• Proceedings of the Korean Institute of Building Construction Conference
• /
• 2017.05a
• /
• pp.210-211
• /
• 2017

According to KS F 2560, water-reducing agents used when mixing concrete are to undergo quality evaluation testing slump, air contents, setting time, etc., when delivered from the admixture factory to the ready mixed concrete site. Yet in actual acceptance testing this could be substituted by the score report of the admixture company, in which a possibility of low reliability lies. Therefore this study sought to analyze whether by artificially changing the solid content rate of lignin- and naphthalene-based water-reducing agents and using a liquid densimeter evaluate the quality of the admixture. The results showed that the Type B liquid densimeter was most appropriate and 50cc the most appropriate capacity for the mass cylinder. Also, judging from the changes in density and pH according to the changes in solid content rate, it concludes that a rapid appraisal of the quality of lignin- and naphthalene-based water-reducing agents would be possible using a Type B liquid densimeter.

• Proceedings of the Korean Institute of Building Construction Conference
• /
• 2005.11a
• /
• pp.71-74
• /
• 2005

The viscosity of high-flowability paste is very high compared to normal concrete for the low water-binder ratio(W/B). Therefore, high-flowability concrete is positively necessary to high-range water reducing agent. High-Flowability paste can make much higher fluidity with no occurrence of segregation, by its higher viscosity and lower yield value than normal concrete. The flowability of high-flowability paste must be evaluated not only by convention consistency test such as slump test but also by the base of the rheological properties of the fresh concrete. The purpose of this study is to analyze the fluidity of high-flowability paste according to the addition ratio of the Melamine Sulphonate high-range water reducing agent.; high-flowability paste is considered as Bingham plastic fluid with the rheology parameters of the plaste viscosity and yield value.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2005.05b
• /
• pp.33-36
• /
• 2005

Recently, the use of volcanic-ash as a part of cement content in concrete is very common. But, it has been indicated that the compressive strength of concrete using large amount of volcanic-ash as a part of cement content in early age is low and carbonation velocity is fast. To solve those problems, High Volume Volcanic-Ash Concrete which contained large amount of volcanic-ash as a part of fine aggregate has been proposed. This is an experimential study to compare and analyze the properties of High Volumn Volcanic-Ash Concrete according to the replacement method and ratio of volcanic-ash. For this purpose, the mix proportion of concrete according to the replacement method(PL, C10, C150, A10, A100, A150) And then slump, setting time, bleeding, compressive strength, tensile strength and carbornation test were performed. According to test results, it was found that the compressive strength of the concrete using the volcanic-ash as a part of fine aggregate(A) was higher than that of the concrete using the volcanic-ash as a part of cement content(C). And, the compressive strength of the A concrete increased in early age as well as in long tern age as the volcanic-ash content increased.

• Steel and Composite Structures
• /
• v.39 no.3
• /
• pp.307-318
• /
• 2021

Utilizing fibers is an effective way to avoid the brittle behavior of the conventional concrete and can enhance its ductility. In particular, propylene fibers can improve concrete properties, including energy absorption, physical and mechanical properties, controlling shrinkage cracks. The increase of fiber density leads to an increase of the overlapping surface of the fiber of concrete and, in turn, a decrease of cracks developed in the concrete. However, the workability of fiber reinforced concrete tends to be lower than the conventional concrete owing mainly to the hairline thickness and excessive concentration of fibers. The low slump of concrete impedes the construction of reinforced concrete members. In this research, we study if the utilization of magnetic water can alleviate the workability issue of young fiber reinforced concrete. To this end, the compressive and flexural strength of four types of concrete (conventional concrete, fiber reinforced concrete, magnetic concrete, magnetic fiber-reinforced concrete) is studied and compared at three different ages of 7, 14, and 28 days. In order to study the influence of the fiber density and length, a study on specimens with three different fiber density (1, 2, 5 kg of fiber in each cubic meter of concrete) and fiber length (6, 12, 18 mm) is undertaken. The result shows the magnetic fiber concrete can result in an increase of the flexural and compressive strength of concrete at higher ages.

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.4 no.2
• /
• pp.187-194
• /
• 2016

In this research, the influence of low-quality aggregate on engineering properties of concrete was experimentally evaluated. From a series of experiment, the results can be summarized as follow: first, the low-quality aggregate in concrete mixture caused up to 83% of decreased slump. For air content, low-quality aggregate increased air content of concrete mixture. Especially, when sea sand was used, because of the narrow gradation with small size, the air content was significantly increased. The compressive strength of concrete mixtures with low-quality aggregates were decreased up to 29% while some cases showed slightly increased compressive strength at early age. Additionally, the concrete mixture mixed with the exploded debris as a coarse aggregate showed approximately 5 to 20% of decreased compressive strength comparing with high-quality of manufacturing rock. In summary, because of the decreased workability of concrete mixture mixed with low-quality aggregates such as exploded debris, clay, and sea sand, it is concerned that worse quality of the ready mixed concrete, produced with the extra water to compensate the decreased workability.

