Sustainable stabilisation of the Lower Oxford Clay by non-traditional binder

Applied Clay Science 52 (2011) 199–208

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Applied Clay Science j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / c l a y

Research Paper

Sustainable stabilisation of the Lower Oxford Clay by non-traditional binder Mohamad Nidzam Rahmat ⁎, Norsalisma Ismail Faculty of Architecture, Planning and Surveying, Universiti Teknologi MARA, 40450 Shah Alam, Selangor, Malaysia

a r t i c l e

i n f o

Article history: Received 6 October 2010 Received in revised form 7 February 2011 Accepted 11 February 2011 Available online 21 February 2011 Keywords: Wastepaper Sludge Ash Clay Strength Linear expansion

a b s t r a c t Wastepaper Sludge Ash (WSA), an industrial by-product from the paper industry can possibly be utilised to modify certain engineering properties of soils for specific uses to conserve non-renewable natural resources. Sulphate-bearing clays (Lower Oxford Clay, LOC) stabilised with various stabilisers on the basis of WSA (such as WSA–lime, WSA–Portland cement and WSA–ground granulated blastfurnace slag) under controlled laboratory conditions. The stabilisers reduced the plasticity index (PI) and maximum dry density (MDD), increased the optimum moisture content (OMC) of LOC. The compressive strength of these stabilised clays was comparable to the clay stabilised by the traditional stabiliser lime (CaO) and was better when WSA was combined with ground granulated blastfurnace slag (GGBS) and with Portland cement (PC). This system also performs better in terms of linear expansion. The results therefore indicate environmental, economic, as well as technological benefits in utilising WSA as soil stabiliser. © 2011 Elsevier B.V. All rights reserved.

1. Introduction Weak or unsuitable sub-grade soils are the result of either low load-bearing capacity, and/or high swelling properties. Volume changes may cause unpredictable movement of structures that are found on such soils. Heaving, shear failure, excessive settlement, high swelling potential, frost susceptibility, cracking, and breaking up are some of the undesirable properties of such soils in geotechnical engineering (Abdullah and Al-Abadi, 2010; Mowafy et al., 1990). Although traditional soil stabilisation using lime and/or cement is well established (Yilmiz and Civelekoglu, 2009), a review of the literature related to soil stabilisation with cement and lime indicated that extensive studies were published by many researchers but there is also a need of alternative technologies which are more sustainable, environmentally friendly and economical. In the paper industry, the environmental impact of paper manufacturing may be reduced by increasing the quantities of paper recycled, and by utilising ash from combusted wastepaper (Frederick et al., 1996). In the UK, one of the principal wastepaper recycling companies, Aylesford Newsprint Ltd. (ANL), combust wastepaper sludge in a fluidized bed, and generates steam for use in the plant. The ash resulting from combustion of sludge is currently dumped to landfills (~700 tonnes/week) (Kinuthia et al., 2001a,b). A chemical and mineralogical study of WSA, at the University of Glamorgan has established that WSA from ANL contains i) 3%–5% CaO, ii) 20%–40% soluble SiO2 and iii) ~5% free lime (Kinuthia et al., 2001a,b). ⁎ Corresponding author at: Civil Engineering Research Unit, Department of Engineering, Faculty of Advanced Technology, University of Glamorgan, Pontypridd, CF37 1DL, UK. Tel.: +44 1443 654289, +44 7527101947 (mobile). E-mail address: [email protected] (M.N. Rahmat). 0169-1317/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.clay.2011.02.011

Chemical analysis of WSA indicated a high amorphous silica and alumina content. Thus, this material possesses both hydraulic and latently hydraulic properties and its cementitious nature should be applicable for soil stabilisation. Its use in this way would reduce environmental damage and minimise the waste by recycling, re-use, and recovery. Investigations on the compressive strength of paste (Bai et al., 2003) showed that the paste made from 100% WSA achieved very low strength as a result of a high level of coarse pores and a significant degree of unsoundness. However, when WSA was blended with GGBS, significant pore refinement occurs and the unsoundness is reduced partially as a result of the increase in the effective water to WSA ratio which enables a greater degree of CaO hydration to occur prior to setting. Bai et al. (2003), reported that the slow hydration of GGBS accompanied with further hydration of WSA significantly increased the compression strength. This hydraulicity can be attributed to the presence of lime, which activates the hydration of GGBS. The objective of the current investigation is to establish the potential of WSA for the soil-stabilised pavement material, with or without blending it with lime (CaO), Portland cement (PC), or with ground granulated blastfurnace slag (GGBS).

