• International Journal of Concrete Structures and Materials
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• v.10 no.1
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• pp.15-28
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• 2016

With the aim to reduce the atmospheric $CO_2$, utilization of the carbonated lime produced from the aqueous carbonation reaction for the synthesis of a cementitious material would be a promising approach. The present investigation deals with the aqueous carbonation of slaked lime, followed by hydrothermal synthesis of a cementitious material utilizing the carbonated lime, silica fume, and hydrated alumina. In this study, the aqueous carbonation reaction was performed under four different conditions. The TGA, FESEM, and XRD analysis of the carbonated product obtained from the four different reaction conditions was performed to evaluate the efficacy of the reaction conditions used for the production of the carbonated lime. Additionally, the performance of the cementitious material was verified analyzing the physical characteristics, mechanical property and setting time. Based on the results, it is demonstrated that the material produced by the hydrothermal method possesses the cementing ability. Additionally, it is revealed that the mortar prepared using the alternative cementitious material yields $33.8{\pm}1.3MPa$ compressive strength. Finally, a plausible reaction scheme has been proposed to explain the overall performances of the aqueous carbonation as well as the hydrothermal synthesis of the cementitious material.

• Computers and Concrete
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• v.15 no.2
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• pp.167-181
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• 2015

"Mortar or concrete pneumatically projected at high velocity onto a surface" is called Shotcrete. Models that predict shotcrete design parameters (e.g. compressive strength, slump etc) from any mixing proportions of admixtures could save considerable experimentation time consumed during trial and error based procedures. Artificial Neural Network (ANN) has been widely used for similar purposes; however, such models have been rarely applied on shotcrete design. In this study 19 samples of shotcrete test panels with varying quantities of water, steel fibers and silica fume were used to determine their slump, cost and compressive strength at different ages. A number of 3-layer Back propagation Neural Network (BPNN) models of different network architectures were used to train the network using 15 samples, while 4 samples were randomly chosen to validate the model. The predicted compressive strength from linear regression lacked accuracy with $R^2$ value of 0.36. Whereas, outputs from 3-5-3 ANN architecture gave higher correlations of $R^2$ = 0.99, 0.95 and 0.98 for compressive strength, cost and slump parameters of the training data and corresponding $R^2$ values of 0.99, 0.99 and 0.90 for the validation dataset. Sensitivity analysis of output variables using ANN can unfold the nonlinear cause and effect relationship for otherwise obscure ANN model.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.637-640
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• 2008

In this study, the characteristics of strength development on high volume fly ash concrete(HVFAC)with Type 4 cement was experimentally investigated. Three levels of W/B were selected. Four levels of fly ash replacement ratios and two levels of silica fume replacement ratios were adopted. In the concrete mix, the water content of 125kg/m$^3$ was used, which is less than that of usual water content. As a result, it appeared that the compressive strength gradually decreased with increasing fly ash replacement ratio until 91days. However, regarding the compressive strength, the proper replacement ratio is about 20%, which is low compared to Type I cement case. It was observed that the tensile strength is proportional to the 0.72 power of the compressive strength. It appears that the prediction equation presented in Concrete Standard Specification overestimate the tensile strength in the low strength range, underestimate the tensile strength in the hi호 strength range.

• Magazine of the Korea Concrete Institute
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• v.11 no.1
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• pp.141-148
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• 1999

Recently, high performance concrete developed has a good quality at fresh and hardened state, but high binder contents results in spending much money on manufacturing and many cracks by drying and autogenous shrinkage, Therefore, in this paper, not only prevention of cracks caused by drying and autogenous shrinkage, but improvement of quality and accomplishment of economy by applying F.A(fly ash), S.F(silica fume) and CSA(calcium sulfa aluminate) expansive additives as an inorganic admixtures in W/B 35% are discussed. According to the experimental results, when 5% of CSA expansive additives and 15:5(F.A:S.F)are replaced at unit cement content, high performance concrete with both good fluidity at fresh state and high compressive strength, compensation of drying and autogenous shrinkage at hardened state are accomplished.

• International Journal of Highway Engineering
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• v.19 no.6
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• pp.129-137
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• 2017

PURPOSES : The purpose of this study is to develop bridge deck concrete materials based on ordinary Portland cement concrete, and to evaluate the applicability of the developed materials through material properties tests. METHODS : For field implementation, raw material (cement, fine aggregate, and coarse aggregate) properties, fresh concrete properties (slump and air content), strength (compressive, flexural and bond strength) gain, and durability (freeze-thaw resistance, scaling resistance, and rapid chloride penetrating resistance) performance were evaluated in the laboratory. RESULTS : For the selected binder content of $410kg/m^3$, W/B = 0.42, and S/a = 0.48, the following material performance results were obtained. Considering the capacity of the deck finisher, a minimum slump of 150 mm was required. At least 6 % of air content was obtained to resist freeze-thaw damage. In terms of strength, 51.28 MPa of compressive strength, 7.41 MPa of flexural strength, and 2.56 MPa of bond strength at 28 days after construction were obtained. A total of 94.9 % of the relative dynamic modulus of elasticity after 300 cycles of freeze-thaw resistance testing and $0.0056kg/m^2$ of weight loss in a scaling resistance test were measured. However, in a chloride ion penetration resistance test, the result of 3,356 Coulomb, which exceeds the threshold value of the standard specification (1000 Coulomb at 56 days) was observed. CONCLUSIONS : Instead of using high-performance modified bridge deck materials such as latex or silica fume, we developed an optimum mix design based on ordinary Portland cement concrete. A test construction was carried out at ramp bridge B (bridge length = 111 m) in Gim Jai City. Immediately after the concrete was poured, the curing compound was applied, and then wet mat curing was applied for 28 days. Considering the fact that cracks did not occur during the monitoring period, the applicability of the developed material is considered to be high.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2007.04a
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• pp.63-66
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• 2007

