New technology for recycling materials from oily cold rolling mill sludge

Oily cold rolling mill （CRM） sludge is one of metallurgical industry solid wastes. The recycle of these wastes can not only protect the environment but also permit their reutilization. In this research, a new process of ＂hydrometallurgical treatment ＋ hydrothermal synthesis＂ was investigated for the combined recovery of iron and organic materials from oily CRM sludge. Hydrometallurgical treatment, mainly including acid leaching, centrifugal separation, neutralization reaction, oxidizing, and preparation of hydrothermal reaction precursor, was first utilized for processing the sludge. Then, micaceous iron oxide （MIO） pigment powders were prepared through hydrothermal reaction of the obtained precursor in alkaline media. The separated organic materials can be used for fuel or chemical feedstock. The quality of the prepared MIO pigments is in accordance with the standards of MIO pigments for paints （ISO 10601-2007）. This clean, effective, and economical technology offers a new way to recycle oily CRM sludge.

Synthesis and properties of SrFe_(12)O_(19) obtained by solid waste recycling of oily cold rolling mill sludge

The aim of this study was to develop a new approach for the preparation of environmentally friendly, high-value products from oily cold rolling mill(CRM) sludge. Utilizing oily CRM sludge as a source of iron, strontium hexaferrite(SrFe_(12)O_(19)) powders were prepared by multi-step processes involving acid leaching, chemical conversion treatment, and synthesis by a citrate precursor. The influences of citric acid dosage and the pH of the sol system on the formation, crystallite size, and magnetic properties of the obtained SrFe_(12)O_(19) powders were investigated. High saturation magnetization(74.8 mA·m^2·g^(–1)) and intrinsic coercivities(614.46 mT) were achieved for pH 7.0 of the sol system, for which the molar ratio of citric acid dosage to the total dosage of Fe^(3+) and Sr^(2+) was 1.5. This study presents a new approach to utilizing oily CRM sludge, and even refractory iron-containing solid waste.

Performance of RAP in the System of Cold Inplace Recycling of Asphalt Pavement

The property of reclaimed asphalt pavement（RAP） mixture will be affected mainly by composition of old asphalt/soil and cement content in CIR system. We studied the relationship between A/S and cementitious materials. It showed that if there was no soil in RAP, the unconfined compressive strength was only from 0.18 MPa to 1.07 MPa even if adding cement was from 2% to 6%, and RAP samples collapsed during conserving in water. The optimum water content rose from 6.5% to 11% with the declining of A/S from S=0 to A/S=1/5. Five RAP samples all got the maximum compressive strength when A/S=5/5, and the maximum compressive strength of the samples adding 6% cement was 3.17 MPa. It showed that the capacity of RAP was not only affected by A/S, but also by the content of cement. The dynamic modulus of RAP will increase with the rise of loading frequency and decrease with the temperature rising. SEM test showed that C-S-H interlacing formed the netted structure, and it enwrapped the aggregate and improved the strength of RAP.

The Characteristics of Asphalt Mixture in the System of Full Thickness Cold In-place Recycling

A new research method was proposed（A/S method） to study the components and properties of reclained asphalt mixture（RAP）. The RAP was divided into two main parts, one was marked with A that included all the reclaimed old asphalt materials（including some parts of particle materials covered by asphalt）, the other was marked with S which mainly included works soil in the road structure. The actual working conditions were simulated by this kind of new method, and the adaption between the RAP properties, A/S, and the content of cementitious materials were studied. The research indicated that the real working condition could be simulated effectively by means of A/S method. It was also showed that high content of cement could improve the overall performance of RAP significantly, but it would have a negative effect on the properties of RAP if the types and sizes of aggregate particles in RAP mixture were too single. The optimum water content and maximum dry density could not be regarded as the primary basis to evaluate the overall performance of RAP, when S=0 in the experiments, although the maximum density of samples was bigger than that with A/S=1/1, the samples were not strong enough and they were easy to collapse, which indicated that component design of RAP played a great role in improving the overall properties of RAP and the comprehensive tests should be considered to evaluate the stability of RAP. Low frequency load in high temperature environment had the negative effect on the overall stability of RAP, and factors such as the loading state of the materials, the hydration degree of cementitious materials, and the aggregate gradation in the mixture were the determining factors for improving the overall performance of RAP.