2. Materials and methodology 2.1. Lower Oxford Clay (LOC) Lower Oxford Clay was chosen as the principal soil in this investigation, due to its stabilisation. It was supplied by Hanson Bricks Ltd., from their clay brickworks at Stewardby, Bedford. The clay is known to have a high sulphate and sulphide content in the form of gypsum and pyrites. From the mineralogical studies by Hanson Brick

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M.N. Rahmat, N. Ismail / Applied Clay Science 52 (2011) 199–208 Table 1 Oxides, mineral and chemical composition analyses of the Lower Oxford Clay (LOC) (Higgins et al., 2002; Wild et al., 1998).

Table 3 Principal oxides released from WSA and soluble residue (test according to BS 1881 Part 124).

Oxides

Content (mass%)

Component

(%)

SiO2 Al2O3 CaO Fe2O3 MgO K2O Na2O3 TiO2 FeO Mn2O P2O5 L.O.I

46.73 18.51 6.15 6.21 1.13 4.06 0.52 1.13 0.80 0.07 0.17 15.79

Insoluble residue Soluble silica Soluble calcium oxide Soluble sulphate as SO3 CO2 Soluble Al2O3 Soluble MgO Soluble Fe2O3 Total

14.80 22.55 40.90 0.83 2.32 15.60 2.30 0.66 99.96

Minerals Chlorite Illite Gypsum Kaolinite Quartz k-feldspar Calcite Pyrite

7 23 2 10 29 8 10 4

Chemical and other compounds Soluble silica Carbonate Chloride Sulphide Sulphate Total sulphur Organics

size particles. Quicklime (CaO) was supplied by Buxton Lime Industries Ltd., in the form of a fine white powder of cement size fineness. PC was supplied by Rugby Cement UK, and GGBS was supplied by Civil and Marine Slag Cement Ltd. The chemical and oxide composition, physical properties and other data of these stabilisers are given in Tables 1–3. 2.3. Mix compositions

0.43 5.02 0.01 0.018 1.29 1.50 7

Ltd., (Thomas, 2001), LOC contains illite (23%), kaolinite (10%), chloride (7%), calcite (10%), quartz (29%), gypsum (2%), pyrite (4%), feldspar (8%) and organic compounds (7%). Pyrites and gypsum in LOC form expansive minerals such as ettringite and thaumasite after stabilisation with lime, making the stabilisation layer unstable (Higgins, 1998; Higgins et al., 2002; Snedker et al., 1990, 1996; Wild et al., 1998, 1999). Therefore LOC is an excellent challenge for stabilisation.

WSA was the key stabiliser used, with and without blending with lime, PC or GGBS. The control mixes were LOC stabilised with 2%, 4% and 6% CaO. The contents of WSA and WSA blends were 10%, 15% and 20%. These stabiliser levels had been established in a previous study by Kinuthia et al. (2001a,b). These stabiliser levels most likely achieve a minimum California bearing ratio (CBR) of 15% stipulated by Department for Transport (DfT), for a lime-stabilised capping layer (Highway Agency, 2000). For the blended binders, two mix proportions were investigated, 90:10 and 80:20 (WSA:lime and WSA:PC) blends and 70:30 and 50:50 (WSA:GGBS) blends (Table 4). 2.4. Specimen preparation The consistency limit tests were carried out in accordance with BS 1377 (BSI, 1990) on LOC that was dried, crushed and sieved passing 425 μm (in accordance with BS) and containing various contents of different stabilisers to establish the influence of the stabilisers on the Atterberg limits.

