Evaluation of waste slags produced by zinc industry in bituminous hot mixtures

Owing to the large amount of waste slags produced by zinc industry, it has become necessary to recycle it in some areas. Road construction has significant potential for the use of waste materials because more material is always needed. In this study, the engineering behaviour of asphalt concrete was investigated using mineral aggregates with waste slag, which is a by-product of the zinc–lead production industry. The asphalt concrete tested in this study was fabricated using 25, 50, 75 and 100 % mixing ratios instead of the conventional fine mineral aggregate (11, 22, 33 and 44 % rate of total aggregate mixture) to determine the possibility of using slags in the binder course of bituminous hot mixtures. The asphalt concretes, made of waste slags and conventional asphalt concrete, were evaluated in terms of their fundamental engineering properties such as Marshall stability, flow, Marshall quotient (MQ), bulk specific gravity, air voids and voids filled with bitumen in the total mix characteristics. The results indicate that the addition of waste slag as mineral aggregate improves the engineering characteristic performance and that it can be used in bituminous hot mixtures. In addition, principal component analyses were applied to examine the significance of each Marshall parameter, and a regression model was developed to estimate the MQ value using effective parameters.     

Use of recycled plastic in concrete: a review

Numerous waste materials are generated from manufacturing processes, service industries and municipal solid wastes. The increasing awareness about the environment has tremendously contributed to the concerns related with disposal of the generated wastes. Solid waste management is one of the major environmental concerns in the world. With the scarcity of space for landfilling and due to its ever increasing cost, waste utilization has become an attractive alternative to disposal. Research is being carried out on the utilization of waste products in concrete. Such waste products include discarded tires, plastic, glass, steel, burnt foundry sand, and coal combustion by-products (CCBs). Each of these waste products has provided a specific effect on the properties of fresh and hardened concrete. The use of waste products in concrete not only makes it economical, but also helps in reducing disposal problems. Reuse of bulky wastes is considered the best environmental alternative for solving the problem of disposal. One such waste is plastic, which could be used in various applications. However, efforts have also been made to explore its use in concrete/asphalt concrete. The development of new construction materials using recycled plastics is important to both the construction and the plastic recycling industries. This paper presents a detailed review about waste and recycled plastics, waste management options, and research published on the effect of recycled plastic on the fresh and hardened properties of concrete. The effect of recycled and waste plastic on bulk density, air content, workability, compressive strength, splitting tensile strength, modulus of elasticity, impact resistance, permeability, and abrasion resistance is discussed in this paper.     

Properties of concrete containing scrap-tire rubber--an overview

Solid waste management is one of the major environmental concerns in the United States. Over 5 billion tons of non-hazardous solid waste materials are generated in USA each year. Of these, more than 270 million scrap-tires (approximately 3.6 million tons) are generated each year. In addition to this, about 300 million scrap-tires have been stockpiled. Several studies have been carried out to reuse scrap-tires in a variety of rubber and plastic products, incineration for production of electricity, or as fuel for cement kilns, as well as in asphalt concrete. Studies show that workable rubberized concrete mixtures can be made with scrap-tire rubber. This paper presents an overview of some of the research published regarding the use of scrap-tires in portland cement concrete. The benefits of using magnesium oxychloride cement as a binder for rubberized concrete mixtures are also presented. The paper details the likely uses of rubberized concrete.     

Potential To Use Waste Tires As Supplemental Fuel In Pulp And Paper Mill Boilers,Cement Kilns And In Road Pavement

The objective of this paper is to evaluate the recycling potential of waste tires as an energy source and for use in road pavement. North Carolina, U.S.A., is used as a case study. Scrap tires may be burned for supplemental fuel in pulp and paper mill boilers and cement kilns. Five pulp and paper mill boilers in North Carolina could consume over 90% of the 6 million tires generated annually in the state. Cement kilns located within 400 km of North Carolina population centers could consume about 6.6 million tires annually. Based on the quantity of pavement laid in North Carolina, nonproprietary and proprietary versions of asphalt rubber concrete have the potential to consume 1.8 and 7.2 million tires, respectively. Rubber modified asphalt concrete has the potential to consume up to 16.5 million tires. However, technological and economic limitations suggest that large scale implementation is unlikely for the short term. Environmental considerations pertaining to each alternative are discussed. Estimates of this nature are critical as planning regions formulate solid waste management plans which include recycling.     