• Journal of the Korea Institute of Building Construction
• /
• v.16 no.6
• /
• pp.505-512
• /
• 2016

Even though high performance concrete was developed according to the trend of bigger and higher of reinforced concrete building, the rheological evaluations such as viscosity, yield stress are not enough to use as input data to accomplish the numerical analysis for the construction design. So there are many problems in the harden concrete such as poor compaction, rock pocket and crack, etc. in the field. In this study, consistency curves were measured by the viscometer as hydration reaction time passed. At the same time the slump flow test and Vicat setting test were carried out for comparing with the results of rheological properties. The fluidity of the W/B 30% decreased as the increase of replacement ratio of blast furnace slag. But in case of W/B 40%, the replacement ration did not significantly influenced to the slump flow value with the passage of hydration time. By the replacement of blast furnace slag to cement, initial setting was delayed and the time gap between initial and final setting became shorten. Through the regression analysis using Bingham model, there are a sudden changes of viscosity and yield stress around initial setting in case of low W/B 30%. The increase of workability by the change of free water in cement paste was offset by the coating effect of impermeable layer in case of W/B 40%.

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.7 no.3
• /
• pp.194-201
• /
• 2019

This study analyzed the properties of concrete depending on the coal gasification slag(CGS) contents in order to examine the applicability of CGS as the fine aggregate for concrete. Experimental results, trended that the slump and slump flow increased with increasing CGS contents, and air contents has decreased. Evaluation index for segregation of normal strength concrete(EISN) is showed was good from CGS 25% when using crushed sand A(CSa) and CGS 50% when using mixed sand(MS). The compressive strength decreased with increasing CGS contents when CSa was used. However, when MS was used, the maximum value was CGS 50% due to parabolic tendency. Depending on fine aggregates type, compared with compressive strength of CSa was about 8% higher than that of MS, and depending on the use or unuse of CGS, more advantageous at higher strength than low strength. As a result of relative performance study on the quality of concrete according to the CGS contents, it is considered that CGS can be positively contributed to enhancement of workability and strength development when mixed with fine aggregate around 25~50%.

• Journal of the Korea Concrete Institute
• /
• v.28 no.4
• /
• pp.427-434
• /
• 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
• /
• v.27 no.4
• /
• pp.427-434
• /
• 2015

The objective of this study is to establish an rational mixture-proportioning procedure for low-$CO_2$ concrete using supplementary cementitious materials (SCMs) achieving the targeted $CO_2$ reduction ratio as well as the conventional requirements such as initial slump, air content, and 28-day compressive strength of concrete. To evaluate the effect of SCM level on the $CO_2$ emission and compressive strength of concrete, a total of 12537 data sets were compiled from the available literature and ready-mixed concrete plants. The amount of $CO_2$ emission of concrete was assessed under the system boundary from cradle to concrete production stage at a ready-mixed concrete plant. Based on regression analysis using the established database, simple equations were proposed to determine the mixture proportions of concrete such as the type and level of SCMs, water-to-binder ratio, and fine aggregate-to-total aggregate ratio. Furthermore, the $CO_2$ emissions for a given concrete mixture can be straightforwardly calculated using the proposed equations. Overall, the developed mixture-proportioning procedure is practically useful for determining the initial mixture proportions of low-$CO_2$ concrete in the ready-mixed concrete field.

• Journal of the Korea Institute of Building Construction
• /
• v.10 no.4
• /
• pp.11-20
• /
• 2010

This study carried out a Mock-up test to apply Low-heat Cement (CF) that is adjusted to a fineness of $3,000\;{\pm}\;200\;cm^2/g$ by substituting Coarse particle Cement (CC) and fly ash with ordinary Portland Cement (OPC), then applied it on-site. The result of the test is as follows. The Mock-up test showed that the amount of admixture in CF increased SP agent and AE agent slightly more compared to OPC, while temperature history showed that the highest temperature of CF was around $6{\sim}10^{\circ}C$ lower than that of OPC. Compressive strength in CF was low compared to that of OPC, but the strength width became narrow at the age of 28 days, which is not considered to be significant. In on-site application, slump, air content and chloride content all satisfied the target values, while the temperature history showed that the highest temperature in the center by each cast was about $34^{\circ}C$ in the first cast, $42^{\circ}C$ in the second cast, and $39^{\circ}C$ in the third cast. Compressive strength of specimen for strut management showed low value compared to standard curing, but its strength was reduced at the age of 28 days.