Investigations into Replacing Calcined Clay with Sewage Sludge Ash in Limestone Calcined Clay Cement (LC3)
Abstract
:1. Introduction
2. Materials and Methods
2.1. SSA Preparation
2.2. Raw Materials
2.3. Mixture Design
2.4. Sample Preparation and Characterizations
2.4.1. Compressive Strength
2.4.2. The Setting Time
2.4.3. XRD, TG/DTG and SEM
2.4.4. Toxicity Characteristic Leaching Procedure (TCLP)
3. Results
3.1. The Setting Times
3.2. Compressive Strengths
3.3. The Hydration Products
3.4. The Microstructure Observations
3.5. Environmental Impacts
4. Discussions
5. Conclusions
- (1)
- The introduction of SSA into modified LC3 pastes led to a slight prolongation of the final setting time. However, with 30% SSA incorporation, the final setting time of LC3 pastes approximated that of ordinary cement slurry, while exhibiting an earlier initial setting time. Replacing calcined clay with calcined SSA led to a reduction in the compressive strength of LC3 samples.
- (2)
- As the calcination temperature rose, the amorphous phase content within the calcined SSA increased, peaking at an optimal calcination temperature of 800 °C. The primary chemical compositions of SSA, namely Fe2O3, SiO2, Al2O3, and CaO, which mirror the chemical compositions of the clay utilized in LC3, albeit with a higher Fe2O3 and P2O5 content in SSA.
- (3)
- The incorporation of SSA into LC3 did not produce notable alterations in the phase compositions of the modified pastes compared to normal LC3. The primary crystalline minerals observed in the modified LC3 pastes include calcite (CaCO3), portlandite (Ca(OH)2), ettringite (AFt), and quartz (SiO2). Notably, compared to the pure OPC group, the Ca(OH)2 content was lower, while the calcite content was higher in LC3 pastes with SSA.
- (4)
- In samples containing SSA, an increased content of CaCO3 was observed, and the Ca(OH)2 exhibited a radial morphology. The addition of SSA altered the morphologies of Ca(OH)2 and CaCO3, and modified the microstructure of the LC3 paste. Furthermore, LC3 pastes with SSA appeared to possess a more porous microstructure than the normal LC3 group.
- (5)
- Heavy metal ions in SSA can be mostly immobilized in the LC3 pastes containing calcined SSA, thereby alleviating any possible environmental risks associated with utilizing SSA as a calcined clay substitute in LC3.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
References
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Material | CC | FA | LS | Cement | Gypsum | S6 | S7 | S8 | S9 | SS |
---|---|---|---|---|---|---|---|---|---|---|
Chemical composition (%) | ||||||||||
SiO2 | 45.54 | 49.89 | 0.10 | 25.48 | 0.37 | 12.53 | 13.96 | 16.06 | 15.82 | 14.67 |
CaO | 0.10 | 3.53 | 98.03 | 54.45 | 37.09 | 4.57 | 4.12 | 3.61 | 3.69 | 3.23 |
Al2O3 | 51.18 | 36.01 | 0.05 | 7.89 | 0.10 | 4.16 | 4.39 | 4.98 | 5.23 | 4.05 |
Fe2O3 | 0.42 | 4.19 | 0.04 | 4.35 | 0.03 | 61.50 | 59.41 | 54.83 | 55.62 | 58.31 |
MgO | 0.12 | 0.94 | 0.71 | 1.40 | 0.57 | 1.80 | 1.28 | 1.23 | 1.20 | 1.17 |
Na2O | 0.70 | 0.69 | 0.59 | 0.60 | 0.52 | 1.17 | 1.27 | 1.41 | 1.35 | 1.71 |
