Stabilized soils for construction applications incorporating natural resources of Papua new Guinea

Resources, Conservation and Recycling 51 (2007) 711–731

Stabilized soils for construction applications incorporating natural resources of Papua new Guinea K.M.A. Hossain ∗ , M. Lachemi, S. Easa Department of Civil Engineering, Ryerson University, 350 Victoria Street, Toronto, Ont., Canada M5B 2K3 Received 19 May 2006; received in revised form 13 December 2006; accepted 20 December 2006 Available online 9 February 2007

Abstract Papua New Guinea clayey soils are stabilized with various percentages of volcanic ash (VA), finely ground natural lime (L), cement and their combinations. The influence of stabilizers and their combinations is evaluated through Atterberg limits, standard Proctor compaction, unconfined compressive strength, splitting tensile strength, modulus of elasticity and California bearing ratio (CBR) tests. The durability of 38 stabilized soil mixtures is also conducted by studying the influence of water immersion on strength, water sorptivity and drying shrinkage. Correlations between compressive strength, modulus of elasticity and CBR are also established. Theoretical analysis of pavements incorporating subgrades improved by stabilized soils under traffic loads shows technical benefits compared with conventional flexible pavements without improved subgrades. Suitable stabilized soil mixtures using VA, L, cement and their combinations are proposed which can be used for the construction of road pavements, airfields, earth dams and low-cost housing. The use of locally available soils, VA and lime in the production of stabilized soils for such applications can provide sustainability for the local construction industry. © 2007 Elsevier B.V. All rights reserved. Keywords: Soil stabilization; Mechanical properties; Durability; Pavement

∗

Corresponding author. Tel.: +1 416 979 5000x7867; fax: +1 416 979 5122. E-mail address: [email protected] (K.M.A. Hossain).

0921-3449/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.resconrec.2006.12.003

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1. Introduction Construction of roadways over soft subgrades is one of the most common problems in highway construction in many parts of the world. The usual approach to soft subgrade stabilization is to remove the soft soil and replace it with a stronger material of crushed rock. The high cost of replacement has caused highway agencies to evaluate alternative methods of highway construction and one approach is to use stabilized soil for soft subgrade (Edil et al., 2002). The natural durability and strength of the soil can be improved through the process of ‘soil stabilization’ using different types of stabilizers. The aim of soil stabilizers is to increase the resistance against destructive forces of the weather by increasing strength and cohesion, reducing moisture movement in the soil and imparting water proofing characteristics (Winterkorn and Fang, 1975). Stabilization of soils with low-bearing capacity is an economical way to strengthen the earth for building purposes and to diminish the amount of soil exchanges (Kukko, 2000). Soils can be stabilized by mixing the correct proportion of sandy and clay soil or by mechanical compaction of natural soil that increases the strength and cohesion. Use of stabilizers is not new as natural oils, plant juices, animal dung and crushed anthills have been used for many centuries (Ghavami et al., 1999; Bouhicha et al., 2005). The oldest record of the use of straw stabilized mud or clay blocks was found in Greece in the Mediterranean dating back to 4600 b.c. and then spread outward to the establishment of Egyptian dynasties (2900 b.c.) in African continent, Middle East, Europe before reaching other parts of the world (Guiliard and Houben, 1994). Stabilized blocks have different names depending on their locations and techniques of manufacture, like “thobe” in North Africa and “adobe” in Central America (Smith, 1982). In recent years, scientific techniques of soil stabilization have been introduced, and developed largely from methods devised for earth roads (Lunt, 1980). The use of cementitious material like Portland cement, hydraulic lime and lime-pozzolana mixes as stabilizer is quite common (Al-Rawas et al., 2005; Bahar et al., 2004; Bell, 1998; Little, 1995; Prusinski and Bhattacharja, 1999; Sherwood, 1993). The strength of the soil can be increased reasonably by cementing clusters of particles in a manner similar to that of binding aggregates in concrete. Pozzolanic reactions between lime and certain clay minerals form a variety of cement-like compounds that can bind soil particles together and at the same time reduce water absorption by clay particles. Bitumen, asphalt and certain resins as stabilizers act as water proofing agents by providing a physical barrier to the passage of water (BRE, 1996). Stabilization is an economical and ecological method for subgrade reinforcement and its potential is extensive. The potential for using industrial by-products for stabilization of clayey soils such as blast furnace slag, fly ash, rich husk ash and cement kiln dust is promising and has been investigated (Chu and Kao, 1993; Dawson et al., 1995; Ferguson, 1993; Kaniraj and Havanagi, 1999; Miller and Azad, 2000; Rahman, 1986; Sezer et al., 2006; Tsonis et al., 1983; Turner, 1997). Improved engineering properties of fly ash-stabilized soil were reported by Turner (1997) who conducted research on fly ash-stabilized subbase along with nine other stabilization alternatives, such as those using a subbase layer consisting of foundry sand, foundry slag and bottom ash or geosynthetics reinforcement. The studies indicate that increasing fly ash content has a considerable effect on the strength properties

