50MPa급 강섬유보강 순환골재 콘크리트충전 각형강관 기둥의 전단성능 평가 실험

이승우 서울시립대학교 일반대학원 2022 국내석사

재개발, 재건축사업 등 도시정비사업이 활발히 진행됨에 따라 건설폐기물은 19년 기준 221,000톤/일 수준으로 전체 폐기물 발생량의 절반가량을 차지하고 있다. 정부에서는 일반골재의 자원고갈을 넘어 환경적으로 지속가능성의 문제를 야기하면서 세계적으로 순환형 정책을 추진하고 있으며 순환골재를 15~25% 사용하는 건축물에 한하여 용적률을 완화하도록 하는 등 관련제도를 도입하고 있는 실정이다. 하지만, 순환골재를 안정적으로 사용하기 위한 구체적인 설계 및 시방에 관한 지침은 부족하며, 구조물에 적용 시 불안정한 구조성능과 사회적 인식 부족으로 인하여 활용성이 미흡한 상황이다. 순환골재를 구조체로 활용하는데 제한적인 이유는 충격에 의한 성능저하와 시멘트 모르타르로 인한 영향이 있다. 콘크리트용 순환골재는 폐콘크리트를 파·분쇄 후 분리선별하여 생산되며 고품질의 순환골재를 생산하기 위해서는 수차례의 처리과정이 필요하다. 이러한 처리과정에서 충격에의해 발생하는 골재의 미세균열은 순환골재 콘크리트의 성능저하를 유발하는 요소이다. 또한, 미탈거된 시멘트 모르타르로 인해 일반골재 대비 낮은 밀도와 높은 흡수율로 시간의존성 영구변형인 건조수축 및 크리프가 증대되는 경향이 있다. 이러한 순환골재 콘크리트의 기계적인 물성저하를 방지하기 위해 부피변화를 억제하는 강섬유로 보강하여 강도특성과 장기거동 특성을 개선하고자 하였다. 또한, 초기강도와 특성을 개선하고자 강관에 충전하여 외부영향을 최소화하였다. 본 연구에서는 순환골재 콘크리트를 구조체에 적용하기 위해 강섬유와 구조용 각형강관으로 보강하여 순환골재 치환율(0, 25, 50, 100%), 강섬유보강(0, 0.5%), 전단경간비(0.8, 1.6)를 변수로 전단성능 평가 실험을 수행하였다. 따라서, 순환골재 사용량에 따른 건축법규 완화기준을 토대로 순환골재 치환율에 따른 전단강도를 평가하였다. 강섬유 혼입율은 선행연구에 서 강섬유 뭉침현상이 발생하지 않으며 경제성을 고려한 체적비율을 선정하여 강섬유보강이 각형 CFT 기둥의 전단강도에 미치는 영향을 확인하였다.또한, 전단이 거동을 지배하는 전단경간(a)의 범위를 산정하고 전단경간비에 따른 전단거동을 관찰하였다. As urban maintenance projects such as redevelopment and reconstruction projects are actively carried out, construction waste is 221,000 tons/day as of 2019, accounts for about half of the total waste generations. The government is promoting a cyclical policy international, causing environmental sustainability problems beyond the depletion of resources of natural aggregates, and introducing related systems such as easing the floor area ratio only for buildings that use 15 to 25%. However, specific guidelines for the stable use of recycled aggregates are insufficient, and utilization is insufficient due to unstable structural performance and insufficient of social awareness when applied to structures. The reason for the limited use of recycled aggregates as structures is due to low performance due to impact and cement mortar. Recycled aggregates for concrete are produced separately after crushing the Waste concrete, and several processes are required to produce high-quality recycled aggregates. The micro-cracks of aggregates generated by impact in this process are factors that cause performance degradation of recycled aggregate concrete. In addition, dry shrinkage and creep, which are permanent deformation of time dependence, tend to increase with lower density and higher absorption rate compared to natural aggregates due to not removed cement mortar. In order to prevent the mechanical property degradation of the recycled aggregate concrete, it was intended to improve strength characteristics and long-term behavior characteristics by reinforcing with steel fibers that control volume changes. In addition, in order to improve dry shrinkage and creep characteristics, which are initial strength and long-term behavior characteristics, the steel tube was filled to minimize external impact.In this study, shear performance evaluation experiments were conducted with variables such as steel fiber and structural square steel tube to apply recycled aggregate concrete to the structure, and the replacement rate of recycled aggregate (0, 25, 50, 100%), steel fiber reinforcement (0, 0.5%), and shear span-to-depth ratio (0.8, 1.6). Therefore, the shear strength according to the replacement rate of recycled aggregates was evaluated based on the construction law relaxation criteria according to the amount of recycled aggregates used. In previous studies, the effect of steel fiber reinforcement on the shear strength of square CFT columns was confirmed by selecting a volume ratio considering economic feasibility without agglomeration of steel fibers. In addition, the range of the shear span (a) in which the shear controls the behavior was calculated, and the shear behavior according to the shear span-to-depth ratio was observed.

순환골재 콘크리트의 구조성능 예측방법 개선에 대한 연구

한승엽 한양대학교 공학대학원 2025 국내석사

This study aims to analyze the variables that influence the characteristics and structural performance of recycled aggregates and propose an improved method for predicting the structural performance of recycled aggregate concrete. Recycled aggregates exhibit significant variability in quality due to differences in waste material properties and production processes, leading to notable physical differences compared to natural aggregates. In particular, characteristics such as low durability, low density, and high water absorption have a substantial impact on the structural performance of concrete. Consequently, recycled aggregate concrete is perceived as less reliable compared to natural aggregate concrete, resulting in reluctance to use it. By incorporating these characteristics of recycled aggregates, this study seeks to reduce prediction errors and enhance the accuracy of structural performance predictions for recycled aggregate concrete. To achieve this, key variables such as substitution rate, water absorption, and density of recycled aggregates were analyzed, and improvement proposals were made for predicting the structural performance metrics, including compressive strength, shear strength, and tensile strength. The study also validated the proposed improvements for compressive strength through data verification, assessing their practical applicability and limitations. The prediction methods proposed in this research can be further refined in future studies through additional experiments and extensive data verification and accumulation. Ultimately, these efforts are expected to achieve prediction accuracy comparable to that of natural aggregate concrete. 본 연구는 순환골재의 특성과 구조성능을 예측하기 위한 변수를 분석하고, 이를 바탕으로 개선된 순환골재 콘크리트의 구조성능 예측 방법을 제안하는 것을 목표로 한다. 순환골재는 폐기물의 품질과 생산과정에 따라 품질 변동성이 크며, 이로 인해 천연골재와 비교하여 물리적 특성이 크게 차이 난다. 특히, 낮은 내구성과 밀도, 높은 흡수율의 특성은 콘크리트의 구조성능에 큰 영향을 미치는 변수이며, 이로 인해 순환골재 콘크리트는 천연골재 콘크리트와 비교해 신뢰도가 낮아 사용 기피 현상을 보인다. 이러한 순환골재의 특성을 반영한 구조성능 예측 방법의 개선을 통해, 순환골재 콘크리트의 구조성능 예측의 오차를 줄이고, 정확성을 높이고자 한다. 이를 위해 순환골재의 치환률, 흡수율, 밀도 등을 변수로 설정하여 압축강도, 전단강도, 인장강도 등의 구조성능 예측 방법의 개선안을 제안하였으며, 압축강도의 개선안을 데이터 검증을 통해 실제 사용 가능성과 개선안의 한계점에 관해 연구하였다. 본 연구에서 제안한 예측 방법은 차후 연구에서 추가적인 실험과 많은 양의 데이터 검증과 축적을 통해 개선할 수 있으며, 궁극적으로 천연골재 콘크리트에 준하는 예측성능을 기대할 수 있을 것이다.

