Studies on Good Use of Inferior-Quality Aggregates in Concrete Structures for Agriculture

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In order to make good use of inferior-quality aggregates in concrete structures for agriculture, investigations were carried out on aggregates used for this purpose in Tohoku, Kanto, Tokai, Hokuriku, Kansai, Chugoku, and northern and southern Kyushu.It was found that the types of aggregate in each region could be utilized as materials for concrete from experiments to determine grading, specific gravity, absorption, soundness, alkali-aggregate reaction, compressive strength and mechanical properties.In order to control the alkali-aggregate reaction, a small percentage of ash was mixed with the concrete, and the alkali-aggregate reaction of the ash-mixed concrete was investigated. This confirmed the availability of ash for this purpose.In order to extend the life of farm pond concrete walls, it is necessary to ensure that no cracks form as a result of temperature stresses created by the heat generated in the cement during setting and hardening. A three-dimensional heat conduction problem in a Cartesian coordinate system was solved using the finite element method for predicting the temperature distribution in farm pond concrete walls. The maximum temperature and internal concrete temperature difference predicted by the three-dimensional finite element model using normal Portland cement and a steel form are 39ﾟC and 29ﾟC respectively.In order to reduce the difference between the maximum temperature and internal concrete temperature, Portland blast-furnace cement B, an admixture for reducing the water content and a plywood form may be used. The maximum temperature and internal concrete temperature difference predicted by this model are 36ﾟC and 25ﾟC, respectively. This three-dimensional model should be useful for predicting concrete wall temperatures, thus facilitating the study of planning systems.