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摘要: 為探究新型混凝土受硫酸鹽侵蝕后的力學性能，采用質量分數為5%的硫酸鹽溶液全浸泡加速侵蝕法，對11組聚丙烯纖維混凝土（PC）試塊、11組聚丙烯纖維鋰渣混凝土（PLiC）試塊、8根PC大偏心受壓柱和8根PLiC大偏心受壓柱進行侵蝕試驗，得到了不同侵蝕時間下混凝土的力學性能。基于分形理論分析了試塊及構件破壞時表面裂縫分布的分形特征，詳細討論了試塊及構件表面裂縫分形維數與其侵蝕時間、抗壓強度、極限承載力之間的關系。研究表明，PC和PLiC立方體抗壓強度隨侵蝕天數先增加后降低，在120 d達到最大；試塊及構件破壞時表面裂縫分布具有分形特征，試塊表面裂縫分形維數隨侵蝕天數的增加呈現先增加后減少再增加的規律，隨試塊抗壓強度的提高而減少；PC及PLiC混凝土大偏心柱極限承載力隨侵蝕天數的增加先增加后減少，鋰渣的摻入可以提高聚丙烯纖維混凝土柱的抗硫酸鹽侵蝕能力，構件破壞時表面裂縫分形維數隨硫酸鹽侵蝕天數呈現震蕩上升的趨勢；因此混凝土表面裂縫的分形特征可作為判定構件損傷程度的指標之一，可為今后對在役混凝土結構承載力和壽命預測提供參考。Abstract: Natural corrosion of concrete structure due to sulfate poses a serious threat to people's lives and property. Therefore, it is of great practical significance to study the phenomenon of sulfate corrosion on concrete. In order to explore the mechanical properties of a new type of concrete corroded by sulfate, a full immersion accelerated erosion method was used with 5% sulfate solution. Erosion tests were performed on 11 groups of polypropylene fiber reinforced concrete (PC) specimens, 11 groups of polypropylene fiber lithium slag concrete (PLiC) specimens, 8 PC columns with large eccentricity, and 8 PLiC large eccentric columns. The mechanical properties of concrete under different erosion times are obtained. Based on the fractal theory, the fractal characteristics of surface crack distribution of specimens and columns are analyzed. In addition, the relationship between the fractal dimension of surface crack and erosion time, compressive strength, and ultimate bearing capacity is discussed. Results show that the compressive strength of PC and PLiC initially increases and then decreases with increased erosion days, reaching a maximum of 120 days. The distribution of surface cracks is observed to be fractal when they are broken. With increased erosion days, fractal dimension of surface cracks initially increases, then decreases, and finally increases again. On the other hand, a decreasing trend of fractal dimension of surface cracks is observed with increased compressive strength. The ultimate bearing capacity of PC and PLiC columns with large eccentricity increases first and then decreases with erosion days. Addition of lithium slag is observed to improve the sulfate resistance of polypropylene fiber reinforced concrete columns. With broken members, fractal dimension of surface cracks presents a rising trend of shock with sulfate erosion days. Results signify that fractal characteristics of concrete surface cracks can be used as one of the indexes to determine the damage degree of members, which can provide reference for the prediction of bearing capacity and service life of concrete structures in the future.
