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Curing temperature affects the compressive strength of cement paste systems via the pozzolanic reaction. However, different processes, climates, and weather conditions often result in different initial curing temperatures. The relationship between curing temperature and compressive strength is still an underexplored domain. To explore the effect of curing temperature on calcium hydroxide (CH)-based fly ash composites, fly ashes from different carbon sources were used to make CH-based composites, and the compressive strength, reaction rate, CH content, and C-S-H generation were analyzed. The correlation between the reaction rate and C-S-H content was analyzed. High-temperature curing improved the compressive strength of the cement paste system by affecting the CH-based reaction rate in the initial stage, with the highest initial reaction rate reaching 28.29%. However, after cooling to constant temperature, high-temperature curing leads to a decrease in CH and C-S-H content. The average decrease rate of calcium hydroxide content under high temperature curing is 38%, which is about 2.38 times that of room-temperature curing conditions. This led to a decrease in the compressive strength of the cement paste. Therefore, the performance of CH-based fly ash composites produced by low-temperature curing was superior to that of composites produced by high-temperature curing.

The unburned carbon in fly ash inhibits the performance of concrete. A device using the flotation method to remove unburned carbon in fly ash was developed, and the operating condition of the device was experimentally examined. According to the results, the device was able to remove unburnt carbon from fly ash by using the installed micro bubble nozzles and a whirl-type pump. The removal efficiency of unburnt carbon improved when prior forced stirring was carried out by a concrete mixer for 3 min, and a scavenger was added into the fly ash slurry at a density of about 60 wt%. It has also been confirmed that the method of circulating water is more effective than the method of not circulating water. The elements of the modified fly ash slurry (MFAS) have also been experimentally confirmed as not being too different from untreated fly ash, except for the fact that the content of unburned carbon is reduced. The compressive strength and drying shrinkage characteristics of concrete made with MFAS were investigated. The use of MFAS will reduce the performance of concrete compared to that of ordinary concrete. This shows that in a certain range (15–30%), the influence of MFAS on drying shrinkage is constant. The static elastic modulus and dynamic elastic modulus were also investigated. The above results show that the application of MFAS prepared by the flotation method to concrete is feasible.

Recently, seismic diagnosis and earthquake resistant reinforcement works of buildings built before the new earthquake resistant standards are conducted in various places. However, there is no uniformity in sampling methods, and it seems that there are occasional extreme variations in the determination of representative intensity of the building. In addition, the physical properties of structure concrete which factor of the above-mentioned variations are considered to reflect the horizontal and vertical distribution at the time of concrete placing. Therefore, this study, the core of the existing buildings to be disassembled was collected, and the distribution of physical properties of structure concrete was examined. All target buildings were reinforced concrete constructions, and cores were collected from pillars and waist walls. In addition, there are parts that were built at the time without the ready-mixed concrete plant (from 1960) and pump truck (from 1964). Experimental results of horizontal and vertical distributions of compressive intensity at the pillars and waist walls revealed that there was no greatest decrease in strength and there was not much difference between the maximum strength of the pillar and 300 mm from the vicinity of the pillar and about 300 mm from F. L. Therefore, from this study, it seems that the position of 300 mm from the pillar and F. L. is suitable for the measurement position which develops the representative intensity of the building.

Because fly ash has pozzolanic activity, it has been used for a long time as an admixture for concrete. However, unburnt carbon in the fly ash adversely affects the fresh properties of concrete. For this reason, when fly ash having a high unburnt carbon content is used as an admixture for concrete, it is desired to reduce the amount of unburnt carbon. So far, at our university, we have developed a technique to remove unburnt carbon by flotation method. It is necessary to add a scavenger and a foaming agent when using this equipment. However, the appropriate amount is unknown. Therefore, we investigated a method to easily estimate the amount of chemicals suitable for flotation treatment from the physical properties of raw fly ash. It is obvious that efficient treatment can be performed when the addition amount of scavenger and the addition amount of foaming agent is set to 10: 1, and that the addition amount of the agent can be accurately estimated by using the methylene blue adsorption amount of fly ash.

