Permanent deformation and prediction model of construction and demolition waste under repeated loading

This study aims to reveal the macroscopic permanent deformation(PD)behavior and the internal structural evolution of construction and demolition waste(CDW)under loading.Firstly,the initial matric suction of CDW was measured by the filter paper method.Secondly,the PD of CDW with different humidity and stress states was investigated by repeated load triaxial tests,and a comprehensive prediction model was established.Finally,the discrete element method was performed to analyze the internal structural evolution of CDW during deformation.These results showed that the VAN-GENUCHTEN model could describe the soil-water characteristic curve of CDW well.The PD increases with the increase of the deviator stress and the number of cyclic loading,but the opposite trend was observed when the initial matric suction and confining pressure increased.The proposed model in this study provides a satisfactory prediction of PD.The discrete element method could accurately simulate the macroscopic PD of CDW,and the shear force,interlock force and sliding content increase with the increase of deviator stress during the deformation.The research could provide useful reference for the deformation stability analysis of CDW under cyclic loading.

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.

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.

Water Retention Curve and Particle Breakage of Aggregates Recycled from Demolition Waste

CDW （construction and demolition wastes） present a high amount of aggregate chips covered with mortar. This results in high absorption of water with a direct impact in particle breakage or disaggregation. It is supposed that intra particle suction plays an important role in this phenomenon. However, WRCs （water retention curves） of CDW are not well understood. In this work, the WRCs of dynamically compacted specimens of aggregates recycled from the demolition of the National Stadium in Brasilia are studied. The objective of this study is to obtain WRCs of the recycled materials by using the pressure plate and filter paper methods. The breaking effect during compaction is quantified from the grain size distribution curves. The particle breakage during compaction increases when the energy is augmented. The results from the WRCs were incorporated into a pore size capillary model to predict pore size distribution.

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.

Polluter-Pays Principle Applied to Construction and Demolition Debris

The research focused on the analysis of construction and demolition debris in a sample Brazilian city with the objective to propose a management scheme tailored to private initiative intervention. The debris was found to be produced at a rate of 1.55 kg per person per day for a total of 5177 tons per month. The composition report showed 75% material reusable for construction purposes, 15% material recyclable through reverse logistics and 10% refuse to be disposed of at landfills. The study developed legal and managerial instruments that stimulate private operators to achieve landfill diversions in the order of 90% of this waste. The arguments were supported by a flow diagram that indicates the correct destination of all waste items and an economic balance of private waste movement. Proactive legal scriptures were sketched out that can assist the local administration in setting the timeframe for reaching the diversion target.

Use of Masonry Construction &Demolition Waste in Concrete

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.

Construction and Demolition Debris Management for Sustainable Reconstruction after Disasters： Italian Case Studies

The Italian earthquakes of recent decades created an emergency situation that required immediate post-earthquake reconstruction policies, which led to an increase in the demand for construction minerals. In particular, extraction in active quarries has been intensified, and new quarries opened according to extraordinary procedures notwithstanding current regulations. The objective of this work is to investigate the consequences that a seismic event may produce on both the built-up environment, i.e. the totality of urban and suburban settlements and infrastructure, and the natural environment, which is often compromised by hasty emergency procedures aimed at mineral extraction. As a result, correct evaluation of the demand for minerals and the recycling of earthquake debris are the fundamental elements of coherent post seismic reconstruction, by means of which post-earthquake policies could be reconciled with environmental protection.

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.

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.

建筑垃圾资源化利用及其生命周期评价的研究进展

从中国知网(CNKI)与Web of Science数据库中检索国内外关于建筑垃圾资源化利用及其生命周期评价(LCA)的相关文献,系统归纳了国内外建筑垃圾分类和资源化利用技术现状,并对LCA方法及相关模型在建筑垃圾资源化利用中的研究进展及应用情况进行了综述。结果表明,LCA方法是量化建筑垃圾管理体系环境效应的重要方法之一,能够科学评估建筑垃圾资源化利用的能源消耗、环境排放以及再生循环产品效益等,是建筑垃圾可持续管理和“无废城市”建设的重要基础。中国在建筑垃圾资源化利用、LCA模型开发及与其他研究方法集成方面还需继续探索,在建筑垃圾源头减量和建筑垃圾回收体系建立等方面仍面临巨大挑战。

消费者品牌忠诚对建筑废弃物独立再制造商技术创新行为影响

建筑废弃物再制造供应链管理已成为推进城乡建设绿色发展进程中不容忽视的环节。为了揭示消费者品牌忠诚对建筑废弃物独立再制造商技术创新行为决策的影响,综合考虑消费者无品牌忠诚和有品牌忠诚的不同情境,通过Stackelberg博弈模型建立了无品牌忠诚无创新、无品牌忠诚有创新、有品牌忠诚无创新、有品牌忠诚有创新四种模型。研究发现:(1)当消费者有品牌忠诚时,建筑废弃物独立再制造商的技术创新水平会降低。(2)无论建筑废弃物独立再制造商是否有技术创新行为,消费者品牌忠诚都会对建筑废弃物独立再制造商的定价策略产生影响。(3)当消费者有品牌忠诚时,若建筑废弃物独立再制造商无技术创新行为,则建材新产品需求随着无品牌忠诚的消费者市场份额增加而减少,建筑废弃物再制品需求随着无品牌忠诚的消费者市场份额增加而增加;若建筑废弃物独立再制造商有技术创新行为,则建材新产品和建筑废弃物再制品需求均随着无品牌忠诚的消费者市场份额增加而增加。(4)无论建筑废弃物独立再制造商是否有技术创新行为,品牌原制造商的利润都是与无品牌忠诚的消费者所占市场份额呈正相关。(5)建筑废弃物独立再制造商的技术创新行为会导致自身利润降低。

