Concrete stubs confined in circular steel tubes have been tested. Based on the test results, the triaxial stress-strain behavior, and the failure criteria of confined concrete have been studied. The failure of confined concrete is defined as the point at which the volumetric strain changes to expanding. Failure criteria of confined concrete expressed in strains, and in stresses are proposed.
The prestressed composite circular structure was introduced for marine structures, which is composed by precast concrete blocks, filledin concrete and outer ribbed steel pipe pile. In order to verify the mechanical characteristics for such structure, the loading tests were conducted. The results of the tests are : 1) Structural integrity is secured. 2) Structural Strengths and displacements can be obtained by the conventional theoretical approach. 3) Approximate crack widths can be obtained by the conventional formulas.
This paper proposes an absolutely new mixing procedure for improving resistance to freezing and thawing as well as workability by enveloping the lightweight coarse aggregate with cement paste, and compares experimentally the new mixing procedure with the conventional one on consistency, compressive strength and resistance to freezing and thawing (as per ASTM C 666 Method A) of the respective high-strength light-weight concrete of the same mix proportion mixed by both procedures. The results of these tests show that the new mixing procedure will greatly improve consistensy and resistance to freezing and thawing.
The objective of this study is to introduce a equation of shear transfer strength between the steel bracket provided steel shear plates together with anchor bolts and reinforced concrete member. The shear loading test of shear plates which have various type of dimensions was conducted. Based on the results the shear transfer strength equation of shear plates was introduced. Next, shear transfer test was conducted using two model specimens of steel bracket with steel shear plates and anchor bolts. Referring to the result and the shear strength equation of shear plates described above, the shear transfer strength equation of this type of steel bracket was shown as the sum of the bearing strength of concrete under the shear plate located in the lowest portion among plural shear plates and the shear strength caused by anchor bolts and concrete in the region between the two extreme shear plates.
Characteristics of the boundary surfaces of mortar and coarse aggregates in concrete materially affect properties of the concrete. For the purpose of improving characteristics of the boundary surfaces the author devised a new type of reduced pressure mixer. With a view that this mixer will be effective for mixing of concrete containing the blast-furnace slag aggregates, which are composed of slag pasticles of irregular shape and relatively large porosity, the mechanism and effects of the mortar with the slag under reduced pressure were studied. The results are described here. In this mixing process the mortar and aggregates are mixed under reduced pressure near the vacuum. When the mixing has been completed, the mixer is pressured back in a moment to the atmospheric pressure to make the mortar adhere to the blast-furnace slag aggregates with pressure. As a result the adhesiveness water on the aggregates and the free water in the mortar are pressed in the aggregates, thus strengthening the combination of the mortar with the aggregates and improving quality of the mortar with increase of the water cement ratio. In addition about a half of the entrapped air is expelledin the above process, making the parts of mortar denser. The study results proved that the above mentioned improvement in the concrete structure by the reduced pressure mixing secures multifalious effects, such as decrease of bleeding, expansion of the elastic area owing to decrease of bond cracking, wide increase of static strength, and improvement in fatigue strength and water tightness.
Mechanical behaviour of concrete is highly dominated by cracking.Because of the heterogeneity, a large fracture process zone is created along the main crack surface.In this paper, the influence of coarse aggregate size on the fracture energy of concrete was experimentally studied and discussed in connection with the tension softening properties of the fracture process zone.Three dimensional source location analysis of acoustic emission (AE) was also carried out to observe the prospect of the fracture process zone.The properties in the distribution of AE source location coincide with the results of the numerical analyses.
In this paper, durability for frost damage of fly-ash sand mortar, and ones reinforced with vinylon fiber, carbon fiber, pulp and calcium carbonate form is discussed. This fly-ash sand is a kind of new light weight artificial aggregates which were made from fly-ash. Using a probabilistic model of microcrack accumulation, the relation between the relative reduction of dynamic modulus of elasticity and the freezing and thawing cycles was analyzed. Although fly-ash sand mortar has rather low durability for frost damage, the durability of fiber reinforced ones is remarkably improved. Finally the improved mechanism for frost damage is discussed on the basis of the experimental results.
