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 r...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/m<sup>3</sup> ≤ ρ ≥ 2600 kg/m<sup>3</sup> 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 (Rc<sub>28</sub> > 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.展开更多
The feasibility of using different generations of recycled fine aggregate(RFA) in structural concrete in a chloride environment was evaluated by studying the performance of the RFA and the corresponding concrete. Th...The feasibility of using different generations of recycled fine aggregate(RFA) in structural concrete in a chloride environment was evaluated by studying the performance of the RFA and the corresponding concrete. The different generations of RFA were recycled by following the cycle of ‘concrete-waste concrete-fine aggregate-concrete'. The properties of three generations of repeatedly recycled fine aggregate(RRFA) were systematically investigated, and we focused on the compressive strength and splitting tensile strength and chloride ion permeability of the related structural concretes with 25%, 75%, and 100% replacement of natural fine aggregates with RFA. The results indicated that the quality of RRFA presents a trend of slow deterioration, but the overall performance of all RRFA still fulfils the quality requirements of recycled fine aggregate for structural concrete. All RRFA concretes achieved the target compressive strength of 40 MPa after 28 days except for the second generation of the recycled aggregate concrete and the third generation of the recycled aggregate concrete with 100% replacement, and all the concrete mixes achieved the target compressive strength after 90 days. The insights obtained in this study demonstrate the feasibility of using at least three generations of RRFA for the production of normal structural concrete with a design service life of 100 years in a chloride environment.展开更多
In 2007,over 24 million tons of Construction and Demolition(C&D) wastes were generated in Hong Kong.Since the local landfills will be saturated in about 6 years,it is important to find a viable way to reuse these ...In 2007,over 24 million tons of Construction and Demolition(C&D) wastes were generated in Hong Kong.Since the local landfills will be saturated in about 6 years,it is important to find a viable way to reuse these waste materials as to alleviate the demand on public fill capacity.In order to tackle the problem,the Hong Kong government has set up a temporary recycling facility in Hong Kong in 2002 for producing different sizes of recycled aggregate for use in various construction materials.The Hong Kong Polytechnic University has been studying the feasible use of recycled aggregates in Hong Kong for a number of years.A substantial amount of experimental results on the properties of recycled aggregates and the effect of recycled aggregates on the properties of concrete and other construction products(e.g.concrete blocks and granular sub-base) has been published.In this paper,the experience of Hong Kong in using recycled aggregates are summarized and a set of quality control guidelines proposed for governing the use of recycled aggregates in Hong Kong is introduced.The experience and guidelines may also be useful for the recycling of waste materials derived from the recent Sichuan earthquake in China.展开更多
The failure characteristics of recycled concrete containing brick aggregates are still indistinct,especially how the angular aggregates effect the crack propagation.Based on the concept of modeled concrete,the develop...The failure characteristics of recycled concrete containing brick aggregates are still indistinct,especially how the angular aggregates effect the crack propagation.Based on the concept of modeled concrete,the development of cracks in concrete containing the natural aggregate and brick aggregate under a compression loading was studied.The strain distribution was analyzed with the Digital Image Correlation(DIC).The modeled aggregates include circular and squared ones,and the squared modeled aggregates were placed in different orientations,including 0°,22.5°and 45°.The results show that when the aggregate is placed at 45°,the upper and lower vertices of the aggregate lead to the highest critical strain concentration,therefore,cracks are easy to propagate from these areas and the strength of the corresponding modeled concrete is the lowest.When the modeled natural aggregate is placed at the orientation of 0°,the strain concentration first appears at the interface on both lateral sides of the aggregate.The brick aggregate has a lower elastic modulus and strength than the surrounding mortar.As a result,cracks always propagate through the brick aggregate,which is the primary reason for the low strength of the corresponding concrete.展开更多
In some cases of emergency backfill engineering projects, traditional backfill materials cannot meet the requirements of fast construction due to their long curing time. This study presents a new kind of rapid hardeni...In some cases of emergency backfill engineering projects, traditional backfill materials cannot meet the requirements of fast construction due to their long curing time. This study presents a new kind of rapid hardening controlled low strength material, which utilizes both rapid hardening sulphoaluminate cement and recycled fine aggregate from urban red brick construction waste. Totally, sixteen mixtures were prepared for the experiment with different cement-to-sand ratios and water-to-solid ratios. The flowability and bleeding rate of fresh mixture were measured to evaluate its workability, and the compressive strength of hardened mixture was tested to evaluate its rapid hardening and mechanical properties. Test results indicate that rapid hardening controlled low strength material containing recycled fine aggregate from urban red brick construction waste can achieve the desirable flowability, but the bleeding rate increases with the increase of flowability. In addition, 2-hour compressive strength can reach 0.08 - 0.12 MPa, and 4-hour compressive strength is 0.32 - 1.54 MPa, which can meet the requirements of emergency backfill construction. At last, based on the derived compressive strength, a fitting model for predicting compressive strength evolution of this new rapid hardening backfill material is developed, which fits accurately with these experimental data.展开更多