2.2. Stabilisers WSA was supplied by Aylesford Newsprint Ltd. (ANL) in the form of a dry fine grey powder with a small content (10%) of coarse sandTable 2 Oxides and chemical composition, and some physical properties of quicklime, Portland cement, GGBS and WSA. Oxides

Compounds (mass%) Quicklime

Portland cement

GGBS

WSA

SiO2 TiO2 Al2O3 Fe2O3 MnO CaCO3 CaO MgO S2 SO3

0.9 – 0.15 0.07 – 2.2 95.9 0.46 – –

20 – 6 3 0.03–1.11 – 63 4.21 – 2.3

35.34 – 11.59 0.35 0.45 – 41.99 8.04 1.18 0.32

25.70 – 12.00 0.87 0.04 – 43.51 5.15 – 1.05

Physical properties Specific density, kg/m3 Bulk Density, kg/m3 Colour Insoluble residue Glass content

2.3 480 White – –

3.15 1400 Grey 0.5 –

2.9 – Off-white 0.3 ≈ 90

Table 4 Mix design composition and testing. Target material

Stabilisers

Ratio

mass%

Test

LOC

Lime (control) WSA

100% 100%

WSA–Lime

90:10

2, 4, 6 10, 15, 20 10, 20, 30 5, 10, 15, 20 10, 15, 20 10, 20, 30 5, 10, 15, 20 10, 15, 20 10, 20, 30 5, 10, 15, 20 10, 15, 20 10, 20, 30 5, 10, 15, 20 10, 15, 20 10, 20, 30 5, 10, 15, 20 10, 15, 20 10, 20, 30 5, 10, 15, 20 10, 15, 20 10, 20, 30 5, 10, 15, 20

USC, USC, AL C USC, AL C USC, AL C USC, AL C USC, AL C USC, AL C USC, AL C

80:20

WSA–PC

90:10

80:20

WSA–GGBS

70:30

50:50

Lexp, AL, C Lexp

Lexp

Lexp

Lexp

Lexp

Lexp

Lexp

Note: UCS—unconfined compressive strength, Lexp—linear expansion, AL—Atterberg limits, C—Proctor compaction test.

M.N. Rahmat, N. Ismail / Applied Clay Science 52 (2011) 199–208

Several BS Proctor compaction tests were conducted to establish mean values of the dry density and the moisture content to be used for the preparation of test specimens. In all the stabilised systems, the mean value of maximum dry density (MDD) of 1.30 Mg/m3 was adjusted for all mixes. For the optimum moisture content (OMC), mean values of 28% were assumed. All samples were therefore expected, within experimental variations to be of comparable bulk density, volume and moisture content. Dry material of blended LOC + stabiliser, enough to produce one compacted cylindrical test specimen, was thoroughly mixed in a Kenwood Chef mixer for 2 min before slowly adding the pre-calculated amount of water. Intermittent hand mixing with palette knives was necessary to achieve a homogeneous mix. A steel mould fitted with a collar, so as to accommodate all the mixtures, was used to compress the cylinders to the target dry density and moisture content. After compaction in a hydraulic jack, the cylinders were extruded using a steel plunger, trimmed, cleaned of releasing oil and wrapped in several runs of cling film and cured for 7, 28, 90, 180 and 365 days in a temperature controlled chamber at 20±1 °C, before testing for UCS. Three specimens were used for each mix and curing period, and the average strength value was determined. For the linear expansion test, immediately after specimen fabrication, approximately 10 mm of the bottom of the specimen (one for the each mix) was exposed by cutting and removing the cling film. The sample was placed on a porous disc placed on a platform in a Perspex container as shown in Fig. 1. Separate Perspex containers were used for individual test specimens. The Perspex containers were covered with lids fitted with dial gauges, and a layer of water was always maintained below the platforms to provide high humidity and ensure that there was no excessive evaporation from the sample. This process termed moist curing was started immediately after specimen fabrication. After moist curing for 7 days, the specimens were partially immersed in water to a depth of 10 mm above their bases by carefully increasing the water level in the Perspex containers. This process is termed soaking. Linear expansion during moist curing and soaking was monitored on a daily basis for 100 days. 3. Results 3.1. Consistency (Atterberg) limits The plasticity characteristics of soils are normally expressed in terms of their liquid limits (LL), plastic limit (PL) and plasticity index (PI) as

