Waste Material Used In Road Construction

Waste Materials in Construction

Evert Mulder , in Studies in Environmental Science, 1997

Introduction

In The Netherlands most of the demolition waste is being upgraded to a secondary raw material and re-used as a coarse aggregate in concrete, or as a road construction material. To obtain a material of high quality the demolition waste is sieved first, to remove the fines. This fine material (sieve-sand) should not be disposed of, but utilised, both from an economic and environmental point of view. On the other hand, it cannot be applied without due consideration. The sieve-sand may be contaminated with Poly cyclic Aromatic Hydrocarbons (PAHs) to such an extent that, according to the Dutch Building Materials Decree, the sieve-sand is not applicable as a granular building material (as will be explained in the next paragraph).

For this reason Van Bentum Recycling Centrale ordered TNO to carry out a research into the possibilities of stabilising/solidifying the sieve sand in such a way that the PAHs are fixed (immobilised). The intention is to use the stabilised sieve sand to heighten a piece of land for use as an industrial area. The stabilised sieve sand has to be environmentally assessed as a monolithic material, on the basis of leaching.

In this paper the characteristics of sieve sand will be described first. Then a description will be given of the stabilisation process, that was used to immobilise especially the PAHs. After that the results of a leaching test on the stabilised sieve sand are given and the stabilised material is environmentally assessed. Finally the paper ends with some conclusions and a recommendation.

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Waste Materials in Construction

D. Mandin , ... J. Mehu , in Studies in Environmental Science, 1997

2.3 Development of beneficial applications of slags

The following options for beneficial use of slags as substitute for natural raw materials have been evaluated:

–

Aggregates for concrete (partial sand replacement)

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Structural fill in embankments and use as road construction materials

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Base materials for brick and tile manufacture

For different applications different specifications may apply. First the technical suitability of the slags for a given application needs to be determined. When this proves to be the case, the material can be prepared and its actual properties tested. Then the environmental aspects of use of the material in construction will be addressed. For the identification of technical properties end users are involved in the programme.

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Concrete

In the case of application in concrete, the concrete properties will be evaluated at sand replacement levels of 0 (reference), 10, 50 and 100 %. The durability of the concrete is evaluated through measurements of freeze-thaw resistance, alkali-aggregate reaction, long term and autoclave expansion. The leaching behaviour of slag-based mortars and concretes is evaluated using leaching tests focusing on the properties of the intact product rather than studying size reduced material. The major pollutants will be monitored (e.g. heavy metals, Ba, sulphate)as well as major elements or parameters relevant for the leaching behaviour of the material (Al, Ca, Na, K, pH).

–

Application on embankment and road construction

In road construction secondary materials can be applied in different layers of the construction. The investigations have been carried out to compare the properties of the following mixes containing slag :

Road cover	˚ surface bitumen concrete with slag addition as gravel
Road base	˚ slag treated with cement and lime,
	˚ slag concrete with cement and gravel,
	˚ asphalt concrete with lime gravel.

Following the verification of the technical performance of the mix designs, field demonstration has been carried out at a level of 600 m² in 5 sections of different composition.

–

Application in bricks and tiles

The possible application of slag as sand replacement in a special bricks and tiles manufacturing process is based upon transformation of a lime-sand mixture in an autoclave process. The performance has been studied at laboratory scale with various quantities of slag as a partial substitution of sand. After demonstration of satisfactory performance, an experiment on a larger scale has been performed at a sand lime bricks plant.

–

Study of environmental performance of slag containing construction products

The environmental performance of the slag containing construction products is verified in long term laboratory leaching tests (3 months, 6 months, 1 year) under a number of exposure conditions, such as acid rains, alkaline waters, oxidizing and reducing conditions, salted and fresh water, water saturated testing and discontinuous exposure to water. Pilot scale tests have been designed and manufactured in close collaboration with the final product producers and users.

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HARVESTING | Roading and Transport Operations

A.E. Akay , J. Sessions , in Encyclopedia of Forest Sciences, 2004

Selection of Most Economical Road Standard

Forest road design involves simultaneous consideration of and trade-offs between construction costs, road maintenance, vehicle performance, and environmental effects. The trade-offs are not always obvious and vary depending upon local availability of construction materials, road standards, and topography. Based on these factors, the designer should be able to select the best road standard. It is important to know as much as possible about the future performance of a selected road standard so that adequate roads can be designed and built at minimum expense. If forest roads are planned for use during spring thaw conditions, road designers should take extra care in constructing the roads to reduce the road deformation.

