• Resources Recycling
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• v.18 no.3
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• pp.27-35
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• 2009

To solve resource exhaustion and waste management problems caused by mass consumption, there are many efforts to change from resource consumption system to recycling system. Specially, interests about management of construction waste have increased, but efficient recycling system of waste concrete is not established yet. In this study, high quality recycled aggregate processing circuit was developed to recycle waste concrete. From the waste concrete which is a hydrated compound with coarse aggregate, fine aggregate, and cement material, high quality recycled coarse aggregate for concrete making was produced by autogenous milling and heat pretreatment method. After then, refinement process was performed to separate fine aggregate and cement material from waste concrete fines by sink float separation and hindered-settling separation. As a result, high quality recycled aggregate was produced from waste concrete by developed processing circuit.

• Resources Recycling
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• v.25 no.3
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• pp.63-73
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• 2016

With the purpose of concentrating the magnesium from seawater, in this study, we have conducted experiments to precipitate the magnesium using three precipitants (NaOH, cement kiln dust, and paper sludge ash), and then extract it using sulfuric acid. Results show that the precipitation and extraction performance does not depend so significantly on the kind of precipitant: for all the precipitants used, the precipitation efficiency is measured almost 100% and the extraction efficiency is in the short range of 77 - 89%. The magnesium concentration in the extract is measured 4975 - 5775 mg/L, implying that the magnesium in seawater should be 3.8 - 4.4 times concentrated through the precipitation and extraction reactions. The reaction efficiency of the industrial by-product used as a precipitant in this study is almost 100% similar to those of the other existing expensive precipitants.

• Computers and Concrete
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• v.17 no.6
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• pp.801-814
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• 2016

An alternative type of building system with masonry units is extensively used nowadays to reduce the emission of CO2 and embodied energy. Long-term performance of such structures has become essential for sustaining the building technology. This study aims to assess the strength and durability properties of concrete prepared with unprocessed bagasse ash (BA) and silica fume (SF). A mix proportion of 1:3:3 was used to cast concrete cubes of size $100mm{\times}100mm{\times}100mm$ with various replacement levels of cement and tested. The cubes were cast with zero slump normally adopted in the manufacturing of hollow blocks. The cubes were exposed to acid attack, alkaline attack and sulphate attack to evaluate their durability. The mass loss and damages to concrete for all cases of exposures were determined at 30, 60, and 90 days, respectively. Then, the residual compressive strength for all cases was determined at the end of 90 days of durability test. The results showed that there was slight difference in mass loss before and after exposure to chemical attack in all the cases. Though the appearance was slightly different than the normal concrete the residual weight was not affected. The compressive strength of 10% bagasse ash (BA) as a replacement for cement, with 10% SF as admixture resulted in better strength than the normal concrete. Hence concrete with 10% replacement with BA along with 10% SF as admixture was considered to be durable. Besides solid concrete cubes, hollow blocks using the same concrete were casted and tested simultaneously to explore the possibility of production of masonry units.

• Journal of the Korean Recycled Construction Resources Institute
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• v.9 no.4
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• pp.521-528
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• 2021

The high-density fiber composite manufacturing method by the extrusion molding method has the characteristic that continuous production is possible, and the product is molded through a mold forming a specific cross-section. OPC is used as a defect material, an appropriate amount of SiO₂ is supplied for CaO reaction activity, and high density and high strength are expressed through steam and autoclave curing. However, due to the use of organic reinforcing fibers, the flame duration exceeds the regulations during the non-combustible performance test, making it difficult to secure performance. In this study, the product was produced by mixing alkali-resistant organic fiber and fly ash having voids as a binder by replacing the existing polypropylene fiber. appeared to be possible.

