Effect of PVA-steel fiber on the flexural performance of high-strength recycled aggregate concrete beams
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摘要: 为研究纤维对高强再生骨料混凝土梁抗弯性能的影响,以粗骨料类型、纤维种类、纤维掺入方式和纤维体积掺量为变化参数完成了8根混凝土梁的四点弯曲试验,分析了不同参数对高强再生骨料混凝土梁破坏特征、裂缝宽度、挠度、开裂荷载、抗弯承载力和延性的影响。试验结果表明:掺入纤维的高强再生骨料混凝土梁和未掺入纤维的高强再生骨料混凝土梁破坏特征与高强天然骨料混凝土梁相似,均经历了弹性阶段、带裂缝工作阶段和破坏阶段;高强再生骨料混凝土梁的开裂荷载、刚度和变形性能较高强天然骨料混凝土梁均有所降低,且裂缝较宽,挠度较大;掺入聚乙烯醇/钢纤维有效抑制了裂缝的产生和进一步扩展,提高了开裂荷载,增强了变形性能;单掺聚乙烯醇纤维可使开裂荷载和延性显著提高,但抗弯承载力基本没有变化;单掺钢纤维与混掺聚乙烯醇-钢纤维均使再生骨料混凝土梁力学性能有所提高;与未掺纤维的再生骨料混凝土梁相比,混掺0.1vol%聚乙烯醇-1.5vol%钢纤维后,开裂荷载、抗弯承载力和延性分别提高了60.0%、4.2%和20.1%;利用规程对纤维增强再生骨料混凝土梁进行抗弯承载力计算,计算结果与实测结果吻合较好。Abstract: To study the flexural performance of fiber reinforced high-strength recycled aggregate concrete beams (FRHRACB), four-point flexural experimental investigates of eight concrete beams were completed. The main parameters were coarse aggregate types, types of fiber, fiber mixing methods and volumetric fiber dosage. The influences of different parameters on the failure modes, crack width, deflection, crack load, flexural capacity and ductility of recycled coarse concrete beams were analyzed. The experimental results show that the failure modes of recycled aggregate concrete beams with or without fiber are similar to those of natural aggregate concrete beams, which have an elastic stage, a working stage with cracks and a failure stage. The cracking load, stiffness and deformation performance of recycled aggregate concrete beams are lower than those of natural aggregate concrete beams. Furthermore, wider cracks and bigger deflection are found for recycled concrete beams. With the addition of polyvinyl alcohol/steel fibers, the generation and further expansion of cracks in recycled aggregate concrete beam are restrained. Meanwhile, the cracking load is increased, and the deformation performance is enhanced. Single-mixed polyvinyl alcohol fibers have obvious positive influence on the cracking load and ductility of recycled aggre-gate concrete beams, but almost no effect on the flexural capacity. However, single-mixed steel fibers and mixed polyvinyl alcohol-steel fibers improve the flexural performance of recycled aggregate concrete beams significantly. Compared with the recycled aggregate concrete beams without fiber, when 0.1vol% polyvinyl alcohol-1.5vol% steel fiber are added, the cracking load, the flexural capacity and ductility are improved by 60.0%, 4.2% and 20.1%, respectively. According to the standard, the flexural bearing capacity of recycled aggregate concrete beams was calculated, and the calculation results agree well with the test results.
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图 9 梁正截面抗弯承载力计算简图
Mfu—Flexural bearing capacity of normal section of fiber recycled aggregate concrete beam; ffu—Axial compressive strength of fiber recycled aggregate concrete; x—Height of the equivalent rectangular stress pattern in the compression zone; h0—Effective height of the section; h—Section height; as—Distance from the resultant point of the tensile reinforcement to the tensile edge; fy—Yield strength of longitudinal reinforcement in tension zone; As—Cross-sectional area of longitudinal reinforcement in tension zone; ftfu—Tensile strength of the equivalent rectangular stress pattern of concrete in the tensile zone; xt—Equivalent rectangular stress pattern height of the tension zone
Figure 9. Calculation diagram of flexural bearing capacity of beams
表 1 粉煤灰和矿粉物理性能指标
Table 1. Physical properties of fly ash and mineral powder
Program Density/
(kg·m−3)Bulk density/
(kg·m−3)Specific
surface area/
(cm2·g−1)Ignition loss/% Fly ash 2180 1124 3400 1.78 Mineral
powder2980 1440 3850 4.09 表 2 纤维物理性能
