Fly Ash As a Road Construction Material Jenny VESTIN1, Maria ARM2, Desiree NORDMARK3, Anders LAGERKVIST3, Per HALLGREN4, Bo LIND5

Fly ash as a road construction material Jenny VESTIN1, Maria ARM2, Desiree NORDMARK3, Anders LAGERKVIST3, Per HALLGREN4, Bo LIND5

1Swedish Geotechnical Institute, Universitetsallén 32, SE- 851 71 Sundsvall, Sweden [email protected] 2Swedish Geotechnical Institute, SE-581 93 Linköping, Sweden [email protected] 3Division of Waste Science & Technology, Luleå University of Technology, SE-971 87 Luleå, Sweden [email protected]; [email protected] 4Swedish Forest Agency, Hästmarksvägen 2, SE- 89138 Örnsköldsvik, Sweden [email protected] 5Swedish Geotechnical Institute, Hugo Grauers gata 5 B, SE-412 96 Göteborg, Sweden [email protected]

Abstract In June 2009, sections of a gravel road situated in the middle of Sweden were stabilized with gravel and bio fly ash respectively. The aim of this study was to compare the different sections regarding stiffness and environmental impact. The environmental impact of the road was estimated from soil water and leachate from the road and an initial leaching of K, Na, Cl and SO4 was found from the lysimeters. The estimated total leaching from the road was not corresponding to the laboratory leaching tests performed on the ash (L/S10). The bearing capacity of the sections was measured with falling weight deflectometer at four different occasions and the bearing capacity increased with time and ash content. During snow-melting periods, the reference sections showed different disruptions but the test sections were unaffected. These results indicate that this fly ash seems to be suitable for gravel road stabilization.

Keywords: Fly ash; Gravel road; Stabilisation; Bearing capacity

1 Introduction Many gravel roads suffer from reduced bearing capacity mainly during soil frost thawing periods. The bearing capacity is to a large extent influenced by temperature and precipitation. The expected forthcoming climate change will lead to increased average annual temperatures and rainfalls. Thus the soil frost periods will become shorter which will lead to increased rutting and less bearing capacity in gravel roads. This will have implications for the forestry since the forest industry is to a large extent dependent on accessible roads main part of the year to get the timber. To avoid the reduced bearing capacity, the gravel roads may be stabilised.

Fly ash has earlier been used for stabilising roads due to its high content of calcium and silicate oxides which give puzzolanic properties and thus high compression strength (Lahtinen 2001, Mulder 1996). The frost thawing properties and the bearing capacity of road material have also been increased when fly ash is used (Mácsik 2006, Mácsik & Swedberg 2006, Mácsik et al., 2009, Tuncan et al., 2000, Zhou et al., 2000).

During 2008, Swedish Forest Agency, Swedish Geotechnical Institute (SGI) and Luleå University of Technology (LTU) initiated a project with the general aim to analyse and compile methods for adapting forest roads to climate change. Within this project, part of a low-volume gravel road was upgraded and stabilized with fly ash from a local paper mill. The aim of this study was to compare different road sections stabilized with ash and gravel respectively regarding stiffness and permeability. An additional aim was to estimate the environmental impact of the stabilized road.

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2 Materials The stabilized road is situated in Sörkrånge, Timrå in the middle of Sweden and is mainly used by the forestry. The road was built during 1968-1970 mainly on earlier arable soil. The base course consisted of crushed moraine and the soil type was mainly moraine and fine sediments.

The fly ash used in the road was derived from a fluidized bed incinerator at the paper mill Ortviken in Sundsvall. The fuel was mainly bark and sludge containing fibers, ash, organic material and micro organisms.

3 Methods 3.1 Laboratory studies The fly ash and material from the road and mixtures between them (20% and 30% fly ash in combination with road material) were characterized before stabilization of the road. The ash-gravel- mixtures were characterized considering optimal water ratio, density and compression strength (one- dimensional). The compression strength was also measured after six weeks of hardening and after 12 freeze-thawing cycles. A thorough chemical characterization of the ash was performed.

