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Contaminated soil cement stabilizations for application as a construction material
Environmental Aspects of Construction with Wute Materials J.J.J.M. Goumans, H A . van &r S h t and Th.G. Aalbers (Edtors) el994 Elsevier Science B.V. AN rights reserved.
925
Contaminated soil cement stabilizations for application as a construction material. P.J. Kroes' and J. van Leeuwen2 IWACO B.V., Consultants for Water & Environment, P . 0 . b ~8520, 3009 AM Rotterdam, The Netherlands
*
Gemeentewerken Rotterdam, Ingenieursbureau Geotechniek en Milieu, P.O.Box 6633, 3002 AP Rotterdam, The Netherlands
Abstract Possibilities for using non-cleanable contaminated soils as an alternative for sand in cement stabilizations, have been studied with respect to physical properties (compressive strength and durability) and leachability. Typical soil parameters like organic matter content, clay content and contaminant type and concentration that may effect the compressive strength have been investigated. It can be concluded that contaminated soil cement stabilizations conform to the construction engineering criteria and leachability standards and have potential application as an alternative for sand cement stabilizations. 1. INTRODUCTION
The excavation of primary surface minerals like sand meets more and more opposition as a result of the negative environmental aspects. The excavation policy in the Netherlands strongly advocates the application of alternative materials, including waste materials and industrial residues. The policy of the national government regarding waste materials in general offers an additional strong stimulus towards minimizing the dumping (landfilling) of waste materials and where possible, an efficient reuse. In the city of Rotterdam @art of the highly industrialized and densely populated area of the Rijnmond in the west of the Netherlands) large quantities of contaminated soil are being excavated because of remediation of sites and earth works. For the category noncleanable contaminated soil that is being landfilled the possibilities for application as an alternative for sand in cement stabilizations have been investigated [l]. These soil cement stabilizations can find there application in civil engineering constructions as can be shown in figure 1.
In the Netherlands there is little experience with respect to stabilizing contaminated soil with cement. Factors that can influence the compressive strength are the contaminants and the more heterogeneous matrix of soil (organic matter, lutum) in comparison with sand.
926
Figure 1. Application of cement stabilization in a road bed construction
2. MATERIALS AND METHODS Soil samples from 13 different sites in the Rotterdam region, from the above mentioned category, have been selected for this research. Each soil sample consisted of about 150 kg. The typical soil parameter contents and contaminant contents researched are summarized in table 1.
Soil samples 1-13
Dry matter
Organic matter
(%)
(%)
72-94
1-14
Lutum
Pb
cu
(%)
@pm)
(ppm)
Zn (ppm)
Cd (ppm)
As (ppm)
0.34
7-11500
13-790
83-900
<0.5-17
<5-18
@pm)
Fines (<63rm)(%)
1-340
11-36
PAH (16EPA)
Explanation: < below detection limit
The first step was to characterize the soils i.e. grading, humus, clay and moisture content and possible retarding properties on hydratation of cement from the organic matter (organic acids). After the characterization, the soil samples are mixed with different cement contents (up to 22% wlw dry matter) at the initial moisture content. The compressive strengths are investigated according to the RAW Standard Conditions [2]. The durability is tested by carrying out drylwet en freezelthaw cycles on the stabilizates. The leachability of the soil-cement stabilizations is investigated by carrying out a tank leaching test [3] on three selected mixtures. The results are compared with leachability standards [4][5]. The factors that influence the compressive strength have been investigated by carrying out correlation analysis.
927
3. RESULTS AND DISCUSSION The main construction engineering criterium for sand cement stabilizations is a minimum compressive strength of about 5 MPa after 28 days of curing. This criterium has also been chosen for the minimum compressive strength of the contaminated soil cement stabilizations. It is found that the main soil parameter that correlates with (influences) the compressive strength is the moisture content. The ideal maximum water/cement ratio is 1 (table 2). Table 2.
Mixtures at initial moisture content
Soil samples
Moisture content
Cement conlenl
46
46
A (6,8 and 12)
10- 14
C (1,2,3 and 4)
Compressive strength (MPa)
= I -1
5,1 6,l-7,7 63
12
15 - 19 20 - 24
B (5. 10 and 11)
Waterlcementratio
17
= I
22
In table 3 the contaminant contents of the investigated mixtures are summarized. Table 3.
Contaminant contents of the mixtures (mg/kgdm)
Component
A
B
C
14 92 320 300 870 560 24
6,O 0,33 19 61 420
14
~~~
As Cd cu pb
Na Zn PAH (16EPA)
150
23
0.65
330 940 520 250 5.5
The organic matter content also correlates with the compressive strength although the humific acids do not contain retarding properties on the hydration of cement. This may be due to the fact that in the investigated soils the moisture content is related to the organic matter content. The contaminants do not correlate at these concentrations with the compressive strength. With respect to the durability of the contaminated soil cement stabilizations, the dry/wet cycli did cause some mass changes but didn’t cause disintegration of the samples. The freeze/thaw cycli, however, caused volume changes for all samples and disintegration of about 20% of the researched samples. Therefore the products have to be optimized and till then it is not recommended to work under freezing conditions. The leachability research has been carried out on the mixtures of A, B and C from table 2. The results are expressed as cumulative emissions (mg/m*) and are summarized in table 4. The cumulative emissions of these contaminated soil-cement stabilizates are far below the leaching standards for A-type and B-type applications [4][5].
