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Huge amounts of Portland cement which is a main constituent material of concrete is manufactured and carbon dioxide (CO2) emitted by the manufacturing process of cement can cause global warming. Geopolymer (GP) contains no cement as a binder and several industrial by-products such as fly ash and blast furnace slag, so the spread of GP contributes to the reduction of global warming and the environmental load. GP has low CO2 emissions, high durability due to chemical attack and fire resistance, however, viscosity of GP is higher than that of cement concrete. Although chemical admixtures can be effective to the improvement of workability, most commercial products of them are for cement concrete. In this study, mortar flow and compressive strength of GP were experimentally evaluated in order to investigate effects of several chemical admixtures for cement concrete. Water glass and caustic soda solution were used as an alkaline-activating solution, and water glass causes high viscosity of GP mortar, so mortar flow test and compression test were conducted by using GP mortar with and without water glass. Test results indicate that the GP mortar without water glass had lower viscosity and lower compressive strength than that with water glass. The chemical admixture whose base component is naphthalenesulfonic acid was most effective to fluidity and compressive strength of GP mortar without water glass.

Oysters are produced in each district in Japan, and Hiroshima Prefecture is especially famous as a high producing district. Accordingly, the production of oysters has created oyster shells as a by-product. Oyster shell porous concrete (OyPoC) is porous concrete using crushed oyster shells as aggregates. In previous researches, it was found that OyPoC with finely crushed oyster shell had high plant-growing performance. However, all of the planting test periods were less than three months; the long-term plant-growing performance of OyPoC had not been clear. In this study, the plant-growing performance of OyPoC was investigated by conducting long-term planting tests over one year. OyPoC and hybrid porous concrete (HyPoC), which was combined with OyPoC and crushed stone porous concrete, were prepared for the planting tests. From the test results, the plant-growing performance of OyPoC was higher than that of HyPoC because OyPoC had much higher oyster shell aggregate than HyPoC. In contrast, there was a risk of the severe summer drought withering the grass on OyPoC and the watering in the summer was found to be important.

The present study investigates tensile properties of concrete with and without fly ash at early age, such as tensile Young’s modulus, strength and creep. Some Young’s modulus of fly ash concrete for thermal crack analysis was compared with the tensile Young’s modulus, secant modulus, initial tangent modulus and linear modulus obtained from the direct tension test and compression test. The tensile creep test was also performed to obtain the specific creep behavior considering decrease in elastic strain due to stiffness development at early age during creep test. The results show that the Young's modulus for crack evaluation can be obtained from the compression test based on the stress range less than the splitting tensile strength, while the compressive secant modulus was smaller than the tensile Young's modulus. The decrease of the elastic strain at early age contributes more to the evaluation of the tensile creep than the use of the fly ash mixing.

Global warming is the gradual increase in global temperatures owing to trapping of heat in the atmosphere by greenhouse gases. As of January 2020, 121 countries and 1 region, including Japan, pledged to achieve carbon neutrality by 2050. One of the measures for achieving this goal is the promotion of low-carbon urban development, which includes urban greening. Oysters are produced in all districts of Japan but Hiroshima Prefecture is particularly famous for its high production levels. The production of oysters generates oyster shells as a by-product, which are used commercially as livestock feed and a soil conditioner. However, the reuse of oyster shells remains limited. Pervious concrete is a special type of concrete in which single-sized aggregates are bound together with cement paste or mortar and is considered an environmentally friendly material because of its high water permeability. Therefore, we investigated whether oyster shell pervious concrete (OyPC) containing crushed oyster shell aggregate would be suitable for growing plants for potential application as a planting foundation for urban greening. Zoysia tenuifolia sod or Kentucky bluegrass (Poa pratensis) seeds were directly placed or sown in soil on the surfaces of OyPC and crushed stone pervious concrete specimens, which were then placed in plastic containers for either 72 days (short-term planting tests) or 802 days (long-term planting test). OyPC had a higher plant-growing performance than crushed stone pervious concrete in both the short- and long-term planting tests and also pumped the water from the container to moisten the sod and the soil covering the seeds, assisting the growth of plants. The grass on OyPC that has a small particle size could grow without water retention material which is indispensable to crushed stone pervious concrete for greening. These findings indicate that OyPC would be feasible for application as a planting foundation for urban greening.

