• Journal of the Korea Concrete Institute
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• v.29 no.4
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• pp.407-413
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• 2017

The fundamental property of magnesia phosphate cement (MPC) for concrete repair material was investigated in this research. For mechanical properties, setting time, compressive strength and tensile/flexural bond strength were measured, and hydration products were detected by X-ray diffraction. The specimens were manufactured with dead burnt magnesia and potassium dihydrogen phosphate was admixed to activate the hydration of magnesia and a borax was used as a retarder. To observe the pore structure and ionic permeability of MPC mortar, mercury intrusion porosimetry was performed together with rapid chloride penetration test (RCPT). As a result, time to set of Fresh MPC mortar was in range of 16 to 21 min depend on the M/P ratio. Borax helped delaying setting time of MPC to 68 min. The compressive strength of MPC with M/P of 4 was sharply developed to 30 MPa within 12 hours. The compressive strength of MPC mortar was in range of 11.0 to 30.0 MPa depend on the M/P ratio at 12 hours of curing. Both tensile and flexural bond strength of MPC to old substrate (i.e. MPC; New substrate to OPC; Old substrate) were even higher than ordinary Portland cement mortar (i.e. [OPC; New substrate] to [OPC; Old substrate]) does, accounting 19 and 17 MPa, respectively. The total pore volume of MPC mortar was lower than that of OPC mortar. MPC mortar had the entrained air void rather than capillary pore. The RCPT showed that total charge passed of OPC mortar had more than that of MPC mortar, which can be explained by the pore volume and pore distribution.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2009.05c
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• pp.7-12
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• 2009

• Journal of the Korea Concrete Institute
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• v.18 no.6 s.96
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• pp.759-767
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• 2006

This paper presents a method to estimate the setting time of concrete using super retarding agent(SRA) and fly ash(FA) under various curing temperature conditions by applying maturity based on equivalent age. To estimate setting time, the equivalent age using apparent activation energy($E_a$) was applied. Increasing SRA content and decreasing curing temperature leads to retard initial and final set markedly. $E_a$ at the initial set and final set obtained by Arrhenius function showed differences in response to mixture type. It is estimated to be from $24{\sim}35KJ/mol$ in all mixtures, which is smaller than that of conventional mixture ranging from $30{\sim}50KJ/mol$. Based on the application of $E_a$ to Freisleben-Hansen and Pederson's equivalent age function, equivalent age is nearly constant, regardless of curing temperature and SRA contents. This implies that the concept of maturity is applicable in estimating the setting time of concrete containing SRA. A high correlation between estimated setting time and measured setting time is observed. Multi-regression model to determine appropriate dosage of SRA reflecting FA contents and equivalent age was provided. Thus, the setting time estimation method studied herein can be applicable to the concrete containing SRA and FA in construction fields.

• Journal of the Korean Recycled Construction Resources Institute
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• v.7 no.3
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• pp.77-84
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• 2012

It is known that some components of wood obstruct the hydration of cement when wood is mixed with cement. In order to examine the effect of pretreatment of wood chips in hot water, this study conducted the experiments for the setting and compressive strength of mortar by sieving pine wood chips with a 2.4mm sieve, dipping them in waters of different temperatures, and then using them as a part of the fine aggregate. For the experiments, water-cement ratio of the mortar was 0.50 and the amount of the fine aggregate substituted by wood chips was set at 0%, 2%, 4%, 6%, 8%, and 10% of the mass of the fine aggregate. As a result of the test, it was found out that when wood chips were used to substitute fine aggregate for the production of mortar, more usage of wood chips postponed setting more, and the treatment of wood chips with water improved the problem of the delay in setting time. Especially, the final setting time of the mortar which used 2~6% of wood chips treated in $100^{\circ}C$ water for 30 minutes was almost the same as the final setting time of the mortar which used no wood chips. Also, the compressive strength of the mortar which used the wood chips treated with water was compared to that of the mortar which used the wood chips not treated with water. The result showed that the strength improved for age of 7 days and 28 days, while there was little change in strength for age of 3 days.

