• Journal of the Korea Concrete Institute
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• v.23 no.3
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• pp.331-338
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• 2011

The purpose of this study is to use organisms or micro-organism functions for eco-friendly water-purification of cement bricks, utilizing bioremediation. Many researches have been performed in the past to improve water quality by using effective micro-organisms in construction materials. In order to purify water using micro-organisms, this research used soybean paste bacteria, an effective micro-organism that was identified through 16S rDNA sequence analysis performed in Daegu S. Environment Protection Institute in addition to Natto bacteria that was studied in the previous research. With these effective micro-organisms with water-purification ability, this study examined their water-purification possibility on cement bricks. This study used Zeolite to immobilize micro-organisms to bricks, and confirmed that the micro-organisms were attached on Zeolite from SEM analysis. The experimental results showed that specific micro-organisms can be used to effectively remove contamination an used to develop eco-friendly construction materials. The study on micro-organisms for material purification shows great promises as a future research topic.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.2
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• pp.219-226
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• 2020

Over the last decades, great efforts have been devoted to reuse industrial wastes and by-products from various industries as supplementary cementitious materials in order to reduce carbon dioxide(CO₂) emission by reducing the use of Portland cement in construction. Oyster shell waste, originating from the fishery industry, is available in huge quantities in certain areas, and is generally discarded or landfilled. In this study, we aimed to reuse oyster shell as an alternative to limestone in limestone calcined clay cement(LC³). The oyster shell calcined clay cement(OC³) paste were produced and were characterized via X-ray diffraction, isothermal calorimetry, compressive strength tests, and thermogravimetry. The results revealed that OC³ pastes exhibited similar strength development and reactivities by pozzolanic reaction with LC³, which implies that oyster shell could be used as a substitute for limestone in LC³.

• Journal of the Korean Recycled Construction Resources Institute
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• v.9 no.4
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• pp.529-536
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• 2021

In this study, nano-silica and nano-titanium were selected to determine the possibility of applying the binder to reactive nano materials. The basic characteristics of the nano material candidate group were reviewed. and the reactivity of nano materials was reviewed through K-value. The reactivity of the nano silicate materials was measured to be high. Therefore, as a final candidate group, nano silicate materials were selected. The finally selected reactive nano material was reviewed for its usability as a construction binder. The mechanical properties and unit weight of cement paste were reviewed using silica fume and blast furnace slag and nano materials. When cement composites with nano silicate materials, it was confirmed that it was effective in improving the mechanical performance and decrease the unit weight of cement composites.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.2A
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• pp.297-304
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• 2008

It is well known that cracks in concrete decrease permeability and durability of concrete because cracks enhance the penetration of water or corrosive chemicals like as chlorides, carbon dioxides, sulfates and some others. But some of cracks in hardened cements may be sealed in case of contacting water. This phenomenon is called "self healing" and it has a close relation to hydration products newly formed on surfaces of cracks. Many studies on self healing in concretes commonly showed that CSH gel has been observed on crack surfaces. And some studies have reported that calcium hydroxides and ettringite were observed as well as CSH gel on crack surfaces. This study was carried out to investigate hydration products formed by self healing process and also examine the influence of waterproof admixture for concretes on self healing of cement. As a result of XRD, DSC, SEM and EDX analysis of crack surfaces, it was found that self healing of cement was related to CSH gel, calcium hydroxides and ettringite. And waterproof admixture increased fibrous (needle-like) hydration products which were in network form. It is estimated that such fibrous products are effective for self healing process of cement system.

• Journal of the Korea Concrete Institute
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• v.21 no.3
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• pp.255-264
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• 2009

Permeability coefficient of concrete is a substaintial key parameter for understanding the durability performance of concrete and its microstructural densification. Many researches for the issue have been accomplished, however, it is very rare to deal with the theoretical study on permeability coefficient in connection with carbonation of concrete and the the effect of volumetric fraction of cement paste or aggregate on the permeability coefficient. The majority of these researches have not dealt with this issue combined with carbonation of concrete, although carbonation can significantly impact on the permeability coefficient of concrete. The purpose of this study is to establish a fundamental approach to compute the permeability coefficeint of (non)carbonated concrete. When simulating a microstructural characteristics as a starting point for deriving a model for the permeability coefficient by the numerical simulation program for cementitious materials, HYMOSTRUC, a more realistic formulation can be achieved. For several compositions of cement pastes, the permeability coefficient was calculated with the analytical formulation, followed by a microstructure-based model. Emphasis was on the microstructural changes and its effective change of the permeability coefficient of carbonated concrete. For carbonated concrete, reduced porosity was calculated and this was used for calculating the permeability coefficeint. The computational result was compared with experimental outcome.

• Computers and Concrete
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• v.8 no.2
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• pp.125-142
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• 2011

In the present paper, a numerical simulation method based on mesoscopic composite structure of concrete, the truss network model, is developed to evaluate the diffusivity of concrete in order to account for the microstructure of concrete, the binding effect of chloride ions and the chloride concentration dependence. In the model, concrete is described as a three-phase composite, consisting of mortar, coarse aggregates and the interfacial transition zones (ITZs) between them. The advantage of the current model is that it can easily represent the movement of mass (e.g. water or chloride ions) through ITZs or the potential cracks within concrete. An analytical method to estimate the chloride diffusivity of mortar and ITZ, which are both treated as homogenious materials in the model, is introduced in terms of water-to-cement ratio (w/c) and sand volume fraction. Using the newly developed approaches, the effect of cracking of concrete on chloride diffusion is reflected by means of the similar process as that in the test. The results of calculation give close match with experimental observations. Furthermore, with consideration of the binding capacity of chloride ions to cement paste and the concentration dependence for diffusivity, the one-dimensional nonlinear diffusion equation is established, as well as its finite difference form in terms of the truss network model. A series of numerical analysises performed on the model find that the chloride diffusion is substantially influenced by the binding capacity and concentration dependence, which is same as that revealed in some experimental investigations. This indicates the necessity to take into account the binding capacity and chloride concentration dependence in the durability analysis and service life prediction of concrete structures.