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of soil, and the strength strongly depends on the water-binder ratio. Clay soils stabilized with blast furnace slag activated with cement generally give higher strengths than those with cement alone. Stabilized soils can be extremely useful construction materials in many countries of the world, especially if locally available natural resources, such as volcanic ash (VA) and lime are incorporated. VA is found abundantly in volcanic areas and lime deposits are available in many parts of the world including Papua New Guinea (Hossain, 2000). The use of natural lime and VA as stabilizers in soil stabilization can lead to low-cost construction especially for the local population and can provide an environmentally friendly means of disposal of VA from volcanic disaster area (Hossain, 2000; Hossain and Mol, 1999). Limited research had been conducted to investigate the suitability of using VA in soil stabilization in association with cement and natural lime. Such stabilized soils can be used to improve subgrades or capping layers or sub-bases for road or airfield pavements as well as to produce stabilized building blocks for low-cost housing (Hossain and Lachemi, 2005). Making a more productive use of supplementary cementing materials, industrial wastes and other natural resources would have considerable environmental benefits, reducing air and water pollution. Increased use of such materials as partial replacement of cement would also represent savings in energy and greenhouse gas emission. This paper presents the results of a comprehensive investigation of the characteristics of stabilized local clayey soils incorporating cement and two naturally available materials (VA and lime) in Papua New Guinea (PNG). The following sections present the experimental program and the results of various tests conducted on stabilized soils (compaction, unconfined compressive strength, splitting tensile strength, modulus of elasticity, California bearing ratio, and durability). Criteria for selecting stabilizers for different soils, correlation between properties, and practical applications are then presented, followed by the conclusions.

2. Experimental program 2.1. Collection of materials and their properties The volcanic ash used in this investigation was collected from ‘Rabaul’ in the East New Britain province of PNG and the source was a volcano called ‘Mount Tavurvur’ (Fig. 1). The Rabaul area is situated in the worldwide earthquake and volcanic zone known as the ‘Belt of Fire’. The finely ground natural lime (L) used in this investigation was collected from Finschaffen area of Morobe province of PNG (Figs. 1 and 2). The quantity of lime deposit in this area is huge and sits at an average depth of about 30 cm below the ground surface. The investigation was concentrated on lime samples collected from Simbang village situated at the bank of Mape River, Gagidu-Finschaffen in the province. The lime samples were collected from the ground surface and craw bars were used to break lumps into pebble size. Raw lime samples were grounded to fine powder using ring crusher to obtain a Blaine fineness of about 302 m2 /kg. The cement used was locally manufactured ASTM Type I Portland cement. The chemical and physical properties of VA, L and cement are presented in Table 1. The chemical analysis

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Fig. 1. PNG map with location of materials and VA deposits near Tavurvur volcano.

Fig. 2. Natural lime deposits and production of finely ground lime.

indicated that the natural lime is principally composed of silica (12%) and calcium oxide (45%) while the main component of cement and VA is calcium oxide (64%) and silica (59%), respectively. The amount of oxides of sodium and potassium known as ‘alkalis’ is found to be higher in VA (5.8%) compared to cement (1.1% maximum) and lime (1.0%). Table 1 Chemical/mineralogical properties Chemical composition Oxide compounds Calcium oxide (CaO) Silica (SiO2 ) Alumina (Al2 O3 ) Iron oxide (Fe2 O3 ) Sulphur trioxide (SO3 ) Magnesia (MgO) Sodium oxide (Na2 O) Potassium oxide (K2 O) Loss on ignition Physical properties Fineness (m2 /kg)

VA (%) 6.1 59.3 17.5 7.1 0.7 2.6 3.8 2.0 1.0 242

Lime (%) 45 12 1.2 0.5 0 0.7 0.2 0.8 40 302

Cement (%) 64.1 21.4 5.7 3.5 2.1 2.1 0.5 0.6 1.1 320

Minerological composition of lime: moisture content = 7%, CaCO3 = 75%, SiO2 (soluble, tive/combinable) = 11%, SiO2 = 2% (insoluble, inert/un-combinable), MgCO3 = 1%, Others = 3%.

reac-

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Table 2 Laboratory tests on engineering properties of soils Soil ID

Soil 1 (S1) Soil 2 (S2)

Atterberg limits (%) (ASTM, 2000a)

Grain fractions (%) (ASTM, 2000b)

Soil classification (ASTM, 2000b)

LL

PL

PI

Gravel

Sand

Silt

Clay

USCS

AASHTO

USDA

39 52

20 23

19 29

7 0

42 22

35 48

16 30

CL CH

A-6 A-7-6

Loam Clay loam

Natural moisture content: 12.3% for S1 and 13.5% for S2. USCS: unified soil classification system, USDA: United States Department of Agriculture.

Two clayey soils used in this investigation were collected from the sites at a depth of 1.5 m below the ground surface in order to avoid vegetable matter. Soil 1 (S1) was collected from Simbang village Gagidu-Finschaffen in Morobe province close to lime deposits. Soil 2 (S2) was collected from the Rabaul area of East New Britain province where VA deposits are available. A series of tests was carried out to classify each type of soil. The engineering properties of original soils in terms of Atterberg limits, particle size distribution and soil classification are presented in Table 2. Both wet sieving and hydrometer methods were carried out in order to obtain an accurate grain size analysis. S1 and S2 were classified as A-6 and A-7-6, respectively, according to AASHTO (Table 2). 2.2. Stabilized soil mixtures and combination schemes for stabilizer Comprehensive series of laboratory tests consisting of standard Proctor compaction, unconfined compression strength, splitting tensile strength, modulus of elasticity, California bearing ratio (CBR), water resistance, water sorptivity and shrinkage were conducted on the two selected clayey soils (S1 and S2) with various percentages and combination of stabilizers such as VA, lime and cement. Extensive combinations of stabilizers were used for stabilization of the two soils. Table 3 presents a summary of stabilized soil mixtures with various stabilizer combinations. The percentages of VA were 0, 2, 4, 5, 10, 15 and 20%, while the percentages of both lime and cement were 0, 2, and 4%. A total of

