Effect of Curing Regime on Properties 
of Geopolymer Mixtures Containing Basic Oxygen Furnace Slag (BOFS) Aggregates

Student: Zarina Onopriyenko 		Research Supervisor: Professor Chang-Seon Shon






Outline

Introduction
Research Background
Research Objectives
Research Methodology
Results and Discussion
Conclusion
Limitations and Recommendations
References



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Introduction

OPC (Ordinary Portland cement) concrete-widely used construction material.
It consists of cement, water and fine and coarse aggregate.

Cement manufacture generate an overall 1.25 tons of CO₂ per ton of cement [1]. It devotes up to 7% of entire CO₂ emission to the atmosphere worldwide [2].

The cause of global warming is greenhouse gases, one of them is the emission of carbon dioxide (CO₂). 

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Figure 1. OPC production
Figure 2. Global warming







Introduction

Geopolymer material:
Alternative construction material for OPC.
Environmentally friendly in terms of limiting greenhouse gas emissions (cementless) and utilizing industrial by-product materials.

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Figure 3. Geopolymer






Introduction

Basic oxygen furnace slag (BOFS): 
BOFS is a by-product of steel industry.
Over 160 million tons of by-products from the steel industry originate annually [3]. 
BOFS can be utilized as a binder and aggregate in geopolymer manufacture if the problem of BOFS is solved.


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Figure 4. BOFS






Research Background

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The utilization of by-products in construction materials sphere solve two problems:
Environmental/Ecological;
Economical [4].

Basic Oxygen Furnace Slag (BOFS) usage as an aggregate in concrete composition develops:
Mechanical properties;
Microstructural properties;
Durability properties.

Figure 5: By-products of steel and iron industry. Source: Diproinduca





Research Background: Problem Statement

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Free Calcium oxide and Magnesium oxide in the components of steel slag causes expansion of concrete structure during its utilization [6].

f-CaO and f-MgO have low reactivity, thus their hydration occurs after a long period of time.

It causes soundness problems, as the hydration of f-CaO and f-MgO causes internal stress in the matrix of concrete, thus the pores merge into one causing volume instability [7]. 
According to Wang et al. (2010),  the volume increase of concrete ranges from 91.7% to 119.6% as a result of the f-CaO and f-MgO hydration process  [5].
How to control the volumetric expansion of BOFS?
How to minimize CO2 emission (How to utilize CO2)?

f-CaO + H2O → Ca(OH) 2
f-MgO + H2O → Mg(OH) 2





Research Background: Solution for Problem

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During the geopolymerization reaction, vast amount of free silica leaves unreacted.

Sodium silicate and binder are the source of free silica.

Thus, f-CaO and f-MgO react with free silica to form stable compounds, as a result the volume expansion is inhibited [8].
Reaction of f-CaO and f-MgO with CO₂ during carbonization process forms stable and insoluble compound such as calcium carbonate (CaCO₃) [9]. 
f-CaO + SiO2 →CaSiO3
f-MgO + SiO2 →MgSiO3
f-CaO + CO2 → CaCO3
f-MgO + CO2 → MgCO3
Ca(OH)2 + CO2 → CaCO3  + H2O





Research Objectives

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Curing Regimes:
Steam curing (6hr and 12hr);
Water curing;
Ambient curing;
Steam curing(6hr and 12 hr) + CO2 curing (6hr, 12hr and 24hr).

Aggregate combination:
100% BOFS;
75% BOFS+25% Sand;
50% BOFS + 50% Sand.


Aim of this work is to study: 
The effect of curing regime;
The effect of specific curing regime duration;
The effect of aggregate combination;
on the properties of BOFS-based geopolymer
Vast amount of research are conducted on:
Studying the properties of BOFS-based geopolymer. 
However the number of research on the effect of different curing regimes on the properties of BOFS-based geopolymer are limited.





Overall Experimental Program

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Figure 6. Experimental program





Cementitious materials properties
The specific gravities of FA and GGBFS are 1.80 and 2.94 respectively. 

Table 1. Chemical composition of FA and GGBFS (%).
Figure 7. XRD of FA and GGBFS
		SiO2	Al2O3	Fe2O3	TiO2	CaO	MgO	Na2O	K2O	P2O5	SO3
	FA	62.15	20.39	10.53	-	3.72	0.1	-	1.31	0.99	0.24
	GGBFS	23.97	5.9	0.88	2.74	57.99	3.75	-	1.12	-	2,47

Figure 8. PSD of FA and GGBFS
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Fine aggregate properties
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	Table 2. Grading Requirement		
	Passing, sieve #	Retained, sieve #	Weight, %
	4	8	10
	8	16	25
	16	30	25
	30	50	25
	50	100	15






Fine aggregate properties
	Fine aggregate	Specific gravity (SG)	Absorption capacity (AC)
	BOFS	2.7	8.91%
	Sand	3.3	1.84%

