• Journal of the Korea Concrete Institute
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• v.28 no.4
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• pp.427-434
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• 2016

The purpose of this study is to propose a mixture proportioning approach based on the replacement level of natural sand for reducing $CO_2$ emissions from artificial lightweight aggregate concrete(LWAC) production. To assess the effect of natural sand on the reduction of $CO_2$ emissions and compressive strength of LWAC, a total of 379 specimens compiled from different sources were analyzed. Based on the non-linear regression analysis using the database and the previous mixture proportioning method proposed by Yang et al., simple equations were derived to determine the concrete mixture proportioning and the replacement level of natural sand for achieving the targeted performances(compressive strength, initial slump, air content, and $CO_2$ reduction ratio) of concrete. Furthermore, the proposed equations are practically applicable to straightforward determination of the $CO_2$ emissions from the provided mixture proportions of LWAC.

• Journal of the Korea Concrete Institute
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• v.25 no.1
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• pp.3-9
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• 2013

In ultra high strength concrete, when electric arc furnace oxidizing slag is substituted for sea sand as fine aggregate, compressive strength was improved about 15 MPa. To figure out the cause of the improvement in compressive strength, this study considered the dissolution characteristics of Ca component in fine aggregate and examined the microstructure, porosity, microhardness, and Ca/Si mole ratio on the interface of fine aggregate and paste. And to examine the mechanism of strength improvement resulted from the shape of fine aggregate, this study measured the surface roughness of fine aggregate with AFM. According to the result of this experiment, the mechanisms of strength improvement in ultra high strength concrete resulted from the use of electric arc furnace oxidizing slag as fine aggregate can be divided into chemical and physical mechanisms. In the chemical mechanism, the soluble Ca component contained in electric arc furnace oxidizing slag is dissolved and forms a hydrate between fine aggregate and paste to improve the interlocking strength of fine aggregate-paste. Also, it makes the microstructure around the fine aggregate. And in the physical mechanism, electric arc furnace oxidizing slag has a twice greater surface roughness than sea sand, so the interlocking strength between fine aggregate and paste increases, which contributes to the development of compressive strength.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.05a
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• pp.635-640
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• 2001

Recently, it has been processed to study about recycled aggregate but a study about using of recycled powder is producted when manufacturing recycled aggregate has not been acted. So in this study on the fundamental properties and application as cementious admixture by heating temperature for mortar properties of recycled powder and sand is obtained like following results. It is judged that application of recycled powder of heat treatment on $600^{\circ}C$ and cement replacement ratio below 10% is available.

• Computers and Concrete
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• v.19 no.6
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• pp.617-623
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• 2017

This work is conducted with the aim of using waste material to reserve the natural resources. The objective is accomplished by conducting experimentation and verify by modeling based on fuzzy logic. In experimentation, concrete is casted by using natural/river sand as fine aggregate and termed as control specimen. Natural sand is conserved by replacing it with used foundry sand (UFS) by an amount of 10, 20 and 30% by weight. Fresh and hardened properties of concrete are investigated at different ages. It is observed that compressive strength and modulus of elasticity reduced with the increase in amount of UFS. Furthermore, concrete compressive strength is predicted by using fuzzy logic model and verified at different replacement ratio and age with experimental observations.

• Journal of the Korean Society of Hazard Mitigation
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• v.10 no.4
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• pp.47-54
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• 2010

This study is progressed function ratio, it's trued taste by an experiment to present data for human work light weight aggregate development that use clink ash progressed liquid limit, small success limit, wear loss in quantity, sand equivalent, sieve cutting examination. 80:20's match of function rain examination is 1.4, and that use rubble aggregate as recyeled-panit lightweight aggregate's capacity ratio increases by 1.0 increase of function rain many. Also, examination multiplied delicate flavor gradually according to increase of the mixing rate, and absorption coefficient increased. This is judged by phenomenon that appear by special quality upper recycled-panit of polystyrene bid and porosity's increase between lightweight aggregate. It is case that use aggregate of wear loss in quantity is 13.5 in sand equivalent and a wear loss in quantity experiment and although case that mix 20% increases by 14.4, this phenomenon by weak tissue of lightweight aggergate be judged. When it's as a these experiment, the statue prevention floor of a street improvement specifications is prescribing so that satisfy by sand equivalent 20, CBR 10. This is showed result that this satisfies in quality standard all in match experiment ago that see.