Table 3 Stabilizer combination scheme for stabilized soils Soil type

Combinations

Designation

Single stabilizer (11 combination for each soil—total 22 mixes) S1 or S2 0, 2, 4, 5, 10, 15 and 20% VA 2 and 4% C 2 and 4% L

0VA, 2VA, 4VA, 5VA, 10VA, 15VA, 20VA 2C and 4C 2L and 4L

Mixed stabilizers (8 combinations for each soil—total 16 mixes) S1 or s2 5% VA + 2%C, 5%VA + 4%C 10% VA + 2%C, 10%VA + 4%C 5% VA + 2%L, 5%VA + 4%L 10% VA + 2%L, 10%VA + 4%L

5VA2C, 5VA4C 10VA2C, 10VA4C 5VA2L, 5VA4L 10VA2L, 10VA4L

C: cement, L: lime, VA: volcanic ash. Numerics in the designation represent the percentage of stabilizer.

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38 combinations based on S1 and S2 with single and mixed modes of stabilizers were studied. 2.3. Preparation of specimens and testing procedures The oven-dry soils were initially mixed with the predetermined quantity of VA, lime, cement or a combination of VA and lime/cement in a dry state and subsequently mixed with water so that the mix acquired the intended moisture content. The optimum moisture content and dry density for soils with different percentages of stabilizers were determined by the standard Proctor compaction test (ASTM, 2000c). Initially each stabilizer or combination of stabilizers was thoroughly mixed with soil in a large tray, and mixing was carried out by hand. Thereafter, mixing was carried out in a laboratory mixer for at least 3 min and the mix was subsequently put into plastic bags, where the mixing was continued by shaking and overturning the bag for at least 4 min and finally, the air was squeezed out by hand. The prepared soil mixtures were then used for the manufacturing of specimens for various tests. All test specimens were prepared with the static compaction method (ASTM, 2000c) at the optimum moisture content determined by the standard Proctor compaction test. The specimens were demoulded 1 min after completion of the compaction and were stored in a curing room (maintained at 23 ± 2 ◦ C, 95 ± 2% RH) wrapped in thin plastic film until testing at 7, 28, 56 and 91 days. Cylindrical specimens (39 mm diameter and 78 mm length) were used for unconfined compressive strength (S) (ASTM, 2000c) and indirect tensile (splitting) strength tests. Larger cylindrical specimens (75 mm diameter and 150 mm height) were used for the determination of the modulus of elasticity (E). The compressive and indirect tensile strengths were determined on a hydraulic testing machine under strain-control at a loading speed of 1.14 mm/min. On the other hand, the modulus of elasticity was determined with loading at a constant rate of deformation of 1.0 mm/min up to failure in an effort to obtain the stress-strain relationship at a deformation rate similar to that imposed by traffic on pavement subgrades (Croney, 1977). The CBR test on stabilized soil specimens was conducted (ASTM, 2000d). The specimens for the CBR test were moulded in the CBR-mould with the same compactive energy per volume as in the standard Proctor compaction test. Penetration testing was carried out in the CBR test with the help of a plunger of cross-sectional area of 19.35 cm2 . The rate of penetration was 1.27 mm/min. The CBR value was calculated corresponding to 2.54 mm penetration, since this was always higher than the value obtained at a penetration of 5.08 mm. Durability tests were conducted by studying the effect of water immersion on unconfined compressive strength, water absorption by capillarity (sorptivity) and linear shrinkage. Cylindrical specimens (39 mm diameter and 78 mm length) as used for the unconfined compressive strength tests were examined for the effect of water immersion on compressive strength. The specimens were cured for 84 days, wrapped in plastic sheets in the curing room and then unwrapped from plastic sheets and put into water containers stored in the curing room until testing for soaked compressive strength (Ss ) at 91 days. The experimental set-up for the sorptivity tests is shown in Fig. 3. The lower side of cylindrical specimens was immersed at a 5 mm constant head-water tank for a time (t) of 10 min and the quantity

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Fig. 3. Schematic diagram of water sorptivity test.

of water absorbed (W) was determined. The coefficient of water absorption by sorptivity (ψ) was then calculated by ψ=

W At 0.5

(1)

where A the is cross-sectional area of the specimen. The test was conducted on specimens cured for 7 days and repeated on the same specimens at the age of 14 days. Linear shrinkage was measured on cylindrical specimens (39 mm diameter and 78 mm length) using a dial gauge at different ages up to 91 days.