In an earlier study, a comprehensive and critical review of previous investigations into the assessment of the strength of concrete incorporating aggregates from demolished wastes was conducted and it was concluded th...In an earlier study, a comprehensive and critical review of previous investigations into the assessment of the strength of concrete incorporating aggregates from demolished wastes was conducted and it was concluded that there was a stark absence of results from the South African sub-continent including Botswana. In the present study, recycled coarse aggregates (RCA) sourced from demolished wastes collected from a landfill site in Gaborone, Botswana was used in lieu of natural coarse aggregates for the manufacture of concrete. With reference to the natural coarse aggregate, RCA replacement levels of 0%, 20%, 40%, 60%, 80% and 100% were utilized and the results of hardened concrete tests for compressive and flexural strengths were obtained. It was found that in general the compressive and flexural strengths of the recycled aggregate concrete (RAC) decreased with increasing replacement levels of natural coarse aggregates using RCA. It was concluded that RCA could be employed as a substitute for natural aggregate in concrete only up to a certain limit or partial replacement. In this respect, it was also noted that the undesirable properties of RCA were primarily due to the quantity and quality of the adhering mortar.展开更多
In recent decades,the utilization of waste tires,plastic and artificial shale ceramsite as alternative fine aggregate to make self-compacting concrete(SCC)has been recognized as an eco-friendly and sustainable method ...In recent decades,the utilization of waste tires,plastic and artificial shale ceramsite as alternative fine aggregate to make self-compacting concrete(SCC)has been recognized as an eco-friendly and sustainable method to manufacture renewable construction materials.In this study,three kinds of recycled aggregates:recycled tire rubber particles,wood-plastic particles,artificial shale ceramsite were used to replace the sand by different volume(5%,10%,20%and 30%),and their effects on the fresh and hardened properties of SCC were investigated.The slump flow and V-funnel tests were conducted to evaluate the fresh properties of modified-SCC mixtures.The hardened properties include 3,7 and 28-day compressive strengths,axial compressive strength,static elastic modulus,and compressive stress-strain behavior at 28 days.The test results showed that the incorporation of these three kinds of alternative aggregates had a negative impact on the fresh properties of SCC.Besides,the 28-day compressive strength and axial compressive strength decreased with the increase of rubber and wood-plastic particles content.In this experiment,all the three kinds of recycled aggregates can improve the ductility and deformability of SCC,and the most excellent performance comes from SCC with recycled rubber particles.展开更多
Part of an extensive research undertaken by the Concrete and Masonry Research Group at Kingston University-London was reported to demonstrate through scientific research and full-scale site trials,that quality recycle...Part of an extensive research undertaken by the Concrete and Masonry Research Group at Kingston University-London was reported to demonstrate through scientific research and full-scale site trials,that quality recycled concrete aggregates can be produced and can be used successfully in a range of concrete applications.The effects of up to 100% coarse recycled concrete aggregate(RCA) on fresh,engineering and durability related properties were established and assessed its suitability for use in a rage of sustainable applications.展开更多
Recycled concrete aggregate(RCA)derived from demolition waste has been widely explored for use in civil engineering applications.One of the promising strategies globally is to incorporate RCA into concrete products.Ho...Recycled concrete aggregate(RCA)derived from demolition waste has been widely explored for use in civil engineering applications.One of the promising strategies globally is to incorporate RCA into concrete products.However,the use of RCA in high-performance concrete,such as self-consolidating concrete(SCC),has only been studied in the past decade.This paper summarizes recent publications on the use of coarse and/or fine RCA in SCC.As expected,the high-water absorption and porous structure of RCA have posed challenges in producing a high-fluidity mixture.According to an analysis of published data,a lower strength reduction(within 23%regardless of coarse RCA content)is observed in SCC compared with vibrated concrete,possibly due to the higher paste content in the SCC matrix,which enhances the weak surface layer of RCA and interfacial transition zone.Similarly,SCC tends to become less durable with RCA substitution although the deterioration can be minimized by using treated RCA through removing or strengthening the adhered mortar.To date,the information reported on the role of RCA in the long-term performance of SCC is still limited;thus,a wide range of research is needed to demonstrate the feasibility of RCA–SCC in field applications.展开更多
