• Journal of The Korean Society of Agricultural Engineers
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• v.53 no.2
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• pp.35-43
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• 2011

This study aimed to investigate the engineering characteristics of PVA fiber-cement-soil mixture used to prevent or reduce brittle failure of cement-soil mixtures due to the tensile strength increase from the addition of a synthetic fiber. The engineering characteristics of PVA fiber-cement-soil mixtures composed of PVA fiber, soil, and a small amount of cement was analysed on the basis of the compaction test, the unconfined compression test, the tensile strength test, the freezing and thawing test, and the wetting and drying test. The specimens were manufactured with soil, cement and PVA fiber. The cement contents was 2, 4, 6, 8, and 10%, and the fiber contents was 0.4, 0.6, 0.8, and 1.0% by the weight of total dry soil. To investigate the strength characteristics depending on age, each specimen was manufactured after curing at constant temperature and humidity room for 3, 7 and 28 days, after which the engineering characteristics of PVA fiber-cement-soil mixtures were investigated using the unconfined compression test, the tensile strength test, the freezing and thawing test, and the wetting and drying test. The basic data were presented for the application of PVA fiber-cement-soil mixtures as construction materials.

• Advances in concrete construction
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• v.5 no.1
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• pp.31-48
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• 2017

Supplementary cementitious materials (SCM) have turned out to be a vital portion of extraordinary strength and performance concrete. Metakaolin (MK) is one of SCM material is acquired by calcinations of kaolinite. Universally utilised as pozzolanic material in concrete to enhance mechanical and durability properties. This study investigates the fresh and hardened properties of conventional concrete (CC) and self compacting concrete (SCC) by partially replacing cement with MK in diverse percentages. In CC and SCC, partial replacement of cement with MK varies from 5-20%. Fresh concrete properties of CC are conducted by slump test and compaction factor tests and for SCC, slump flow, T500, J-Ring, L-Box, V-Funnel and U-Box tests. Hardened concrete characteristics are investigated by compressive, split tensile and flexural strengths at age of 7, 28 and 90 days of curing under water. Carbonation depth, water absorption and density of MK based CC and SCC was also computed. Fresh concrete test results indicated that increase in MK replacement increases workability of concrete in a constant w/b ratio. Also, outcomes reveal that concrete integrating MK had greater compressive, flexural and split tensile strengths. Optimum replacement level of MK for cement was 10%, which increased mechanical properties and robustness properties of concrete.

• Computers and Concrete
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• v.21 no.6
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• pp.697-703
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• 2018

Compressive strength is one of the most important engineering properties of concrete, and testing of the compressive strength of concrete specimens is often costly and time consuming. In order to provide the time for concrete form removal, re-shoring to slab, project scheduling and quality control, it is necessary to predict the concrete strength based upon the early strength data. However, concrete compressive strength is affected by many factors, such as quality of raw materials, water cement ratio, ratio of fine aggregate to coarse aggregate, age of concrete, compaction of concrete, temperature, relative humidity and curing of concrete. The concrete compressive strength is a quite nonlinear function that changes depend on the materials used in the concrete and the time. This paper presents an adaptive neuro-fuzzy inference system (ANFIS) for the prediction of concrete compressive strength. The training of fuzzy system was performed by a hybrid method of gradient descent method and least squares algorithm, and the subtractive clustering algorithm (SCA) was utilized for optimizing the number of fuzzy rules. Experimental data on concrete compressive strength in the literature were used to validate and evaluate the performance of the proposed ANFIS model. Further, predictions from three models (the back propagation neural network model, the statistics model, and the ANFIS model) were compared with the experimental data. The results show that the proposed ANFIS model is a feasible, efficient, and accurate tool for predicting the concrete compressive strength.

• Advances in concrete construction
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• v.11 no.4
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• pp.307-314
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• 2021

Activated hwangtoh (ACT) is a natural resource abundant in South Korea, approximately 15.0% of soil. It is an efficient mineral admixture that has activated pozzolanic properties through high-temperature heating and rapid cooling. The purpose of this study is to improve a curb mixture that can reduce NOx outside and investigate durability performance. To this end, mortar curb specimens were manufactured by replacing OPC with ACT. The ACT substitution ratios of 0.0, 10.0, and 25.0% were considered, and mechanical and durability tests on the curb specimens were conducted at 28 and 91 days of age. Steam curing was carried out for three days for the production of curbs, which was very effective to strength development at early ages. The reduction in strength at early ages could be compensated through this process, and no significant performance degradation was evaluated in the tests on chloride attack, carbonation, and freezing and thawing. The mortar curb with an ACT of 10.0~25.0% replacement ratio exhibited clear NOx reduction through photocatalytic (TiO2) treatment. This is due to the increase in physical absorption through surface absorption and the photocatalyst-containing TiO2 coating. In this study, the reasonable range of the ACT replacement ratio for NOx reduction was quantitatively evaluated through a comprehensive analysis of each test.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2013.11a
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• pp.23-25
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• 2013

