• Steel and Composite Structures
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• 제46권5호
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• pp.689-707
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• 2023

Geopolymer concrete production is interesting as it is an alternative to portland cement concrete. However, workability, setting time and strength expectations limit the sustainable application of geopolymer concrete in practice. This study aims to improve the production of geopolymer concrete to mitigate these drawbacks. The improvement in the workability and setting time were achieved with the additional use of NaOH solution whereas an increase in the strength was gained with the addition of recycled steel fibers from waste tires. In addition, the use of 25% basalt powder instead of fly ash and the addition of recycled steel fibers from waste tires improved its environmental feature. The samples with steel fiber ratios ranging between 0.5% and 5% and basalt powder of 25%, 50% and 75% were tested under both compressive and flexure forces. The compressive and flexural capacities were significantly enhanced by utilizing recycled steel fibers from waste tires. However, decreases in these capacities were detected as the basalt powder ratio increased. In general, as the waste wire ratio increased, the compressive strength gradually increased. While the compressive strength of the reference sample was 26 MPa, when the wire ratio was 5%, the compressive strength increased up to 53 MPa. With the addition of 75% basalt powder, the compressive strength decreases by 60%, but when the 3% wire ratio is reached, the compressive strength is obtained as in the reference sample. In the sample group to which 25% basalt powder was added, the flexural strength increased by 97% when the waste wire addition rate was 5%. In addition, while the energy absorption capacity was 0.66 kN in the reference sample, it increased to 12.33 kN with the addition of 5% wire. The production phase revealed that basalt powder and waste steel wire had a significant impact on the workability and setting time. Furthermore, SEM analyses were performed.

• 한국건축시공학회지
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• 제3권1호
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• pp.139-146
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• 2003

The special requirements of high-performance concrete(HPC) could be enhanced property over others such as compressive strength, durability, and construction practices. In order to satisfy these requirements a series of laboratory trial mixes and following mock-up test of reinforced concrete wall at field were performed in this study. The objective of this study was to quantitatively evaluate the workability, compressive strength, and the increased heat of hydration caused by the increase of the specific weight of cement according to various variables. Six example series designed about a minimum compressive strength of 500kgf/$\textrm{cm}^2$ at 28 days, and an approximately slump and slump flow of 25cm and 60cm respectively were tested. The selection process of the specific weight of water and the percentage of fly-ash transposition determined to be most suitable for the production of HPC is presented in the following paper.

• International Journal of Concrete Structures and Materials
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• 제8권2호
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• pp.165-172
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• 2014

Recycled coarse aggregate (RCA) made from waste concrete is not a suitable structural material as it has high absorption of cement mortar, which adheres on the aggregate surface and on the tiny cracks thereon. Therefore, when using RCA made from waste concrete, much water must be added with the concrete, and slump loss occurs when transporting. Hence, its workability is significantly worse than that of other materials. In this study, surface of RCA was coated with water-soluble polycarboxylate (PC) dispersant so that its characteristics improved. Each possibility was evaluated: whether its slump loss can be controlled, by measuring its workability based on the elapsed time; and whether it can be used as a structural material, by measuring its strength. Moreover, the carbonation due to cement mortar adhesion was measured through a carbonation test. As a result, RCA coated with PC dispersant was found to be better than crushed coarse aggregate and RCA when the physical properties of the fresh concrete and the mechanical, durability of the hardened concrete were tested.

• 한국건축시공학회지
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• 제14권1호
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• pp.11-20
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• 2014

This research examined the effect of the quality of aggregate on concrete workability and compressive strength through an investigation into regional aggregate used in domestic ready mixed concrete plants. Through the research, it was found that aggregate for ready mixed concrete shows poor quality overall. The main factor of deterioration in the quality of the concrete is the particle size of fine aggregate and fine particle content in coarse aggregate. The quality of aggregate significantly influences concrete's workability, which is defined based on 0.08mm passage related with powder and absorption. In addition, poor aggregate quality leads to increased water content in concrete to secure workability, which is related with a decline in the compressive strength and durability of concrete.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2001년도 봄 학술발표회 논문집
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• pp.507-512
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• 2001

