specimens cured for 20 hours at 120°C shows significant increase in strength compared to the 4 and 6 hours specimens and reached its maximum strength (33 MPa) at 7 days.

Fig. 2. Compressive strength of geopolymer mortar cured at 100°C for 4, 6, and 20 hours.

Fig. 3. Compressive strength of geopolymer mortar cured at 120°C for 4, 6, and 20 hours.

3.2. Strength comparison of OPC mortar, air cured and heat cured geopolymer mortar

The strength development of air and heat cured geopolymer mortar compared to OPC mortar is presented in Fig. 4. It can be seen that the heat cured geopolymer mortar exhibited higher strength as compared to OPC mortar and air cured geopolymer mortar however no further increase in strength after 14 days was observed in heat cured geopolymer mortar. The air cured geopolymer mortar has the lowest early strength but continue to increase at constant rate.

Fig. 4. Strength comparison of OPC mortar, air cured and heat cured geopolymer mortar.

4. Conclusions

The temperature and duration of heat curing plays a major role for the strength development of fly ash based geopolymer mortar. The optimum heat curing regime in this study was at 120° for 20 hours.

Acknowledgments

• The Directorate General for Higher Education, Ministry of Education and Culture, for funding this research

• PLTU Tawaeli for providing fly ash for this research

References

[1] J. Davidovits, 30 Years of Successes and Failures in Geopolymer Applications. Market Trends and Potential Breakthroughs, in Geopolymer Conf. 2002,Melbourne, Australia, 2002.

[2] A.V. Kirschner, H. Harmuth, Investigation of geopolymer binders with respect to their application for building materials. Ceramics-Silikaty, 2004, 48(3),pp. 117-120.

[3] D.L.Y. Kong, J.G. Sanjayan, K. Sagoe-Crentsil, Factors affecting the performance of metakaolin geopolymers exposed to elevated temperatures, in Journal of Materials Science, Springer Science & Business Media B.V., 2008, pp. 824-831.

[4] D. Khale, R. Chaudhary, Mechanism of geopolymerization and factors influencing its development: a review. Journal of Materials Science, 2007, 42(3),pp. 729-746.

[5] X. Song, Development and Performance of Class F Fly Ash Based Geopolymer Concretes against Sulphuric Acid Attack, in School of Civil and Environmental Engineering,The University of New South Wales, Sydney, 2007.

[6] A. A. Adam, I. Patnaikuni, D.W. Law, T.K. Molyneaux, Strength of Mortar Containing Activated Slag and Fly Ash, in The 23rd Biennial Conference of the Concrete Institute of Australia, Concrete Institute of Australia, Adelaide, Australia, 2007.