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Waste Materials in Construction

Shin-ichi Sakai , Masakatsu Hiraoka , in Studies in Environmental Science, 1997

5 'Effective Reuse Manual' of MSW Melted Slag (draft)

As I mentioned above, high-temperature treatment technologies for incinerator residues (melting and solidification methods) have been developed, and it is becoming possible to reuse the residues effectively by melting. It is important to reuse them as road construction materials or concrete aggregate and so prevent environmental disruption caused by quarrying. Some basic ideas for the effective utilization of incinerator residue products are as follows:

(1)

Incinerator residues should be reduced through waste discharge control and recycling,

(2)

Incinerator residue products should be positively promoted for reuse, in order to reduce the final landfill volume, and

(3)

Incinerator residue products have to be stable in order not to cause environmental pollution, such as soil contamination and ground water pollution.

With this in mind, the Ministry of Health and Welfare is discussing the drafting of an 'effective reuse manual', aiming at promoting the safe reuse of incinerator residues, by setting reprocessing technologies, reuse standards and their evaluation methods. I would like to introduce an outline of the manual here. It deals with the following:

(1)

Slag produced by melting MSW incinerator residues under the temperature of 1200 ∼ 1400°C or higher,

(2)

Slag produced by gasification/melting of MSW under the temperature of 1200 ∼ 1400°C or higher, and

(3)

Solid substances produced by sintering MSW incinerator residues under the temperature of 1000 ∼ 1300°C.

The Ministry of Construction is also considering applying standards for the reuse of melted slag from sewage sludge, and the Environment Agency is examining standards for various recycling flows such as iron slag from steel production or coal ash.

The effective reuse standards have to incorporate physical standards such as strength and durability and quality standards focusing on environmental impact. Within the quality standards, hazardous substances exposure routes to human body should be considered. The routes are roughly classified into three, or food, air, and drinking water. Among them, the most important exposure route is drinking water, that is, hazardous substances leaching from residue products into ground water through rain. Therefore, leaching tests were adopted for quality confirmation and drinking water standards were applied for slag standards. At present, 29 items of drinking water standards are concerned with human health. 23 items including cyanogen and other organic compounds are considered to decompose because melted slag and sintered products are manufactured under the temperature of a thousand and some hundreds degrees centigrade (refer to Table 2). Thus, they were left out of the effective reuse standards. For the following six heavy metals, standard values were set;

Table 2. Leaching Test Methods

Test name	Environmental Agency Notification No. 13 (Note 1)	Environmental Agency Notification No. 46 (Note 1)	Ministry of Health and Welfare Tentative draft of slag test (Note 2)	Ministry of Construction Tentative draft of CO2 method	Availability test (NEN 7341)	pH dependency test (Author et al's commonly used method)	TCLP (EPA Method 1311)
Leaching vessel	Unspecified	Unspecified	Airtight bottle (CO2 method) or beaker (pH-static method), (1L polyethylene bottle or 1L glass beaker)	Unspecified (1L glass beaker at this test)	1L beaker	1L beaker at this test	Any material compatible with waste, zero-head space container
Sample	< 5 mm	< 2 mm	10-30 mm	20-50 mm (< 50 mm: uncrushed)	< 125 μm	Uncrushed (fly ash, hydropulped slag)	< 9.5 mm
Sample mass	> 50 g	> 50 g	> 50 g	> 50 g	16 g	50 g at this test	100 g
Solvent	Distilled water (Adjusting to pH 5.8-6.3 by HCl or NaOH)	Distilled water (Adjusting to pH 5.8-6.3 by HCl)	1) pH 4, CO2 saturated water (CO2 method) 2) Adding HNO3 to deionized water, and keeping the 1st elution pH 7 and the 2nd one pH 4. (pH-static method)	pH 4 through the way of 20 min-bubbling of deionized water by CO2 gas.	Adding HNO3 to deisonized water, and keeping the 1st elution pH 7 and the 2nd one pH 4.	- At this test, distilled water and HNO3 or NaOH - Using solvent different in acidity (alkalinity) or keeping the leachate a certain pH	1) Acetic acid buffer solution (pH 4.93) 2) Acetic acid solution (pH 2.88) (Note 4)
L/S ratio	10: 1	10 : 1	10:1 (5:1×2)	10; 1	100:1 (50:1×2)	10: 1	20 : 1
Leaching frequency	1	1	1 (CO2 method), 2 (pH-static method) (Note 5)	1	2 (Note 5)	1	1
Agitation	Horizontal shaking (200 times/m, amplitude: 4-5 cm)	Horizontal shaking (200 times/m, amplitude: 4-5 cm)	- Horizontal shaking, 200 times/m, amplitude: 4-5 cm (CO2 method) - Stirring and splashing (pH-static method)	Stirring and splashing (200 rpm)	Stirrer	Stirrer	Rotating and shaking (30 ± 2 rpm)
Duration	6 hours	6 hours	24 hrs (CO2 method), 3 hrs × 2 (pH-static method)	24 hours	3 hours × 2	23 hours at this test	18 hours
Filtration	1 μm GFP	After 20 min centrifugal separation at 3000 rpm, 0.45 μm MF	0.45 μm MF	After 20 min-centrifugal separation at 3000 rpm, 0.45 μm MF	0.45 μm MF	At this test, 0.45 μm MF	0.6 – 0.8 μm GFF
Temperature	Ordinary (approx. 20°C)	Ordinary (approx. 20°C)	Ordinary (approx. 20°C)	Ordinary (approx. 20°C)	Ordinary	Ordinary	22.3 ± 3°C

