1 Introduction
Mixing technique | Aluminosilicate precursor | Alkaline activator | Superplasticizer-based | Effect of superplasticizer on the properties of AAMs | Applicable superplasticizer (recommended from previous studies) | References | ||
---|---|---|---|---|---|---|---|---|
Type | Concentration | Workability | Strength | |||||
Two-part | Steel slag | NaOH + Na2SiO3 solution | Na2O = 4% | Vinyl | Not affected | Decreased | None | Puertas et al., (2003) |
Polyacrylate | Not affected | Slightly decreased | ||||||
Steel slag | NaOH solution | Na2O = 5% | Vinyl | Not affected | Slightly increased | Naphthalene | Palacios and Puertas (2005) | |
Polycarboxylate | Not affected | No effect | ||||||
Melamine | Slightly increased | Slightly increased | ||||||
Naphthalene | Increased | Increased | ||||||
Steel slag | NaOH solution | 3% | Polycarboxylate | Decreased | Not affected | None | Refaie et al., (2023) | |
Naphthalene | Increased | Decreased | ||||||
Fly ash | NaOH solution | 8 M | Naphthalene | Increased | Not affected | Naphthalene | Nematollahi and Sanjayan (2014) | |
NaOH + Na2SiO3 solution | Na2SiO3/NaOH = 2.5 | Polycarboxylate | Increased | Decreased | Polycarboxylate | |||
Melamine | Decreased | Decreased | ||||||
Naphthalene | Slightly increased | Decreased | ||||||
85% Fly ash + 15% Steel slag | Na2SiO3 solution | 7% | Polycarboxylate | Slightly decreased | N/A | Naphthalene | Xiong and Guo (2022) | |
Naphthalene | Increased | N/A | ||||||
Dry-mix one-part | 50% steel slag + 50% Fly ash | Na2SiO3 powder | 12% | Polycarboxylate | Increased | Slightly decreased | Naphthalene or polycarboxylate depending on the water/binder ratio | Alrefaei et al., (2019) |
Melamine | Increased | Slightly decreased | ||||||
Naphthalene | Increased | Slightly increased | ||||||
50% steel slag + 50% Fly ash | Ca(OH)2 + Na2SO4 powder | Ca(OH)2/Na2SO4 = 2.5 | Polycarboxylate | Increased | Increased | Polycarboxylate | Alrefaei et al., (2020) | |
Melamine | Increased | Increased | ||||||
Naphthalene | Increased | Increased |
2 Materials
2.1 Ground Granulated Blast Furnace Slag and Alkaline Activator
SiO2 | Al2O3 | Fe2O3 | CaO | MgO | MnO | TiO2 | SO3 | LOI | Total |
---|---|---|---|---|---|---|---|---|---|
35.40 | 17.40 | 1.40 | 36.87 | 6.83 | 0.35 | 0.11 | 0.24 | 0.5 | 99.1 |
2.2 Superplasticizers
Type | Color | Solid content (%) | Density (gm/ml) |
---|---|---|---|
Nb-SP | Brown liquid | 42.50 | 1.09 |
PCb-SP | Reddish liquid | 44.70 | 1.17 |
PFS-SP | Reddish brown | 25.00 | 1.25 |
3 Experimental Program
3.1 Preparation Fresh Pastes
Mix ID | Blended treated powder | Residual mixed slag g | Water/binder ratio | ||
---|---|---|---|---|---|
GGBFS (g) | NaOH (g) | Temp. ( °C) | |||
OP300 | 300 | 90 | 300 | 600 | 0.35 |
OP300-N25 | 0.34 | ||||
OP300-N75 | 0.31 | ||||
OP300-PC25 | 0.35 | ||||
OP300-PC75 | 0.33 | ||||
OP300-PFS25 | 0.31 | ||||
OP300-PFS75 | 0.31 | ||||
OP500 | 500 | 0.35 | |||
OP500-N25 | 0.34 | ||||
OP500-N75 | 0.33 | ||||
OP500-PC25 | 0.35 | ||||
OP500-PC75 | 0.33 | ||||
OP500-PFS25 | 0.31 | ||||
OP500-PFS75 | 0.31 |
3.2 Testing Procedures
3.2.1 Mini Slump Test
3.2.2 Setting Time Test
3.2.3 Compressive Strength
3.2.4 Phase Composition
4 Results and Discussion
4.1 Characterizations of Superplasticizers
Wave number (cm−1) | Peak assignment | Type of superplasticizer related to peak assignment |
---|---|---|
3133–3663 | O–H stretching | Nb-SP, PFS-SP and PCb-SP |
3082 | C–H stretching | PCb-SP |
1636 | C=O stretching (Ester group) | PCb-SP |
1601, 1627 and 1646 | C=C stretching | Nb-SP and PFS-SP |
618, 1097 and 1352 | C–O stretching | PCb-SP |
1174 | C–C stretching (aromatic) | Nb-SP |
1038 | C–H bending (–CH2, –CH3) | Nb-SP and PFS-SP |
680 | S–O deformation (–SO3) | Nb-SP and PFS-SP |
Superplasticizer | Mw | Mn | PDI |
---|---|---|---|
Nb-SP | 11,280 | 10,393 | 1.085 |
PFS-SP | 9988 | 7009 | 1.425 |
PCb-SP | 129,568 | 38,934 | 3.328 |
4.2 Characterizations of Thermo-chemical Treated Powder
4.3 Setting Time
4.4 Mini Slump
4.5 Compressive Strength
4.6 Mineralogical Analysis Through XRD
5 Conclusion
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Utilizing the thermal treatment process in fabricating OP-AAS is an effective method for mitigating the effect of the highly alkaline medium by impeding the NaOH in the aluminosilicate precursor structure. This was clarified by forming the sodium aluminum silicate phase after sintering a mixture from GGBFS with 10 wt% NaOH at 500 °C, as identified by XRD.
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The thermo-chemical treatment process will become a promising way to solve the problem of using chemical admixtures in alkali-activated materials by allowing the use of superplasticizers available in the market. This was inferred from the workability and compressive strength results.
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Increasing the sintering temperature improved the workability of all admixed OP-AAS. Laboratory-prepared superplasticizer (PFS) showed the highest enhancement percentage in workability in the case of OP-AAS prepared from TCT-P at 300 °C, which refers to its high stability in the highly alkaline medium.
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In the TCT-P prepared at 500 °C, PCb-SP enhanced the workability by 199%, which clarified the role of the thermal treatment process in limiting the hydrolysis of the polycarboxylate polymer. This is the biggest evidence that the commercial PCb-SP can operate in OP-AAS (prepared from TCT-P-500) with the same efficiency as in Portland cement.
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Nb-SP has the highest retardation impact on the OP-AAS fabricated from TCT-P-300 and TCT-P-500, referring to its strong adsorption on the binder grains. The main reasons for Nb-SP's adsorption are the high molecular weight and high anionic charge density than PFS-SP and PCb-SP, respectively.
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Nb-SP negatively impacts the mechanical properties, while OP-AAS, admixed with PFS and PCb-SPs, demonstrated the highest compressive strength values.
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In this work, a radical solution to the problem of using SPs in alkali-activated materials was found by using an invented laboratory-prepared SP (PFS-SP) and commercial superplasticizer (PCb-SP).