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Stripping of aggregate from mortar in waste concrete heated by microwave:Mechanisms of differential-temperature stress and vapor expansion pressure

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Journal of Traffic and Transportation Engineering(English Edition) 2024年第3期11卷 538-558页

作者： Yanping Sheng Xiao Huan Peizhen Hu Liangliang Li Ahmed Abdulakeem Zhoujing Ye Linbing Wang Yanping Yin School of Materials Science and Engineering Chang'an UniversityXi'an 710064China Engineering Research Center of Transportation Materials Ministry of EducationChang'an UniversityXi'an 710064China National Center for Materials Service Safety University of Science and Technology BeijingBeijing 100083China School of Environmental CivilAgricultural and Mechanical EngineeringCollege of EngineeringUniversity of GeorgiaAthensGA 30602USA

Microwave heating,which is used for pre-treatment of concrete before it is comminuted,stands as a strong candidate for selective liberation of multiphase materials like concrete.This paper is concerned with the selective liberation of concrete's raw constituents(particularly aggregate)for recycling by considering the water content of concrete as a parameter of microwave heating for the first time.The deterioration law of the concrete's performance was characterized by the variation in the splitting tensile strength and relative dynamic modulus after heating by microwave at different water contents.Besides,tests were conducted to evaluate the performance of the interface transition zone(ITZ)between aggregate and mortar as well as to investigate the reasons for the stripping behavior of aggregate-mortar,which included the interface tensile strength test,temperature measurement,and porosity test.The deterioration law of splitting tensile strength and relative dynamic modulus revealed that the performance of concrete was subject to different degrees of damage depending on the water content.Furthermore,experimental results showed that interface bonding strength between aggregate and mortar was dramatically impaired,and a large temperature difference was generated between the aggregate and mortar during microwave heating.Meanwhile,the permeable pores increased considerably even when the specimens were dried.In the presence of water,the intactness of ITZ between aggregate and mortar was destroyed by microwave heating,and its performance was significantly lowered,which led to the occurrence of stripping behavior between aggregate and mortar.This was reaffirmed by the microstructure presented by scanning electron microscopy.Thus,the newly developed microwave pretreatment improved by providing appropriate water contents for concrete corresponding to different strength grades is a promising method for recycling aggregate from waste concrete.

关键词： Waste concrete recycled aggregate Microwave heating Stripping behavior Differential-temperature stress Vapor expansion pressure

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Comparative carbon emission assessments of recycled and natural aggregate concrete: Environmental influence of cement content

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Geoscience Frontiers 2021年第6期12卷 66-75页

作者： Marian Sabǎu Dan V.Bompa Luis F.O.Silva Department of Civil and Environmental Engineering Universidad de la Costa080020 BarranquillaColombia Department of Civil and Environmental Engineering University of SurreyGuildford GU27XHUK Departamento de Ingeniería Civil y Arquitectura Universidad de LimaAvenida Javier Prado Este 4600Santiago de Surco 1503Peru

This work examines the environmental and geochemical impact of recycled aggregate concrete production with properties representative for structural applications.The environmental influence of cement content,aggregate production,transportation,and waste landfilling is analysed by undertaking a life cycle assessment and considering a life cycle inventory largely specific for the region.To obtain a detailed insight into the optimum life cycle parameters,a sensitivity study is carried out in which supplementary cementitious materials,different values of natural-to-recycled aggregate content ratio and case-specific transportation distances were considered.The results show that carbon emissions were between 323 and 332 kgCO_(2)e per cubic metre of cement only natural aggregate concrete.These values can be reduced by up to 17%by replacing 25%of the cement with fly ash.By contrast,carbon emissions can increase when natural coarse aggregates are replaced by recycled aggregates in proportions of 50%and 100%,and transportation is not included in analysis.However,the concrete with 50%recycled aggregate presented lower increase,only 0.3%and 3.4%for normal and high strength concrete,respectively.In some cases,the relative contribution of transportation to the total carbon emissions increased when cement was replaced by fly ash in proportions of 25%,and case-specific transportation distances were considered.In absolute values,the concrete mixes with 100%recycled aggregates and 25%fly ash had lower carbon emissions than concrete with cement and natural aggregates only.Higher environmental benefits can be obtained when the transportation distances of fly ash are relatively short(15–25 km)and the cement replacement by fly ash is equal or higher than 25%,considering that the mechanical properties are adequate for practical application.The observations from this paper show that recycled aggregate concrete with strength characteristics representative for structural members can have lower carbon emissions than conventional concrete,re

