【作者】 蔡新华；

【导师】 徐世烺；

【作者基本信息】 大连理工大学 ， 结构工程， 2010， 博士

【摘要】 超高韧性水泥基复合材料(Ultra High Toughness Cementitious Composites,简称UHTCC)具有拉伸荷载作用下的应变硬化特性和优异的裂缝控制能力,在拉伸荷载作用下极限拉应变可稳定地达到3%以上,可形成多缝开裂形式且达到极限拉应变时对应的裂缝宽度小于0.1mm。这种新型的高性能纤维增强水泥基复合材料在提高钢筋混凝土结构耐久性、提高结构抗震性能、对旧结构进行维修和翻新等方面具有广阔的应用前景,近十几年来一直是国内外的研究热点。而目前对UHTCC材料的基本力学性能、与钢筋及混凝土复合构件等方面的研究较多,对于其耐久特性的报道却较少。因此,本文在课题组对UHTCC基本力学性能及UHTCC与钢筋混凝土复合构件研究的前期大量工作基础上,对其抗冻性、抗碳化性能、渗透性能等基本耐久特性进行了试验研究和分析,并对UHTCC和锈蚀钢筋的粘结性能,UHTCC取代保护层混凝土梁抵抗钢筋锈蚀性能等进行了试验和分析。论文主要研究内容如下：(1)通过试验室快速冻融试验方法,研究了不同冻融循环次数下UHTCC的质量损失、动弹性模量变化、UHTCC小梁弯曲性能、UHTCC薄板弯曲性能,并与相同试验条件下普通混凝土、钢纤维混凝土和引气混凝土的试验结果进行了对比。结果显示,UHTCC在不掺加引气剂的条件下具有良好的抗冻性能,经过300次冻融循环仍能保持较高的弯曲抗拉强度和弯曲韧性。依据试验结果给出UHTCC在寒冷地区使用时的建议。(2)通过试验室快速碳化试验方法,对UHTCC的抗碳化性能进行了试验研究。包括无裂缝状态下UHTCC的碳化性能、UHTCC小梁预裂后带裂缝状态下的碳化性能以及UHTCC薄板碳化后的弯曲性能,并与同条件下的普通混凝土试验结果进行对比。结果显示,UHTCC抗碳化性能随龄期的增长逐渐增强,且在承受荷载后具有多条细密裂缝的开裂模式,在裂缝状态下的抗碳化性能明显优于普通混凝土试件；碳化作用能小幅提高UHTCC薄板的抗压强度和初裂弯曲应力,对其弯曲韧性基本没有影响,并依据试验结果和分析对如何评价UHTCC抗碳化性能给出了参考建议。(3)通过试验室抗渗性试验、快速氯离子渗透试验以及自由氯离子含量测定试验,研究了UHTCC的渗透性能,并与同条件下普通混凝土进行对比。结果显示,UHTCC具有明显优于普通混凝土的抗渗性能、较低的氯离子扩散系数,并随着龄期的逐步增加,UHTCC抗渗性能提高幅度较普通混凝土明显,氯离子扩散系数也随龄期增长而逐步降低。(4)通过电化学加速锈蚀方法和直接拉拔试验对UHTCC和不同锈蚀率下锈蚀钢筋的粘结性能进行了试验研究和分析,并与普通混凝土试件进行了对比。得到不同锈蚀率下UHTCC与钢筋的平均粘结应力-滑移曲线,采用粘结-滑移连续曲线模型描述了UHTCC与钢筋的平均粘结应力-滑移关系；分析了UHTCC与钢筋之间平均粘结强度随锈蚀率变化的规律,发现UHTCC能够延缓由于钢筋锈蚀而导致的UHTCC与钢筋之间粘结力的减小,起到类箍筋的作用。(5)采用UHTCC取代钢筋混凝土梁中保护层混凝土的思路,制作了4种不同类型的梁,包括UHTCC层厚度为15mm和50mm,以及钢筋增强混凝土梁和钢筋增强UHTCC梁,通过加速锈蚀试验方法使主筋锈蚀,研究了各梁在经历不同锈蚀时间后的破坏形态、弯曲承载力、弯曲裂缝特征等性能。结果显示,UHTCC具有优越的抵抗保护层锈胀开裂的功能,在较低的锈蚀率水平下UHTCC厚度层为50mm的梁和钢筋增强UHTCC梁极限承载力降低幅度较小,且弯曲裂缝宽度在梁荷载接近屈服时仍然维持在100μm以下,仍然发挥了其优异的裂缝控制能力。(6)采用弹塑性力学和圆孔扩张分析方法,考虑了UHTCC极限拉应变的影响,得出了UHTCC作为钢筋保护层时发生锈蚀开裂失效时钢筋临界锈蚀率的计算公式,并通过算例说明了UHTCC在抵抗钢筋锈胀力作用方面的有效性,并通过参数分析讨论了UHTCC保护层锈蚀开裂失效时钢筋临界锈蚀率的影响因素。更多还原