• Journal of the Korea Concrete Institute
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• v.27 no.3
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• pp.265-272
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• 2015

In this study, a method to reduce temperature rise due to hydration in mass concrete is investigated. It is to use retarder (glucose) for reducing heat of hydration and to use calcium silicate hydrate (C-S-H) for compensating the retardation effect due to its role as a nucleation seed. For this purpose, the temperature rise of cement paste due to hydration was measured and the effect of using both C-S-H and glucose on setting and 28-day compressive strength of mortar specimens was investigated. According to the experimental results, using C-S-H and glucose caused the reduction in the maximum temperature but accelerated the time to reach the maximum temperature compared to that of retarded cement paste using glucose. In addition, using C-S-H and glucose did not show significant effect on 28-day compressive strength of mortar specimens, indicating that the method shown in this study can be a successful alternative to control maximum temperature rise in mass concrete.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2009.05b
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• pp.73-76
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• 2009

Autogenous shrinkage of high-strength mass concrete is affected high temperature history. So to evaluate autogenous shrinkage of high-strength mass concrete accurately, thermal expansion in it should be removed. In this study, compensated autogenous shrinkage was calculated after gathering thermal expansion coefficient at early age experimentally. As a result of the study. Autogenous shrinkage of mass specimen (300 ${\times}$ 300 ${\times}$ 300mm) was remarkably higher than it of standard specimen (100 ${\times}$ 100 ${\times}$ 400mm). So it was found that compensation on thermal expansion should in evaluating autogenous shrinkage of high-strength mass concrete. And this study shows results on opc and similar own contraction, if used retarder.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2020.11a
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• pp.10-11
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• 2020

This research is part of the research for unifying the mass concrete and utilizing the rate of super retarding agent. We analyzed the performance of super retarding agent under low temperature conditions. It was found that there was no deterioration in fluidity and air quality due to the change in the super retarding agent mixing rate. It was found that when super retarding agent was mixed up to 0.5 %, it was delayed for 22.3 hours at 20℃, 48.2 hours at 10℃, and 48.5 hours at 5℃. Therefore in order to ensure the performance required at the site, the super retarding agent mixing rate must be determined by fully considering the situation at the site. In addition it will be analyzed that super retarding agent performance analysis at high temperature will be required in subsequent studies.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.5A
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• pp.307-315
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• 2012

Recently, ultra high performance fiber reinforced concrete (UHPFRC) having over 180 MPa compressive strength and 10 MPa tensile strength has been developed in Korea. However, UHPFRC represents different material properties with normal concrete (NC) and conventional high performance concrete (HPC) such as a high early age autogenous shrinkage and a rapid dry on the surface, because it has a low water-binder ratio and high fineness admixtures without coarse aggregate. In this study, therefore, to propose suitable experimental methods and regulations, and to evaluate mechanical properties at a very early age for UHPFRC, setting, shrinkage and tensile tests were performed. From the setting test results, paraffin oil was an appropriate material to prevent drying effect on the surface, because if paraffin oil is applied on the surface, it can efficiently prevent the drying effect and does not disturb or catalyze the hydration of cement. From the ring-test results, it was defined that the shrinkage stress is generated at the time when the graph tendency of temperature and strain of inner steel ring is changed. By comparing with setting test result, the shrinkage stress was firstly occurred as the penetration resistance of 1.5 MPa was obtained, and it was about 0.6 and 2.1 hour faster than those of initial and final sets. So, the starting time of autogenous shrinkage measurement (time-zero) of UHPFRC was determined when the penetration resistance of 1.5 MPa was obtained. Finally, the tensile strength and elastic modulus of UHPFRC were measured from near initial setting time by using a very early age tensile test apparatus, and the prediction models for tensile strength and elastic modulus were proposed.

• Proceedings of the Korea Concrete Institute Conference
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• 2010.05a
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• pp.459-460
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• 2010

For the application of slip form method to the pylon of Yi Sun-shin bridge which has much variation in its cross section, the change of setting properties of concrete due to changing weather and long pumping distance has to be taken into consideration. Different setting properties of several types of cement according to the amount of compound and ambient temperature were observed in this paper.

• Proceedings of the Korea Concrete Institute Conference
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• 2010.05a
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• pp.273-274
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• 2010

This study investigated on the early hydration and physical characteristics of blast furnace slag through pH variation. The pH values applied to the experiments were, 12.0 and 13.0 which are the pH values of OPC, and type 3 of pH 14.0 which is a strong alkali condition. A paste and mortar method was used to test blast furnace slag and blast furnace slag containing 2wt% of gypsum. It was found that CAH and CSH phases were formed as key hydrates during the early hydration of blast furnace slag, and ettringites were produced extra during the early hydration of blast furnace slag containing 2wt% of gypsum.