• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.4
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• pp.1095-1104
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• 2014

This paper presents the results of experimental work on both strength characteristics and durability of concrete or mortar having 50% ground granulate blastfurnace slag(GBS) with different fineness levels (4,450, 6,000 and $8,000cm^2/g$). Compressive and split tensile strength test results indicated that the concrete with a higher fineness level of GBS exhibited a better strength development due to the acceleration of latent hydraulic property at the later curing stage compared with ordinary portland cement concrete. Meanwhile, it was found that a higher fineness level of GBS showed some negative effects on the resistance against freezing-thawing action. However, incorporation of GBS to concrete, irrespective of fineness levels, significantly enhanced the chloride ions penetration resistance. The resistance against sulfate attack of mortar with GBS was greatly dependent on the attacking sources from sulfate environments.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.637-640
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• 2008

In this study, the characteristics of strength development on high volume fly ash concrete(HVFAC)with Type 4 cement was experimentally investigated. Three levels of W/B were selected. Four levels of fly ash replacement ratios and two levels of silica fume replacement ratios were adopted. In the concrete mix, the water content of 125kg/m$^3$ was used, which is less than that of usual water content. As a result, it appeared that the compressive strength gradually decreased with increasing fly ash replacement ratio until 91days. However, regarding the compressive strength, the proper replacement ratio is about 20%, which is low compared to Type I cement case. It was observed that the tensile strength is proportional to the 0.72 power of the compressive strength. It appears that the prediction equation presented in Concrete Standard Specification overestimate the tensile strength in the low strength range, underestimate the tensile strength in the hi호 strength range.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.593-596
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• 2008

The bleeding of concrete is defined as a kind of separation of materials. The durability of concrete, as well as the quality caused by the bleeding. Therefore, This study is intended to find influence of cement and mixing time factor on the bleeding of concrete. We want to know two factors that determine the change, to provide it to our customers. According to the results, The bleeding ratio increase by the increase of mixing time factor. At the 90 second of mixing time, the amount of bleeding differ greatly from cement properties. This paper presents an experimental study on bleeding ratio, slump and compressive strength properties with three days. In addition, the mixing time is inversely related slump loss ratio, the initial value of the compressive strength is only affected by the mixing time. As a result, the bleeding of concrete was obtained that their characteristics depends on the cement and mixing time factor, also in the future, to derive optimum mixing time for a variety of review is necessary.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.661-664
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• 2008

The structure which is located in special surroundings like ocean-environment is physically and chemically eroded by seawater or salt damage, and then concrete-structure becomes deteriorated by iron corrosion and swelling pressure which leads to remarkably decline durability due to cracks and exploitation. As a measure against salt damage, it is actively being examined to use the blended cement that controls salt damage and fix chloride in the process of hydration. In this study, therefore, to examine the property of marine concrete added admixture, marine concrete is manufactured by adding high-strength admixture(omega2000) by 0, 5, 10, and 15% to low heat-blended cement. Then it shows that the compressive strength of manufactured marine cement tends to increase and chloride penetration resistance improves.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.665-668
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• 2008

Portland cement production-1.5billion tonnes yearly worldwide-contributes substantially to global atmospheric pollution($\sim$7% of total of CO$_2$ emissions). Attempts to increase the utilization of fly ash, a by-products from thermal power plant to partially replace the cement in concrete are gathering momentum. But most of fly ash is currently dumped in landfills, thus creating a threat to the environment. Therefore, In this study, influence of curing temperature(30, 60, 90$^{\circ}$C) on the strength of properties fly ash based cement ZERO mortar was investigate, measured a weight change and pH change according to each care of curing temperature. The test results that a curing at 90$^{\circ}$C is appropriate in case of the high strength concrete is required in the early-age of the curing and 60$^{\circ}$C is efficient for the case of requiring high strength at age 28 days. Furthermore pH variation and value of compressive strength are judged to correlate but change of weight is not the case.

