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In this study, supercooling effects on the hygrothermal behavior of fired clay materials under various experimental conditions, such as water content, cooling rates, and size of specimens were investigated using experimental methods and hygrothermal simulations. We report results of the differential scanning calorimetry (DSC) and temperature distribution changes during a freeze–thaw (FT) experiment using unsaturated specimens. Also, we developed a numerical model of the freezing and thawing processes including the supercooling processes. The DSC results show the freezing of the supercooled water in a fired clay material is considerably faster than that in cement-based materials. It was also found that the dependency of the supercooling effects on the cooling rates seemed to be small. When the water saturation of a material decreases, the rate of the ice saturation increase during the freezing of the supercooled water is decreased while the freezing points of the supercooled water was not changed considerably. The comparison of the results of the FT experiment and hygrothermal simulations show that the combination of the existed hygrothermal model and a modified kinetic equation can reproduce the rapid temperature rise during the freezing of the supercooling water in the FT experiment. Finally, the size effects of specimens on the supercooling phenomenon was discussed based on the experimental and calculation results. The freezing points got higher when a specimen was larger. Due to differences in the ratio of the surface area to the volume, hygrothermal behavior in small specimens and relatively large specimens like that of the DSC and the FT experiment, respectively were markedly different. Water in a relatively large specimen with a small ratio of surface area to volume can achieve the thermodynamic equilibrium in a short period after the freezing starts.

Microcracks inside concrete have close relations with the mechanical properties and the durability of concrete. The purpose of this study is to investigate the relationship between the mechanical properties of damaged concrete and the cracks with the width of several micro meter. This study proposes a quantitative evaluation method for damage of concrete through the crack observation using a microscope. In this proposed method, the density of cracks is evaluated based on the number of cracks and the traverse length in a similar way with the linear traverse method for the air-void system. Several damaged concrete specimens were prepared with uniaxial cyclic compression loading. The compressive stress ratios and the number of loading cycles were varied as the experimental parameters. The experimental results showed that the number of cracks increased with the increase of the compressive stress ratios and the number of loading cycles. The increase of micro cracks showed good agreement with the decrease of ultrasonic pulse velocity. In addition, the density of cracks have a direct correlation with the modulus of static elasticity, the consumed energy, and the residual strain of the damaged concrete. Finally, this study suggests a possibility to estimate the mechanical properties of the damaged concrete through the crack observation.

Frost action is one of the main causes for deterioration of porous building materials under defined hygrothermal conditions. For an accurate assessment of the frost damage risk under various environmental conditions, thermal, moisture, and mechanical properties should be considered; the hygrothermal properties affect the distribution of temperature and amount of frozen water in the material, whereas the mechanical properties are necessary to predict deformation and damage. Moreover, the dependency of these properties on the moisture content should be understood. Therefore, in this study, thermal, moisture, and mechanical properties of wet and dry fired clay materials were measured. The fired clay materials were sintered at two different temperatures, 1000 °C and 1100 °C (samples T10 and T11, respectively) for comparison. The measured thermal and mechanical properties are considerably different in the wet state compared to the dry state. Freeze–thaw tests were conducted to investigate the relation between the material properties and the frost resistance under a simple experimental condition. As expected, based on the pore structure and obtained mechanical properties, T10 exhibited lower frost resistance than T11 in the freeze–thaw test. Finally, frost damage risk was assessed under various environmental conditions based on the obtained hygrothermal and mechanical properties.

This paper presents the results of an experimental investigation on the material properties and self-healing ability of a blended cement mortar incorporating blast furnace slag (BFS). The effect of different types and Blaine fineness of BFS on the material properties and self-healing was investigated. Thirteen cement mixtures with BFS of different types and degrees of Blaine fineness are tested to evaluate the mechanical properties, namely compressive strength, bending strength, freeze&ndash, thaw, and accelerated carbonation. The pore structure is examined by means of mercury intrusion porosimetry. Seven blended mortar mixtures incorporating BFS for cement are used to evaluate the mechanical properties after applying freeze&ndash, thaw cycles until the relative dynamic modulus of elasticity reached 60%. The experimental results reveal that incorporating BFS improves the mechanical properties and self-healing ability. In the investigation of self-healing, smaller particle and high replacement ratios of BFS contribute to increasing the relative dynamic modulus of elasticity and decreasing the carbonation coefficient in the mortar after re-water curing. Moreover, BFS&rsquo, s larger particles and high replacement ratio are found to provide better self-healing ability. A regression equation is created to predict the relative dynamic modulus of elasticity in mortar considering the Blaine fineness, BFS replacement ratio, and curing conditions.

