掺矿物掺合料盾构管片混凝土的高温性能研究

Study on High Temperature Performance of Shield Tunnel Segment Concrete Containing Mineral Additive

混凝土作为盾构隧道中钢筋混凝土管片结构的关键组成部分,与钢筋混凝土结构的稳定性与耐久性密切相关,而不同矿物掺合料制备的混凝土性能存在差异。在800℃条件下,以所设计的混凝土钢筋保护层厚度处(50 mm)温度达到250℃的时间确定为耐火极限,研究了不同矿物掺合料制备的盾构管片混凝土在高温作用下的性能。结果表明:混凝土试件在经历高温作用时,其中心处的温度变化速率包括成峰,波动和平稳三个阶段。掺加25%矿粉试件(J2)的耐火极限为19 min,爆裂面积为7.06 cm2,测试结果优于纯水泥体系试件(J0)和掺加20%粉煤灰试件(J3)。J0,J2和J3达到耐火极限后冷却36 h的物理力学性能损失率相近:抗压强度损失率约为50%,弹性模量损失率约为40%。此外,J0,J2和J3的超声波声速值约为2.5 km/s。

Concrete is a key part of the reinforced concrete structure for shield tunnel segments, and is closely related to the stability and durability of the structure. There is a difference between concrete performances prepared with different mineral additives. The limit of fire resistance （as defined by this paper） is the time when the temperature at the surface of rebar has reached 250℃ in a oven temperature of 800℃ for the RC with a cover of 25mm. The high- temperature performance of concretes prepared with different mineral additives is studied. The results show that the temperature variation rate of concrete specimens experience three stages： peak, fluctuation and a smooth one. In addition, the sample with 25% ground granulated slag （J2） has better performance than the pure cement sample （J0） and the sample with 20% fly ash （J3）. As far as J2 is concerned, the limit of fire resistance is 19 min with a spalling area of 7.06 cm^2. After cooling for 36 hours after the concrete arrives at limit of fire resistance, J0, J2 and J3 are similar in physical and mechanical properties： loss of compressive strength is about 50%, loss of elastic modulus is about 40%, and the ultrasonic velocity is about 2.5 km/s.