This study investigates the fire resistance properties of high strength concrete, around 60MPa class, designed with various admixture types and fiber content. Test showed that the increase of fiber content decreased the fluidity and slightly inclined the air content of fresh concrete. However, the fiber content in concrete did not affect the compressive strength. For the addition of admixture, specimens adding the shrinkage-reducing-agent (SR) indicated the strength value at 70MPa, which is followed by incorporating silica fume (SF) at 66MPa, the combination of expansive admixture (EA) and SR at 63MPa, only EA at 59MPa, blast furnace slag (BS) at 58MPa and fly ash (FA) at 50MPa in an order. After completing the fire test, all specimens adding 0.05vol.% of polypropylene fiber exhibited protection of spatting, except for the specimens incorporating loft of SF and incorporating 20% of SF with only SR and the combination of EP and SRA, respectively. Therefore the most effective result of this study was shown in the specimens incorporating love of FA and 30% of BS and incorporating 20% of SF with 5 % of EA. It is expected that this test results will be crucial references in near future to develope the spatting resistance method of high strength concrete.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.417-420
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• 2008

In this study, the characteristics of strength development and hydration heat on high volume fly ash concrete(HVFAC) was experimentally investigated. Two levels of W/B were selected. Seven levels of fly ash replacement ratios and two levels of silica fume replacement ratios were adopted. In the concrete mix, the water content of $125kg/m^3$ was used, which is less than that of usual water content. As a result, it appeared that the compressive strength gradually decreased with increasing fly ash replacement ratio at the early age, but the difference of strength up to replacement ratio of 50% was little at the age of 91 days because of the pozzolanic reaction of fly ash. The effect of hydration heat reduction on the concrete was affected by the fly ash replacement ratio. When the replacement ratio was over 30%, the reduction efficiency of hydration heat was large.

• Journal of the Korea Institute of Building Construction
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• v.22 no.4
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• pp.337-345
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• 2022

The foundation of high-rise concrete building in coastal areas generally must be installed in an integrated manner, not separately, in order to prevent defects caused by stress on the upper and lower parts of the mounting surface and to manage the process smoothly. However, when performing integrated punching, there is a concern that temperature stress cracks may occur due to hydration heat. Due to the large member size, it is difficult to make a sufficient commitment, so it is necessary to mix concrete with high self-charging properties to ensure workability. In this research, the amount of high-performance spray and admixture used was adjusted as experimental variables to satisfy this required performance. Through the analysis of the results for each blending variable, it was found that the unit quantity was 155kg/m³ and the cement ratio in the binder was 18%, and the target values of the pre-concrete properties and compressive strength were satisfied. A four-component binder(18% cement, 50% slag fine powder, 27% fly ash, 5% silica fume) was used.

• Journal of the Korea Institute of Building Construction
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• v.23 no.5
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• pp.547-558
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• 2023

This research delves into the fabrication of an ultra-high-strength concrete, enriched with oxidized graphene nanoplatelet(GO) and hollow glass powder(HGP), notably eschewing the conventional inclusion of silica fume(SF). The primary objective was to scrutinize the autogenous shrinkage characteristics of this innovative formulation. It was discerned that the NewMix specimen, which incorporated the cGO(sourced from Company C) and HGP, and intentionally bypassed SF, showcased a commendable 13% reduction in autogenous shrinkage relative to the benchmark(Ref) specimenthat incorporated SF. Moreover, the proclivity for crack formation owing to autogenous shrinkage in the NewMix was observed to manifested by NewMix at the juncture of cracking emerged as the apex value. Attributed to the expansive specific surface area and exemplary dispersibility of cGO, it was postulated that the concrete's pore structure benefitted from enhanced infill, leading to a reduction in autogenous shrinkage. Additionally, the cGO integration fortified the concrete's resistance to crack initiation. Consequently, such an enhancement is posied to be pivotal in mitigating crack propagation resulting from autogenous shrinkage in ultra-high-strength concrete.

• Journal of the Korea Concrete Institute
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• v.26 no.1
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• pp.63-70
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• 2014

This experimental study was intended to improve the compressive strength of multi-walled CNT reinforced cementitious composites with efficiency. The variables considered are the degree of sonication, the amount of surfactant, the replacement ratio of silica fume, etc. Optical microscope informed that fiber dispersion of CNT was improved with the increase of sonication time, and the compressive strength was proved to be enhanced as the degree of sonication increased. When superplasticizer as a surfactant had SP/CNT ratio of 4~6, the best improvement in strength was obtained. Silica fume was shown to produce the highest compressive strength at 10% replacement. Microstructure of CNT composites was also analyzed; XRD and SEM results indicated that CNT addition hardly changed hydration products and microstructure, and MIP analysis found the reduction of total porosity as well as the increase of nano-pores with the size of tens of nm instead of the decrease of pore distribution in the region of around 10 ${\mu}m$ and 100 nm. The results of microstructure analysis explains that the strength improvement is closely related to physical contribution rather than chemical influence by adding CNT.