3. Results and discussion 3.1. Standard proctor compaction tests This test was used to determine the effect of stabilizers on maximum dry density and optimum moisture content. A summary of the results of compaction tests on stabilized soils with various percentages of VA, lime and cement is shown in Figs. 4–6. The variation of dry density with moisture content for S1 stabilized with 0–20% VA is shown in Fig. 4 in terms of the initial moisture content of the mix (calculated based on the amount of added water) and measured actual moisture content (calculated from samples taken from the compacted specimen). There is a difference of about 2–3% between the two moisture contents. This may be attributed to the chemical combination of water with free lime that is possibly present in VA since minimal evaporation could take place as every precaution was taken to avoid drying during the procedures of mixing, compacting and storing. Similar behaviour is also observed for S2. The changes in maximum dry density and optimum moisture content with the increase in VA contents for S1 and S2 are presented in Fig. 5. The maximum dry density decreases and the optimum moisture content increases as VA content increases from 0 to 20%. It should be pointed out that the high optimum moisture contents may be difficult and costly to achieve

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Fig. 4. Variation of dry density with moisture content.

during dry seasons. On the other hand, during wet seasons the high water demand of VA will facilitate compaction. The maximum dry density of cement and lime stabilized soils decreases and optimum the moisture content increases when cement/lime content is increased from 0 to 4% (Fig. 6). Similar behaviour was also observed in other research studies in the case of lime, fly ash and rice husk ash stabilized clayey soils (Rahman, 1986). The compaction characteristics depend on both grain size distribution and specific gravities of the soil and stabilizer. The stabilizers initially coat the soils to form large aggregates that consequently occupy larger spaces. Therefore, the tendency of fine-grained soils is to initially decrease the dry density until the stabilizer (which tends to increase the dry density) compensates for the larger spaces. Only cement with high specific gravity can produce this effect as confirmed from the increase of dry density of stabilized soil with higher cement content beyond 4% (Rahman, 1986).

Fig. 5. Variation of maximum dry density and optimum moisture content with VA content.

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Fig. 6. Variation of maximum dry density and optimum moisture content for stabilized soils.

The addition of VA and lime to the soil raises the optimum moisture content. The pozzolanic reaction of VA and lime with the soil constituents tends to increase the optimum moisture content. The increase in optimum moisture content with the addition of cement is attributed to the extra water required for hydration of cement. S2 produced higher optimum moisture content and higher maximum dry density compared with those of S1 when stabilized with various stabilizers such as VA, L, cement and their combinations (Fig. 6). 3.2. Unconfined compressive strength, splitting tensile strength and modulus of elasticity Fig. 7 shows the development of the unconfined compressive strength of stabilized soils S1 and S2 with age for various percentages of VA. In general, the compressive strength increases with the increase in age. The unconfined compressive strength increases with the increase in VA content from 0 to 20% for both S1 and S2 with S1 producing higher strength

Fig. 7. Influence of VA content and age on unconfined compressive strength.

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Fig. 8. Influence of C, L and VA stabilization on unconfined compressive strength.

than S2. The 91-day compressive strength of 20VA-S1 was 3.1 MPa compared with 1.9 MPa of 20VA-S2. For S1, it is possible to achieve a 91-day compressive strength of 1.3 and 2 MPa with 5 and 10% VA, respectively. For S2, it is possible to achieve a 91-day compressive strength of 0.4 and 0.8 MPa with 5 and 10% VA, respectively. Fig. 8 compares the compressive strength of soils stabilized with VA, L and cement. The addition of lime and cement also increases the compressive strength of stabilized soil specimens. The strength increases with the increase in lime and cement content from 0 to 4% for both S1 and S2. In the case of cement, the increase in compressive strength is higher compared to lime and VA, with lime stabilization producing the lowest strength. The effect of combining 2 and 4% cement and lime with 5 and 10% VA in mixed mode of stabilization is shown in Fig. 9. Stabilizer combinations with higher dosages produce higher compressive strength. The combination of stabilizers with cement produces higher compressive strength than combinations with L and VA. It can be noted that the 91-day strength of both S1 and S2 is higher when 20% of VA (20VA) is used compared to the combination of 10% VA and 2 or 4% cement (10VA2C or 10VA4C).

Fig. 9. Influence of mixed mode of stabilization on unconfined compressive strength.

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Fig. 10. Influence of VA content and age on splitting tensile strength.

Fig. 11. Influence of C, L and VA stabilization on splitting tensile strength.

Figs. 10–12 present the splitting tensile strength development of S1 and S2 for various percentages of stabilizers (VA, L and cement) and their combinations. The splitting tensile strength increases with the increase in age. The effect of different stabilizers and their combination on the splitting tensile strength is similar to that observed in the case of compressive

Fig. 12. Influence of mixed mode of stabilization on splitting tensile strength.

