• KCI Concrete Journal
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• v.11 no.3
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• pp.79-88
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• 1999

Most difficulties of inducing high fluidity on the concrete mixing design with a strength range of 210 to 240kg/$\textrm{cm}^2$ result from the segregation of aggregates due to the shortage of cementitious binders. To solve the problem, this study concentrated on finding the optimized amount of binder material which does not affect the concrete strength and is also economical. Also there were studies on the use of intermediate sized aggregates to avoid the gap-grading between coarse and fine aggregates so that the material segregation in high flowing concrete was and minimalized the fluidity and penetration capacity of the reinforcing bars was enhanced. Throughout the parametric study with respect to water/binder ratio. superplasticizer. replaceable mineral admixture, the size of coarse aggregate and mixing methods, the effect of each constituent on the characteristics of high flowing concrete could be observed. As a result or partially using stone powder or an intermediate class of aggregate (max. diameter 13mm) . it was fund that the fluidity of concrete significantly increased without material segregation and any change of compressive strengths. It was also proved in this study that proper mixing time and speed are significant factors influence the performence of high flowing concrete.

• Journal of the Korean Recycled Construction Resources Institute
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• v.3 no.1
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• pp.7-14
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• 2015

The aim of this research is suggesting dry processed bottom ash as a new and economical source of lightweight aggregate for mortar and concrete. The dry process of bottom ash is an advance method of water-free and no chloride because only cooled down by double dry conveyer belt systems. Furthermore, because of relatively slow cooling down process helps burning up the remaining carbon in bottom ash. Using this dry process bottom ash, to evaluate the feasibility of using as a lightweight aggregate for mortar and concrete, two-phase of experiments were conducted: 1) improving shape of the bottom ash, and 2) controlling grade of the bottom ash. From the first phase of experiment, additional abrasing process was conducted for round shape bottom ash, hence improved workability and compressive strength was achieved while unit weight was increased comparatively. Based on the better shape of bottom ash, from the second phase, various grades were adopted on cement mortar, standard grade showed the most favorable results on fresh and hardened properties. It is considered that the results of this research contribute on widening sustainable method of using bottom ash based on the dry process and increasing value of bottom ash as a lightweight aggregate for concrete.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.2
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• pp.536-544
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• 2016

Recently, with the increase in the number of high rise and huge scaled buildings, ultra-high strength concrete with 80~100 MPa has been used increasingly to withstand excessive loads. Among the components of concrete, the effects of the kinds and properties of fine aggregates on the performance and economic advantages of ultra-high strength concrete need to be evaluated carefully. Therefore, this study examined the effects of the type of fine aggregates and mixing methods on the engineering properties of ultra-high strength concrete by varying the fine aggregates including limestone fine aggregate (LFA), electrical arc slag fine aggregate (EFA), washed sea sand (SFA), and granite fine aggregate (GFA) and their mixtures. Ultra-high strength concrete was fabricated with a 20 % water to binder ratio (W/B) and incorporated with 70 % of Ordinary Portland cement: 20 % of fly ash:10 % silica fume. The test results indicate that for a given superplasticizer dose, the use of LFA resulted in increases in slump flow and L-flow compared to the mixtures using other aggregates due to the improved particle shape and grading of LFA. In addition, the use of LFA and EFA led to enhanced compressive strength and a decrease in autogenous shrinkage due to the improved elastic properties of LFA and the presence of free-CaO in EFA, which resulted in the formation of C-S-H.

• Magazine of the Korea Concrete Institute
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• v.11 no.2
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• pp.139-145
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• 1999

The objective of this study is to provide the information on the small-scale model mix proportion when the behavior of prototype concrete pavement is studied through small-scale model experiments. However it is difficult to obtain a model material to simulate the prototype concrete by scaling the individual components according to the laws of similitude. In this paper, the stress-strain behavior in uniaxial compression is used as a means to correlate material similitude between the prototype and the model concrete. Based on the results of experiments, we compared the stress-strain curves of prototype and model concrete mixes using a nondimensional basis. In order to simulate the stress-stain curves of prototype concrete, it is important that various mix proportions of model concrete selected properly which are varied from aggregate grading, cement-aggregate and sand-aggregate ratio.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.6 no.1
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• pp.69-78
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• 1986

The properties of ready mixed concrete are affected largely by quality of cement, grading and adhesive surface area water content of aggregate. The amount of variation must be found as soon as possible to minimize the variation of concrete properties. In this paper, a computer program is presented for fast and accurate calculation and modification of mix proportion according to property variation of concrete materials. The program calculates specified mix proportion, job mix proportion and batch weight of ready mixed concrete.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.20 no.4
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• pp.185-191
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• 2010

To effectively utilize resources of reject ash and dredged soil, globular shape-formed artificial lightweight aggregate were manufactured in 8~10 mm size. Starting materials were changed various grading and composition, sintered at $1050{\sim}1250^{\circ}C$. The specific gravity, water absorptance of artificial lightweight aggregates were measured on the basis of the KS. In this study could make a prediction about application of bloating mechanism by ferrous materials and alkali/alkali-earth oxide at high temperature.

