• Journal of the Korea Institute of Building Construction
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• v.8 no.3
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• pp.111-117
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• 2008

This study provides the setting time prediction method of super retarding concrete incorporating mineral admixtures at the same time including fly ash(FA), blast furnace slag(BS) based on maturity method. The setting time was retarded, as super retarding agent contents increase and curing temperature decreases. In addition, apparent activation energy by Arrhenius function was ranged from $24{\sim}35KJ/mol$ with slightly difference along with mixture proportion. This value is smaller than existing value $30{\sim}50KJ/mol$. It is Indicated that equivalent age using setting time can be a proper method to predict setting time and it also exhibited comparable relativity between prediction value and measurement value. Therefore, this study provided setting time prediction value with super retarding agent contents and mineral admixture combination. Setting time prediction equation provided herein is possibly valid for estimating precise setting time of the super retarding concrete at the job site.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.11a
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• pp.643-646
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• 2005

This paper reports the influence of super retarding agent(SRA) on the setting time of concrete incorporating mineral admixture including fly ash(FA), expansive additive(EA), silica fume(SF), blast furnace slag(BS) and blast furnace slag along with fly ash(BS+FA). An increase in SRA resulted in retarding the setting time of control concrete, while the use of mineral admixture led to a delay of setting time markedly, compared with that of control concrete under no SRA content. Meanwhile, An increase in SRA in concrete with mineral admixture exhibited comparable setting delay with control concrete. Furthermore, in case of the use of BS and SF, acceleration of setting time was observed with increase of SRA content. It is considered that proper dosage of SRA of concrete with SF and BS to secure similar setting delay with control concrete require rather larger than that of control concrete. Accordingly, For concrete with mineral admixture, in order to decide the proper dosage of SRA, application of correction factors is needed.

• Journal of the Korea Institute of Building Construction
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• v.8 no.5
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• pp.119-125
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• 2008

In this paper, the estimation of super retarding concrete incorporating mineral admixtures at the same time including fly ash(FA), blast furnace slag(BS) are studied based on maturity method. The setting time was retarded, as super retarding agent contents increase and curing temperature decreases. In addition, apparent activation energy by Arrhenius function was ranged from $24\sim35$ KJ/mol with slightly difference along with mixture proportion. This value is smaller than existing value $30\sim50$ KJ/mol. Based on strength development estimation. it exhibited comparable relativity between prediction value and measurement value. Therefore, this study provided effective strength development prediction value with super retarding agent contents and mineral admixture combination. Strength development prediction equation provided herein is possibly valid for estimating accurate strength development of the super retarding concrete at the job site.

• Computers and Concrete
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• v.32 no.2
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• pp.185-206
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• 2023

This article aimed to explore the optimization of mineral admixtures and retarding admixture for high-performance concrete. In essence, fresh concrete can be regarded as a mixture in which both coarse and fine aggregates are suspended in a cement-based matrix paste. Based on this view, the test procedure was divided into three progressive stages of binder paste, mortar, and concrete to explore their rheological behavior and mechanical properties respectively. At each stage, there were four experimental control factors, and each factor had three levels. In order to reduce the workload of the experiment, the Taguchi method with an L9(3⁴) orthogonal array and four controllable three-level factors was adopted. The test results show that the use of the Taguchi method effectively optimized the composition of high-performance concrete. The slump of the prepared concrete was above 18 cm, and the slump flow was above 50 cm, indicating that it had good workability. On the other hand, the 28-day compressive strength of the hardened concretes was between 31.3-59.8 MPa. Furthermore, the analysis of variance (ANOVA) results showed that the most significant factor affecting the initial setting time of the fresh concretes was the retarder dosage, and its contribution percentage was 62.66%. On the other hand, the ANOVA results show that the most significant factor affecting the 28-day compressive strength of the hardened concretes was the water to binder ratio, and its contribution percentage was 79.05%.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.505-508
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• 2004