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strength. For single stabilization, the 91-day splitting tensile strength is maximum for Mix 20VA (0.43 MPa for S1 and 0.27 MPa for S2) while Mix 2L produces the lowest strength (0.08 MPa for S1 and 0.04 MPa for S2). For mixed mode of stabilization, the 91-day splitting tensile strength is maximum for Mix 10VA 4C (0.37 MPa for S1 and 0.16 MPa for S2), while Mix 5V2L produces the lowest strength (0.22 MPa for S1 and 0.06 MPa for S2). Table 4 presents the 91-day modulus of elasticity (E) of stabilized soil mixtures. Considerably higher values of E are obtained with S1 compared to S2 and E increases with the increase in age. The effect of different stabilizers and their combinations on E is similar to that observed in the case of strength. For single stabilization, the 91-day E is maximum for Mix 20VA (5 GPa for S1 and 2.5 GPa for S2) while Mix 4L produces the lowest E (1.18 GPa for S1 and 0.62 GPa for S2). For mixed mode of stabilization, the 91-day E is maximum for Mix 10VA 4C (3.9 GPa for S1 and 2.2 GPa for S2) while Mix 5V2L produces the lowest E (1.9 GPa for S1 and 1.1 GPa for S2). S2 stabilized soils with single or combination mode of stabilizers produce lower compressive strength, splitting tensile strength and E compared to S1 soils. It is evident therefore that the soil type greatly influences the mechanical properties of stabilized soils. The increase in unconfined compressive strength, splitting tensile strength and E with the increase in stabilizer contents indicates that the cohesion of the clayey soils increases due to the addition of VA, lime and cement. The higher strength of VA-stabilized soil compared to lime-stabilized soil is due to hydraulic and pozzolanic reactions of VA. The beneficial effect of combining VA with cement can be attributed to the transformation of the soil, as VA allows better distribution of cement and increases its effectiveness. The use of high percentages of VA, in certain cases, is more effective than the combination of VA and cement, but the problems associated with the use of large quantities of VA would need to be addressed. These problems include transport costs, practical problems of spreading and mixing these large quantities of VA and increased water demand. On the other hand, there are soils (such as S1) that may be satisfactorily stabilized with small percentages of VA and cement. 3.3. CBR tests Table 4 and Fig. 13 show the 91-day CBR for stabilized soil mixtures. For both S1 and S2, CBR values are found to increase with the increase of age and VA content (from 0 to 20%). As expected (like strength and modulus of elasticity), higher CBR values are obtained for S1 compared with S2. The cement-stabilized soil has much higher CBR values than lime and VA-stabilized soil. The better performance of VA-stabilized soil compared to NL-stabilized soil can be attributed to the pozzolanic properties of VA. The results of CBR tests indicate that the appreciable improvement of both S1 and S2, has taken place with all these three stabilizers and their combinations. It should be noted, however, that the 15% minimum CBR value usually required by many specifications is by far attained by S1 with 4% VA, 2% cement and 2% L (5% VA, 4% C and 4% L for S2). It is also interesting to note that many of the stabilized soil mixtures especially with S1 produced very high CBR values (>80%—a value that normally characterizes an excellent compacted pavement subgrade) and have the potential to be used for manufacturing bricks for building construction.

Soil mix

0VA 2VA 4VA 5VA 10VA 15VA 20VA 2C 4C 2L 4L 5VA2C 5VA4C 10VA2C 10VA4C 5VA2L 5VA4L 10VA2L 10VA4L

91-day unconfined compressive strength (MPa)

CBR (%)

E (GPa)

Absorption coefficient, ψ (%)

Shrinkage (%)

S

91-day

91-day

7-day

91-day

Ss

14-day

S1

S2

S1

S2

S1

S2

S1

S2

S1

S2

S1

S2

S1

S2

0.10 0.35 0.81 1.30 2.00 2.60 3.10 0.75 0.92 0.60 0.70 1.90 2.10 2.40 2.55 1.52 1.72 1.93 2.09

0.10 0.35 0.44 0.40 0.80 1.30 1.90 0.38 0.52 0.30 0.39 0.52 0.80 0.99 1.10 0.42 0.68 0.82 0.97

0.05 0.22 0.61 1.05 1.76 2.34 2.82 0.51 0.75 0.39 0.49 1.67 1.89 2.12 2.40 1.22 1.41 1.58 1.76

0.05 0.20 0.31 0.30 0.65 1.09 1.61 0.24 0.40 0.18 0.25 0.43 0.67 0.83 0.96 0.31 0.52 0.63 0.76

11 30 64 72 140 165 180 53 63 43 49 125 138 154 167 101 114 127 137

10 20 25 30 60 82 115 29 38 24 30 38 56 68 75 32 48 57 67

– – 1.2 1.5 3.0 4.0 5.0 – 1.6 – 1.2 2.6 3.0 3.5 3.9 1.9 2.2 2.66 2.98

– – 0.6 0.8 1.5 2.0 2.5 – 0.8 – 0.6 1.4 1.7 1.9 2.2 1.0 1.2 1.47 1.64

12.2 – 8.5 8.3 6.1 – 5.1 – 8.1 – 9.2 – 7.1 – 5.3 – 7.6 – 5.8

12.7 – 8.6 8.3 6.2 – 5.1 – 8.6 – 9.4 – 7.3 – 5.5 – 7.8 – 5.8

20.7 – 14.5 14.1 10.4 – 8.7 – 13.8 – 15.6 – 12.1 – 9.0 – 12.9 – 9.9

22.9 – 15.5 14.9 11.2 – 9.2 – 15.5 – 16.9 – 13.1 – 9.9 – 14.0 – 10.4

3.3 – 2.6 – 2.4 – 2.3 – 2.8 – 2.9 – – – 2.3 – – – 2.4

3.5 – 2.7 – 2.6 – 2.4 – 2.9 – 3.0 – – – 2.5 – – – 2.6

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Table 4 Summary of mechanical and durability properties of stabilized soil mixtures

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Fig. 13. CBR and residual strength of stabilized S1 and S2 soil mixtures.

