坦桑尼亚尼雷尔大桥高性能混凝土试验研究与应用

坦桑尼亚尼雷尔大桥主桥为主跨200 m的双塔单索面斜拉桥,按美国标准设计,主梁、桥塔混凝土按28 d圆柱体抗压强度60 MPa设计,相当于我国28 d立方体抗压强度72 MPa(简称C72高性能混凝土)。为制备出满足要求的混凝土,采用超细掺合料技术、优选各类原材料以及掺加超塑化剂的方法,从基准配合比设计、重复性试验、稳定性试验和小批量生产等方面进行试验研究。结果表明:采用0.30的水胶比、粉煤灰和硅粉双掺技术及掺加优质超塑化剂,在胶凝材料总量低于550 kg/m³条件下,可制备出流动性、力学性能和耐久性满足要求的混凝土;基准配合比经过6次重复性试验,抗压强度、弹性模量和电通量的变异系数均小于5%;通过不同批次原材料组合的稳定性试验,确定了理论配合比;小批量生产的混凝土28 d抗压强度变异系数为1.2%。该C72高性能混凝土已在尼雷尔大桥上应用,效果较好。

Experimental Research and Utilization of High Performance Concrete for Nyerere Bridge in Tanzania

The Nyerere Bridge in Tanzania is a two-pylon cable-stayed bridge with a main span of 200 m.The stay cables are fanned out in single cable plane.The bridge is designed conforming to US standards,the compressive strength of concrete used for main girder and pylons reaches 60 MPa,which is designed in accordance with the 28-d compressive strength of concrete cylinder,equal to the 28-d compressive strength of concrete cube in Chinese codes,that is 72 MPa(C72 high performance concrete for short).To prepare the required concrete,superfine admixtures are used,high-quality raw materials are selected and super plasticizer is added.And experimental tests are carried out from aspects of basic mix proportion design,repeatability test,stability test and small batch production.The results show that when the water-to-cement ratio is set at 0.3 and when fly ash,silica fume and high-quality superplasticizer are added,it is possible to prepare the concrete that can meet the required level of flow ability,mechanical property and durability,even though the total amount of cementitious material is less than 550 kg/m³.After 6 repeatability tests of the benchmark mix proportion,the variation coefficients of compressive strength,elastic modulus and electric flux are all less than 5%.By the stability tests with different raw materials combinations,the theoretical mix proportion is determined.The variation coefficient of 28-d compressive strength of concrete produced in small batches is 1.2%.The C72 high performance concrete has been used in the Nyerere Bridge,with good utilization effect.