The influence of NaCl on initial strength enhancement effect of concrete using seawater as mixing water is dominant, which is the main component of seawater. The initial hydration of the C3S is promoted by NaCl. Compared with the case of using tap water, it was confirmed that the formed tissue is denser. Previously, self-compacting concrete using sea water and unwashed sea sand for urgent restoration works as well as for construction work at isolated islands and other similar region where fresh water is not sufficient was developed. In this study, strength, drying shrinkage and thermal properties of concrete with sea water and unwashed sea sand are experimentally examined. It is found that initial strength development increased as compared with the control concrete made of tap water and land sand. Drying shrinkage strain and autogenous shrinkage strain of concrete were almost equal or higher than the control concrete, but the improvement of crack resistance was observed. Furthermore, in regard to the thermal properties, the rate of temperature rise due to the accelerated hydration reaction and the coefficient of thermal expansion was slightly larger. Considering these properties, the proposed concrete can possibly be used for un-reinforced concrete application.
This paper introduces the results of tensile fracture analysis of Fiber Reinforced Cementitious Composites (FRCC) with reinforcing bar by means of meso-scale analysis concerning discretized short fibers. The effects of fiber volume fraction, steel reinforcement ratio, bond characteristic between steel reinforcement and FRCC, and fiber distribution on the tensile fracture are numerically investigated. The analytical result shows that there are cases in which cracks were localized in post-yield range of reinforcing bars. The localization mechanism was numerically explained and method for inhibiting the localization was demonstrated by focusing on the amount of bridging forces of fiber and steel bar. In the case of Strain Hardening Cementitious Composites (SHCC), it was clarified that the usage of steel reinforcement is effective to enhance strain capacity.
Simple modeling method of corrosion degree in rebar existing the cavity caused by the expansive stress in concrete due to the corrosion in rebar in RC structure is investigated. Employing the thermal on concrete surface by the thermography, heat stored in reinforcing steel-bar (rebar) due to electro-magnetic heating is applied to estimate qualitatively the thickness of cavity and the corrosion degree. The thickness of corroded layer in rebar is identified by the difference of the increased value of temperature on concrete surface between the measured value and the analyzed value assumed the rebar as non corroded state. On the other hand, the thickness of cavity is identified by the rate of the temperature increase on the concrete surface. An applicability of the analysis is demonstrated by the comparison between the analyzed and those measured value.
Environment conditions are the external factor that affect the durability of concrete structures. Especially, early-age cracking such as thermal cracking and drying shrinkage cracking influences concrete durability. Therefore, it is important to understand this external factor accurately in order to evaluate the durability of a concrete structure. Meteorological conditions such as the ambient temperature and humidity are especially important in an external factor because meteorological conditions influence deterioration such as the crack and the steel corrosion. In this study, the seasonal fluctuation models of vapour pressure, ambient temperature and relative humidity were constructed by using the latest meteorological data.
An experimental study was conducted to develop an evaluation method for the resistance of concrete to chloride ingress by using chloride penetration depths measured with a colorimetric method after non-steady-state migration experiments. The evaluation method was quicker and simpler than other existing laboratory-accelerated tests because the non-steady-state chloride penetration depths were utilized to evaluate the resistance of concrete to chloride ingress. An appropriate procedure to determine the applied voltage and the testing period was proposed on the basis of the experimental results obtained by using mortar and concrete specimens. The movement of chloride during the non-steady-state migration experiments was also clarified by analyzing the tested specimens. The test results derived from the evaluation method were compatible with those given by the immersion test; both test results accurately indicated the improvement of the resistance of concrete to chloride ingress due to mixing supplementary cementitious materials. Moreover, the evaluation method was found useful for measuring the time-dependent development of the resistance of concrete to chloride ingress.
The causes of deterioration observed in the concrete elements of two removed highway bridges were examined. One is decks taken from a 75-year-old reinforced concrete bridge showing numerous horizontal cracks. The other is an element cut out from the pier of a 47-year-old bridge, of which cracks and spalling along a water leakage from expansion joints were found on the side. The splitting of coarse aggregates was remarkably found along the cracks in both the elements. In each the concrete element, gravel containing reactive aggregates was used, and the several signs of alkali silica reaction (ASR) were recognized. In addition, since the bridges suffered from repeated freezing and thawing cycles and deicing salt used in winter, the effects of frost-induced deterioration were examined. From the results, it was found that the cracks and the necessary conditions for cracking were similar to those as exhibited in the initial symptom of D-cracking shown around joints in concrete pavements, so that the potential causes of the cracks might contain not only the ASR but also the splitting of the coarse aggregates due to the freeze-thaw action.
As the upper filler concrete material applied in the cavern type radioactive waste disposal facility is poured just over the radioactive waste packages stored in the facility where the environment may be in a high temperature because of the decay heat, it is concerned that the filling efficiency and the hardening character of the filler may be affected by the temperature. As the construction of upper filler material is done under radiation condition, there are some issues as follows; the filler must be constructed by unmanned remote operation, the filler needs to keep a certain thickness to guarantee the shielding capacity, and so on. In this paper, we have designed the mix proportion of upper filler concrete through filling efficiency experiments simulating high-temperature environment, and have revealed the effect of the temperature on the hardening properties with high-temperature curing tests. Moreover, by doing a full-scale demonstration, we confirmed the feasibility of unmanned construction of upper filler concrete by pumping and movable bucket method.