Note 1 For tri-, tetra-, 1,2-di- and cis-1,2-di-chloroethylene, dichloromethane, carbon tetrachloride, 1,2-di-, 1,1,1-tri- and 1,1,2-tri-chloroethane, 1,3-dichloropropene and benzene (volatile matters), an Erlenmeyer flask with screw cap (500 ml) was used. As for agitation, 4h-stirring by stirrer was implemented. Regarding filtration of elution, the filtrate was extracted by syringe and filter paper was attached to the syringe. This is the same method that is applied to the examination of volatile substances in sludge (Environmental Agency, notification no.13) or soil (Environmental Agency, notification no.46).

Note 2 Test in CO₂ method or in pH-static method is selected.

Note 3 pH targets at this test were 2, 4, 6, 8, 10, 12 and 13.

Note 4 Distilled water is added to the sample of 5 g and they are shaken for 5 min. pH is measured, the solvent of 1) is chosen if pH is over 5. If pH is below 5, 1.0 N HCl of 3.5 ml is added and 10 min-shaking is done at 50°C. If pH 5>, 1) is selected, and if pH 5<, 2) is used.

Note 5 New solvent is added to filter residues and the leaching operation is repeated.

Cadmium: 0.01 mg/l, Lead: 0.05 mg/l, Hexavalent chromium: 0.05 mg/l, Arsenic: 0.01 mg/l, Total mercury: 0.0005 mg/l and Selenium: 0.01 mg/l.

Non-processed melted slag is used as filling and road-bed materials, concrete and asphalt aggregate and cement materials. Processed-melted slag, secondary products, are used for concrete, asphalt and interlocking bricks. As they are used in many ways it is difficult to identify the places where they are used. Therefore the standards were established to be applied in all cases regardless of place or purpose. Looking at these utilization, it is considered that melted slag products would be more useful than shapeless melted slag. Products like bricks seem to leach smaller amounts of hazardous substances than shapeless melted slag because of the decrease of the rate from surface area, the less permeability and the encapsulation of hazardous substances by solidification. Present leaching tests, however, (JTL13 and JTL46) can be applied only to crushed samples (less than 5 mm on JLT13 and less than 2 mm on JLT46). These tests can not evaluate the effects of solidification, stabilization and formation. Considering the difference in form between shapeless materials and solid products, adequate leaching test methods should be applied for the evaluation. Test methods under discussion are shown in Table 2, and the basic ideas are drawn in Fig. 5 . The test samples were regulated 10∼30 mm in size because a certain strength and high reproducibility are required. Taking into account changes of chemical properties, including acidification by acid rain or carbon dioxide, acid solvents have to be used. Reprocessed melted slag is now being used close to our living environment, as opposed to landfill sites. Evaluation of the environmental impact should be carried out as close as possible to our living environment and prior to its use. The further development is expected.

