Recently it has been pointed out that the phenomenon of “a heat island” as one of the social problem in Japan. The author et al. developed a special mortar that suppresses radiation during the nighttime by improving water-holding capability using the activated alumina. Activated Alumina is manufactured from aluminum hydroxide by de-hydroxylating it in a way that produces a highly porous material. It is made of aluminum oxide (alumina ; Al2O3). It has a very high surface-area-to-weight ratio. In the research, three sorts of experiments were carried out. Firstly we carried out the outdoor full-scale test having the real house using the mortar roof with activated alumina and white mortar roof without activated alumina. These mortars were made of white Portland cement. Secondly we carried out the laboratory test having halogen lights in order to explain the relationship between the evaporation heat and received heat of specimen. Finally we measured the pore size distribution in order to prove the porous body of mortar with activated alumina. As a result, it was considered that the special mortar mixing the activated alumina was able to suppress the temperature rise.
The compressive strength and the electrical resistivity of mortar specimens using mineral admixture (fly ash and ground granulated blast-furnace slag) were measured to evaluate the influence of mineral admixture on the mortar hardening process. Comparing the changes in compressive strength and electrical resistivity of mortar using the mineral admixture was compared, compressive strength tended to start increasing from a relatively early stage, while electrical resistivity tended to increase after a slight delay. The formation factor variation shows that the increase in electrical resistivity is due to changes in the pore structure, such as tortuosity, rather than changes in the pore solution concentration. Then, the apparent diffusion coefficient of chloride ion was estimated from electrical resistivity. The diffusion coefficient of mortar using blast-furnace slag tended to fall below that of ordinary Portland cement at 7days, and then gradually improved. Until 14days, the diffusion coefficient of mortar using fly ash exceeds that of ordinary Portland cement mortar, but declines below the latter after 91days. This study shows that the periods of the surge in permeability and compressive strength differ, and that these features vary depending on the type of mineral admixture used.
Concrete structures and members show performance degradation due to materials deterioration through their service life. In particular, frost damage due to freeze-thaw cycles causes deterioration of concrete structures in cold regions. Chloride of deicing agents accelerates the deterioration due to frost damage under freeze-thaw environment. It is generally known that phase changes of hydration products, such as formation of Friedel's salt and ettringite, occur due to penetration of chloride ion into cement hardened matrix. Ettringite formation leads volume expansion and cracks. Thus, alteration of pore structure in cement matrix could be shown with propagation of micro cracks. It is considered that connective pores can be indicated in a result of mercury intrusion porosimeter. In this study, as for mortar samples subjected to freeze-thaw environment, alteration of pore structure was investigated by using information of pore connectivity shown in depressurization behavior after mercury intrusion. As the results, it was confirmed that residual strain, cumulative pore volume and pore diameter increased due to expansion of original pores influenced by freeze-thaw cycles and chloride ion from deicing agents. In addition to absolute amount of pores presented in mercury intrusion, residual mercury and mercury evacuation volume shown after depressurization of mercury were indicating geometric characteristics of pore structure, such as inkbottle pores and pore connectivity.
Frost damage due to freeze thaw action of pore water in concrete is an important issue on durability of concrete structures in cold regions. It is generally known that different temperature histories in freeze-thaw cycles affect scaling of concrete, in which the pore structure might be changed due to propagation of micro cracks. In previous research, 3D images from X-ray computed tomography have been used to analyze the pore structure of concrete. This study aimed to evaluate the pore structure of mortar under freeze-thaw cycles with different temperature histories by using X-ray computed tomography. As the results, 1) the temperature histories gave different progress of residual strain and void distributions, in which decrease of toutuosity and spacing factor were shown with more residual strain due to frost damage ; 2) propagation of micro cracks due to frost damage probably increases spacing factors and tortuosity calculated from information obtained in analysis using X-ray computed tomography; and 3) tortuosity and spacing factor linearly correlated with diffusion coefficient although void ratio did not correlated with diffusion coefficient. Thus, this study showed that pore connectivity informed from tortuosity and spacing factor evaluated by X-ray computed tomography, in addition to pore structural indicators such as total pore volume, were reasonably discussed with progress of frost damage and alteration of diffusion coefficient.
Volcanic rocks such as andesite have popularly been used for aggregates in the Hokuriku District. Therefore, the andesitic aggregates have contributed to a steady occurrence of alkali-silika reaction (ASR) in concrete. Taking into account the effective utilization of local materials, so-called “Chisan-chisho”, both the reduction in the environmental impact and the rationalization of natural resources, positive countermeasures for mitigating ASR by using blended cements with fly ash (FA) or blast-furnace slag (BFS) are most expected. This paper examines the mitigating effects of mineral admixtures on ASR of mortars by the accelerated mortar-bar test (ASTM C 1260). As the result of test, the replacement with FA or BFS at normal percentages recommended by JIS A 5308 decreased significantly the expansion of mortar bars using reactive andesitic aggregates in the Noto peninsula. Especially, a high-quality fine FA produced in the Hokuriku District is hopeful in its practical use of concrete mixtures. Furthermore the ASR mitigating effects by mineral admixtures are assessed with a good performance by the test method “ASTM C 1260”.
