The bonded overlay type of repairment for concrete pavement is commonly used in Japanese highway. This paper describes the shrinkage stress introduced by the difference of material properties and age between overlayed concrete and original pavement. A method of numerical analysis is proposed in order to estimate shrinkage stresses. Several factors which affect the shrinkage stress were obtained from the results of the analysis.
The strength of hardened cement paste, mortar and concrete depends on their pore structure and morphology, surface energies and streangth of the hydrate, etc. The pore structure including the pore size distribution, the volume and morphology of pores is the main factor controlling the strength. Strength, morphology and surface energy of hydrate itself is an important strength-controlling factor next to the pore structure. Although a lot of research has been focused on the morphology and surface energy of the hydrate and the influence of pore structure on strength, only a little research on the structural factors controlling the strength of hydrate itself has been carried out. This paper deals with the relationship between the polycondensation degree of silicate anion and the strength of mortar, focusing on the polycondensation degree of silicate anion as a structural factor. Polycondensation degree of silicate anion in C-S-H in a mortar specimen increases with the increase of the curing temperature and age. There are large amounts of silicate anions of heptamer or more and dimer in mortar developing high strength. The higher strengths per unit volume of total pore of autoclaved mortar and silica fume blended white cement mortar cured in water are mainly attributed to the increase in fine pore (20 nm or less) on which the stress caused by load is poorly concentrated. The higher strengths per unit volume of pore of 20 nm or more of white cement mortar and blastfurnace slag blended white cement mortar autocalaved are attributed to the increase in strength of hydrate itself by the increase of polycondensation degree compensating the decrease in cohesive energy caused by the increase in crystallinity and the formation of different kinds of hydrates.
Practical application of FRP reinforcement to reinforced concrete structures is at present attracting technical attention. The object of this study is to make an analytical examination on how FRP rods influence the impact resistance of concrete slabs. The concrete slabs are modeled using the layered finite element method and the Newmark-β method is employed to solve the equations of motion during discrete time intervals. As a result, FRP rods are efficient as reinforcement, and the degree of contribution to impact resistance can be evaluated quantitatively by the following indexes ; impact force at failure, volume displaced, impact failure mode, etc.
Recently, it is easy to produce concrete with compressive strength more than 1 000 kgf/cm2 by use of silica fume. However, the mechanical properties of RC members using such ultra high strength concrete have not known sufficiently. The purpose of this study is to investigate experimentally and analytically the mechanical properties of ultra high strength concrete beams subjected to pure bending moment. As a result, the evaluation methods of flexural capacity and of minimum steel ratio of such beams are proposed, and it is confirmed that ρ/ ρb (ρ : tensile steel ratio, ρb : balanced steel ratio) is a main factor influencing the ductility of such members.
The basic design criterion for reinforced concrete structures in Japan is in a limit state design format. However, the customary Allowable Stress Design method has been used for reinforced concrete bridges. The purpose of this study is to develop the method of estimating optimum load factors for reinforced concrete bridges. The distributions of the bending moments arising from wheel loads at slabs and beams respectively, are estimated by using Monte Carlo simulation. Examples are presented for highway bridges both of Hanshin Express-way and Tokyo bay Route. The results obtained here show that both TL-20 and TT-43 loadings should be modified. In addition, some methods in calculating reliabilities of structures are proposed.
Many RC viaducts have been used for traffic facilities for example railway and highway bridges. So it is very important to establish the rational design method of such structures against big earthquakes. The purpose of this study is to evaluate analytically the relationship between the damage index of each member of RC 2-story viaduct and several factors by means of dynamic response analysis. In this study, ductility factor and accumulated plastic strain energy are used as measures of damage index.
Steel tubular column structure is one of the best structure to construct highrise condominium building. It had been difficult, however, to fill concrete into high steel tubular without non-filled zone because of segregation of concrete in the middle of filling. So the authors will try to apply super workable concrete, which have superior deformability and segregation resistance, to this case. According to results of experimental studies, it is possible to fill super workable concrete into abut height 40 m's steel tubular column by ordinary mobile concrete pump, and to calculate pumping pressure cosidered hydraulic pressure. Furthermore, the result of actual steel tubular columns construction, height ; 39.4 m, at MM 21 LANDMARK TOWER was satisficble.
Organic admixtures including fluidizing agent, air entraining agent and water-reducing agent are indispensable for manufacturing high-performance multi-functional concrete. However, various phenomena concerning the setting and hardening of concrete caused by the addition of admixtures are at present dealt with by symptomatic measures without any elucidation of the causes because the working mechanism have hardly been clarified yet. Using the samples prepared by mixing β-naphthalenesulfonic acid-and lignin sulfonic acid-based organic admixtures, and by dipping the polished surface of clinker into the water containing admixture for a specified time, the effect of the adsorption of admixture on the hydration of cement and the adsorptive behavior of admixtures were examined and the relationships of them with the physical properties of fresh paste including fluidity, variation of fluidity with time and setting time were discussed with the advanced method of micro surface characterization such as in-lens FESEM, ESCA-imaging AES and AFM to elucidate the cause of phenomena observed in concrete containing organic admixtures.
The latex-modified ultra rapid hardening cement mortars were composed of aggregates, ultra rapid hardening cement and latex. The latex as a modifier for normal portland cement is apt to be destroyed its protective colloidal layer around the polymer particle surface, and then to form the coagulation of polymer whenever it is attacked by a mechanical operation, a thermal operation and polyvalant positive ion such as Ca+, Al3+ in liquid phase with ultra rapid hardening cement paste. Specially the positive ion, Al3+ ion concentration of the liquid phase with ultra rapid hardening cement paste is remarkably larger than that of the normal portland cement paste. In order to settle these problems, it is necessary to add surfactants and antifoarmer to the latex for the normal portland cement. The author, first of all, introduces the recipe for special SBR (Styrene-butadine rubber) latex containing surfactant as a modifier in ultra rapid hardening cement as a result of the mechanical stability test, the chemical stability test, the strength test and the water-proofing test. This paper describes the properties such as strengths, drying shrinkage, water-proofing property and abrasion resistance of the special SBR latex modified ultra rapid hardening cement mortars at various polymer cement ratio.
It is possible to improve resistance of high-strength light-weight concrete to freezing and thawing by using the new mixing procedure, in which both mixing water and cement are divided into two and added. In this paper, the mechanism of improvement on resistance of high-strength light-weight concrete to freezing and thawing was studied experimentally. As the results, the causes of this improvement were as follows : (1) flaws in concrete were reduced by reducing bleeding. (2) surface properties of light-weight coarse aggregates were improved by enveloping coarse aggregates with cement paste and the bond strength between coarse aggregates and mortar matrix in concrete was strengthened.
The workability of high-strength concrete with high-performance AE water reducing agent or various kinds of admixture cannot be evaluated only by conventional slump test because of its high viscosity. Therefore, it is important to establish a method for evaluating quantitatively workability of such concrete based on rheological properties such as yield value and plastic viscosity. In this report, apparent yield values and plastic viscosity of various concretes have been measured by means of Two-Point Method which had been made clear to be applicable to high-strength concrete. As a result, the effects of mix proportion factors on rheological properties have been clarified and flow properties among various concretes have been classified in terms of yield value and plastic viscosity.