Experimental study on the degradation law of f-CaO and optimization of expansion performance in steel slag treatment under different carbonation conditions
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摘要: 为解决钢渣在道路工程应用中因游离氧化钙（f-CaO）水化导致的膨胀隐患及资源化利用率低的问题，采用碳化处理技术，通过单因素试验与正交试验探究温度、湿度、CO2浓度及碳化时间对钢渣中f-CaO含量的影响，并结合膨胀率试验验证碳化处理对钢渣体积稳定性的改善效果。结果表明：碳化处理可显著降低钢渣中f-CaO含量，且f-CaO含量随温度升高、湿度增大、CO2浓度提高及碳化时间延长呈降低趋势；正交试验优化得出最佳碳化工艺条件为温度25 ℃、湿度70%、CO2浓度20%、碳化时间90 min，此条件下f-CaO含量降至最低，碳化效率最优，各因素影响程度依次为温度＞CO2浓度＞碳化时间＞湿度。膨胀率试验显示，最佳碳化组10 d浸水膨胀率仅0.86%，远低于未碳化组的1.8%，显著改善了钢渣体积稳定性。同时，将钢渣加入沥青混合料中，钢渣沥青混合料膨胀率也显著降低且表面结构完好，验证了碳化处理对改善钢渣体积稳定性的有效性。研究表明，钢渣碳化处理既能有效抑制膨胀、提升集料性能，又能实现CO2固存，为钢渣资源化利用及 “双碳” 战略实施提供了可行路径。Abstract: To address the issues of expansion risks caused by the hydration of free calcium oxide (f-CaO) in steel slag and its low utilization rate of resources in road engineering applications, a carbonation treatment technology was employed. Single-factor and orthogonal experiments were conducted to investigate the effects of temperature, humidity, CO2 concentration, and carbonation time on the f-CaO content in steel slag. The improvement effect of carbonation treatment on the volume stability of steel slag is verified by expansion rate tests. The results show that carbonation treatment can significantly reduce the f-CaO content in steel slag, and the f-CaO content decreases with the increase of temperature, humidity, CO2 concentration, and carbonation time. The optimal carbonation process condition, derived from orthogonal experiments, were temperature of 25 ℃, humidity of 70%, CO2 concentration of 20%, and carbonation time of 90 minutes. Under these conditions, the f-CaO content is minimized and carbonation efficiency was optimal, with the influence factors in descending order being temperature > CO2 concentration > carbonation time > humidity. Expansion rate tests revealed that the optimal carbonation group exhibited a water immersion expansion rate of only 0.86% after 10 days, significantly lower than 1.8% of the uncarbonated group, demonstrating a significant improvement in the volume stability of steel slag. Additionally, incorporating carbonated steel into asphalt mixtures also significantly reduced the expansion rate while maintaining intact surface structure, confirming the effectiveness of carbonation treatment in improving the volume stability of steel slag. This study demonstrates that steel slag carbonation treatment not only effectively suppresses expansion and improves aggregate performance but also achieves CO2 sequestration, providing a feasible pathway for the resource utilization of steel slag and the implementation of the "dual carbon" strategy.
