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International Journal of Geotechnical Engineering

ISSN: 1938-6362 (Print) 1939-7879 (Online) Journal homepage: http://www.tandfonline.com/loi/yjge20

Durability of nanostructured biomasses ash (NBA)stabilized expansive soils for pavement foundation

K. C. Onyelowe & B. V. Duc

To cite this article: K. C. Onyelowe & B. V. Duc (2018): Durability of nanostructured biomassesash (NBA) stabilized expansive soils for pavement foundation, International Journal of GeotechnicalEngineering, DOI: 10.1080/19386362.2017.1422909

To link to this article: https://doi.org/10.1080/19386362.2017.1422909

Published online: 09 Jan 2018.

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InternatIonal Journal of GeotechnIcal enGIneerInG, 2018https://doi.org/10.1080/19386362.2017.1422909

Durability of nanostructured biomasses ash (NBA) stabilized expansive soils for pavement foundation

K. C. Onyelowea and B. V. Ducb

aDepartment of civil engineering, Michael okpara university of agriculture, umuahia, nigeria; bfaculty of civil engineering, hanoi university of Mining and Geology, hanoi, Vietnam.

ABSTRACTThe effect of NBA on the durability of the hydraulically bound cemented lateritic soil was investigated and results were observed. Preliminary tests conducted showed that the natural soil was an A-2-7 soil according to AASHTO classification system, poorly graded, highly plastic and had high swell potential. The treatment exercise showed that the gradation and strength properties improved with the addition of the NBA materials at the rate of 5, 10 and 15% by weight of the solid. The erodibility and loss of strength on immersion tests conducted showed that the cemented soil improved on these properties from a highly erodible and non-durable stabilized matrix to a very less erodible and very durable stabilized matrix with a consistent durability index above 80%. With the foregoing, the nanostructured material additives have proved to be good materials for use in the stabilisation of a more durable, and less erodible subgrade, backfill or foundation material.

Introduction

There has been less sentiments and consideration towards the evaluation, estimation, prediction, calibration and modelling of the durability of stabilized lateritic matrixes by researchers and designers in the field of Geotechnical Engineering. Rather, atten-tion has concentrated on the geometric results that are achieved by puzzle-treating weak soils using various cementing and admix-ture materials as well as applying different chemical, mechani-cal and electrokinetic procedures. It is important to note at this point that the performance of any engineering design or pro-ject depends on stability and durability. Durability is the ability of a structure to withstand those factors that attempt to cause a failure over time thereby living out its design life (AASHTO 2014; Bolarinwa, Adeyeri, and Okeke 2017; Dariush et al. 2013; Hafshejani, Mohammad, and Alborz 2015; Noraida, Norazzlina, and Abdul 2015; Richard et al. 2014). Geotechnical engineer-ing structures are not left out in this and being founded on soil, they exert their load on the underlain subgrade material (US Department of Transportation 2006). This also translates to the fact that the life of these structures depends on the strength and of course the durability of the foundation soil (AASHTO 2014; Bolarinwa, Adeyeri, and Okeke 2017; Dariush et al. 2013; Hafshejani, Mohammad, and Alborz 2015; Noraida, Norazzlina, and Abdul 2015; Richard et al. 2014). For this reason, the informa-tion from a soil subsurface exploration should be taken seriously to improve the insufficient properties of the soil through stabi-lisation. Over the years, experts have applied various materials to achieve this purpose. They included bagasse ash, palm bunch