Initial cracks due to volume changes at an early age affect the durability of concrete structures, so numerical simulations are often conducted in order to predict cracks. Such prediction requires some mechanical properties of early age concrete. Tensile Young's modulus is directly dependent on the prediction of tensile stress and is one of the important input data for FEM analysis. However, direct tension test for tensile Young's modulus needs a unique apparatus and specimen, and such test is not suitable for evaluating Young's modulus at early ages of concrete. The present study compared tensile Young's modulus with compressive Young's moduli of Fly ash concrete. Compressive Young's moduli used in this study were secant modulus and initial tangent modulus. In addition, linear modulus taken from a regression line of a compressive stress-strain curve in the range of stresses less than the splitting tensile strength was also evaluated. It is found that the secant modulus, which is generally used as Young's modulus in Japan was clearly smaller than the tensile Young's modulus, which means that, tensile stresses evaluated using a secant modulus might be underestimated. On the other hand, linear modulus and initial tangent modulus were almost equal to the tensile Young's modulus. This result indicates that tensile stresses can be evaluated using Young's modulus obtained from a compression test with general apparatus and specimens.

Tensile properties are important for predicting tensile stress which causes thermal cracking. Fly ash, a by-product from coal-fired power plants, has been recently used to reduce such thermal cracks. However, investigations dealing with tensile properties of fly ash concrete are still limited. This study focuses on the tensile properties of concrete mixed with fly ash at an early age. Fly ash was mixed in general purpose concrete with a cement-replacement ratio of 20% by mass to simulate fly ash concrete used in Japan. To examine tensile Young's modulus and tensile creep, direct tension test was conducted using dog-bone shaped specimens. The tensile creep tests were conducted at the age of 3 days or 7 days, and the loading (30% of splitting tensile strength at the loading age) was sustained for 14 days. Past investigations usually assumed a constant elastic strain during creep test. It should be noted however that elastic strain at early age decreases with the age of concrete as hydration continues. This study takes a consideration of Young's modulus development during creep test to distinguish actual creep and elastic strains. Test results show that creep strain has been underestimated when assuming constant elastic strain.

Hiroshima prefecture is famous for a producing district of oyster in Japan. While the production of oyster in Hiroshima prefecture was about 60％ in Japan, oyster shell of about 100,000t was produced as a by-product. The authors have studied on utilization of oyster shell as concrete material. In this study, oyster shell fine aggregate was produced by crushing oyster shell finely, and the effect of oyster shell fine aggregate on fresh and strength properties of Oy-Con was investigated. Oy-Con（oyster shell concrete） was the concrete substituted oyster shell fine aggregate for a part of fine aggregate. The substitution rates of oyster shell fine aggregate were varied from 0％ to 50％. Tests for content of chloride ion, bleeding in percent, setting time, compressive strength, static modulus of elasticity, tensile strength, flexural strength were conducted as fresh and strength properties tests. From the test results, the content of chloride ion increased proportionally as the substitution rate increased. Including oyster shell fine aggregate in concrete, the bleeding in percent degreased, and the initial and the final setting times were short. The strength properties of Oy-Con increased as well as usual concrete with the age, but decreased as the substitution rate increased in all age.広島県は全国有数の牡蠣の産地であるが、その一方で大量の牡蠣殻が発生するという問題も抱えている。本研究では、細骨材の一部を破砕した牡蠣殻で置換した牡蠣殻コンクリート（Oy-Con）について試験を行い、その基礎特性に及ぼす牡蠣殻細骨材の影響について検討を行った。試験結果より、牡蠣殻細骨材置換率の増加に伴い、Oy-Con中の塩化物イオン含有量は比例的に増加した。また、牡蠣殻細骨材をコンクリート中に混入することにより、ブリーディングは少なくなり凝結時間は早まる傾向を示した。Oy-Conの圧縮強度などの強度特性は材齢の経過に伴い増加するが、いずれの材齢においても置換率の増加に伴い強度特性は低下する傾向を示した。