关键词： Life cycle assessment recycled aggregate Natural aggregate Transportation distance OpenLCA

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Effects of recycled aggregate Content on Pervious Concrete Performance

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Journal of Renewable Materials 2020年第12期8卷 1711-1727页

作者： Lei Guo Zi Guan Lixia Guo Weiping Shen Zhilong Xue Pingping Chen Mingru Li School of Water Conservancy North China University of Water Resources and Electric PowerZhengzhou450046China Henan Water Valley Research Institute Zhengzhou450046China Henan Key Laboratory of Water Environment Simulation and Treatment Zhengzhou450002China

A recycled aggregate(RA)was prepared by crushing and sieving demolished discarded concrete pavements and was subsequently tested and analyzed to determine its various physical properties.On this basis,pervious concrete(PC)mix proportions were designed.Coarse RA particles with sizes of 5–10 and 10–20 mm were selected.Concrete specimens were prepared with a water–cement ratio of 0.3,an aggregate–cement ratio of 4.5,the substitute rates of RA with 0,25%,50%,75%and a single-/double-gap-graded RA mix(mass ratio of particles with sizes of 5–10 mm to particles with sizes of 10–20 mm:1:1,1:2,2:1,2:3 and 3:2).Various properties of the RA-containing PC(RPC)were determined by analyzing the compressive strength,splitting tensile strength,effective porosity,permeation coefficient and impact and abrasion resistance of the specimens.The results showed the following:The density of the RPC decreased with an increasing RA replacement ratio.The density of the RPC prepared with a double-gapgraded RA mix was lower than that prepared with a single-gap-graded RA(particle size:10–20 mm)mix.The permeation coefficient of the RPC increased with increasing porosity.The splitting tensile strength of the RPC was positively correlated with its compressive strength.The compressive strength of the RPC decreased with increasing porosity.The regression analysis showed that the impact and abrasion resistance of the RPC increased with increasing compressive strength.In addition,all of the RPC specimens met the strength and permeation requirements.This study can provide theoretical support for the application of RPC.

关键词： recycled aggregate recycled pervious concrete strength permeability wear resistance mix proportion

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Effects of Polypropylene Fibers on the Physical and Mechanical Properties of recycled aggregate Concrete

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Journal of Wuhan University of Technology(Materials Science) 2019年第6期34卷 1327-1344页

作者： Pierre Matar Gérard-Philippe Zéhil Lebanese University Faculty of EngineeringBranch 2RoumiehLebanon Notre Dame University-Louaize Faculty of EngineeringZouk MosbehLebanon

The viability of using polypropylene fibers(PPF) in concrete was largely studied. Yet, few of the existing research studies investigated the effects of PPF on the properties of concrete containing recycled concrete aggregate(RCA). Mixes with different RCA replacement ratios and different PPF content were designed and tested. The test results showed that the addition of PPF did not change significantly the compressive strength and the density of the concrete, but slightly decreased its modulus of elasticity and Poisson’s ratio. The drop in the splitting tensile strength and the flexural strength due to RCA inclusions was to a large extent compensated by the PPF addition. The water absorption decreased and the percent voids increased with increased PPF addition. Correlations between the RCA content, the PPF content and the properties of concrete were studied. Useful regression models were proposed to predict the properties of concrete in relevant ranges of RCA and PPF content.

关键词： concrete recycled aggregate fiber reinforcement physical properties mechanical properties

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Test Study on the recycled aggregate and Concrete Regenerated from Worn Cement Concrete Pavement

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武汉理工大学学报 2010年第17期32卷 241-245页

作者： DONG Y HE W Z Faculty of Architecture and Civil Engineering of Huaiyin Institute of Technology Huaiyin 223001China