928
Table 4.
Cumulative emission ranges (mg/m2) at t=64 days
Component
Na Zn phenanthrene
Min. emission
2,944.9 0-0,9 5570-6640 0.05-0,lI
Max. emission
4,O-34,9 7,O-7.1 5570-6640 140-142 0,05-0,1I
U1A
U2A ti, U1B
40
300 7s 350
1,o
50 100 200
800
I500
Explanation of symbols of table 4: min. emission; concentrations below the detection limit are accounted for as zero in calculating the cumulative emission; max. emission; concentrations below the detection limit are accounted for as the detection limit in calculating the cumulative emission; U1 = leachability standard for category 1 restrictions (no blending with the underlying soil and duty to take the material back in the case that the construction has lost it's function) U2 = leachability standard for category 2 restrictions (next to category 1 restrictions also isolation and 0,7 meter above ground water level) A = A-type application (continuous wet) B = B-type application (only wet during the period of rain fall).
4. CONCLUSIONS It can be concluded that contaminated soil cement stabilizations have a potential application as an alternative for sand cement stabilizations. A critical parameter with respect to the compressive strength is the moisture content of the soils involved in relation to the amount of cement added. The leachability of the researched samples is far below the current leaching standards in the Netherlands. A demonstration project is intended to be carried out as a follow up to this feasibility study in
1994.
5. REFERENCES 1 2 3 4 5
IWACO B.V., "Immobilisatie van verontreinigde grond ten behoeve van toepassing als fundering in de wegenbouw", rapportnummer 10.2614.0, September 1993. RAW Standard Conditions of Contract for works of Civil Engineering construction 1990. Draft NEN 7345, Leaching characteristics of building and solid waste materials- Leaching tests - Determination of the leaching behaviour of inorganic components from building materials, monolithic waste and stabilized waste materials, October 1992. Tweede Kamer-stuk 22683: Brief van de Minister van VROM inzake het Bouwstoffenbesluit bodem- en opervlaktewaterenbescherming, ISSN 0921-737 1, Sdu Uitgeverij Plantijnstraat 's-Gravenhage 1992. Dr Th.G. Aalbers et al, "Milieuhygi5nische kwaliteit van primaire en secundaire bouwmaterialen in relatie tot hergebruik en bodembescherming", RIVM-rapport no. 77 1402005, 20 juni 1992.
925
Contaminated soil cement stabilizations for application as a construction material. P.J. Kroes' and J. van Leeuwen2 IWACO B.V., Consultants for Water & Environment, P . 0 . b ~8520, 3009 AM Rotterdam, The Netherlands
*
Gemeentewerken Rotterdam, Ingenieursbureau Geotechniek en Milieu, P.O.Box 6633, 3002 AP Rotterdam, The Netherlands
Abstract Possibilities for using non-cleanable contaminated soils as an alternative for sand in cement stabilizations, have been studied with respect to physical properties (compressive strength and durability) and leachability. Typical soil parameters like organic matter content, clay content and contaminant type and concentration that may effect the compressive strength have been investigated. It can be concluded that contaminated soil cement stabilizations conform to the construction engineering criteria and leachability standards and have potential application as an alternative for sand cement stabilizations. 1. INTRODUCTION
The excavation of primary surface minerals like sand meets more and more opposition as a result of the negative environmental aspects. The excavation policy in the Netherlands strongly advocates the application of alternative materials, including waste materials and industrial residues. The policy of the national government regarding waste materials in general offers an additional strong stimulus towards minimizing the dumping (landfilling) of waste materials and where possible, an efficient reuse. In the city of Rotterdam @art of the highly industrialized and densely populated area of the Rijnmond in the west of the Netherlands) large quantities of contaminated soil are being excavated because of remediation of sites and earth works. For the category noncleanable contaminated soil that is being landfilled the possibilities for application as an alternative for sand in cement stabilizations have been investigated [l]. These soil cement stabilizations can find there application in civil engineering constructions as can be shown in figure 1.
In the Netherlands there is little experience with respect to stabilizing contaminated soil with cement. Factors that can influence the compressive strength are the contaminants and the more heterogeneous matrix of soil (organic matter, lutum) in comparison with sand.
926
Figure 1. Application of cement stabilization in a road bed construction
2. MATERIALS AND METHODS Soil samples from 13 different sites in the Rotterdam region, from the above mentioned category, have been selected for this research. Each soil sample consisted of about 150 kg. The typical soil parameter contents and contaminant contents researched are summarized in table 1.