3.4. Durability characteristics of stabilized soils 3.4.1. Effect of water immersion on compressive strength Table 4 compares the 91-day normal curing unconfined compressive strength (S) and those obtained after 7-day water immersion (Ss ). The effect of the 7-day water immersion on the 91-day compressive strength is presented in Fig. 13 in terms of strength ratio expressed as percentage (100 Ss /S). The ratio increases with the increase in VA, cement and lime content. In general, for similar dosages of stabilizer, the cement-based soil shows higher strength ratio than that of VA or lime. The strength retaining capacity of S1 is found to be better than S2. For S1, the ratio was greater than 80% for all mixes except 0VA, 2VA, 4VA, 2C, 2L and 4L. For S2, the ratio was lower than 80% for all mixes except 10VA, 15VA, 20VA, 5VA2C, 5V4C, 10VA2C and 10VA4C. 3.4.2. Water absorption by sorptivity Higher coefficient of water absorption (ψ) is observed at 14 days of testing compared with those obtained at 7 days (Table 4). In general, the single or mix mode of soil stabilization with cement, lime and VA is found to reduce the sorptivity substantially. The sorptivity of S1 is found to be lower compared to S2. The cement-stabilized soils produced lower sorptivity than VA and lime with lime-stabilization showing the highest values. The increase in VA content seems to reduce the sorptivity of stabilized soils. The positive effect of reducing the sorptivity of soils with combined chemical (with different stabilizers) and mechanical (with compaction by standard Proctor) stabilization can be attributed to the cementation of the soil particles together, filling of pore space in the soil and prevention of the reorientation and flocculation of soil particles which precluded formation of enlarged pores and cracks (Borderick and Daniel, 1990). 3.4.3. Shrinkage Fig. 14 shows a typical variation of shrinkage with time for stabilized soils. Shrinkage rapidly increases during the first 7 days for both stabilized and non-stabilized soil specimens and then at later ages, the increase is very slow. Hence, curing for the first 7 days could be beneficial in reducing drying shrinkage and cracking. The shrinkage of stabilized soils is lower compared to that of non-stabilized soils.

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Fig. 14. Shrinkage characteristics of stabilized soil mixtures.

Table 4 shows the final shrinkage at the age of 91 days for stabilized and non-stabilized soil specimens. In general, VA-stabilized specimens show lower shrinkage compared to cement/lime-stabilized specimens with lime-specimens showing the highest values. The shrinkage decreases with the increase in VA content. The 91-day shrinkage is decreased by 32% when VA content is increased from 0 to 20%. The shrinkage also decreases with the increase in dosages of stabilizers in both single and mixed modes of stabilization (Fig. 14). The addition of cement, lime, VA and their combinations reduces the shrinkage as particles of such stabilizers oppose the shrinkage movement.

4. Criteria for selecting stabilizers for different soils The two main criteria for selecting stabilizers are the US Bureau of Public Roads Method (Cook and Spence, 1983) and the Plasticity Chart Method (Mukerji and Stulz, 1993). The former is based on particle size analysis and mainly considers the finer fractions from sand to clay. Cook and Spence stated that a soil containing 65–85% sand, 5–20% silt and 5–25% clay is suitable for stabilization. They also stated that soils with LL less than 40% and PI within the range of 22–2.5% are most suitable for stabilization. According to the Plasticity Chart (Fig. 15), S1 is suitable for lime or cement-lime stabilization and S2 falls outside the suitability zones. However, soils do not have to satisfy the two criteria, and may still be suitable for stabilization (Mukerji and Stulz, 1993). It is, therefore, important to investigate the suitability of a soil to be stabilized using different types and combination of stabilizers. The performance of plasticity chart in choosing suitable stabilizer for a particular soil is verified with the performance of soils S1 and S2. According to the plasticity chart prediction, S1 should be suitable for lime or cement-lime stabilization and S2 should not be suitable for cement/lime/bitumen or their combinations. Better performance of cement/lime/VA stabilized S1 soil compared to S2 in terms of strength, CBR and durability characteristics indicates that the Plasticity chart can be used as a guideline for selecting stabilizers. However, soils that fall outside the suitability zone (such as S2) may be still suitable for stabilization. For such soils, investigations should be conducted to select the best stabilizer.

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Fig. 15. Plasticity chart showing suitability of stabilization (Mukerji and Stulz, 1993).

5. Correlation between properties The relationships between CBR and compressive strength, and between modulus of elasticity and compressive strength at 91-day are shown in Fig. 16a and b, respectively. For the two soils studied, a linear relationship between CBR and compressive strength as well as E and compressive strength exists. Similar linear relationships between CBR and compressive strength have been found for cement-stabilized soils (Sherwood, 1993). On the other hand, a nonlinear relationship exists between CBR and modulus of elasticity (E) of stabilized soils (Fig. 16c). However, such a relationship can be applied strictly to the soils investigated in this study.

6. Practical applications The developed stabilized soil mixtures can be used in manufacturing building blocks and as subbase layers in road pavements. The recommended mixtures and their properties are summarized in Table 5. In the context of Papua New Guinea, the use of local materials such as natural lime and VA in the stabilization of locally available soils has special significance. The Table 5 Recommended stabilized soil mixtures and range of their properties Unconfined compressive strength (MPa) 7-day 91-day

0.11–0.6 0.39–3.1

91-day CBR (%) 91-day Modulus of elasticity (GPa)

25–252 0.62–3.9

Single mode: 4VA, 5VA, 10VA, 15VA, 20VA, 4C, 4L; mixed mode: 5VA2C, 5VA4C, 10VA2C, 10VA4C, 5VA2L, 5VA4L, 10VA2L, 10VA4L.

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Fig. 16. (a) Correlation between E and compressive strength. (b) Correlation between compressive strength and CBR. (c) Correlation between CBR and E.

developed stabilized soils can be used in the construction of low-cost houses and road infrastructure for local population. The viability of implementing such stabilized soils (developed in this study) in the production of building blocks has been extensively investigated and the research shows promising results (Hossain, 2000; Hossain and Lachemi, 2005).