建設 産業用 高品質 循環잔骨材의 乾式 生産시스템에 關한 實驗的 硏究

신승봉 충남대학교 2008 국내석사

Recently, the recycling and reusing of construction and demolition waste concrete is urgently required because production quantity of construction and demolition waste concrete is greatly increased according to the rapid increasing of urban redevelopment project. On the other hand, the problem solution for demand and supply unbalance of fine aggregate is urgently required because of the restriction of collecting sea fine aggregate by intensification of environment influence evaluation and the shortage of river fine aggregate. Therefore, the utilization of high quality recycled fine aggregate using construction and demolition waste concrete as new fine aggregate for construction industry is urgently required to accomplish the middle and long scaled construction project without failure. In this background, manufacture technology which can produce recycled fine aggregate from construction and demolition waste concrete has been developed already. However, washing method has the problem which poor quality, the environment pollution by washing water, production of micro powder sludge and necessity of expensive additional process for disposing micro powder sludge. On the other hand, heating and trituration method has problem which cost increase according to the establishment of heating equipment and restriction of a large quantity production, etc. So the development of dry manufacture technology of high quality recycled fine aggregate which efficient elimination of micro powder, improvement of productivity and quality and decrease of production cost are possible is urgently required. objective Hence, the ultimate goal of this study is to develop dry process production system of high quality recycled fine aggregate by TS type sorting separator and gravity cyclone for the purpose of solving problem of demand and supply unbalance of construction fine aggregate and environment load. For this, in the second year, it was developed the technologies of pre-treatment, specific gravity separation and a dust collection process, and equipment according to production process of high quality recycled fine aggregate was complemented and improved by deducing for problems and improvement directions of high quality recycled fine aggregate system which was developed in the first year. In addition, problems and improvements of dry process production was deduced through quality evaluation of recycled fine aggregate which was produced in the work of pre-treatment and specific gravity. Eventually, this study developed a production process technology of high quality recycled fine aggregate for increasing productivity. The contents and scope of the study are as follows. For ultimate goal of this study, development of dry process production system of high quality recycled fine aggregate by TS type sorting separator and gravity cyclone, it is to develop high quality recycled fine aggregate production process technology. ? Development of pre-treatment, specific gravity separation, and dust collection process technology ? Development of pre-treatment process technology ? Development of specific gravity separation and dust collection process ? Development and improvement of equipment of high quality recycled fine aggregate by production process for advancing quality ? Deduction of problems and improvement directions of high quality recycled fine aggregate system which was developed in the first year ? Complement and improvement of high quality recycled fine aggregate by production process ? Deduction of Improvement direction of production system by elevating recycled fine aggregate`s quality produced by process ? Quality evaluation of recycled fine aggregate`s produced by pre-treatment and specific gravity separation process ? Deduction of problem and improvement direction of dry manufacturing system The conclusions derived from the present experimental investigation are presented below. The goal of study development in this year, development of production process technology of high quality recycled fine aggregate for increasing productivity, is as follows. 1) Development of pre-treatment, specific gravity separation, and dust collection process technology To produce high quality recycled fine aggregate satisfying with target demand level in this study, pre-treatment`s process technology was developed after analyzing type of crush and sorting equipment, functioning principal and production quantity which is used in the inside and outside of the country. By improving revolution wing of specific gravity separation equipment of High-speed rotation impact type which was developed in 1st year, specific gravity separation technology whose grade, absolute dry density, water absorption ratio are improved was developed. Also by designing and making dust collection equipment and exhaustion filter equipment, the dust collection process technology which is able to collect minute powder produced by specific gravity separation equipment of High-speed rotation impact type and minimize the minute powder into the air was developed 2) Development and improvement of equipment by production process of high quality recycled fine aggregate for advancing quality It is developed dry manufacturing system including pre-treatment process composed crush and sorting equipment, specific gravity separation composed specific gravity separation equipment of High-speed rotation impact type, dust collection process composed centrifugal force minute powder collector, precipitation particle powder collector of sedimentation type and exhaustion filter equipment. Also fine particle separation equipment was established to improve grade of recycled fine aggregate. To prevent clog of exhaustion filter and minimize production of scattering dust, vibrator was established in the of exhaustion filter equipment and capacity of exhaust fan was improved. And minute powder ventilation equipment was established and diameter of minute powder transfer tube was enlarged to enlarge a output increase of minute powder and extend machine service life. 3) Deduction of Improvement direction of production system with evaluating recycled fine aggregate`s quality produced by process With evaluating quality of recycled fine aggregate by process produced in dry manufacturing system which is composed specific gravity separation equipment of High-speed rotation impact type and centrifugal force minute powder collector for high quality of the recycled fine aggregate, it is deduced problem that grade, density and water absorbtion ratio of the recycled fine aggregate. For solving this problem, it is to improve grade of recycled fine aggregate by improving the crush and sorting equipment, specific gravity separation equipment of High-speed rotation impact type and establishing fine particle separation equipment as to improve the crush and separation efficiency of aggregate. And it is to improve absolute dry density and water absorbtion of recycled fine aggregate by improving main body and revolution wing of specific gravity separation equipment of High-speed rotation impact type as to increase exclusion efficiency of mortar adhered in recycled fine aggregate. The application plan and expectative effect of study development results about development of dry process manufacture and production system of high quality recycled fine aggregate using waste concrete are the follow (1) It is possible to decrease environmental pollution by construction waste with reusing waste concrete of substantial amount as fine aggregate for concrete. Specially, it is considered that supplying and demanding imbalance problem for the construction can be solved by using of high quality recycled fine aggregate as fine aggregate for structure concrete (2) Dry process production method of high quality recycled fine aggregate, developing through this study, has more excellent productivity and economic efficiency than existing recycled aggregate production method such as heating trituration and water treatment. Moreover, wash water and sludge were not produced and powder of dry condition which is easy to practical use as secondary product was produced, so it is possible to prevent additional environmental pollution by production of recycled fine aggregate. (3) Recycled fine aggregate production system can be applied to aggregate production field such as powder separation process in producing crushed and river fine aggregate. Also, it is considered that powder, separated in dry condition, can be used various secondary product such as repair material.