3.2 Stabilization The road was upgraded in June 2009. The upgraded part is 1500 meters and divided into four reference sections and two test sections. All sections were upgraded with ditching and grading. Reference section 1 and 2 were stabilized with gravel. Test sections 1 and 2 were stabilized with different amount of fly ash in proportion 30% fly ash to 70% road material. Reference section 0 and 3 were not stabilized. (Table 1)

Table 1. Description of the test and reference sections Test 1 Test 2 Ref 0 Ref 1 Ref 2 Ref 3 Stabilization fly ash fly ash gravel gravel Length (m) 240 260 400 320 160 120 Fly ash (depth cm) 12 20 Milling depth (cm) 20 39 Depth after compaction (cm) 16 20-25 Base course (depth cm) (size 0-32mm) 15 15 Surface course (depth cm) (size 0-18mm) 7 7 7 7

The fly ash was transported to the road and was stored for one week before it was laid out by trucks. The test sections were graded and the ash was milled twice into the existing road (back and forth along the sections). Thereafter the road was graded again before watering (33 liters per meter) and compaction (6 tons vibration roller, 5 passages). The reference sections 1 and 2 were upgraded with a base course of gravel (grain size 0-32 mm). Finally all sections except reference 0 and 3 were covered by a surface course of gravel (grain size 0-18 mm).

3.3 Field studies The infiltration capacity was measured in June 2011 using double-ring infiltrometers. During the measurements the water level in the inner ring was held constant and the amount of water that was added to maintain a constant level was measured (Figure 1). When the infiltration rate had been constant for about one hour the measurements were stopped. The surface course was removed before measuring. The measurements were performed in the middle of the road (four replicates) and in the wheel track (four replicates) both at reference section 2 and at test section 2.

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Figure 1. Measuring of infiltration capacity using double ring infiltrometer.

Lysimeters (size 25*25 cm) were installed at a depth of 50 cm below the surface course in reference sections 2 and 3 and in test section 2. Samples from the lysimeters have been collected at four occasions (Oct 2009, May 2010, Jun and Sep 2011).

Samplers for soil water (Macro rhizon, Eijkelkamp, Netherlands), (length 9cm and diameter 4,5mm) were installed at a depth of 30cm nearby reference sections 2 and 3 and test section 2. Triplicate of these samplers were installed at 0,5 m, 1 m and 2 m from the road side. Altogether 27 soil water samplers were installed. Samples from soil water have been collected at three occasions (May 2010, Jun and Sep 2011). The soil and lysimeter water has been analyzed in regard to pH, electrical conductivity, elements, chloride (Cl) and sulphate (SO4).

The bearing capacity of the different sections was measured by falling weight deflectometer (FWD) at four occasions (Sep 2009 and 2010, May 2010 and 2011) (VVMB 112, VVMB 114). At each occasion, the surface modulus was calculated at every 20 meters. The surface modulus indicates the mean stiffness from a certain depth and further below.

4 Results and discussion 4.1 Laboratory studies The two mixtures with 20% and 30% fly ash had similar initial compression strength. After hardening of the samples during six weeks the compression strength was enhanced with increased amount of ash in the sample. After 12 freeze-thawing cycles, the compression strength was reduced for the mixture with 20% ash but increased for the mixture including 30% ash. The hardening process in this mixture was probably continuing during the freezing experiments which gave rise to the increased strength (Table 2). Based on these results, it was determined to use a mixture of 30% fly ash and 70% road material in the test sections without any other additional binders.

Table 2. Characterization of the road material, fly ash and the mixtures between them. G100 denotes 100% road material, FA100 denotes 100% fly ash, FA20G80 denotes 20% fly ash and 80% road material, FA30G70 denotes 30% fly ash and 70% road material. G 100 FA20G80 FA30G70 FA100 Optimal water ratio (%) 12 19 25 54 Density (kg/dm3) 1 1,5 1,6 1,9 Compression strength (MPa) 1,3 4,7 4,4 6,2 Compression strength after hardening (MPa) 6,7 9,7 36,4 Compression strength after freezing (MPa) 5,6 13,9

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4.2 Field studies The infiltration rate was higher for the reference section than for the test section which indicates that the carbonisation and puzzolanic reactions have hardened the ash/gravel layer in the test sections (Table 3). The infiltration capacity measured in the reference section and in the middle of the test section was in the same order as of natural Swedish till soils that are surrounding the investigation site (Lind & Nordin 1978; Ericsson & Hård 1978). The infiltration capacity measured in the wheel tracks of the test section was in the magnitude of vegetated clay and silt soils. The results show that all precipitation from normally occurring rain can infiltrate into the road surface. Only extreme rain showers can cause surface runoff. The average annual precipitation at the road location is about 700 mm with 30 % (210 mm) distributed as snow (SMHI 2012) but the infiltration from melting snow can be neglected since the road is continuously cleaned from snow and kept open. The number of rain occurrences may very rough be estimated to 100 times per year and thus the total average yearly infiltration can be estimated to 700 – 35 (5% runoff) – 100 (interception) – 210 (snow) = 355 mm.