The needs of the construction sector are still increasing for concrete. However the shortage of natural resources of aggregate could be a problem for the concrete industry. In addition, the negative impact on the envi...The needs of the construction sector are still increasing for concrete. However the shortage of natural resources of aggregate could be a problem for the concrete industry. In addition, the negative impact on the environment is due to the construction demolition;where disposal wastes create a severe ecological and environmental hazard. In the last decade, a major interest has been developed for the reuse of recycled aggregates that present more than 70% of the concrete volume. The reused products should fulfill the requirements of lower cost and better quality, in order to establish its role in the concrete. The aim of this study is to assess the effect of the local admixtures on the mechanical behavior of recycled aggregate concrete (RAC). Physical and mechanical properties of RAC were investigated including density, compressive and flexural strength. The non-destructive test methods (NDT: pulse-velocity and rebound hammer) were used to determine the concrete strength. The results obtained were compared with crushed aggregate concrete (CAC) using the normal compressive testing machine test method. Thus, the convenience of indirect tests in the case of a recycled aggregate concrete were demonstrated.展开更多
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 select...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.展开更多
Japan lacked resources is a large import country and also a large consuming country.So it is turned society structure system of consumption goods stocked in domestic,which leads to 450 millions ton waste material.Rece...Japan lacked resources is a large import country and also a large consuming country.So it is turned society structure system of consumption goods stocked in domestic,which leads to 450 millions ton waste material.Recently,because of continuing development of intermediate handling and recycled utilization technology,finally disposed waste materials approximately 30 millions ton.The quantity of concrete product is consumed 300 millions ton per year unprecedented,beau case of large scope,it is expected valid and large absorption industry of recycled material. The purpose of this paper is to do a report on applied present status and future assignment of recycled material and building structure in Japan.展开更多
With time concrete / reinforced concrete has become the popular material for construction. Modern industry utilizes this material a lot and has produced various beautiful, eye catching and amazing structures. Due to m...With time concrete / reinforced concrete has become the popular material for construction. Modern industry utilizes this material a lot and has produced various beautiful, eye catching and amazing structures. Due to modern requirements for living and developed construction industries, the old buildings (usually constructed with brick masonry) are demolished and are replaced with new modern buildings. Demolition of buildings results in waste materials which can create waste related problems and environmental issues. By using recycled aggregates weight of concrete can also be reduced, which can also solve problems related to self-weight of concrete. In this paper attempt has been made to use local used bricks from vicinity of Nawabshah, Pakistan, as coarse aggregate. Concrete cubes made with local recycled bricks are cast and tested for overall weight of concrete, moisture content, dynamic modulus of elasticity and compressive strength (nondestructive and destructive methods). The results showed that concrete derived from recycled aggregates attained lower strength than regular concrete. More detailed elaborated work is recommended with different mix ratios and different proportions recycled aggregates for better conclusions.展开更多
Massive amounts of brick waste are obtained from demolition of old buildings and structures around the world. With the increased stress on sustainable construction, and environmentally friendly materials and greener c...Massive amounts of brick waste are obtained from demolition of old buildings and structures around the world. With the increased stress on sustainable construction, and environmentally friendly materials and greener concreting practices, a large proportion of such waste bricks are crushed and mixed with normal aggregates for use in concrete. The performance of concrete containing waste brick aggregates partially replacing normal aggregates have not been investigated for their performance. This paper covers investigations carried out on concrete with such aggregates obtained from demolition waste and mixed with varying proportions of normal aggregates to produce concrete. Two types of crushed brick aggregates were mixed with gravel in the ratios of 30:70 and 40:60 by weight and specimen were cast for investigations. Two w/c ratios were investigated. Various tests were carried out to assess the compressive strength of cubes and cylinders of mixed aggregates concrete along with f1exural strength, stress/strain behavior, moduli of elasticity, ultrasonic pulse velocity determination, densities, surface absorption, shrinkage and frost resistance. The values obtained from these tests were compared with the values of concrete with normal aggregates (gravel) with similar w/c ratios. While the strength tests and durability tests more or less gave satisfactory results however the larger moisture absorption by the waste brick aggregates reduces the frost resistance capacity somewhat thereby care needs to be exercised in using these mixes in regions/areas susceptible to frost.展开更多
文摘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/m<sup>3</sup> ≤ ρ ≥ 2600 kg/m<sup>3</sup> 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 (Rc<sub>28</sub> > 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.
