The fracture mechanics is applied in order to quantify mechanisms and effects of fiber reinforcement in fiber reinforced concretes. In this paper, experimental and analytical investigations were conducted to evaluate tension-softening relations of fiber reinforced concretes by means of a reverse analysis of the cohesive force model and the followings were quantified ; effects of different types of fiber on fiber reinforcement, interactions of factors of mix proportion such as fiber length, fiber volume fraction and matrix strength on fracture toughness of steel fiber reinforced concretes, and effects of fiber reinforcement on restraints of expansion degradation for concretes.
It is well known that the fluidity and the setting time of fresh concrete are affected by kind and added timing of organic admixture including fluidizing agent, air entraining agent and water-re-ducing agent. The fluidity, setting time and time dependency of fluidity are measured using fresh cement paste prepared with four kinds of organic admixtures, polycalboxylic acid-based, aminosulfonic acid-based, β-naphthalenesulfonic acid-based and lignin sulfonic acid-based admixture, by two different methods of addition, that is, together with mixing water (simultaneous addition) and specified time after mixing with water (later addition). Hydration of cement, adsorptive behavior of organic admixture to clinker minerals, formation of calcium complex with organic admixture and flocculation structure of cement paste are also estimated with the state-of-the-art method such as Auger electron spectroscopy, X-ray photoelectron spectroscopy and environmental electron microscopy in order to clarify the influence of kind and added timing of admixture on the properties of fresh cement paste and concrete and elucidate the mechanism of the improvement of fluidity of cement paste and concrete in later addition of admixture.
Shear bending cyclic tests of reinforced concrete flexural failure beam were carried out in order to clarify the failure mechanism under reversed cyclic loading, in which axial strain and lateral strain in the plastic hinge region were measured in detail. On the basis of the experimental results, “Reversed cyclic loading failure” was proposed. This failure mode is caused by the change of shear resistance mechanism which occurs under reversed loading when accumulated strain in the plastic hinge region becomes large. This change is closely connected with the stiffness deterioration of cracked concrete in the plastic hinge region. The deterioration of strength is produced during the recovery process of stiffness under reversed loading. This failure mode does not occur without reversed loading and this means the proposed failure mode is peculiar to reversed cyclic loading.
In regard to low-Heat and high flowable concrete for underground diaphragm walls using low-Heat cement and high range water reducing and AE agent, the effects of kinds of binders or water reducing and AE agent on the properties of the concrete were examined. The effects of factors for mixture and manufacturing of concrete or of pumping on properties of the concrete were also appreciated. Based on these experiments, it was clarified that the concrete, utilized high range water reducing and AE agent of polycarboxylic acid system, has faster velocity of deformation than that of β-naphthalene sulfonic acid system and the setting time and the loss time of flowability after sufficient retention time of flowability were also faster than that one. The retention time of flowability could be controled by the quantity of cross-linking polymer in high range water reducing and AE agent. The viscosity of that concrete become inferior due to pumping. The reason of loss of slumpflow was considered that the quantity of high range water reducing and AE agent in the concrete was decreased because of adsorption of the agent to the surface of cement particles which were came from shear deformations by pumping.
In recent years, the application of multilayered resin materials for repair of deteriorated concrete structures is widening and also attracting technical attention. In engineering design of multilayered resin materials, it is important to evaluate the mechanical behaviors of interface among layers and concrete surface during various stages under service conditions as well as providing adequate chemically and physically stable bonding between them. This paper discusses not only the determination of functional needs which vary according to the performance requirements, such as shear stress in the adhesive layer, shear stress concentration at end of adhesive joint, etc., required for application of multilayered resin materials to repair of deteriorated concrete structures, but also a design concept of the multilayered resin materials based on a few indexes which represent their mechanical behaviors.
Mechanical performance of grout-filled coupling sleeves of electric resistance welded steel tube with interior projections and bond stress-slip relations of reinforcing bars in the splices under uniaxial tensile loads are discussed using the results of experimental studies, in this paper. Experimental variables adopted in the investigations are development length of reinforcing bars, kinds and compressive strength of grout as filler materials, some mechanical devices to improve the splice performance, and so on. Following, main conclusions are obtained. (1) The mechanical performance of the splices employed herein are improved significantly with increase in development length of reinforcing bar and compressive strength of grout. (2) Assumption of respective constant bond stress in pre-and post-yield region of reinforcing bars in the splices leads equations to estimate practically both load capacities and failure modes of the splices.
For long-time deflection analysis of two-way slab systems we have proposed finite difference procedures : initially to calculate their deflection in flexure, allowing for both structural cracking in terms of Branson's effective stiffness and time-dependency ; then to consider the additional effect of elongation of reinforcement anchorage. Those methods earlier tested on all-edge-fixed cases for slab-beamgirder systems are currently applied to RC and PRC flat plates, as a unified analytical system to cover major structural variations. Solutions thereby obtained are examined in comparison with available overseas flat plate deflection measurements and are used for checking slab design thickness exempt from deflection hazards.
Usually, the truck agitator is used to transport fresh concrete which is mixed at a concrete plant. In case of placing of concrete at a construction site, discharging efficiency of the truck agitator influences on construction efficiency and quality of concrete. In this report, we observed flow of fresh concrete in agitator, while we can't observe untill now, with help of the visualization technique, and investigated about influence of blade rolling pitch angle and rotational speed on discharging efficiency. As a result, it was cleared that the agitator can have most suitable angle for discharging efficiency, and that the higher sliding resistance between concrete and surface of blade, the lower discharging efficiency.
Concrete walls or concrete structures are often associated with hardness and coldness. None has verified this idea. First, words and phrases describing concrete walls and structures were collected among students and working people, and analysed. It revealed that the idea is true. Second seventeen architectural concrete specimens of 900 mm square with a variety of surface finishing were made and psychologically measured with eight seven-rated-scales. The finding is that the concrete with smooth surface, such as casted in plywood or metal panels gives people the impression of hardness and coldness, whereas concrete with rough surface the impression of softness and warmness. This concept obtained from the small specimens was proved to be applicable to actual concrete walls and structures with actual size.
A horizontal loading test of three-story, half-scale concrete frame reinforced with FRP reinforcement was conducted to investigate the possibility of structural design. The dimensions of the frame were based on a prototype structure that was decided by trial design. Objectives of this study are to research the structural performances and limit state of the frame, to verify the trial design and to compare the behaviors with those of steel reinforced concrete by inelastic analyses. The results of the experimental and analytical studies prove that it is possible to design the FRP reinforced concrete frame structures. Some interesting characteristics of FRP reinforced concrete frame are clarified in this paper.