Fig. 5. Frame Work of Leaching Tests by the Form of MSWI Residue Products (draft)

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HARVESTING | Forest Operations in the Tropics, Reduced Impact Logging

R. Heinrich , U. Arzberger , in Encyclopedia of Forest Sciences, 2004

Forest Operations in the Tropics

In tropical countries, harvesting operations are fundamentally different from those applied in temperate zones. Stand densities in temperate forests are considerably higher than in the tropics, generating much higher potentials for commercial timber volumes per hectare. There is less diversity of tree species in temperate zones, and the utilization of commercial tree species permits simplified forest operations. Due to the application of both selective and clear-cutting as well as the higher standing timber volumes per hectare, harvesting densities in general greatly exceed those in the tropics. Directional felling is easier to carry out in temperate zones due to the usually smaller-sized trees and crowns; and soil conditions are better for skidding operations. In spite of varying seasons, climatic conditions allow the appropriate implementation of harvesting operations throughout the whole year.

In the tropics, forest operations are generally more complex to organize and implement than in temperate zones. Natural forests in the tropics are characterized by a higher abundance of different species with many diverse sizes of timber and ample stand densities with only a few species of commercial interest. The harvestable wood volumes per hectare vary considerably depending on the occurrence of commercial tree species. The situations that most often complicate harvesting operations are the following:

•

large trees with large crowns

•

low carrying capacity and high vulnerability of forest soils

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extensive variety of timber sizes

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high precipitation rates, which often contribute to soil erosion

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lack of forest road and skid trail infrastructure

•

long transport distances on poorly paved roads due to scarcity of appropriate road construction material.

Preharvest Planning

The main objectives of preharvest planning are to optimize harvesting operations and to minimize environmental impacts. A harvest plan should consist of a written description of the planned operation and a detailed topographic map of the harvesting operation area. Preharvest plans should also include information on harvestable tree species, as well as data on other factors to be taken into consideration in harvesting planning, such as soil and terrain conditions or existence of watercourses. Detailed information about specific working equipment and the workforce involved plus careful attention to the integration of local communities in the projected operation are additionally preconditions for well-planned harvesting operations.

Forest Road Engineering

The goal of forest road engineering is to provide reliable access to the forest for management purposes and for silvicultural and harvesting operations. It involves specifying design standards and field layout, followed by construction and maintenance of forest roads including setting of skid trails, location and layout of landings as well as constructing subsidiary structures, such as bridges and culverts.

Forest roads are unquestionably the most environmentally problematic feature of timber harvesting operations, since a major part of the total soil erosion can be attributed directly to them because of inadequate design and construction standards, as well as poor maintenance practices.

Tree Felling and Cutting

Tree felling and cutting includes all activities from felling the standing tree to its preparation into logs for wood extraction. These activities include the felling process itself, cutting off tree crowns and limbs, crosscutting stems into logs and sometimes debarking of logs.

In tropical regions, trees may be large and heavy with huge crowns and might be connected by strong vines to each other. They fall with a tremendous force which can uproot neighboring trees; and stems may shatter, bounce, and roll uncontrollably. Therefore felling operations are both the most hazardous part of harvesting operations for the labor force. They are also a major cause of damage to the forest stand and result in the generation of a large amount of wood waste.

Wood Extraction

Extraction of wood is the process of moving trees or logs from the felling site to a landing or roadside. Extraction practices can be distinguished by the system used and the harvesting equipment employed (Table 1). Regardless of the type of logging system used, extraction can inflict substantial damage on forest ecosystems.

Table 1. Advantages and disadvantages of different extraction systems

Extraction system	Advantage	Disadvantage
Ground skidding	Low cost extraction system	Tendency to cause the greatest environmental problems
	Short training requirement	High density of skid trails
	Simple technology	Limited by slope gradient and soil conditions
Draft animals	Low soil and stand damage	Limited extraction distances
	Extremely narrow skidding paths	Mostly limited to small timber sizes and small-scale operations
	Low investment and maintenance costs
Cable	Low density of roads	High investment costs
	No skid trails	Laborious assembly and disassembly of the cable system
	Very low environmental impact when properly done
Helicopter	High production rates	Very expensive
	Low density of forest roads	Thorough planning and precise organization needed
	Very low environmental impact	Extremely highly skilled team of workers needed
Manpower	Narrow skid trails	Hard and slow work
	Necessary equipment very simple	Limited extraction distances
	Cheap

In the tropics the most common method of wood extraction is the ground-skidding system. A conventional set of ground-skidding equipment consists of ground-dependent machines, which may consist of either crawler tractors, wheeled or tracked skidders, or a combination of them. They are generally equipped with winches.

