This research developed the new concrete manufacturing method “surface wetting method” for the purpose of utilization of waste SANSYU roof tiles (porous material) as concrete aggregate. In this method, use the air-dry aggregate and sprinkle water on it using spray just before mixing. On the basis of experiments, confirmed that it is possible to make good concrete in terms of workability, strength and durability (frost damage and drying shrinkage) by using the surface wetting method. In addition, we considered about influence of inner liquid (amount and distribution) on frost damage and drying shrinkage of concrete using porous material. And we suggested the model paying attention to inner liquid.
During leaching alteration of hardened cementitious materials, Ca/Si ratio of C-S-H phase will decrease following the disappearance of calcium hydroxide (CH). Though the progression rate of CH alteration front and decreasing rate of Ca/Si ratio in C-S-H phase depend on the type of cementitious material, chain structure of Si tetrahedron in C-S-H phase will extend with increasing Q2/Q1 signal ratio in 29Si-NMR analysis, regardless of the type of cement. When the leaching alteration of C-S-H progressed further to 1.0 in Ca/Si ratio, Q3 signal which indicates the status of three-directional bonding of the Si tetrahedron with other Si had generated. Granular substance with 10 to 30 nm diameter which was thought to be the unit of C-S-H phase would shrink during the leaching alteration with forming minor pore in C-S-H phase.
It is widely known that cracks occurred in reinforced concrete structures are important problems when the structures are maintained for a long period, and prediction methods and control techniques of these cracks in reinforced concrete structures are necessary to be established. Therefore, many useful methods for controlling crack widths have been proposed. Recently, net-type continuous fiber reinforcements have been developed for controlling mainly the crack widths. As for the usual continuous fiber reinforcements, they are called materials with high durability such as excellent resistance to corrosion and chemical attack, as well as with lightweight, and many application examples have been reported for ocean and salt attack environments and so on. In addition to these merits, the transportation and construction methods of the net-type continuous fiber reinforcement are very easy. Then they have been used for common structures to control crack widths, for example as the retaining wall and the slab structures. However, the investigation studies have been hardly carried out about flexural behaviors and a quantitative evaluation of the crack width when these net-type continuous fiber reinforcements are used. In this study, flexural behaviors of reinforced concrete beams with net-type continuous fiber reinforcements placed near the main reinforcing bars are reported with the focus of arrangement shape and numbers of the net-type continuous fiber reinforcements, and concrete strength. It is confirmed that the influence of the number of net-type continuous fiber reinforcements was ascertained, and the arrangement of three net-type continuous fiber reinforcements can distribute the cracks and can control the flexural crack widths efficiently, because the bearing tensile force can increase in proportion to number of the continuous fiber reinforcement. In addition, it is exhibited that the flexural behaviors of reinforced concrete beams using the net-type continuous fiber reinforcement can be calculated numerically by the proposed laminated model method.
In this study, the influences of both rain and solar radiation on shrinkage and shrinkage cracking under actual environmental conditions are investigated. Moisture loss, shrinkage, shrinkage cracks were measured under three different outdoor conditions in order to examine the effects of rain and solar radiation separately. It was experimentally found that the penetration of rain into concrete greatly inhibits moisture loss, shrinkage and shrinkage cracking. While the solar radiation accelerates the evaporation of moisture in concrete, shrinkage of plain concrete cannot increase so much due to the drying but shrinkage cracking can be significantly promoted by solar radiation. It is concluded that the actual environmental actions such as rain and solar radiation should be taken into account in design in order to appropriately predict the deterioration of concrete structure.
To evaluate the scaling resistance of concrete exposed to a chloride environment, the representative testing methods of ASTM C672 and RILEM CDF are frequently used. However, facilities for conducting such tests are limited, because of the necessity using costly large-scale equipment. In this study, a simple testing method for evaluating the scaling resistance of concrete, in which a commercial freezer and small specimens are used, was examined in comparison with the ASTM and RILEM testing methods. The behavior of scaling resistance and chloride ion penetration, as well as the change in strain due to freezing/thawing, was clarified by using this simple testing method. By comparing the experimental results obtained by the simple testing methods and the specification testing methods, the utility of the simple testing method was verified.
Effective method for the enhancement of performance of structural lightweight concrete was experimentally studied. Water cement ratio was reduced to 30%. Steel fiber was added as much as 1% by volume. The mix proportion of the high-performance lightweight concrete was designed by determining the optimum combination of unit water and dosage of superplasticizer so that self-compactability was assured. As results, the lightweight concrete having 65N/mm2 compressive strength and 28.5kN/mm2 elastic modulus was made. It was confirmed that the lightweight aggregate used can effectively reduce the autogenous shrinkage of concrete. It was verified that a reinforced concrete beam made of the high-performance lightweight concrete has enough performance in both flexural capacity and crack dispersion in comparison with RC beams with ordinary concrete.