• Resources Recycling
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• v.30 no.5
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• pp.17-24
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• 2021

Natural aggregate regular exploitation has led to environmental and resource depletion issues; consequently, construction waste has become an important raw material in the supply of aggregate smoothly. The recycled aggregate produced in the most of recycled aggregate processing company in Korea has a high adhesion ratio of cement paste and mortar, which affects the water absorption ratio and density. Therefore, the quality of recycled aggregate needs to be improved. In this study, we improved the quality of recycled aggregate through the use of a multistage separation ball mill. This ball mill has a sieve which protects the ball mix and improves the motion. Products produced by using multistage separation ball mill were compared with various quality standard for utilization as recycle aggregate. Finally, we confirmed that the multistage separation ball mill can efficiently separate cement paste and mortar from natural aggregate and that it is suitable for the production of recycled aggregates.

• Computers and Concrete
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• v.27 no.4
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• pp.333-341
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• 2021

Steel slag, an industrial reject from the steel rolling process, has been identified as one of the suitable, environmentally friendly materials for concrete production. Given that the coarse aggregate portion represents about 70% of concrete constituents, other economic approaches have been found in the use of alternative materials such as steel slag in concrete. Unfortunately, a standard framework for its application is still lacking. Therefore, this study proposed functional model equations for the determination of strength properties (compression and splitting tensile) of steel slag aggregate concrete (SSAC), using gene expression programming (GEP). The study, in the experimental phase, utilized steel slag as a partial replacement of crushed rock, in steps 20%, 40%, 60%, 80%, and 100%, respectively. The predictor variables included in the analysis were cement, sand, granite, steel slag, water/cement ratio, and curing regime (age). For the model development, 60-75% of the dataset was used as the training set, while the remaining data was used for testing the model. Empirical results illustrate that steel aggregate could be used up to 100% replacement of conventional aggregate, while also yielding comparable results as the latter. The GEP-based functional relations were tested statistically. The minimum absolute percentage error (MAPE), and root mean square error (RMSE) for compressive strength are 6.9 and 1.4, and 12.52 and 0.91 for the train and test datasets, respectively. With the consistency of both the training and testing datasets, the model has shown a strong capacity to predict the strength properties of SSAC. The results showed that the proposed model equations are reliably suitable for estimating SSAC strength properties. The GEP-based formula is relatively simple and useful for pre-design applications.

• Advances in concrete construction
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• v.16 no.6
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• pp.303-316
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• 2023

Using industrial wastes and construction and demolition (C&D) wastes is potentially advantageous for concrete production in terms of sustainability improvement. In this paper, a sustainable Self-Compacting Concrete (SCC) made with industrial wastes and C&D wastes was proposed by considerably replacing natural counterparts with recycled coarse aggregates (RCAs) and supplementary cementitious materials (SCMs) (i.e., Fly ash (FA), ground granulated blast furnace slag (GGBS) and silica fume (SF)). A total of 12 SCC mixes with various RCAs and different combination SCMs were prepared, which comprise binary, ternary and quaternary mixes. The mechanical properties in terms of compressive strength and static elasticity modulus of recycled aggregates (RA-SCC) mixes were determined and analyzed. Microstructural study was implemented to analyze the reason of improvement on mechanical properties. By means of life cycle assessment (LCA) method, the environmental impacts of RA-SCC with various RCAs and SCMs were quantified, analyzed and compared in the system boundary of "cradle-to-gate". In addition, the comparison of LCA results with respect to mechanical properties was conducted. The results demonstrate that the addition of proposed combination SCMs leads to significant improvement in mechanical properties of quaternary RA-SCC mixes with FA, GGBS and SF. Furthermore, quaternary RA-SCC mixes emit lowest environmental burdens without compromising mechanical properties. Thus, using the combination of FA, GGBS and SF as cement substitution to manufacture RA-SCC significantly improves the sustainability of SCC by minimizing the depletion of cement and non-renewable natural resources.

