Experimental study on bond behavior of GFRP bar and seawater coral aggregate concrete after exposure to high temperatures
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摘要: 为了研究高温后玻璃纤维增强树脂复合材料(GFRP)筋与海水珊瑚混凝土的残余粘结性能,对54个GFRP筋珊瑚混凝土试件及钢筋珊瑚混凝土对比试件进行了高温作用后的中心拔出试验,最高温度为350℃,混凝土强度等级考虑C20~C30。观察了高温后试件的表观变化及粘结破坏形态,获取了各试件的粘结-滑移曲线、粘结强度、粘结刚度和峰值滑移量,分析了不同温度、GFRP筋直径、海水珊瑚混凝土强度等因素对高温后GFRP筋与海水珊瑚混凝土粘结性能的影响。基于烧失率和XRD分析,剖析了GFRP筋海水珊瑚混凝土的高温劣化机制。最后,提出高温后GFRP筋与珊瑚混凝土的剩余粘结强度计算式和粘结-滑移本构模型。研究结果表明:高温作用后,尽管GFRP筋与珊瑚混凝土的粘结破坏形态与常温相似,GFRP筋的碳化和珊瑚混凝土的分解使得二者界面发生显著劣化;随着温度的提高,GFRP筋与珊瑚混凝土的粘结强度逐渐降低,峰值滑移量增大;GFRP筋直径越小,高温后的剩余粘结强度和剩余粘结刚度越小;珊瑚混凝土强度等级越高,剩余粘结刚度越大,峰值滑移量越小。所提出的高温后GFRP筋与珊瑚混凝土剩余粘结强度和粘结-滑移本构关系计算结果与试验结果均能较好吻合。Abstract: To study the residual bond performance of glass fiber reinforced polymer (GFRP) bars and seawater coral aggregate concrete after exposure to high temperature, the pull-out tests were performed through 54 GFRP bars coral aggregate concrete specimens and steel bars coral aggregate concrete specimens. The highest temperature of 350℃ and concrete classes of C20 to C30 were considered in this experiment. The surface changes and bond failure modes of specimens after high temperatures were observed. The bond stress-slippage curves, bond strength, stiffness and peak slippage were obtained. The influences of temperatures, bar diameters and concrete strengths on the bond properties of GFRP bars and coral aggregate concrete after high temperatures were analyzed. Furthermore, the deterioration mechanism of GRFP bars seawater coral aggregate concrete after high temperatures was revealed based on the analysis of mass loss rate and XRD tests. Finally, the bond stress-slippage constitutive relation and residual bond strength of GFRP bars and coral aggregate concrete after high temperatures were proposed. The results show that even though the failure modes of specimens after high temperature are similar to those at room temperature, the interface of GFRP bar and coral aggregate concrete is degraded significantly due to the carbonization of GFRP bar and pyrolysis of coral aggregate concrete. The bond strength of specimens decreases and the peak slippage increases as the temperature increasing. The smaller the diameter of GFRP bars, the lower the residual bond strength and stiffness of specimens after high temperatures. The higher the strength classes of coral aggregate concrete, the greater the residual bond stiffness and the smaller the peak slippage. The calculated results of the proposed bond stress-slippage constitutive model and residual bond strength of GFRP bars-coral aggregate concrete after high temperatures show a good agreement with the experimental results.
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表 1 筋材几何参数及力学性能
Table 1. Geometrical parameter and mechanical properties of bars
Type of reinforcement Diameter/mm Rib spacing /mm Rib depth/mm Tensile strength f/MPa Elasticity modulus E/GPa GFRP bar 8 8.61 0.49 855.46 43.69 12 10.59 1.05 853.59 41.32 16 9.84 1.40 730.85 33.73 Steel rebar 12 8.00 1.20 629.08 219.84 表 2 海水珊瑚混凝土配合比及抗压强度
Table 2. Mixture ratio and compressive strength of seawater coral aggregate concrete
Strength class Composition/(kg·m−3) Slump/
mmfc/
MPaBasic sea water Additional sea water Total sea water Cement Silica fume Sea sand Coral Plasticizer C20 190 89 279 350 30 820 710 0.007 142 21.83 C30 190 91 281 400 70 810 720 0.012 190 25.44 Notes: fc—Axial compressive strength of concrete. 表 3 试件设计参数
Table 3. Design parameters of specimens
