Mechanism Investigation Of Crack Prevention Using Expansive Agent In Integrated Concrete Structure

Based on laboratory test and field test and numerical simulation,this study analysis the shrinkage cracking problem of integrated concrete structure through theoretical analysis,laboratory test study,field test study and numerical simulation study,following issues was undertaken for purpose:(i)the deformation regularity of expansive agent varied with time and the influence of different water binder ratio and content of expansive agent to expansive property;(ii)the expansive property of concrete with expansive agent in field test;(iii)the influence of concrete expansion in structure on stress and strain.The main results are as follows:(1)Explored the regularity of the expansion of free concrete varied with time: the expansion rate increases rapidly to maximum value after 14 hours,and then remains unchanged in the first 14 days.The expansion of restrained concrete shows the same regularity,the restrained expansion rate(RER)of the concrete with expansive agent rapidly increases in the first 3 days and reaches the peak value after 14 days,then decrease slightly with time.The RER keeps a value of about 0.030% after 28 days.(2)Explored the regularity of different water binder ratio and content of expansive agent influencing the expansion rate of structure: with the increase of water binder ratio of 0.3,0.43 and 0.6,expansion rate shows initial increasing and decreasing afterwards.The expansive property is best of concrete piece with w/b=0.43.It was supposed to carry on measures to raise expansive property of expansive agent when the water binder ratio was more of less than 0.43.With the increase of content of expansive agent of 5%,10% and 15%,expansion rate shows nonlinear increasing.It shows that the higher content of expansive agent the bigger additional value of expansion rate.The recommendation content of expansive agent is 10% for unstable expansion with content of 15%.(3)Concluded the expansive property of structure in field test after adding expansive agent: the regularity of expansive deformation is similar between field test and laboratory test in mixing station,but the maximum value of field test is smaller and the deceasing of restrained expansion rate is bigger after 14 days.The concrete strain increase to maximum value earlier and then shows less decrease compared with restrained expansion rate.(4)Concluded the regularity of strain and stress of integrated structure in different layout of expansion reinforcing band and provided designing advises: expansion reinforcing band can significantly raises up the stress and strain of concrete plate,it shows bigger expansive stress in the middle of expansion reinforcing band,and expansive stress decreases through its two sides.The influence of restraint to concrete stress and strain is influenced by the condition of adding expansive agent.When it constructs expansion reinforcing band,the structure almost shows expansive strain except the place near expansion reinforcing band,and the rest place shows shrinkage stress.When it constructs expansion reinforcing band and added expansive agent in other concrete,the structure almost shows compressive strain.The structure shows overall expansive stress in this condition.