青岛海湾大桥承台混凝土寒季养护技术

Cold Weather Curing of Cushion Cap Concrete in Qingdao Bay Bridge

青岛海湾大桥位于海水含盐度高且存在较严重自然冻融循环的胶州湾海域,施工环境与服役环境都比较恶劣。非通航孔桥承台位于潮差区与浪溅区,为了保证施工期及运营期的混凝土耐久性,采用低水胶比、大掺量矿物掺和料、适量引气的混凝土配制技术,并利用外部围水设施实现海上干法施工。在冬季,为了降低施工期外界环境对混凝土性能的不利影响,将围水设施顶部用帆布覆盖,内部空间布置加热水箱,承台侧面利用蓄水型模板衬里提供不间断的保湿养护。自浇筑至14d养护龄期内,承台侧面及顶面温度始终高于15℃,相对湿度高于95%,模板衬里内积蓄的水量高于混凝土养护所需要的水量,采取该养护方案实现了承台混凝土的持续保温保湿养护,保证了承台混凝土的各项性能健康发展。

The saline concentration of seawater is comparatively high and there are 50 times of freezing and thawing cycles in Kiaochow bay where the Qingdao Bay Bridge is located,moreover,the construction and service environment are very severe for reinforced concrete structure.The cushion caps of approach bridge are all among tidal zone and splash zone.Low water-cement-ratio,high volume mineral admixtures,and air entraining are the main technology to prepare cushion cap concrete.Some cofferdams are utilized to make the construction environment seawater free.In winter,the top of cofferdams are covered with canvas,the space between cushion cap and canvas are heated by several boiling water tanks,and the lateral surface of cushion cap are curing by controlled permeability formwork liner in order to reduce the disadvantage influence of construction factor to concrete.During the first 14 days curing,the environment temperature around the cushion cap are kept above 15℃,and the RH is above 95%.The free water contained among controlled permeability formwork liner is more than the need of concrete curing.The curing program of cushion cap concrete utilized in Qingdao Bay Bridge under negative temperature can satisfy the need,and concrete performance develops well.