Blast furnace slag cement pastes were hydrated under different curing temperatures. Hydration ratio of cement compounds and amount of hydration products were determined quantitatively by Rietveld method. Unhydrated slag was crystallized to be tempered the sample, hydration ratio of slag was also determined by Rietveld method. Hydration of slag is progressed until 28days, but practically halted thereafter. Hydration of C3S is accelerated, and hydration of C2S is delayed with the presence of slag. Strength development of mortar can be predicted by using the gel space ratio model. Hydration rate equation of C3S, C2S and slag can be expressed as a function of curing age and temperature.
This paper presents the development of new heat resisting fiber reinforced polymer (FRP) bars and tneir applieuiam the concrete members. Experiments were conducted on commercially available FRP bars and newly developed carbon and aramid FRP bars impregnated with PH (phenol) and CP (cross-linked polyesteramide resins). Heat resistance tests, alkaline durability tests, pullout tests of FRP bars and flexural tests of FRP reinforced concrete beams at various temperatures were carried out. It was observed that newly developed FRP bars impregnated with PH show high heat resistance and less deterioration of bond strength at high temperature than the other FRP bars. The concrete beam reinforced with FRP bar composed of carbon fiber impregnated with PH shows an excellent performance at high temperature which is comparable to that reinforced with steel bars. FRP bars impregnated and cured with PH also showed a good alkaline durability.
Recently, to prevent the falling of the concrete flakes from viaducts and to keep the third person away from getting damaged by concrete flakes due to expansion of corroded steel bar, the concrete surface treatment works have been done widely. In the case that the chloride ion in concrete is less than critical value, corrosion of steel bar in concrete is governed by the progress of neutralization of concrete. In this paper, as one of the tools for the preventative maintenance works of RC-structures, the neutralization reaction model was constructed and calculated and time-dependant progressing patterns of cracking in cover concrete which caused by steel bar corrosion were analyzed. The results were compared with those of the foregone research and the efficacy of the model and problems were discussed.
The reinforcing steel in concrete corrodes due to various degradation factors. Since apparent volume of corroded reinforcement is larger than original one, expansive pressure is introduced. The mechanism of spalling of cover concrete and expansion of corrosion has mainly been studied in 2-dimensional sections. However, the 3-dimensional effect should be considered to make clear the spalling mechanism. In this paper, 3-dimensional finite element analysis that covers the 3-dimension effect is conducted. With considering coefficient of variation of maximum pressure in experimental tests, the corrosion length factor (Lemin/k) where the 3-dimensional effect can be ignored is proposed.
Concrete filled double steel tubular members (CFDT) consist of two centric steel tubes and filled concrete between them. By the arrangement of the inner tube, own weight can be reduced in comparison with concrete filled steel tubular members. Four point loading tests on twelve specimens of CFDT were performed. Experimental parameters are inner-to-outer diameter ratios and outer tube's diameter-to-thickness ratios. The purpose of this study is to investigate effect of inner-to-outer diameter ratios on bending capacities. Experimental strengths were good agreement with bending strengths calculated using axial load (N)-bending moment (M) relation, where N was equal to zero. Failure modes were local buckling and fracture of outer tube. The larger inner-to-outer tube's diameter ratios, yield the smaller confinement strength.