Incineration Slag in Road Constructions

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INCINERATION SLAG IN ROAD CONSTRUCTIONS example of an application by Mank, J.A.M.’ ; Brulot, J.* ; Janssen van d e Laak, W.H.’ ’Road and Hydraulic Engineering Division of the Min. of Transport and Public Works 2Regional office South Holland of the Ministry of Transport and Public Works

ABSTRACT Application of incineration slag in embankments for roadbuilding meets uncertainties, both in material-technical and constructional and environmental aspects. The latter led to a large-scaletest in Highway 15 near Rotterdam. The results are given below. 1. INTRODUCTION

In Holland two important reasons are recognised to stimulate the use of secundary materials in roadbuilding and hydraulic engineering [l].The first is that a number of these materials can replace primary minerals that become more and more scarce in this country. The second is that the dumping of industrial residues and waste can be prevented. Incineration slag, produced when domestic waste is incinerated, belongs to that category. One

of the possible solutions is to apply incineration slag in road-embankments in stead of the usual sand 121. Experience existed moderately, but the possible environmental and hygienic consequences proved sufficient reason for the Rijkswaterstaat to realise a large-scale-test. More insight in the environmental risk and relevant engineering parameters may contribute to a larger use of this material.

2. INCINERATION SLAG AS BUILDING MATERIAL

Much industrial and domestic waste is dumped or incinerated in Holland. Globally is it separated at its sources, between heavily polluted waste (chemical waste e.g.) and lesser polluted waste (e.g. domestic). The former should be dumped in an acceptable manner or incinerated in specialized furnaces; the latter, when incinerated, is the basis for AVI-slag (the incineration slag referred to in this paper) [3]. AVI-slag is, in tact, the solid residual result of the incineration o f domestic waste and similar

light industrial waste. The fly-ash resulting from this process is polluted so heavily that they have to be separated, and they may not b e added to the AVI-slag in a later stage. The market supplies annually 700,000 tons at this moment. increasing to over 2,000,000 tons at the beginning of the new century.

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AVI-slag contains high concentrations of heavy metals, varying according to the nature of the waste to be incinerated. The spreading of this polluting matter through lixiviation is one of the greatest environmental risks. In order to enable application of this slag in roadbuilding the Rijkswaterstaat determined the following (temporary) conditions: - to prevent pollution of the soil, AVI-slag may not be applied in critial areas, such as soilprotection-areas and waterexploitation areas. Furthermore AVI-slag must be applied in such a way that they can be removed at any later stage; top and sides of the layer must be covered with a watertight layer; the AVI-slag must remain permanently at a level of 50 cms above the average highest groundwaterlevel; - limitations are set to the composition of the slag (admissible percentage of iron-containing

elements, non-incinerated parts and compostable parts); - concerning the lixiviation certain conditions must b e fulfilled, such as grain sizes and crushing

factor.

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the actual use is subject to conditions regarding the compaction of the material in the construction.

The first two conditions are mainly of an environmental nature, the latter two concern the engineering. The environmental conditions meet the requirements laid down in the interimpolicy of the administration, pending the Decree on Building Materials.

3. THE TESTPROJECT 3.1. General asoects

The application of AVI-slag in large-scale, constructive embankments is a fairly new field. Both in Holland and abroad the experience is modest. The Rijkswaterstaat made an inventory of the available knowledge and experience and decided to realise a testproject. This proved to be possible in 1988 in Highway 15 near Rotterdam. 3.2. Situation

Highway 1.5 connects the Rotterdam industrial and harbour area t o the Ruhr in Germany (see figure 1). Industrial development in the western Rotterdam area caused serious circulationproblems at the end of the existing highway. As a solution, the Rijkswaterstaat decided to extend highway 15 to the west. The first phase of the extension is a 4.5 km trajectory. Here a four-lane highway was planned. The complex infrastructure with many viaducts, and the relatively short distances between these viaducts, led to the decision to design the whole highway elevated.

Fig. 1. Situation At first, the embankment was to b e made of sand. T h e contractor however suggested to replace sand by 400,000 tons of incineration slag, mainly available from the nearby furnaces. T h e Rijkswaterstaat agreed, considering the future policy and the industrial location. It was the first lime for the Rijkswaterstaal to apply AVI-slag in such quantities in a roadconstruction. 3.3. Eneineerine asDects

T h e engineering design o f the embankment with AVI-slag was highly influenced by environmental demands, i.e. the covering of top and sides with a watertight layer, so that rainwater does not perpetrate the slag and, in the long run, pollutes the underground and groundwater. In agreement with the licensing authority it was decided to use for this purpose a mixture of natural materials, i.e. sand and bentonite (a swelling clay). To prevent frequent disturbance and perforations of the watertight layer by transportation activities during the work, or when installing road-furniture, a 1 meter layer of sand over the watertight layer was provided for. T h e design further reckons that the bottom of t h e body of AVI-slag, after setting of the subsoil, will remain at least 0.5 meter above the highest groundwaterlevel.

