The Experts below are selected from a list of 48 Experts worldwide ranked by ideXlab platform
Xu Yang - One of the best experts on this subject based on the ideXlab platform.
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a novel double Drum Mixing technique for plant hot mix asphalt recycling with high reclaimed asphalt pavement content and rejuvenator
Construction and Building Materials, 2017Co-Authors: Huijun Shao, Xu YangAbstract:Abstract Hot mix asphalt (HMA) recycling has been widely used in pavement engineering. When the content of reclaimed asphalt pavement (RAP) is high, asphalt rejuvenator is often used to improve the performance of asphalt mixtures. The existing Mixing technique of HMA recycling with rejuvenator is adopted from the traditional hot mix asphalt plant with one Mixing Drum. The drawbacks of this Mixing technique are that the rejuvenator cannot fully interact with RAP and some aggregates may not be well coated with virgin asphalt binder. In recognition of these, a novel Mixing technique, namely double-Drum Mixing, is proposed and evaluated. A comparative study was carried out to investigate the effect of double-Drum Mixing on the performance of hot recycled asphalt mixtures. In detail, the volumetric properties, tensile strength, moisture damage resistance, rutting resistance, and low temperature cracking resistance were evaluated. Two asphalt mixtures (AC-13 and AC-25) with three RAP contents (40%, 50% and 60%) were investigated. The results showed that the proposed new Mixing technique can improve the performance of hot recycled asphalt mixtures in several aspects. The double-Drum Mixing process can reduce the air voids if all other mix design parameters are the same. Additionally, the tensile strength, moisture damage resistance, rutting resistance, and low temperature cracking resistance were improved to a certain extent.
Huijun Shao - One of the best experts on this subject based on the ideXlab platform.
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a novel double Drum Mixing technique for plant hot mix asphalt recycling with high reclaimed asphalt pavement content and rejuvenator
Construction and Building Materials, 2017Co-Authors: Huijun Shao, Xu YangAbstract:Abstract Hot mix asphalt (HMA) recycling has been widely used in pavement engineering. When the content of reclaimed asphalt pavement (RAP) is high, asphalt rejuvenator is often used to improve the performance of asphalt mixtures. The existing Mixing technique of HMA recycling with rejuvenator is adopted from the traditional hot mix asphalt plant with one Mixing Drum. The drawbacks of this Mixing technique are that the rejuvenator cannot fully interact with RAP and some aggregates may not be well coated with virgin asphalt binder. In recognition of these, a novel Mixing technique, namely double-Drum Mixing, is proposed and evaluated. A comparative study was carried out to investigate the effect of double-Drum Mixing on the performance of hot recycled asphalt mixtures. In detail, the volumetric properties, tensile strength, moisture damage resistance, rutting resistance, and low temperature cracking resistance were evaluated. Two asphalt mixtures (AC-13 and AC-25) with three RAP contents (40%, 50% and 60%) were investigated. The results showed that the proposed new Mixing technique can improve the performance of hot recycled asphalt mixtures in several aspects. The double-Drum Mixing process can reduce the air voids if all other mix design parameters are the same. Additionally, the tensile strength, moisture damage resistance, rutting resistance, and low temperature cracking resistance were improved to a certain extent.