Asphalt Pavement Cold Recycling and Basic Characteristics of RAP Materials and their application

In the developed countries significant proportion of reclaimed asphalt pavement(RAP)materials are used in the construction of pavements.Until recently,milled asphalt from old roads was sent to tip as waste.However,in recent years there has been increased use of waste materials in many road projects within the capital city and federal road network.Use of RAP materials is relatively new to Ethiopia and understanding its characteristics and related technology with all its potential environmental,economic and social benefits is important.Cold recycling is desired due to its potential economic benefit.In this study characteristics of RAP materials are assessed both from literature and laboratory investigations in order to better understand its performance and use.Questionnaire survey was undertaken to identify factors that are hindering recycling of materials in pavements in Ethiopia and what is to be done to overcome these factors.A policy statement is derived to support a quick start and implementation of asphalt pavement recycling in Ethiopia.Currently,a huge asphalt pavement network is being constructed and virgin construction material exploration and import materials such as bitumen is costing the country a lot of money.Over USD 7 Billion worth asphalt pavement have been constructed over the last 23 years to serve the public and freight transport,which requires about USD 176 million annually for maintenance and rehabilitation works.Therefore,any saving obtained from recycling will have meaningful impact on cost saving and environment preservation.

Cold In-Place Recycling as a Sustainable Pavement Practice

Pavement rehabilitation and reconstruction methods with CIR （cold in-place recycling） are alternatives that can effectively reduce the high stresses and waste produced by conventional pavement strategies. An attempt was made to predict the performance, particularly low-temperature cracking resistance characteristics of CIR mixtures. These were prepared with the mix design procedure developed at the URI （University of Rhode Island） for the FHWA （Federal Highway Administration） to reduce wide variations in the application of CIR mixtures production. This standard was applied to RAP （reclaimed asphalt pavement） to produce CIR mixtures with CSS-Ih asphalt emulsion as the additive. By adjusting the number of gyrations of the SGC （Superpave gyratory compactor） for compaction, the field density of 130 pcf was represented accurately. To secure a base line, HMA （hot mix asphalt） samples were produced according to the Superpave volumetric mix design procedure. The specimens were tested using the IDT （indirect tensile） tester according to the procedure of AASHTO T 322 procedure at temperatures of-20, -10 and 0 ℃ （-4, 14, and 32°F, respectively）. The obtained results for the creep compliance and tensile strength were used as input data for the MEPDG （mechanistic empirical pavement design guide）. The analysis results indicated that no thermal or low-temperature cracking is expected over the entire analysis period of 20 years for both HMA and CIR mixtures. Thus, it appears that CIR is a sustainable rehabilitation technique which is also suitable for colder climates, and it is recommended to conduct further investigation of load-related distresses such as rutting and fatigue cracking.

Research and Analysis on the Principle in Plant Cold Recycling for Foamed Bitumen and Mixture Performance

The early asphalt pavement in our country severely reduced the road performance due to various external factors during the use process.According to incomplete statistics,there are more asphalt pavements that need to be renovated and repaired every year in China,and the amount of construction waste such as asphalt concrete and other construction waste reaches 1,000.About ten thousand tons.If such a huge amount of construction waste is not used,it will inevitably cause great pollution to the environment.If it can be reused,not only will it be environmentally friendly and energy-saving,it will also save more than one billion yuan in costs.In view of the above problems,this article conducts related Research and Analysis on the Principle in Plant Cold Recycling for Foamed Bitumen and Mixture Performance to provide reference for future projects.