순환골재 및 입상 인공Zeolite를 이용한 포러스콘크리트의 해수정화 특성에 관한 연구

김정희 충남대학교 대학원 2008 국내석사

21세기에 들어 지구 온난화 현상에 의한 기상이변의 속출로 환경보존 문제가 인류의 공통과제로 인식되어 감에 따라 전 세계적으로 환경을 배려한 신개념·신기술의 개발이 요구되고 있는 실정이다. 특히, 국내 연안해역의 생태계는 근래에 들어 도시하수, 공장폐수 및 산업폐기물의 바다유입과 무분별한 개발 등으로 해양생태계가 급속하게 훼손되고 있으며, 자연정화 능력이 감소하여 폐쇄성 해역에서 적조, 녹조현상이 빈번히 발생하고 있다. 따라서, 이에 대한 해결방안으로 주변 자연환경과의 조화가 가능하고 투수, 투기, 식생 및 수질정화 등의 환경친화적 기능을 보유한 포러스콘크리트를 해양생태계의 조기복원에 적용할 수 있는 연구?개발이 주목받고 있다. 또한 최근 도시 재개발사업 및 사회기반 시설의 확충 등으로 건설현장에서는 막대한 양의 건설폐기물이 발생되고 있으며, 그 발생량은 매년 증가하는 추세에 있다. 이에 따라 천연골재 자원이 부족한 국내 실정을 감안할 때 자원의 유효이용 및 환경보존 측면에서 대체 골재 자원으로서의 다양한 용도개발 연구가 시급한 실정이다. 따라서 본 연구에서는 건설폐기물인 순환골재의 유효활용 방안 제시와 해수정화용 포러스콘크리트의 현장적용 및 성능향상을 위하여 순환골재 및 입상 인공Zeolite를 이용한 포러스콘크리트의 배합요인별 물리?역학적 특성 검토와 해수정화 특성을 분석하였으며 그 결과를 요약하면 다음과 같다. (1) 해수정화용 포러스콘크리트의 성능향상 요소로 Zeolite를 적용하기 위한 최적입상화 조건은 시멘트분말 5%와 Zeolite분말 95%를 혼합, 성형하는 경우이고 입상 인공Zeolite의 적정 입도는 5mm인 것으로 나타났다. 또한 포러스콘크리트의 배합설계시 목표공극률을 만족시키고 우수한 강도특성을 확보할 수 있는 입상 인공Zeolite의 적정 혼입률은 10%인 것으로 나타났다. (2) 순환골재 및 입상 인공Zeolite를 이용한 해수정화용 포러스콘크리트의 공극률 및 투수계수는 순환골재의 혼입률이 증가함에 따라 다소 증가하는 것으로 나타났으나 그 차이는 미미하였다. 강도특성은 목표공극률 및 순환골재의 혼입률이 증가함에 따라 감소하는 것으로 나타났으며, 보강재료로 유리섬유 및 실리카퓸을 적정량 혼입함으로서 압축강도는 순환골재 혼입률 50%까지, 휨강도는 75%까지 부순돌만을 사용한 경우보다 우수한 강도 특성을 나타내어 순환골재의 유효 활용가능성을 확인할 수 있었다. (3) 순환골재 및 입상 인공Zeolite를 이용한 해수정화용 포러스콘크리트의 알칼리 용출량은 침지 90일에서 목표공극률이 증가함에 따라 최대 11.3%까지 감소되는 것으로 나타났으며 입상 인공Zeolite를 혼입할 경우 3.8~4.8% 정도 저감되는 것으로 확인되었다. 또한 목표공극률이 증가할수록 용존산소 소비량이 증가되는 것으로 나타나 미생물의 배양 및 서식능력이 향상되는 것으로 나타났으며 순환골재의 혼입에 따른 영향은 미비한 것으로 나타났다. (4) 순환골재 및 입상 인공Zeolite를 이용한 포러스콘크리트의 해수정화 특성은 목표공극률이 클수록 콘크리트 내부에 형성되는 비표면적의 증가와 더불어 미생물의 부착량 또한 증가되어 해양미생물의 대사작용에 의한 질소 및 인의 소비정도가 빠른 시간 안에 일어나 총질소(T-N), 총인(T-P)의 제거율이 향상되는 것으로 나타났다. 또한, 입상 인공Zeolite를 혼입함으로서 총질소(T-N) 및 총인(T-P)의 제거효율은 혼입하지 않은 경우에 비하여 15.5~42.9% 정도 향상되는 것으로 나타났고 순환골재의 혼입에 따른 영향은 미미한 것으로 나타났다. (5) 이상의 실험결과로부터 순환골재 및 입상 인공Zeolite를 이용한 포러스콘크리트의 해수정화 특성을 종합하여 보면, 골재를 순환골재로 대체하더라도 적정량의 혼화재료를 혼입하면 물리?역학적 특성 및 해수정화 성능에 효과적임을 확인하였으며, 적정 공극률 및 순환골재의 활용 가능 정도는 각각 20%와 50%인 것으로 판단된다. 또한, 해수정화의 성능향상을 위한 입상 인공Zeolite의 적정 혼입률은 10%인 것으로 판단된다. In the twenty first century there happens climate change caused by global warming so the protection of the earth environment has become humans' urgent task and the whole world try to develop the new environment friendly ideas and technology. Especially, the coastal areas of Korea have had their ecosystem destroyed by the pollution by municipal sewage, industrial wastewaters and solid wastes. Moreover, its natural purification capability has been reduced, causing frequent occurrence of red tide and green algae in closed waters. To overcome this become, a type of concrete needs to be developed that can not create visual harmony with the surrounding natural environment but also water permeability, air permeability, planting and water purification. Also, recently, urban redevelopment programs and expansion of social infrastructure cause massive amount of construction waste in construction cites and the mounts of it keep increasing every year. Considering that South Korea does not possess enough natural aggregate resources, research on various usages of alternative aggregate resources is definitely necessary in terms of valid use of resources and protection of the environment. Therefore, this study aims at searching for application of the field and performance improvement of sea-water purification porous concrete. And this study analyzes sea-water purification properties and physical and mechanical characteristics according to mixing factors of porous concrete of recycled aggregate and granular artificial zeolite. (1) It was thought that the appropriate mixing ratio of cement for the granulation of zeolite powder was approximately 5% and grading was 5mm. Also, the appropriate mixing ratio of granular artificial zeolite for satisfying target void ratio and obtaining excellent strength was approximately 10%. (2) The measurement result of the void ratio and permeability coefficient of the sea-water purification porous concrete using recycled aggregate showed that the void ratio increased as the mixing ratio of the recycled aggregate was increased. The effect according to the mixing ratio of recycled aggregate is insignificant. Also, the strength showed a tendency to decrease as the recycled aggregate mixing ratio and target void ratio was increased. However, by mixing the appropriate amount of glass fiber and silica fume as the admixture in the porous concrete, at the mixing ratio of the recycled aggregate up to 50% the compressive strength of the porous concrete was greater than that of the plain concrete and at the mixing ratio of the recycled aggregate up to 75% the flexural strength was also greater than that of the plain concrete. From this it was found that the recycled waste concrete aggregate could be used effectively. (3) The alkali elution characteristics of the sea-water purification porous concrete using recycled aggregate showed a tendency to 11.3% decrease as target void ratio was increased at 90 days of immersion. when the granular artificial zeolite was mixed, the pH value was reduced by approximately 3.8~4.8% at 90 days of immersion. Also, the dissolved oxygen consumption was increased as the target void ratio was increased, suggesting that the culture and inhabitation ability were greater than before. The effect according to the mixing ratio of recycled aggregate is insignificant. (4) With regard to the change in the T-N and T-P concentrations according to the immersion period, the nitrogen consumption by the metabolism of microorganisms occurred within a short period of time since the amount of attached microorganisms amplified along with the increase in the specific surface area formed inside the concrete as the target void ratio became greater. The T-N and T-P removal performance of the sea-water purification porous concrete into which granular artificial zeolite was mixed was greater than that of the porous concrete with no granular artificial zeolite mixed by approximately 15.5~42.9%. (5) From the above experiment results it is thought that even though the aggregate was replaced with recycled aggregate when making porous concrete for seawater purification, if an appropriate amount of admixture was mixed, the recycled aggregate was effective for the physical and mechanical properties as well as the seawater purification characteristics. It was thought that the appropriate mixing ratio of the recycled aggregate was approximately 50% when the target void ratio was set to 20%. Also, the appropriate mixing ratio of granular artificial zeolite for sea-water purification performance improvement was approximately 10%.