The use of draft animals, such as elephants, oxen, horses, or water buffaloes, can be economically attractive, particularly in remote areas. They are often used by local communities in small-scale operations and in forest stands with smaller-sized trees.

Cable systems are a preferred method for wood extraction in hilly to steep terrain. With this method, logs are transported either partially (as in ground and high lead operations), where logs may drag on the ground causing soil disturbance, or fully suspended in the air (as in skyline operations). Ordinarily, the timber is transported by carriages which are moving on a cable. The power source – a winching machine, also called a yarder – is located either at the top or the lower station, depending on the type of system used.

Helicopter systems are the most productive as measured by cubic meters of timber produced per hour or day and yet are the most expensive wood extraction system. Helicopters are only used in difficult and steep terrain where high-value tree species are extracted and where intensive forest road development would be too expensive and not appropriate.

With the introduction of the crawler tractor, log skidding by manpower has almost disappeared in tropical Africa. However, it is still being used in Asia and in the Pacific region where it is called kuda-kuda. Short wooden wedges, driven into the sides of the log, give the men a hold to control and push the log lengthwise over wooden cross-skids. Skidding distances may exceed 1   km where there are no alternative methods of extraction.

Landing Operations

Work on landings include all activities in connection with sorting, storing, and preparing the extracted stems or logs for further transportation to the processing facility or any other final production destination. Landings are always connected to roads so as to provide access to the stored timber by transport vehicles.

Transport Operations

At present the most common form of log transport in the tropics is by means of logging trucks. In remote areas, however, often a combination of land and water transport is used: hauling timber from the landing to an embarkation point by trucks, where the journey is continued by water transport, using barges or rafts. In some rare cases, railways are an alternative means of transport.

Harvesting Intensity

Harvesting intensity is a decisive criterion that influences the degree of impact on forests. Generally the total standing timber volume may range from 50 to over 200   m³  ha⁻¹ in the tropics. Harvesting intensity in tropical forests varies considerably between regions, countries, and even within countries. In Africa a low logging intensity forest operation is usually practiced with a mean extracted timber volume of 8–25   m³  ha⁻¹. Medium and moderately high logging intensity operations as practiced in South America often reach 10–50   m³  ha⁻¹ of harvested timber. In Asia and the Pacific region, logging intensity is higher than in the other two regions, reaching about 40–100   m³  ha⁻¹.

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Harvesting the unexplored potential of European waste materials for road construction

L.D. Poulikakos , ... M.N. Partl , in Resources, Conservation and Recycling, 2017

2.8 Steel slag

Steel slag has been successfully used as a road construction material because of its advantageous characteristics and mechanical properties. For example, road surface layers constituted of Blast Furnace (e.g. crystallized and vitrified) granulated slag (BF) and Basic Oxygen steel slag (BO) are commonly used in European countries such as England and France ( Dunster, 2002; Rockliff et al., 2002; Pascal et al., 2009; Morone et al., 2014). An alternative source of artificial aggregates is given by Electric Arc Furnace (EAF) steel slags which are obtained after a specific industrial production process, (Ellis, 1999; Morone et al., 2014).

The use of steel slag was recently investigated in a numbers of studies. Sofilic et al. (2010) evaluated the feasibility of using EAF steel slag as alternative aggregate source in asphalt pavement by performing a number of micro-structure analyses such as Scanning Electron Microscopy (SEM) showing that this material can be used for asphalt pavement construction and surface treatments. Liapis and Likoydis (2012) evaluated the field response of asphalt mixtures prepared with EAF steel slag demonstrating satisfactory performance in terms of skid resistance and surface texture. The possibility of using EAF steel slag for preparing Warm Mix Asphalt (WMA) mixtures (mixtures prepared at lower temperatures) in substitution for natural limestone was investigated by Mahmoud et al. (2013). Their results show enhanced resilient modulus and tensile strength, as well as reduced moisture sensitivity and permanent deformation for mixtures containing steel slag.

More recently, steel slags such as Linz-Donawitz (LD) slag, were used for preparing porous asphalt (PA) and SMA mixtures (Cannone Falchetto and Moon, 2015) and for partially or entirely replacing the conventional aggregate skeleton (Grönniger et al., 2015). The experimental results indicated that asphalt mixtures prepared with slag are suitable for asphalt pavement construction and that, in most cases they perform better than conventional asphalt mixtures prepared with natural aggregates.