Recycle of valuable products from oily cold rolling mill sludge

Oily cold rolling mill （CRM） sludge contains lots of iron and alloying elements along with plenty of hazardous organic components, which makes it as an attractive secondary source and an environmental contaminant at the same time. The compound methods of ＂vacuum distillation ＋ oxidizing roasting＂ and ＂vacuum distillation ＋ hydrogen reduction＂ were employed for the recycle of oily cold rolling mill sludge. First, the sludge was dynamically vacuum distilled in a rotating furnace at 50 r/rain and 600℃ for 3 h, which removed almost hazardous organic components, obtaining 89.2wt% ferrous resultant. Then, high purity ferric oxide powders （99.2wt%） and reduced iron powders （98.9wt%） were obtained when the distillation residues were oxidized and reduced, respectively. The distillation oil can be used for fuel or chemical feedstock, and the distillation gases can be collected and reused as a fuel.

Cement-fly Ash Stabilization of Cold In-place Recycled (CIR) Asphalt Pavement Mixtures for Road Bases or Subbases

For lack of laboratory and field performance data on stabilization of reclaimed asphalt pavement （RAP） aggregate and stabilized soil （S） for road bases and subbases construction, the influences of RAP/S ratio, cement and fly ash content, modifying agent （MA） on the compact, unconfined compressive strength, indirect tensile strength and water stability of the CIR mixtures were investigated. The experimental results showed that the maximum dry density and the optimum moisture content of the mixture changed significantly with the RAP/S ratio and cement-fly ash content. Unconfined compressive strength, indirect tensile strength and water stability were improved significantly by the addition of MA, and the water stability was improved by nearly 20% on average. Scanning electron microscopy（SEM） images indicated that MA accelerated the hydration of cement-fly ash system. Needle-like AFt and fibrous C-S-H gel were observed in the mixtures, which resulted in the cementation effect among the CIR mixture particles and a more compact microstructure. All these could be the cause of high strength of the CIR mixtures with MA.

乳化沥青冷再生混合料强度特征与失效断裂演变机制研究进展

“双碳”背景下,将乳化沥青冷再生混合料作为冷拌路面材料已受到道路工程界的广泛关注.针对乳化沥青冷再生混合料设计与应用中关键技术问题的研究进展进行了综述,系统地汇总了乳化沥青冷再生混合料在施工控制、强度发展机理和损伤行为特征3个方面的研究成果.混合料制备工艺方面,总结了目前国内外乳化沥青冷再生混合料生产工艺的相关技术,阐述了乳化沥青冷再生混合料的材料特性、拌和工艺、成型方式和养生条件等对其施工和易性的影响;混合料强度发展机理方面,阐明了乳化沥青冷再生混合料在不同影响因素下的微观结构特征,凝练了材料强度形成过程中的内部界面行为;混合料断裂失效行为特征方面,归纳了研究断裂行为和断裂机理的理论方法和实验手段,探讨了乳化沥青冷再生混合料的断裂机制与疲劳特性.研究表明:构建全面的材料组成特性认知体系,利用多尺度手段揭示乳化沥青冷再生混合料强度形成机理,实时动态感知混合料疲劳损伤过程的阶段性演化规律,将对改善乳化沥青冷再生混合料的力学性能和延长冷再生路面的使用寿命具有重要意义.

Strontium ferrite powders prepared from oily cold rolling mill sludge by solid-state reaction method

Oily cold rolling mill （CRM） sludge is one of the pollutants emitted by iron and steel plants. Recycling oily CRM sludge can not only reduce pollution but also bring social and environmental benefits. In this study, using oily CRM sludge as sources of iron oxide, the strontium ferrite powders were synthesized in multiple steps including vacuum distillation, magnetic separation, oxidizing roasting, and solidstate reaction. The optimal technological conditions of vacuum distillation and oxidizing roasting were studied carefully. To consider the effects of Fe203/ SrCO3 tool ratio, calcination temperature, milling time and calcination time on magnetic properties of prepared strontium ferrite powders, the orthogonal experimental method was adopted. The maximum saturation magneti- zation （62.6 mA-m2.g-1） of the synthesized strontium ferrite powders was achieved at the Fe203/SrCO3 mol ratio of 6, 5 h milling time, 1250 ~C calcination temperature, and 1 h calcination time. Strontium ferrite powders syn- thesis method not only provides a cheap, high quality raw material for the production of strontium ferrite powders, but also effectively prevents the environmental pollution.

