Gum-Sung Ryu

Strength Development and Durability of Geopolymer Mortar Using the Combined Fly ash and Blast-Furnace Slag

In this study, we investigated the strength development and durability of geopolymer mortar using blast furnace slag only, and admixed with blast-furnace slag and fly ash as cementious materials in oder to develop cementless geopolymer concrete. In order to compare with the geopolymer mortar, the normal mortar using ordinary portland cement was also test. In view of the results, we found out that strength development, the resistance to freezing-thawing of the geopolymer mortar have better than the mortar using ordinary portland cement. Especially, using the combined with blast furnace slag and fly ash develop high strength of above 60 MPa, and improve the resistance of freezing-thawing of approximately 20%, but promote the velocity of carbonation of 2.2~3.5 times.

Study on Mechanical Properties of Geopolymer Concrete using Industrial By-Products

This study examines the compressive strength, elastic modulus and splitting tensile strength of geopolymer concrete in order to evaluate its mechanical characteristics according to the admixing of fly ash and blast furnace slag. Moreover, identical tests are also conducted considering the amount of powder, the mixing ratio of alkali activator and the mixing ratio of silica fume for furthe r comparative analysis considering various variables. The comparison with the formulae specified in Korean and overseas codes reveal that a mixing ratio of 18% is adequate for the alkali activator and that a replacement ratio of 5% by silica fume is recommended for silica fume. The elastic modulus of the geopolymer concrete appears to increase slightly with the increase of the compressive strength per variable and age and to be smaller than the values predicted by the formulae specified in Korean and overseas codes. In addition, the examination of the stress-strain curves shows that the geopolymer concrete exhibits ductile behavior compared to the convention al OPC. In view of the splitting tensile strength, high strength is observed for a powder content of 400kg/m 3 and a replacement ratio of 18% by silica fume. The resulting ratio of the compressive strength to the splitting tensile strength is seen to range between 8.7 and 10.2%.

Effects of Mineral Admixture on the Characteristics of Grout for PSC Bridge

The study investigates the effects of the type, replacement ratio and method of use of mineral admixtures on the fluidity, bleeding ratio, volumetric change and compressive strength of the grout in order to provide basic data for the development of high-quality grout for PSC bridges. In view of the results relative to the type and replacement ratio of the mineral admixtures, it appears that fly ash has practically no effect on the improvement of the fluidity nor on the reduction of bleeding and shrinkage of the grout. On the contrary, blast furnace slag and silica fume appear to have significant effect on the improvement of the fluidity or on the reduction of bleeding and shrinkage of the grout. With regard to the combined use of mineral admixtures, the combination of fly ash and blast furnace slag provides satisfactory fluidity but with significant increase of bleeding and shrinkage, whereas the combination of blast furnace slag and silica fume reduces bleeding and shrinkage but with large loss of the fluidity. On the other hand, the combination of fly ash and silica fume results in satisfactory fluidity accompanied with fair reduction of bleeding and shrinkage of the grout. In view of these results, the type, replacement ratio and method of use of the mineral admixtures are seen to influence the fluidity, bleeding and volumetric change of the grout. Accordingly, it is necessary to select the mineral admixtures considering these effects for their exploitation in the grout of PSC bridges.

An Evaluation of Elasticity Modulus and Tensile Strength of Ultra High Performance Concrete

*(ReceivedSeptember10,2015/RevisedSeptember25,2015/AcceptedSeptember28,2015)Recently, for UHPC (Ulta High Performance Concrete) which is researched actively, as the tensile strength is absolutely influen ced onthe content of steel fiber, in this paper, experiments of compressive strength, elasticity modulus and tensile strength were pe rformed according to compressive strength and content of steel fiber as variables. By the test results, compressive strength, elasticit y modulus and tensile strength are proportioned and have a good correlation and according to content of steel fiber, compressive and tens ile strength are also proportioned and have a good correlation. In case of elasticity modulus, the difference between test and pres ent design code is not large, so it is possible to adapt to present design code. On the other hand, in case of tensile strength, as there is nospecification of present design code, new prediction equation is proposed by using nonlinear regression analysis and the propos ed equation have a good correlation to test results.키워드 : UHPC, 인장강도, 탄성계수, 섬유혼입률Keywords : UHPC, Tensile strength, Elasticity modulus, Content of steel fiber* Corresponding author E-mail: imysw@woosuk.ac.kr