ash, palm kernel shell ash, coconut shell ash, snail shell ash, per-iwinkle shell ash, waste paper ash, groundnut shell ash, rice husk ash, egg shell ash, reclaimed asphalt pavement, quarry dust, etc. (Abdullahi, Ojelade, and Auta 2017; Dharamveer, Dheeraj, and Feipeng 2017; Osinubi, Bafyau, and Eberemu 2009; Moses, Peter, and Osinubi 2016; Onyelowe 2017a, 2017b, 2017c; Onyelowe, Ekwe, et al. 2017; Onyelowe and Okafor 2015; Onyelowe, Okafor, and Nwachukwu 2012; Onyelowe, Onuoha, et al. 2017; Onyelowe and Ubachukwu 2015; Rathan, Banupriya, and Dharani 2016) and various other ash materials from municipal solid waste (Oluborode and Olofintuyi 2015). It is important to note again that the above mentioned ash materials are by products of the direct combustion of biomasses. Also note that biomass is the source of renewable energy, which also falls into a conversion cycle that has fly ash, ground granulated slag, ash and charcoal as byproducts. Various binders have also been in use for this same purpose and they included ordinary Portland cement, fly ash, bitumen, slag, lime and various other cementitous materials (Abdolreza et al. 2017; Jawad et al. 2014; Lakshmi and Sivaranjani 2014; Rafat and Mohammad 2011; Rogers and Glendinnings 1993). There has been equally the binary application of binders and ash materials in the stabilisation of weak soils for construction purposes. In recent years, there have been attempts by researchers to synthe-sise nanostructured ash materials from the biomasses that have been in use in the stabilisation process and successes have been recorded in this attempt (Onyelowe 2017b; Onyelowe and Okafor 2015). And before this time, there have been other nanostructured materials from chemical compounds in use for the stabilisation process (Ahmad, Yaser, and Ehsan 2013; Ali, Mohammad, and

© 2018 Informa uK limited, trading as taylor & francis Group

KEYWORDSDurability potential; nanostructured biomasses materials; unconfined compressive strength; soil stabilisation; loss of strength on immersion; erodobility

ARTICLE HISTORYreceived 14 october 2017 accepted 27 December 2017

CONTACT K. c. onyelowe konyelowe@mouau.edu.ng, konyelowe@gmail.com

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2 K. C. ONYELOWE AND B. V. DUC

weight to treat the lateritic soil. Ordinary Portland cement used as a binder at a fixed percentage of 5% was Dangote cement bought from the Umuahia Timber Market in accordance with ASTM C150 (2013). The other amorphous ash materials were synthesised from biomass materials; palm bunch, waste paper, snail shells and periwinkle shells, disposed as solid waste, through direct combustion, pulverisation and nanosieving procedure (Onyelowe 2017b; Onyelowe and Okafor 2015). The resultant nanostructured materials were characterised using the UV-vis Spectrophotometric machine at 25 °C to determine their aver-age particle size and the absorbance of the different materials (Onyelowe 2017b). DOPC was used to cement the stabilized soil at a steady rate of 5% by weight of the stabilized matrix while the five different nanostructured materials were added to the mixture at the rates of 5, 10 and 15% by weight of the stabilized soil.

Testing procedures

The preliminary and stabilisation tests were conducted follow-ing the scheme in Figure 2. Sieve Analysis test was conducted with a vertically arranged sieve sizes mounted on an automatic shaker on both soil and biomass ash materials in accordance with BS 1377-2 (1990) and BS 1924 (1990), Compaction test (Standard Proctor test) was conducted with 2016 ELE Automatic Compactor Machine in accordance with BS 1377-2 and BS 1924 (1990), California Bearing Ratio test (CBR) was conducted with a 2015 S211 KIT CBR penetration machine, motorised 50KN ASTM used to load the penetration piston into the soil sample at a constant rate of 1.27 mm/min (1 mm/min to BS Spec.), and to measure the applied loads and piston’s penetrations at determined intervals in accordance with BS 1377-2 (1990), Atterberg Limit test; was conducted using a 2013 cassagrande apparatus in accord-ance with BS 1377-2 (1990) and BS 1924 (1990), Specific Gravity test was conducted by Pycnometer method in accordance with BS 1377-2 (1990) and BS 1924 (1990) and Chemical Composition test on both the DOPC, natural soil and the biomass materials. Also Erodibility cylindrical test specimens, of dimension 152 mm diameter and 114 mm high (CBR mould), were compacted in five layers, and after removal from the mould, folded in wet paper and foils of aluminium, and then cured for 14 days at room tem-perature. Two specimens were prepared for each mixture of each biomass, which gave a total of 30 test specimens. The methods presented in Australian protocol TM T186 (Roads and Maritime Services 2012) were used. After the curing process, the test spec-imens were kept in a metal container with a constant water level