described in British Standard (BS 1377-2:1990). Figs. 2 and 3(a–d) illustrate the Atterberg limits of LOC after addition of the stabilisers. In the control system (LOC+ lime), the addition of a small amount of lime (2%) increased LL from 66% to 77%. PL also increased steadily with the addition of lime. Further increase in lime (4% and 6%) did not further increase LL whereas PL continued to increase up to 54% at 4% and 6% lime. PI decreased from 31% to 20% with increasing lime content. This trend of the consistency of lime-stabilised LOC was also observed by many researchers (Kinuthia, 1997; Thomas, 2001; Veith, 2000). It was also observed on other lime–clay mixtures (Bell, 1996; Rogers et al., 1997; Sherwood, 1993). The same trend was also observed in the LOC +WSA system. For LOC+ WSA–lime, LOC +WSA–PC, and LOC+ WSA–GGBS, the trends for LL and PL were comparable to the control system. PI showed a maximum within 5%–10%. The lowest PI (19% at 30% stabiliser) was recorded with WSA–lime 80:20. PI was reduced only by 3% for WSA– GGBS 50:50 at the same amount of stabiliser. This is thought to be a consequence of the increased consumption of free lime by GGBS. This was confirmed by the considerable reduction of PI for the 70:30 WSA– GGBS which contained a lower amount of GGBS. The cause is the increased coagulation and aggregation of the clay mineral particles under the influence of the calcium ions. The increase of the optimum moisture content is due to the increased void volume of the specific surface area. Some researchers have also suggested that the formation of cementitious products such as ettringite (in the presence of sulphate ions) immediately after mixing the clay with lime may cause resistance to compaction and reduce the density (Wild et al., 1993).

3.2. Compaction characteristics Addition of lime to LOC lowered MDD and raised OMC. Addition of 2% lime, yielded the greatest decrease of MDD from 1.36 Mg/m3 to 1.29 Mg/m3, and the greatest increase of OMC from 25% to 29%. Further increase in the lime content (4% and 6%) steadied MDD and increased OMC by a smaller degree (Fig. 4(a)). WSA–lime 90:10 and 80:20 showed similar trends to the control (lime) system. WSA alone generally lowered MDD and increased OMC more than WSA–lime, particularly at lower stabiliser contents. At all stabiliser contents WSA–PC 90:10 yielded the lowest MDD and highest OMC followed by WSA stabilised LOC. The WSA–GGBS 50:50 led to the highest MDD and lowest OMC at all stabiliser contents, followed by the 70:30

Dial Gauge

Inlet

Perspex disc Perspex Container Test Specimen 50x 100mm

10 mm

Perspex platform

201

water

Porous disc Water level during moist curing Outlet

Fig. 1. Diagram of the test set-up for measuring the linear expansion during moist curing and subsequent soaking.

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M.N. Rahmat, N. Ismail / Applied Clay Science 52 (2011) 199–208

(a)

(b)

LOC + LIME 90 LL

PL

PI

LL

80

80

70

70

Atterberg Limits (%)

Atterberg Limits (%)

LOC + WSA 90

60 50 40

PI

60 50 40

30

30

20

20 10

10 0

2

4

0

6

Stabilizer (%)

(c)

10

20

30

Stabilizer (%)

(d)

LOC + 90:10 ( WSA-LIME) 90

LOC + 80:20 ( WSA-LIME) 90

LL

PL

PI

LL

80

80

70

70

Atterberg Limits (%)

Atterberg Limits (%)

PL

60 50 40

PL

PI

60 50 40

30

30

20

20 10

10 0

10

20

30

Stabilizer (%)

0

10

20

30

Stabilizer (%)

Fig. 2. (a–d) Consistency (Atterberg) limits of LOC after addition of the stabilisers.

sample and then WSA alone. The results suggest that WSA is responsible for the reduction of MDD and increase of OMC.

3.3. Unconfined compressive strength (UCS) Fig. 5 shows the UCS of lime and WSA stabilised LOC. Addition of 2% lime, did not significantly improve the strength development with increasing curing period as there is not enough lime to form significant amounts of cementing products. The material stabilised with relatively higher lime levels of 4% and 6% lime addition improved the strength after the prolonged curing period, particularly after 180 days. The stabilised material showed superior strength development. This indicates that sufficient unreacted lime was present to continue the cementation. The stabilised material with 6% lime showed the highest strength of 1064 kN/m2. When LOC was stabilised with 10% WSA the strength increased rapidly after 28 days of curing. Thus, WSA stabilised LOC performs better than lime.