基金Funded by the National Natural Science Foundation of China(No.51278073)State Key Laboratoryfor GeoMechanics and Deep Underground Engineering,China University of Mining&Technology(No.SKLGDUEK1704)
文摘The feasibility of using different generations of recycled fine aggregate(RFA) in structural concrete in a chloride environment was evaluated by studying the performance of the RFA and the corresponding concrete. The different generations of RFA were recycled by following the cycle of ‘concrete-waste concrete-fine aggregate-concrete'. The properties of three generations of repeatedly recycled fine aggregate(RRFA) were systematically investigated, and we focused on the compressive strength and splitting tensile strength and chloride ion permeability of the related structural concretes with 25%, 75%, and 100% replacement of natural fine aggregates with RFA. The results indicated that the quality of RRFA presents a trend of slow deterioration, but the overall performance of all RRFA still fulfils the quality requirements of recycled fine aggregate for structural concrete. All RRFA concretes achieved the target compressive strength of 40 MPa after 28 days except for the second generation of the recycled aggregate concrete and the third generation of the recycled aggregate concrete with 100% replacement, and all the concrete mixes achieved the target compressive strength after 90 days. The insights obtained in this study demonstrate the feasibility of using at least three generations of RRFA for the production of normal structural concrete with a design service life of 100 years in a chloride environment.
文摘In 2007,over 24 million tons of Construction and Demolition(C&D) wastes were generated in Hong Kong.Since the local landfills will be saturated in about 6 years,it is important to find a viable way to reuse these waste materials as to alleviate the demand on public fill capacity.In order to tackle the problem,the Hong Kong government has set up a temporary recycling facility in Hong Kong in 2002 for producing different sizes of recycled aggregate for use in various construction materials.The Hong Kong Polytechnic University has been studying the feasible use of recycled aggregates in Hong Kong for a number of years.A substantial amount of experimental results on the properties of recycled aggregates and the effect of recycled aggregates on the properties of concrete and other construction products(e.g.concrete blocks and granular sub-base) has been published.In this paper,the experience of Hong Kong in using recycled aggregates are summarized and a set of quality control guidelines proposed for governing the use of recycled aggregates in Hong Kong is introduced.The experience and guidelines may also be useful for the recycling of waste materials derived from the recent Sichuan earthquake in China.
基金the National Natural Science Foundation of China(Nos.52078358,51325802)China Postdoctoral Science Foundation(No.2018M642079)are highly acknowledged.
文摘The failure characteristics of recycled concrete containing brick aggregates are still indistinct,especially how the angular aggregates effect the crack propagation.Based on the concept of modeled concrete,the development of cracks in concrete containing the natural aggregate and brick aggregate under a compression loading was studied.The strain distribution was analyzed with the Digital Image Correlation(DIC).The modeled aggregates include circular and squared ones,and the squared modeled aggregates were placed in different orientations,including 0°,22.5°and 45°.The results show that when the aggregate is placed at 45°,the upper and lower vertices of the aggregate lead to the highest critical strain concentration,therefore,cracks are easy to propagate from these areas and the strength of the corresponding modeled concrete is the lowest.When the modeled natural aggregate is placed at the orientation of 0°,the strain concentration first appears at the interface on both lateral sides of the aggregate.The brick aggregate has a lower elastic modulus and strength than the surrounding mortar.As a result,cracks always propagate through the brick aggregate,which is the primary reason for the low strength of the corresponding concrete.