• Journal of the Korea Institute of Building Construction
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• v.12 no.3
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• pp.284-290
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• 2012

Cement Fineness Modulus (CFM) is a method of expressing the distribution of particle sizes of cement in numeric form. If CFM is controlled through crush process of cement without modifying the chemical components or mineral composition of cement, it is judged to be able to produce a cement satisfying various requirements because it is estimated to enable various approaches to cement such as high early strength, moderate heat, low heat cement and so on. Therefore, in this study, as basic research for manufacturing special cement utilizing the controls of CFM, the intention was to review the impacts of CFM on the fundamental properties of concrete. To summarize the result, as mixture characteristics of fresh concrete, ratio of small aggregate and unit quantity were gradually increased, securing greater fluidity, with an increase in CFM, while the amount of AE and SP were reduced gradually. In addition, setting time was delayed as CFM increased. Furthermore, compression strength was relatively high during initial aging as CFM became smaller, but as time passed, compression strength became smaller, and it showed the same level of strength as aging time passed about three years.

• Journal of the Korea Concrete Institute
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• v.14 no.2
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• pp.249-256
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• 2002

High performance concrete is prone to large autogenous shrinkage due to its low water to binder ratio (W/B). The autogenous shrinkage of concrete is caused by self-desiccation as a result of water consumption by the hydration of cement. In this study, the autogenous shrinkage of high performance concrete with and without fly ash was Investigated. The properties of fresh concrete, slump loss, air content, and flowability as well as the mechanical properties, compressive strength and modulus of elasticity, were also measured. Test results was shown that the autogenous shrinkage of concrete increased as the W/B decreased. For the same W/B, the autogenous shrinkage of high strength concrete with fly ash was considerably reduced although the development of its compressive strength was delayed at early ages. Furthermore, the autogenous shrinkage and compressive strength of high strength concrete were more rapidly developed than those of normal strength concrete. It was concluded that fly ash could improve the quality of high strength concrete with respect to the workability and autogenous shrinkage.

• Journal of the Korea Concrete Institute
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• v.28 no.1
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• pp.41-48
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• 2016

This research investigates the effects of shrinkage reducing agent (SRA) on the mechanical behavior of strain-hardening cement composite (SHCC). SHCC material with specified compressive strength of 50 MPa was mixed and tested in this study. All SHCC mixes reinforced with volume fraction of 2.2% polyvinyl alcohol (PVA) fiber and test variables are type and dosage of shrinkage reducing agents. The shrinkage reducing materials used in this study are phase change material as the thermal stress reducing materials that have the ability to absorb or release the heat. The effect of SRA was examined based on the change in length caused by shrinkage and hardened mechanical properties, specially compressive, tensile and flexural behaviors, of SHCC material. It was noted that SRA reduces change in length caused by shrinkage at early age. SRA can also improve the tensile and flexural strengths and toughness of SHCC material used in this study.

• Journal of the Korean GEO-environmental Society
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• v.21 no.11
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• pp.11-20
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• 2020

For water barrier and reinforcing grout in soft ground, the verification of durability was conducted over the initial and long-term ages under various curing conditions. The grout was made of water glass system, fast-hardening mineral (FHM) system, and acrylic polymer system. There were three types of curing conditions that were tab water curing, artificial seawater curing, and atmospheric curing. And the various tests were performed for each sample by age, uniaxial compressive strength, length change, and weight change. As artificial seawater, MgCl₂ and MgSO₄ aqueous solutions were prepared and used, respectively. As the test results, the fast-hardening mineral system and acrylic polymer system were cured stably without significant change in durability in tap water and artificial sea water, whereas water glass system showed a very rapid drop in durability under artificial sea water conditions compared to tap water. In atmospheric curing conditions, durability is lowered compared to water curing in all cases, and in particular, the weight loss in the FHM system and water glass system is about 62% and 60%, respectively, resulting in a significant decrease in durability.

• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.6
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• pp.82-89
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• 2014

The purpose of this study is to propose a simple model to evaluate the compressive strength development of concrete with various supplementary cementitious materials (SCMs) and cured under different temperatures. For the generalization of the model, the ACI 209 parabola equation was modified based on the maturity function and then experimental constants A and B and 28-day compressive strength were determined from the regression analysis using a total of 265 data-sets compiled from the available literature. To verify the proposed model, concrete specimens classified into 3 Groups were prepared according to the SCM level as a partial replacement of cement and curing temperature. The analysis of existing data clearly revealed that the 28-day compressive strength decreases when the curing temperature is higher and/or lower than the reference curing temperature ($20^{\circ}C$). Furthermore, test results showed that the compressive strength development of concrete cured under $20^{\circ}C$ until an early age of 3 days was marginally affected by the curing temperature afterward. The proposed model accurately predicts the compressive strength development of concrete tested, indicating that the mean and standard deviation of the ratios between predictions and experiments are 1.00 and 0.08, respectively.