The purpose of this study is to estimate mix proportion of shotcrete, which changed a dosage of accelerator and water-cement ratio. The shotcreting mechanism was considered on the basis of the estimated mix proportion. The occurrence of rebound and dehydration phenomenon gives variety to base concrete. For changing a dosage of accelerator, amount of the cement in the shotcrete decreased with an increase in a dosage of accelerator, and amount of the aggregate in shotcrete increased with an increase in a dosage of accelerator. For changing the water-cement ratio, amount of the cemet in the shotcrete increased with a decrease in the water-cement ratio, and amount of the aggregate in the shotcrete decreased with a decrease in the water-cement ratio. The acceleration of hydration and decrease in water-cement ratio were increased the viscosity of paste. The increase in viscosity of paste also gives variety to the base concrete. Accordingly, the viscosity of paste affects shotcreting mechanism.
A corrosion of reinforcing-bar by salt injury is one the serious issues for concrete because it damages : durability and strength of concrete structure. We re-examined a rest potential method which has been generally, applied for diagnosis of the reinforcing-bar corrosion. We revealed that the rest potential could be influenced by sime properties of covering concrete since the rest potential of the renforcing-bar was normally measured across the covering, and we proposed a new potential correction procedure taking the properties of covering into account. At the same time, we synthesized an anion adsorbent that could absorb excess amount of chlorine ion in concrete whiclcaused the salt injury, releasing nitrite ion which suppressd the reinforcing-bar corrosion. We also developed an inorganic repair material which contained the adsorbent. Based on the effectiveness of the new material for suppressing the reinforcing-bar corrosion, we propose a new repair method named Suppressing Salt Injury method (SSI method).
In this paper, a fundamental study is carried out to develop a kind of intelligent concrete with selfhealing capability for strength. Conceptual methodology consisting of three functions of sensing, processing and executing is proposed. In the method, crack repairing agents are installed as core materials in shell bodies embedded in concrete structures. The feasibility of the proposed approach is clarified experimentally by making use of glass pipes as shell bodies containing crack repairing agents
The bambo reinforced soil-cement concrete is consisted by a mixture of cohesive soil, sand, cement and sufficient water on site, using bamboo instead of steel bar. The soil-cement concrete was produced taking into account of effective water of soil and sand on the basis of saturated surface-dry condition. This construction method can be used for a temporary road constructed on the soft ground using soils of the site and for low-rise housing construction using a structural unit with strength larger than adobe bricks. This paper proves the feasibility of bamboo reinforced soil-cement concrete construction by experiments comprising bonding between bamboo and soil-cement concrete, outdoor exposure test of slabs and flexural test of beams.
Experimental studies were carried out in aiming for utilization of fusion slag manufactured by melting ash produced in high-temperature incineration of common waste materials as fine aggregate for concrete. Results obtained in the studies were ascertainment that there is no problem about safety of the fusion slag, that physical qualities as fine aggregate are approximately the same as those of ordinary sand, that there is little scatter in quality when manufactured, and that quality is stable. Furthermore it was verified that the quality of concrete using the slag as fine aggregate, when replacement ratio is not more than 40%, is roughly the same as with concrete using ordinary fine aggregate, both when fresh and when hardened. There is no problem about durability when water cement ratio is not more than 50%, and the fusion slag can be used as fine aggregate for concrete.
It is well known that freezing of capillary water causes frost damage of concrete. The authors hadproposed the modified mechanism of frost damage as follows1) . When supercooled water freezes ice crystal grows very rapidly. Therefore the increase of volume makes unfreezing water flow very quickly. Subsequently large hydraulic pressure causes fracture of pore system and length change. Those are recognized as frost damage. The proposed mechanism mentioned above was just qualitative. In this paper the authors proposed quantitative model that describes length change under a freezing and thawing cycle. The proposed model is verified from the result of TMA measurement of mortar. Furthemore correspondence to the result of freezing and thawing test of concrete is examined. Consequently the quantitative estimation of frost resistance of concrete is capable by measuring temperature, air void system, pore structure and tensile strength of Cementitious material.
Soil saving dam, break water and pavement that are located in severe wearing condition are often subjected to rapid deterioration of structure. Ultra-High strength concrete exceeding 200 MPa with or without steel fiber, has a possibility of becoming high abrasion resistance concrete. The effect of addition of steel fibers, water-binder ratio and compaction method on abrasion resistance and mechanical properties of ultra-high strength steel fiber reinforced concerete were studied. It was concluded that, the combination of addition of steel fibers and using hot-press compaction for ultra-high strength mortar is particularly effective in improving abrasion resistance.
The anchors for the infill shear wall should be designed in consideration of the condition of construction site. In this study, the experiment was carried out to make clear the strengthening effects of the infill shear walls constructed with actual specifications using resin type anchors. In this experiment, the following parameters were considered. 1) The amount of anchors, 2) The compressive strength of concrete of the infill wall panel, 3) The sectional configuration of the boundary columns, 4) The additional shear walls with or without finish mortar. Also, the estimation method for the ultimate strength of the infill shear wall was investigated. The following conclusions were obtained. 1) The ultimate flexural strength of the infill shear wall is properly estimated in consideration of the effectiveness of the anchors. 2) In cases of a small amount of anchors and high compressive strength of the infill wall panel, its ultimate shear strength estimated by the guide line for the seismic retrofit in Japan is underestimated. 3) The ultimate shear strength estimated by the modified formulas good coincides with the tested value.
The effects of early hydration reactivity of cement on the dispersing force of polycarboxylate type superplasticizer (PC) were investigated by using normal Portland cement (NPC) and belite-rich low heat Portland cement (LHC). Early hydration reactivities were controlled for both NPC and LHC by exposing them to an condition of 80%RH and 20°C. Regardless the differences in cement type and in early hydration reactivities of cements, the fluidity of PC-added paste was positively related to PC adsorption amount per BET specific surface area of the solid phase of the paste, AdPC/BET. The dispersing force of PC was determined by the amount of PC adsorbed on the unit surface area of the solid phase. In each cases of NPC or LHC, AdPC/BET corresponded to the variation of BET specific surface area of the solid phase of the paste, SSApc. The variation of SSApc was caused by the variation of cement early hydration reactivity. AdPC/BET was also affected by the sulfate ion concentration in the solution phase of the paste, because sulfate ions act as competitive adsorbates with PC. AdPC/BET for LHC was larger than AdPC/BET of NPC at the same SSApc because of the lower alkaline sulfate content of LHC.