The best strength improvement and the highest UCS were recorded for the material stabilised with the blend richer in WSA (90:10), i.e. 2337 kN/m2 at 20% stabiliser. Increasing the lime content from the 90:10 (WSA:lime) ratio to the 80:20 ratio did not increase the strength. The effect of blending WSA with PC is illustrated in Fig. 7. Strength enhancement of blending WSA with PC was only marginally greater than blending WSA with lime (Fig. 6). Increased contents of stabiliser again increased the strength especially when the samples were cured for 365 days. A rapid strength enhancement was observed after 90 days of curing at all stabiliser contents. Fig. 8 illustrates the effects of blending WSA with GGBS. The strength development was comparable with that of WSA–lime and WSA–PC. The highest long term (365 days) strength was reached by WSA–GGBS 50:50 (2883 kN/m2). 3.4. Linear expansion In most cases about 90% of the expansion occurred within the first 30 days of soaking.

M.N. Rahmat, N. Ismail / Applied Clay Science 52 (2011) 199–208

(a)

(b)

LOC + 90:10 (WSA-PC) LL

PL

PI

80

80

70

70

Atterberg Limits (%)

Atterberg Limits (%)

LOC + 80:20 (WSA-PC) 90

90

60 50 40

LL

PI

50 40 30

20

20 10

10 0

10

0

30

20

10

Stabilizer (%)

(c)

20

30

Stabilizer (%)

(d)

LOC + 70:30 (WSA-GGBS)

LOC + 50:50 (WSA-GGBS) 90

90 LL

PL

PI

LL

80

80

70

70

Atterberg Limits (%)

Atterberg Limits (%)

PL

60

30

60 50 40

PL

PI

60 50 40

30

30

20

20

10

203

10 0

10

20

30

0

Stabilizer (%)

10

20

30

Stabilizer (%)

Fig. 3. (a–d) Consistency (Atterberg) limits of LOC after addition of the stabilisers.

In the lime-stabilised LOC system, the highest expansion was observed. The linear expansion was immediate when the specimens were soaked in water after 7 days moist-curing. WSA-stabilised LOC showed significantly lower expansion values compared with the limestabilised LOC (Fig. 9). Blending WSA with small quantity of lime (90:10 or 80:20) resulted in a reduction of linear expansion of LOC, compared with either lime-stabilised or the WSA-stabilised LOC. By blending WSA with PC, the linear expansion trend was very similar to that observed with WSA, lime and WSA–lime. WSA–PC showed the least expansion compared to all the other systems. This is an indication of significant enhancement of the cementing capability of WSA when blended with PC. Interestingly there was very little expansion of the specimens stabilised with WSA–GGBS 70:30 and 50:50 (Fig. 10). The reduction of the linear expansion is likely due to the formation of cementitious products. The formed gels cement the soil particles together and enable them to resist the considerable swelling pressure which is generated when ettringite forms in the presence of water. The hydration of WSA, PC and/or GGBS was much more rapid compared with the pozzolanic reaction of lime with clay. This hydration reaction is known to consume lime and, therefore, the resistance to swelling in

all WSA containing systems was enhanced by the reduction of residual lime.

4. Discussion The main objective of stabilising a clay soil is to reduce the plasticity index (PI). PI is reduced by the coagulation of the clay mineral particles by the calcium ions of the lime. The addition of lime changes the consistency (Atterberg) limit of a clay soil as the coagulated particles accommodate a larger volume of water. Further additions of stabiliser increased coagulation, hence increasing the water holding capacity. This continues up to a certain point at which the stabiliser will no longer participate in coagulation process due to cation saturation of the clay mineral particle. This point was termed “stabiliser fixation point” (Hilt and Davidson, 1960). Previous studies identified many trends and general characteristics of changes in soil properties due to the addition of lime. The main effect of mixing lime with plastic soils is the reduction of plasticity. Little (1995) reported that lime addition caused a substantial reduction of plasticity and the soil often became non-

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M.N. Rahmat, N. Ismail / Applied Clay Science 52 (2011) 199–208

(a)

(c)

