This paper presents results of an experimental investigation of the strength of lap splices of headed longitudinal bars which intend to decrease the splice length to 15db (db : bar diameter). Ten 1/2.5 scale R/C beams were tested to estimate the influence of joint type, shear reinforcement, concrete strength and shape of headed bars to the strength of lap splice. Seven simple beam type tests and three double curvature type tests were done. Based on the test, the equations of the strength of lap splices of headed bars in constant moment region and flexural shear region were proposed.
This study focused on the properties of high-strength concrete reinforced by steel fiber with different shapes and contents. First, bond tests of steel fibers in high-strength mortar were conducted. Bond behaviors of six types of steel fibers with different shapes were investigated. Then, fresh and hardening properties of steel fiber reinforced high-strength concrete were examined. The effects of shapes and contents of steel fibers to slump, air content, compressive strength, flexural strength and toughness were investigated.
The microstructures formed by cement hydration affect the physical properties of hardened cement, such as strength and durability, and the cement hydration is influenced by the conditions at early age. When concrete structures are exposed to air i.e. drying conditions at early age, the water in the concrete evaporates from surface. After that, cement hydration is stopped due to lack of water for hydration. However we hope that cement can re-hydrate by replenishing water through rain, re-curing and changing humidity. After re-hydration, we hope to recover the strength and durability. In this research, the effect of cement hydration and physical properties in view of microstructure on changing the condition on early age is evaluated. And it is aimed to make a model of microstructure development on re-supplying water.
Although sea sand has been taken from Inland Sea for long time, it will be eventually banned by 2006 from the environmental preservation's point of view. Sea sand substitutes have to be developed urgently. In this study, crushed sand as a sea sand substitute was tentatively manufactured using granite and an extensive examination on the fundamental properties of fresh and hardened concrete and the durability was conducted. From the results, it was concluded that even if crushed sand as fine aggregate is fully used in addition to crushed stone as coarse aggregate, concrete with required fresh performance can be manufactured by an appropriate utilization of admixtures, and compressive strength and durability of concrete, which are equal to or higher than concrete with sea sand, are obtained.
For the purpose of streamlining the concrete pumping work, the author proposes an equation for predicting the pipe flow of concrete as a result of theoretical and experimental studies on the flow of concrete in piping. In addition, the author also proposes an inclined pipe testing method capable of simply estimating different factors used for the calculation using the enuntion. Furthermore. on the basis of studies of pressure losses in bends and vertical piping, the author introduces a practical calculation program for approximating the pressure required for transfer of concrete through piping under pressure.
It has been pointed out until now that diagnosis of the concrete structure by the infrared thermography method has a high possibility of incorrect-detecting reflection and thermal radiation, and that judgment of the time suitable for investigation cannot be checked spot. Furthermore, even if it judges it as the unusual part by the infrared thermography method, the damage situation of the unusual part cannot be guessed. To solve such a problem, by this research, a damage situation can be guessed to some extent by performing heat conduction analysis and the scope of an infrared camera was checked by conducting an indoor experiment. In the main issue, the new check technique is proposed based on these research results. While this technique can judge objective time suitable for investigation, it becomes possible to guess a damage situation in a certain amount of accuracy.
The influence of reinforcement corrosion on shear strength capacity of reinforced concrete (RC) beams was discussed based on the experimental results obtained by the loading tests. The reinforcing bars in concrete were artificially corroded by electrical method means prior to the loading test. It was found that shear strength capacity of the beams contributed by web reinforcement decreases, with the increase of corrosion rate, but that the contribution of concrete to shear strength capacity increases. Cracking induced by steel corrosion causes the failure mode change. The failure mode change the specimens; shear-tension type to shear-compression type, was observed by using the Image based-measurement system developed by the authors.
The 32.5 N/mm2 grade cement (325 cement) using slowly cooled blast furnace slag and granulated blast furnace slag, has a tendency of small fluidity change in course of time compared with the 325 cement prepared with the ordinary portland cement (OPC) and limestone powder (LSP). On the other hand, this has a long setting time, and is slow in developing the early age strength. However, those were improved by substituting the high early strength cement for OPC. In addition, the compressive strength in 28 days was equal to the 325 cement from OPC and LSP, and the neutralizing resistivity has been improved keeping the high resistivity of the blast furnace slag cement to chloride ion permeation as it is. Besides, ecological evaluation results proved that the carbon discharge due to the cement manufacturing and the natural resources of limestone consumption will be largely reduced, thereby this 325 cement can be a cement of small environmental load. The industrial byproduct of the blast furnace slag is proportioned more than in the blast furnace slag cement, therefore this 325 cement can be serviceable also in view of increasing the byproduct reuse.
In this study, the effects of concrete strength and reinforcing clear distance on the damage of reinforced concrete (RC) slabs subjected to contact detonations have been experimentally investigated to establish the design and damage estimation methods of RC shelters. The main results obtained are as follows : 1) The concrete strength and the clear distance don't affect cratering and spalling significantly. 2) The dimensions of the crater and spall are relatively well predicted with the authors' method for the RC slabs with the ultra high strength concrete and much longer reinforcing clear distance than diameters of the crater and spall. 3) The surface and inside cracking tends to occur more remarkably with higher strength concrete and longer reinforcing clear distance.
This research intended to improve jointing method of re-bars between PCa (precast) block and cast-in-place concrete especially for large structure, and experiments were conducted against bending moment and shear force. Main target of the improvement was put on reduction of the extruding length of re-bars from PCa block to cast-in-place side in order to raise productivity of PCa blocks as well as easiness of transportation from a PCa factory to construction sites. In our research, several new jointing methods other than the lapped joint were proposed and tested under action of the bending moment and shear force, and we found that a type with loop-shaped re-bars displayed approximately same load bearing capacity and deformation capability if compared with genuine specimen which had non-jointed re-bars.