Research on the Investment Mode and Path of China’s Construction Waste Resourceization Industry

At present,China’s construction waste accounts for about 40%of the total municipal solid waste,with a large stock,a large increment,and a low rate of resource utilization,which is still a big gap compared with developed countries.However,the market prospect of the construction waste industry is relatively broad,the reuse value of the construction waste is high,so these resources should be fully utilized.This paper presents an in-depth analysis of projects in the construction waste resourceization industry,examining the industrial chain,development history,current status,investment and financing modes,and case studies.It proposes targeted strategies for companies to focus on the upstream and downstream segments of the construction industry’s value chain and explores the implementation of investment opportunities in construction waste resourceization.

Application of Construction Waste Recycled Material Processing in Road Engineering

In order to promote the recycling of construction waste in China and reduce the cost of road engineering materials,this paper expounds on the technical indexes,road performance,durability,and the impact on the compressive strength of road engineering of construction waste recycled materials based on the analysis of the processing technology of construction waste recycled materials to provide reference for future research.

An Experimental Study of Self-Compacting Concrete Made with Filler from Construction and Demolition Waste

This study evaluated the influence of the Portland cement replacement by 0, 5%, 10%, 15% and 20% of Construction and Demolition Waste (CDW) filler contents in the production of self-compacting concrete (SCC). The SCC mixtures were evaluated on fresh state by slump flow, J-ring, resistance of segregation, specific gravity, and on hardened state by compressive and splitting tensile strength, specific gravity, air voids and absorption rate. The results indicated that all SCC produced with CDW filler met the limits established at any level of substitution without changes of the w/c ratio or superplasticizer content. It was possible to verify that the presence of CDW filler, in substitution of cement, by volume, improves the resistance to segregation and up to 5% of CDW filler decreases the loss of fluidity with time as compared to reference. It was found that all SCC mixtures, at 28 days, had the average compressive strength above 50 MPa, without showing significant loss with up to 20% of CDW filler. For splitting tensile strength, SCC recycled mixtures reached up to 92.5% of the SCC used as reference. Absorption rate and air voids index of SCC recycled mixtures had a maximum increase of 1.60%Compared to the reference one. So, it is possible to conclude that the use of the CDW filler up to 20% in substitution of cement, by volume, is feasible for SCC production.

Construction and Demolition Waste Management Scenario in Republic of Cape Verde—The Case Study of City of Praia

Globally, the construction industry is one of the leading producers of solid waste. The city of Praia, the capital of the Republic of Cape Verde has been suffering from environmental degradation with the irregular disposal of waste caused by inadequate management of waste from construction and also the demolition. The research was developed based on local inspections in the context of environmental laws, in semi-structured interviews with people who deal with this activity and bibliographic references. The main conclusion is that the city does not have a CDW management plan consequently leading to environmental problems. On the other hand, waste of recycled construction can be used as inert reducing the consumption of raw materials that can be used as base and sub-base for paving, landfills, aggregate in mortars and raw materials to be manufactured blocks, bricks concrete tiles, etc.

Characterization of Mechanical Properties of Waste Slurry Modified by Recycled Sand and Cement

In order to study the modification effect of recycled sand on cement reinforced waste slurry(CWS),triaxial test,scanning electron microscope test and X-ray diffraction test were carried out.The mechanical test of recycled sand and cement reinforced waste slurry(RCWS)shows that the deviatoric stress–strain curve of RCWS samples changes from hardening type to softening type with the increase of recycled sand content;the peak stress increases with the increase of recycled sand content;recycled sand can enhance the shear strength of CWS by increasing both cohesion and internal friction angle.The microscopic test shows that recycled sand can improve the structural compactness by cementing with hydrated calcium silicate and can reduce the void ratio and orientation index of RCWS samples.Finally,the mathematical model between shear strength parameters and void ratio is established.The research shows that adding an appropriate amount of recycled sand and cement has a good modification effect on waste slurry.This is an effective method to treat two kinds of construction wastes:construction waste slurry and waste concrete.

Guide for Barriers when Using Soils and Construction Materials with Environmentally Sensitive Contents

On 16 July 2021,the German“Mantelverordnung”(Construction Materials Regulation)was published in the Federal Law Journal.From August 1,2023,this regulation is to be applied nationwide and,for the first time,regulates legally nationwide binding requirements for mineral construction waste and its use in technical structures.It also refers to specific construction methods with construction waste material.In the course of the construction of infrastructure traffic routes,it is possible to use these construction materials with limited contamination for the construction of,e.g.,noise barriers,dams or embankments.The German M TS E(Merkblattüber Bauweisen für Technische Sicherungsmaßnahmen beim Einsatz von Böden und Baustoffen mit umweltrelevanten Inhaltsstoffen im Erdbau)Guideline of the FGSV(Road and Transportation Research Association)lists various alternatives for barriers in such structures.Geosynthetic barriers,e.g.,GCLs(Geosynthetic Clay Liners,also known as bentonite mats)or polymeric geomembranes as well as other geosynthetics can have economic and design advantages over conventional mineral barriers.Depending on the proposed construction method,the guideline sets out certain requirements,not only but also for permittivity and confining stress.In the following,the construction methods in general and the design solutions with GCLs in particular are presented.