An investigation into using Oyster Shells partially or wholly as aggregate in concrete is reported. The proportion of shells was varied with ratios of 10, 30, 50 and 100% by volume of fine and coarse aggregate. Two water/cement ratios of 0.45, 0.55 were considered and air-entraining superplasticizer was used to improve concrete workability Two strength properties (compressive and flexural) were considered. Strength tests were carried out at the ages of 1, 3, 7, 14 and 28 days. The variations of workability, weight and density of the specimens with different proportions of Oyster Shells were also studied. Results showed that compressive and flexural strengths decreased with increase in proportion of Oyster Shells to aggregate in the reference mixes. The workability of concrete batches decreased with increase in the proportion of Oyster Shells in the mixes. The same trend was observed with density and weight of the specimens

• 한국세라믹학회지
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• 제13권3호
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• pp.37-42
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• 1976

Although the water mixed into the concrete plays the role of hydration and acquiring the necessary workability, the more portion of water acts to obtain the substantial workability rather than to complete the hydration. However, the excess amount of water causes the poor quality of concrete, therefore it is useful to add the minimum amount of water as required as to acquire the proper workability. There have been the considerable numbers of investigations in which the dispersion phenomena of strong eletrolytic high polymer compounds such as lignosulfate and some of surface activation agents were studied to utilize as the dispersion agent of concrete. In the present study, Na-lignate, dispersion properties of which has not been studied yet, were investigated with the purpose of utilizing as a dispersion agent of concrete. The microscopic observations showed a great improvement in the dispersion of cement particles, also the fluidity and compressive strength of concrete were remarkably increased with the addition of Na-lignate: The addition of Na-lignate by 0.02% showed the increase of 1.76 times and 1.27 times of slump value and flow value respectively, and the compressive strength was increased by 1.07 times.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1994년도 가을 학술발표회 논문집
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• pp.161-166
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• 1994

Production of high strength concrete requires a low water-cement ratio and this leads to the high cement content. Mineral admixture like fly ash(FA) is often cheaper than ordinary portland cement(OPC) and this factor in combination with possible improvement in workability and moderation of the heat evolution of the cement-rich mixes tends to encourage its use. The other mineral admixture that its use has been widly advocated is silica fume that increases compressive strength due to its pozzolanic reaction. The objective of this study is to assess the contribution of mineral admixtures(FA, SF) to the workability and the strength of concrete with low water-binder ratios. In this experimental study that investigates and analyzes the properties of fresh concrete, it is presented that using admixtures like flysh and silica fume as binding material increases properties of high strength flowing concrete having very low water cementitious ratios of 0.25 and 0.30.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1995년도 추계학술대회 논문집
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• pp.165-168
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• 1995

The quality of products is depend on the performance of machine and machining conditions. In this study the runout of spindel is selected as a parameter through which we could appreciate the workability of machine and the quality of products. Throigh the runout of high speed machining center on freeload machining, the revolution accuracy and the characteristics in connection with spindle speed are evaluated. It was experimented flat and ball end milling for estimating machine accuracy and workability by measuring spindel runout. In end, This paper shows the effects of runout on surface roughness through analysis of runout and roughness profiles.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 춘계 학술발표회 논문집(II)
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• pp.393-396
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• 2006

This study present the experimental research investigating the influence of material factors such as a type or amount of superplasticizer, velocity agent, mineral admixture and steel fiber on the construction performance of fiber reinforced cementitious composites. As for the test results, it was found that the workability of fiber reinforced cementitious composites can be improved when the material factors were matched properly in amount and composition. Furthermore, it was shown that the smaller value of the aspect ratio of fiber improved the workability of fiber reinforced cementitious composites. And the fiber reinforced cementitious composites with better workability showed the enhanced compressive strength and flexural strength.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1996년도 봄 학술발표회 논문집
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• pp.12-17
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• 1996

It is true that aggregate strength is usually not a factor in normal concrete strength because, the aggregate particle is several times stronger than the matrix and the transition zone in concrete. In other words, with most natural aggregates the strength of the aggregate is hardly utilized because the failure is determined by the other two phases. But aggregate characteristics that are significant to concrete technology include porosity, grading or size distribution, moisture absorption, shape and surface texture, crushing strength, elastic modulus, and the type of deleterious substances present. Therefore, in the area of high strength concrete, concrete is much more influenced by properties of aggregate. This experiment is performed to investigate how kinds of aggregare influence on the workability of high strength concrete. In this experiment, four types of aggregate is used, that is crushed river aggregate, crushed stone, recycled aggregate of low strength and recycled aggregate of high strength. In this study, we scrutinize a fundmental study on the workability of high strength concrete according to kinds of aggregate.