高品質 循環骨材를 使用한 鐵筋콘크리트 보의 長ㆍ短期 構造性能

임승철 충남대학교 2007 국내박사

The construction wastes are increasing due to the increased re-construction and re-development activities along with the continuous growth of domestic construction industry, and this trend will accelerate with various social demands and the desire for improved quality of life. According to a report of the Ministry of Environment of the Republic of Korea, about 100 thousand tons of construction wastes are produced on the daily average and create a serious environmental hazard. Thus, the Republic of Korea recognized the problems of environmental pollution and shortage of aggregate supply and recently stipulated <Proposal for the Legalization of the Promotion for the Recycling of Construction Waste> to mandate the use of recycled aggregate in construction of a specified size. Additionally, the ministry is preparing various policies to promote the use of recycled aggregate in such efforts as easing on the restriction of the volumetric ratio and height of an architectural structure up to 15% by the weight ratio of the construction waste usage to the total quantity of aggregate used in the frame construction of the architecture. However, it is required based on a research to establish a governmental policy on the promotion of the recycled aggregate and to secure the reliability of the short-term and long-term structural performance of recycled aggregate and the steel concrete structural member with recycled aggregate, first of all, in order for the recycled aggregate to be widely used for various structural members in the construction field. Accordingly, this study prepares recycled coarse aggregate and recycled fine aggregate having the quality performance equivalent to natural aggregate for the active use of the concrete with recycled aggregate and evaluates the dynamic performance of the concrete with recycled aggregate so that the quality and reliability of the concrete with recycled aggregate can be established. Additionally, (1) the short-term behavior of the steel concrete member with recycled aggregate such as bending, shear, bonding, and splicing (or coupling) and (2) the long-term behavior due to long-term loading and fatigue loading are analyzed based on this research. This study aims to examine the structural performance of the recycled-aggregate concrete in the actual architecture by comparing the experimental result with the theoretical result from the existing research, standard equations, and prediction equations for the strength and deflection. This research employed three mixtures of concrete - natural coarse aggregate + natural fine aggregate, recycled coarse aggregate (100%) + natural fine aggregate, natural coarse aggregate + natural fine aggregate (50%) + recycled fine aggregate (50%). A total of thirteen test specimens including four specimens for bending test, three specimens for bonding-splicing test, and six specimens for shear test were prepared for the examination of their short-term structural performance. Additionally, three specimens for bending test and three specimens for fatigue test were prepared for long-term structural performance test. The result of experiment on short-term structural behavior revealed that all test specimens of the steel concrete beam reinforced for shear manifested equivalent performance in crack strength, shear strength, and shear bearing capacity. Moreover, they exhibited higher strength than the shear capacity as specified by the ACI code and values of fundamental research. Additionally, as the replacement ratio of the recycled coarse aggregate increases, all test specimens exhibited lower experimental values compared to the calculated, predicted values. The RH30-0.75 specimen of flexural yield-type of steel concrete beam, which replaced 50% of the fine aggregate with recycled fine aggregate, exhibited the diagonal tensile crack propagating deeper into the flexural compressive side and a rapid decline in the strength after reaching the maximum bearing capacity. Additionally, when the experimental values were compared with the predicted values from the equation of ACI code on bending strength, they exhibited 18.5~23.6% higher in bending strength and 23.5~26.3% higher in bonding-slicing strength than the computed values. Thus, the result of examining the short-term structural performance of shear and flexural behavior revealed that the possibility of applying recycled aggregate to a structural member was deemed to be very feasible. The result of a long-term structural behavior test revealed that the CEB-FIP equation for the prediction of long-term deflection such as the creep coefficient and dry shrinkage was more accurate in the prediction of the long-term deflection than the predicted values from ACI 209 equation. Moreover, the equation of ACI 318 code over-estimated the long-term deflection. Meanwhile, Branson, EMM, and AEMM predicted the long-term deflection very well. Especially, AEMM predicted the long-term deflection of the recycled aggregate concrete beam within 1% error so that these prediction equations were also very useful in the rational consideration for the long-term behavior of recycled aggregate concrete structures. When the steel concrete beam with recycled aggregate, which was damaged due to long-term loading, was tested for short-term bending behavior, the experimental values were in the safe side in comparison with the values computed from the ACI standard equation. Thus, it is construed that the applicability of current standard equations are very high in designing of the bending strength for the recycled aggregate concrete beam within the scope of this research. The result of the experiment on fatigue behavior showed that the steel concrete beam with recycled aggregate exhibited a great deal of deflection and various deformations during the initial fatigue loading test than the test specimen with natural aggregate. Moreover, all specimens resulted in a total failure due to the fracture of the steel bar from the repetitive fatigue loading. Thus, it is deemed that additional research on these initial stiffness characteristics, which influence the durability of the concrete structural member with recycled aggregate, is required. Additionally, it was found that the prediction equation on deflection due to fatigue loading as proposed by Balaguru and Shah considered the concrete strength only among the elements of flexural strength reduction and repetitive creep of concrete and did not predict accurately the amount of deflection of the concrete with recycled aggregate due to fatigue loading. Thus, an extensive research on the fatigue behavior characteristics of the recycled aggregate concrete under repetitive stress and the bonding capacity of the concrete member and rebar member of a concrete beam with recycled aggregate during fatigue loading should be conducted. The result of evaluating the dynamic characteristics of the concrete with recycled aggregate and the experimental analyses of the short-term and long-term structural performance of steel concrete beam with recycled aggregate revealed that their behaviors were very similar to the behavior of concrete with natural aggregate as a whole. Accordingly, it is deemed that the application of recycled aggregate of good quality to a steel concrete member is possible within the scope of this research, which satisfied existing specifications on the concrete standard. Nonetheless, it is also deemed that future research, which considers various environmental factors such as freezing-thaw and salt damage during the time period of durability, and the re-establishment of the standards on the performance of the concrete with recycled aggregate should be carried out in order to apply these recycled aggregate widely to actual construction structures.