Recovery of MSWI and soil washing residues as concrete aggregates

The aim of the present work was to study if municipal solid waste incinerator (MSWI) residues and aggregates derived from contaminated soil washing could be used as alternative aggregates for concrete production.Initially, chemical, physical and geometric characteristics (according to UNI EN 12620) of municipal solid waste incineration bottom ashes and some contaminated soils were evaluated; moreover, the pollutants release was evaluated by means of leaching tests. The results showed that the reuse of pre-treated MSWI bottom ash and washed soil is possible, either from technical or environmental point of view, while it is not possible for the raw wastes.Then, the natural aggregate was partially and totally replaced with these recycled aggregates for the production of concrete mixtures that were characterized by conventional mechanical and leaching tests. Good results were obtained using the same dosage of a high resistance cement (42.5R calcareous Portland cement instead of 32.5R); the concrete mixture containing 400 kg/m³ of washed bottom ash and high resistance cement was classified as structural concrete (C25/30 class). Regarding the pollutants leaching, all concrete mixtures respected the limit values according to the Italian regulation.     

A study on engineering characteristics of asphalt concrete using filler with recycled waste lime

This study focuses on determining the engineering characteristics of asphalt concrete using mineral fillers with recycled waste lime, which is a by-product of the production of soda ash (Na(2)CO(3)). The materials tested in this study were made using a 25%, 50%, 75%, and 100% mixing ratio based on the conventional mineral filler ratio to analyze the possibility of using recycled waste lime. The asphalt concretes, made of recycled waste lime, hydrated lime, and conventional asphalt concrete, were evaluated through their fundamental engineering properties such as Marshall stability, indirect tensile strength, resilient modulus, permanent deformation characteristics, moisture susceptibility, and fatigue resistance. The results indicate that the application of recycled waste lime as mineral filler improves the permanent deformation characteristics, stiffness and fatigue endurance of asphalt concrete at the wide range of temperatures. It was also determined that the mixtures with recycled waste lime showed higher resistance against stripping than conventional asphalt concrete. It was concluded from various test results that a waste lime can be used as mineral filler and, especially, can greatly improve the resistance of asphalt concrete to permanent deformation at high temperatures.     

Utilization of bottom ash from the incineration of separated wastes as a cement substitute.

Waste incineration is still an essential technology in the concept of integrated waste management. Most of the combustion residues are incinerator bottom ash. It has been discovered that incinerator bottom ash from the incineration of separated waste in the primary chamber of the modular two-stage incinerator mainly consists of metal oxides, especially SiO2 and CaO, in proportions that are quite similar to those in cement and so the feasibility of its application as a substitute for cement in concrete was investigated. It was found that after 28 days, the flexural and compressive strengths of the binder using bottom ash were practically comparable with those of a pure cement mixture. The results show that it is reasonable to use a binder containing incinerator bottom ash for applications in which an early-stage lower strength of concrete element is acceptable.     

Utilization of municipal solid waste bottom ash and recycled aggregate in concrete

In the combustion process of municipal solid waste (MSW), bottom ash (BA) represents the major portion of the solid residue. Since BA is composed of oxides, especially SiO(2) and CaO, the feasibility of its application in concrete as a substitute for cement was tested. It was found that at the age of 28 days, the flexural and compressive strengths of the binder linearly decrease at the rate of 0.03 and 0.02 MPa per wt% of BA in the binder, respectively. According to the results it may be recommended to replace up to 15 wt% of cement by BA and to use such binder where a low strength of concrete elements is required. Furthermore, the aggregate used for low strength concrete need not be of a very good quality. Therefore, gravel aggregate was partially replaced by recycled aggregate (RA). Consistency measured by slump was significantly reduced (>50%) when BA or/and RA were introduced into the mixture. However, concrete density and compressive strength were not affected and were approximately 2300 kg/m(3) and approximately 40 MPa, respectively.     

