C-S-H is a dominant hydration product of cementitious materials. Therefore, its chemical composition and physical properties affect the properties of concrete. With regard to the pore structure of C-S-H, it is known that the gel pore volume of C-S-H is 28% and the gel pore size is about 2nm. However, the gel pore of C-S-H generated from various materials, such as cement, blast furnace slag, fly ash and silica fume have not been completely clarify. Therefore, the purpose of this study is to estimate chemical composition and gel pore of C-S-H, such as pore volume and pore size distribution. From the experimental results, The gel pore volume of C-S-H was affected by the C/S ratio. Based on the composition of C-S-H, the inversely relationship between the gel volume and the C/S ratio of C-S-H was clarified. And, it was clarified that the gel pore size distribution of C-S-H was not influenced by the change of the C/S ratio from these results.
In order to evaluate the utilization of anti-washout underwater concrete for RC marine submerged structures, RC beam specimens and cylindrical specimens prepared in artificial seawater have been exposed into actual marine environment in Tokyo bay for 20 years. RC beam specimens were arranged for four types of beam specimens (with or without flexural cracks, with a concrete cover 40mm or 70mm). This report describes a series of test including tests on flexural capacity and reinforcement corrosion of RC beam specimens, and physical properties of concrete such as compressive strength, Young's modulus, ultrasonic wave propagation velocity and chloride content. The results of test showed RC beam specimens have kept on sufficient flexural capacity as compare with the design requirement after 20 years marine exposure. The prediction the future change of flexural capacity of RC beam specimens was conducted, and it can be said RC beam specimens could maintain sufficient performance over 100 years long. Furthermore, the progressive period until the initiation of longitudinal cracking on RC beam specimens could be estimated approximately 69 years.
It is always required for fresh concrete to provide a proper flowability with least segregation. Mix proportion of concrete to satisfy such requirements is usually determined by trial and error. The authors propose a mechanical model on bleeding taking account of the behavior of cement particles under the usage of superplasticizer. Experimental test was conducted on mortar with parameters of three levels of W/C, three types of sand and four levels of mortar flow. The proper amount of superplasticizer was determined so as to satisfy the target value of mortar flow in each case. Comparing with experimental results, it is found that the proposed model can indicate how to determine a proper mix proportion of mortar with least bleeding under given conditions of mortar flow, W/C, properties of sand and cement.
This paper presents an experimental investigation of the effects of short fiber reinforcement on the local damage of concrete plates. Three fiber reinforced cementitious composites including polypropylene fiber and polyvinyl alcohol short fiber with concrete and mortar matrix were used. In order to determine static and dynamic material properties, static and rapid speed tensile loading tests were conducted. To examine the relation between dynamic mechanical properties and impact resistant performance, high velocity impact tests were carried out. Test results indicated that the reinforced plates with high ductility in static loading showed very brittle in the high velocity impact test and that, in contrast, the reinforced plates with low fracture energy in static loading showed extremely high impact resistant performance in the high velocity impact tests.
In this study the effect of drainage behavior on coarse aggregate to drying shrinkage of concrete was investigated in two experiments. In the first experiment the strain and weight of several kinds of coarse aggregate were measured in the conditions of six types of relative humidity and relationship between strain and drainage of coarse aggregate was obtained. In the second experiment drying shrinkage of concrete and strain of coarse aggregate inserted into the same concrete were measured and drainage rate of coarse aggregate inserted into concrete was presumed using the result of first experiment. Comparing water vapor behavior of concrete with drainage behavior of coarse aggregate, it is clear that relationship between water vapor of concrete and drainage of coarse aggregate influences on drying shrinkage of concrete.
Recently, receiving combined actions due to chloride induced deterioration by spraying deicing salt and fatigue by live load, RC road bridge decks in cold regions are suffering from serious damages. Therefore, this study aimed at investigating the influence of corrosion of rebars on fatigue resistance in RC road bridge deck, experimentally and analytically. First of all, specimens supposing full-sized RC road bridge deck were prepared and 3 types of accelerating tests for chloride induced deterioration were conducted. Then the relationship between corrosion condition of rebars in each specimen and its fatigue resistance was investigated by wheel load trucking test. Secondly, the influence of fatigue fracture in RC road bridge decks on the difference in quantity of corrosion between upper rebars and lower rebars was researched by 3-D nonlinear finite element analysis. These experimental and analytical results revealed that the fatigue resistance of RC bridge deck was clearly declined even if the corrosion rate of rebar was approximately 5%, and the corrosion of upper rebars would be the dominant factor in the fatigue resistance of RC bridge deck rather than that of lower rebars.
CSG (Cemented Sand and Gravel) has come to be used as a new material for large civil structures such as impounding dams in recent years because of its advantages of producing by using materials easily obtained in and around each project site and simpler facilities compared to conventional concrete. However, its material properties other than the compressive strength that is used for basic structural design have not been fully clarified. In this paper, the effects of loading rate effects on the tensile strength and tension softening properties including fracture energy and tension softening diagram of CSG, those are essential to evaluate the seismic performance of CSG structures during large earthquakes, are experimentally investigated. The test results indicate that both tensile strength and fracture energy increase as the loading rate increases. Based on these results, experimental formulae of dynamic tensile strength and fracture energy of CSG are proposed. The tension softening diagram of CSG is also estimated and its practical model for numerical analysis is proposed.
Honeycombing is one of the surface imperfections in concrete structures. In the conventional repair method of honeycombing, the bond compatibility of the repair material with the existing sound concrete is important issue. If it is not enough, it may cause spalling of the repaired part and deteriorate the structural performance and durability of the structures. In this study, we proposed a new repair method which injects the resin without removing the honeycombed area. At first, to evaluate the degree of the honeycombing, the non-filled concrete ratio of the honeycombed concrete specimen was defined based on the densities. Then, the procedure of the new repair method was established. Finally, it was shown that the compressive, tensile and flexural strengths of the specimens repaired by the proposed method were almost the same or more than those of the sound concrete specimens.
Applicability of material damage indices has been evaluated for previous nonlinear two dimensional seismic finite element analyses of RC structures with surrounding soil, a railway pier damaged in Tokachi earthquake 2003 and a subway culvert structure damaged in Hanshin-Awaji great earthquake 1995. Then, by using the second invariant of deviatoric strain tensor and consume strain energy averaged over certain region, seismic damage processes of RC structures and/or members can be approximately explained, as well as static experiments whose applicability has been already evaluated.