1.38 1.36 1.34 1.32 1.3 1.28 1.26 0

0.02

0.04

0.06

Maximum Dry Density (MDD) (Mg/m3)

Maximum Dry Density (MDD) (Mg/m3)

1.38

Lime Content (%)

1.36 1.34 1.32 1.3

WSA WSA-Lime (90:10)

1.28

WSA-Lime (80:20)

1.26

WSA-PC (90:10)

1.24

WSA-PC (80:20)

1.22

WSA-GGBS (70:30)

1.2

WSA-GGBS (50:50)

1.18 1.16 0.1

0

0.2

0.3

Stabilizer Content (%)

(b)

(d)

31 30 29 28 27 26 25 0

0.02

0.04

0.06

Optimum Moisture Content (OMC) (%)

Optimum Moisture Content (OMC)

34 32

Lime Content (%)

33 32 31 WSA

30

WSA-Lime (90:10)

29

WSA-Lime (80:20)

28

WSA-PC (90:10) WSA-PC (80:20)

27

WSA-GGBS (70:30)

26

WSA-GGBS (50:50)

25 24 0

0.1

0.2

0.3

Stabilizer Content (%) Fig. 4. (a) Maximum dry density and (b) optimum moisture content of lime-stabilised LOC and (c) MDD vs. stabiliser content, and (d) OMC vs. stabiliser content of stabilised LOC.

However, in the case of LOC the process is more complex due to the formation of significant quantities of ettringite which although contributing to strength also cause expansion in the presence of water. PC (unlike GGBS) did not require an alkaline environment to hydrate. Also, unlike lime Ca(OH), PC produces a CSH gel and CAH phases as cementing products during its hydration. In addition, lime from PC and WSA were involved in significant pozzolanic reactions with

plastic. Lugaros (1965) found that the PI of a clay soil was reduced by 32% after addition of 6% hydrated lime. Increasing the addition of lime to LOC increased the strength after an extended curing period due to increased pozzolanic reaction between lime and the clay components. The principal cementitious product of the pozzolanic reaction is the calcium aluminosilicate hydrate (CASH) gel (Bell and Coulthard, 1990; Brandle, 1981; Diamond and Kinter, 1964).

Lime-stabilized LOC and WSA stabilized LOC

Compressive Strength (kN/m2)

3000

2500 2%L

2000

4%L 6%L

1500

10%WSA 15%WSA 20%WSA

1000

500

0 0

30

60

90

120

150

180

210

240

270

300

330

360

Curing Period (days) Fig. 5. Unconfined compressive strength of lime and WSA-stabilised LOC.

M.N. Rahmat, N. Ismail / Applied Clay Science 52 (2011) 199–208

205

LOC + WSA-Lime

Compressive Strength (kN/m2)

3000

2500 10% (80:20)

2000

15% (80:20) 20% (80:20) 10% (90:10)

1500

15% (90:10) 20% (90:10)

1000

500

0 0

30

60

90

120

150

180

210

240

270

300

330

360

Curing Period (days) Fig. 6. Unconfined compressive strength of WSA–lime stabilised LOC.

influences the chemical interactions within the clay–lime system, thereby altering the types of reaction products and thus potentially altering any disruptions that the reaction products may cause.

the clay minerals, particularly significant in the WSA–PC stabilised soil, producing cementitious products over time. In all the stabiliser systems investigated, the highest long-term strength was shown by the WSA–GGBS system. In this system, both WSA and GGBS are involved in hydration. GGBS hydrates after activation by the alkaline environment provided by free-lime in WSA. These reaction release silica and alumina compounds and eventually CSH gels and other cementing products improved the long-term strength, compared to lime-stabilised LOC. Swelling and linear expansion of sulphate-bearing soil are common and are associated with the formation of colloidal particles (a precursor to ettringite formation), which form on the surface of the clay particles during curing (Wild et al., 1993). When in a saturated condition, ettringite grows by consuming these colloidal products. Ettringite takes up large amounts of water and increases steeply the swelling potential of lime-stabilised soil. However, the introduction of a cementing agent such as WSA or PC with or without GGBS,

