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Cheolwoo Park - One of the best experts on this subject based on the ideXlab platform.
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early age behavior of recycled aggregate concrete under steam curing regime
Journal of Cleaner Production, 2017Co-Authors: Zeyu Lu, Asad Hanif, Cheolwoo ParkAbstract:Abstract This study addresses the effects of accelerated hydration in recycled aggregate concrete (RAC) due to the incorporation of High Early Strength Cement (HESC) and employing the steam curing method. The RAC was formulated by the complete replacement of natural aggregates with recycled aggregates. The resulting compressive Strength, elastic modulus, and shrinkage strain results at early-ages were assessed and compared with concretes incorporating natural aggregates and ordinary Portland cement (OPC). By employing steam curing with HESC as binder, 70% of the Design Strength could be achieved in one day, however for the contemporary concretes with OPC as binder, the 1-day Strength was about 60% of Design Strength. With HESC as binder, the change in mechanical properties was found to be minimal after 48 h of casting whereas such change was observed at 72 h age for OPC containing concretes. Utilizing recycled aggregates led to a lower net shrinkage strain indicating improvement against early-age cracking. The cost-benefit analysis showed that for accelerated hydration in concrete, utilizing recycled aggregates leads to lower associated CO 2 emissions at reduced cost. Replacing OPC with HESC improves the resulting early – age properties, but the production cost also increases. The study suggests RAC and HESC are beneficial for concrete elements with larger surface area to depth ratio, like road pavements, floorings, reinforced concrete slabs, and precast elements.
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compressive Strength and resistance to chloride ion penetration and carbonation of recycled aggregate concrete with varying amount of fly ash and fine recycled aggregate
Waste Management, 2011Co-Authors: Cheolwoo ParkAbstract:Construction and demolition waste has been dramatically increased in the last decade, and social and environmental concerns on the recycling have consequently been increased. Recent technology has greatly improved the recycling process for waste concrete. This study investigates the fundamental characteristics of concrete using recycled concrete aggregate (RCA) for its application to structural concrete members. The specimens used 100% coarse RCA, various replacement levels of natural aggregate with fine RCA, and several levels of fly ash addition. Compressive Strength of mortar and concrete which used RCA gradually decreased as the amount of the recycled materials increased. Regardless of curing conditions and fly ash addition, the 28 days Strength of the recycled aggregate concrete was greater than the Design Strength, 40 MPa, with a complete replacement of coarse aggregate and a replacement level of natural fine aggregate by fine RCA up to 60%. The recycled aggregate concrete achieved sufficient resistance to the chloride ion penetration. The measured carbonation depth did not indicate a clear relationship to the fine RCA replacement ratio but the recycled aggregate concrete could also attain adequate carbonation resistance. Based on the results from the experimental investigations, it is believed that the recycled aggregate concrete can be successfully applied to structural concrete members.
Asad Hanif - One of the best experts on this subject based on the ideXlab platform.
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early age behavior of recycled aggregate concrete under steam curing regime
Journal of Cleaner Production, 2017Co-Authors: Zeyu Lu, Asad Hanif, Cheolwoo ParkAbstract:Abstract This study addresses the effects of accelerated hydration in recycled aggregate concrete (RAC) due to the incorporation of High Early Strength Cement (HESC) and employing the steam curing method. The RAC was formulated by the complete replacement of natural aggregates with recycled aggregates. The resulting compressive Strength, elastic modulus, and shrinkage strain results at early-ages were assessed and compared with concretes incorporating natural aggregates and ordinary Portland cement (OPC). By employing steam curing with HESC as binder, 70% of the Design Strength could be achieved in one day, however for the contemporary concretes with OPC as binder, the 1-day Strength was about 60% of Design Strength. With HESC as binder, the change in mechanical properties was found to be minimal after 48 h of casting whereas such change was observed at 72 h age for OPC containing concretes. Utilizing recycled aggregates led to a lower net shrinkage strain indicating improvement against early-age cracking. The cost-benefit analysis showed that for accelerated hydration in concrete, utilizing recycled aggregates leads to lower associated CO 2 emissions at reduced cost. Replacing OPC with HESC improves the resulting early – age properties, but the production cost also increases. The study suggests RAC and HESC are beneficial for concrete elements with larger surface area to depth ratio, like road pavements, floorings, reinforced concrete slabs, and precast elements.
Erhan Guneyisi - One of the best experts on this subject based on the ideXlab platform.
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Strength permeability and shrinkage cracking of silica fume and metakaolin concretes
Construction and Building Materials, 2012Co-Authors: Erhan Guneyisi, Mehmet Gesoglu, Seda Karaoglu, Kasim MermerdasAbstract:Abstract Using mineral admixtures as cement replacement substance in concrete has a tendency to increase by the future in order to provide greater sustainability in construction industry. This paper investigates the effectiveness of metakaolin (MK) and silica fume (SF) on the mechanical properties, shrinkage, and permeability related to durability of high performance concretes. Mechanical properties were evaluated by means of compressive and splitting tensile Strength. Water sorptivity and gas permeability tests were carried out to find out the permeation characteristics of the concretes due to the incorporation of MK and SF. Shrinkage behavior of the concretes with and without mineral admixtures were dealt through measurements of free shrinkage strains and weight loss of the specimens due to drying. Moreover, crack formation and propagation of the restrained specimens were observed to better understanding the effect of MK or SF incorporation on the restrained shrinkage properties. For concrete production, replacement levels of 5% and 15% of MK or SF by the weight of cement were assigned. Water-to-cementitious (w/cm) material ratios of 0.25 and 0.35 were used in production of concrete. The Design Strength level ranging from75 to 86 MPa was achieved. Test results revealed that replacement level of MK and SF had significant effects on the mechanical and especially durability characteristics of high performance concretes.