Fig. 2. T h c engineering design of the embankment

I90 As to the permeability of the layer of sandbentonite a limit of 10'O meter per second is

required by the administration. 3.4. Plannine the test

Given the preferred construction a researchplan was made. Targets are: - to obtain and increase general knowledge of AVI-slag and sand-bentonite; - to obtain insight in engineering and environmental consequences as a result of the

application of these materials in embankments. Research would take place in the field and in laboratory-conditions. 3.4.1. Civil eneineerine research

Aspects requiring attention were: - in the laboratory:

* geotechnical properties of AVI-slag. The angle of friction and cohesion of the slag is determined through large-scale triaxial tests, to be used as input in stability-calculations. Compression-constants are determined by way of large-scale compression tests. This is to obtain knowledge of the behaviour in setting. Both tests use the material graded as used in the project

* frictional properties of the sand-bentonite mixture by triaxial testing. Bentonite is a natural clayproduct, which came to be by sedimenting vulcanic ashes. The primary element is found in many countries, but not in Holland. It is marketed in powdery form. Its character is to swell greatly when water is added. In a correct mixture with sand it forms a watertight sealant.

* permeability of sand-bentonite for water, also in the long run. - in the field:

* how AVI-slag sets in the long run; * the compaction of AVI-slag; * the quality of the watertight sealant; its permeability. With experimental tests, such as the mobile ring-infiltration-meters and the permanently built-in lysimeter the permeability of the sealant can be determined.

* the quality of the sealing layer: it must be checked whether the added bentonite is sufficiently and homogeneously mixed in the actual construction; determination of the quantity through the methylene-blue test.

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3.4.2. Environmental research Special attention in this test-project will go t o the environmental consequences of the application of AW-slag in a n embankment.

To follow this, synthetic sheets were placed under the layer of AVI-slag (testsites 1 and 2) as well as directly under the sand-bentonite layer (testsite 3). If water will percolate it will be caught. T h e length of the testsites is about 10 meter each.

The contents of pollution in the AVI-slag itself, the degree of hiviation possible, and long-term developments in the contents of polluting elements in water samples, will b e determined. Important information is expected t o result from this, concerning: - quality and quantity of water emitted by the AW-slag during the construction phase, before the sealant is applied, and which may result from:

* compaction of AW-slag, expelling present water; in order to determine this, moisturemntents a r e defined per layer carried into the construction, both before and after compaction;

* intrusion of rain into the AVI-slag between the depositing and the sealing; -

effectivity of the sealant of sand-bentonite; how much water percolates through sealant and slag can be defined by a frequent sampling of testsite 3. where sheets a r e applied directly beneath the sealant;

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quality and quantity of water, coming horn the layer o f slag, during the actual use of the construction, i.e. after the sealant has been applied. This information can b e obtained by registring during a long period of time of the quantity of water coming from testsites 1 and 2, where sheets a r e applied under the layer of slag.

Periodic sampling and analysis of this water, during a period of 3 years, leads t o definition of the degree of pollution. Sampling frequency depends o n the quantity of expelled water. Indicative, concentrations found will b e checked against limitvalues as published in the Soil Protection Standard. T h e research results have to b e processed. That implies the necessity to have information on the quality and quantity of rain over the testing period. Near the testsite automatic rainmeters were installed for this purpose. Slightly remote from the test sites, near to the road, sampling tubes were installed. Before the job was started, the begin situation was defined and reported on. From these tubes groundwatersamples will b e extracted periodically, whereas samples of the soil in the near vicinity are taken as well.

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It is to be analyzed whether possible diffusion of polluted percolation water outside the roadconstruction will affect the quality of soil and groundwater. The concentrations to b e found will again be checked against limitvalues as published in the Soil Protection Standard. This will eventually lead to answering the question whether the application of incineration slag according to the actual designs is acceptable. In the laboratory the lixiviational behaviour and the actual composition of the slag, used at the testsite, will be analyzed. Three different lixiviation tests will be executed:

* maximal lixiviation at p H 7 and pH 4

* cascade test and * column test, according to the Dutch standard NEN 2508 The samples will b e analyzed to their contents of heavy metals cadmium, chromium, copper, molybdeen, lead, nickel, antimonium, zinc, mercury and arsenic. Furthermore on barium, fluorine, sulphate, chlorine and sulphide and the acidity (pH) and electrical conductivity.