Table 3. SG and AC of fine aggregates
		CaO	Fe2O3	SiO2	MnO	MgO	Al2O3	SO3	TiO2	K2O	P2O5
	BOFS	52.38	29.39	7.39	4.33	3.13	1.53	0.23	-	-	-
	Sand	16.27	13.81	54.51	1.51	0.78	5.71	0.51	1.73	3.65	0.63

Table 4. Chemical composition of BOFS and RS (%).
Figure 9. XRD of BOFS
Figure 10. XRD of Sand
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Mixture Design
Variables:
Curing method/duration
BOFS to Sand ratio

Fixed:
GGBFS to FA ratio
Alkali activated solution (AAS) content
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Table 5. Mix design parameters





Samples preparation

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	Description	Tests			
		Compressive strength	Dielectric constant	Drying shrinkage	1M NaOH and water expansion
	Size (mm)	50×50×50	70×70×70	25×25×285	25×25×285
	Number of specimens	16	2	4	8
	Testing age	3, 7, 28 and 56-day	3, 7, 31-day interval	3, 7, 31-day interval	3 and 7-day interval
	Volume (m³)	2.000×10⁻³	0.686×10⁻³	0.712×10⁻³	1.425×10⁻³
	Total volume (m³)	(4.823×10⁻³) × 10%=5.305×10⁻³			

Table 6. Quantity of samples and mixture volume calculation





Research Methodology

Curing regimes: 


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Figure 11. Steam curing




Steam curing
Vapor curing method under atmospheric pressure conditions.
Usually carried out at a temperature from 40 to 100℃
In the current work curing is carried out at 80 ℃.
CO2 curing
Is carried out in a special storage tank under specific temperature, humidity, and CO₂ concentration.
The temperature is set up at 23℃, humidity at 50%, and CO₂ concentration at 20%.

Figure 12. CO2 curing
 





Research Methodology

Curing regimes: 


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Figure 13. Ambient and water curing
Ambient air curing
Curing under room temperature and normal atmospheric pressure.


Water curing
Carried out by following the ASTM C511 [10] standard specification.
Lime added to the potable water to prevent the washout of calcium hydroxide.








Test Methods: Fresh Properties

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Figure 14. Flowability test
Figure 15. Air content test





Test Methods: Hardened & Durability Properties
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Figure 16. Compressive strength test
Figure 17. Dielectric constant test
Figure 18. Drying shrinkage test
Figure 19. 1M NaOH and water expansion test





Test Methods: Microstructural Properties

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Figure 22. FTIR
Figure 20. XRD
Figure 21. SEM





Test Results & Discussion
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Flowability and Air content

Figure 23. Flowability
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Figure 24. Air content







Compressive Strength
Figure 25. Compressive strength
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(a) Steam curing 6hr
(b) Steam curing 12hr
(c) Ambient air curing
(d) Water curing
(e) Steam curing 6hr + CO2(6,12,24hr)
(f) Steam curing 12hr + CO2(6,12,24hr)











Dielectric constant
Figure 26. Dielectric constant
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(a) Steam curing 6hr
(b) Steam curing 12hr
(c) Ambient air curing
(d) Water curing
(e) Steam curing 6hr + CO2(6,12,24hr)






(f) Steam curing 12hr + CO2(6,12,24hr)





Drying Shrinkage (length)

Figure 27. Drying shrinkage (length loss)
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(a) Steam curing 6hr
(b) Steam curing 12hr
(c) Ambient air curing
(d) Water curing
(e) Steam curing 6hr + CO2(6,12,24hr)






(f) Steam curing 12hr + CO2(6,12,24hr)





Drying Shrinkage (mass)

Figure 28. Drying shrinkage (mass loss)
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(a) Steam curing 6hr
(b) Steam curing 12hr
(c) Ambient air curing
(d) Water curing
(e) Steam curing 6hr + CO2(6,12,24hr)
(f) Steam curing 12hr + CO2(6,12,24hr)











Expansion

Figure 29. 1M NaOH expansion test
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Figure 30. Water expansion test







X-ray Diffraction (XRD) 

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Figure 31. Crystalline phases








Scanning Electron Microscope (SEM)
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C-A-S-H
FA
 
 
C-A-S-H
Figure 33. SEM image ambient cured sample (M6)
Figure 32. SEM image steam cured sample (M2)





Scanning Electron Microscope (SEM)
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FA
C-A-S-H
		С	O	Na	Mg	Al	Si	K	Ca	Ti	Total
	Mass, %	13.44±0.15	50.83±0.29	3.38±0.07	1.33±0.04	6.79±0.08	17.36±0.13	0.33±0.02	6.30±0.08	0.23±0.02	100.00
	Atom, %	20.21±0.23	57.37±0.33	2.66±0.06	0.99±0.03	4.55±0.05	11.16±0.08	0.15±0.01	2.84±0.04	0.09±0.01	100.00

Figure 34. SEM image water cured sample (M8)
Table 7. EDS analysis





Fourier-transform infrared spectroscopy (FTIR)

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Figure 35. FTIR





Conclusion
The highest relative flowability was obtained for the geopolymer mixture with a BOFS/Sand ratio of 75/25, and the lowest value was obtained for the mixture with a BOFS/Sand ratio of 100/0.The air content of mixtures increases with the decrease of BOFS aggregate content.