M. Mohajeri - One of the best experts on this subject based on the ideXlab platform.
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Hot Mix Asphalt Recycling: Practices and Principles
2015Co-Authors: M. MohajeriAbstract:Hot mix asphalt recycling has become common practice all over the world since the 1970s because of the crisis in oil prices. In the Netherlands, hot recycling has advanced to such an extent that in most of the mixtures more than 50% of reclaimed asphalt (RA) is allowed. These mixtures with such a high RA content are produced in a batch plant to which a parallel Drum is attached. In this Drum RA is pre-heated to approximately 130°C. Since 2007 another hot mix recycling techniques became available in which RA is mixed in cold and moist condition in contrary to conventional methods. It is a so called double barrel Drum mixer. In this method virgin aggregates are superheated in the inner Drum and mixed with cool and moist RA and fines and virgin bitumen in the outer Drum. In both cases, double Drum and partial heating methods, the virgin aggregates have to be pre-heated to higher temperatures than with mixtures without RA in order to achieve a Mixing temperature of around 170°C. Dependent on RA amount, moisture, pre-heating, etc. in the batch plant the virgin aggregates have to be pre-heated to around 300° C and in the double barrel Drum to around 500°C. These high temperatures have led to concerns about the quality of the produced mixtures. Since 2008, a new Dutch specification system for asphalt mixtures is in place in line with the European standards (EN13108 series). The new regulation gives contractors freedom to select their own material such as bitumen grade and the amount of recycling; however, in return it makes them responsible for the quality of the mixture. The mixture should fulfill the requirement of fundamental performance characteristics of the mixtures such as resistance to fatigue and permanent deformation. In this research two major questions have been investigated. One of the questions is whether these high temperatures have a negative effect on the bituminous binder, while the other important question is whether the RA binder will blend totally with the virgin binder that is added. The focus of this research was on four objectives. The first objective was to develop a laboratory Mixing method to simulate the real recycling process in the field. The second objective was to assess the effect of the double barrel Drum on the mixture quality in comparison with conventional batch plant. Third, it was aimed to measure the blending degree between two binders. And finally, to increase the understanding of the mechanism behind blending RA binders with virgin bitumen, with focus on their micro structure. To cover all research topics, this dissertation is organized in two parts in which the first part is devoted to laboratory and field mixture evaluation while the second part is presenting the exploratory research on the fundamental aspects of blending. Research in part 1 is conducted in two phases, laboratory simulation and field experimentation. The conventional partial warming recycling method (PW) the upgraded double Drum Mixing method (UPG) were simulated in the lab and the quality of mixtures were compared with the standard Mixing method (SM) in the lab at different RA content and different moisture content. This research showed that higher percentages of RA results in higher stiffness and lower fatigue life. However in the UPG method with 4% moisture and 60% RA, the mixture became remarkably lower in stiffness and durable against fatigue. This might be because of the lack of blending or the effect of foaming of bitumen. It was concluded that the UPG method could not effectively be simulated in the lab. In the next experimental phase of the study, three identical mixtures were produced with 50% RA and 4.3% bitumen. One mixture was produced in a batch plant (BB) while the second one was mixed using a double Drum mixer by the same contractor (A). The third mixture was produced in the laboratory (L) using a lab pugmill mixer. The comparison between three mixtures shows that mixture L has a higher stiffness than A and BB. Mixture BB has as slightly higher stiffness than A. Furthermore, mixture A has the lowest stiffness which is most probably due to the system of cold and moist RA feeding into the double Drum system. Besides the 4PB fatigue and stiffness test, monotonic uniaxial tension (UT) and compression (UC) tests were performed to be used in material modeling and to determine a fatigue endurance limit. The limit value of the stress ratio parameter (Rlimit) was determined which is useful in the determination of the endurance limit in a three-dimensional state. It shows that different Mixing methods lead to different endurance limits. It turns out that the plant produced mixture has a higher endurance limit than the laboratory mixture. In this research an infrared thermography method was used in every material preparation stage. The temperature homogeneity of the mixtures in the lab and in the field was investigated. It proved to be a useful method in visualizing the temperature exchange during Mixing and compaction. In Part 2, the effect of superheating aggregates is studied by simulating RA and real aggregates with glass beads and artificial aged binder. The stage extraction method was evaluated in this research with respect to size and shape of aggregates. The blending and diffusion mechanism between old and new bitumen is studied at the microstructure level by means of Nano indention and Nano-CT scanning. The morphology of different types of bitumen was detectable by these techniques; however the blending zone couldn’t be characterized.
M.i. Ojovan - One of the best experts on this subject based on the ideXlab platform.