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Recycling waste rubber tyres in construction materials and associated environmental considerations: A review

Abbas Mohajerani , ... Farshid Maghool , in Resources, Conservation and Recycling, 2020

9 Conclusion

Waste tyre recovery has come a long way since the initial conception, with a global shift in mindset towards environmental awareness and sustainability continuing to gain momentum. In order to sustain future prospects for the use of recycled tyres, it is important to recognise that three main objectives exist in the recovery of waste tyres: reducing excessive stockpiles, providing beneficial use, and preserving natural resources. The aim of this study was to analyse the properties of waste tyre rubber and conduct a comprehensive review of the applications of waste tyre rubber in pavement and construction materials, as well as highlight the environmental, economic, and technical factors.

Based on these objectives, this review paper explored the recycling of waste rubber tyres in concrete and road construction materials. Depending on the situation, waste tyres are capable of being recycled in many applications. In summary, the following conclusions have been derived from this investigation:

•

Rubberised concrete mixtures demonstrated improvement in freeze/thaw durability when tested in 40 MPa concrete mixes and at 0.6% rubber crumb replacement. Air entrainment of the concrete matrix was improved, reducing the modulus of elasticity, and improving resiliency to periodic expansion and contraction at minimal loss to the compressive strength.

•

60 MPa high-strength concrete was achieved containing up to 12.5% varying-sized rubber crumb as a fine aggregate substitute and 9% silica fume as a bonding agent. Minimal losses in flexural tensile and pull-off strengths were observed with increasing abrasion resistance and water penetration. Furthermore, water penetration in rubberised samples decreased in specimens containing up to 7.5% rubber content when compared with plain concrete.

•

Crumb rubber and rubber aggregate inclusion in standard composition concretes improved the chemical resistance of concrete material when assessing samples against the effects of hydrochloric acid, sodium sulphate, and chloride ion exposure. Rubberised concretes are ideal for use in marine climates due to their ability to resist a corrosive environment comparative to standard concretes.

•

Soil stabilised with rubber and cement inclusions, received an improvement in the bearing capacity and shear strength.

•

In unbound pavement applications, increasing the rubber content adversely affected the bearing capacity; however, the permeability was shown to increase.

•

Flowable fill containing rubber crumb showed a considerable reduction in density and greater strength-to-weight ratio, allowing for larger fills to be constructed.

•

Rubber sub-ballast experienced a significant decrease in bearing capacity and resilience, which was amplified by an increase in the rubber content, but improved resistance to degradation.

•

Seismic Isolation (resistance to earthquake forces) achieved a 60–70 % reduction in horizontal ground acceleration with rubber-soil; however, the bearing capacity was severely reduced, limiting the method to low-medium rise structures.

•

Railway "rubber-stone blowing" maintenance procedures observed decreases in vertical settlement and increases in the load-dampening effects and track durability.

•

Whole-tyre reinforcement of granular embankments significantly reduced vertical settlement to approximately half that of non-reinforced granular embankments and demonstrated more than twice the strength capabilities. Horizontal deformation reduction was also observed, and no obvious plastic zone was detected when compared with the control models.

•

The leachate of heavy metals is a primary concern when considering tyre derived products (TDP) for reuse, due to the chemical composition and the toxicity of the constituent materials, particularly zinc, manganese, and iron.

•

Mercury (Hg) and Aluminium (Al) were detected in the crumb rubber asphalt concrete (CR-AC) leachate at concentrations of 0.116 mg/l and 1.81 mg/l after 7 days, respectively. Both metals exceeded the toxic concentrations for aquatic toxicity tests, and, therefore, can potentially be harmful to the surrounding environment.

•

Benzothiazole leachate concentrations were detected at 0.45 mg/l for short term and 0.54 mg/l for long term, respectively. The compound is considered as highly toxic and is used in the manufacture of tyre rubber. The leachate of benzothiazole can be detrimental to the health of the local fauna and flora.

•

Further comprehensive studies on the leachate analysis of concrete, asphalt concrete and other construction and road materials incorporating waste rubber for heavy metals and PAHs, for products with exposure to air, are recommended.

The recent methodologies and framework published by the US Environmental Protection Agency (USEPA) should be enforced within the Australian regulations regarding the leachates from waste rubber products and construction materials with recycled waste rubber tyres, as, specifically, Methods 1314 (USEPA(E)), 2013) and 1315 (USEPA(F)), 2013) are performed for assessing the leachate of various metals under different pH, liquid to solid ratios, and monolithic sample conditions. Further research for the development of improved leachate testing methods and standards, and for the development of maximum acceptable limits of heavy metals for different applications and products manufactured with or incorporating waste rubber (and other similar waste materials) are recommended.