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Fig. 17. (a) Effect of stabilized soil layer (SSL) on stress. (i) Pavement 1 and (ii) Pavement 2. (b) Equivalent pavements: (i) Proposed with SSL and (ii) Conventional without SSL.

Theoretical investigation on the possible use of the developed stabilized soils for road pavements is conducted. Stabilized soil layers used as pavement subbases are prone to cracking caused by drying shrinkage and thermal contraction. Adequate curing should be provided immediately after the completion of compaction to avoid such cracking. On the other hand, construction traffic may also cause severe cracking if they are allowed before the material is not strong enough to withstand the stresses imposed by the traffic. It is generally recommended that a 200-mm thick protective overlay of unbound well-graded crushed granular material is placed immediately after compaction of the stabilized soil layer to take advantage of the high values of the modulus of elasticity, and consequently reduce

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the required pavement thickness. This will ensure efficient curing of the stabilized layer and simultaneously reduce any stresses induced by site traffic (Fig. 17a). Since strength development of this type of stabilized material is slow, the construction of the unbound layer will not cause any damage to the green stabilized layer if the construction is carried out immediately after compaction. The unbound granular material should also eliminate any danger of reflection cracking. Theoretical analysis is carried out for pavements with variable thickness of stabilized soil layer (SSL) with and without protective granular layer (PGL) to calculate flexural tensile stress at the bottom of SSL due to axle loads. Typical results using an SSL with ESSL = 1 GPa (since all recommended stabilized soils except 4VA and 5VA have an E-value greater than 1 GPa) and a PGL with EPGL = 0.1 and 0.9 GPa are shown in Fig. 17a. The beneficial effect of the PGL is evident from the fact that the placement of a PGL substantially reduces the required thickness of SSL. Fig. 17b shows two equivalent pavements designed so that they have the same subgrade strain εvv (same deformation) and the same horizontal strain (εhh ) at the bottom of the asphalt layer (AL) (same fatigue behaviour). Pavement 1 is a proposed pavement with SSL and Pavement 2 is a conventional flexible pavement without SSL. The analysis of both pavements was made taking into consideration the modulus of elasticity and other properties as shown in Fig. 17b. It can be seen that there is considerable saving in asphalt layer thickness for Pavement 1 illustrating the beneficial effect of placing an in-situ SSL on top of a poor subgrade.

7. Conclusions This study presents the characteristics of clayey soils stabilized with volcanic ash (VA), finely ground natural lime (L) and cement and their effect on pavement thickness. On the basis of the test results obtained from 38 stabilized soil mixtures, the following conclusions can be drawn: • In general, stabilized soils exhibit enhanced mechanical properties such as strength (compressive and tensile), modulus of elasticity and California bearing ratio as well as durability in terms of water resistance, water sorptivity and shrinkage. Although this research is based on materials obtained from Papua New Guinea, it provides useful information for the manufacture of stabilized soils using similar materials available in other parts of the world. • The potential benefit of stabilization was found to depend on the type of soil, the amount of stabilizers, stabilizer combinations and the age. Cement stabilized soils showed better mechanical and durability characteristics compared to cement and lime. However, a high percentage of VA up to 20% can be more effective than the combination of VA and cement. Combinations mode such as VA-cement or VA-L also produces acceptable mechanical and durability characteristics. • The use of stabilized soils in road pavement construction can lead to substantial reduction in the total pavement thickness, and in particular the asphalt course. However, suitable measures should be taken to avoid or minimize cracking of the stabilized layer and

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to maintain the high modulus values. Better shrinkage resistance of VA-stabilized soil mixtures compared to cement/lime-stabilized soils suggests the viability of using such stabilized soils. • The potentials of VA in the soil stabilization are considerable compared to lime and cement. Since VA and lime deposits as well as clayey soils are abundant in many parts of the world, VA or lime stabilized soils can be potentially utilized as a substitute of comparatively costly cement-stabilized soil to reduce construction cost, particularly in the rural areas of the less developed countries including Papua New Guinea. • The benefits of the proposed stabilized soil layer using VA and lime have been illustrated using a full-depth asphalt concrete layer. However, similar benefits would be realized for other types of asphalt concrete pavements, including pavements consisting of asphalt concrete layer over emulsified asphalt layer and pavements consisting of asphalt concrete layer over emulsified asphalt layer and untreated aggregate layer. The proposed use of stabilized soil layer should help promote sustainable development in the construction industry.

Acknowledgements The authors would like to thank Mr. Lucas Mol and Mr. Dason Geveken, graduate students supervised by the first author at The Papua New Guinea (PNG) University of Technology for their assistance in the laboratory work. The authors also acknowledge various local authorities of Rabaul and Finschaffen of PNG for their assistance in the collection of volcanic ash, lime and soil samples.