Shadi 2011; Anamika et al. 2012; Anand 2016; Anitha and Haresh 2014; Farzad, Mohammad, and Masoud 2016). The need for the stabilization of lateritic soils used during construction processes is among other things to improve on the durability of structure with which the soil is constructed. However, durability can be defined in another way as the resistance to weathering, erosion as well as resistance to soil chemistry. Note that the important factor which facilitates the physical parameters that influence durability is moisture. Hence, it is very important that the sensitivity of the stabilized soil to moisture is evaluated to determine its ability to withstand erosion, capillary action, swelling and frost actions by moisture ingress in the case of pavements, etc. (Yawen et al. 2014; Mohammad, Amir, and Mahya 2016; Gidigasu and Dogbey 1980; AASHTO 2010). There are two major reasons why these could occur in both the natural soil and the stabilized matrix; (i) the abil-ity of the lateritic soils to adsorb moisture and change their volume due to the mineral components, gradation, voids, etc. of the soil and (ii) the chemical durability of the soils, which is the resist-ance to chemical reactions such as ettringite formation, which may also result in volumetric changes and a reduction/increase in performance compared to its designed durability. There is always a desire to improve and upgrade lateritic soils strength or stiffness and consequently improve its durability. Hence, the primary aim of this research work was to evaluate the durability potential of the biomass ash stabilized lateritic soils at a steady 5% by weight addition of Dangote ordinary Portland cement (DOPC) using the compressive strength test loss of strength on immersion method and the erodibility procedure. However, the specific objectives were; (i) to review relevant literature materials (ii) to prepare the biomass ash materials by UV-vis Spectrophotometric characteri-sation method (iii) to conduct preliminary experiments on the soil to determine its natural properties (iv) to conduct a stabilisation exercise on the soil applying the biomass ash materials at the rate of 5, 10 and 15% by weight of the dry solid (v) to conduct the erod-ibilty procedure exercise and the loss of strength on immersion experiment to determine the durability potentials of the biomass stabilized soil and tabulate results.

Materials preparation and methods

Soil samples and dangote ordinary portland cement (DOPC)

Lateritic soil sample (Figure 1) used for this study was col-lected from the borrow pit located at Olokoro, on latitude of 05°28′36.700″ North and longitude 07°32′23.170″ East from a depth of 1.5 metres, a distance of 5 km off Ubakala road from the Ishi Court junction, Umuahia, Abia state capital, Nigeria. The sample collected was in solid state and reddish brown in colour. The soil obtained from this location was air dried in trays for six days, after which the soil was tapped with a rubber pestle to remove lumps. DOPC used satisfied the binding materials requirement according to ASTM C150 (2013) and ASTM C618 (1978).

Synthesis of biomass ash and preparation of soil/cement/biomass ash

Quarry Dust was collected from the Quarry Factory in Amasiri, Afikpo, Nigeria. This was used at the rate of 5, 10 and 15% by

Figure 1. lateritic soil preparation (sieving through 2 mm aperture sieve).

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INTERNATIONAL JOURNAL OF GEOTECHNICAL ENGINEERING 3

at 25.5 mm for 1 h. In order to model and simulate traffic loads, surcharges which are the same as used in California Bearing Ratio test with a total mass of 6.75 kg were fixed on the top of the test specimens. Test specimens and surcharges were placed in a metal watertight container with 200.1 mm in diameter filled with 200 millilitre of moisture exposure. The metal container was secured to a vibrating platform and the test specimens were vibrated for 10 min. Test specimens and metal container were washed and then the washing water was wet sieved over a 2.36 mm sieve. The detached and eroded fine materials passing the 2.36 mm sieve were dried to constant weight in an oven at temperature of 55 °C and results were tabulated. Erodibility, generally described as loss of material, was calculated dividing the dry weight of the fines in grams by the vibration time at 10 min and expressed in g/min. UCS cylindrical test specimens of geometry, 100 mm in diameter and 200 mm high, were compacted in five layers and cured in a wet chamber at room temperature. For each of the 3 mixtures, 5 biomass ash materials and at the curing time of 28 days, three specimens were prepared, which gave a total of 45 test specimens. The testing methods used were the AASHTO T22-03 (2014) test protocol. Tests were carried out using an automatic loading machine that placed a constant load rate of 250kN/m2/s. The loss of strength in immersion experiment was proposed in Series 800 (Manual of Contract documents for Highway Works: Volume 1 2007) using the procedure given in Section 880.4. Two sets of test cylinders with a ratio of 1:1 (Diameter: Height) are prepared and air-cured for 14 days. While ‘Set A’ continued air-curing, ‘Set B’ of the test cylinders were then cured for a further 14 days completely immersed in water. The compressive strength of these immersed samples UCSimm was determined together with that of the control specimens UCScontrol. The control specimens are cured for 28 days at room temperature. All curing is undertaken at room temperature for the materials assessed in this research

work (Figure 3). The mixture is considered to be durable if the following applies (Manual of Contract documents for Highway Works: Volume 1 2007):

where, UCSVS = relative volumetric stability, which is assumed to be durable if ≥80%, ID = durability index