The thermal power generation is one of main generation of electricity in Japan. The fuels of thermal power generation are coal, oil and liquefied natural gas. While the price of coal is stabilized, the emission rates of CO₂ , SOx, NOx, dust and soot from coal fired power station are very large compared with other fossil fuels. Integrated coal Gasification Combined Cycle（IGCC）is new technology of coal fired power generation with low environmental impact. In IGCC, the gas is produced from the coal at the gasifier, and the electricity is generated by combined cycle. The coal gasification slag is collected from the gasifier in IGCC. In this study, the application of coal gasification slag to fine aggregate for concrete was investigated. Two types of coal gasification slag, which were original and grinded slag, were used for the tests. From the test results, the physical properties of coal gasification slag, especially grading and particle shape, were improved by grinding slag particle. Both original and grinded slag had no effect on the fresh properties of concrete when the substitution rate of slag was 25％. However, the substitution rate of slag was over 50％, slag concrete showed little tendency of segregation in spite of low water content. The air content of slag concrete was very low within a range of 1.1 to 1.4％. The strength properties of slag concrete were equal to or greater than concrete without slag when the substitution rate of original slag was less than 25％.高い発電効率を持つ石炭ガス化複合発電では、石炭灰がガラス状の石炭ガス化溶融スラグとして排出される。本研究は、石炭ガス化溶融スラグのコンクリート用細骨材への適用性について検討を行った。試験では、排出されたままの未処理スラグと磨砕処理を行った磨砕スラグの2種類を用いた。試験結果より、スラグを磨砕することで細骨材としての物理的性質は向上し、特にスラグ全体の粒度、粒形が改善されることが分かった。本研究で使用した2種類のスラグでは、置換率25％程度であればコンクリートの練上がり状態および強度特性に対して大きな影響は及ぼさなかったが、空気量はスラグの種類や置換率に関わらず、約1％の低い値を示した。

本研究は形状寸法の異なる鋼繊維で補強したコンクリートの水密性および曲げ特性について研究を行ったものである. 1種類の繊維のみを混入した単一繊維補強の試験結果より, 使用繊維を長繊維と短繊維に分類することができ, 各繊維の補強効果はそれぞれ異なることを明らかにした. 2種類の繊維を組み合せて混入したハイブリッド繊維補強の試験結果より, 水密性に対して効果的な繊維の組合せが, 必ずしも曲げ特性に対して効果的でないことから, 繊維の組合せ効果は水密性と曲げ特性に対してそれぞれ異なることが分かった. また, 水密性と圧縮強度の相関が良いことから, コンクリートの強度を説明するセメント空隙比説を用いて, 水密性に対する繊維の組合せ効果の定量化を行った.

The structure inspections are to check out safety problems of the public facilities and to ensure a high level of safety for all users. Generally, the initial inspection of concrete structures is carried out using visual inspection. These methods are qualitative and based on empirical knowledge. There are few data and useful system for supporting visual inspection. The goal of this paper is to evaluate structure damages for the visual inspection, for developing the computer aided system of the deterioration diagnosis of concrete structures. This system is based on Kansei engineering since the concrete experts have such kinds of human feelings (Kansei) of "safety". Kansei engineering is able to transfer feelings to the field of visual design. We could obtain the databases of diagnosis information to identify the relationship between the structure damage and expert estimation. The structure inspectors are able to ensure high safety of structures using this information.