References Al-Rawas AA, Hago A, Al-Sarmi H. Effect of lime, cement and Sarooj (artificial pozzolan) on the swelling potential of an expansive soil from Oman. Build Environ 2005;40:681–7. ASTM. Standard test method for liquid limit, plastic limit and plasticity index of soils. ASTM D 4318-98. West Conshohocken, Pennsylvania: Annual Book of ASTM Standards; 2000a. ASTM. Standard test method for particle size analysis of soils. ASTM D 422-98. West Conshohocken, Pennsylvania: Annual Book of ASTM Standards; 2000b. ASTM. Standard test method for unconfined compressive strength of cohesive soil. ASTM D 2166-98. West Conshohocken, Pennsylvania: Annual Book of ASTM Standards; 2000c. ASTM. Standard test method for CBR (California Bearing Ratio) of laboratory-compacted soils. ASTM D 1883-99, West Conshohocken, Pennsylvania: Annual Book of ASTM Standards; 2000d. Bahar R, Benazzoug M, Kenai S. Performance of compacted cement-stabilised soil. Cement Concrete Composit 2004;26:811–20. Bell FG. Stabilisation and treatment of clay soils with lime. Ground Eng Lond 1998;21(1):12–5. Borderick GP, Daniel DE. Stabilizing compacted clay against chemical attack. J Geotech Eng 1990;116(10):1549–67. Bouhicha M, Aouissi F, Kenai S. Performance of composite soil reinforced with barely straw. Cement Concrete Composit 2005;27(5):617–21. BRE, 1996. Library bibliography 250, Soil stabilization. England: Building Research Establishment (BRE). Chu SC, Kao HS. A study of engineering properties of a clay modified by fly ash and slag. In: Sharp KD, editor. Fly ash for soil improvement-geotechnical special publication. New York: ASCE; 1993. p. 89–99.

K.M.A. Hossain et al. / Resources, Conservation and Recycling 51 (2007) 711–731

731

Cook DJ, Spence RJS. Building materials in developing countries. Chichester, UK: John Willey and Sons; 1983. Croney D. The design and performance of road pavements. London: HMSO; 1977. p. 52. Dawson AR, Elliot RC, Rowe RC, Williams GM. Assessment of suitability of some industrial by-products for use in pavement bases in the United Kingdom. Transp. Res. Rec. 1486, TRB, Washington, DC: National Research Council; 1995, p. 114–23. Edil TB, Benson CH, Bin-Shafique MS, Kim W, Tanyu BF, Senol A. Field evaluation of construction alternatives for roadway over soft subgrade. Transp. Res. Rec. 1786, TRB, Washington, DC: National Research Council; 2002, p. 36–48. Ferguson G. Use of self-cementing fly ash as a soil stabilizing agent. New York: ASCE; 1993. Ghavami K, Filho RDT, Barbosa NP. Behaviour of composite soil reinforced with natural fibres. Cement Concrete Composit 1999;21:39–48. Guiliard H, Houben H. Earth construction: A comprehensive guide. London: Intermediate Technology Publications; 1994, 112p. Hossain KMA, Lachemi M. Stabilized building blocks incorporating volcanic ash and finely ground natural lime. In: Proceedings of the 1st Canadian Conference on Effective Design of Structures; 2005. Hossain KMA. Strength and durability characteristics of stabilized Papua New Guinea soil blocks incorporating commercial and natural stabilizers. Research Report No. CE-SE-06-2000, Dept. of Civil Eng., The Papua New Guinea University of Tech., Lae; 2000, p. 187. Hossain KMA, Mol L. Structural performance of stabilized Papua New Guinea soil blocks. In: Proceedings of the 7th East Asia-Pacific Conference on Structural Engineering and Construction (EASEC7), vol. 2; 1999. p. 1454–9. Kaniraj SR, Havanagi VG. Compressive strength of cement stabilized fly ash-soil mixtures. Cement Concrete Res 1999;29:673–7. Kukko H. Stablization of clay with inorganic by-products. J Mater Civil Eng 2000;12(4):307–9. Little DN. Handbook for stabilization of pavement subgrades and base courses with lime. Dubuque, IA, US: Kendall/Hunt publication Company; 1995, 123p. Lunt MG. Stabilised soil blocks for buildings. Overseas Building Notes, No. 184, Watford, England: Building Research Establishment; 1980. Miller G, Azad S. Influence of soil type on stabilization with cement kiln dust. Construct Build Mater 2000;14(2):89–97. Mukerji K, Stulz R. Appropriate building materials: A catalogue of potential solutions. St. Gallen, Switzerland: SKAT and IT Publications; 1993. Prusinski JR, Bhattacharja S. Effectiveness of Portland cement and lime in stabilizing clay soils. Transp. Res. Rec. 1652, TRB, Washington, DC: National Research Council; 1999, p. 215–22. Rahman MA. The potentials of some stabilizers for the use of laterite soil in construction. Build Environ 1986;21(1):57–61. Sezer A, Inan G, Yilmaz HR, Ramyar K. Utilization of a very high lime fly ash for improvement of Izmir clay. Build Environ 2006;41:150–5. Sherwood P. Soil stabilization with cement and lime. State of the art review. Berkshire, England: Transport Research Laboratory; 1993. Smith EW. Adobe bricks in New Mexico. Circular 188, Socorro: New Mexico Bureau of Mines & Mineral Resources; 1982. Tsonis P, Christoulas S, Kolias S. Soil improvement with coal ash in road construction. In: Proceedings of the 8th European Conference on Soil Mechanics and Foundation Engineering; 1983. p. 961–4. Turner JP. Evaluation of western coal fly ashes for stabilization of low-volume roads. In: Wasemiller MA, Hoddinott B, editors. Testing soils mixed with waste or recycled materials. ASTM STP; 1997. p. 1275. Winterkorn HF, Fang HY. Foundation engineering handbook. London: Van Nostrand Reinhold; 1975. p. 176.