Results and discussions

Characterisation of samples

Tables 1 and 2 and Figure 4 showed the preliminary tests con-ducted on the materials from which can be concluded that the soil was an A-2-7 soil according to AASHTO classification system, highly plastic with a plasticity index >17%, and a dry density of 1.76 g/cm3 and specific gravity of 2.6. The biomass ashes, because of their texture and gradation as nanostructured materials of an amorphous nature had less specific gravity values than the soil

(1)UCSVS(I

D) =

UCSimm

UCScontrol

×100

1≥ 80%

Cement5%

Lateriticsoils

Biomass Ash,5%

Biomass Ash,10%

Biomass Ash,15%

Erodibilitytest

Gradationtest

Loss of strengthon immersion test

UV - Visspectrophotometric

characterization

Standard protorcompaction test

Atterberg limitstest

28 daysUCS test

28 dayscuring control

14 days curing14 days immersion

Liquidlimit

Plasticlimit

Casagrandeapparatus

Figure 2. Summarized schematic experimental programme.

Figure 3. curing and immersion tank.

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4 K. C. ONYELOWE AND B. V. DUC

Table 3 shows the oxide rates and bonding potentials of the nanostructured biomass ashes, which satisfied that the mate-rial bonding is a very important factor in soil stabilisation and strength optimisation because the soil and the admixture need to form a homogeneous and cohesive bond (Rafat and Mohammad 2011). Material requirement for cementitious materials states that the sum of the oxide rates of SiO2, Al2O3 and Fe2O3 should not be less than 70%. The results of the analyzed ashes shown in Table 3 show that the percentage of SiO2+FeO3+Al2O3 for each of the materials is greater than 70%, which makes the admixture samples highly pozzolanic (Rafat and Mohammad 2011). This property was of great advantage because it brought about a high degree of interaction, poz-zolanic reaction, carbonation reaction and bonding between the studied soils and the admixtures (Das and Sobhan 2012; Kenichiro and Tomomi 2015).

Effect of biomass ashes on the gradation of the stabilized soil

Table 4 showed the behaviour of the gradation of the soil + DOPC with the addition of different rates of different biomass ashes. The addition of the NBA materials, improved on the gradation of the treated soil from poorly graded soil to a well graded soil hence a more serviceable soil for use as a construction material.

Effect of biomass ashes on the consistency of the stabilized soil

Table 5 and Figure 6 summarised the behaviour of the stabilized lateritic soil as regards its consistency limits with the addition of different rates of different biomass ash materials. The natural soil had a high plastic consistency of PI greater than 17%. But the behaviour reduced, drastically to ‘medium plastic’ consistency at

except for NQDA which is not an amorphous ash. The absorb-ance of the nanostructured materials characterised with UV-vis spectrophotometric method showed that the particle absorbance enhances the mechanism whereby size can potentially promote cohesion between the admixture and stabilized soil by present-ing a larger reactive surface, characterisation of the molecular composition of organic matter in soil fundamental mass, lateral distribution of carbon forms in soil microaggregates, characteri-sation of the composition of dissolved organic carbon in the ash during stabilization, etc. The nanopores of the ash material due to nanosization will contribute 99% of the surface areas to the mixture homogeneity because it was less kinetically restricted at the temperature when its isotherm, constructed during the mixing and stabilisation mechanics.

Table 1. untreated soil and nanostructured biomass materials preliminary test results.

Soil properties

NMC (%) LL (%) PL (%) PI (%) OMC (%) MDD (g/cm3) GS

GS(NWPA) GS(NPBA) GS(NSSA) GS(NSPA) GS(NQD)

AASHTO soil classGs(NPBA)

Gs(NSSA)

Gs(NSPA)

Gs(NQD)

12.1 40 18 22 13.1 1.76 2.60 1.05 1.31 1.65 1.74 2.71 a-2-7

Table 2. uV-vis spectrophotometric characterisation of biomasses ash at 25 °c.