It has been clarified that the particle shape and particle size distribution of fine aggregate have influenced the fresh properties of concrete and mortar in the past research. But it has not been sufficiently studied how each particle size and particle size distribution of fine aggregate affects the fresh properties of mortar and concrete. In this study, we adjusted the particle size of fine aggregate, and evaluated fresh properties of mortar by indicators. We investigated the fluidity of mortar, which changed depending on the composition of particle size distribution. In addition, the behavior of fresh properties of mortar contained powder substituted as part of cement and fine aggregate adjusted particle size distribution was compared with that when no powder was mixed. Its behavior was discussed. It became clear that, the factor influencing the fluidity varied depending on the composition of particle size distribution. The influence of fine particles on fluidity of mortar varied depending on the content of fine particle and the particles size distribution. When combined with the large particles, the fluidity was improved as compared with the combination with the intermediate particles. In addition, the same tendency as in powder-free mixing was confirmed at powder mixing and increase rate of the relative flow area ratio when fly ash was contained became larger than when the limestone fine powder was contained.

Using fly ash as an admixture for concrete can contribute to environmental load reduction and concrete quality improvement. However, as the quality of fly ash fluctuates depending on the ash source, quality stabilization is required. It was proved that concrete with fly ash of Japanese Industrial Standardized class II has different strength properties depending on curing temperature, but it is not obvious whether concrete with modified fly ash by flotation method has similar properties. In this study, the influence was examined on the mechanical properties when changing the curing temperature of mortar using fly ash modified by the flotation technique. The sealing curing was set to 5°C, 20°C, 40°C and 60°C. Also, after 7 days, 5°C, 40°C and 60°C, is changed to 20°C and compression strength and static elasticity coefficient were measured. The value of compressive strength and static elastic modulus showed that mortar using modified fly ash had the same characteristics as mortar with ordinary fly ash. Because it was represented by one strength compressive estimation curve regardless of the curing temperature, it became clear that compressive strength can be evaluated by roughly using accumulated temperature as an indicator.

In Japan, it is forecasted that massive amounts of concrete waste material will be generated in the future as a result of demolition of many buildings, and expansion of the use of recycled aggregate is expected. In this study, it was verified the effect when relatively large amount of admixture is mixed, a combination of recycled fine aggregate of different quality and various admixtures, combination of each admixture in order to realize high strength and high durability by using recycled aggregate. The increase in the drying shrinkage ratio due to the deterioration of the recycled fine aggregate quality was larger than the fluctuation due to the admixture mixing ratio and the drying shrinkage ratio was distributed by forming a group for each quality of recycled fine aggregate. In the relationship between the pore volume and the compressive strength, when evaluated with pore volume of 2 μm or less in both cases, a good linear relationship could be confirmed. The relationship between the pore volume and the drying shrinkage rate was similar. Therefore, it was suggested that compressive strength and drying shrinkage ratio of mortar contained composite recycled fine aggregate and admixture could be predicted by evaluating with the pore volume of 2 μm or less.

Cement concrete requires strength, durability, and workability. Furthermore, the appearance of concrete must be good. Recently, the concrete industry has a tendency to actively utilize byproducts, all over the world. But, consumers dislike the color of concrete using byproducts. This is an obstacle to the active use of byproducts. However, it is not clearly understood how consumers make the impression to color of concrete using byproducts. Therefore, we conducted a questionnaire survey using concrete using byproducts, and analyzed the answers with factor analysis and covariance analysis. As a result, the following was clarified: (1) three factors, such as beauty, massiveness and familiarity, were extracted as a factor of exposed concrete appearance, (2) the beauty of concrete was enhanced by the whiteness of the surface and was worsened by pits and surface yellowing, (3) the massiveness of concrete was worsened by the beauty and surface whiteness, and (4) even though the subjects knew that recycled byproducts were used in concrete, the evaluation of beauty did not change.

Problems with filling can lead to rebar corrosion and impair the durability and all other functional aspects of reinforced concrete structures. However, the prevention of concrete filling defects is left to the skill, judgment, and experience of on-site operators. In this research, we develop a methodology for quantitatively estimating the rate of occurrence of concrete filling defects. By this, we hope to promote the efficient and effective prevention of such defects at construction sites. Therefore, as a model for defective filling, we propose a mortar loss model in which the mortar component of concrete free falling into the frame adheres to the reinforcing bars in the frame, and based on that, we conducted an experiment. Using actual measurement data, we quantitatively estimated the risk of defective filling.