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Re-cycling of remediated soil in Sweden: An environmental advantage?

Patrick A.W. van Hees , ... Thomas von Kronhelm , in Resources, Conservation and Recycling, 2008

The use of waste and secondary aggregates (various ashes, demolition waste, slate ash, etc.) as road construction material has been an area of intense research over the last 20 years. This is a field of application that has spurred a lot of research (e.g. Wahlström et al., 2000; Roth and Eklund, 2003; Petkovic et al., 2004). In Sweden SGI (Swe. Geological Institute) has been a major contributor and in 2006 general recommendations for a number of rest and by products were published. The scientific and regulatory evaluation of road construction aggregates is of interest for the fate of treated soils, not only from the perspective of a potential application, but provides a framework for environmental assessment. This is especially the case since materials are used in the "natural environment" and can contribute to a 'diffuse' contamination.

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Basic oxygen furnace slag: Review of current and potential uses

Tamlyn Sasha Naidu , ... Lizelle Doreen van Dyk , in Minerals Engineering, 2020

2.1.3 Road filler

BOF-S aggregates show many favourable technical and environmental characteristics, especially in comparison to natural stone aggregates. In addition to being suitable for concrete aggregate reuse, this also makes them potentially valuable road construction materials. BOF-S-bitumen mixes have shown better structural and resilient characteristics than mixes with natural aggregates. These characteristics include rutting resistance, bonding and moisture damage resistance and stripping resistance.

Assessments made on a 2 km long and 24 m wide BOF-S and asphalt test road, showed that a road with natural aggregates replaced by BOF-S performs as well as a conventional asphalt pavement (Kambole, Paige-green, Kupolati, Ndambuki, & Adeboje, 2017; Xue et al., 2006). After nearly 2 years, the slag-asphalt section showed no signs of any rutting, cracking or stripping. The performance of a porous asphalt and BOF-S mixture was evaluated and showed a higher Marshall Stability, lower abrasion, and a better stripping and rutting resistance than that of equivalent crushed stone and asphalt mixtures (Shen, Wu, & Du, 2009). Tensile strength measurements made on all the mixtures also exceeded the minimum requirements. Furthermore, slag asphalts exhibited sound absorption characteristics which could have potential benefits in reducing traffic noise generated from tyre-road interactions. Other similar studies that were conducted suggested that the replacement of natural aggregate with steel slag in paving mixes should be done for either the fine or the coarse aggregate fraction but not both (Asi, Qasrawi, & Shalabi, 2007). This is due to the fact that if slag is used to replace both the coarse and fine aggregate components the mix is likely to have a lot of air voids necessitating the use of high quantities of bitumen which in turn could lead to bulking and flushing problems in the road pavement.

In some countries road specifications do not cater for slag reuse which results in limited BOF-S reuse. This is likely due to pavement performance problems that arise from some chemical constituents in some slag. Free calcium and magnesium oxides which are present in large quantities in slags, react with water, resulting in large volume expansions which can in turn lead to structural and failure when used in roads (volume stability issues as discussed above). Thus, hydration treatment or other chelating treatment before use as road aggregates must be undertaken to ensure allowable expansion (Kambole et al., 2017).

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Mercury flow via coal and coal utilization by-products: A global perspective

Arun B. Mukherjee , ... Ryunosuke Kikuchi , in Resources, Conservation and Recycling, 2008

There is nowadays encouragement from the Chinese government to use coal-FA in different sectors. It has been reported that about 70   Mt of FA (F type according ASTM C618) is used as building materials, road construction, cement industry and agricultural land applications (Cheng et al., 2004). The utilization pattern will increase slowly but surely and become more diverse in the future. Chinese coal ash can be divided into high and low calcium. There is better market when FA contains low carbon (>5.0%) and finer the ash particles. There is general consensus leading towards decreased environmental pollution by increased utilization of the FA. In 2005, China utilized about 65% of coal FA due to new construction regulation (Barnes and Sear, 2004).

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https://www.sciencedirect.com/science/article/pii/S0921344907001796

Source: https://www.sciencedirect.com/topics/earth-and-planetary-sciences/road-construction-material

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