To investigate the supercooling phenomenon in fired clay materials, low-temperature differential scanning calorimetry (DSC) and a one-dimensional freeze-thaw (FT) experiment were performed on saturated specimens. The rate of increase in ice saturation during freezing was calculated from the DSC result. Rapid ice growth over a relatively narrow temperature range (within about 0.2 K) was observed at a cooling rate of 0.25 K/min. In the FT experiment, the temperature distribution of a specimen was measured with inserted thermocouples. According to the results of the FT experiment, a rapid temperature increase was observed at sub-zero temperatures accompanied by freezing of the supercooled water. When the supercooled water began to freeze, the released latent heat was found to strongly prevent the specimen temperature from dropping even during the cooling period. Finally, a hygrothermal model of freezing and thawing including a non-equilibrium supercooling process was developed. The freezing rate of the supercooled water was modelled based on the DSC result. The validity of the model was verified by comparing the results of the FT experiment and calculations. The model was found to be able to replicate the rapid temperature rise during the cooling period of the FT experiment.

The aim of this study is to demonstrate the enhanced durability of concrete using volcanic ash instead of fine aggregate. There are many types of volcanic ash with various characteristics in Hokkaido, Japan. Four types of volcanic ash were selected for use in this study. The focus is placed on the role of the amorphous phase in the fine particles of volcanic ash, and finally on the chemical composition of the amorphous phase that is linked with pozzolanic reactivity. Pozzolanic reactivity of volcanic ash is then evaluated by paste experiments. Also, a concrete experiment is performed and tested to check durability (carbonation).

This study investigated the effect of temperature and time at temperatures lower than 0 &deg, C on mortar mixed with antifreezing admixture to determine the temperature&ndash, time function with the aim of expressing the effect universally. As a result, the maturity equation for temperatures lower than 0 &deg, C proposed in previous studies was verified to be applicable to type-B blast furnace slag cement. The applicability of this equation at temperatures lower than 0 &deg, C had not been investigated hitherto. The strength development attributable to the effect of the antifreezing admixture can be expressed as the reference temperature, and the reduction in the chemical potential of water chemical potential reduction was found to depend on the reaction rate. A new maturity equation for temperatures lower than 0 &deg, C was proposed considering the effect of the antifreezing admixture.

This report deals with the effects of normal air temperature obtained from 3 measurement periods(1961-1990,1971-2000,1981-2010) on change of applicable period of cold weather concreting and maturity related to construction plan. According to the results of this study, it made clear that applicable period of cold weather concreting based on latest normal value is shorter than the previous period which are described in JASS5-2009. And maturity based on latest normal value is also bigger than the maturity based on previous normal value.

In recent years, use of low heat Portland cement is promoted. However, there was no general method to predict the strength development of the concrete using cement which has wide range of mineral composition. In low heat Portland cement, it was pointed out that application of “Maturity method” was difficult. We considered application of the equivalent age to predict the strength development of concrete using various type of cement. Then, we examined the strength development of mortar using cement has wide range of mineral composition under different curing temperature. As a result, the temperature dependency of strength development of various cements was explained by the equivalent age. The values of the apparent activation energy of cement were dependent on its mineral composition.

The aim of this research is to propose a method to predict the strength development of concrete using equivalent age. The experiment of strength development was carried out. Ordinary Portland cement, moderate-heat Portland cement and low-heat Portland cement were used for concrete specimen. Water cement ratio was ranged from 0.3 to 0.6. Strength development of concrete cured below subzero temperature was examined too. The result showed that the apparent activation energy in equivalent age equation depends on mineral composition of cement. Furthermore, the effect of freezing on the reaction rate of strength development was shown. Consequently, the strength development of concrete can be estimated from mineral composition of cement, nominal strength of concrete and curing temperature by the method proposed in this paper.

Compressive strength prediction of concrete is essential in cold weather concreting. Maturity method and strength prediction method using logistic curve have been used for cold weather concreting in Japan. This method is limited within the range from water to cement ratio 45% to 65%. In this paper, we propose a strength prediction method for enhancing the range of water to cement ratio. The experimental data in the past was used and analyzed. As a result, the approximation by Gompertz curve showed high accuracy in the strength prediction of the concrete within the wide range of water-cement ratio. We propose the new strength prediction method for applying Gompertz curve.

Compressive strength development of concrete is essential for cold weather concreting. It is well known that strength development of concrete under the freezing point is much delayed. But the evaluation method has not been shown clearly yet. Therefore when average outside air temperature is under the freezing point planning method of cold weather concreting is not clear. We focus on the concept of equivalent maturity method proposed by Sudo, attempted to propose a time-temperature function representing the strength development of concrete under sub-zero temperature. As a result, we have proposed a function to calculate the maturity under sub-zero temperature. The proposed function could explain the strength development of the concrete exposure in winter.