Specimen number Strength class Reinforcement Bar diameter/mm Temperature/℃ GFRP8/CC30-20 C30 GFRP bar 8 20 GFRP8/CC30-200 C30 GFRP bar 8 200 GFRP8/CC30-350 C30 GFRP bar 8 350 GFRP12/CC30-20 C30 GFRP bar 12 20 GFRP12/CC30-150 C30 GFRP bar 12 150 GFRP12/CC30-200 C30 GFRP bar 12 200 GFRP12/CC30-250 C30 GFRP bar 12 250 GFRP12/CC30-300 C30 GFRP bar 12 300 GFRP12/CC30-350 C30 GFRP bar 12 350 GFRP16/CC30-20 C30 GFRP bar 16 20 GFRP16/CC30-200 C30 GFRP bar 16 200 GFRP16/CC30-350 C30 GFRP bar 16 350 GFRP12/CC20-20 C20 GFRP bar 12 20 GFRP12/CC20-200 C20 GFRP bar 12 200 GFRP12/CC20-350 C20 GFRP bar 12 350 SR12/CC30-20 C30 Rebar 12 20 SR12/CC30-200 C30 Rebar 12 200 SR12/CC30-350 C30 Rebar 12 350 Note: In GFRP8/CC30-20, GFRP8 means the GFRP bars with diameter of 8 mm, CC30 means coral concrete strength grade, 20 means test temperature. 表 4 高温后GFRP筋珊瑚混凝土粘结性能
Table 4. Bond properties of GFRP bar and coral aggregate concrete after high temperatures
Specimen number τu/MPa s1/mm κ/(MPa·mm−1) Failure mode GFRP8/CC30-20 7.57 1.73 7.79 P GFRP8/CC30-200 5.93 1.99 4.10 P GFRP8/CC30-350 3.61 2.33 2.45 P GFRP12/CC20-20 7.22 0.99 9.05 S GFRP12/CC20-200 5.84 1.06 10.92 S GFRP12/CC20-350 3.73 1.27 5.63 S GFRP12/CC30-20 10.92 0.37 30.29 S GFRP12/CC30-150 8.95 0.40 35.10 S GFRP12/CC30-200 8.72 0.40 31.02 S GFRP12/CC30-250 6.21 0.54 25.35 S GFRP12/CC30-300 5.85 0.61 14.78 S GFRP12/CC30-350 5.01 0.61 11.37 S GFRP16/CC30-20 8.07 0.65 11.92 S GFRP16/CC30-200 7.11 0.66 12.25 S GFRP16/CC30-350 4.33 0.89 6.07 S SR12/CC30-20 13.18 0.60 55.20 S SR12/CC30-200 13.99 0.91 71.20 S SR12/CC30-350 9.15 1.80 19.32 S Notes: τu—Bonding strength; s1—Peak slippage; κ—Bond stiffness; P—Pull-out of bar; S—Splitting of concrete. 表 5 GFRP筋珊瑚混凝土试件剩余粘结强度计算值与试验值
Table 5. Calculated values and test values of residual bond strength of GFRP bars-coral concrete specimens
Specimen number T/℃ d/mm L/mm fc/MPa $\tau _{\text{u}}^{\text{c}}(T)/{\text{MPa}}$ $\tau _{\text{u}}^{\text{e}}(T)/{\text{MPa}}$ $\tau _{\text{u}}^{\text{c}}(T)/\tau _{\text{u}}^{\text{e}}(T)$ GFRP8/CC30-20 20 8 50 25.44 7.57 7.57 1.00 GFRP8/CC30-200 200 8 50 25.44 5.87 5.93 0.99 GFRP8/CC30-350 350 8 50 25.44 3.79 3.61 1.05 GFRP12/CC20-20 20 12 60 21.83 8.59 7.22 1.19 GFRP12/CC20-200 200 12 60 21.83 6.66 5.84 1.14 GFRP12/CC20-350 350 12 60 21.83 4.30 3.73 1.15 GFRP12/CC30-20 20 12 60 25.44 9.71 10.92 0.89 GFRP12/CC30-150 150 12 60 25.44 8.25 8.95 0.92 GFRP12/CC30-200 200 12 60 25.44 7.53 8.72 0.86 GFRP12/CC30-250 250 12 60 25.44 6.73 6.21 1.08 GFRP12/CC30-300 300 12 60 25.44 5.84 5.85 1.00 GFRP12/CC30-350 350 12 60 25.44 4.87 5.01 0.97 GFRP16/CC30-20 20 16 80 25.44 8.07 8.07 1.00 GFRP16/CC30-200 200 16 80 25.44 6.26 7.11 0.88 GFRP16/CC30-350 350 16 80 25.44 4.04 4.33 0.93 Notes: T—Temperature; d—Nominal diameter of GFRP bars; L—Embedded length of GFRP bars; fc—Axial compressive strength of concrete; $\tau _{\text{u}}^{\text{c}} $(T)—Calculated value of bond strength between GFRP bars and coral concrete at different high temperatures; $\tau _{\text{u}}^{\text{e}} $(T)—Test value of bond strength between GFRP bars and coral concrete at different high temperatures. 表 6 GFRP筋珊瑚混凝土试件粘结-滑移曲线计算结果
Table 6. Calculation results of bond stress-slippage curves of GFRP bars-coral concrete specimens
Specimen number sc(T)/mm se(T)/mm sc(T)/se(T) α β p R2 GFRP8/CC30-20 1.73 1.73 1.00 0.72 1.10 0.25 0.99 GFRP8/CC30-200 1.81 1.99 0.91 0.92 1.72 0.39 0.98 GFRP8/CC30-350 2.38 2.33 1.02 1.00 1.30 0.53 0.96 GFRP12/CC20-20 0.99 0.99 1.00 1.26 1.87 4.01 0.99 GFRP12/CC20-200 1.04 1.06 0.98 0.20 0.05 0.21 0.97 GFRP12/CC20-350 1.36 1.27 1.07 0.94 1.83 0.40 0.97 GFRP12/CC30-20 0.44 0.37 1.19 1.14 2.28 4.99 0.99 GFRP12/CC30-150 0.44 0.41 1.07 0.74 1.47 0.09 0.95 GFRP12/CC30-200 0.46 0.40 1.15 0.75 1.50 1.38 0.86 GFRP12/CC30-250 0.50 0.54 0.93 0.92 1.81 0.16 0.98 GFRP12/CC30-300 0.55 0.61 0.90 1.16 1.65 0.86 0.95 GFRP12/CC30-350 0.61 0.61 1.00 0.97 1.44 0.21 0.90 GFRP16/CC30-20 0.65 0.65 1.00 1.02 1.02 2.10 0.91 GFRP16/CC30-200 0.69 0.66 1.05 1.20 1.58 11.71 0.96 GFRP16/CC30-350 0.90 0.89 1.01 0.99 1.98 0.15 0.93 Notes: sc(T)—Calculated value of peak slippage; se(T)—Test value of peak slippage; α, β—Design conditions; p—Softening coefficient of descending stage; R2—Correlation coefficient. -
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