This research examined the use of Lapilli as a concrete aggregate resource for the purpose of effective utilization and reduction of weight. And various design of mix proportion that replaced an artificial coarse light-weight aggregate with Lapilli was carried out, and their basic nature was examined. As a result, the strength felled when replacement rate of Lapilli was heightened. However, when water-cement ratio has become 50% or less and when unit cement quantity was made 400 kg/m3, compressive strength was recorded 24N/mm2 with 50% replacement rate and recorded 15N/mm2 at 100% replacement rate. Also between the compressive strength and static modulus of elasticity, comparatively favorable correlation nature was shown in 50% of replacement rates. And the increase of concrete strength was confirmed when concrete was cured for a long length of time. Therefore, the effectiveness of case that replaced a light-weight concrete with Lapilli within 50% was confirmed.
Compressive strength of cement based materials is affected by moisture states. There have been various discussions about the mechanism, but no consensus has yet been reached. In this study, the influence of moisture states on compressive strength of cement based materials was investigated from the perspective of surface energy. The relationship between compressive strength and surface tension of liquid saturating mortar specimen was experimentally examined. It was revealed that the bigger the surface tension, the smaller the compressive strength. It is considered that the reason of lowering of compressive strength of cement based materials in wet condition is attributed to decreasing of surface energy which is required to form new microcracks.
Compressive fatigue strength of concrete under the water is known to drop considerably, but the reason has not yet been cleared. The fracture process of concrete is the generation and propagation process of internal microcracks. Considering that forming each microcrack requires surface energy which is reduced by surface tension of water, the deterioration of fatigue strength of concrete under the water is likely to be explained as the decreasing of surface energy. In this study, compressive fatigue strength of concrete was investigated from the perspective of surface energy. It became clear that K value in Goodman-type S-N curve equation decreased linearly with increasing surface tension of liquid saturating internal void of specimen. It was also indicated that when a static strength of concrete saturated with water was set as the standard value of stress ratios, sufficient attention should be paid to the fatigue strength of concrete saturated with liquids with higher surface tension than water while it hardly mattered in the air.
In the reinforced concrete with the crack, the corrosion rate becomes high because the macrocell is formed. This study proposed the analytical model, whose input data were the anodic and cathodic polarization curves, the polarization resistance and the concrete resistance, while output data were the macrocell and macrocell corrosion rates. Also, the experiments using the mortar specimen with the different cracks, the humidity and the water cement ratios were carried out to verify the model. As the result, 1) the corrosion rate analytical model of the reinforced concrete with the crack was proposed. 2) It was confirmed that the model was appropriate by the experiment using the mortar specimen.
In this study, the improvement mechanisms of fluidity and strength development of the steam cured polymer-modified mortar (PMM) with low water cement ratio were investigated. The fluidity was estimated from the rheological property, the flocculation formation structure of the fresh PMM and the rate of hydration reaction. The strength development was estimated from the hydration reaction of cement, the hydration products, and the composition and structure of hardened PMM. The results obtained are as follows : The rheological property of PMM for high self-compactablility was optimized by adjusting of polymer and superplaticizer contents. The transition zone was not observed and the uniformly dense hydration structure was formed in PMM because of its low water to cement ratio. The polymer in PMM filled pore space by mesh structure. PMM with high early strength Portland cement accelerates the hydration reaction and forms more dense structure compare to that with ordinary Portland cement.
For the purpose of the quality assurance of porous concrete (PoC) with continuous voids, it is necessary to control the flow condition of the binder adhering to the surface of aggregate in the vibration. This paper describes the flow characteristic of the binder by Rheological treatment at the fresh stage, since the flow pattern of the binder generally shows pseudo-plastic (pp) flow having a yield value in a state wherein grouting. As the result, it became clear that the flow condition which does not flow down to the bottom in the vibration was given by apparent viscosity and vibrational acceleration.
In this study, experimental and analytical estimation of residual flexural strength of RC beams with reinforcement corrosion was carried out. As a result, it is noted that the factors, which influence on residual flexural strength and failure behavior of RC beams were not only corrosion rate, bond stress behavior but also the corrosive crack characteristics of concrete. Moreover, it seems impossible to estimate the characteristics of bond splitting failure along reinforcement and sudden drop of external forces in the current analysis, in which only corrosion rate and bond stresses are taken into consideration.
In this study, a quantitative estimation for influence of lapped splices on the residual flexural strength and failure behavior of RC beams with corroded reinforcement was carried out. As a result, it is noted that residual flexural strength of RC beams with lapped splices decreases greatly and failure behavior is different from that of RC beams without lapped splices. Moreover, in the detailed prediction of the flexural behavior, it is pointed out that it is necessary to introduce corrosive crack characteristics by comparing the experimental results between RC beams with lapped splices and without lapped splices.
Nonlinear response of multi-story unsymmetric buildings regular in elevation with elasto-plastic seismic control devices under bi-directional excitation is discussed and the effect of elastio-plastic seismic control devices are examined. Then a nonlinear static procedure to estimate the maximum drift of multi-story unsymmetric buildings with elasto-plastic seismic control devices is presented and its applicability is discussed. The results obtained by the proposed procedure are compared with the nonlinear time-history analysis results, and satisfactory prediction can be found by the presented procedure.
Fiber reinforced light-weight foamed mortar (air mortar) showing multiple cracking behavior was developed by means of adding prefoamed air bubble to fiber reinforced mortar including ECC (Engineered Cementitious Composites). The effects of air contents and fiber types, namely Polyethylene (PE) fiber, Polyvinylalcohol (PVA) fiber and Polypropylene (PP) fiber, on the properties such as compressive strength and ductility, the shape of flexural load-displacement curves, and the cracking behavior of the fiber reinforced light-weight foamed mortar were investigated. The continuous or discontinuous air bubbles and the pulled-out or ruptured fibers were observed by means of a digital microscope on the fractured surface of specimens after flexural tests. As a result, in the range of this study, the absorbed energy at fracture, which was indicated with the area under flexural load-displacement curves, was large in turn of PE>PVA>PP. In all three types of fibers, the air bubbles were discontinuous up to about 40% in the volume of air content. As increasing of the air content, the strength decreased, but both the flexural deformability and the multiple cracking behavior became remarkable.