Steam curing and the combined steam and CO₂ curing enhanced the compressive strength, prevented the shrinkage strain and 1M NaOH expansion  of the BOFS-based geopolymer mixture compared to water and ambient curing regimes. The water expansion characteristic was not affected by the curing regime. Water curing curing supported the dielectric constant value with the time, while the CO₂, steam and ambient curing decreased the dielectric constant value.

Steam curing duration only affected the early-age compressive strength, longer duration is preferable. The longer duration of steam curing results in less drying shrinkage and  less expansion fluctuation. 

The longer CO₂ curing duration promoted the formation of stable calcium carbonate compounds, thus enhancing the compressive strength, stabilizing the expansion curve fluctuation and reducing the shrinkage strain of only 6-hour steam cured samples. The duration of steam and CO₂ curing do not affect the dielectric constant value.

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Conclusion
The SEM image of steam and CO₂ cured samples demonstrated the homogeneously packed and dense geopolymer structure, and XRD results revealed the reduction of quartz and mullite peaks intensity, the FTIR analysis showed that the Si-O-Si and Si-O-Al bonds shifted to a higher wavenumber.

The steam and CO₂ curing duration do not significantly affect the microstructural properties of the geopolymer.

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Limitations and Recommendations
Determining the effect of BOFS/sand ratio on the setting time of BOFS-based geopolymer mortar;
Setting time affect the compressive strength and durability of the mortar. It provides control of hydration process.
Determining the effect of curing on flexural and tensile strength of geopolymer mortar;
Flexural strength controls the ability of mortar to bear loads and withstand external forces
Tensile strength control the failure occurrence, arise due to unsound aggregate, weathering action.
 Conducting the SEM, FTIR, and XRD analysis on expanded mortar samples that emerged in 1M NaOH to determine the reason for expansion.
The expansion of bar samples in 1M NaOH occurred, the formation of what compounds caused the expansion?


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References
[1] D. Babor, D. Plian, and L. Judele, “ENVIRONMENTAL IMPACT OF CONCRETE.” Available: https://www.bipcons.ce.tuiasi.ro/Archive/161.pdf.
[2] P. K. Mehta, “Reducing the environmental impact of concrete,” Concrete international, vol. 23, no. 10, pp. 61-66.Available: https://ecosmartconcrete.com/docs/trmehta01.pdf.
[3] J. Liu and D. Wang, “Influence of steel slag-silica fume composite mineral admixture on the properties of concrete,” Powder Technology, vol. 320, pp. 230–238, Oct. 2017, doi: https://doi.org/10.1016/j.powtec.2017.07.052.
[4] J. Guo, Y. Bao, and M. Wang, “Steel slag in China: Treatment, recycling, and management,” Waste Management, vol. 78, pp. 318–330, Aug. 2018, doi: https://doi.org/10.1016/j.wasman.2018.04.045.
[5] G. Wang, Y. Wang, and Z. Gao, “Use of steel slag as a granular material: Volume expansion prediction and usability criteria,” Journal of Hazardous Materials, vol. 184, no. 1–3, pp. 555–560, Dec. 2010, doi: https://doi.org/10.1016/j.jhazmat.2010.08.071.
[6] Q. Wang, D. Wang, and S. Zhuang, “The soundness of steel slag with different free CaO and MgO contents,” Construction and Building Materials, vol. 151, pp. 138–146, Oct. 2017, doi: https://doi.org/10.1016/j.conbuildmat.2017.06.077.
[7] A. S. Brand and J. R. Roesler, “Steel furnace slag aggregate expansion and hardened concrete properties,” Cement and Concrete Composites, vol. 60, pp. 1–9, Jul. 2015, doi: https://doi.org/10.1016/j.cemconcomp.2015.04.006.
[8] W. H. Lee, T. W. Cheng, K. Y. Lin, K. L. Lin, C. C. Wu, and C. T. Tsai, “Geopolymer Technologies for Stabilization of Basic Oxygen Furnace Slags and Sustainable Application as Construction Materials,” Sustainability, vol. 12, no. 12, pp. 5002–5002, Jun. 2020, doi: https://doi.org/10.3390/su12125002.
[9] S. Y. Pan, P. C. Chiang, Y. H. Chen, C. D. Chen, H. Y. Lin, and E. E. Chang, “Systematic Approach to Determination of Maximum Achievable Capture Capacity via Leaching and Carbonation Processes for Alkaline Steelmaking Wastes in a Rotating Packed Bed,” Environmental Science & Technology, vol. 47, no. 23, pp. 13677–13685, Nov. 2013, doi: https://doi.org/10.1021/es403323x.
[10] ASTM C511, “Standard specification for mixing rooms, moist cabinets, moist rooms, and water storage tanks used in the testing of hydraulic cements and concretes,”, 2013.





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Thank You!

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