Wave length (nm)

Absorbance (nm)

NWPA NPBA NSSA NQD NPSA0 1.016 1.116 1.116 1.206 1.115200 1.107 1.115 1.007 1.122 1.112250 1.015 1.115 0.115 0.076 0.114300 1.136 1.106 1.046 1.042 1.051350 1.103 1.103 0.501 0.911 0.621400 1.116 1.106 0.417 0.411 0.422450 1.005 1.105 1.105 1.111 1.110500 1.154 1.094 1.054 1.162 1.044550 1.166 1.066 1.119 1.311 1.109600 1.075 1.045 0.085 0.062 0.091650 1.102 1.120 0.182 0.144 0.191700 1.003 1.003 1.003 1.000 1.003750 1.062 1.062 1.103 1.211 1.102800 1.045 1.045 1.110 1.142 1.111850 1.031 1.031 0.131 0.911 0.132900 1.045 1.045 1.245 0.322 1.241950 1.07 1.070 1.070 1.090 1.5121000 1.191 1.091 0.081 0.011 0.0091

0 200 400 600 800 10000

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

NWPA NPBANSSA

NQDNPSA

Wave length (nm)

Abs

orba

nce

(nm

)

Figure 4. uV-vis spectrophotometric characterisation of nBa additives.

10-11001010

20

40

60

80

100

120 5% NWPA10%NWPA

15%NWPA5% NPBA10%NPBA15%NPBA

5% NSSA10%NSSA15%NSSA5% NQD10%NQD15%NQD

5% NPSA10%NPSA15%NPSA

Sieve size (mm)

Pass

ing

(%)

Figure 5. Influences of biomass ashes on the gradation of the stabilized soil.

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INTERNATIONAL JOURNAL OF GEOTECHNICAL ENGINEERING 5

molecular rearrangement in the formation of transitional com-pounds. This improvement is due to the hydration of the highly pozzolanic additives with the stabilized mixture which reduced the PI consistently thereby producing a stiff mixture of stabi-lized soil. Also, the release of cations from the ash materials and quarry dust during the cation exchange reaction has contrib-uted to the behaviour of the stabilized mixture. This behaviour agrees with Meegoda and Ratanweera (1994), which showed that if water is used as pore fluid, the influence of the mechanical factors would remain same with a general decrease in LL on addition of an admixture. However, if an organic fluid other than water is used, the physical properties of the fluid such as viscosity and density would influence the LL. With the varying behaviour with the addition of additives, it can be seen that the LL depends on the mechanical factors other pore fluid viscosity and density (Das and Sobhan 2012; Gidigasu and Dogbey 1980) and to a higher degree on the physicochemical properties of carbonation and cation exchange. The lowering of the LL and PI is therefore as a result of the mechanical and physicochemical factors of the soil such as a low dielectric constant. This results from high absorbance values, which causes the clay particles to behave more like granular matrix with attendant reduction in adsorbed water and the physicochemical factors of the admix-ture such as carbon and hydroxide content, which lead to the formation of carbon silicates and aluminates with soil when

the addition of the ash materials. This trend showed that further addition of the admixtures will equally reduce the PI further. Hence, the most ideal plasticity index was achieved at 15% by weight addition of the admixtures except the addition of NWPA which achieved its ideal consistency at 10% by weight addition. The hydration of the stabilized mixture and its increased reactive surface has contributed to behaviour of the soil and also due to

Table 3. oxide composition of test materials.

Materials

Oxides composition (content wt %)

CaO MnO MgO ZnO CuO Fe2O3 Al2O3 SiO2 Na2O P2O5 K2O TiO2 LOI SO3 nWPa 9.21 3.67 trace trace trace 1.11 17.23 52.11 7.41 7.99 1.27 – – –nPBa 12.7 0.13 0.01 0.78 trace 0.95 20.12 64.45 0.71 0.64 0.14 – – –nSSa 17.83 1.16 trace trace trace 2.44 6.11 65.01 2.31 5.12 0.02 – – –nQD 20.25 0.44 0.86 4.67 2.76 3.89 17.77 44.88 0.01 2.91 1.64 – – –nPSa 18.31 2.87 0.02 trace trace 3.98 17.34 55.19 0.09 1.11 1.09 – – –DoPc 63.81 – 2.42 – – 3.07 4.45 21.45 0.20 0.11 0.83 0.22 0.81 2.46

Table 4. effect of biomass ash plus 5% DoPc treatment on soil gradation.