표면마모방식을 적용한 콘크리트용 순환골재의 품질 개선에 관한 연구

최광윤 대구대학교 대학원 2024 국내박사

본 연구에서는 기존의 크러셔와 같이 파ㆍ분쇄 기계와 차별화된 방법을 제안하여 기존의 문제점으로 제시되고 있는 부착모르타르 및 골재화된 시멘트 모르타르, 그리고 충격으로 인한 골재의 약화(균열)를 방지할 수 있는 기술을 적용하여 고품질 순환골재의 생산기술을 연구ㆍ개발하고자 하였으며, 본 연구에서는 표면마모방식을 적용한 순환골재 생산방식을 제시하고 이를 통하여 생산된 순환굵은골재의 품질시험을 통하여 그 성능을 평가하고 콘크리트에 혼입하여 콘크리트의 특성에 미치는 영향을 실험하였다. 1) 실험에 사용한 순환골재의 부착모르타르 및 골재화된 시멘트 모르타르의 비율을 확인하기 위하여 육안에 의한 분류를 통하여 부착모르타르 및 골재화된 시멘트 모르타르를 4단계로 분류하였으며, 부착모르타르 또는 골재화된 시멘트 모르타르의 비율이 98.4%를 차지하였다. 표면마모를 적용한 결과 본실험에 적용한 Type 1:2, 가동시간 40분에서부터는 확연하게 시멘트 모르타르가 많이 제거되었으며, 시멘트 모르타르가 제거됨에 따라 골재가 서로 붙어 있거나 골재에 시멘트 모르타르가 붙어 있는 것이 골재 본연의 형상과 표면마모에 따른 순환굵은골재의 품질개선 정도를 육안으로 확인할 수 있었다. 또한 순환골재 중 부착모르타르를 육안으로는 찾아볼 수 없는 즉, 골재100%가 표면마모전 1.6%에서 표면마모후 15.1%로 그 비중이 증가하여 표면마모시간이 증가할수록 고품질의 순환골재생산이 가능함을 보여주었다. 2) 본 실험에 사용된 순환굵은골재의 절대건조밀도(평균 2.17g/㎤), 흡수율(평균 6.5%), 안정성(평균 13%), 입자모양판정실적률(평균 52.2%), 0.08㎜체 통과량(평균 0.91%), 골재 입도는 콘크리트용 골재(KS F 2527) 기준에 미달하였으나, 마모율(평균 35%), 점토덩어리량(평균 0.15%), 유기 이물질 , 무기 이물질은 콘크리트용 골재(KS F 2527) 기준을 만족하는 것으로 나타났다. 표면마모를 적용한 결과, 순환굵은골재의 절대건조밀도(평균값 2.54g/㎤, 기존 대비 약 17.1% 증가), 흡수율(평균값 2.82%, 기존 대비 약 56.9% 감소), 안정성(평균값 6.8%, 기존 대비 약 47.7% 증가), 마모율(평균값 25%, 기존 대비 약 28.2% 증가), 입자모양판정실적률(평균값 61.2%, 기존 대비 약 17.2% 향상), 점토덩어리량(평균값 0.09%, 기존 대비 약 40.0% 감소), 0.08㎜체 통과량(평균값은 0.39%, 기존 대비 약 57.1% 감소)은 콘크리트용 골재(KS F 2527) 기준을 만족하는 것으로 나타났다. 3) 콘크리트용 골재(KS F 2527)로 사용하기 위한 순환골재에 부착되어 있는 부착모르타르 및 골재화된 시멘트 모르타르에 관한 KS 기준은 별도로 규정되어 있지 않으나, 기존 많이 시행되고 있는 방법을 준용하여 시험 결과 본 실험에 사용된 순환굵은골재에 부착되어 있는 부착모르타르 및 골재화된 시멘트 모르타르의 양은 평균 약 36.9% 정도인 것으로 측정되었다. 표면마모를 적용한 결과, 순환골재에 부착되어 있는 부착모르타르 및 골재화된 시멘트 모르타르량의 시험을 진행하였으며, 측정 결과, 기존 대비 약 36.3% 정도 부착모르타르 및 골재에 포함된 시멘트 모르타르가 감소한 것으로 나타났다. 4) 표면마모를 적용한 결과, 표면마모를 적용하지 않은 순환굵은골재보다 슬럼프 및 압축강도가 증가하는 것으로 나타났으며, 탄산화 깊이는 감소하는 것으로 나타났다. 본 연구에서는 순환굵은골재의 품질개선을 위해 표면마모방식을 적용하였으며, 실험 결과, 순환굵은골재의 품질이 개선되어 콘크리트용 골재(KS F 2527) 기준을 만족하였으며, 콘크리트의 강도 및 내구성을 개선하는 것으로 나타났다. In this study, we proposed a method differentiated from the wave and pulverization machine like the conventional crusher, and applied the existing problems such as attachment mortar, aggregated cement mortar, and technology to prevent the weakening (cracking) of aggregates due to impact to research and develop a high-quality recycled aggregate production technology. In this study, a circular aggregate method applied with a surface abrasion method was presented, its performance was evaluated through quality tests of the recycled aggregate produced through it, and the effect of mixing it into concrete was tested. 1) In order to confirm the ratio of attached mortar and aggregated cement mortar of recycled aggregates used in the experiment, attached mortar and aggregated cement mortar were classified into four stages through visual classification, and the ratio of attached mortar or aggregated cement mortar accounted for 98.4%. As a result of applying surface wear, a large number of cement mortar was clearly removed from Type 1:2 and 40 minutes of operation time applied to this experiment. As the cement mortar was removed, the aggregate was attached to each other or cement mortar was attached to the aggregate. In addition, it was shown that 100% of the aggregates, which cannot be found with the naked eye, increased their proportion from 1.6% before surface wear to 32.2% after surface wear, enabling the production of high-quality recycled aggregates as the surface wear time increased. 2) The absolute dryness (average 2.17g/㎤), absorption rate (average 6.5%), stability (average 13%), particle shape determination performance rate (average 52.2%), 0.08mm body penetration (0.91% average), and aggregate particle size of the recycled aggregate used in this experiment did not meet the standards of concrete aggregate (KSF 2527), but the wear rate (average 35%), clay mass (average 0.15%), organic and inorganic substances were found to satisfy the standards of concrete aggregate (KSF 2527). According to the application of surface wear, the absolute dryness of the circular solid aggregate (average value of 2.54g/㎤, an increase of about 17.1% compared to the previous one), absorption rate (average value of 2.82%, an increase of about 56.9% compared to the previous one), stability (average value of 6.8%, an increase of about 47.7% compared to the previous one), wear rate (average value of 25%, an increase of about 28.2% compared to the previous one), particle shape determination performance (average value of 61.2%, improvement of about 17.2% compared to the previous one), clay mass amount (average value of 0.09%, decrease of about 40.0% compared to the previous one), and 0.08 mm body passing amount (average value of 0.39% and decrease of about 57.1% compared to the previous one) meet the standard of concrete aggregate (KS F 2527). 3) KS standards for attached mortar and aggregated cement mortar attached to recycled aggregates for use as concrete aggregates (KSF 2527) are not separately specified, but the test results showed that the average amount of attached mortar and aggregated cement mortar attached to the recycled aggregate used in this experiment was about 36.9%. As a result of applying surface wear, the amount of attached mortar and aggregated cement mortar attached to recycled aggregates was tested, and the measurement showed that cement mortar contained in attached mortar and aggregates decreased by about 36.3% compared to the previous one. 4) As a result of applying surface wear, it was found that slump and compressive strength increased compared to circular thick aggregate without surface wear, and the carbonation depth decreased. In this study, the surface wear method was applied to improve the quality of circulating thick aggregates, and as a result of the experiment, the standard of concrete aggregate (KSF 2527) was satisfied by improving the quality of circulating thick aggregates, and it was found to improve the strength and durability of concrete.

