To identify the condition of in filtration of sodium sulfate into mortar and grasp the relationship between ettringite and the period of in filtration, with mortar specimens immersed in sodium sulfate solutions having different concentrations (5%, 10%) for one year, this research newly studies and proposes an analytic thchnique using an X-ray micro-analyzer, etc. and observes in detail the condition of infiltration of sulfate ion, etc. into mortar and the growth of ettringite, on the basis of this technique. As a result, the growth depth of ettringite was found to be proportional to the square root of the infiltration period, and the relationship with the condition of deterioration (change in weight, change in deflection oscillation, etc.) owing to that effect was in dicated.
This paper Is devoted In developing a detection system for Interfacial defect between concrete and FRP sheet by using Laser Doppler Velocitometer. A piezoceramics is attached specimen's surface as an elastic-wave actuator. Through measurement of the elastic velocity-wave across the specimen and carbon fiber sheets by the LDV the Interfacial defect can be detected by comparing with the normal bond. It is concluded that detecting the position of the Interfacial between concrete surface and FRP sheets is effective, and the detection ability on area may be dependent on the capacity of the piezoceramic actuator. The detectability on surface area ceramics scope detected area is in a circle with 10cm-radius from the wave source point located on same face or the projecting point on the opposite face of wave source point through the piezoceramic actuator.
We proposed a method to reuse returned or residual waste fresh concretes, hereafter referred to as waste fresh concretes that are 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 wastes emission. A super set-retarding agent to halt the cement hydration of the waste fresh concretes and a superplasticizer to improve the efficiency of the subsequent wet-screening and pumpability were added to the waste fresh concretes. Resulting Eco-mortar can be used as a preceding mortar for the next day or later. Effects of mixture proportions and the type of cement of waste fresh concretes on the fluidity, set-retardation and compressive strength of Eco-mortar were examined. As a results, availlable ranges of the original waste concrete quality satisfying the requirements of Eco-mortar and the Eco-mortar production system were determined.
This research features the bond behavior between fiber sheet and concrete. To obtain the local bond stress versus slippage relationship, doubleface shear test is conducted. The test variables are mainly the types of fiber and concrete. The test results show that sheet stiffness influences both of bond strength and shape of stress distribution. However, the obtained local bond stress-slippage relationships are not influenced by types of fiber sheet. Only the maximum local bond stress has an increment as concrete compressive strength also increases. A new model representing the relationship is proposed using Popovics formula, which is adapted to present the concrete compressive stress-strain relation. A numerical analysis is performed to confirm the model with experimental results. The analytical results show a good agreement in bond strength and strain distribution with experimental results.
Recently, researches for ultra-high strength concrete exceeding 200MPa including RPC or DSP composites, which apply special consideration to the selection of granular components and granular mixtures have been carried out. In this study, to enhance mechanical properties of ultra-high strength mortar without special treatment of materials, hot-press compaction was adopted and steel powder was used as aggregate. The influence of pressure of hot-press compaction, water-binder ratio, and using steel powder on the mechanical properties were investigated. Compressive strength was incremented 40 to 60% by using hot-press compaction, and 315 MPa was obtained when steel powder was also used
The effects of slag content and polymer-binder ratio on the strength properties of combined wet/dry-cured polymer-modified concretes using ground granulated blastfurnace slag (slag) and a styrene-butadiene rubber (SBR) latex are examined. As a result, the compressive, tensile and flexural strengths of the combined wet/dry-cured SBRmodified concretes using slag increase with increasing polymer-binder ratio, and reach maximums at a slag content of 40%. Such high strength development is attributed to the high tensile strength of SBR polymer and the improved bond between cement hydrates and aggregates because of the incorporation of SBR latex.
Manufactures of the conventional reinforced concrete segment involved the application of heavy vibrating compaction to concrete with an extremely stiff consistency. Focusing on one of distinctive features of high flowing concrete, that is self-compacting into the steel form, the authors developed and put into practice a new segment manufacturing system to rationalize the manufacturing process and equipment, as well as the simplifying steel form. This paper describes the adjusted mix proportion of high flowing concrete best suited for segment manufactures, the structure of the closed-type steel form that saves the surface finishing work on the back of segment, and the method of placing high flowing concrete. It also shows that this new type of segment proved to have an engineering performance equal to or better than the conventional one in various tests.
The fitness of Poisson distribution on the number of internal cracks and the fitness of log-normal distribution on the length of cracks was discussed. Concrete specimens were observed for internal cracking by means of digital microscope after they were subjected to several types of cyclic loading. The agreement of shapes between expected distribution and observed histogram was verified. The expedience of applying probability distribution to the number as well as length of cracks was substantiated. The research also indicated that the consideration for the number is more important than for the length of cracks. This paper is limited to work on internal cracks observed on the surface cut perpendicular to the direction of the compressive loading.