文摘In some cases of emergency backfill engineering projects, traditional backfill materials cannot meet the requirements of fast construction due to their long curing time. This study presents a new kind of rapid hardening controlled low strength material, which utilizes both rapid hardening sulphoaluminate cement and recycled fine aggregate from urban red brick construction waste. Totally, sixteen mixtures were prepared for the experiment with different cement-to-sand ratios and water-to-solid ratios. The flowability and bleeding rate of fresh mixture were measured to evaluate its workability, and the compressive strength of hardened mixture was tested to evaluate its rapid hardening and mechanical properties. Test results indicate that rapid hardening controlled low strength material containing recycled fine aggregate from urban red brick construction waste can achieve the desirable flowability, but the bleeding rate increases with the increase of flowability. In addition, 2-hour compressive strength can reach 0.08 - 0.12 MPa, and 4-hour compressive strength is 0.32 - 1.54 MPa, which can meet the requirements of emergency backfill construction. At last, based on the derived compressive strength, a fitting model for predicting compressive strength evolution of this new rapid hardening backfill material is developed, which fits accurately with these experimental data.
文摘In an earlier study, a comprehensive and critical review of previous investigations into the assessment of the strength of concrete incorporating aggregates from demolished wastes was conducted and it was concluded that there was a stark absence of results from the South African sub-continent including Botswana. In the present study, recycled coarse aggregates (RCA) sourced from demolished wastes collected from a landfill site in Gaborone, Botswana was used in lieu of natural coarse aggregates for the manufacture of concrete. With reference to the natural coarse aggregate, RCA replacement levels of 0%, 20%, 40%, 60%, 80% and 100% were utilized and the results of hardened concrete tests for compressive and flexural strengths were obtained. It was found that in general the compressive and flexural strengths of the recycled aggregate concrete (RAC) decreased with increasing replacement levels of natural coarse aggregates using RCA. It was concluded that RCA could be employed as a substitute for natural aggregate in concrete only up to a certain limit or partial replacement. In this respect, it was also noted that the undesirable properties of RCA were primarily due to the quantity and quality of the adhering mortar.
基金the financial support from the National Natural Science Foundation of China,grant number 11772351Double Shield TBM Material Optimization and Supporting Technology Research-TBM Segment Rapid Support Scientific Research Project[contract NO:PM2017/D02]the National Key R&D Program of China(No.2018YFC0406604).
文摘In recent decades,the utilization of waste tires,plastic and artificial shale ceramsite as alternative fine aggregate to make self-compacting concrete(SCC)has been recognized as an eco-friendly and sustainable method to manufacture renewable construction materials.In this study,three kinds of recycled aggregates:recycled tire rubber particles,wood-plastic particles,artificial shale ceramsite were used to replace the sand by different volume(5%,10%,20%and 30%),and their effects on the fresh and hardened properties of SCC were investigated.The slump flow and V-funnel tests were conducted to evaluate the fresh properties of modified-SCC mixtures.The hardened properties include 3,7 and 28-day compressive strengths,axial compressive strength,static elastic modulus,and compressive stress-strain behavior at 28 days.The test results showed that the incorporation of these three kinds of alternative aggregates had a negative impact on the fresh properties of SCC.Besides,the 28-day compressive strength and axial compressive strength decreased with the increase of rubber and wood-plastic particles content.In this experiment,all the three kinds of recycled aggregates can improve the ductility and deformability of SCC,and the most excellent performance comes from SCC with recycled rubber particles.
文摘Part of an extensive research undertaken by the Concrete and Masonry Research Group at Kingston University-London was reported to demonstrate through scientific research and full-scale site trials,that quality recycled concrete aggregates can be produced and can be used successfully in a range of concrete applications.The effects of up to 100% coarse recycled concrete aggregate(RCA) on fresh,engineering and durability related properties were established and assessed its suitability for use in a rage of sustainable applications.
基金Financial support from the National Natural Science Foundation of China(Contract No.897201143)。
文摘Recycled concrete aggregate(RCA)derived from demolition waste has been widely explored for use in civil engineering applications.One of the promising strategies globally is to incorporate RCA into concrete products.However,the use of RCA in high-performance concrete,such as self-consolidating concrete(SCC),has only been studied in the past decade.This paper summarizes recent publications on the use of coarse and/or fine RCA in SCC.As expected,the high-water absorption and porous structure of RCA have posed challenges in producing a high-fluidity mixture.According to an analysis of published data,a lower strength reduction(within 23%regardless of coarse RCA content)is observed in SCC compared with vibrated concrete,possibly due to the higher paste content in the SCC matrix,which enhances the weak surface layer of RCA and interfacial transition zone.Similarly,SCC tends to become less durable with RCA substitution although the deterioration can be minimized by using treated RCA through removing or strengthening the adhered mortar.To date,the information reported on the role of RCA in the long-term performance of SCC is still limited;thus,a wide range of research is needed to demonstrate the feasibility of RCA–SCC in field applications.