Tensile Behavior of Strain Hardening Cementitious Composites (SHCC) Containing Reactive Recycled Powder from Various C&D Waste

This work investigates the feasibility of utilizing reactive recycled powder(RP)from construction and demolition(C&D)waste as supplementary cementitious material(SCM)to achieve a ductile strain hardening cementitious composites(SHCC).The recycled mortar powder(RMP)from mortar waste,recycled concrete powder(RCP)from concrete waste and recycled brick powder(RBP)from clay brick waste were first prepared,and the micro-properties and tensile behavior of SHCC containing various types and replacement ratios of RPs were determined.The incorporated RP promotes pozzolanic and filler effects,while the hydration products in cementitious materials decrease with RP incorporation;therefore,the incorporated RP decreases the compressive strength of SHCC.Attributed to the reduction in the matrix strength,the incorporated RP increases the crack-bridging extent and ductility of SHCC;the irregular micro-structure and high reactivity of RP also help the strain-hardening performance of the prepared SHCC.In addition,the strainhardening performance of SHCC containing RMP and RBP is surperior to that of SHCC with RCP and is slightly lower than that of SHCC with fly ash(FA);for instance,the ultimate strain of SHCC containing 54%FA,RMP,RCP and RBP is 3.67%,3.61%,2.52%and 3.53%,respectively.In addition,the strain-hardening behavior of an SHCC doubled mix with FA and RMP or RBP has a similar ultimate strain and a higher ultimate stress than SHCC containing only FA.

Nano-treatment of Autoclaved Aerated Concrete Waste and Its Usage in Cleaner Building Materials

Autoclaved aerated concrete waste(AACW)was used as a raw material to prepare nucleation seed for acceleration of Portland cement.Nano AACW seed with median particle size of 324 nm was prepared by wet grinding method.Both the electrical conductivity and pH value of nano AACW suspension were obviously improved.Both the setting times and intensity of the main hydration heat peak were promoted by nano AACW,indicating the possibility of AACW suspension as nucleation seed.The early age compressive strength before 3 days was also clearly improved by nano AACW,with no negative effect on the late age strength.Furthermore,the reduced CH content with dosage of nano AACW indicates that nano AACW not only plays a role of nucleation seed in cement hydration,but also has a certain pozzolanic reaction.

Feasibility Study of Applying Recycled Aggregate from Building Debris in Concrete

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.

Optimization of Grasping Efficiency of a Robot Used for Sorting Construction and Demolition Waste

The recycling of construction and demolition waste(CDW)remains an urgent problem to be solved.In the industry,raw CDW needs to be manually sorted.To achieve high efficiency and avoid the risks of manual sorting,a sorting robot can be designed to grasp and sort CDW on a conveyor belt.But dynamic grasping on the conveyor belt is a challenge.We collected location information with a three-dimensional camera and then evaluated the method of dynamic robotic grasping.This paper discusses the grasping strategy of rough processed CDW on the conveyor belt,and implements the function of grasping and sorting on the recycling line.Furthermore,two new mathematical models for a robotic locating system are established,the accuracy of the model is tested with Matlab,and the selected model is applied to actual working conditions to verify the sorting accuracy.Finally,the robot kinematics parameters are optimized to improve the sorting efficiency through experiments in a real system,and it was concluded that when the conveyor speed was kept at around 0.25 m/s,better sorting results could be achieved.Increasing the speed and shortening the acceleration/deceleration time would reach the maximum efficiency when the load would allow it.Currently,the sorting efficiency reached approximately 2000 pieces per hour,showing a high accuracy.

Progress in developing self-consolidating concrete(SCC)constituting recycled concrete aggregates:A review

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.

Recycled Aggregates:Production,Properties and Value-added Sustainable Applications

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.