• Advances in concrete construction
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• v.10 no.5
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• pp.381-391
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• 2020

This study aimed to develop reference materials (RMs) for mortar that can simulate the initial flow characteristics with constant quality over a long period. Through the previous research on the development of RMs for cement paste, the combination of limestone, glycerol, and water was used as the basic matrix for developing RMs for mortar in this study. In addition, glass beads of three particle sizes (0.5, 1.0, and 2.0 mm) and ISO standard sand were selected as tentative candidates to derive fine aggregate substitutes. The mixture of glass beads could simulate the initial flow characteristics of mortar, but under the same mixing ratio, replicates showed an unstable tendency to indicate inconsistent values due to the generation of electrostatic properties between materials and equipment. On the other hand, the mixture using ISO standard Sand not only simulates the constant flow characteristics for a long period of time, but also shows stable results with little error in replicates. Therefore, limestone, glycerol, ISO standard sand, and water were finally determined as components that met the required properties of RMs for mortar. The effect of each component on the flow characteristics of RMs was analyzed. It was found that glycerol increased the cohesion between the particles of standard sand, resulting in a constant increase both in the plastic viscosity and yield stress. Both limestone and standard sand had a dominant effect on the yield stress. The relationships between various mortar mixing ratios and the corresponding mixing ratios of RMs were established. In addition, the results of the verification experiment showed that the rheological properties of the RMs obtained through the relationships correlated with various water/cement ratios and the fine aggregate volume fractions of mortar obtained with same manner. In other words, the RMs for mortar developed in this study can be used as standard samples because they can simulate the initial flow characteristics of mortar of various mixing ratios for a long period without any chemical changes.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.04a
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• pp.647-652
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• 1999

The purpose of this study is to find the bond properties of deformed bars in hign-strength concrete by experimental and analytical method. In this study the following variables were adopted, i.e. (1) the compressive strength of concrete : 270, 400 and 600kg/$\textrm{cm}^2$ (2) the corrosion the bars : corroded and normal bars (3) the mixing ratio of natural and smashed fine aggregate : 7 : 3 and 5 : 5 (natural sand : smashed sand) For analytical method, the finite element analysis is performed. And the Pull-out test is performed as the experimental method.

• Proceedings of the Korea Concrete Institute Conference
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• 1996.04a
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• pp.202-207
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• 1996

Recently, the mortar crack on floor is very serious in construction field, e.g. the crack due to plastic shrinkage and the crack due to drying shrinkage. To prevent this kind of crack, optimum mix propertions not only satisfying the required workability but also minimizing the unit water content were selected. And the expansion admixtures were used to compensate the shrinkage of mortar. This study shows that water/cement ratio used in construction field is about 64%. Even if we reduce water/cement ratio of mortar by the appropriate use the fine aggregate with high fineness modulus and superplastizer, floor mortar can have the required workability. The equations between mortar flow and water/cement ratio, sand/cement ratio, fineness modulus of fine aggregate were proposed in this study. And this equation may provide available mix proportions of floor mortar.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.11a
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• pp.322-325
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• 2003

Recently, as quality river aggregates like sands and gravels become scarce, use of crushed stones and sands, seashore sands, and seashore gravels is increasing abruptly. And, aggregates recycled from slags and waste concretes are used. However, since the converter slag easily expands and breaks due to free lime, differently from the blast-furnace slag, it is not suitable for use as concrete aggregates. Since the atomized steel slag aggregate has slippery surface and spherical shape, the mortar flowing characteristics improved as the atomized steel slag content increases, without regard to the aggregates coarseness and water/cement ratio. The flow characteristics loss rate of the mortar manufactured from steel slag aggregates was similar to that of the mortar manufactured from washed sand only. The compact strength of the mortar manufactured from coarse PS Ball were larger than that manufactured from washing sand only.

• Advances in concrete construction
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• v.5 no.3
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• pp.183-199
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• 2017

This paper reports an experimental study into the rheological behaviour of Smart Dynamic Concrete (SDC). The investigation is aimed at quantifying the effect of the varying amount of mineral admixtures on the rheology, setting time and compressive strength of SDC containing natural sand and crushed sand. Ordinary Portland cement (OPC) in conjunction with the mineral admixtures was used in different replacement ratio keeping the mix paste volume (35%) and water binder ratio (0.4) constant at controlled laboratory atmospheric temperature ($33^{\circ}C$ to $35^{\circ}C$). The results show that the properties and amount of fine aggregate have a strong influence on the admixture demand for similar initial workability, i.e., flow. The large amounts of fines and lower value of fineness modulus (FM) of natural sand primarily increases the yield stress of the SDC. The mineral admixtures at various replacement ratios strongly contribute to the yield stress and plastic viscosity of SDC due to inter particle friction and cohesion.