This paper deals with the influence of neutralization depth of concrete on rebar corrosion occuring in concrete structures containing chlorides such as those found in sea sand. First, while investigating the relationship between rebar corrosion and the depth of neutralization by conducting an accelerated neutralization test on concrete into which chlorides were mixed in, surface analysis by means of an EPMA was conducted for chlorine and sulfur for a concrete cross-section. Based on the findings, this paper elucidates that rebar corrosion is initiated before neutralization reaches the surface of the reinforcing bars, because, when neutralization of concrete containing chlorides advances, it causes enrichment of chlorides to move toward the non-neutralized zone
The flexural crack width of a beam reinforced with grid shape fiber reinforced plastics (FRP) is larger than that of a RC beam reinforced with reinforcing steel bars due to a small tensile rigidity of FRP. As expected from the strain increment of tensile reinforcement in a FRP beam, the deflection of a FRP beam is larger than that of a RC beam. In calculating the shear capacity of a FRP beam, the cross sectional area of FRP should be decreased by the ratio of Young's modulus of elasticity of FRP to that of reinforcing steel bar in a RC beam. During the sustained flexural moment for a year, the value of deflection increment of a FRP beam is larger than that of a RC beam. However, the ratio of deflection increment to the deflection immediately after loading of a FRP beam is about half as much as that of a RC beam. In order to improve the mechanical behaviors of a FRP beam, chemical prestress was introduced by use of an expansive concrete. Based on the test results, it was assured that the effects of chemical prestress on the flexural crack width and the shear capacity of a FRP beam were obtained.
Microstructural aspect of the Critical Degree of Saturation for Freeze/Thaw Resistance (Scr) of Autoclaved Lightweight Concrete (ALC) was studied. Measurement of the phase transition of adsorbed water, length chage during freezing and the cryo-SEM observation of the microscopic ice segregation on air pores were carried out. It was proven that Scr is a moisture content slightly higher than capillary saturation, and an analytical formula of Scr as a function of bulk density of ALC was derived.
In order to investigate the response characteristics of a reinforced concrete column under earthquake forces and to evaluate the seismic design method in JSCE's Standard Specification of Concrete in 1986, static and pseudo-dynamic tests using reinforced concrete column specimens and related analyses were carried out. It was confirmed that the classification of the level of serviceability after the earthquake stipulated in the Specification was adequate from the cracking pattern of columns subjected to static cyclic loadings. From the results of pseudo-dynamic test, the appropriateness of the limit state modification factor specified in the Specification was verified. The response of a reinforced concrete column under an actual earthquake which caused definite shear failure was presented properly by pseudo-dynamic test. Analytical models to evaluate the static inelastic displacement and the seismic response of reinforced concrete columns were proposed and were confirmed to be adequate.
Recently, two concrete-admixture-makers developed the new-type non-freezing agent. They are said to have following excellent qualities. 1) Lower alkalinity and no chloride. 2) Freezing temperature of concrete will be dropped and initial frost damage after placing concrete will be protected. 3) Hydration of cement will be promoted at lower temperature. Experimental Results. (1) Using concrete with non-freezing agent, water content per unit volume will be reduced to common AE concrete without agent. (2) Properties for time proceed of fresh concrete was done by the measuring values of slump, air content and temperature for 90 minutes at air temperature about-9.0°C those values were similar to the non-freezing agent. (3) The initial frost damage was not suffered from concrete with non-freezing agent and concrete strength increased favorably. At 91-day, as to 20°C curing concrete strength with no agent, low temperature curing concrete strength with agent reached to nearly values. (4) The period on purpose to pro-tect early age frost damage of concrete with 50 kgf/cm2 strength was reduced highly using an agent. (5) If we add new-type non-freezing agent for the concrete, period of cold weather concreting can be shortened greatly.
Recently, some mathematical models for the prediction on progress of carbonation of concrete were reported. These models were taking account of CO2 diffusion and chemical reaction of Ca (OH) 2 and CO2. These models were based on the assumption that CO2 diffused in the carbonation zone and reacted with Ca (OH) 2 at the boundary face of carbonation zone and uncarbonation zone. In these models did not coexist. According to previous studies, however, it was know that Ca (OH) 2 and CaCO3 do coexist in carbonation progress zone. In this study, a mathematical model to predict the progress of carbonation of concrete has been established based on the reducing concentration of Ca (OH) 2 in the carbonation progress zone where Ca (OH) 2 reacts with CO2 and Ca (OH) 2 and CaCO3 coexist.
Recently a number of examples of premature deterioration caused by alkali-silica reaction have been reported. This paper deals with concrete surface treatment adopted in maintenance work. The long term performance of typical surface treatments is examined and the effect of surface treatment on expansion of concrete due to alkali-silica reaction is investigated experimentally. The fundamental concept to determine the effect of surface treatment for alkali-silica reaction is discussed.