Sieve Size (mm)

% Passing

(Soil)

NWPA soil treatment by wt (%)

NPBA soil treatment by wt (%)

NSSA soil treatment by wt (%)

NQD soil treatment by wt (%)

NPSA soil treatment by wt (%)

5 10 15 5 10 15 5 10 15 5 10 15 5 10 156.35 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 1004.75 89 92 98 98 91 99 99 89 96 98 86 97 99 90 93 982.36 67 86 89 90 87 86 89 86 87 87 76 82 86 81 87 861.18 59 61 76 85 81 71 86 79 75 86 66 69 76 71 73 770.6 44 55 67 76 62 62 77 59 65 78 54 58 61 58 60 620.425 36 42 55 68 41 46 67 42 58 61 39 42 58 42 51 560.3 22 28 41 39 32 36 42 28 42 39 21 32 42 31 39 420.15 15 18 32 25 16 25 32 17 32 33 18 25 31 28 25 320.075 2.85 5.15 19 20 6.8 12 16 5.8 18 20 6.2 12 25 14 21 24Pan 0 2.45 6.2 11 1.15 7.8 14 2.15 8.6 13.1 4.1 6.5 13 2.6 7.7 16.1

Table 5. effect of biomass ash materials plus 5% DoPc on the consistency of the treated lateritic soil.

Test Control

NWPA soil treatment by wt (%)

NPBA soil treatment by wt (%)

NSSA soil treatment by wt (%)

NQD soil treatment by wt (%)

NPSA soil treatment by wt (%)

5 10 15 5 10 15 5 10 15 5 10 15 5 10 15WLwL 47 52.1 41.6 37.56 49.85 42.25 36.85 46.85 41.95 35.62 47.85 42.20 32.10 45.11 44.85 40.85WPwP 25.15 23.16 26.75 21.50 22.65 24.62 22.55 23.11 24.65 21.62 23.60 22.10 21.10 23.11 24.11 26.85IPIP 21.85 28.94 14.85 16.06 27.20 17.63 14.30 23.74 17.30 14.00 24.25 20.10 11.00 22.00 20.74 14.00

Figure 6. Plasticity index behaviour of the 5% cemented soil with nBa additives.

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6 K. C. ONYELOWE AND B. V. DUC

Effect of biomass ashes on the erodibility potential of the stabilized soil

Table 7 and Figure 7 show the average values of particle detach-ment (erodibility) which varied between 1.8 and 6.7  g/min recorded as the average erodibility of the 5% DOPC stabilized natural soil. The cement content and compaction effort may have reduced the erodibility potential, but the use of high cement content should be avoided because it enhances shrinkage index, which eventually leads to cracking. This promotes the ingress of moisture into the pavement structure or underlain subgrade through the voids created by the cracks and increasing erosion process. The reduction in the average erodibility of the treated soil may be due to the fine and reactive surface of the nanostruc-tured materials and their ability to fill into the gaps between the soils particles to form a more consistent matrix. The reduction in the average erodibility by the addition of the ash materials and quarry dust shows the ability of these materials to promote durability of the stabilized soils in a field condition. Secondly, the correct degree of compaction is another factor to be taken seri-ously because erodibility is sensitive to it. The use of less cement content has been achieved in this procedure thereby preventing the occurrence of shrinkage effect on the stabilized soils which encourages cracking and consequently erosion.

mixed as a stabilized mass. Consequently, the use of the stabi-lized soil as a subgrade and base material has been improved by the presence of the additives and achieved non-frost-suscepti-ble materials with PI < 15; a very important function affecting the durability of pavements and other civil engineering works founded on soil (Das and Sobhan 2012; Gopal and Rao 2011; Smith and Smith 1998). The achieved subgrade improvement will reduce the required pavement thickness; wearing course plus base course, hence a cost effective and durable pavement construction (Gidigasu and Dogbey 1980; Gomes, Winter, and Puppala 2016).