In the field of concrete, Fly ash and crushed stone powder which are by-product powders andlimes stone powder are used as admixture materials for concrete from the viewpoint of environmental load.Then we should use by-product powders as materials of the concrete as a substitute of fine aggregate.Therefore, it is necessary to predict fluidity of the concrete with powders in large quantities. In this study, wetried a fluid evaluation of mortar with various by-products powders and a fluid prediction by grasping a fluidtendency of mortar with various powders as a part of fine aggregate, and adopted the thickness of a surpluswater film theory and the relative flow area ratio as an evaluation index. We clarified when used by-productpowders as a part of fine aggregate, we can use excess water film for an index. But the value of the relativeflow area ratio was different because of the same thickness of a surplus water film depending on the kind ofthe powder. It was thought that the fluidity of mortar was able to predict by applying the correction valueproposed by this study in various mixtures that used the by-product powder.

It is known that the risk of the industrial injury according to the age of workers is high in the low age workers and advanced age workers. And it is clarified that one of the reasons of the risk of advanced age workers is high, is decrease of the physical strength of them by aging. Then, for about 1000 workers, we surveyed the relation between the age and physical strength of workers, and this report is a summary of the result of the survey.

The concretes containing large quantity of fly ash with constant portland cement content were produced at the ready-mixed concrete plants, and placed into full scale formworks. Their fresh and hardened properties were measured and discussed.1.At various fly ash content per unit volume, for example 455kg/m3, the concretes which have various flowability, such as medium or high fluidity concrete, were produced easily. And they could be filled smoothly into narrow space of wall formworks with reinforcements.2.The fly ash concretes appeared higher compressive strength from the early age and carbonation resistance than those of the concrete without fly ash.

In this study, we examined method of test for setting time of concrete mixtures. Generally, the setting time of concrete mixtures is demanded by variation of penetration resistance, which is measured by manual labor for about eight hours. This measurement takes considerable effort. In late years, automatic devices to measure penetration resistance are commercially available, however the price is high. To solve these problems, we proposed a new low-effort and low-cost method: Embedded Weight Test. In the Embedded Weight Test, an embedded weight is hung with a line in the concrete mixture, and the tension of the line is measured by a data logger. The tension of the line had a variation point. The variation point is regarded as the time when the concrete mixture begins to vary from liquid to solid. As a result pf Embedded Weight Test with cement paste, the variation point of the tension was correlated with the initial setting time, which was defined by ISO 9597.Similar results were obtained when Embedded Weight Test was carried out with mortar. The variation point of the tension was correlated will help to estimate the time such as limits from mixing to the completion of placing or limit for intervals placing operations.

When we use the fly FA-As a concrete admixture, it is known that the properties of the concrete improve. But when we made concrete with fly FA-Fresh property of concrete is adversely affected by unburnt carbon in the fly ash. If there are much quantities of unburnt carbon in the fly ash, they inhibit air entraining performance and fluidity of flesh concrete. So we developed the device removing unburnt carbon from the fly FA-By flotation method in previous studies. It was succeeded remove of unburnt carbon in the fly FA-And to clean the surface of the fly FA-By used the developed device removing unburnt carbon in the fly FA-By flotation method. In this study, it was purpose to confirm the change in the composition and physical properties between the original fly FA-And the reformed fly FA-By flotation method, and to grasp the effects that the physical properties of fly FA-Gave to the unburnt carbon removal when using flotation method. As a result, the specific surface area of reformed fly ash is larger than original fly ash. However, the change of chemical composition for reformed fly FA-By flotation method was as small as 4% at the maximum. It was considered that the addition rate of kerosene and pine oil and the pre-treatment time were changed by difference in sizes and shapes of unburnt carbon in the fly ash. Percent flow and activity index were influenced by the different of physical properties of original fly ash.

In this study, we examined the compressive component of half precast concrete. Form work is unnecessary in half precast concrete, and it is able to reduce cost of the construction. In Japan, the damage of housing by Typhoon and Tornado occurs frequently in recent years. Therefore, there is a possibility that the construction of half precast concrete house will increase in the future. The section of half precast concrete is consisted of two kinds of concrete. However, most studies of concrete engineering have focused on single layer concrete. The studies of double layer concrete are not enough. It was confirmed that the maximum compressive load of the compression member increased by making the aspect of the mortar double layer of a shell and a core by the past study. In this study, we made non-line mortar specimen (diameter: 100mm) imitated half precast concrete column. By the experiment, we examined the design formula of maximum compressive load of half precast concrete. We proposed a design formula to add ΔP (increment by sectional constitution of plural concrete, 28 kN in this experiment) to Pms (maximum compressive load by calculating the product of the compressive strength, in consideration of the distortion in the specimen fracture, and cross-sectional area of the shell and core).