Table 3. Infiltration rate of test section 2 and reference section 3, n=4. Measurements were performed in the middle of the road and in the wheel tracks. Ref. section Ref section Test section Test section middle wheel track middle wheel track 83 mm/h 79 mm/h 47 mm/h 12 mm/h

Leaching of elements from the sections was observed for K, Na, Cl and SO4 and the initial leaching of Cl and SO4 exceeded the Swedish limits recommended for using waste as construction materials (NV 2010). These results are in accordance with other studies (Mácsik & Svedberg, 2006; Thurdin et al., 2006). The leaching of the these elements (K, Na, Cl and SO4) seems to decline and two years after the road was stabilized with fly ash, the concentrations were similar between reference and test sections (Figure 2). Also the concentrations of trace elements in soil water were similar between reference and test sections after two years.

300 300

2010-05-27 2010-05-27 200 2011-06-22 200 2011-06-22

2011-09-21 2011-09-21 Chloride(mg/l) 100 Sulphate(mg/l) 100

0 0 Test section 2 Ref. section 2 Ref. section 3 Test section 2 Ref. section 2 Ref. section 3

Figure 2. Concentrations of Cl and SO4 in leachate from lysimeters installed in the road.

A comparison was made between the results from the leaching test of fly ash (L/S10) and the results from the road lysimeters converted to mg/kg dw of ash in the road. The road infiltration was expected to be 350 mm/yr. For Ni, S, P and Al the leaching in the road exceeded the laboratory experiments but for all other elements the leaching in the laboratory experiments exceeded the road results. (Figure 3) The largest differences were found for Sr, Ba and Ca. These large discrepancies between laboratory and field results questions the relevance of using laboratory leaching tests for predicting the leaching of elements in field as also discussed by Izquierdo et al., 2008, Lidelöw & Lagerkvist, 2007 and Lind et al., 2008.

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Cu Cr

K Fe

1,E-01 1,E+01 1,E+03 1,E+05 1,E+07 Figure 3. Ratios between leached elements from fly ash (leaching test L/S10) and leachate from the road. A ratio above one indicates a higher leaching from the ash (laboratory experiments) and below one indicates a higher leaching in the road.

The bearing capacity measurements showed that the mean stiffness of the test sections was increased with time and this was more evident for test section 2 with the thicker ash layer (Figures 4 and 5). In general, the stiffness of the road was higher during autumn than during spring measurements due to the higher content of water in the road close to soil frost thawing period (Figure 4). In relation to reference section 1 which was stabilized with gravel, the test sections showed less reduction in stiffness during spring measurements. At the latest measurement, the stiffness of test section 2 with the thicker ash layer was almost 180 % higher than that of reference section 1 (Figure 5). The results for reference section 2 and reference section 1 were similar and the non-stabilized sections (reference section 0 and 3) showed lower surface modulus (data not shown).

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FWD Surface modulus 2009-09-29, 2010-05-19, 2010-09-29 och 2011-05-18

180

160

140

120

100 2009-09-29 2010-05-19 80 2010-09-29 60 2011-05-18

40 Surface modulusSurface (MPa) 20

0 Ref 1 Test 1 Test 2

Figure 4. Surface modulus of the whole road construction at the different sections. (Ref 1 n=33; Test 1 n=23; Test 2 n=27)

FWD Surface modulus in relation to ref section 1 2009-09-29, 2010-05-19, 2010-09-29 och 2011-05-18

180%

160%

140%

120%

100% 2009-09-29 2010-05-19 80% 2010-09-29 60% 2011-05-18

40%

20%

0% Ref 1 Test 1 Test 2

Figure 5. Surface modulus of the whole road construction at the different sections. The values are given in relation to reference section 1 for each sampling occasion. (Ref 1 n=33; Test 1 n=23; Test 2 n=27)

5 Field performance The road was inspected during the snow-melting period in 2010 and 2011 and will be further inspected in 2012. The first year after stabilization, 2010, the non-stabilized sections (Ref 0 and Ref 3) had large cracks but the sections stabilized with ash or gravel (Ref 1, Ref 2, Test 1 and Test 2) seemed unaffected with no cracks. Two years after stabilization, 2011, the sections stabilized with gravel had cracks in lengthwise direction but the test sections, stabilized with ash, showed no disruptions (Figure 6).