• Journal of Korean Society of Environmental Engineers
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• v.36 no.12
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• pp.843-850
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• 2014

This study investigated to recycle ash produced in the sewage sludge incinerator using reduction/stabilization. Nonsintering process was performed by binding cement, geobond and sand mixed with sewage sludge ash (SSA). Results showed that unconfined compressive strength could be obtained components of sewage sludge ash. it exceeded more than double score of the 22.54 Mpa ($229.7kg/cm^2$) Korean standard. chemical ingradients of the sewage sludge ash was mainly composed of $SiO_2$, $Al_2O_3$, $Fe_2O_3$, CaO and others, which were similar to those of the each binders consisting cement and geobond. microstructure of solidified speceimen for the different admixture was related to the compressive strength according to SEM analysis. optimum mixing range of the sewage sludge ash to inorganic binder was found to be 10~40% which can widly safely regulate the confined compressive strength. This study revealed the sewage sludge ash can be partial replacement of the inorganic binder for recycling.

• International Journal of Concrete Structures and Materials
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• v.7 no.2
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• pp.95-110
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• 2013

We report various synchrotron radiation laboratory based techniques used to characterize cement based materials in nanometer scale. High resolution X-ray transmission imaging combined with a rotational axis allows for rendering of samples in three dimensions revealing volumetric details. Scanning transmission X-ray microscope combines high spatial resolution imaging with high spectral resolution of the incident beam to reveal X-ray absorption near edge structure variations in the material nanostructure. Microdiffraction scans the surface of a sample to map its high order reflection or crystallographic variations with a micron-sized incident beam. High pressure X-ray diffraction measures compressibility of pure phase materials. Unique results of studies using the above tools are discussed-a study of pores, connectivity, and morphology of a 2,000 year old concrete using nanotomography; detection of localized and varying silicate chain depolymerization in Al-substituted tobermorite, and quantification of monosulfate distribution in tricalcium aluminate hydration using scanning transmission X-ray microscopy; detection and mapping of hydration products in high volume fly ash paste using microdiffraction; and determination of mechanical properties of various AFm phases using high pressure X-ray diffraction.

• Advances in concrete construction
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• v.10 no.5
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• pp.381-391
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• 2020

This study aimed to develop reference materials (RMs) for mortar that can simulate the initial flow characteristics with constant quality over a long period. Through the previous research on the development of RMs for cement paste, the combination of limestone, glycerol, and water was used as the basic matrix for developing RMs for mortar in this study. In addition, glass beads of three particle sizes (0.5, 1.0, and 2.0 mm) and ISO standard sand were selected as tentative candidates to derive fine aggregate substitutes. The mixture of glass beads could simulate the initial flow characteristics of mortar, but under the same mixing ratio, replicates showed an unstable tendency to indicate inconsistent values due to the generation of electrostatic properties between materials and equipment. On the other hand, the mixture using ISO standard Sand not only simulates the constant flow characteristics for a long period of time, but also shows stable results with little error in replicates. Therefore, limestone, glycerol, ISO standard sand, and water were finally determined as components that met the required properties of RMs for mortar. The effect of each component on the flow characteristics of RMs was analyzed. It was found that glycerol increased the cohesion between the particles of standard sand, resulting in a constant increase both in the plastic viscosity and yield stress. Both limestone and standard sand had a dominant effect on the yield stress. The relationships between various mortar mixing ratios and the corresponding mixing ratios of RMs were established. In addition, the results of the verification experiment showed that the rheological properties of the RMs obtained through the relationships correlated with various water/cement ratios and the fine aggregate volume fractions of mortar obtained with same manner. In other words, the RMs for mortar developed in this study can be used as standard samples because they can simulate the initial flow characteristics of mortar of various mixing ratios for a long period without any chemical changes.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.1053-1056
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• 2008

Permeability coefficient of concrete is a substantial key parameter for understanding the durability performance of concrete and its micro-structural densification. Many researches to deal with the issue have been accomplished, however, it is very rare to deal with the theoretical study on permeability coefficient in connection with carbonation of concrete and the effect of volumetric fraction of cement paste or aggregate on the permeability coefficient. The majority of these researches have not dealt with this issue combined with carbonation of concrete, although carbonation can significantly impact on the permeability coefficient of concrete. The purpose of this study is to establish a fundamental approach to compute the permeability coefficient of (non)carbonated concrete. When simulating micro-structural characteristics as a starting point for deriving a model for the permeability coefficient by the numerical simulation program for cementitious materials, HYMOSTRUC, a more realistic formulation can be achieved. For several compositions of cement pastes, the permeability coefficient is calculated with the analytical formulation, followed by a microstructure-based model. Emphasis is on the micro-structural changes and its effective change of the permeability coefficient of carbonated concrete. The results of micro-structural water permeability coefficient model will be compared with results achieved from permeability experiments.