Chemical and olfactive impacts of organic matters on odor emission patterns from the simulated construction and demolition waste landfills

The explosive increase of construction and demolition waste(CDW) caused the insufficient source separation and emergency disposal at domestic waste landfills in many developing countries. Some organic fractions were introduced to the CDW landfill process and resulted in serious odor pollution. To comprehensively explore the impacts of organic matters on odor emission patterns, five CDW landfills(OIL), with organic matters/inert CDW components(O/I) from 5% to 30%, and the control group only with inert components(IL) or organics(OL) were simulated at the laboratory. The chemical and olfactive characters of odors were evaluated using the emission rate of 94 odorants content(ER_(total)), theory odor concentration(TOC_(total)), and e-nose concentration(ER_(ENC)), and their correlations with waste properties were also analyzed. It was found that the main contributors to ER_(total)(IL: 93.0% NH_(3);OIL: 41.6% sulfides, 31.0% NH_(3), 25.9% oxygenated compounds) and TOC_(total)(IL: 64.1% CH_3SH, 28.2% NH_(3);OIL: 71.7% CH_(3)SH, 24.8% H_(2)S) changed significantly. With the rise of O/I, ER_(total), TOC_(total), and ER_(ENC) increased by 10.9, 20.6, and 2.1 times, respectively. And the organics content in CDW should be less than 10%(i.e., DOC < 101.3 mg/L). The good regressions between waste properties(DOC, DN, pH) and ER_(total),( r = 0.86, 0.86,-0.88, p < 0.05), TOC_(total),( r = 0.82, 0.79, -0.82, p < 0.05) implied that the carbon sources and acidic substances relating to organics degradation might result in that increase. Besides, the correlation analysis results( ER_(ENC) vs. TOC_(total,, r = 0.96, p < 0.01;vs. ER_(ENC), r = 0.86, p < 0.05) indicated that e-nose perhaps was a reliable odor continuous monitoring tool for CDW landfills.

The use of fine portions from construction and demolition waste for expansive soil stabilization: A review

Construction and demolition waste(CDW)are the largest waste products in the world today and competes as a viable recycled additive material in place of natural aggregates.Due to the increase in compressive strength of different mix proportions of CDW,it is also considered for reuse in concrete and subbase construction.This study shows the effect of CDW in expansive soil stabilization.The chemical and mechanical properties of these materials have shown that they are capable of developing compressive strength properties for replacement of cement with significant reduction in carbon emission.The inherent compositional properties of recycled CDW compared in this review suggests that CDW have good filler properties in highly expansive soils.Mixtures of crushed brick and recycled aggregates characterised based on chemical properties of different replacement ratios suggests that CDW of good-quality aggregates reduces swell potential of expansive soils and increased mechanical strength in pavement construction.

The Behavior of Recycled Concrete through the Application of an Isotropic Damage Model

The main goal of this paper is to describe the mechanical behavior of the CDW recycled concrete in compression, using an isotropic damage model adapted to the variation of the replacement rate of natural aggregates by recycled ones. The isotropic model by Mazars was used as a constitutive equation for the CDW concrete and its adjustment parameters, A and B, were written as quadratic polynomials according to the aggregates replacement rate. The model was evaluated for conventional and recycled concretes. For the latter ones, the aggregates replacement ratios evaluated were 50% and 100%. The results show good approximation between the analytical and numerical values obtained with the adapted isotropic damage model and experimental concrete results for both compressive and flexural strength.

Bond Behavior between Recycled Concrete Containing CDW and Different Types of Steel Bars

The operation of reinforced concrete structures is directly associated with the adhesion between the steel bar and the concrete,which allows the inter­nal forces to be transferred to the reinforcement during the process of load­ing the structural elements.The modification of the concrete composition,with the introduction of recycled aggregate from construction and demoli­tion waste(CDW),affects the steel-concrete interface and can modify the bonding stress,which is also influenced by the type and diameter of the bar used.In this work,the influence of the recycled fine aggregate(RFA)and types of steel bar on the steel-concrete bond was experimentally evaluated using the pullout test.Conventional concrete and recycled concrete,with RFA replacement level of 25%,were produced.Two types of steel rebars(i.e.,plain and deformed)with diameters of 10.0 and 16.0 mm were con­sidered in this paper.The results indicate a reduction in the adhesion stress with the introduction of recycled aggregate,but this trend is influenced by the diameter of the bar used.The use of ribbed bars modifies the stress bon-slip behavior,with an increase in the average bond strength,which is also observed with the reduction of the diameter of the bar.

