In the Hokuriku district, ready-mixed concrete plants using both classified fine fly ashes and limestone aggregates have been steadily increasing in order to produce a highly durable concrete against ASR and chloride attack problems. Therefore, in order to investigate on the mechanisms of improvement in compressive strength of concretes using both classified fine fly ashes and limestone aggregates, the development of compressive strength in concretes with and without classified fine fly ashes and limestone aggregates was respectively tested. Then, the specimens of 4 cases of a combination of the concretes were examined by means of mercury porosimeter, polarization microscope and scanning electron microscope. As the result of tests, it was confirmed that the limestone aggregate and its powder contributed the increase in compressive strength of concretes, due to the refinement in the texture of cement pastes and the reduction of interfacial transition zone around aggregates mainly at early ages until 7days, also that classified fine fly ashes contributed them mainly at late ages after 7days, in which both beneficial effects were complementary at both early and late ages.
When the classified fly ash will be used for concrete, the performance improvement is expected. However, these information are result of the basic study, and there is few example which the fly ash is normally used to ready mixed concrete of region. Herein, in recent years, the classifier device had been operated at Nanao-ota and Tsuruga fired power plants, and the classified fly ash whose quality was high and stability could be supplied. From the above backgrounds, this study was planed the utilization promotion of the classified fly ash in these two plants from the viewpoints of the environmental effect and the local production for local consumption to target the Hokuriku region extends over plural prefectures. Therefore, the various properties of concrete mixed with the classified fly ash for the aggregate of 6 types circulating at Hokuriku region were investigated in the indoor test. Moreover, the various properties of concrete mixed with the classified fly ash for the aggregate in Noto were investigated at an actual ready-mixed concrete plant in the prototype test. The conclusions were as follows; 1) in the indoor test, when the classified fly ash in Nanao-ota or Tsuruga used, the workability, the unti-segregation, the long age strength, the heat of hydration and the unti-chloride permeability were same or good, compared with those of concrete with N or BB. 2) in the prototype test, the workability, the strength and the heat of hydration were good, and it could be confirmed that the effective diffusion coefficient was same, compared with those of the indoor test.
Thermal power plant has occupied 90% of electric power supply after the earthquake disaster in Japan. Hence amount of coal-ash has increased gradually. Coal-ash, especially fly-ash, should be used for civil infrastructures, and concrete pavement must be a typical application using fly-ash. Fly-ash is a pozzolanic material, so it can contribute to various properties, such as strength development at mature age. The strength development at early age, however, is significantly slow and may negatively affect traffic service. Early strength may be improved when limestone filler is mixed in fly-ash concrete. In addition, the fly-ash concrete made with limestone aggregate may be recyclable as raw material for cement production. This study aims at developing the fly-ash pavement concrete which can make a traffic opening early and can be recycled. The paper describes the flexural strength properties of pavement concrete made with fly-ash of 40% replacement of cement. The result indicates the flexural strength at early age can be improved by using limestone filler, and assures sufficient strength development for traffic service at age of 2 days. In addition, the report shows flexural fatigue strength of the fly-ash pavement concrete is equal to or higher than the durability of conventional concrete pavement.
Considering environmental impact of construction materials, especially concrete, mineral admixtures like fly ash or blast furnace slag should be used as much as possible. Such concrete using mineral admixture generally has dense micro pore structure and high durability due to high resistance performance against the ingress of damage factors into concrete can be expected. However, as the chemical reaction of mineral admixtures consumes Ca(OH)2 in concrete, the pH value decreases with the age of concrete. Such dropping of pH value may decrease the critical chloride content for the initiation of steel corrosion in concrete. This study experimentally investigated the critical chloride content in some cases of concrete or mortar with mineral admixtures including the cases of combination of blast furnace slag cement and fly ash. As a result, although the combination of blast furnace slag cement and fly ash could realized highly dense pore structure, Cl-/OH- molar ratio in mortar pore solution extracted by high compressive pressure remarkably increased compared with the case of normal mortar because of the synergistic effect of reduction of OH- concentration and the rise of Cl- concentration. However, correlation between Cl-/OH- molar ratio and half-cell potential was not so clear, which suggested that Cl-/OH- molar ratio is not the unique factor to determine the initiation of steel corrosion.
Lithium nitrite injection method has been employed in recent years to prevent ASR due to the presence of lithium ion. Meanwhile, in the presence of nitrite ion, lithium nitrite is also expected to inhibit steel corrosion in concrete when water, oxygen and chloride ion may ingress through ASR-induced cracks. Consequently, lithium nitrite is applied to repair concrete section either combined in patching material or being a coating material. Despite of its widespread application, quite a few problems on corrosion-inhibiting mechanism of nitrite ion have not been fully understood yet. How to evaluate the effect of nitrite ion and its related risk of macro-cell corrosion is among them. Purpose of this study is to investigate the corrosion-inhibiting mechanism of nitrite ion based on polarization tests of steel bars corroded under various kinds of corrosion conditions. A further discussion on the application of nitrite ion is present upon the test results.
Viscosity of water under high pressure is an important property to calibrate high-pressure viscometers. On the other hand, the high-pressure viscosity of water has to be measured using the high-pressure viscometers. In the present review, we show evaluation of an equipment constant under high pressure to measure the high-pressure viscosity of water, using our high-pressure rolling-ball viscometer as an example.
Final goal of this series of papers is to formulate a method to evaluate stress, or residual stress induced in the steel substrate in nitriding process. Non-equilibrium state is considered, in the first paper, to simulate nitrogen concentration successively by simple diffusion into α-Fe in the first stage of the process followed by formation of γ' and ε compounds associated with phase transformation due to crystallographic structure change. The volume dilatation by such diffusion and phase change processes is estimated, where emphasis is placed on that by considering the nitrogen dependence on lattice parameters for each unit cell. The volume dilatation thus evaluated is to be used to formulate elastic plastic strain and stress in the second paper.
Based on the nitrogen distribution and associated volume dilatation in substrate during nitriding process evaluated in the first report of this series of papers, a method to simulate induced strain and elastic-plastic stress by incremental strain hypothesis is proposed. Bearing in mind that the process is limited in the very thin layer of the substrate, stress and strain condition is carefully discussed to clarify to be plain stress state. Strain incremental theory by use of Prandtl-Reuss constitutive equation with bilinear stress-strain relation is applied. Simulated results on residual stress distribution gives reasonable correspondence with experiments.