Soil samples 1-13
Dry matter
Organic matter
(%)
(%)
72-94
1-14
Lutum
Pb
cu
(%)
@pm)
(ppm)
Zn (ppm)
Cd (ppm)
As (ppm)
0.34
7-11500
13-790
83-900
<0.5-17
<5-18
@pm)
Fines (<63rm)(%)
1-340
11-36
PAH (16EPA)
Explanation: < below detection limit
The first step was to characterize the soils i.e. grading, humus, clay and moisture content and possible retarding properties on hydratation of cement from the organic matter (organic acids). After the characterization, the soil samples are mixed with different cement contents (up to 22% wlw dry matter) at the initial moisture content. The compressive strengths are investigated according to the RAW Standard Conditions [2]. The durability is tested by carrying out drylwet en freezelthaw cycles on the stabilizates. The leachability of the soil-cement stabilizations is investigated by carrying out a tank leaching test [3] on three selected mixtures. The results are compared with leachability standards [4][5]. The factors that influence the compressive strength have been investigated by carrying out correlation analysis.
927
3. RESULTS AND DISCUSSION The main construction engineering criterium for sand cement stabilizations is a minimum compressive strength of about 5 MPa after 28 days of curing. This criterium has also been chosen for the minimum compressive strength of the contaminated soil cement stabilizations. It is found that the main soil parameter that correlates with (influences) the compressive strength is the moisture content. The ideal maximum water/cement ratio is 1 (table 2). Table 2.
Mixtures at initial moisture content
Soil samples
Moisture content
Cement conlenl
46
46
A (6,8 and 12)
10- 14
C (1,2,3 and 4)
Compressive strength (MPa)
= I -1
5,1 6,l-7,7 63
12
15 - 19 20 - 24
B (5. 10 and 11)
Waterlcementratio
17
= I
22
In table 3 the contaminant contents of the investigated mixtures are summarized. Table 3.
Contaminant contents of the mixtures (mg/kgdm)
Component
A
B
C
14 92 320 300 870 560 24
6,O 0,33 19 61 420
14
~~~
As Cd cu pb
Na Zn PAH (16EPA)
150
23
0.65
330 940 520 250 5.5
The organic matter content also correlates with the compressive strength although the humific acids do not contain retarding properties on the hydration of cement. This may be due to the fact that in the investigated soils the moisture content is related to the organic matter content. The contaminants do not correlate at these concentrations with the compressive strength. With respect to the durability of the contaminated soil cement stabilizations, the dry/wet cycli did cause some mass changes but didn’t cause disintegration of the samples. The freeze/thaw cycli, however, caused volume changes for all samples and disintegration of about 20% of the researched samples. Therefore the products have to be optimized and till then it is not recommended to work under freezing conditions. The leachability research has been carried out on the mixtures of A, B and C from table 2. The results are expressed as cumulative emissions (mg/m*) and are summarized in table 4. The cumulative emissions of these contaminated soil-cement stabilizates are far below the leaching standards for A-type and B-type applications [4][5].
928
Table 4.
Cumulative emission ranges (mg/m2) at t=64 days
Component
Na Zn phenanthrene
Min. emission
2,944.9 0-0,9 5570-6640 0.05-0,lI
Max. emission
4,O-34,9 7,O-7.1 5570-6640 140-142 0,05-0,1I
U1A
U2A ti, U1B
40
300 7s 350
1,o
50 100 200
800
I500
Explanation of symbols of table 4: min. emission; concentrations below the detection limit are accounted for as zero in calculating the cumulative emission; max. emission; concentrations below the detection limit are accounted for as the detection limit in calculating the cumulative emission; U1 = leachability standard for category 1 restrictions (no blending with the underlying soil and duty to take the material back in the case that the construction has lost it's function) U2 = leachability standard for category 2 restrictions (next to category 1 restrictions also isolation and 0,7 meter above ground water level) A = A-type application (continuous wet) B = B-type application (only wet during the period of rain fall).
4. CONCLUSIONS It can be concluded that contaminated soil cement stabilizations have a potential application as an alternative for sand cement stabilizations. A critical parameter with respect to the compressive strength is the moisture content of the soils involved in relation to the amount of cement added. The leachability of the researched samples is far below the current leaching standards in the Netherlands. A demonstration project is intended to be carried out as a follow up to this feasibility study in
1994.
5. REFERENCES 1 2 3 4 5
IWACO B.V., "Immobilisatie van verontreinigde grond ten behoeve van toepassing als fundering in de wegenbouw", rapportnummer 10.2614.0, September 1993. RAW Standard Conditions of Contract for works of Civil Engineering construction 1990. Draft NEN 7345, Leaching characteristics of building and solid waste materials- Leaching tests - Determination of the leaching behaviour of inorganic components from building materials, monolithic waste and stabilized waste materials, October 1992. Tweede Kamer-stuk 22683: Brief van de Minister van VROM inzake het Bouwstoffenbesluit bodem- en opervlaktewaterenbescherming, ISSN 0921-737 1, Sdu Uitgeverij Plantijnstraat 's-Gravenhage 1992. Dr Th.G. Aalbers et al, "Milieuhygi5nische kwaliteit van primaire en secundaire bouwmaterialen in relatie tot hergebruik en bodembescherming", RIVM-rapport no. 77 1402005, 20 juni 1992.