The Crack control system developed by Yamaguchi prefecture has been operated since 2007. Under this system, appropriate concrete construction following standard specifications was achieved utilizing a check sheet to grasp construction conditions. In this research, the effects of this crack control system were analyzed both in terms of reducing thermal cracks and improving the covercrete quality of concrete structures. The covercrete quality of concrete structures was investigated by the visual evaluation method and Surface Water Absorption Test (SWAT) developed by the authors.
Through application of this system, the incidence of cracks caused mainly by poor construction, such as non-penetrating cracks in the top slabs of box culverts and settlement cracks, was drastically reduced. Analysis with 3D thermal stress simulation found that the concrete structures constructed with this system have less quality variance and higher cracking strength than normal structures.
The improvement of covercrete quality by this system was proved both by the visual evaluation method and SWAT. The analysis of core specimens also proved the effectiveness of this system.
The effects of construction factors on covercrete quality were analyzed by the investigation combining the “Recommendations for Durability Design of Concrete Structures - Draft” and SWAT. It was suggested that the concrete placing rate, quality control when receiving of ready-mixed concrete, compaction by form vibrators, and curing after form removal might improve the resistance of covercrete against water absorption.
The significance of controlling cracks in quality assurance of concrete structures was discussed, and it was emphasized that cracks should be appropriately utilized as visual indices to improve the total quality of structures.
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