Physical and Mechanical Properties of Eco-Friendly Composites Made from Wood Dust and Recycled Polystyrene

The development of alternative wood composites based on the use of waste or recycled materials can be beneficial due to over exploitation of natural resources.Under this frame,an option for the successful utilization of waste polystyrene which avoids environmental problems that formaldehyde adhesives cause and also reduces waste dis-posal,is its potential application as a binder for the production of value-added environmentally friendly and low cost wood composites.Two types of panel were successfully made,consisting of wood dust and two recycled poly-styrene contents,namely,15%and 30%.Both physical properties,water absorption and thickness swelling,and mechanical properties,modulus of rupture,shear strength parallel in the plane of the board and glue line shear strength,were significantly improved as the recycled polystyrene content increased from 15%to 30%.Water absorption and thickness swelling after 24 h immersion in water were improved by 165%and 750%as the recycled polystyrene content increased from 15%to 30%.The magnitude of the improvement in mechanical properties however,was less pronounced than of the physical properties since modulus of rupture,shear strength parallel in the plane of the board and glue line shear strength were increased by 43.6%,50%and 61.5%,respec-tively.The low viscosity of the recycled polystyrene caused more mobility inside the panel matrix and therefore,an improved penetration took place into adequate depth of the compressed dust particles.It is concluded that boards can be successfully produced using these waste raw materials,wood dust and recycled polystyrene in organic solvent as a binder,and therefore it can reduce waste disposal and provide cleaner production for the development of wood-based boards.

二次热压实作用对乳化沥青冷再生混合料性能的影响

为了量化分析现场二次热压实作用对乳化沥青冷再生混合料性能的影响,基于常规力学性能试验、Overlay Tester反射裂缝试验、低应变水平下的四点弯曲疲劳试验,对比分析了现场铺筑上覆热拌沥青混合料前后乳化沥青冷再生芯样与室内马歇尔试样的力学性能差异。量化分析了现场二次热压实作用对乳化沥青冷再生混合料力学性能及耐久性能的增强效果,并基于工业CT无损检测技术,分析了现场二次热压实作用对乳化沥青冷再生混合料微细观空隙结构的影响规律。结果表明:现行规范推荐的马歇尔二次击实方法并不能很好地模拟现场实际压实状况,现场二次热压实对乳化沥青冷再生混合料力学性能、抗反射裂缝性能和抗疲劳耐久性能均有明显增强作用;现场压实乳化沥青冷再生混合料内部的大空隙数量和等效空隙直径均小于马歇尔击实成型,二次热压实作用对乳化沥青冷再生混合料空隙级配影响显著;现场二次压实作用对乳化沥青冷再生混合料力学性能和疲劳性能的改善机理在于二次压实作用增强了乳化沥青冷再生混合料密实度,降低了微细观空隙直径,改善了微细观空隙级配。