지속가능한 건설을 위한 폐콘크리트 자원화 모르타르의 성능 평가

편가현 서울시립대학교 일반대학원 2025 국내석사

본 논문은 현 건설업이 당면한 건설폐기물 발생량 증가 및 천연자원 고갈에 따른 품질 문제, 시멘트 생산 과정의 CO2 발생으로 인한 환경오염에 대처하고자 하였다. 따라서 건설폐기물을 매립하지 않고 자원으로 활용하기 위해 폐콘크리트로부터 생산 혹은 발생하는 순환골재와 슬러지를 건설재료로 사용하여 실험을 진행하였다. 순환골재와 슬러지 각각을 혼입한 모르타르를 타설하여 성능을 검증하고, SEM, XRD, TGA를 통해 미세구조 및 화학적 조성을 분석하였다. 또한 친환경적인 건설재료를 사용함으로써 기대되는 경제성과 환경성을 평가하였다. 첫 번째로, 모르타르에 사용되는 천연강사를 순환골재로 대체한 실험을 진행하였다. 천연골재의 입도 불량을 개선하기 위해 순환골재를 50% 혼입한 모르타르(R5N5)와 입도 기준을 만족하는 순환골재 모르타르(RM)의 성능을 입도가 불량한 천연골재 모르타르(NM)와 비교하였다. 그 결과, 강도 측면에서는 순환골재를 50% 혼입한 모르타르가 가장 우수하였으며, 순환골재만 사용한 모르타르의 강도는 천연골재 모르타르보다 감소하였으나, 그 차이가 미미하였다. 천연골재 모르타르와 순환골재 모르타르의 SEM 이미지를 분석하였을 때, 일반적으로 순환골재 모르타르 또는 콘크리트에서 문제를 유발하는 ITZ의 부착 모르타르가 관찰되지 않았다. 실험 결과로부터 부착 모르타르가 잘 제거된 고품질의 순환골재를 사용할 경우. 골재로 인해 발생하는 성능 저하가 크게 관찰되지 않음을 확인하였다. 두 번째로, 폐콘크리트를 순환골재로 생산하는 과정에서 발생하는 슬러지 케이크를 미분말 상태로 잘 분쇄하여 시멘트 대체재로 활용한 연구를 수행하였다. 슬러지룰 전처리하지 않은 일반 슬러지(PS)와 700도에서 3시간 소성한 전처리 슬러지(CS)를 준비하여 원재료의 화학 조성 및 포졸란 반응성을 확인하였으며, 각 슬러지를 시멘트 중량 대비 5, 10, 15, 20% 치환한 모르타르의 성능을 검증하고자 하였다. 일반 슬러지 모르타르의 경우, 슬러지의 치환율이 증가할수록 강도가 감소한 반면, 소성 슬러지 모르타르의 경우, 15% 혼입율까지 치환율이 증가할수록 강도가 증가하였으며, XRD 및 TGA 분석을 통해 소성 슬러지 모르타르의 포졸란 반응이 일반 슬러지에 비해 원활하게 발생하는 것을 확인하였다. 세 번째로, 슬러지를 건설 현장에 적용하였을 때, 현장 상황을 고려하여 슬러지 케이크의 분쇄 정도를 줄임으로써 전처리를 최소화한 슬러지를 사용하여 실험을 진행하였다. 또한 경제성 및 환경성을 확보하기 위해 슬러지(S*)의 치환율을 0, 20, 40, 60, 80%로 확대하고, 포졸란 재료(P*)를 0, 20, 40% 혼입하였다. 포졸란 재료를 혼입하여 슬러지 치환율 증가에 따른 강도 저하를 일부 개선할 수 있었으며, 포졸란 치환율이 20%일 때 강도 특성이 가장 우수하였다. 각 모르타르의 강도, 경제성, 환경성을 종합적으로 고려하였을 때, 일반 콘크리트 블록 또는 벽돌의 압축강도 기준을 만족하는 S2P2, S4P2, S2P4를 고강도를 필요치 않는 상황에 적용함으로써 절대적 비용 절감 효과 및 환경성을 확보할 수 있을 것으로 보았다. This study aims to address several current challenges in the construction industry, including the increasing volume of construction waste, depletion of natural resources leading to quality concerns, and environmental pollution caused by CO2 emissions during cement production. Therefore, in order to utilize construction waste as a resource rather than disposing of it in landfills, experiments were conducted using recycled aggregates and sludge, both of which are produced or generated from waste concrete, as construction materials. Mortars incorporating either recycled aggregates or sludge were cast to verify their performance, and microstructural and chemical analyses were carried out using SEM, XRD, and TGA. Furthermore, the economic and environmental performance of using these eco-friendly construction materials was evaluated. First, an experiment was conducted to replace the natural fine aggregate used in mortar with recycled aggregate. Mortars with 50% recycled aggregate (R5N5), designed to improve the poor particle size distribution of the natural aggregate, and mortars using only recycled aggregate(RM) that satisfied particle size distribution standards were compared with mortar using poorly graded natural aggregate (NM). The results showed that R5N5 exhibited the highest strength. The strength of RM was slightly lower than that of natural aggregate mortar, the difference was negligible. SEM images of NM and RM revealed no significant presence of adhered mortar at the ITZ(Interfacial transition zone), which typically causes issues in recycled aggregate mortar or concrete. These findings suggest that when high-quality recycled aggregate with well-removed adhered mortar is used, performance degradation attributable to the aggregate itself is minimal. Second, a study was conducted on utilizing sludge cake, generated during the production of recycled aggregate from waste concrete, as a cement substitute after finely grinding it into powder. Two types of sludge were prepared: untreated sludge (Plain Sludge, PS) and sludge pretreated by calcination at 700°C for 3 hours (Calcined Sludge, CS). Following this the chemical composition and pozzolanic reactivity of the raw materials were examined. Mortars were prepared by replacing cement with 5%, 10%, 15%, and 20% of each sludge type to evaluate performance. In the case of PS mortars, compressive strength decreased as the replacement rate increased. Conversely, CS mortars exhibited increased strength up to a 15% replacement rate. XRD and TGA analyses confirmed that pozzolanic reactions occurred more actively in CS mortars than in PS ones. Third, in consideration of on-site application, an experiment was conducted using sludge with lower degree of grinding than the previously tested untreated sludge(PS). To secure economic and environmental performance, the replacement rate of this sludge (S*) was expanded to 0%, 20%, 40%, 60%, and 80%, and pozzolanic materials (P*) were incorporated at 0%, 20%, and 40%. The incorporation of pozzolanic materials partially mitigated the strength reduction associated with increasing sludge replacement, and the best strength performance was observed at a pozzolanic replacement rate of 20%. Considering compressive strength, economic and environmental performance, it was concluded that mortars such as S2P2, S4P2, and S2P4, which met the compressive strength standards for concrete blocks or bricks, could be applied in situations where high strength is not required, thereby achieving cost savings and environmental benefits.

섬유보강 순환골재 콘크리트의 역학적 특성에 관한 연구

신수민 조선대학교 2010 국내석사

The purpose of this study was to examine mechanical and material properties which recycled aggregate and fiber had upon reinforced concrete. This study was initiated to use recycled concrete as a substitutive coarse aggregate of structural concrete. For this, the investigator worked out experimental specimens according to the replacement rate of recycled aggregate (30%, 60%), the kinds of fibers and whether or not fiber-reinforced, and then carried out an experiment of materials and secondary materials. Study findings are as follows. First, the results of age-oriented compressive strength test showed that when the replacement rate of recycled aggregate increased, specimens' age-oriented compressive strength decreased, such as a fiber-reinforced specimen decreasing by about 3.1∼18.4%, a steel fiber-reinforced specimen by about 1.7∼18.5%, a polypropylene fiber-reinforced specimen by about 2.4%∼19.8%, and a structural synthetic fiber reinforced specimen by about 2.3~13.4%. Second, the results of age-oriented splitting tensile strength test showed that when the replacement rate of recycled aggregate increased, specimens' splitting tensile strength decreased, such as a non-reinforced specimen decreasing by about 1.6∼19.5%, a steel fiber-reinforced specimen by about 3.6∼13.0%, a polypropylene fiber-reinforced specimen by about 8.4∼17.1%, and a structural synthetic fiber reinforced specimen by about 1.9∼8.4%. Third, the results of compressive strength test after the experiment of refractoriness showed that specimens' persistence rate of compressive strength increased by refractory temperatures, such as a non-reinforced specimen increasing by about 0.5∼7.7%, and a fiber-reinforced specimen by about 0.1∼15.8%. Fourth, the results of freezing and thawing experiment showed that when the replacement rate of recycled aggregate increased, specimens' relative dynamic modulus of elasticity decreased by about 0.7∼%, whereas comparing to a non-reinforced specimen a steel fiber-reinforced specimen increased by about 0.2∼0.9%, a polypropylene fiber-reinforced specimen by about 0.2∼1.1%, and a structural synthetic fiber reinforced specimen by about 0.1∼0.9%. In particular, the reinforcement of recycled aggregate concrete with fibers seems to change the brittle fracture behavior, a disadvantage point of recycled aggregate concrete, to the ductile fracture behavior. In addition, since the specimen of 30% fiber-reinforced recycled aggregate showed more compressive strength, tensile strength and shear resistance than a standard specimen did, the 30% replacement of recycled aggregate could be applied to actual structures.