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Key words:
- carbonation treatment /
- steel slag /
- free calcium oxide (f-CaO) /
- volume stability /
- orthogonal test
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图 1 钢渣在扫描电镜下的微观表面形态
(a)钢渣微观形貌; (b)钢渣空隙局部放大
Figure 1. The microscopic surface morphology of steel slag under scanning electron microscope
图 2 各因素对钢渣微粉游离氧化钙含量的影响
(a)温度；(b)湿度；(c)CO2浓度；(d)碳化时间
Figure 2. The influence of various factors on the free calcium oxide content of steel slag powder
图 3 碳化前后钢渣中游离氧化钙（f-CaO）的残留与消耗
（a）碳化后钢渣中f-CaO含量;（b）碳化钢渣消耗的f-CaO含量
Figure 3. The influence of carbonated steel slag f-CaO content - Comparison chart of experimental groups
图 4 不同碳化条件下膨胀率随时间变化试验
Figure 4. Test on the variation of expansion rate over time under different carbonation conditions
图 6 钢渣沥青混合料表面松散、开裂情况
(a)未碳化钢渣沥青混合料; (b)最佳碳化钢渣沥青混合料
Figure 6. The steel slag asphalt mixture showing signs of looseness and cracking
图 7 钢渣沥青混合料浸水膨胀率
Figure 7. Expansion rate of steel slag asphalt mixture after water immersion
表 1 钢渣的物理性能
Table 1. Physical properties of steel slag
Crushing
valueApparent relative
densityBulk density relative
to massWater absorption/% Los Angeles suffered
damage/%The content of needle-like and
flake-like particles/%Adhesion
level13.6 3.585 3.462 1.0 18.4 4.5 5 
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表 2 利用 X 射线荧光光谱（XRF）测定钢渣的化学组分
Table 2. Chemical composition of steel slag determined by X-ray fluorescence spectrometry (XRF)
% SiO2 Fe2O3 Al2O3 CaO MgO f-CaO Cl- P2O5 loss 15.33 21.47 6.66 36.76 7.66 1.9 0.103 1.17 9.14
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表 3 石油沥青试验结果
Table 3. Test results of petroleum asphalt
Penetration/0.1 mm Softening point of
bitumen/℃10 ℃ Ductility
/cmDynamic viscosity
/(Pa·s)Wax content/% TFOT aging Penetration ratio/% Residual ductility/cm 74 47.5 ＞100 229.8 2.0 62 12
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表 4 集料性能检测结果
Table 4. Test results of aggregate performance
Project Apparent relative
densityWater
absorption/%Crushing
value/%Soundness/% Flaky and elongated
particles content/%Los Angeles suffered
damage/%Sand
equivalent/%Angularity/s Basalt coarse aggregate 2.792 0.80 17 2.4 4.6 20.2 Basalt fine aggregate 2.826 18 74 40 Steel slag coarse aggregate 3.585 1.0 13.6 4.5 18.4
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表 5 矿粉检测基本性能
Table 5. Basic performance test results of mineral powder
Performance density/（t·m−3） Water content/% Hydrophilic coefficient Plasticity index/% Heat stability 2.650 0.2 0.82 3.8 stability
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表 6 正交试验设计
Table 6. Orthogonal experimental table
Level A(Temperature) /℃ B(Humidity)/% C(Concentration of CO2)/% D(Carbonization time) /min 1 5 30 20 30 2 15 50 40 60 3 25 70 60 90
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表 7 正交试验结果及分析
Table 7. Orthogonal experiment results and analysis
Numbering A(Temperature) /℃ B(Humidity)/% C(Concentration of CO2)/% D(Carbonization time) /min The content of f-CaO/% 1 5 30 20 30 1.5623 1.5724 1.692 2 5 50 40 60 1.5123 1.535 1.5432 3 5 70 60 90 1.2052 0.7227 1.181 4 15 30 40 90 1.4454 1.5687 1.5514 5 15 50 60 30 1.4132 1.4321 1.4422 6 15 70 20 60 0.9777 0.998 0.8941 7 25 30 60 60 0.9623 0.9732 0.9115 8 25 50 20 90 0.4847 0.4346 0.3532 9 25 70 40 30 0.9426 1.2144 1.1212