寒区低温环境下泡沫沥青冷再生混合料性能研究

我国西藏、青海等省区全年气候寒冷,平均气温低,昼夜温差和年温差大,冻融循环频繁,公路建设普遍面临着生态环境脆弱、建筑材料数量匮乏且质量较差等问题。针对上述寒区气候特点,采用5℃、10℃、22℃、40℃、60℃和110℃分别模拟低温、室温、中温和高温养生条件下泡沫沥青冷再生混合料现场养生条件,基于室内试验分析了寒区低温环境温度对泡沫沥青冷再生混合料力学性能、路用性能、耐久性能的劣化影响;进而基于数字图像处理技术和工业CT无损检测技术,探讨了养生温度对泡沫沥青冷再生混合料内部泡沫沥青分散性状及微细观空隙结构的影响规律。结果表明:随着养生温度升高,泡沫沥青冷再生混合料的单轴贯入强度、无侧限抗压强度、动态回弹模量等力学指标均呈指数函数关系增大;相较于标准养生条件,在低温条件下拌和、养生的泡沫沥青冷再生混合料,其高温稳定性、抗反射裂缝性能及抗疲劳性能下降明显,并且环境温度越低,泡沫沥青冷再生混合料的综合路用性能降低幅值越大。升高养生温度后,泡沫沥青在破坏试件界面的分散面积增大,微细观空隙直径减小,并且微细观空隙结构中体积小于0.05 mm3的空隙占比增大。养生温度对泡沫沥青冷再生混合料的作用机理主要在于提高养生温度对泡沫沥青分散性状的促增作用和微细观空隙结构的细化作用。建议在泡沫沥青冷再生路面施工期间加强施工和养生期间的温度控制,并且结合寒区施工季节温度调整室内配合比设计养生温度。本研究成果可为泡沫沥青冷再生技术在寒区的推广应用提供借鉴。

水反应型全比例冷再生沥青混合料的路用性能研究

针对常规热拌再生沥青混合料应用时工序繁杂的问题,采用再生AC-20C矿料级配制备了水反应型全比例冷再生沥青混合料、热拌再生沥青混合料和泡沫沥青再生混合料,并对比了3种再生沥青混合料的性能。研究结果表明:水反应型全比例冷再生沥青混合料的性能优于泡沫沥青再生混合料,接近热拌再生沥青混合料。水反应型全比例冷再生沥青混合料7 d的马歇尔稳定度和动稳定度分别可达9.52 kN、4 228次/mm,其水稳定性能、低温抗裂性能和疲劳耐久性能均满足现行施工技术规范对热拌沥青混凝土的要求。随着时间的推移,反应型稀释剂与固化剂的交联络合反应会持续进行,水反应型全比例冷再生沥青混合料的物理力学性能也会持续增强。

沥青路面冷再生试验路车辙变形的时空分布

为了揭示冷再生沥青混合料在结构中的力学行为,为道路维修养护中的结构设计提供依据,研究依托山东省某高速公路试验路的冷再生沥青路面结构及其中传感器监测数据,分析冷再生结构层在行车荷载作用下的动态响应特点及规律。依托实测温度场数据,构建黏弹性有限元仿真模型,分析了冷再生沥青路面结构车辙的分布规律。结果表明:对于试验路结构的冷再生沥青混合料层,行车速度与结构内部应变响应持续时间呈幂函数关系,在60~80 km/h的速度下,其结构层内部的力学响应频率接近10 Hz;在路面设计时,冷再生层可取其在20℃、10 Hz下的动态模量作为结构模量;对于冷再生沥青试验路结构,其一天中逐小时车辙量的分布主要与交通量相关,一年中的月车辙量的分布主要与温度相关,其中,一年之内的车辙累积主要发生在5—10月,冬季期内发生的车辙量几乎可以忽略不计;为避免由于结构层厚度增加导致过高的车辙预估量,需在计算沥青混合料层永久变形等效温度时对沥青层的厚度进行限制;此外,在高温条件下,相较于动态模量的改变,控制上、中面层沥青混合料在40~45℃左右的塑性变形发展速率对于减小路面永久变形的累积具有更为显著的作用。