순환골재 콘크리트충전 원형 강관기둥의 구속효과 연구

김환진 서울시립대학교 일반대학원 2023 국내석사

Domestic construction waste is increasing every year, accounting for 42.5% of the total waste generation in 2021. Recycled aggregate can be used to reduce the amount of construction waste. Recycled aggregate is an eco-friendly aggregate made by recycling construction waste, and it is a material that can practice carbon neutrality by reducing carbon emissions generated during concrete production. However, the performance of recycled aggregate is lower than that of normal aggregate due to the attached mortar that is not removed during the production process and the micro cracks generated during the crushing process. In addition, the production method of recycled aggregate, the production area, and the characteristics of the parent concrete are complexly affected, resulting in a large deviation in quality. In order to overcome these disadvantages, many studies have been conducted on the performance of recycled aggregate concrete at home and abroad, and methods for improving performance by filling recycled aggregate concrete into steel tube columns has been proposed. However, research on recycled aggregate concrete-filled steel tube columns has not been conducted in Korea, and only in foreign countries, research on recycled aggregate concrete-filled steel tube columns is needed. The great advantage of concrete-filled steel tube columns is that they increase the strength of concrete due to the confinement effect and reduce the local buckling effect of steel tubes. However, since recycled aggregate concrete shows lower performance than normal aggregate concrete and the variation is large, it is necessary to investigate the confinement effect on steel tube columns filled with recycled aggregate concrete. The purpose of this study is to evaluate the confinement effect of a steel tube column filled with recycled aggregate concrete. Through theoretical considerations such as the characteristics of recycled aggregate and the mechanism of confinement effect, the confinement effect of the steel tube column filled with recycled aggregate concrete is analyzed, and the confinement effect is evaluated through experiments. In this study, in order to evaluate the confinement effect of a steel tube column filled with recycled aggregate concrete, nine specimens were produced using the recycled aggregate replacement rate and the diameter of the steel tube as variables. Compression experiments were conducted by loading only the surface of concrete. The confinement effect according to the replacement rate of recycled aggregate and the diameter of the steel tube were analyzed, and the confinement effect was evaluated by comparing with the compressive strength models of confined concrete presented in the past. As a result, the following conclusions were drawn. (1) Concrete was placed according to the replacement rate of recycled aggregate of 0, 25, and 100%, and a compression test was conducted in which the load was applied only to the surface of concrete. The yield strength decreased by 6.4 to 17.2% when replacing 25% of recycled aggregate and by 15.9 to 22.8% when replacing 100% of recycled aggregate. When using 100% recycled aggregate, it is judged that the compressive strength of the test specimen decreased more significantly than the concrete specimen compression test due to the greater contribution of performance degradation and quality variance. (2) In order to evaluate the confinement effect of recycled aggregate concrete-filled steel tube columns according to the replacement rate of recycled aggregate, the ratio of the strength of the concrete cross section and the experimental compressive strength was expressed as a Strength Index and compared. As a result, When 25% of recycled aggregate was replaced, the strength index increased by 0 to 12.9% compared to general aggregate concrete, and when 100% of recycled aggregate was replaced, the strength index decreased by 1.1 to 9.1%. Therefore, the confinement effect did not decrease when 25% of the recycled aggregate was replaced, and the confinement effect decreased due to the performance degradation of the recycled aggregate when 100% was replaced. (3) In order to evaluate the confinement effect of steel tube columns filled with recycled aggregate concrete according to the diameter of the steel tube, the Strength Index according to the diameter of three sizes of steel tubes was compared. As a result, At 25 and 100% recycled aggregate replacement rates, as the diameter of the steel tube increased, the reduction rate of the confinement effect decreased from 4.2% to -0.3% and from 6.7% to 5.7%, respectively. Accordingly, it was confirmed that the size of the steel tube diameter did not affect the confinement effect of the steel tube column filled with recycled aggregate concrete. (4) The strength index of the recycled aggregate concrete-filled steel tube column and the compressive strength prediction model of the confined concrete were compared. In the prediction model of Hatzigeorgiou, Tang, and Yang, the compressive strength of concrete replaced with 100% recycled aggregate is estimated to be 5 to 24% higher. Therefore, when 100% recycled aggregate replacement concrete is used, it is judged that the reduced confinement effect should be applied in consideration of the performance decrease and deviation of recycled aggregate. 국내 건설폐기물은 매년 늘어나는 추세이며 2021년 총 폐기물 발생량의 42.5%를 차지한다. 이러한 건설폐기물 발생량을 줄이기 위해 순환골재를 사용할 수 있다. 순환골재는 건설폐기물을 재활용하여 만드는 친환경 골재이며 콘크리트 생산 시 발생하는 탄소배출량을 줄여 탄소중립을 실천할 수 있는 재료이다. 그러나 순환골재는 생산 과정에서 탈거되지 않은 부착모르타르와 분쇄 과정에서 생기는 미세 균열로 인해 일반골재에 비해 성능이 저하된다. 또한 순환골재의 생산 방법, 생산 지역, 모 콘크리트의 특성 등에 복합적으로 영향을 받아 품질에 큰 편차를 보인다. 이를 극복하기 위해 국내외에서 순환골재 콘크리트의 성능에 대한 많은 연구가 이루어지고 있으며 강관기둥에 충전하여 성능을 개선하는 방법이 제시되었다. 하지만 국내에서는 순환골재 콘크리트충전 강관기둥에 대한 연구가 진행되지 않았으며 해외에서만 일부 진행되어 순환골재 콘크리트충전 강관기둥의 연구가 필요한 실정이다. 콘크리트충전 강관기둥의 큰 이점은 구속효과로 인해 콘크리트의 강도가 상승하며 강관의 국부좌굴 영향을 감소시킨다는 점이다. 그러나 순환골재 콘크리트는 일반골재 콘크리트에 비해 낮은 성능을 보이고 편차가 크기 때문에 순환골재 콘크리트충전 강관기둥에 대한 구속효과에 대한 규명이 필요하다. 본 연구에서는 순환골재 콘크리트충전 강관기둥의 구속효과를 평가하는 것을 목적으로 한다. 순환골재의 특성과 구속효과 매커니즘 등 이론적 고찰을 통해 순환골재 콘크리트충전 강관기둥의 구속효과를 분석하고 실험을 통해 구속효과를 평가한다. 본 연구에서는 순환골재 콘크리트충전 강관기둥의 구속효과를 평가하기 위하여 순환골재 치환율과 강관 직경을 변수로 9개의 실험체를 제작하였고 순환골재 콘크리트의 영향을 평가하기 위해 콘크리트 단면에만 하중을 재하하여 압축실험을 진행하였다. 순환골재 치환율에 따른 구속효과와 강관 직경에 따른 구속효과를 분석하였으며 과거 제시된 구속된 콘크리트의 압축강도 모델들과 비교하여 구속효과를 평가하였다. 그 결과 다음과 같은 결론을 도출하였다. (1) 순환골재 치환율 0, 25, 100% 콘크리트를 타설하여 순환골재 콘크리트충전 강관기둥의 콘크리트 단면에만 하중을 재하한 압축실험을 진행한 결과 순환골재 25% 치환 시 6.4 ~ 17.2%, 순환골재 100% 치환 시 15.9 ~ 22.8%의 내력이 감소하였다. 순환골재 100% 사용 시 성능 저하와 품질의 편차가 더 크게 기여하여 콘크리트 공시체 압축시험보다 실험체의 압축 내력이 더 크게 감소한 것으로 판단된다. (2) 순환골재 치환율에 따른 순환골재 콘크리트충전 강관기둥의 구속효과를 평가하기 위해 콘크리트 단면의 내력과 실험 압축 내력의 비를 Strength Index로 나타내어 비교한 결과 순환골재 25% 치환 시 일반골재 콘크리트 대비 Strength Index가 0 ~ 12.9% 증가하였으며 순환골재 100% 치환 시 Strength Index가 1.1 ~ 9.1% 감소하였다. 따라서 순환골재 25% 치환 시 구속효과가 감소하지 않으며 100% 치환 시 순환골재의 성능 저하로 인해 구속효과가 감소하였다. (3) 강관의 직경에 따른 순환골재 콘크리트충전 강관기둥의 구속효과를 평가하기 위해 세 가지 크기의 강관 직경에 따른 Strength Index를 비교한 결과 순환골재 치환율이 25, 100%에서 강관 직경이 증가함에 따라 구속효과의 감소율이 각각 4.2%에서 –0.3%, 6.7%에서 5.7%로 감소하였다. 이에 강관 직경의 크기는 순환골재 콘크리트충전 강관기둥의 구속효과에 영향을 미치지 않음을 확인하였다. (4) 순환골재 콘크리트충전 강관기둥의 Strength Index와 구속된 콘크리트의 압축강도 예측 모델을 비교하였다. Hatzigeorgiou, Tang, Yang의 예측 모델에서 순환골재 100% 치환 콘크리트의 내력을 5 ~ 24% 크게 평가하고 있다. 따라서 순환골재 100% 치환 콘크리트 사용 시 순환골재의 성능 감소와 편차를 고려하여 감소된 구속효과를 적용해야 할 것으로 판단된다.