An investigation of waste foundry sand in asphalt concrete mixtures.

A laboratory study regarding the reuse of waste foundry sand in asphalt concrete production by replacing a certain portion of aggregate with WFS was undertaken. The results showed that replacement of 10% aggregates with waste foundry sand was found to be the most suitable for asphalt concrete mixtures. Furthermore, the chemical and physical properties of waste foundry sand were analysed in the laboratory to determine the potential effect on the environment. The results indicated that the investigated waste foundry sand did not significantly affect the environment around the deposition     

Properties of asphaltic paving mixes containing hydrated lime waste

This investigation presents the results of the study conducted to utilize carbide lime waste as a filler in asphaltic paving mixes, and to study the effect of the incorporation of the waste on the properties of asphaltic paving mixes. The waste, which consists mainly of calcium hydroxide, is generated from two acetylene plants in Bahrain, and the amount is estimated to be 5000 tonnes annually. Physical and chemical properties of the waste were studied. A total of 450 asphaltic concrete mixes were prepared at five different percentages by weight of the waste and the limestone (control). The percentages employed in the mixes were 2, 4, 6, 8, and 10 by weight of the aggregate. Marshall test methods were used to evaluate the compacted mix density, percent air voids, voids in mineral aggregate, stability, and flow. The Marshall stability was carried out at 40 °C, 60 °C, and 70 °C. The results revealed that the minimum 8 KN criteria adopted by the Bahrain specifications was met by all the waste mixes. Also, the waste mixes had much better resistance to high temperatures compared with mixes using conventional limestone filler. The results of the investigation suggest that the incorporation of the waste in asphaltic concrete mixes improves some of its properties, and that it is especially advantageous for use in arid environments, such as Bahrain.     

An investigation on the use of shredded waste PET bottles as aggregate in lightweight concrete

In this work, the utilization of shredded waste Poly-ethylene Terephthalate (PET) bottle granules as a lightweight aggregate in mortar was investigated. Investigation was carried out on two groups of mortar samples, one made with only PET aggregates and, second made with PET and sand aggregates together. Additionally, blast-furnace slag was also used as the replacement of cement on mass basis at the replacement ratio of 50% to reduce the amount of cement used and provide savings. The water–binder (w/b) ratio and PET–binder (PET/b) ratio used in the mixtures were 0.45 and 0.50, respectively. The size of shredded PET granules used in the preparation of mortar mixtures were between 0 and 4 mm. The results of the laboratory study and testing carried out showed that mortar containing only PET aggregate, mortar containing PET and sand aggregate, and mortars modified with slag as cement replacement can be drop into structural lightweight concrete category in terms of unit weight and strength properties. Therefore, it was concluded that there is a potential for the use of shredded waste PET granules as aggregate in the production of structural lightweight concrete. The use of shredded waste PET granules due to its low unit weight reduces the unit weight of concrete which results in a reduction in the death weight of a structural concrete member of a building. Reduction in the death weight of a building will help to reduce the seismic risk of the building since the earthquake forces linearly dependant on the dead-weight. Furthermore, it was also concluded that the use of industrial wastes such as PET granules and blast-furnace slag in concrete provides some advantages, i.e., reduction in the use of natural resources, disposal of wastes, prevention of environmental pollution, and energy saving.     