基于CT图像的水泥稳定RAP材料细观结构研究

研究沥青混合料回收料(RAP)掺加对混合料组成与结构特性的影响,可为其应用在路面结构层以及材料参数设计提供理论支撑。基于X-ray CT与图像处理技术,提出了一种可区分新旧集料的冷再生混合料细观结构识别方法,分析了RAP团粒、旧集料与新集料的细观特征的差异,研究了RAP的掺加对水泥稳定材料细观结构的影响。结果表明:提出的细观结构识别方法可准确识别水泥稳定RAP材料断面图像中的空隙、砂浆、新集料与旧集料四类区域,完整地保留新旧集料的原始轮廓、大小与形状等信息;RAP团粒中分布较多初始微细裂缝,且旧集料扁平比与棱角性系数均大于新集料;RAP的掺加一方面增加了再生混合料中体积小于0.01 mm3的微空隙与大于100 mm3的大空隙数量,导致材料的密实度降低;另一方面也增加了材料的沥青砂浆含量,提高了再生混合料的平均砂浆膜厚度,使混合料骨架内部力传导更均匀;提高水泥稳定RAP材料中石屑与碎石比例,可使材料的平均空隙体积减小、平均砂浆膜厚度增大,从而改善再生混合料的骨架填充状态。

不同养生龄期下VAE改性乳化沥青冷再生混合料的路用性能

乳化沥青冷再生技术应用于道路工程时,常因养生龄期的限制和冷再生混合料自身水稳定性不足导致出现各种路面病害。以提高冷再生混合料的水稳定性为出发点,采用一种新型的改性剂醋酸乙烯-乙烯共聚物(VAE)对乳化沥青进行改性;探究VAE改性乳化沥青冷再生混合料在较长养生期间其路用性能的变化规律,以普通乳化沥青冷再生混合料为参照,采用干湿劈裂试验、冻融劈裂试验、20℃肯塔堡飞散试验、车辙试验和-10℃弯曲试验综合分析VAE改性乳化沥青冷再生混合料的路用性能,并从微观角度分析VAE改性乳化沥青冷再生混合料性能提升的机理。试验与分析结果表明:养生3~7 d是乳化沥青冷再生混合料发育形成强度的关键阶段;无论从水稳定性、抗剥落性方面还是高低温性能方面,VAE改性乳化沥青混合料的各项性能均优于普通乳化沥青冷再生混合料,具有推广应用价值。

100%RAP的废机油-乳化沥青冷再生沥青及混合料性能试验

基于100%RAP再生率,采用废机油预润再生老化沥青,并对其进行三大指标和红外光谱试验,同时对其混合料进行干湿劈裂试验、冻融试验及马歇尔稳定度试验,以评价其力学及水稳性能。试验结果表明:废机油可以在三大指标上使老化沥青接近新沥青,但掺量过高会导致软化点过低,使冷再生混合料性能降低;红外光谱表明废机油具有降低亚砜基和羰基极性官能团指数的作用;经过废机油预润再生后,RAP表面老化沥青初步激活,与乳化沥青更好的粘结,可提高混合料的强度及水稳性能;废机油掺量为10%的乳化沥青再生混合料性能较差,这与废机油过量有关。

乳化沥青冷再生混合料断裂性能试验研究

乳化沥青冷再生沥青路面的开裂问题是制约其大规模推广使用的主要原因之一。为了研究冷再生沥青混合料断裂性能的评价指标及抗裂性能提升措施,以普通乳化沥青、外掺玄武岩纤维和SBR改性乳化沥青3种冷再生混合料为研究对象,开展了有预制裂缝中梁的四点弯曲强度试验及其断裂过程的声发射测试;以应变能释放速率、应力强度因子和声发射测试中所采集的能量及振铃计数‒撞击数等参数为评价指标,对比分析了3种不同乳化沥青冷再生混合料的断裂性能。试验结果表明:使用SBR改性乳化沥青和外掺玄武岩纤维均对乳化沥青冷再生混合料的抗断裂性能有较为显著的提升,且相比于使用SBR改性乳化沥青,外掺玄武岩纤维更为有效。振铃计数和撞击数参数可以较好地描述材料的断裂特征,声发射试验结果与断裂力学参数计算结果满足较好的线性相关性。声发射信号参数能够很好地描述乳化沥青冷再生混合料在四点弯曲试验中的断裂特征。