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Optimization of humidification stabilization for SRF co-firing ash: Balancing expansion inhibition and drying shrinkage Cover

Optimization of humidification stabilization for SRF co-firing ash: Balancing expansion inhibition and drying shrinkage

Materials Science-Poland
Volume 44 (2026): Issue 1 (March 2026)
By: ,   and    
Open Access
|Aug 2026
Figures & tables

Figures & Tables

Table 1

Bulk chemical composition of the processed SRF co-firing ash via XRF (wt%)

ComponentSiO2 Al2O3 Fe2O3 CaOMgOSO3 ClLOI
SRF34.7024.303.7026.101.307.100.3013.70
Figure 1

SEM image of SRF ash.

Figure 2

The XRD analysis of SRF ash.

Table 2

Trace heavy metal profile of SRF ash via ICP-OES (mg/kg)

ElementArsenic (As）Barium (Ba)Chromium (Cr)Lead (Pb)Zinc (Zn)Copper (Cu)
SRF5.2321.4015.8012.6045.208.45
Figure 3

Sequential flowchart outlining the collection, homogenization, and standardized pre-processing protocol.

Table 3

Mortar mix proportions and experimental testing standards

ParameterValue/ProtocolReferenced standards
Ash: sand1:3─
W/B ratio0.4─
Expansion70°C water bath (7 days)CNS 15311 ASTM D4792
Shrinkage23°C, 50% RH (28 Days)CNS 14603 ASTM C157[1]
Humidification0, 30, 50, and 100%Experimental ratios

[1]Note: Curing and water bath protocols conducted in accordance with CNS 15311 (the Taiwanese standard for testing the expansion of aggregates).

Figure 4

Weight change chart of SRF co-firing ash during the humidification stabilization test.

Figure 5

XRD pattern of the co-fired CFB fly ash after 30% humidification stabilization.

Figure 6

XRD pattern of the co-fired CFB fly ash after 50% humidification stabilization.

Figure 7

XRD pattern of the co-fired CFB fly ash after 100% humidification stabilization.

Table 4

Quantitative crystalline phase identification via XRD and functions

Mineral phase2θ peakStructural function
Quartz26.70°Inert filler: provides physical skeleton
C3S/C2S29.50°, 37.50°Latent hydraulic activity; self-cementing [10]
Anhydrite25.60°Expansion precursor; Delayed ettringite formation driver [16]
Portlandite34.10°Hydration product; provides alkalinity
Calcite29.40°Carbonation product; stabilizes AFt
Table 5

Thermodynamic stability of hydration products at 25°C (based on [19,21])

Chemical reactionsProductΔr G 0 (kJ/mol)Stability tendency
C3A + 3Gypsum + 26H2OAFt−265.19Very high (primary sink)
C3A + CaCO3 + 11H2OMonocarboaluminate (Mc)−217.61High (secondary sink)
C3A + 3CaCO3 + 32H2OTricarboaluminate (Tc)−207.91Moderate (late stage)
Figure 8

TGA/DTG profile of raw co-fired fly ash at 0% humidification.

Figure 9

TGA/DTG profile of stabilized ash at 30% humidification.

Figure 10

TGA/DTG profile of stabilized ash at 50% humidification.

Figure 11

TGA/DTG profile of stabilized ash at 100% humidification.

Table 6

Quantitative TGA mass loss across key thermal decomposition regions (%)

HumidificationAft/C–S–H (50–200°C)Ca(OH)2 (400–500°C)CaCO3 (600–800°C)
0%1.120.8511.45
30%3.452.6010.90
50%5.124.0210.55
100%6.885.4210.20
Figure 12

SEM-EDS of raw ash (0%): Silica-carbon-rich porous shards.

Figure 13

SEM-EDS of 30% humidified ash: Aggregation onset.

Figure 14

SEM-EDS of 50% humidified ash: Dense Portlandite clusters.

Figure 15

SEM-EDS of 100% humidified ash: Needle-dense AFt matrix.

Table 7

SEM-EDS localized elemental weight percentage evolution (wt%)

Element0% (Control)30% (Humidified)50% (Humidified)100% (Humidified)
Carbon (C)16.234.644.995.31
Oxygen (O)35.0649.6946.6244.90
Magnesium (Mg)───0.23
Aluminum (Al)19.0611.395.807.33
Silicon (Si)26.6124.9219.6516.63
Sulfur (S)───4.16
Calcium (Ca)3.046.9022.9421.43
Table 8

Accelerated linear expansion results for stabilized SRF ash (%)

Humidification0 Day1 Day2 Day3 Day7 Day
0%1.62 ± 0.12────
30%1.14 ± 0.090.39 ± 0.040.22 ± 0.020.01 ± 0.010.01 ± 0.01
50%0.82 ± 0.070.25 ± 0.030.15 ± 0.010.01 ± 0.010.01 ± 0.01
100%0.55 ± 0.050.18 ± 0.020.12 ± 0.010.01 ± 0.010.01 ± 0.01
Table 9

28-day drying shrinkage rate of SRF ash mortar (%)

Humidification7 Day14 Day21 Day28 Day
0%0.12 ± 0.010.18 ± 0.020.22 ± 0.030.25 ± 0.03
30%0.25 ± 0.020.38 ± 0.030.45 ± 0.040.52 ± 0.04
50%0.48 ± 0.030.62 ± 0.040.78 ± 0.050.88 ± 0.06
100%0.72 ± 0.050.98 ± 0.061.10 ± 0.071.21 ± 0.08
Figure 16

28-day length change rate (drying shrinkage) of SRF co-firing mortars.

Table 10

Suitable balance assessment vs engineering and safety limits

Criteria30% optimized group valueSafety limit/specification valueJudgment result
7-day linear expansion rate0.39%<0.50% (CNS 15311)Pass
28-day drying shrinkage rate0.52%<0.60% (Controlled low-strength material)Pass
Lead (Pb) leaching concentration<0.12 mg/L<5.0 mg/L (Toxicity characteristic leaching procedure)Pass
Stabilization efficiency100%Industrial application requirementsExcellent
DOI: https://doi.org/10.2478/msp-2026-0011 | Journal eISSN: 2083-134X (formerly 2083-124X) | Journal ISSN: 2083-1331
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Language: English
Page range: 191 - 207
Submitted on: Apr 7, 2026
Accepted on: Jun 24, 2026
Published on: Aug 10, 2026
Published by: Wroclaw University of Science and Technology
In partnership with: Paradigm Publishing Services
Keywords:
Atypical fly ash,
Capillary tension,
Carbonation,
Drying shrinkage,
Humidification stabilization,
Solid recovered fuel
Related subjects:
Materials sciences,
Materials sciences, other,
Nanomaterials,
Functional and smart materials,
Materials characterization and properties

© 2026 Chun-Chin Hwang, Ran Huang, Sung-Ching Chen, published by Wroclaw University of Science and Technology
This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 License.

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