In this study, the results are compared with the case of the concrete with embedded heating wire to verify the performance of the IB made in order to improve the workability and affordability, and to determine the effectiveness of early frost damage prevention. The IB was made using the 5W heating wire and layed on the upper surface of the concrete. The temperature was reduced to below 0℃ approximately within 24 hours, then approached the external temperature thereafter. On the other hand, when the 20W heating wire was used to make the IB and applied the same way, the temperature remained around -2 to 3℃ on the average even through the temperature was reduced to below 0℃, due to the heating wire with relatively large heating capacity. It appeared to reach 85% of the direct heating by embedding the heating wire relatively deeper in the concrete. However, it was determined that using the IB made with the 20W heating wire will prevent the early frost damage to some degree in -10℃.

• Advances in nano research
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• v.15 no.6
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• pp.533-539
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• 2023

This study aims to examine four machine learning (ML)-based models for their potential to estimate the splitting tensile strength (STS) of manufactured sand concrete (MSC). The ML models were trained and tested based on 310 experimental data points. Stone nanopowder content (SNPC), curing age (CA), and water-to-cement (W/C) ratio were also studied for their impacts on the STS of MSC. According to the results, the support vector regression (SVR) model had the highest correlation with experimental data. Still, all of the optimized ML models showed promise in estimating the STS of MSC. Both ML and laboratory results showed that MSC with 10% SNPC improved the STS of MSC.

• Computers and Concrete
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• v.32 no.6
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• pp.567-576
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• 2023

In this study, a 3D microstructure-based model is established to simulate the effective thermal conductivity of cement paste, covering varying influencing factors associated with microstructure and thermal transfer mechanisms. The virtual cement paste divided into colloidal C-S-H and heterogeneous paste are reconstructed based on its structural attributes. Using the two-level hierarchical cement pastes as inputs, a lattice Boltzmann model for heat conduction is presented to predict the thermal conductivity. The results suggest that due to the Knudsen effect induced by the nanoscale pore, the thermal conductivity of air in C-S-H gel pore is significantly decreased, maximumly accounting for 3.3% thermal conductivity of air at the macroscale. In the cement paste, the thermal conductivities of dried and saturated cement pastes are stable at the curing age larger than 100 h. The high water-to-cement ratio can decrease the thermal conductivity of cement paste.

• Journal of the Korea institute for structural maintenance and inspection
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• v.11 no.4
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• pp.71-78
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• 2007

Schmidt hammer and ultra-sonic method are commonly used for crushed sand concrete compressive strength test in a construction field. At present, various of equations for prediction of strength are present, which have been used in a construction field. The purpose of this study is to evaluate the correlation between prediction strength by presentation equations and destructive strength to test specimen, and find out which is a suitable equation for the construction site. In this study, a strength test was carried out destructive test by means of core sampling and traditional test. The experimental parameter were concrete age, curing condition, and strength level.

• Journal of the Korean Recycled Construction Resources Institute
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• v.1 no.2
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• pp.93-100
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• 2013

A variety of researches on the concrete with high volume mineral admixture have increased in recent years. In fact, it is very important to find appropriate replacement ratio of concrete with high volume mineral admixture in order to apply in the field. In this study, compressive strength according to fly ash and blast furnace slag replacement ratio as well as curing temperature was measured in the conditions of obtaining the same workability in order to examine the characteristics of concrete with high volume mineral admixture. In conclusion, it was found that the compressive strength at the age of 3 days decreased by 1.4MPa and the compressive strength at the age of 28 days decreased by 3.8MPa when the fly ash replacement ratio increased by 10%. Also, it was found that the compressive strength at the age of 3 days decreased by 1.0MPa and the compressive strength at the age of 28 days decreased by 0.9MPa when the blast furnace slag replacement ratio increased by 10%. Through the tests, we obtained the basic data for developing the future research on the concrete with high volume mineral admixture for housing structure.

• International Journal of Highway Engineering
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• v.6 no.4 s.22
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• pp.75-89
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• 2004

Long term performance of concrete pavement significantly depends on the given construction and environmental condition. It means that random cracks and extreme crack width due to inappropriate quality control at the early age might lead to decreasing the pavement service life. The temperature and moisture during the construction, cement and aggregate types, curing condition are major components to affect the quality of the concrete pavement at the early age. First of all, the high temperature differential, that is made by increasing air temperature and the heat of cement hydration, is known as the major contributor to severe cracks. In this study, tent covering was used for controlling temperature of the concrete slab. The field measurement data indicates that the effect of the tent covering is very significant to decrease possibilities of random crack occurrence and curling stress and enhance the long-term concrete strength. HIPERPAV(High PERformance PAVing software), a program predicting the strength and stress of an earty-age concrete pavement (72 hour after placement), is used for simulating the effects of tent covering. The HIPERPAVE results showed that the section with the tent covering has higher reliability than the section without the tent covering by 22.5%. In details, reliability is increased 72.5% (without the tent covering) to 95% (with the tent covering).