Regenerate utilization of worn cement concrete is the key technical problem to be solved in traffic field while the cement concrete pavement built long ago durative disrepair. The study aimed at the worn cement concrete which can not be reused in site,get recycled aggregate according to the practically technics of regenerate,and then carry out test study on the aggregate and recycle aggregate cement concrete. Test results show recycled fine aggregate is about 26% of recycled aggregate,and substantive sand pulps are adhere on the surface of recycled while the distinct crackle appears on this sand pulp surface. relative to the natural aggregate,one of the remarkable characters of the recycled aggregate is that the inartificial water ratio is relatively low and the water-absorbing ratio can reach 4%～12%,and the water-absorbing ratio increased while the grain getting fine. the second remarkable characters of recycled coarse aggregate is that the weared stone value and crushed stone value of recycled coarse aggregate are both bigger,the Los-angeles weared stone value is 32.7,the crushed stone value is 26.5. So,the recycled aggregate can not meet the criterion,but after mixed into 40% natural aggregate,it can meet. The mixture ratio test results proved that based on the dosage of cement we can through reduce water cement ratio and augment water quantity to improve the working performance of recycled concrete. The destroy form of recycled concrete goes all the way with natural concrete,the recycled aggregate can absolutely used in cement concrete under C50.

关键词： cement concrete pavement recycled aggregate gradation weared stone value crushed stone value water cement ratio

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Feasibility Study of Applying recycled aggregate from Building Debris in Concrete

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沈阳建筑大学学报（自然科学版） 2011年第6期27卷 1137-1145页

作者：彭予柱 Taiwan Hospitality and Tourism College

Coarse and fine aggregate constitutes an average of approximately 55% to 80% of the total volume of concrete materials.Concrete remains the most commonly-used building material worldwide.As a result,the massive use of aggregate will have a direct impact on the earth′s natural resources if an appropriate replacement material is not found,violating the spirit of sustainable development.This study makes a preliminary examination of using coarse and fine aggregate produced from discarded construction materials in concrete.Results indicate that the compressive strength of densified mixture concrete at 28 days can reach 56.88 MPa(recycled materials used as coarse aggregate,and natural sand used as fine aggregate)and 53.33 MPa(recycled materials used as both coarse and fine aggregate).While this type of material is not yet fully understood,further research into this area should enable feasible applications in concrete.However,unsuitable mixtures have serious impact on the durability and overall economy of concrete.Pending further research on suitable mixture designs,a complete application of recycled aggregate in concrete can be expected.

关键词： sustainable development construction waste materials recycled aggregate densified mixture

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The Experimental Research on Durability of recycled aggregate Concrete

The Experimental Research on Durability of Recycled Aggregat...

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2010年建筑环境科学与技术国际学术会议

作者： KITATSUJI Masa-humi TANAKA Rei-ji Miyagi University Faculty of Engineering Tohoku Institute of Technology

＜正＞Eco-cement recycled aggregate concrete was fabricated with low absorption recycled aggregate,eco-cement and portland cement,as one of effective methods to use solid waste,and durability experiment was carried out.It was concluded that eco-cement recycled concrete expressed almost the same performance compared with portland cement concrete,and it was also judged that it was possible for eco-cement to use in recycled aggregate concrete.

关键词： recycled aggregate durability eco-cememt solid waste

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Properties of recycled aggregate Concrete by Two-Stage Mixing Approach

Properties of Recycled Aggregate Concrete by Two-Stage Mixin...

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首届全国再生混凝土研究与应用学术交流会

作者： V.W.Y.Tam D.Kotrayothar F.N.Neser C.Y.Lo Griffith School of Eng. Griffith UniversityAustraliaPMB 50 Gold Coast Mail Centre Griffith School of Eng. Griffith University Australia PMB 50 Gold Coast Mail Centre

＜正＞A two-stage mixing approach（TSMA）was developed to improve the quality of recycled aggregate concrete（RAC）.It has been established that this new method can produce concrete with strength of up to 70 MPa. This paper examines compressive strength of RAC manufactured using RA from local centralized recycling plant in SEQ.aggregate properties are tested and compared between RA and natural aggregate（NA）.The RA sample collected has a high water absorption rate of about 5.67%,while water absorption of NA is relating low of about 0.59%.Due to weak mortar surrounding RA,its aggregate crushing value（ACV）is about 42.8% larger than that of NA.A comparison with the strength data from concrete made of the same ingredients but produced using the standard mixing approach（$MA）confirms the superiority of the TSMA.It is conclusive that RA manufactures inferior concrete strength to NA concrete.A 100% replacement of NA with RA deteriorated the 28-day strength of concrete by up to 10.8% in compressive strength.The optimal RAC mixture design would be about 20% of RA replacement,since it produced superior 28-day strengths compared to other RAC designs in most concrete strength departments,and achieved these results for both the SMA and TSMA.The strength of RAC can be improved by implementing the TSMA,with overall 28-day strength improvements of up to 4.3%.