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Ref 1 Ref 2 Test 1

Figure 6. The stabilized road during snow-melting period 2011, two years after stabilization. Ref 1 is not stabilized, Ref 2 is stabilized with gravel and Test 1 is stabilized with ash.

6 Conclusions Laboratory and field studies have shown that this fly ash was suitable for stabilizing gravel roads. This conclusion is based on the following results:

An initial leaching of K, Na, Cl and SO4 was found from the test sections but the leaching decreased with time and after two years the concentrations were similar between reference and test sections. The sections had high infiltration capacity but despite that a discrepancy was found between leaching from the road and leaching of fly ash in laboratory experiments. The bearing capacity of the test sections increased with time and showed less reduction during spring measurements compared to the reference sections. During snow-melting periods, the reference sections showed different disruptions but the test sections were unaffected.

Acknowledgements This project has mainly been funded by European Regional Development Fund, Värmeforsk, Swedish Forest Agency and Swedish Geotechnical Institute. The laboratory and field studies have been performed by Luleå University of Technology and Swedish National Road and Transport Research Institute.

References Ericsson L-O, Hård S, Infiltraionsmätning i stadsdelen Ryd, Linköping, Geohydrologiska forskningsgruppen, Chalmers tekniska högskola, Meddelande nr. 32, Göteborg (1978) In Swedish Izquierdo M, Querol X, Josa A, Vazquez E, López-Soler A, Comparison between laboratory and field leachability of MSWI bottom ash as a road material, Science of The Total Environment, 389(1), 10-19 (2008) Lahtinen P, Fly ash mixtures as flexible structural materials for low-volume roads, Finnra reports 70/2001 (2001) Lidelöw S, Lagerkvist A, Evaluation of leachate emissions from crushed rock and municipal solid waste incineration bottom ash used in road construction, Waste Management, 27(10), 1356-1365 (2007) Lind B, Nordin G, Geohydrologi och vegetation i Dalen 5, Karlskoga, Geohydrologiska forskningsgruppen, Chalmers tekniska högskola, Meddelande nr. 34, Göteborg (1978) In Swedish Lind B, Norrman J, Larsson L B, Ohlsson S-Å, Bristav H, Geochemical anomalies from bottom ash in a road contruction – Comparision of the leaching potentioal between an ash road and the surroundnings, Waste Management, 28(1), 170-180 (2008) Mácsik J, Flygaska som förstärkningslager i väg. Värmeforsk Rapport 949, Stockholm (2006) In Swedish with English summary

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Mácsik J, Svedberg B, Skogsbilvägsrenovering av Ehnsjövägen, Hallstavik. Värmeforsk Rapport 968, Stockholm (2006) In Swedish with English summary Mácsik J, Erlandsson Å, Wexell B-A, Flygaska–Grönlutslamstabiliserad skogsbilväg – Fallstudie Iggesund. Värmeforsk Rapport 1101, Stockholm (2009) In Swedish with English summary Mulder E, A mixture of fly ashes as road base construction material, Waste Management, 16(1–3), 15–20 (1996) NV 2010, Återvinning av avfall i anläggningsarbeten, Handbok 2010: 1, Naturvårdverket, Stockholm, (2010) In Swedish Thurdin R T, van Hees P A W, Bylund D, Lundström U S, Bio fuel ash in a road construction: Impact on soil solution chemistry, Journal of waste Management, 26 (6), 599-613 (2006) Tuncan A, Tuncan M, Koyuncu H, Use of petroleum-contaminated drilling wastes as sub-base material for road construction, Waste Management and Research, 18(5), 489-505 (2000) VVMB 112, Vägverkets publikation 1998:80, Deflektionsmätning vid provbelastning med fallviktsapparat Metodbeskrivning 112:1998, Vägverket, Borlänge (1998) In Swedish VVMB 114 Vägverkets publikation 2000:29, Bearbetning av deflektionsdata, erhållna vid provbelastning av väg med FWD-apparat Metodbeskrivning 114:2000, Vägverket, Borlänge (2000) In Swedish Zhou H, Smith D W, Sego D C, Characterization and use of pulp mill fly ash and lime by-products as road construction amendments, Canadian Journal of Civil Engineering, 27 (3), 581-593 (2000) www.smhi.se (2012)

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