Table 2. Physical and mechanical properties of fibers
Fiber
types$ {d}_{\mathrm{f}} /$μm l/mm ν/(g·cm−3) $ {f}_{\mathrm{f}\mathrm{y}} /$MPa $ {E}_{\mathrm{f}} $/GPa $ {\delta }_{\mathrm{f}} $/% PVA 15 27 1.27 1060 29 6.00 Steel 600 19 7.80 1500 220 8.00 Notes: $ {d}_{\mathrm{f}} $—Fiber diameter; l—Fiber length; ν—Fiber density; $ {f}_{\mathrm{f}\mathrm{y}} $—Tensile strength of fiber; $ {E}_{\mathrm{f}} $—Elastic modulus of fiber; $ {\delta }_{\mathrm{f}} $—Fiber elongation. 表 3 混凝土配合比
Table 3. Mix ratio of concrete
Replacement
ratio of RCA/%Material composition/(kg·m−3) Cement Fine aggregate NCA RCA Base water Additional water Fly ash Mineral powder 0 337 634 1126 0 154 0 48 96 100 337 634 0 1126 154 25 48 96 Notes: RCA—Recycled coarse aggregate; NCA—Natural coarse aggregate. 表 4 纤维增强高强再生骨料混凝土梁(FRHRACB)的设计参数
Table 4. Design parameters of fiber reinforced high-strength recycled aggregate concrete beams (FRHRACB)
Specimen γ/% Fiber content/(kg·m−3) $ {f}_{\mathrm{c}\mathrm{u}} $/MPa $ {f}_{\mathrm{c}} $/MPa K/(kN·mm−1) Slump/mm PVA Steel NACB 0 0.0 0.0 69.0 49.9 17.4 201 RACB 100 0.0 0.0 66.4 41.1 15.7 176 0.1vol%PVA/RACB 100 1.3 0.0 62.1 40.1 16.9 150 0.3vol%PVA/RACB 100 3.9 0.0 57.4 39.4 17.4 112 0.5vol%S/RACB 100 0.0 39.0 66.2 42.3 18.3 161 1.5vol%S/RACB 100 0.0 117.0 70.4 46.8 19.1 132 0.3vol%PVA-0.5vol%S/RACB 100 3.9 39.0 61.4 40.8 17.6 75 0.1vol%PVA-1.5vol%S/RACB 100 1.3 117.0 64.7 43.9 17.8 110 Notes: γ—Replacement ratio of RCA; $ {f}_{\mathrm{c}\mathrm{u}} $—Compressive strength of concrete; $ {f}_{\mathrm{c}} $—Axial compressive strength of concrete; K—Initial stiffness of specimens; NACB—Natural aggregate concrete beams; RACB—Recycled aggregate concrete beams; S—Steel fibers. 表 5 钢材性能
Table 5. Material properties of steel bars
Steel bars type d/mm $ {f}_{\mathrm{y}} /$MPa $ {f}_{\mathrm{u}} / $MPa $ {E}_{\mathrm{c}} $/MPa HRB400 22 401 530 2.1×105 12 443 584 2.1×105 HPB300 6 332 456 2.2×105 Notes: d—Diameter of rebar; $ {f}_{\mathrm{y}} $—Yield strength of rebar; $ {f}_{\mathrm{u}} $—Tensile strength of rebar; $ {E}_{\mathrm{c}} $—Elastic modulus of rebar. 表 6 各FRHRACB特征点荷载
Table 6. Characteristic load of FRHRACB
Specimen $ {P}_{\mathrm{r}} $/kN $ {P}_{\mathrm{y}} $/kN $ {P}_{\mathrm{p}} $/kN NACB 35 177 212 RACB 25 196 213 0.1vol%PVA/RACB 30 200 213 0.3vol%PVA/RACB 35 199 213 0.5vol%S/RACB 30 201 218 1.5vol%S/RACB 40 200 221 0.3vol%PVA-0.5vol%S/RACB 30 199 219 0.1vol%PVA-1.5vol%S/RACB 40 202 222 Notes: $ {P}_{\mathrm{r}} $—Crack load; $ {P}_{\mathrm{y}} $—Yield load; $ {P}_{\mathrm{p}} $—Peak load. 表 7 各FRHRACB特征点挠度及延性系数
Table 7. Characteristic deflection and ductility coefficient of FRHRACB
Specimen $ {\varDelta }_{\mathrm{y}} $/mm $ {\varDelta }_{\mathrm{p}} $/mm μ NACB 11.15 30.80 2.76 RACB 13.55 34.91 2.58 0.1vol%PVA/RACB 12.63 35.21 2.79 0.3vol%PVA/RACB 13.23 40.12 3.03 0.5vol%S/RACB 13.24 37.25 2.81 1.5vol%S/RACB 12.79 36.07 2.82 0.3vol%PVA-0.5vol%S/RACB 13.21 40.30 3.05 0.1vol%PVA-1.5vol%S/RACB 11.89 36.80 3.10 Notes: $ {\varDelta }_{\mathrm{y}} $—Yield displacement; $ {\varDelta }_{\mathrm{p}} $—Peak displacement; μ—Displacement ductility coefficient. 表 8 试验结果与计算结果比较
Table 8. Comparison of test results with calculation results
Specimen Mt/(kN·m) Mc/(kN·m) Mt/Mc NACB 81.27 79.18 1.026 RACB 81.65 79.07 1.033 0.1vol%PVA/RACB 81.65 78.87 1.031 0.3vol%PVA/RACB 81.65 78.61 1.039 0.5vol%S/RACB 83.57 83.13 1.005 1.5vol%S/RACB 84.72 91.93 0.922 0.3vol%PVA-0.5vol%S/RACB 83.95 82.55 1.017 0.1vol%PVA-1.5vol%S/RACB 85.10 91.04 0.935 $ \mu ' $ 1.001 $ D $ 0.0434 $ {C_{\text{v}}} $ 0.0434 Notes: Mt—Test results; Mc—Calculation results; µ'—Mean; $ D $—Variance; $ {C_{\text{v}}} $—Coefficient of variation. -
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