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.
A long-term ASR-expansive HPFRCC was developed. As an application, chemical prestress was introduced into this material by restraining the ASR expansion using reinforcing bars. Uniaxial tension tests were then performed on dumbbell-shaped HPFRCC specimens involving accelerated ASR expansion. The tensile yield strength and tensile ultimate strength were not adversely affected by the expansion. Although the ultimate strain of all specimens was reduced by the expansion, the multiple-cracking properties were observed and the average and standard deviations of crack widths were not affected by the expansion. The length change tests on small size HPFRCC beams reinforced with steel bars showed that the chemical energy conservation law of expansive concrete was valid regarding ASR-expansive HPFRCC. Bending tests on the reinforced HPFRCC beams showed that the cracking strength increased due to chemical prestress induced by ASR. The expansion of chemically prestressed beams was retained even after drying shrinkage. The possibility of controlling ASR expansion by means of LiNO2 impregnation was also ascertained.
The authors have been developed the anchoring method using Highly Expansive Material (HEM) for Continuous Fiber Reinforcing Materials such as CFRP strands. This anchoring method is confirmed that it was very useful for a anchoring method in prestressed concrete using PC strands as well as CFRP strands as tendon. In this study, tensile loading tests for CFRP strands and PC strands with HEM anchors were carried out, and the HEM anchoring mechanism based on the experimental results was investigated using shear transfer mechanics. Nonlinear simultaneous differential equations were introduced assuming that HEM layer behaves as shear spring, the numerical analyses were carried out. It was found that the proposed analytical method was very effective, because the results of numerical simulation agreed well with the experimental results. Also, it was clarified that the relationship between the amount of expansive pressure and the length of steel sleeve to grip firmly up to breaking of CFRP strands and yield point of steel strands. Moreover, the design concept of HEM device was also discussed.
The representative pore size of permeability (RPSP) was defined as the smallest pore through which mass had to pass to penetrate concrete with a specific thickness compared with various types of mass transfer resistance. A new method to extract the RPSP was proposed by mercury injection porosimetry (MIP) with epoxy-resin-coated samples. The obtained RPSP showed good correlation with water and surface air permeability. A high correlation with RPSP was also observed in gas diffusion and water penetration through a concrete specimen. The results indicated that the mass transfer phenomena examined in this paper was governed by the pore structure, and the RPSP can be a representative indicator of various types of mass transfer resistance.
Finding an index which can be abstracted from displacement field for shear failure of reinforced concrete members is an important subject for interpretation of both finite element analysis and inspection of real structures. In the present paper the displacement distribution measured from images in the variable damage stages of static loading tests was analyzed and the relationship between some indices and load capacity was investigated. Especially the expansion in the thickness direction resulted in the monotonic reduction of load capacity and tended not to be cancelled after unloading process. It was confirmed that this trend could be simulated quantitatively by finite element analysis considering material non-linearity.
Concrete cured by steam can not have high resistance to freezing and thawing attack even if AE agent is added at mixing. However, the concrete with blast furnace slag fine aggregate can have high resistance to freezing and thawing attack even if AE agent is not mixed. That is why the concrete with blast furnace slag fine aggregate can have high resistance to freezing and thawing attack even if it is cured by steam. The calcium hydroxide deposits around the coarse aggregate in ordinary concrete. The calcium hydroxide is easier to dissolve in water at low temperature. The water is accumulated in a gap made by dissolved calcium hydroxide. The accumulated water expands when it freezes and cracks yields around aggregate. In this paper, it is shown that calcium hydroxide does not deposit around the aggregate and the resistance to freezing and thawing of concrete is improved when blast furnace slag is used as fine aggregate.
The relationship between temperature during curing and the ultimate drying shrinkage of concrete is shown in this paper. The concrete temperature used even in prestressed concrete member tends to increase because the strength of concrete becomes higher and the thickness of member also becomes larger as the span of bridges are getting longer. The effect of temperature due to hydration on concrete drying shrinkage strain is examined in this paper by using the concrete member with the size of actual structure. It is clarified that the ultimate drying shrinkage strain of concrete becomes smaller when the concrete temperature during curing is high. The constitutive equation which expresses the relationship between ultimate drying shrinkage of concrete and constant temperature during curing is proposed. Furthermore, the hardening rule which is used for calculation of ultimate drying shrinkage strain under various temperature history is also proposed in this paper.