순환 굵은골재를 사용한 무세골재 폴리머 콘크리트의 성능 발현 특성

김도헌 동양대학교 2022 국내박사

The purpose of this study was to experimentally investigate the performance characteristics of no-fines polymer concrete using recycled aggregates to promote the sustainability of precast products for infrastructure. The novelty of this study is using combined technologies encompassing previous recycled aggregate concrete, porous concrete, and polymer concrete. The materials used were polymeric binders (unsaturated polyester resins), initiator, cross-linking agents, filler, and mixed aggregates, in which recycled coarse aggregates and crushed coarse aggregates were mixed. Experimental studies were conducted for different contents of polymeric binders because it dramatically affects both the cost-effectiveness and material properties. The main contents of the experiment were nine items: density, absorption, void content, permeable voids, coefficient of permeability, compressive strength, flexural strength, flexural strength after exposure to freeze and thaw cycles, and acid resistance (mass loss by acid attack), all of which showed superior results compared to those of the existing concrete without fine aggregates. Among them, density, void content, permeable voids, coefficient of permeability, compressive strength, and flexural strength were found to be greatly affected by the change in the content of polymeric binder. According to the results of the study, if the content of the polymeric binder is 5.0 to 6.0 wt.%, it was beneficial in cost effectiveness. In addition, although there was no significant difference in the absorption, acid resistance, and flexural strength after exposure to freezing and thawing with respect to the binder content, it was confirmed that it was superior to those of concrete without fine aggregates. The correlations between the density and void content, and permeable voids and coefficient of permeability were found to be linear, while the correlations between the density and compressive strength, and void content and compressive strength were exponential. Compared to previous porous and no-fines concrete using cement or polymer as a binder, the improved strength performance was due to the improvement of adhesion by the addition of cross-linking agents and their excellent surface hydrophobicity. No-fines polymer concrete using recycled coarse aggregates can be useful for eco-friendly precast products such as wall structure and embankments for inclined protection, reinforced earth retaining wall, blocks for river levee, eco-friendly fences and tidal landscape structure, building exterior wall finishes, and sound-absorption panels. 본 연구에서는 순환 굵은골재를 사용한 무세골재 폴리머 콘크리트에 대한 성능 발현 특성을 실험적으로 구명함으로써 사회기반시설용 프리캐스트 제품의 개발에 기여하는 한편, 궁극적으로는 순환골재의 효율적 이용을 통한 부가가치의 증대와 재활용의 촉진을 도모하는데 그 목적이 있다. 그리고 본 연구는 기존의 순환골재 콘크리트, 다공질 콘크리트 및 폴리머 콘크리트 등에 대한 기술이 융합되었다는 점이 특징적이라고 할 수 있다. 사용된 재료는 폴리머 결합재(불포화 폴리에스터 수지), 촉매제, 가교제, 충전재, 그리고 순환 굵은골재와 부순 굵은골재를 섞은 혼합 골재 등이며, 재료비와 성능 발현 측면에서 영향이 가장 큰 폴리머 결합재의 함량을 연구변수로 하였다. 실험의 주요 내용은 밀도, 흡수율, 공극률, 연속공극률, 투수계수, 압축강도, 휨강도, 동결융해 후 휨강도, 내산성 등 9개 항목이며, 이러한 성능들은 기존의 무세골재 콘크리트에 비하여 모두 우수한 결과를 보였다. 이 가운데에서도 특히 밀도, 공극률, 연속공극률, 투수계수, 압축강도, 휨강도는 폴리머 결합재 함량의 변화에 영향을 크게 받는 것으로 나타났다. 연구의 결과를 보면 폴리머 결합재의 함량이 5.0~6.0 wt.%일 경우 경제적 측면에서 유리할 것으로 판단된다. 그리고 흡수율과 동결융해 후 휨강도, 내산성은 결합재 함량에 큰 차이를 보이지 않았지만 기존의 무세골재 시멘트 콘크리트에 비하여 매우 우수함을 확인할 수 있었다. 주요 성능 사이의 상관성을 분석하여 본 결과 밀도와 공극률, 연속공극률과 투수계수는 직선적인 관계, 밀도와 압축강도, 공극률과 압축강도는 지수적인 관계로서 모두가 높은 상관성을 보였다. 시멘트나 폴리머를 결합재로 사용한 기존의 다공성 콘크리트나 무세골재 콘크리트에 비해 강도 관련 성능이 뛰어난 것은 가교제(cross-linking agent)의 첨가에 의한 부착력 향상 때문이고, 흡수성 관련 성능이 우수한 것은 폴리머 자체가 가진 표면 소수성(surface hydrophobicity) 때문인 것이다. 이상에서와 같은 성능 발현 특성을 보면 순환 굵은골재를 사용한 무세골재 폴리머 콘크리트는 ① 경사면 보강용 벽체 및 축대, ② 보강토 옹벽 블록, ③ 하천 호안 블록, ④ 친환경 담장 및 조경제품, ⑤ 건물외벽 마감재, ⑥ 흡음성 패널 등과 같은 사회기반시설용 친환경 프리캐스트 제품용으로서 유용하게 이용될 수 있을 것이다.