Review of construction and demolition waste management tools and frameworks with the classification,causes,and impacts of the waste

This review looks over the current construction and demolition waste management(C&DWM)situations by scrutinizing the definition,classification,components,compositions,generated sources and causes,impacts of generated construction and demolition wastes(C&DWs),waste management hierarchy(WMH),3R principles(Reduce,Reuse,and Recycle),Circular Economy(CE),frameworks,tools,and approaches of C&DWM.After reviewing the literature this study contributes to the literature by the following means:(a)suitable working definitions of C&DW and C&DWM are provided,(b)an expanded WMH for construction and demolition operations is presented,(c)frameworks of C&DWM are identified and listed as follows:frameworks based on WMH,including 3R principles and CE concept,frameworks focusing on the quantification,estimation,and prediction of generated C&DW,frameworks focusing on effective and sustainable C&DWM,frameworks focusing economic,social,and environmental performance assessment,frameworks based on multi-criteria analysis(MCA),frameworks based on post-disaster recovery period,and other miscellaneous frameworks,and(d)four categories of tools utilized in C&DWM are identified and explained,namely,approaches employed in C&DWM,information technology(IT)tools employed in C&DWM,multi-criteria decision analysis(MCDA)tools employed in C&DWM,and C&DWM technologies.Moreover,this study also found that CE,and green rating system(GRS)are widely used approaches,Building Information Modeling(BIM),Radio Frequency Identification(RFID),Geographic Information System,and Big Data are the extensively used IT tools,Analytical Hierarchy Process,FUZZY,TOPSIS(Technique for Order Preference by Similarity to the Ideal Solution),Weighted Summation,Elimination and Choice Expressing the Reality II,Elimination and Choice Expressing the Reality III,Evaluation of Mixed Data,and REGIME(REG)are the widely used MCA tools in C&DWM,and Prefabricated Construction and Modular Construction are broadly used C&DWM technologies.Furthermore,it has been observed that the application of the Analytic Networking Process(ANP)and hybridization of ANP,FUZZY,and TOPSIS tools do not catch considerable attention in the literature for conducting MCA,although it yields more precise outcomes.Additionally,most previous research has focused on the estimation of generated C&DW,but less attention has been given to forecasting the generated C&DW due to inadequate available C&DW data.This review article also assists C&DWM practitioners,academics,stakeholders,and contractors in choosing appropriate frameworks and tools for C&DWM while managing C&DW.

Research on the mechanical properties and electrical conductivity of cement mortar based on recycled nano-iron boride

Traditional cement-based materials are being gradually replaced by nanomodified cement-based materials because the traditional materials cannot meet the production needs of modern society.Nano-iron boride(nano-FeB)is a high-performance nanomaterial prepared from waste iron powder during construction.Its one-dimensional structure is similar to that of carbon nanotubes,which makes it a potential candidate for nano-reinforcement materials.In this paper,the effects of different contents of recycled nano-FeB(0%,0.05%,0.075%,and 0.1 wt.%,based on cement weight)on the mechanical properties and electrical conductivity of cement mortar were studied.The results showed that the mechanical properties of the composite cement mortar were improved with the addition of nano-FeB.When the content of nano-FeB was 0.075%,the 28 d compressive strength and flexural strength of the composite cement mortar increased by 60.2%and 42.1%,respectively.In addition,a 0.075%nano-FeB content favorably improved the conductivity of cement mortar.Compared with that of the control group,the volume resistivity of the composite cement mortar decreased by one order of magnitude.

Control of hydrogen sulfide emissions using autotrophic denitrification landfill biocovers:engineering applications

Hydrogen sulfide(H_(2)S)emitted from construction and demolition waste landfills has received increasing attention.Besides its unpleasant odor,longterm exposure to a very low concentration of H_(2)S can cause a public health issue.In the case of construction and demolition(C&D)waste landfills,where gas collection systems are not normally required,the generated H_(2)S is typically not controlled and the number of treatment processes to control H_(2)S emissions in situ is limited.An attractive alternative may be to use chemically or biologically active landfill covers.A few studies using various types of cover materials to attenuate H_(2)S emissions demonstrated that H_(2)S emissions can be effectively reduced.In this study,therefore,the costs and benefits of H_(2)S-control cover systems including compost,soil amended with lime,fine concrete,and autotrophic denitrification were evaluated.Based on a case-study landfill area of 0.04 km^(2),the estimated H_(2)S emissions of 80900 kg over the 15-year period and costs of active cover system components(ammonium nitrate fertilizer for autotrophic denitrification cover,lime,fine concrete,and compost),ammonium nitrate fertilizer is the most cost effective,followed by hydrated lime,fine concrete,and yard waste compost.Fine concrete and yard waste compost covers are expensive measures to control H_(2)S emissions because of the large amount of materials needed to create a cover.Controlling H_(2)S emissions using fine concrete and compost is less expensive at landfills that provide on-site concrete recovery and composting facilities;however,ammonium nitrate fertilizer or hydrated lime would still be more cost effective applications.