5. Conclusion 1. The blended stabilisers WSA–lime, WSA–PC and WSA–GGBS and WSA increased the liquid limit and plastic limit (the former two blends more steeply than the latter) of LOC, thus reducing the plasticity index, except for the 50:50 WSA–GGBS blend. 2. The addition of WSA increased the optimum moisture content (OMC) and lowered the maximum dry density (MDD). MDD values of LOC stabilised with WSA–GGBS were higher and the OMC was lower compared to stabilisation with the WSA–lime and WSA–PC. 3. Increased amounts of stabiliser contents increased the unconfined compressive strength with increasing curing period. Lime addition and curing for up to 365 days did not significantly improve the

LOC + WSA-PC 3000

Compressive Strength (kN/m2)

2500 10% (80:20)

2000

15% (80:20) 20% (80:20) 10% (90:10)

1500

15% (90:10) 20% (90:10)

1000

500

0

0

30

60

90

120

150

180

210

240

270

300

330

Curing Period (days) Fig. 7. Unconfined compressive strength of WSA–PC stabilised LOC.

360

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M.N. Rahmat, N. Ismail / Applied Clay Science 52 (2011) 199–208

LOC + WSA-GGBS 3000

Compressive Strength (kN/m2)

2500

10% (50:50)

2000

15% (50:50) 20% (50:50) 10% (70:30)

1500

15% (70:30) 20% (70:30)

1000

500

0 0

30

60

90

120

150

180

210

240

270

300

330

360

Curing Period (days) Fig. 8. Unconfined compressive strength of WSA–GGBS stabilised LOC.

(a)

LOC stabilized with WSA and Lime 2.5

Linear Expansion (%)

2

1.5

10% WSA 15% WSA 20% WSA

1

2% L 4% L 6% L

0.5

0

-0.5

Days

(b)

Linear Expansion at 100 days 2.5

Linear Expansion (%)

2

1.5

1

0.5

0

2% L

4% L

6% L

10% WSA

15% WSA

20% WSA

Stabilizers (%) Fig. 9. Linear expansion of LOC stabilised with WSA and lime (a) over 100 days and (b) expansion after 100 days.

M.N. Rahmat, N. Ismail / Applied Clay Science 52 (2011) 199–208

207

0.9

Linear Expansion at 100 days of soaking 0.8 LOC+WSA

LOC+WSA-LIME

LOC+WSA-PC

LOC+WSA-GGBS

0.7

Linear Expansion (%)

0.6

0.5

0.4 90:10

80:20

90:10

80:20

70:30

50:50

0.3

0.2

0.1

0 10% 15% 20%

10% 15% 20%

10% 15% 20%

10% 15% 20%

10% 15% 20%

10% 15% 20%

10% 15% 20%

Stabilizer content Fig. 10. Linear expansion of stabilised LOC after 100 days of curing.

strength development because not enough amounts of cementing products were formed. The highest unconfined compressive strength values were recorded for the system stabilised with WSA–GGBS. The strength development was very similar for WSA– PC and WSA–lime stabilised LOC. 4. Over a 100-day period, specimens stabilised with, WSA–lime, WSA–PC and WSA–GGBS showed less expansion compared to traditional lime-stabilised specimens. 5. Due to these results WSA can be used for the stabilisation of sulphate-bearing clays such as LOC. This provides technological, economic as well as environmental advantages. By blending WSA with a controlled amount of lime, the stabilising effect of WSA was greatly enhanced, improving the strength and volume stability. PC and GGBS may also be used to blend WSA. Acknowledgements The author would like to thank University Technology MARA, Shah Alam, Malaysia for their sponsorship of this research. Thanks also go to the technical staff of the School of Technology, University of Glamorgan for their technical support and use of test facilities and Aylesford Newsprint Ltd., The Cementitious Slag Maker Association, Buxton Lime Industries Ltd., and Hanson Brick Ltd., for providing research materials—Wastepaper Sludge Ash, ground granulated blastfurnace slag, lime and Lower Oxford Clay respectively. References Abdullah, W.S., Al-Abadi, A.M., 2010. Cationic–electrokinetic improvement of an expansive soil. Allpied Clay Science 47, 343–350. Bai, J., Chaipanich, A., Kinuthia, J.M., O'Farrell, M., Sabir, B.B., Wild, S., Lewis, M.H., 2003. Compressive strength and hydration of wastepaper sludge ash-ground

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