• Economic and Environmental Geology
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• v.54 no.2
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• pp.285-297
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• 2021

Globally, nuclear-decommissioning facilities have been increased in number, and thereby hundreds of thousands of wastes, such as concrete, soil, and metal, have been generated. For this reason, there have been numerous efforts and researches on the development of technology for volume reduction and recycling of solid radioactive wastes, and this study reviewed and examined thoroughly such previous studies. The waste concrete powder is rehydrated by other processes such as grinding and sintering, and the processes rendered aluminate (C3A), C4AF, C3S, and ��-C2S, which are the significant compounds controlling the hydration reaction of concrete and the compressive strength of the solidified matrix. The review of the previous studies confirmed that waste concretes could be used as recycling cement, but there remain problems with the decreasing strength of solidified matrix due to mingling with aggregates. There have been further efforts to improve the performance of recycling concrete via mixing with reactive agents using industrial by-products, such as blast furnace slag and fly ash. As a result, the compressive strength of the solidified matrix was proved to be enhanced. On the contrary, there have been few kinds of researches on manufacturing recycled concretes using soil wastes. Illite and zeolite in soil waste show the high adsorption capacity on radioactive nuclides, and they can be recycled as solidification agents. If the soil wastes are recycled as much as possible, the volume of wastes generated from the decommissioning of nuclear power plants (NPPs) is not only significantly reduced, but collateral benefits also are received because radioactive wastes are safely disposed of by solidification agents made from such soil wastes. Thus, it is required to study the production of non-sintered cement using clay minerals in soil wastes. This paper reviewed related domestic and foreign researches to consider the sustainable recycling of concrete waste from NPPs as recycling cement and utilizing clay minerals in soil waste to produce unsintered cement.

• Journal of the Korea Concrete Institute
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• v.18 no.5 s.95
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• pp.589-594
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• 2006

The recycling of industrial wastes in the concrete manufacturing is of increasing interest worldwide, due to the high environmental impact of the cement and concrete industries and to the rising demand of infrastructures, both in industrialized and developing countries. The production of municipal wastes in the South Korea is estimated at about 49,902 ton per day and only 14.5% of these are incinerated and principally disposed of in landfill. These quantities will increase considerably with the growth of municipal waste production, the progressive closing of landfill, so the disposal of municipal solid waste incinerator(MSWI) ashes has become a continuous and significant issue facing society, both environmentally and economically. MSWI ash is the residue from waste combustion processes at temperature between $850^{\circ}C\;and\;1,000^{\circ}C$. And the main components of MSWI ash are $SiO_2,\;CaO\;and\;Al_2O_3$. The aim of this study is to find a way to useful application of MSWI ash(after treatment) as a structural material and to investigates the hydraulic activity, compressive strength development composition variation of such alkali-activated MSWI ashes concrete. And it was found that early cement hydration, followed by the breakdown and dissolving of the MSWI-ashes, enhanced the formation of calcium silicate hydrates(C-S-H). The XRD and SEM-EDS results indicate that, both the hydration degree and strength development are closely connected with a curing condition and a alkali-activator. Compressive strengths with values in the 40.5 MPa were obtained after curing the activated MSWI ashes with NaOH+water glass at $90^{\circ}C$.

• Journal of the Korean Recycled Construction Resources Institute
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• v.5 no.4
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• pp.114-121
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• 2010

Portland cement production is under critical review due to high amount of CO2 gas released to the atmosphere. Attempts to increase the utilization of a by-products such as fly ash and ground granulated blast-furnace slag to partially replace the cement in concrete are gathering momentum. But most of by-products is currently dumped in landfills, thus creating a threat to the environment. Many researches on alkali-activated concrete that does not need the presence of cement as a binder have been carried out recently. However, most study deal only with alkali-activated ground granulated blast furnace slag or fly ash, as for the combined use of the both, little information is reported. In this study, we investigated the influence of mixture ratio of fly ash/ blast furnace slag tand curing condition on the flowability and compressive strength of mortar in oder to develop cementless alkali-activated concrete. In view of the results, we found out that the mixture ratio of fly ash/blast furnace slag always results to be significant factors. But the influence of curing temperature in the strength development of mortar is lower than the contribution due to other factors. At the age of 28days, the mixture 50% fly ash and 50% ground granulated blast furnace slag activated with 1:1 the mass ratio of 9M NaOH and sodium silicate, develop compressive strength of about 65 MPa under $20^{\circ}C$ curing.