The Research Of Preventing And Curing Early Cracks Of Concrete Structure

Early cracks of concrete appear in constructing or before using due to design,construction,material or environment. For example: temperature cracks, plastic cracks, dry and shrunken cracks and load cracks, etc. Early cracks are ubiquitous in concrete structure. There are three variational trends along with time: close, split periodically and enlarge. More and more early cracks appear because of using market concrete, pumping concrete, high strength and high-powered concrete, at the same time, structures are more complex and bigger. Early cracks are nearly correlative with material, mix proportion, design, temperature, construction and maintenance, load, etc.There are different influence to structure with different character and reason of cracks, for example: time, depth and breadth, stability and position. Part of Early cracks reduce carrying capacity of structure, but most of Early cracks don't affect structure observably. The result would be emergence when structure endure dynamic load or in the corrasive (alternant dry and damp) circumstance, for example: meshy cracks, desquamating safeguard layer, crack wider and deeper, leakage, carbonization, reinforcing steel bar rusted and deflection increase. Carrying capacity and durability of structure would reduce because of early cracks, and there would be complain and insecurity for user. Therefore, most structure control appearance of early cracks.Searching reasons of early cracks are difficult. There are divergent opinion with owner, designer, builder, management and supervisor. No means or scheme can be put forward. The false means may bring hidden harm or durability for structure in the future. Preventive measure would be taken for reducing early cracks of structure.The ultimate causation of early cracks of concrete structure is that the tensile stress of early concrete is higher than the ultimate tensile stress. In this paper, the interface between cement-stone and aggregate is ameliorated adulterating fly ash and mineral additive. The base of early cracks is eliminated and adherence(cement mortar) cracks are decreased, then early cracks are reduced because the ability of resisting shrinking , tension and deformation are increased. The fibre can increase resisting shrinking and deformation of early concrete, relax the internal concentrated stress, decrease shrinking and increase capability of resisting cracks.The common concrete(C40) mixing fly ash, mineral additive and Dolanit? Type 18 fibre, big circle, big concrete board resisting craze and scanning lens were experimentalized. According as statistic the craze time, the average maximal and longth of cracks, we researched the trend of resisting craze and width of cracks with time, the influence resisting chlorion osmosis, and the effect improving the interface between cement-stone and aggregate by adulterating fly ash and mineral additive. So economical amount of fibre and adulterant can be choosed by test. The capability of resisting shrinkage craze was advanced evidently when 0.9kg·m-3 fibre mixed. The amount of cracks and area were reduced. Ca(OH)2 reduced evidently because of eruption reaction while concrete mixed fly ash and mineral additive. So joint between grout and aggregate is closer. The thickness of intergrade section was decreased. Concrete was close-grained and connected intensity was increased.According to testing, the concrete was mixed with 20% fly ash and mineral additive and 0.9 kg·m-3fibre. The figure of dry and shrinkage, coefficient of chlorion osmosis, tensile breaking strength and ultimate stress, press breaking strength and working performance were tested and contrasted with common concrete. Both the figure of dry and shrinkage and the coefficient of chlorion osmosis were decreased. Slump preceded the common concrete. Axial tensile breaking strength and ultimate tense stress were increased evidently. The form of crazing was ameliorated after fibre mixed. The result of tests proved that early concrete tensile breaking strength were increase evidently after mixing fly ash, mineral additive and fibre. It is predominant for preventing early cracks. Fibre high-powered concrete have well working performance.Besides improving materials of concrete, measures must be taken in design, building and circumstance for preventing appearing early cracks. Single method is deficient, which is the cause of universal early cracks. those are good methods in design reducing structure inner restrict stress and deformation, adopt prestress, etc. We must control s qualities of materials strictly, optimize mix proportion, mix, transport and cast normally. prestress properly and maintain in time. When cracks are found, we should judge their character according simple methods by forms, analyse the reason of cracks and put forward measures to assure using structure normally, for example: enveloping, infusing slurry or reinforcing.