文摘The needs of the construction sector are still increasing for concrete. However the shortage of natural resources of aggregate could be a problem for the concrete industry. In addition, the negative impact on the environment is due to the construction demolition;where disposal wastes create a severe ecological and environmental hazard. In the last decade, a major interest has been developed for the reuse of recycled aggregates that present more than 70% of the concrete volume. The reused products should fulfill the requirements of lower cost and better quality, in order to establish its role in the concrete. The aim of this study is to assess the effect of the local admixtures on the mechanical behavior of recycled aggregate concrete (RAC). Physical and mechanical properties of RAC were investigated including density, compressive and flexural strength. The non-destructive test methods (NDT: pulse-velocity and rebound hammer) were used to determine the concrete strength. The results obtained were compared with crushed aggregate concrete (CAC) using the normal compressive testing machine test method. Thus, the convenience of indirect tests in the case of a recycled aggregate concrete were demonstrated.
基金the financial support from the open project funds for National Major Science and Technology Infrastructure of Materials Service Safety Assessment Facilities,China(MSAF-2020-106)the National Natural Science Foundation of China(No.51808051)。
文摘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.
文摘Japan lacked resources is a large import country and also a large consuming country.So it is turned society structure system of consumption goods stocked in domestic,which leads to 450 millions ton waste material.Recently,because of continuing development of intermediate handling and recycled utilization technology,finally disposed waste materials approximately 30 millions ton.The quantity of concrete product is consumed 300 millions ton per year unprecedented,beau case of large scope,it is expected valid and large absorption industry of recycled material. The purpose of this paper is to do a report on applied present status and future assignment of recycled material and building structure in Japan.
文摘With time concrete / reinforced concrete has become the popular material for construction. Modern industry utilizes this material a lot and has produced various beautiful, eye catching and amazing structures. Due to modern requirements for living and developed construction industries, the old buildings (usually constructed with brick masonry) are demolished and are replaced with new modern buildings. Demolition of buildings results in waste materials which can create waste related problems and environmental issues. By using recycled aggregates weight of concrete can also be reduced, which can also solve problems related to self-weight of concrete. In this paper attempt has been made to use local used bricks from vicinity of Nawabshah, Pakistan, as coarse aggregate. Concrete cubes made with local recycled bricks are cast and tested for overall weight of concrete, moisture content, dynamic modulus of elasticity and compressive strength (nondestructive and destructive methods). The results showed that concrete derived from recycled aggregates attained lower strength than regular concrete. More detailed elaborated work is recommended with different mix ratios and different proportions recycled aggregates for better conclusions.
文摘Massive amounts of brick waste are obtained from demolition of old buildings and structures around the world. With the increased stress on sustainable construction, and environmentally friendly materials and greener concreting practices, a large proportion of such waste bricks are crushed and mixed with normal aggregates for use in concrete. The performance of concrete containing waste brick aggregates partially replacing normal aggregates have not been investigated for their performance. This paper covers investigations carried out on concrete with such aggregates obtained from demolition waste and mixed with varying proportions of normal aggregates to produce concrete. Two types of crushed brick aggregates were mixed with gravel in the ratios of 30:70 and 40:60 by weight and specimen were cast for investigations. Two w/c ratios were investigated. Various tests were carried out to assess the compressive strength of cubes and cylinders of mixed aggregates concrete along with f1exural strength, stress/strain behavior, moduli of elasticity, ultrasonic pulse velocity determination, densities, surface absorption, shrinkage and frost resistance. The values obtained from these tests were compared with the values of concrete with normal aggregates (gravel) with similar w/c ratios. While the strength tests and durability tests more or less gave satisfactory results however the larger moisture absorption by the waste brick aggregates reduces the frost resistance capacity somewhat thereby care needs to be exercised in using these mixes in regions/areas susceptible to frost.