不同建筑固废再生骨料取代率下粗粒土填料永久变形特性及安定行为研究

为探究城市建筑拆除固废再生骨料部分或全部取代天然骨料用于粗粒土路基填料的可行性,开展不同再生骨料取代率、含水率、围压和剪应力比等组合下的室内大型静动三轴试验,定量研究土性参数和应力状态对试样抗剪强度和累积塑性应变特性的影响规律。基于半对数坐标下累积塑性应变发展的多阶段特征,分别考虑不同阶段塑性变形累积速率以及相邻两阶段的塑性变形累积速率的差异,提出适用于建筑固废再生骨料路基填料的新型安定行为判定准则。研究结果表明:再生骨料路基填料试样的累积塑性应变随含水率和剪应力比的增大而增大,当再生骨料路基填料试样在剪应力比为0.3和0.5时,抗累积变形性能与天然骨料路基填料试验所得的抗累积变形性能接近,综合考虑抗剪强度和累积塑性变形特性的再生骨料路基填料最优取代率为85%;新安定行为判定准则具有较高的准确性,可为相似路基填料的长期路用性能评定提供理论依据。

建筑固废高效利用对采空区精准充填试验研究

为了解决建筑固废对采空区精准充填的问题,开展采空区充填新型浆液研发,建立考虑静置稠化、剪切稀释特性的强触变浆液流变模型,进行室内模拟堆积试验。结果表明:采用0~2mm、0~5mm两种颗粒组的建筑固废材料,得到复配强触变浆液触变剂、稳定剂、流变剂、水泥和建筑固废砂的最优配比,并得到浆液的触变性、稳定性、流变性、凝固过程及结石体强度等基本性能指标,以及浆液流动堆积坡面函数的表达式。该项研究成果的应用,可减轻采空区对生态环境的影响,减少老旧建筑物拆除所产生的大量建筑固废对土地资源的占用和环境污染。

老旧建筑外立面病害检测与拆除施工技术

随着我国建筑行业迈入存量提质、改造更新的发展阶段,老旧建筑物外立面成为城市更新的关注重点。根据“无体检不更新”的政策要求,老旧建筑外立面衍生了病害检测与拆除施工两个重要的工程问题。本研究依次对检测手段、施工平台、拆除设备与垃圾运输4个方面进行了既有技术总结,并基于绿色环保、智慧建造的理念提出了新的发展趋势。在病害检测方面,宜采用无损高精检测设备实现对外立面全覆盖检测,并根据人工智能实现准确快速识别,摆脱传统的以点概面、依赖人工判断的现状;在拆除施工方面,作业平台、拆除设备与垃圾运输相辅相成,决定了拆除作业的施工质量,应从作业平台承载力、高效微扰动的拆除设备、垃圾垂直运输通道进行综合改进。

基于DIC技术的固废粒料包裹格栅加筋试验研究

为了控制高速公路改扩建新老路基拼接后的差异沉降,该文针对老路台阶松散、含水率过高,提出一种层状处置结构,即在老路台阶面设置一层固废层包裹格栅,对比了其与砂包裹、掺入消解石灰等措施的处置效果,并采用数字散斑相关技术(DIC)观测加筋影响带,进而确定路基不同层位固废包裹层厚度。进一步分析颗粒旋转与位移情况,验证DIC观测所确定加筋影响带的可靠性与准确性。试验结果表明:①在提高老路台阶筋土界面强度的措施中,效果由优至劣依次为:固废C(粒径为10~20 mm)>固废B(粒径为5~10 mm)>砂>固废A(粒径为1~5 mm)>掺灰6%>掺灰4%,增强效果随包裹固废粒径的增大而提升;②DIC试验结果表明:加筋影响带随法向应力的增大而减小,且格栅上方厚度大于格栅下方,发生旋转的颗粒主要集中在格栅下方3 cm内,格栅上方5 cm内;③基于加筋影响带厚度确定固废包裹层最佳厚度建议值:对于路基中部约为20 cm,路基底部铺设厚度约为15 cm,路基上部铺设层厚度应不小于25 cm。

基于建筑垃圾成因分析的设计策略研究——选材、构材、营材

近年来,由于我国高速城市化发展和大规模的建造活动,导致大量建筑垃圾产生,已对自然环境造成严重的负面影响。过去几年,政府推行了一系列有关建筑垃圾减量化的政策,但实际效果并不明显。本研究以垃圾减量化为目标,着眼于国内建筑垃圾排放现状,分析成因,通过文献研究与案例分析,梳理概括出“选材、构材、营材”三方面建筑设计策略,以期为建筑垃圾减量化的可持续发展目标提供参考。

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.

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.