4. DESIGNING TESTSITES

4.1. Where to situate testsites?

When choosing locations for the testsites, the expected settings were taken into consideration. A disturbance of the body of the road, a possible depression in the middle, makes it harder to interpret research results. Starting point of the calculations was that rain would flow sideways off the sealant. Therefore testsites are situated where, as a result of earlier preliminary load the primary setting was already effected. An added advantage is the lesser risk of damages to sampling systems. 4.2. Desiyn Testsite 1 and 2 under the core of AVI-slag capping layer : drainsand lnclneratlon slag watcrprooflng Layer ' sand bentonite road surface

sarnolina tube

collector HOPE g c o n c h r a n c groundwattr Lcvcl COnCrett rccclving tank

fig. 3. Testsites 1 and 2

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f i l t e r i n g sand

L drain

193 After ample considerations, the choice was in favour of a system that buffers the percolate temporarily in the embankment construction itself (see figure 3). Primarily the percolate is received from the body of slag in foil troughs filled with gravel. The foil, a geomembrane of 2mm HDPE, meets at its sides the sand-bentonite sealing layer. The percolate is guided sideways to drains at the foil. These drains are made of HDPE-drain and are filled with filtering sand. To improve drainage, a slight difference in level is made. The draintubing (8 cm HDPE) transports the percolate to concrete containers, next to the slope. The foil and the drains form together a temporary bulfer. To guarantee this, valves were mounted at the end of the draintubes, inside of the concrete receiving tanks. Periodically the system is drained.

To check the level of the buffered percolate and to have an indication of the quantity to be drained, each testsite has a sampling tube connected to the drain. The expection was that during the first phase, when the sealant is not yet applied. the flow will be app. 4000 liters per hour. Once sealed, the flow will decrease to app. 0.1 liter per hour. The system is large enough to contain the water, received in each sampling period. The frequency of draining the system

during the open period will be once every one or two days, decreasing t o once every 2 or 3 months in the contained phase. Testsite 3. directlv under the sealant This design is basically not different from the other two sites (see figure 4).

capping l a y e r . drainsand inclneratlon s l a g waterprooflng l a y e r . sand b e n t o n l t e

road surface

HDPE geomrmbizne groundwater l e v e l concrete r e c e i v i n g

Fig. 4. Testsite 3 Here too, a foil is provided, this time directly under the layer of sand-bentonite; a (smaller) buffering capacity for the infiltrated water; and a draining system to concrete receiving tanks on either side of the slope, where the buffer can b e drained periodically.

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The shape however is different: where at sites 1 and 2 a trough construction is used, at site 3 a reverse trough construction was needed. A general condition was that the situation at the testsites should differ as little as possible from the situation outside the testsites. Therefore the layer of draining sand, applied under the AVIslag in general, is also applied at sites 1 and 2. On the other hand, drainage of the percolate towards the drains had to be guaranteed, which called for a layer of filtering gravel under the draining sand. The HDPE-drains had to b e provided with a poly-propylene jacket to prevent clogging in the long run; and the draincanals were filled with filtering sand for the same reason. During the drainage, periodic partial samples are taken from the drainwater of the testsites 1 and 2. This is in favour of a qualitative analysis of the percolate. These partial samples allow for a general sample to be analyzed. 4.3. SamolinE The sampling provisions were made for longterm sampling. We think that sampling should take place over a period of 20 to 30 years. During the first three years, sampling will have to be intensive. With the advancement of time, the frequency will decrease noticeably. Sampling of the "open" phase started in September 1990, sampling of the "covered" phase began in October 1990. Sampling of testsite 3, directly from under the sealant, started early 1991.

5. RESULTS

Although the testing sites were completed only recently, and reports on the laboratory research are only partly finished, we can report the following on the actual constructing activities: - application of AVI-slag did not lead to problems: the compaction that is measured complies

with standards and does not decrease as the construction of the actual embankment progresses - so far only a marginal setting of AVI-slag could be found; -

the temperature of the AVI-slag decreases with time;

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the mix-in-plant method led to a homogeneous product as to the sand-bentonite mix

As far as the environment is concerned, only modest sampling results are available. As far as the flow of percolate is concerned, the information can be given in figure 5. It shows the cumulative quantities of percolate, as drained. It also shows the moment at which the layer of slag was covered with the sealant.

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0

20

40

60

80

I00

120

140

160

days alter atan sampllng teststto 1

Fig. 5. The cumulative quantity of percolate after start sampling testsite 1.

The first analyses concerning the quality of percolated water have been made. Before publishing their outcome, and expressing views on the contents of polluting matter, we need the as yet not available information about the quality of AVI-slag, draining sand e n rainwater. It is expected that most results will become available halfway 1991. A definite judgement whether the use of AVI-slag in constructive road-embankments is acceptable can be expected in

or about 1994.

6. LITERATURE 1 "Gegrond ontgronden", Landelijke beleidsnota voor d c oppervlaktedelfstoffenvoorziening

voor d e lange termijn. Ministerie van Verkeer en Waterstaat, 's Gravenhage, 1987 2 "Resten zijn geen afval (meer): Afvalverbrandingsslakken",publikatie 15, Stichting Centrum

voor Regelgeving en Onderzoek in d e Grond- , Water- en Wegenbouw e n d e Verkeerstechniek (C.R.O.W.), oktober 1988 3 "Resten zijn geen afval (meer): Bijzondere ophoogmaterialen", publikatie 16, Stichting

Centrum voor Regelgeving e n Onderzoek in d e Grond- , Water- en Wegenbouw en d e Verkeerstechniek (C.R.O.W.), oktober 1988