• Journal of the Korea Institute of Building Construction
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• v.13 no.6
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• pp.602-608
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• 2013

The aim of this study is to investigate experimentally the effect of the combination of fine particle cement with high Blaine fineness (FC) and recycled aggregates on the engineering properties and micro structure of high volume blast furnace slag (BS) concrete with 75% BS and 21 MPa. FC manufactured by particle classification at the plant with Blaine fineness of more than $7000cm^2/g$ was used as additional alkali activator for high volume blast furnace slag concrete made with recycled fine and coarse aggregates. FC was replaced by 15, 20 and 25% OPC. Test results showed that the incorporation of FC resulted in an increase in the compressive strength compared to BS concrete without FC by as much as 30% due to accelerated hydration and associated latent hydraulic reaction. It was found that the use of FC and recycled aggregates played an important role in activating BS for high volume BS concrete by offering sufficient alkali.

• Journal of the Korea Concrete Institute
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• v.23 no.5
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• pp.581-590
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• 2011

Since ultra-high performance cementitious composites (UHPCC) not only represents high early age shrinkage strain due to its low water-to-binder ratio (W/B) and high fineness admixture usage but also reduces the cross section of structure from the higher mechanical properties, it generally has more shrinkage cracks from the restraints of formwork and reinforcing bars. In this study, free and restrained shrinkage experiments were conducted to evaluate the suitability of incorporating both expansive admixture (EA) and shrinkage reducing agent (SRA). The test results indi-cated that approximately 40~44% of free shrinkage strain was decreased. Also, the results showed that 35% and 47% of residual tensile stresses were relieved by synergetic effect of SRA and EA, respectively. Residual tensile stresses from ringtest were relaxed by approximately 61% and 64% of elastic shrinkage stresses due to SRA and EA, respectively, because of the tensile creep effect. Therefore, the creep effect should be considered to precisely estimate the restrained shrinkage behavior of concrete structures. The degree of restraint of UHPCC was approximately in the range of 0.78~0.85. The addition of combined EA and SRA showed minute influence on the degree of restraint. However, the effect decreased when thicker concrete ring was used. Tensile creep strains were measured and compared to the predicted values from 4-parametric prediction model considering time dependent restrained forces.

• Geotechnical Engineering
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• v.14 no.6
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• pp.113-125
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• 1998

At the end of 1997 about 3 million tons of coal ash was produced as byproducts from the coal fired electrical power plants in Korea. Only about 27% of that byproducts was utilized as the admixtures of cement and concrete industry. But the large quantity of coal fired fly-ash has been used as the soil improvement materials in other countries. So the aim of this study is the estimation of the applicability of the coal fired fly-ash as microfine grouting materials by admixing the superfine particles which were separated from the coal fired fly-ash for the higher values. The 6 types of specimens were manufactured in the laboratory for the purpose of estimating the chemical and physical properties of cement and grouts. These specimens consisted of 2 specific surfaces of 6, 000 and 8, 000$cm^2$/g in Elaine method. And these specimens are devide into 3 ratios (30%, 50%, 70%) of fly-ash by weight. From the estimated properties of the coal fired fly-ash microflne cements and grouts, 50% fly-ash is the most suitable ratio for grouting materials. However, further study of durability is necessary for using fly-ash grouts practically at the field projects. The higher content of the unburned carbon of fly-ash increases the thinner layer of carbon on the surface of solution of grouts, and requires more quantity of surface active agent. As a results of this study, it is found that the microfine fly-ash is very useful as a good grouting material if 50% of fly-ash is added with the microfine portland cement. So, in the near future, if the coal fired fly-ash is able to be used as grouting material in Korea, the demand of fly-ash will increase rapidly.

• Journal of the Korean Recycled Construction Resources Institute
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• v.7 no.2
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• pp.166-173
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• 2019

In this paper, the reaction properties of silica source in the accelerated curing conditions using autoclave and the fundamental properties of inorganic Micro Defect Free(MiDF) concrete using silica source are studied. Studies show that Si ions elution rate from silica source in autoclave curing is higher in amorphous source. In tap water conditions, solids which is source after autoclaved curing show a higher mass reduction in amorphous materials, which is attributed to the higher elution rate of ion. In $Ca(OH)_2$ solution conditions, amorphous materials show higher mass increase, due to increase in C-S-H minerals. From experiment for influence on the properties of MiDF concrete by using nano silica materials, the specimen with silica fume shows an increase in compressive strength and a decrease in absorption depending on replacement rate up to 5.5%, while nano silica with amorphous phase and high-fineness shows a decrease in compressive strength and decrease in the water absorption. The specimen with nano silica increases the pore below 10,000nm, but reduces pore between 10,000 and 100,000nm. The above results show that the porosity and absorption rate of MiDF concrete can be reduced by using amorphous nano-size silica. However, to reduce the pore of 50 to 10,000nm, better dispersion of nano material in the cement matrix will be necessary. We will focus on the this item in the next research.

• Journal of the Korean Geosynthetics Society
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• v.16 no.3
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• pp.21-30
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• 2017

Cement grouting method is generally applied for the purpose of reinforcement of deteriorated reservior. Problems have been raised due to the limit of the injection material. In order to solve these problems, various grout materials have been developed. However, there are many cases in which the grounds are disturbed in actual field. In this study, the physical properties of hybrid grout with high fineness and high viscosity characteristics were analyzed to enable penetration into the ground. Optimum inflation agent was selected and mixed with the grout. The pressure and compaction effect on expansion was examined and its effectiveness was verified. From the result of confirming expansion ratio, uniaxial compressive strength, expansion pressure and compaction effect, the HI-E (2%) sample was analyzed to be excellent in improvement effect by the inflation agent. Hence, hybrid grout can be effectively applied for the impermeable and reinforcement method of deterioration reservoir and tide embankment.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.5A
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• pp.307-315
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• 2012

Recently, ultra high performance fiber reinforced concrete (UHPFRC) having over 180 MPa compressive strength and 10 MPa tensile strength has been developed in Korea. However, UHPFRC represents different material properties with normal concrete (NC) and conventional high performance concrete (HPC) such as a high early age autogenous shrinkage and a rapid dry on the surface, because it has a low water-binder ratio and high fineness admixtures without coarse aggregate. In this study, therefore, to propose suitable experimental methods and regulations, and to evaluate mechanical properties at a very early age for UHPFRC, setting, shrinkage and tensile tests were performed. From the setting test results, paraffin oil was an appropriate material to prevent drying effect on the surface, because if paraffin oil is applied on the surface, it can efficiently prevent the drying effect and does not disturb or catalyze the hydration of cement. From the ring-test results, it was defined that the shrinkage stress is generated at the time when the graph tendency of temperature and strain of inner steel ring is changed. By comparing with setting test result, the shrinkage stress was firstly occurred as the penetration resistance of 1.5 MPa was obtained, and it was about 0.6 and 2.1 hour faster than those of initial and final sets. So, the starting time of autogenous shrinkage measurement (time-zero) of UHPFRC was determined when the penetration resistance of 1.5 MPa was obtained. Finally, the tensile strength and elastic modulus of UHPFRC were measured from near initial setting time by using a very early age tensile test apparatus, and the prediction models for tensile strength and elastic modulus were proposed.