【Abstract】 Ultra High Toughness Cementitious Composites (UHTCC) is featured with its tensile strain-hardening characteristic and outstanding crack controlling capacity. Its tensile strain capacity can be steadily up to 3% and form multiple cracking with tight crack with below 0.1mm. This unique high performance fiber reinforced cementitious composite can be applied into improving the durability of concrete structures, enhancing the seismic resistance of structures, repairing or retrofitting old structures. Design and application of UHTCC have been developed throughout the world among these decades. Many researches on the mechanical properties and structural applications of UHTCC have been carried out, but few investigations on its durability. So this thesis investigates the durable properties of UHTCC based on its design and structural properties excuted by my group. The basic durable properties of UHTCC, including the frost resistance, the carbonation properties and the permeability, are experimental studied firstly. Then the bond characteristic between UHTCC and corroded rebar is investigated. At last the corrosion resistance of RC beams with UHTCC cover has been experimentally studied and theoretically analyzed. The detailed content of this thesis are as follows:(1) Accelerated freezing thawing test on UHTCC has been conducted, and the mass loss, the dynamic elasticity modulus changes and the bend properties of UHTCC are gained. The test results are compared with the ones of ordinary concrete, steel fiber reinforced concrete and air-entrained concrete. The results show that UHTCC behaved good frost resistance without any air-entrained agent. UHTCC can retain high flexural strength and flexural toughness after 300 freezing-thawing cycles. The suggestions on the application of UHTCC in cold area are given.(2) Accelerated carbonation test on UHTCC with and without bending cracks have been carried out. The bending cracks are gained by preloading tests before carbonation test. The test results are compared with the ones of ordinary concrete. The results show that the carbonation rate of UHTCC decreases with age increasing. The carbonation depth of UHTCC at cracks is evidently lower than the one of ordinary concrete at the cracks. Carbonation can slightly enhance the compressive strength and first cracking flexural strength of UHTCC, and have no effect on the its toughness. Suggestions of evaluating the carbonation properties of UHTCC have been given based on the test results and analyses. (3) The permeability of UHTCC and ordinary concrete has been investigated through permeability test, rapid chloride ions penetration test and free chloride ions measurement after ponding test. The results show that UHTCC behaves much better impermeability, lower chloride ions diffusion coefficient than ordinary concrete. Furthermore, the impermeability of UHTCC increased with age goes.(4) The bond behaviors of UHTCC and rebar with different corrosion ratios have been investigated through accelerated corrosion test and pull out test, and compared with the ones of ordinary concrete. The average bond stress to slip curves have been gained with different rebar corrosion ratios. A continuous curve model of bond-slip has been applied for illustrating average bond stress-slip relation. The relationship between average bond strength and rebar corrosion has been analyzed. The results show that UHTCC could delay the occurrence of the bond strength decreasing due to rebar corrosion.(5) 4 kinds of beams, RC beam, reinforced UHTCC beam, RC beam with the concrete cover replaced by 15mm and 50mm UHTCC respectively, are manufactured. The beams are undertaken accelerated corrosion for different period of time. Bending tests are conducted when these beams finished corrosion tests, and the failure mode, flexural bearing capacity, flexural crack pattern have been studied. The results show that UHTCC can effectively restrain cover cracking due to rebar corrosion, retain the bending capacity of members, and control the flexural crack width when subjected to rebar corrosion.(6) Considering the tensile strain capacity of UHTCC, a formula for calculating the critical rebar corrosion ratio when the UHTCC cover cracking due to rebar corrosion through the theory of plasticity and cylindrical cavity expansion theory. The effectiveness of UHTCC for restraining the cover cracking due to rebar corrosion has been proved by a calculated example. The influences on critical rebar corrosion when the UHTCC cover cracking due to rebar corrosion have been analyzed.更多还原