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Key words:
- sulfate attack /
- fractal theory /
- large eccentric column /
- polypropylene fiber /
- lithium slag
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圖 2 混凝土柱侵蝕及試驗圖。（a）已施加荷載的鋼筋混凝土柱；（b）混凝土柱大偏心受壓試驗
Figure 2. Corrosion and test of reinforced concrete column: (a) loaded reinforced concrete column; (b) large eccentric compression test of reinforced concrete column
圖 3 不同侵蝕時間下的聚丙烯纖維鋰渣混凝土外觀形貌。（a）0 d；（b）30 d；（c）60 d；（d）90 d；（e）120 d；（f）150 d
Figure 3. Appearance morphology of polypropylene fiber lithium slag concrete under different erosion times: (a) 0 d; (b) 30 d; (c) 60 d; (d) 90 d; (e) 120 d; (f) 150 d
圖 4 PC混凝土柱和PLiC混凝土柱破壞形態
Figure 4. Failure modes of PC concrete column and PLiC concrete column
圖 7 不同侵蝕時間下立方體抗壓強度
Figure 7. Compressive strength of cube at different times of erosion
圖 9 試塊抗壓強度與分形維數的關系
Figure 9. Relationship between the compressive strength of test block and fractal dimension
圖 10 PLiC?30受壓柱破壞裂縫圖
Figure 10. Failure fracture diagram of PLiC?30 compression column
圖 11 PLiC?30受壓柱裂縫lnN(r)?ln(1/r)曲線
Figure 11. lnN(r)?ln(1/r) curve of PLiC?30 compression column crack
圖 14 分形維數與極限承載力的關系
Figure 14. Relationship between fractal dimension and ultimate bearing capacity
表 1 鋰渣粉末主要成分
Table 1. Main components of lithium slag powder
% Chemical composition SiO2 AI2O3 Fe2O3 SO3 CaO Li2O Mass fraction 54.30 1.80 1.40 8.30 7.90 0.70 
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表 2 聚丙烯纖維參數
Table 2. Parameters of polypropylene fibers
Fiber type Length/mm Density/(g·cm?3) Tensile strength/MPa Diameter/μm Elasticity modulus/GPa Polyprorylene fiber 19 0.91 530 33 >3.5
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表 3 混凝土配合比
Table 3. Mix proportions of concrete
Type of test
blockPolypropylene fiber/
(kg·m?3)Lithium slag/
%Cement/
(kg·m?3)Cobblestone/
(kg·m?3)Sand/
(kg·m?3)Water/
(kg·m?3)Water reducer/
(kg·m?3)PC 1.2 0 382 1161 682 172.8 1.92 PLiC 1.2 20 308 1161 682 172.8 1.92
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表 4 不同侵蝕時間下試塊抗壓強度及裂縫分形維數
Table 4. Compressive strength and fracture fractal dimension of test block under different erosion times
Type of test block Cube compressive strength /MPa Fractal dimension R2 Type of test block Cube compressive strength /MPa Fractal dimension R2 PC?0 41.3 1.407 0.982 PC?sulfate?0 41.3 1.407 0.988 PC?30 42.7 1.425 0.991 PC?sulfate?30 42.0 1.415 0.987 PC?60 43.9 1.435 0.994 PC?sulfate?60 43.4 1.402 0.995 PC?90 46.6 1.451 0.991 PC?sulfate?90 45.0 1.396 0.994 PC?120 57.8 1.379 0.982 PC?sulfate?120 54.3 1.364 0.981 PC?150 54.3 1.375 0.993 PC?sulfate?150 51.6 1.438 0.989 PLiC?0 43.9 1.391 0.991 PLiC?sulfate?0 43.9 1.391 0.985 PLiC?30 44.7 1.401 0.989 PLiC?sulfate?30 44.0 1.402 0.993 PLiC?60 49.7 1.474 0.992 PLiC?sulfate?60 45.8 1.356 0.987 PLiC?90 52.3 1.441 0.987 PLiC?sulfate?90 49.5 1.365 0.986 PLiC?120 59.6 1.425 0.994 PLiC?sulfate?120 57.5 1.385 0.993 PLiC?150 55.3 1.483 0.992 PLiC?sulfate?150 55.8 1.435 0.991 Note：PC?sulfate?30 represents that polypropylene fiber concrete corroded in sodium sulfate solution for 30 days.
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表 5 PC和PLiC大偏心受壓柱承載力及破壞裂縫分形維數
Table 5. Bearing capacity of large eccentric compress reinforced concrete column and fractal dimension of failure crack
Type of test block Ultimate load/ kN Fractal dimension R2 Type of test block Ultimate load/ kN Fractal dimension R2 PC?0?0 175 1.261 0.997 PLiC?0?0 180 1.253 0.991 PC?30?0.1 180 1.224 0.991 PLiC?30?0.1 194 1.233 0.993 PC?60?0.1 188 1.142 0.995 PLiC?60?0.1 200 1.133 0.994 PC?90?0.1 192 1.342 0.993 PLiC?90?0.1 205 1.291 0.995 PC?120?0.1 200 1.212 0.994 PLiC?120?0.1 220 1.181 0.991 PC?150?0.1 185 1.265 0.997 PLiC?150?0.1 205 1.324 0.996 PC?90?0.2 198 1.228 0.996 PLiC?90?0.2 220 1.267 0.994 PC?90?0.35 175 1.279 0.994 PLiC?90?0.35 182 1.265 0.993 Note：PC?30?0.1 represents polypropylene fiber concrete with stress ratio of 0.1 and erosion days of 30 d.
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