• Journal of the Korea Concrete Institute
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• v.26 no.4
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• pp.449-456
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• 2014

Material properties of geopolymer, whose the reaction is very complicated, have been influenced by chemical compositions and particle size distributions of fly ash, concentrations and types of alkali-activators and curing conditions such as temperatures and time. In this research, experiments with several variables such as curing temperatures, preset prior to the high temperature curing and high temperatures have been conducted in order to evaluate to investigate effects on the compressive strengths of geopolymer caused by curing condition. Experiment results were evaluated with compressive strengths and micro-structures such as SEM and MIP of geopolymer pastes. As a result, as higher curing temperature or longer preset time were applied to the pastes, higher compressive strengths were observed. However, compressive strengths of geopolymer pastes declined due to increases in macropores (>50 nm) under high temperatures elapsed after 24 hours. In this sense, it can be considered that strengths and microstructures of geopolymers depends on curing temperature and time.

• Journal of the Korean Society of Hazard Mitigation
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• v.10 no.5
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• pp.17-25
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• 2010

We studied on the watertightness improvement of cementitious material for durability enhancement of concrete. For improvement of watertightness of OPC and OPC with fly ash, we used various materials with watertightness properties to OPC and OPC with fly ash. The performance of watertightness improvement of cementitious materials closely related to formation of CSH by pozzolanic reaction and to reducing of size of contact angle in cement pore by using organic fatty acid. And volume of CSH formation at early hydration have an influence of watertightness improvement and reduction of long-term water absorption rate. In using of fly ash, improvement of workability by using the spherical fly ash caused to densify on the structures of cement material and CSH formation by pozzolanic reaction and cement using fly ash also caused watertightness improvement of cementitious materials. For improvement of concrete durability by watertightness, cementitious materials need using watertightness materials and at using fly ash, also it have to the effect of improvement of watertightness of cementitious materials by pozzolanic reaction.

• Journal of Korean Society of Environmental Engineers
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• v.30 no.1
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• pp.61-68
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• 2008

A new cementitious material has been developed, called alkali-activated fly ash cement(AAFC), which is used to produce AAFC-concrete for construction. The effect of acid attack, sodium chloride solution, carbonation, freeze-thaw cycling, and SEM, XRD analysis of the AAFC-concrete prepared using alkali-activated fly ash cement and OPC-concrete were experimentally investigated. It was found that the acid resistance of AAFC-concrete(35 MPa) prepared from alkali-activated fly ash at 85$^{\circ}C$ for 24 hrs is far better than OPC-concrete(35 MPa). Also, the AAFC-concrete(35 MPa) had a similar resistance of OPC-concrete(35 MPa) to attack, such as sodium chloride solution, carbonation and freeze-thaw cycling.

• 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.

• Journal of the Korean Recycled Construction Resources Institute
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• v.4 no.1
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• pp.25-30
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• 2016

The purpose of this study is to investigate experimentally the effect of reinforcement of polyetylene fiber, inclusion of silica sand, and replacement of cement with fly ash on the compressive and tensile behavior of fiber reinforced composite. Five types of mixture proportions were determined and compressive strength and uniaxial tension tests were performed. Test results showed that strength, ductility, and control of cracking were improved by the reinforcement of fiber. Although the strength was improved by the inclusion of dried silica sand, the ductility was reduced and the crack width was increased. On the other hand, the increase of ductility, the decrease of crack width, and the decrease of strength were observed by the replacement of cement with fly ash.

• Journal of the Korean Recycled Construction Resources Institute
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• v.2 no.2
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• pp.152-157
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• 2014

The objective of this study is to examine the drying shinkage and autogenuous shrinkage strains of heavyweight magnetite concrete. As a main parameters, cement was partially replaced by fly ash (FA) from 5% to 35%. The measured shrinkage strains were compared with predictions obtained from CEB-FIP equations and Yang et al.'s model. Test results showed that the magnitite of the autogenous and total shrinkage strains of heavyweight concrete slightly increased as the amount of fly ash increases up to 15%, beyond which the strains tended to decrease. The CEB-FIP equations considerably underestimated the shrinkage behavior of heavyweight concrete, indicating that this trend was more notable with the age. On the other hand, Yang et al.'s model predicted accurately the shrinkage of heavyweight concrete.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.653-656
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• 2008

The main purpose of this research was to enhance the durability in both the design and construction of dams. Especially, in case of rockfill dams, the durability of face slab concrete in a concrete-faced rockfill dam(CFRD) is achieved by optimizing the fly ash replacement for cement and application of blended fiber. The effect on durability and thermal property corresponding to the increasing replacement of fly ash and application of blended fiber was evaluated, and the optimum value of fly ash replacement and blended fiber application was recommended. The results show that 15% of fly ash replacement and 0.9kg/m3 of blended fiber application was found to be an optimum level and demonstrated excellent performance in durability and thermal property.

• Magazine of the Korea Concrete Institute
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• v.10 no.4
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• pp.163-169
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• 1998

The strength and freeze-thaw test were carried out in order to use recycled aggregate as crushed aggregate in concrete. The recycled concrete had a lower flexture and compressive strengths than ordinary concrete, but the inclusion of fly ash shows similar results in both concretes. The resistance of freeze-thaw was strongly influenced by W/C ratio, content of recycled aggregate and fly ash, and it was also found that the resistance was higher when W/C ratio and fly ash content was lower. and was superior when replacement level of recycled aggregate reached to 80%.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.5
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• pp.3535-3541
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• 2015

In this study, series of tests were performed for drying shrinkage characteristics of concrete with power type shrinkage reducing agent (SRA) and fly ash as a part of research to reduce drying shrinkage of concrete. Firstly, for the mechanical properties, a target strength was acquired securely. In the unrestraint shrinkage tests, the SRA decreased the drying shrinkage about $200{\mu}{\varepsilon}$. Lastly, in the ring tests, due to the tensile creep effect, the concrete with SRA showed the cracking times as much again as the concrete with ordinary Portland cement only did.

• Journal of the Korea Concrete Institute
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• v.16 no.6 s.84
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• pp.777-783
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• 2004

In this study, for improving of concrete properties, those are used ground granulated blast slag(GGBS) and fly ash(FA). There are some advantage to add the GGBS and FA in plain concrete. The objective of this study is to find the characteristics of fresh and hardened antiwashout underwater concrete which is followed by blended ratio of GGBS and FA. Experimental parameters were chosen that W/C was 50%, S/a was 40% and as the blended ratio of GGBS was set at 0, 10, 20, 30, 40, 50, 60% and FA was set at 0, 10, 15, 20, 25, 30, 35% in order to prove the properties of antiwashout underwater concrete can be changed by blended ratio of GGBS md FA. It was measured pH, suspension and slump flow of fresh antiwashout underwater concrete and compressive strength of hardened antiwashout underwater concrete in age of 7 days, 28 days and 56 days. The experimental results of fresh concrete show that pH, suspension and slump flow were all satisfied with KSCE (Korea Society of Civil Engineering) standard value and mix design standard value. To synthetically consider, the optimum blended ratio is about 30% of GGBS and FA.