The Research Of Quality Control Technology Of Precast Box Girder Concrete In Qinghai Plateau Region

Tibetan Plateau has a unique climate characteristics, such as high altitude, large temperature difference between day and night, solar radiation, low humidity, and other harsh freeze-thaw cycle which will inevitably bring some negative impact on the quality and construction of concrete bridges, such as concrete strength rises slowly, freeze-thaw cycles increased, the drying shrinkage increases. In addition, construction of power at high altitude is relatively weak, construction technology is lagging behind. Therefore, how to improve the quality of the bridge concrete structure in the plateau region and improve the life of the concrete structure is very important.In highway construction, precast box girder has been widely used due to its many advantages. However, due to the unique characteristics of plateau environment, concrete of box girder prone to a variety of problems such as poor appearance quality, lower intensity, large shrink which impact on the quality of precast box girder directly.This paper relies on concrete box girder in Qinghai. At first it conducts an investigation on environment and climate in Qinghai, such as temperature, temperature difference, wind speed, analyzes the influence of special environment in Qinghai on the concrete structure, summarizes the typical problems of local concrete that existed, such as weak quality control of raw materials, traditional mix design method, insufficient attention to the concept of high performance concrete.Secondly, based on the conventional concrete mix design method which consider safety, workability and economy combined with the typical problems in Qinghai concrete mix design process, this paper proposes high performance concrete mix design method of precast box girder which mainly takes into account the durability.The paper mainly research the influence of water-cement ratio, sand ratio, unit of water and fly ash volume to the performance(performance, mechanical properties, drying shrinkage performance)of precast box girder concrete.The results show that choosing appropriate sand rate, unit water and fly ash, reducing the water-cement ratio can achieve a good effect of enhancing the performance of concrete.Climate in plateau region will directly affect the early strength of precast box girder concrete, thus affect the tensile time and duration, but also exacerbate the contraction of concrete. So it is necessary to ensure the precast box girder quality from the standpoint of optimizing the concrete mix and strengthening early curing.Finally, the paper does a simple introduction to the construction preparation of precast box girder and the specific construction process, and does a survey to the prone diseases such as poor perception of quality, appearing white of web, appearing water wave of web, strength developing slowly. Then it analyzes the main reasons of disease and proposes the corresponding control measures.