Recycling building demolition waste in hot-mix asphalt concrete: a case study in Kuwait

Building demolition waste constitutes a major component of municipal solid waste in Kuwait. Over 90% of this waste is currently land-filled, causing extreme pressure on the available land-fill sites. At the same time, the sources of natural aggregates are almost depleted, and there is an increasing demand because of the increased construction and maintenance activities. This article presents the results of a technical feasibility study into meeting this need by recycling the aggregates obtained from building demolition waste for asphalt concrete. The Marshall test, the immersion compression test, the loss of stability test, and the wheel track test were performed to evaluate the asphalt concrete made with recycled aggregate. The results showed that the asphalt concrete produced using an aggregate of demolition waste met all the requirements of local specifications.     

Utilization of industrial by-products for the production of controlled low strength materials (CLSM)

Industrial by-products were used for the production of controlled low-strength material (CLSM). CLSM, also known as 'flowable fill' is used as a replacement of compacted soil in cases where the application of the latter is difficult or impossible. The low mechanical requirements (compared with structural concrete) enable the use of industrial by-products for the production of CLSM. In this study cement kiln dust, asphalt dust, coal fly ash, coal bottom ash and quarry waste were tested for the possibility of producing CLSM with large proportions of those wastes. The results showed that in most cases, CLSM with good properties could be made with significant amounts of dust (25-50%w), especially when the dust has some cementing or pozzolanic potential as do fly ash and cement kiln dust.     

Use of flue gas desulphurisation (FGD) waste and rejected fly ash in waste stabilization/solidification systems

Stabilization/solidification (S/S) processes have been used as the final treatment step for hazardous wastes prior to land disposal. Fly ash is a by-product of coal-fired power generation; a significant proportion of this material is low-grade, reject material (rFA) that is unsuitable as a cement replacement due to its high carbon content and large particle size (>45 microm). Flue gas desulphurization (FGD) sludge is a by-product from the air pollution control systems used in coal-fired power plants. The objective of this work was to investigate the performance of S/S waste binder systems containing these two waste materials (rFA and FGD). Strength tests show that cement-based waste forms with rFA and FGD replacement were suitable for disposal in landfills. The addition of an appropriate quantity of Ca(OH)2 and FGD reduces the deleterious effect of heavy metals on strength development. Results of TCLP testing and the progressive TCLP test show that cement-rFA-Ca(OH)2 systems with a range of FGD additions can form an effective S/S binder. The Leachability Index indicates that cement-based waste forms with rFA replacement were effective in reducing the mobility of heavy metals.     

Reuse of municipal solid wastes incineration fly ashes in concrete mixtures

This study is aimed at assessing the feasibility of concrete production using stabilized m.s.w. (municipal solid waste) incineration fly ashes in addition to natural aggregates. The tested fly ashes were washed and milled, then stabilized by a cement-lime process and finally were reused as a "recycled aggregate" for cement mixture production, in substitution of a natural aggregate (with dosage of 200-400 kg m(-3)). These mixtures, after curing, were characterized with conventional physical-mechanical tests (compression, traction, flexure, modulus of elasticity, shrinkage). In samples containing 200 kg(waste) m(-3)(concrete), a good compressive strength was achieved after 28 days of curing. Furthermore, concrete leaching behavior was evaluated by means of different leaching tests, both on milled and on monolithic samples. Experimental results showed a remarkable reduction of metal leaching in comparison with raw waste. In some cases, similar behavior was observed in "natural" concrete (produced with natural aggregates) and in "waste containing" concrete.     

An alternative method for the treatment of waste produced at a dye and a metal-plating industry using natural and/or waste materials.