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表 8 正交试验极差分析
Table 8. Orthogonal experiment range analysis
Factor A(Temperature) / ℃ B(Humidity)/% C(Concentration of CO2)/% D(Carbonization time) /min K1 12.5276 12.2399 8.9703 12.3931 K2 11.7239 10.1513 12.4350 10.3089 K3 7.3981 9.2584 10.2444 8.9477 k1 1.3919 1.3599 0.9967 1.3771 k2 1.3026 1.1127 1.3816 1.1454 k3 0.8220 1.0287 1.1382 0.9941 Range analysis R R1: 0.5699 R2: 0.3312 R3: 0.3849 R4: 0.3828
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表 9 L9 (34)正交试验结果及方差分析
Table 9. L9 (34) orthogonal experiment results and variance analysis
Sum of squares of deviations Degree of freedom Mean square F P Significant A 1.8346 2 0.9173 67.1256 4.51237 E-09Significant B 0.5410 2 0.2705 19.7950 2.84659 E-05Significant C 0.7556 2 0.3778 27.6476 3.24909 E-06Significant D 0.7433 2 0.3716 27.1957 3.63299 E-06Significant Error 0.2459 18 0.0136 Total 3.8745 26
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表 10 钢渣粒度分布
Table 10. Granular size distribution of steel slag
% 31.5 mm 26.5 mm 13.2 mm 4.75 mm 2.63 mm 0.3 mm 0.075 mm 0 2.5 30 52.7 65 80 94
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表 11 1～9碳化条件表
Table 11. 1～9 Carbonation conditions table
Numbering Temperature/℃ Humidity/% Concentration
of CO2/%Time/min 1 5 30 20 30 2 5 50 40 60 3 5 70 60 90 4 15 30 40 90 5 15 50 60 30 6 15 70 20 60 7 25 30 60 60 8 25 50 20 90 9 25 70 40 30
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表 12 不同碳化条件下钢渣膨胀率随时间变化试验结果
Table 12. Test results showing the variation of steel slag expansion rate over time under different carbonation conditions
Carbonization test Expansion rate/% 1 day 2 day 3 day 4 day 5 day 6 day 7 day 8 day 9 day 10 day Un-carbonized 0.05 0.26 0.42 0.70 0.97 1.11 1.30 1.43 1.64 1.80 1 0.02 0.17 0.32 0.41 0.46 0.58 0.65 0.74 0.91 0.99 2 0.03 0.08 0.41 0.65 0.83 0.90 1.05 1.18 1.39 1.55 3 0.03 0.14 0.30 0.44 0.51 0.60 0.66 0.77 0.85 1.02 4 0.02 0.24 0.39 0.67 0.84 0.92 1.05 1.21 1.41 1.58 5 0.03 0.08 0.41 0.48 0.56 0.66 0.72 0.87 0.98 1.11 6 0.02 0.08 0.29 0.44 0.50 0.61 0.67 0.80 0.84 1.06 7 0.03 0.08 0.29 0.43 0.49 0.62 0.68 0.75 0.88 1.06 8 0.01 0.05 0.20 0.25 0.43 0.54 0.63 0.73 0.82 0.98 9 0.03 0.08 0.29 0.42 0.49 0.61 0.67 0.72 0.84 1.05 Optimum 0.00 0.05 0.18 0.22 0.40 0.51 0.60 0.67 0.74 0.86
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表 13 AC-16C钢渣沥青混合料级配组合设计
Table 13. Design of the grading combination for AC-16C steel slag asphalt mixture
Steel slag
content/%Basalt aggregate/% 5～10 mm
steel slag
aggregate/%Mineral
filler/%10～20 mm 5～10 mm 3～5 mm 0～3 mm 0 30 28 13 25 0 4 25 30 21 13 25 8 4 50 30 14 13 25 15 4 75 30 6 13 25 23 4 100 30 0 13 25 29 4
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表 14 AC-16C钢渣沥青混合料路用性能试验结果
Table 14. Test results of the pavement performance of AC-16C steel slag asphalt mixture
Item High temperature
stability/mm−1Low temperature
stabilitWater stability/% Residual
stabilityTensile
strength
ratioSteel slag
asphalt mixture2 431 3 250 80.6 79.1 Asphalt mixture 1 941 2513 81.2 78.4 Technical
requirements≥800 ≥ 2300 ≥75 ≥75
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