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effects of end conditions on compressive Strength and static elastic modulus of very high Strength concrete
Cement and Concrete Research, 2002Co-Authors: Mehmet Gesoǧlu, Erhan Guneyisi, Turan OzturanAbstract:Abstract The use of bonded and unbonded caps in testing very high Strength concrete cylinders has been investigated experimentally. A hundred and ninety-two concrete cylinder specimens of 150-mm diameter and 300-mm height were cast and tested using packing with softboard, neat cement paste, neoprene pad and sulfur mortar. The Design Strength level of 75–100 MPa was achieved using water-cementitious material ratios of 0.22, 0.26 and 0.31. The results of the study were compared considering compressive Strength and static elastic moduli values. A two-way analysis of variance was performed at a .01 level of significance in order to compare the effect of end conditions. It was found that the overall mean compressive Strengths of specimens capped with neat cement paste, neoprene pad sulfur mortar were not significantly different. The packed specimens exhibited a significant difference from the others. On the other hand, there was no statistical difference in the static elastic moduli values when different capping types were used. Several modulus prediction equations were also examined. Experimental values were consistently higher than the predicted values.
Megat Azmi Megat Johari - One of the best experts on this subject based on the ideXlab platform.
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evaluation of ultra high performance fiber reinforced concrete binder content using the response surface method
Materials & Design, 2013Co-Authors: M A A Aldahdooh, Muhamad N Bunnori, Megat Azmi Megat JohariAbstract:Abstract One of the major disadvantages in ultra-high-performance-fiber reinforced concrete (UHP-FRC) is its high ordinary Portland cement (OPC) content, which directly translates into an increase in OPC production. More OPC production results in increased emission of greenhouse gases, as well increased electrical energy consumption and concrete price. This study is aimed at adjusting the binder content (OPC and silica fume (SF) contents) of UHP-FRC using the response surface method. The present investigation shows that, for a given water/binder and superplasticizer/OPC, the compressive Strength is independent of the binder content, whereas the flow depends on the binder content. Increasing the binder content does not enhance the Strength compared with the required Design Strength because the capillary porosity increases with increasing OPC content; however, the workability increases. The final result is the production of a UHP-FRC with an OPC content of 720.49 kg/m 3 , an SF content of 214.25 kg/m 3 , a compressive Strength of 181.41 MPa, a direct tensile Strength of 12.49 MPa, a bending tensile Strength of 30.31 MPa, and a flow of 167 mm.
Ben Young - One of the best experts on this subject based on the ideXlab platform.
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material properties and structural behavior of cold formed steel elliptical hollow section stub columns
Thin-walled Structures, 2019Co-Authors: Mantai Chen, Ben YoungAbstract:Abstract Material properties, residual stress distributions and cross-sectional behavior of cold-formed steel elliptical hollow sections are investigated in this study. Four cross-section series with the nominal section aspect ratio ranging from 1.65 to 3 were included in the experimental investigation. The material properties for each cross-section series and material properties distribution on half of the cross-section profile of a representative section were measured through tensile coupon tests. The distributions of bending and membrane residual stresses in both longitudinal and transverse directions were measured on the half-section profile of the same representative section. Initial local geometric imperfections were measured on five stub column specimens. Besides, stub column tests were conducted between fixed ends to ascertain the material properties of the complete cross-section in the cold-worked state as well as to study the structural behavior of cold-formed steel elliptical hollow section stub columns. In addition to experimental investigation, a finite element model was developed and verified against the test results, with which an extensive parametric study covering a broad range of cross-section geometries was carried out. Currently, there is no codified Design rule for elliptical hollow section compression members. The stub column Strengths obtained from experimental program and numerical analysis were only compared with the predicted Strengths by the equivalent diameter method and equivalent rectangular hollow section approach proposed by previous researchers for Design of hot-finished steel elliptical hollow sections, the existing traditional Design rules originally developed for circular hollow section with equivalent diameter incorporated as well as the Direct Strength Method and the Continuous Strength Method that the equations were not calibrated for cold-formed steel elliptical hollow sections. The comparisons show that the Direct Strength Method offers the most accurate and reliable Design Strength predictions among the existing Design methods, but further improvement remains possible. In this study, modifications on the Direct Strength Method and the Continuous Strength Method are proposed, which are shown to improve the accuracy of the Design Strength predictions.
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experimental study of ferritic stainless steel tubular beam column members subjected to unequal end moments
Journal of Structural Engineering-asce, 2016Co-Authors: Ou Zhao, Leroy Gardner, Ben YoungAbstract:AbstractThis paper presents a comprehensive experimental study of the buckling behavior of ferritic stainless steel tubular section beam-column structural members subjected to unequal end moments. Testing was carried out on two cold-formed and seam-welded cross sections—one rectangular hollow section (RHS) 100×40×2 and one square hollow section (SHS) 60×60×3 made of grade AISI 410 (EN 1.4003) stainless steel. The experimental investigation included a series of material tensile coupon tests, initial local and global geometric imperfection measurements and 24 beam-column tests under unequal end moments. The experimental setup and procedures are described, and the test observations, including the key test results, the load-deformation histories, and the failure modes, are fully reported. The experimental results were carefully analyzed and then compared with the Design Strength predictions determined according to the current European code, American specification, and Australian/New Zealand standard for stain...