The aim of this study was to develop cost-effective, appropriate solidification technologies for treating hazardous industrial wastes that are currently disposed of in ways that may threaten the quality of local groundwater. One major objective was to use materials other than cement, and preferably materials that are themselves wastes, as the solidification additives, namely using wastes to treat wastes or locally available natural material. This research examines the cement-based and lime-based stabilization/solidification (S/S) techniques applied for waste generated at a metal-plating industry and a dye industry. For the lime-based S/S process the following binder mixtures were used: cement kiln dust/ lime, bentonite/lime and gypsum/lime. For the cement-based S/S process three binder mixtures were used: cement kiln dust/cement, bentonite/cement and gypsum/cement. The leachability of the wastes was evaluated using the toxicity characteristic leaching procedure. The applicability and optimum weight ratio of the binder mixtures were estimated using the unconfined compressive strength test. The optimum ratio mixtures were mixed with waste samples in different ratios and cured for 28 days in order to find the S/S products with the highest strength and lowest leachability at the same time. The results of this work showed that the cement-and lime-based S/S process, using cement kiln dust and bentonite as additives can be effectively used in order to treat industrial waste.     

Value-added utilisation of recycled concrete in hot-mix asphalt

The feasibility of partial substitution of granite aggregate in hot-mix asphalt (HMA) with waste concrete aggregate was investigated. Three hybrid HMA mixes incorporating substitutions of granite fillers/fines with 6%, 45% untreated, and 45% heat-treated concrete were evaluated by the Marshall mix design method; the optimum binder contents were found to be 5.3%, 6.5% and 7.0% of grade Pen 60/70 bitumen, respectively. All three hybrid mixes satisfied the Marshall criteria of the Singapore Land Transport Authority (LTA) W3B wearing course specification. The hybrid mix with 6% concrete fillers gave comparable resilient modulus and creep resistance as the conventional W3B mix, while hybrid mixes with higher concrete substitutions achieved better performance. X-ray diffraction (XRD) showed the distinct presence of free lime in the heat-treated concrete, while the scanning electron microscope (SEM) provided an in-depth perspective of the concrete grains in the HMA matrix. The results suggest feasible use of waste concrete as partial aggregate substitution in HMA.     

Modelling the effects of waste components on cement hydration

Ordinary Portland Cement (OPC) is often used for the solidification/stabilization (S/S) of waste containing heavy metals and salts. These waste components will precipitate in the form of insoluble compounds on to unreacted cement clinker grains preventing further hydration. In this study the long term effects of the presence of contaminants in solidified waste is examined by numerically simulating cement hydration after precipitation of metal salts on the surface of cement grains. A cement hydration model was extended in order to describe pore water composition and the effects of cement grain coating. Calculations were made and the strength development predicted by the model was found to agree qualitatively with experimental results found in literature. The complete model is useful in predicting the strength and leaching resistance of solidified products and developing solidification recipes based on cement.     

Research on recycle of waste fluorescent lamp glasses and use as mineral filler in asphalt mixture

Journal of Material Cycles and Waste Management - In this study, utilization of waste fluorescent lamp as mineral filler in asphalt mixture was investigated. The phosphorus powder of fluorescent...     

Assessment of the recycling potential of fresh concrete waste using a factorial design of experiments

Recycling of industrial wastes and by-products can help reduce the cost of waste treatment prior to disposal and eventually preserve natural resources and energy. To assess the recycling potential of a given waste, it is important to select a tool capable of giving clear indications either way, with the least time and work consumption, as is the case of modelling the system properties using the results obtained from statistical design of experiments. In this work, the aggregate reclaimed from the mud that results from washout and cleaning operations of fresh concrete mixer trucks (fresh concrete waste, FCW) was recycled into new concrete with various water/cement ratios, as replacement of natural fine aggregates. A 3² factorial design of experiments was used to model fresh concrete consistency index and hardened concrete water absorption and 7- and 28-day compressive strength, as functions of FCW content and water/cement ratio, and the resulting regression equations and contour plots were validated with confirmation experiments. The results showed that the fresh concrete workability worsened with the increase in FCW content but the water absorption (5–10 wt.%), 7-day compressive strength (26–36 MPa) and 28-day compressive strength (32–44 MPa) remained within the specified ranges, thus demonstrating that the aggregate reclaimed from FCW can be recycled into new concrete mixtures with lower natural aggregate content.