| Now China's economic has a rapid development, which brought a peak of China's marine infrastructure. Most of these infrastructures are concrete structures and costly, the requirement of service life is more than 100 years. Due to the erosion of the marine environment, steel bar and concrete material premature destruction of constructed projects is very serious, so the durability of marine concrete becomes a focus problems of civil engineering.With the aim of high durability, the high performance concrete is much-favored since its inception, however in recent years people have found that high performance concrete also easy to crack during the early periods, even earlier than traditional concrete. Early cracks will greatly reduces the durability of concrete, hindering the further promoting of high performance concrete, so to study how to control and reduce early-age cracking of high performance concrete is particularly important.Now the mainly laboratory evaluation methods of early-age shrinkage and cracking are flat-restraint test, ring-restraint test and single-axis-restraint and so on. To inhibit early-age crack of HPC there are many ways, which can be summarized into three areas:design, materials, curing. Starting from theory, based on the experiment data, this article analyses the early-age cracking mechanism of marine HPC. Using evaporation test and flat-restraint test, the paper researches the influence on early-age cracking of HPC on natural environment with different water cement ratio (0.4and 0.38and 0.36), high volume fly ash (60%and 45%and 30%) and polypropylene short fiber (0.6kg/m3 and 0.9kg/m3 and 1.2kg/m3). Results show that: the lower the water binder ratio is, the more shrinkage and cracking is found; fly ash or polypropylene fiber can restrain the early-age cracking alone, having both of them gets better results. Finally with microscopic image the paper analyses fly ash and polypropylene short fiber on cement hydration and internal structure of concrete. |
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