K2O | 0.10 | 1.71 | -- | 0.64 | 0.02 | 0.81 | 0.92 | 1.08 | 1.06 | 0.97 |
P2O5 | 0.40 | 0.38 | 0.08 | 0.15 | 0.07 | 8.98 | 10.02 | 11.97 | 11.08 | 9.04 |
SO3 | 0.19 | 1.13 | 0.26 | 4.12 | 61.06 | 3.02 | 2.70 | 2.23 | 2.62 | 3.10 |
Physical property | ||||||||||
D50 (μm) | 3.80 | 18.8 | 9.24 | 19.5 | 33.2 | 85.6 | 44.3 | 97.7 | 83.0 | 55.11 |
Specific surface area (m2/kg) | 1776 | 420.5 | 837.3 | 393.1 | 283.6 | 184.4 | 349.7 | 303.8 | 213.3 | 479 |
System | w/b | OPC | CC | SSA | FA | CaO | LS | Gypsum | ||
---|---|---|---|---|---|---|---|---|---|---|
Proportions | Calcination Temperature | |||||||||
pre-laboratory | SSA30-600 | 0.5 | 50 | 0 | 30 | 600 | 0 | 0 | 15 | 5 |
SSA30-700 | 0.5 | 50 | 0 | 30 | 700 | 0 | 0 | 15 | 5 | |
SSA30-800 | 0.5 | 50 | 0 | 30 | 800 | 0 | 0 | 15 | 5 | |
SSA30-900 | 0.5 | 50 | 0 | 30 | 900 | 0 | 0 | 15 | 5 | |
OPC | 0.5 | 95 | 0 | 0 | 0 | 0 | 0 | 0 | 5 | |
LC3 | 0.5 | 50 | 30 | 0 | 0 | 0 | 0 | 15 | 5 | |
SSA10-FA20 | 0.5 | 50 | 0 | 10 | 800 | 20 | 0 | 15 | 5 | |
SSA20-FA10 | 0.5 | 50 | 0 | 20 | 800 | 10 | 0 | 15 | 5 | |
SSA20-CaO10 | 0.5 | 50 | 0 | 20 | 800 | 0 | 10 | 15 | 5 |
System | Initial Setting Time (min) | Final Setting Time (min) |
---|---|---|
OPC | 201 | 298 |
LC3 | 187 | 492 |
SSA30 | 120 | 283 |
SSA10-FA20 | 245 | 295 |
SSA20-FA10 | 200 | 370 |
SSA20-CaO10 | 28 | 150 |
Application | Concentration of HM (mg/L) | |||||||
---|---|---|---|---|---|---|---|---|
Ag | Cd | Cr | Cu | Pb | Zn | Ba | Ni | |
OPC | ND | 0.0150 | 0.5576 | 0.4345 | 0.3952 | 0.8894 | 0.7153 | ND |
SSA30 | ND | 0.0500 | 1.3856 | 1.6498 | 0.9394 | 27.6620 | 1.4744 | 0.2084 |
SSA10-FA20 | ND | 0.0234 | 0.5529 | 0.7450 | 0.6131 | 7.3584 | 1.9619 | 0.0566 |
SSA20-FA10 | ND | 0.0383 | 0.9468 | 1.2535 | 0.7756 | 18.4746 | 1.0816 | 0.1657 |
SSA20-CaO10 | ND | 0.0323 | 0.9819 | 1.0713 | 0.6113 | 16.5055 | 0.8852 | 0.1156 |
TCLP a Regulatory Limit | 5 | 1 | 5 | 15 | 5 | 25 | 100 | 25 |
GB 5085.3-2007 b Limit | 5 | 1 | 15 | 100 | 5 | 100 | 100 | 5 |
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Gu, H.; Meng, Z.; Wang, Y.; Gao, X.; Wang, R.; Wang, D.; Sheng, J.; Wang, J. Investigations into Replacing Calcined Clay with Sewage Sludge Ash in Limestone Calcined Clay Cement (LC3). Materials 2025, 18, 782. https://doi.org/10.3390/ma18040782
Gu H, Meng Z, Wang Y, Gao X, Wang R, Wang D, Sheng J, Wang J. Investigations into Replacing Calcined Clay with Sewage Sludge Ash in Limestone Calcined Clay Cement (LC3). Materials. 2025; 18(4):782. https://doi.org/10.3390/ma18040782
Chicago/Turabian StyleGu, Hui, Zhaobo Meng, Yilei Wang, Xiaohui Gao, Ruihua Wang, Dongfang Wang, Jianxiong Sheng, and Junjie Wang. 2025. "Investigations into Replacing Calcined Clay with Sewage Sludge Ash in Limestone Calcined Clay Cement (LC3)" Materials 18, no. 4: 782. https://doi.org/10.3390/ma18040782
APA StyleGu, H., Meng, Z., Wang, Y., Gao, X., Wang, R., Wang, D., Sheng, J., & Wang, J. (2025). Investigations into Replacing Calcined Clay with Sewage Sludge Ash in Limestone Calcined Clay Cement (LC3). Materials, 18(4), 782. https://doi.org/10.3390/ma18040782