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Immobilisation of Radioactive Waste in Cement
An Introduction to Nuclear Waste Immobilisation, 2020Co-Authors: M.i. OjovanAbstract:This chapter discusses the cementation technology used for immobilization of radioactive waste. The practice of encapsulating radioactive waste in ordinary Portland cement (OPC) began during the early years of the nuclear industry due to its low cost, availability and compatibility with aqueous waste. OPC cements can be modified by using a range of additives. These may be defined as additives such as gypsum, which acts to retard hydration, replacements in blended or composite cements or as admixtures. The main cement modifiers include slaked lime, sodium silicate, natural pozzolans and blast furnace slag (BFS). Waste–cement mixtures is prepared either directly in the container (in- Drum Mixing), which is the final product container, or prior to pouring into the container (in-line Mixing). After in-Drum Mixing, the cement–waste mixture is allowed to set, the container is capped with a different composition cement to minimize void spaces and to avoid surface contamination, a lid is fitted. In-line Mixing processes combines the waste, any additives, water and cement before they are placed into a disposal container. The cement–waste mix is released directly from the mixer into the container. The container is then sealed, decontaminated, monitored and sent for storage. Furthermore, this discussion describes the types of cements as: type-I, used when there are no extenuating conditions; type-II, which aids in providing moderate resistance to sulphate attack; type-III, used when high-early strength is required; type-IV, used when a low heat of hydration is desired (in massive structures); and type-V, used when high sulphate resistance is required.
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Chapter 15 – Immobilisation of Radioactive Wastes in Cement
An Introduction to Nuclear Waste Immobilisation, 2020Co-Authors: M.i. OjovanAbstract:Publisher Summary This chapter discusses the cementation technology used for immobilization of radioactive waste. The practice of encapsulating radioactive waste in ordinary Portland cement (OPC) began during the early years of the nuclear industry due to its low cost, availability and compatibility with aqueous waste. OPC cements can be modified by using a range of additives. These may be defined as additives such as gypsum, which acts to retard hydration, replacements in blended or composite cements or as admixtures. The main cement modifiers include slaked lime, sodium silicate, natural pozzolans and blast furnace slag (BFS). Waste–cement mixtures is prepared either directly in the container (in- Drum Mixing), which is the final product container, or prior to pouring into the container (in-line Mixing). After in-Drum Mixing, the cement–waste mixture is allowed to set, the container is capped with a different composition cement to minimize void spaces and to avoid surface contamination, a lid is fitted. In-line Mixing processes combines the waste, any additives, water and cement before they are placed into a disposal container. The cement–waste mix is released directly from the mixer into the container. The container is then sealed, decontaminated, monitored and sent for storage. Furthermore, this discussion describes the types of cements as: type-I, used when there are no extenuating conditions; type-II, which aids in providing moderate resistance to sulphate attack; type-III, used when high-early strength is required; type-IV, used when a low heat of hydration is desired (in massive structures); and type-V, used when high sulphate resistance is required.
J.r. Weber - One of the best experts on this subject based on the ideXlab platform.
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Testing and evaluation of alternative process systems for immobilizing radioactive mixed particulate waste in cement
1994Co-Authors: K.m. Weingardt, J.r. WeberAbstract:Radioactive and Hazardous Mixed Wastes have accumulated at the Department of Energy (DOE) Hanford Site in south-central Washington State. Ongoing operations and planned facilities at Hanford will also contribute to this waste stream. To meet the Resource Conservation and Recovery Act (RCRA) Land Disposal Restrictions most of this waste will need to be treated to permit disposal. In general this treatment will need to include stabilization/solidification either as a sole method or as part of a treatment train. A planned DOE facility, the Waste Receiving and Processing (WRAP) Module 2A, is scoped to provide this required treatment for containerized contact-handled (CH), mixed low-level waste (MLLW) at Hanford. An engineering development program has been conducted by Westinghouse Hanford Company (WHC) to select the best system for utilizing a cement based process in WRAP Module 2A. Three Mixing processes were developed for analysis and testing; in-Drum Mixing, continuous Mixing, and batch Mixing. Some full scale tests were conducted and 55 gallon Drums of solidified product were produced. These Drums were core sampled and examined to evaluate Mixing effectiveness. Total solids loading and the order of addition of waste and binder constituents were also varied. The highest confidence approach to meet the WRAPmore » Module 2A waste immobilization system needs appears to be the out-of-Drum batch Mixing concept. This system is believed to offer the most flexibility and efficiency, given the highly variable and troublesome waste streams feeding the facility.« less
