In this paper, we present a fracture mechanics based micromechanics model for predicting the mechanical properties of polypropylene discontinuous fiber reinforced cementitious composites manufactured by extrusion molding. The mechanical properties of the polypropylene fiber composite were measured by conducting tensile tests and four-point flexural tests. SEM observation has shown that approximately 80% of incorporated fibers in the composite was aligned with respect to the extrusion direction. It has been demonstrated that the critical fiber volume fraction for multiple crarking, Vf, crit predicted by our micromechanics model was close to the experimentally determined value.
This paper presents a study on statistical feature of internal cracks developed within frost-damaged concrete. Concrete specimens were observed for internal cracking by means of digital microscope after they were subjected to a series of rapid freezing-and-thawing cycles. The intensity of cracking was estimated by means of the intersections of traverse line and cracks. The agreement of shapes between normal distribution and observed histogram of intersects was verified. Furthermore, the expedience of using intersections for quantification as well as applying a probability distribution to the estimation of cracks was substantiated. Consequent findings might provide useful information for assessing the feature of damaged concrete due to freezing and thawing.
This paper reports the observed deformation composed of autogenous shrinkage (AS) and thermal expansion/contraction in high-strength concrete with water-binder ratio of 0.4-0.2. While AS in concrete with Portland cement subjected to high temperature history becomes smaller than that under 20°C, AS in concrete with blended cement becomes larger when amount of the additives is large. By taking increase of thermal expansion coefficient with age into account, it may be able to estimate the composed deformation in high-strength concrete structures.
We have proposed a method of reusing waste fresh concretes, now being treated in ready-mixed concrete plants, as a preceding mortar for concrete pumping constructions taking into consideration of the resource saving and control of construction waste emissions. A super set-retarding agent to halt thecement hydration and a superplasticizer to improve the fluidity were added to the waste fresh concretes, and the subsequent wet-screening resulted in Eco mortar that can be used as a preceding mortar for concrete pumping constructions. This paper deals with the quality of Eco mortar obtained from waste fresh concretes with various type of raw materials and with different ages after mixing. A full-scale pumping constructions was also executed on site using Eco mortar manufactured in a ready-mixedconcrete plant in the previous day, resulting in a confirmation of the feasibility of Eco mortar.
This study describes properties of concrete with ground granulated blast furnace slag to 30000cm2/g in specific surface area. 2 types of standardized slag of 4000 and 8000 cm2/g in specific surface area and 3 types of much finer slag within the range from 11000 to 30000 cm2/g in specific surface area were used in this study. Properties of concrete with these slags were experimentally investigated, changing the replacement ratios for cement. Influences of the specific surface area of the slag and replacement ratio on the concrete properties, bleeding, setting, compressive strength, drying shrinkage, resistance to chemical attack and resistance to freezing and thawing, were clarified.
This research is carried out to investigate the effects of scale on bond strength of deformed bar using lap-splice and pull-out specimens with and without stirrup. The bar diameters are17.4 mm, 34.8 mm and 52.2 mm. This research also verifies the effect of rib shape on bond strength, using 2 kinds of rib shape. As a result, the effect of scale on both lap-splice and pull-out specimens with stirrup is smaller than those without it. Especially large scale-effect is observed in the pull-out specimens without stirrup and with thin cover concrete, where the bond strength is proportional to about-0.5 power of bar diameter. In the case of lap-splice specimens, the bond strength is proportional to about-0.2-0.3 power of bar diameter. Furthermore, a Larger confinement-effect due to stirrup is observed for pull-out specimens than lap-splice specimens, which results in the larger effect of rib shape on lap-splice specimens is larger than pull-out specimens.
In this paper, the properties of fresh and hardened concrete containing “pulverized dry sludge (PDS)” as both a mineral admixture and a fine powder for high-fluidity concrete were investigated. The so-called pulverized dry sludge is a very fine powder with a Blaine specific surface area of 5,000-15,000 cm2/g made from sludge cake by a process of drying and crushing. It was found that when PDS is used as a part of cement such as mineral admixture, PDS has no harmful effects on hardened concrete although the dosage has sometimes to be limited to about 10% of the cement content because high content of PDS significantly increases the demand of mixing water. Experimental results on high-fluidity concrete showed that concrete containing up to 30 % of PDS content had a good performance in both fresh and hardened properties. This research shows the potential for the effective use of concrete sludge disposed from ready-mixed concrete plants.
It was found that the strength of concrete was risen when it was wrapped up in a steel tube. Accordingly we expect that the effect of confined were especially contributes to lap splices. Then we made an experiment and investigation on lap splices with a rectangular steel jacket for reinforced concrete members. Therefore we propose an equation for the strength of lapped splices of deformed bars that are reinforced by being wrapped up in a rectangular steel jacket.
The authors are challenging to place much concrete in a shorter term by adopting rational construction methods (RCD/ELCM), for the first case in hot-weather areas in the world. However, fresh concrete under the hot-weather are easy to lose its workability, so main subject of this study is to improve this characteristics by adding flyash or retarder. After many concretes experiments, it is concluded from the test that flyash addition in high ratio was quite effective to keep the workability, at the same time, it is sure that 91 days concrete strengths were enough over the design standards of T dam. Further, the authors confirmed this results through the field concrete works in H dam site; using highly replaced flyash concretes in hot weather.
The Adhered Steel Brace is one effective retrofitting method of the earthquake-resistance strengthening work that can be done with little noise and little vibration. In this method, the steel frame with brace is bonded to the existing columns and beams by epoxy resin. The work also can be done in a shorter period of time. The seismic behavior of the adhered steel brace with middle or one-side doorway was investigated. The five specimens were tested under constant compressive loads and repeated lateral forces. The main parameters are the stories, adhesion area and width of flat-plate under opening for doorway. The strength of beam over the doorway is very important to estimate the ultimate strength. In case of one-side doorway, the failure mode is different from that in the direction of lateral force. The ultimate lateral strength and ductility are discussed
Drop weight impact experiments, in which two kinds of mass were dropped from various height, were carried out to investigate shear failure behavior of PC beams. From the experiment on the effect of momentum and the kinetic energy of the steel weight on the shear failure, it becomes clear that the ultimate shear failure of PC beams depends on the kinetic energy of the steel weight rather than the momentum. In addition, effects of the stirrups and absorbed energy are examined. These conclusions are compared with results of static and rapid speed shear loading tests as well as existing formula
In this paper a simplified maximum strength formula of framed RC shear walls with an opening is proposed, and its analytical accuracy is investigated by analyzing the maximum strength of one hundred and seventeen specimens executed in Japan since 1981. This simplified maximum strength formula is derived from equilibrium conditions of the simplified macroscopic model based on the lower bound theorem of the limit analysis. From the analysis using the simplified maximum strength formula, it is obtained that the values of mean, standard deviation, and coefficient of variation for the ratios of the observed maximum strengths to the analytical ones are 1.002, 0.142, and 0.142, respectively. This result shows that the simplified maximum strength formula is adequate for evaluating the maximum strength of the RC framed shear walls with an opening.