Biodegradable resin concrete is a kind of new concrete. The strength of the biodegradable resin concrete is decreased over time by many external factors such as microbial degradation and water. The aim of this study is to use biodegradable resin concrete as a temporary construction material in the future. Temporary construction materials have to maintain adequate strength during the construction period. Therefore, it is very important to estimate fatigue life and determine how long biodegradable resin concrete applied as a temporary construction material retains the expected strength. This study describes some mechanical test results and reveals the degradation characteristics and the degrading factors of biodegradable resin concretes. Furthermore, statistical deterioration prediction formulas were designed using the Weibull distribution. From the estimation model, the strength retention period of biodegradable resin concrete can be estimated.
In recent years, cases of temporary construction materials being left in the ground following excavation work have been increasing. In this context, the application of biodegradable resin concrete as a new temporary construction material that does not require removal might be useful. Currently, various types of biodegradable resin are used, each with different degradation characteristics. In order to investigate the level of degradation of biodegradable resin concrete according to the resin, PBSA and PLA resins were used, and comparison experiments examining mechanical characteristics and surface degradation were conducted. As a result, the surface degradation of the biodegradable resin concrete made using PBSA was found to be more remarkable compared with that made using PLA. On the other hand, the early-age strength of PLA specimens was found to be higher than PBSA specimens, and the strength retention period of PLA specimens was longer than that of PBSA specimens.
Against a backdrop of depleted supplies and the declining quality of natural aggregate, concrete with crushed aggregate is widely used in the construction of important concrete structures. This report introduces research on quality improvements achieved using the SEC (Sand Enveloped with Cement) method, a two-stage mixing method, for the purpose of improving segregation qualities (including bleeding) and workability, which often present issues when using concrete with crushed aggregate. The research results confirmed reductions in bleeding, as well as dramatic improvements in properties closely associated with concrete durability, including compressive strength, drying shrinkage, and water and gas permeability. It was concluded that the SEC method helps achieve uniformity of the concrete within concrete structures and effectively improves quality.
This This paper describes an evaluation method for the nondestructive inspection of chloride concentration in concrete using electrical characteristic. First, the fluctuations of impedance-frequency characteristic, phase-frequency characteristic, water content of concrete and water vapor content of the air were measured over a long period. Next, the interrelationships of these parameters were confirmed, and an evaluation formula of chloride concentration was proposed. Finally, evaluation values corresponding to three chloride concentrations (0.0, 1.2, 2.4 kg/m3) were calculated and t-testing was performed. Each of the resulting evaluation values was found to meet the significance level of 0.1%. Thus, the proposed method is shown to be suitable for evaluating the chloride concentration in concrete.
This paper describes the modeling of early age strain behavior of high performance fiber reinforced mortar with high compressive strength of about 100 N/mm2, based on experimental results and taking into account the effect by both adding expansive admixtures and the volume content of short steel fibers. The effect of early-age strain on the tension softening properties of HPFRM in the hardened state was found to be small except in the case of excess expansion caused by high content of expansive admixture. On the other hand, the volume content and length of short steel fibers affected these properties to a greater extent in terms of tensile residual stress and effective fracture energy.
Evaluation methods for the reduced area ratio of rebars based on non-destructive tests are examined for RC beam specimens with two rebars having different corrosion ratios. Measurement of crack widths and ultrasonic wave velocities are applied as non-destructive tests. It is shown that the reduced area ratio of rebars can be estimated with a sufficient margin of safety even though the tests are carried out under conditions that prevent determination of the influences caused by the corrosion of the two rebars. In addition, the flexural capacity of the beam specimens is calculated by substitutions of the reduced rebar areas estimated from the tests into the formula given in the Standard Specifications for Concrete Structures of JSCE.
The relationship between the surface permeability and pore volume of heavyweight concrete made using metal slag-type heavyweight aggregate with SSD density of over 4.0 g/cm3 was investigated. This concrete was proportioned to provide a density of 3.0 t/m3. Within the scope of this experiment and for practical reasons, adopting 0.1μm as the reference size, the surface permeability and pore volume of this concrete showed a high correlation, with the permeation rate increasing as the percent volume of pores larger than 0.1μm increased. Moreover, the addition of an appropriate amount of an expansive additive or fly ash was found to decrease the percent volume of pores 0.1μm or higher, while reducing the permeation rate. In this study, volume ratios were used instead of weight ratios to compare the pore volume of concretes with different densities.
The isosteric heat of adsorbed pore water in hardened cement pastes was determined under atmospheric pressure and a prediction model of isosteric heat using an absorption isotherm model was proposed. An experimental system in which changes in vapor pressure can be calculated according to the temperature data during heating and cooling was developed, and the isosteric heat was evaluated with the Van’t Hoff plot. The value of isosteric heat was found to increase with decreases in water content, and the increase was particularly pronounced for water content of less than 15%. The calculation results of the proposed model agree well with the experimental results on the whole, indicating that the proposed model may be suitable as a constitutive law expressing the relationships between water content and isosteric heat.