This paper investigated the setting and compressive strength of concrete with the combination of mineral and chemical admixture. According to test results, plain concrete with high early strength development type AE water reducing agent(HEAEWRA) and $10\%$ of CKD respectively had earlier setting time than concrete with AE water reducing agent by $0.5\~1.5$ hours. Setting time of concrete with retarding type AE water reducing agent(RAEWRA) and FA $30\%$, BS $60\%$ respectively retarded by as much as $4\~7.5$ hours compared with plain concrete. Plain concrete with HEA WRA, $10\%$ of CKD and RAEWRA had higher strength than that of AE water reducing agent by as much as 5MPa at 28days. From the result of the paper, it is found that the combination of mineral admixture and setting accelerating or retarding agent can reduce the hydration heat cracks by setting time difference and hydration heat reduction effects.

• Magazine of the Korea Concrete Institute
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• v.18 no.2 s.91
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• pp.46-51
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• 2006

• Proceedings of the Korea Concrete Institute Conference
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• 1998.10a
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• pp.297-300
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• 1998

Usually the flowing concrete manufactured upon normal-mixed base concrete would segregate due to the less of fine particle content. In the previous studies, a new type admixture(liquid segregation reducing type superplasticizer) has been developed to prevent such segregation without modification of base concrete mixture. In this study, the tests are performed in laboratory to evaluate the admixture by analyzing the properties of flowing concrete with different water to cement ratios, so that it could be used in the fields. According to the results, this kind of superplasticizer could improve the fluidity of concrete without causing segregation. However, it seems to be more desirable of the superplasticizer could be adjusted, before it is put into the practical use, not to cause some other problems such as rapid rate of slump and air loss and retarding of setting time.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.2
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• pp.103-113
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• 2017

In the current study, retarding type and standard type admixture design of concrete have been proposed to control the generation of hydration heat for foundation members that use high strengths concrete. Finite element analysis also has been conducted to understand the rational placing heights of concrete. In addition, real-size structures have experimented and their results were compared to the analytical results to evaluate the reducing effect of thermal stress. For a large $6.5m{\times}6.5m{\times}3.5m$ member with retarding and standard type horizontal partition placement of concrete showed the manageable possibility of temperature difference within 25-degree Celcius between the middle and surface portion while the maximum temperature was 77-degree Celcius. Also, temperature cracking index from the finite element analysis appeared to be 1.49 that predicts no formation of cracking due to the effects of temperature. Finally, it appeared that horizontal partition placement of retarding and standard type concrete has the significant effect of reducing the thermal stress that generated by the hydration heat in the high strengths mass concrete.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.4
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• pp.48-56
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• 2022

Controlling the setting time of cementitious materials is one of the most important factors in securing early-age performance of concrete structures. Recently, the use of retarding admixtures, which enable the inhibition of some hydration products to control the securing time due to average temperature rise is suggested. Although various non-destructive evaluation methods have been proposed to evaluate cement hydration and hardening of cement-based materials to overcome the limitations of Vicat needle test, experimental research is still required to use the non-destructive evaluation method with added retarding admixtures. In this study, measurements of electrical resistivity and ultrasonic wave velocity in early-aged cement pastes were performed according to the addition of retarding admixture(tartaric acid). The setting time of the cement pastes was evaluated by obtained rising time of the both non-destructive measurements. As a result, the possibility of evaluating the setting delay in cement pastes was confirmed through comparative analysis with the initial and final setting times by Vicat test. In addition, X-ray diffraction results at the rising time of electrical resistivity showed a key hydration product affecting the setting delay.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2005.05a
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• pp.9-12
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• 2005

This paper investigated the temperature history of mass concrete mock up structure considering different heat generation by varying with mixture proportion. Setting time difference between high early strength mixture (E-P) and retarding mixture (R-F30) was 14.5hours. Incorporation of $30\%$ of fly ash contributed to $10^{\circ}C$ of hydration heat reduction. In generally used C and D combination, bottom concrete shows earlier hydration, while E-J combination showed reverse tendency and thus, this method can reduce the crack occurrence. Therefore, heat generation difference method has beneficial effect on reducing crack induced by hydration heat resulting from heat generation difference between surface and center section.