In this paper, the authors studied the physical properties of sewage sludge melt-solidified slag to determine their effects on the properties of concrete for use in PCa concrete. Tests were conducted to determine the physical properties of slag aggregate, properties of fresh concrete, strength of concrete, drying shrinkage of concrete, and leaching of trace elements. We tested seven air-cooled slag aggregates obtained from the same sewage works at different times. Most of the slag was of a low quality, but the resultant slag concrete was not badly affected by the slag aggregate according to the results of the tests for bleeding, concrete strength, drying shrinkage, and leaching of trace elements. In the test for leaching of trace elements, it was particularly interesting to note that there were no notable releases of trace elements from hardened concrete containing slag. In the estimation of the relation between the quality of slag and the strength of concrete, the aggregate crushing value and the abrasion loss of slag were the best indexes for estimating the compressive strength of concrete. However, our findings showed that the relation between the indexes and the split tensile strength and the flexural strength of concrete did not exhibit the same tendency as in the case of the compressive strength of concrete.
Corrosion of paint-coated steel exposed to marine environment is one of the serious problems and there are many researches related to such corrosion. Also it is recognized that the defect plays very important roles in such corrosion. Nevertheless, there are still few studies about the deterioration progress of paint-coated steel around defect. Therefore, the objective of present study is to clarify the corrosion progress of paint-coated steel around defect based on experimental and mathematical approach. In the experiments, accelerated test simulating the sub-tidal zone was conducted to observe the macrocell corrosion behavior as well as microcell corrosion. Here, temperature of the solution was changed as parameter in order to clarify the influence of temperature on corrosion rate. Also a mathematical model for calculation of the macrocell corrosion current around defect was proposed. The conclusions derived from present study were as follows. (1) Anodic current of macrocell corrosion at defect parts and its cathodic current at paint-coated parts increased, as time passed. After much cathodic reaction of macrocell corrosion occurred on steel plate under paint-coating, the coating was blistered and/or ripped, and then microcell corrosion current increasingly occurred there. (2) The higher corrosion current observed with temperature elevation. Also it was estimated that the diffusion of oxygen or Fe2+ controlled the corrosion current after coating's degradation based on the activation energy obtained in present study. (3) A mathematical model for macrocell corrosion current was proposed and the trends of the model agreed with experimental data.
Researches into underground corrosion of steel structures are very few because of its mildness. And corrosion rates in underground corrosion are given only qualitatively or as a certain value based on statistical analysis of mass exposure test result without evaluation of soil condition. So we started to try to evaluate quantitatively the effect of environmental factors on underground corrosion. In this research, the basic underground corrosion properties of steel could be clarified. High temperature acceleration tests were carried out with the parameters of soil grain size, pH of solution, chloride ion concentration and aeration condition. The conclusions are as follows ; (1) Under aerated condition : 1) Corrosion rate of steel in clay, containing no chloride ion, is much smaller than that in aerated water, and can be regarded almost constant between pH 2 to pH10. 2) Corrosion rate of steel in clay and in fine sand, containing chloride ion, is almost constant regardless of the chloride concentration. And uniform corrosion is observed in fine sand while ununiform corrosion is observed in clay, and the corrosion rate is much higher in clay. With electrochemical hydrogen permeation method, pH on the surface of steel goes down from almost 8 to almost 4 in Sumi clay. Furthermore, at the result of polarization resistance measurement, Rp in clay and that in fine sand are not so much difference. 3) In clay, the aeration has little effect on the corrosion rate because of the low oxygen diffusion. (2) Under deaerated condition : 1) Effect of pH without chloride ion : i) In spite of the soil type the effect of pH to corrosion rate is small from pH 2 to pH 12 under soil environment, ii) Under non-soil environment the effect of pH to corrosion rate is small in pH 6 and over, while corrosion rate become very large under pH 2. iii) Corrosion rate is almost the same regardless of soil existence in 6 and over. 2) Larger the grain size, the corrosion rate increases in pH 1, while corrosion rate is almost the same from pH 2 to pH 12 regardless of the grain size with the exception of clay.
In these days, many repair examples of the concrete structure have been reported and the durability of concrete structure is taken up as an important issue. Outdoor exposure test is the most practical way to evaluate the durability of surface coating material on the concrete structure but it requires long time to complete. Therefore it is also a big issue to propose an accelerated weathering test to shorten the time for evaluation. The Subcommittee on Polymers for Repairing and Strengthening Concrete Structures under the Committee on Polymers in Concrete (Chair: Toyoaki Miyagawa) within the Society of Materials Science Japan (JSMS), has conducted common tests on the surface coating materials since 2006. The purposes of common tests are to propose common test procedures which enable comprehensively to evaluate the durability of the surface coating material on concrete. Furthermore the Subcommittee carried out another two weathering tests (accelerated) in the secondary part of the common test to obtain the durability of surface coating material in short time. As a result of investigation on adhesion performance focusing on the relationship between the actual outdoor exposure test and the accelerated weathering tests, it was concluded that an accelerated weathering test was effective for some of the coating systems.