关键词： recycled aggregate recycled aggregate concrete compressive strength tensile strength modulus of elasticity

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The applied research on centrifugation confectioning product fetched recycled aggregate

The applied research on centrifugation confectioning product...

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首届全国再生混凝土研究与应用学术交流会

作者： KITATSUJI Masafumi Miyagi University

＜正＞Based on viewpoint of constructing circular form society in future,recycled aggregate is positively used.While it is difficulty to apply,because high strength of recycled aggregate fetched from utility pole of precast concrete product and so on,small maximum particle size of aggregate, more aggregate absorbed cement mortar and contained AE water reducing agent,drying shrinkage of recycled concrete,low ability of resisting cycle of freezing and thawing. Expanding agent is used,and alkali-aggregate reaction is depressed used B blast-furnace slag cement and recycled aggregate of low water absorption.It is expected to produce design strength 30 MPa performing concrete product. The results of this paper indicate that the property strength and durability of recycled aggregate concrete is almost the same or a little higher than common concrete,and it is judged possibly to use recycled aggregate in performing concrete product.

关键词： pole recycled aggregate precast concrete product strength resistance of freezing and thawing

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Experimental Evaluating of the Physical, Mechanical and Durability Properties of Natural, recycled and Both Combined aggregates Based Concretes

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Materials Sciences and Applications 2023年第3期14卷 117-141页

作者： Etienne Malbila Arba A.T. Ouedraogo Nicolas Kagambega Gilbert G. Nana Sié Kam David Y. K. Toguyeni Ecole Supérieure d’Ingénierie (ESI) Université de Fada N’Gourma (UFDG) Fada-N’Gourma Burkina Faso Laboratoire d’Energies Thermiques Renouvelables (LETRE) Université Joseph KI ZERBO Ouagadougou Burkina Faso Laboratoire de Géosciences et Environnement (LaGE) Université Joseph KI ZERBO Ouagadougou Burkina Faso Laboratoire de Physique et Chimie de l’Environnement (LPCE) Université Joseph KI ZERBO Ouagadougou Burkina Faso Ecole Polytechnique de Ouagadougou (EPO) Ouagadougou Burkina Faso

This experimental study aims at the reuse of recycled aggregates (RA), resulting from the demolition of concrete, cement block and cement mortar, in the manufacture of common construction in Burkina Faso. The RA can readily replace natural aggregates in concrete. Then five formulations of natural and recycled aggregates based concrete for characteristic strength of 25 Mpa were prepared in addition to the natural aggregates base concrete named reference concrete (BN): two types of recycled aggregates concrete (BR), three types of recycles and natural combined aggregates base concrete (BC). The properties of natural and recycled aggregates were characterized and the physical, mechanical strength and durability properties were also evaluated for all concrete specimens. All the studied concrete formulation present a density between 2000 kg/m3 ≤ ρ ≥ 2600 kg/m3 and an average slump of 4.9 ± 0.1 cm. The obtained results indicate that the recycled aggregates are suitable for current concrete. Two out of the five combinations studied, such as the natural (BN) and combined aggregate (BC2) based concretes satisfy the mechanical characteristics (Rc28 > 25 MPa) at 28 days of age and an average absorption coefficient of 2.93% and 3.98%. The recycled aggregate based concrete (BR1, BR2) and combined aggregate based concrete (BC1), gave respective average compressive strength of 21.55 MPa, 20.50 MPa and 20.30 MPa, i.e. a difference of 13.80% to 18.80% under the characteristic strength (25 MPa) aimed at 28 days of age. Thus, the recycled aggregates are in conformity with the normative prescriptions and their use for standard concrete gives adequate physical, mechanical and durability properties for the production of the C20/25 concrete series in the common civil engineering applications.

关键词： Concrete Demolition Waste aggregate recycled aggregate Strength Water Absorption

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