• Journal of the Korea Institute of Building Construction
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• v.12 no.5
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• pp.468-477
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• 2012

This study aimed to mix and test mortar incorporating activated Hwangtoh to improve the Hwangtoh brick bond strength of brick structures. To do this, the bond strength correlation of mortar was analyzed by means of materials and experiment factors and levels, and the optimum conditions were suggested after analyzing the physical properties of brick and the mix ratio of mortar and additive. Furthermore, the compressive strength and bond strength were found to be in inverse proportion, and in terms of the materials and mixing level, W/C ratio, substitution ratio of activated Hwangtoh, and fine aggregate grading were shown to have a considerable influence on the strength. In conclusion, the optimum mixing conditions to improve the bond strength are found to set W/C ratio at 65% and replacmenet ratio of activated Hwangtoh at 10%.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2017.11a
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• pp.43-44
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• 2017

In this study, mortar strength was measured by grinding oyster shell and changing the particle size distribution. For the experiment, the oyster shells were processed to a fine aggregate size of 10mm or less. In this experiment, seven particle size distribution conditions were selected and tested. Because oyster shells are different in density from sand, their volume ratios were calculated and converted to mass ratios of 1: 3. The strength test was carried out one day after the steam curing.

• Korean Journal of Agricultural Science
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• v.23 no.1
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• pp.120-130
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• 1996

Concrete is the most commonly used structural materials, but in concrete construction, its self-weight represents a very large proportion of the total load on the structure, and there are clearly considerable advantages in reducing the density of concrete. This study was carried out to investigate the stress-strain properties of no-fines synthetic lightweight concrete with synthetic lightweight coarse aggregates. The used synthetic lightweight coarse aggregate were two types, one was expanded clay with grading 3~8mm, the other is pumice stone with grading 4.75~10mm. The results of this study were summarized as follows ; The static modulus of elasticity of the synthetic lightweight concrete was $1.8{\times}10^5kg/cm^2$ at type CE using the expanded clay and $1.6{\times}10^5kg/cm^2$ at type CL using the pumice stone. The dynamic modulus of elasticity was $1.9{\times}10^5kg/cm^2$(CE) and $2.0{\times}10^5kg/cm^2$(CL). The dynamic modulus of elasticity was 10~30% larger than that of the static modulus of elasticity. The load-time curves of synthetic lightweight concrete were shown approximately similar to each other type except for added foaming agent. The stress-strain curves in uniaxial compressive of synthetic lightweight concrete were similar to each other.

• Journal of the Korea Concrete Institute
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• v.20 no.3
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• pp.405-412
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• 2008

Six alkali-activated (AA) concrete mixes were tested to explore the significance and limitations of developing an environmental friendly concrete. Ground granulated blast-furnace slag and powder typed sodium silicate were selected as source material and an alkaline activator, respectively. The main parameter investigated was the replacement level of lightweight fine aggregate to the natural sand. Workability and mechanical properties of lightweight AA concrete were measured: the variation of slump with time, the rate of compressive strength development, the splitting tensile strength, the moduli of rupture and elasticity, the stress-strain relationship, the bond resistance and shrinkage strain. Test results showed that the compressive strength of lightweight AA concrete sharply decreased when the replacement level of lightweight fine aggregate exceeded 30%. In particular, the increase in the discontinuous grading of lightweight aggregate resulted in the deterioration of the mechanical properties of concrete tested. The measured properties of lightweight AA concrete were also compared, wherever possible, with the results obtained from the design equations specified in ACI 318-05 or EC 2, depending on the relevance, and the results predicted from the empirical equations proposed by Slate et al. for lightweight ordinary Portland cement concrete. The stress-strain curves of different concrete were compared with predictions obtained from the mathematical model proposed by Tasnimi. The measured mechanical properties of lightweight AA concrete generally showed little agreement with the predictions obtained from these equations.