Effect of biomass ashes on the compactibility of the stabilized soil

The compaction results of the investigated soil with the addition of biomass ashes were observed to improve in terms of dry den-sity and OMC as shown in Table 6. There was a reduction in the maximum dry density at 5% by weight addition of NWPA with a corresponding increase in the OMC, while there was a consist-ent increase in MDD with the addition of the other biomasses. There was a possibility that the formation of new compounds occurred which consequently led to the increase in the MDD with addition of the admixtures. This behaviour may also be due to cation exchange reactions and the admixtures filling the voids within the soil matrix and in addition, the flocculation and agglomeration of the clay particles due to polarisation, release and exchange of ions (Osinubi, Bafyau, and Eberemu 2009). The trend is in conformity with the results reported by (Onyelowe 2017a). An explanation that was offered for this trend is that there was increasing desire for water, which commensurate with the higher amount of additives because more water was required for the dissociation of admixtures with Ca2+ and OH- ions to supply more Ca2+ for the cation exchange reaction (Rafat and Mohammad 2011). The decrease in the OMC with increased pro-portions of admixture content might be due to cation exchange also that caused the flocculation of clay particles. Moreover, the additives are highly pozzolanic materials and require water for hydration thereby improving the strength gain and the durability of the DOPC + additives + Soil matrix.

Table 6. effect of biomass ash materials plus 5% DoPc on the compaction properties of stabilized lateritic soil.

TestCon-trol

NWPA soil treatment by wt (%)

NPBA soil treatment by wt (%)

NSSA soil treatment by wt (%)

NQD soil treatment by wt (%)

NPSA soil treatment by wt (%)

5 10 15 5 10 15 5 10 15 5 10 15 5 10 15MDD 1.84 1.79 1.88 1.76 2.10 1.89 1.77 1.86 2.06 1.96 1.87 2.15 2.01 1.95 2.15 2.65oMc (w) 13.00 13.85 11.81 15.89 9.86 10.85 12.90 12.10 11.85 11.95 12.15 9.95 10.65 12.01 10.50 9.85GSGs 2.67 2.89 3.01 3.45 2.76 2.89 2.99 2.90 3.78 4.05 2.91 3.81 4.06 2.91 3.79 4.14

Table 7. erodibility potential of the 5% by weight DoPc + biomass ash stabilized lateritic soil.

Erodibility of stabilized lateritic soil (g/min)

Control

NWPA soil treatment by wt (%)

NPBA soil treatment by wt (%)

NSSA soil treatment by wt (%)

NQD soil treatment by wt (%)

NPSA soil treatment by wt (%)

5 10 15 5 10 15 5 10 15 5 10 15 5 10 156.7 6.1 5.3 5.3 5.2 4.6 4.2 4.1 3.5 2.4 4.1 2.4 1.8 4.1 3.4 2.1

NBA AdditivesNWPA NPBA NSSA NQD NPSA

Erod

ibilit

y (g

/min

)

1

2

3

4

5

6

7

NBA at 0% NBA at 5% NBA at 10% NBA at 15 %

Figure 7. erodibility potential for the nBa 5% cemented lateritic Soil.

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INTERNATIONAL JOURNAL OF GEOTECHNICAL ENGINEERING 7

Effect of biomass ashes on the compressive strength of the stabilized soil at 28 days

The addition of the biomass admixtures to the stabilized soil consistently increased the strength of the soil at a curing period of 28 days as shown in Table 8 and Figure 8. Twenty Eight (28) days curing time was used here because durability of the stabi-lized matrix is the primary property being evaluated. The soil mixed with the additives maintained a consistent improvement, which showed that further addition will bring further increase in the strength of the stabilized soil. The presence of the admix-ture in the soil increased the strength properties of the stabilized mixture attributed to the physicochemical and highly pozzo-lanic properties of the admixtures and to its ability to reduce adsorbed water thereby making soils with higher clay content to behave like granular soil. This behaviour improved the shear

Table 8. effect of biomass ash materials +5% DoPc on the compressive strength properties of stabilized lateritic soil at 28 days.

**Signifies that the 0% content is the control experiment which is the same for all the test additives.

Strain (%)

Axial stress (kN/m2)

NWPA soil treatment by wt (%)NPBA soil treatment by

wt (%)NSSA soil treatment by

wt (%)NQD soil treatment by

wt (%)NPSA soil treatment by

wt (%)

0** 5 10 15 5 10 15 5 10 15 5 10 15 5 10 150 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 00.05 95.5 116.3 121.1 191.4 99.6 121.7 181.4 129.6 134.7 198.4 119.6 124.7 180.4 139.6 144.7 199.40.1 115.5 119.9 127.7 212.5 119.9 129.7 210.5 130.9 139.0 270.5 122.9 141.0 215.5 142.9 159.0 275.50.15 118.6 120.7 129.5 286.4 131.7 139.5 276.4 134.7 159.5 296.4 144.6 159.1 316.4 154.7 169.5 306.40.2 135.7 138.4 145.6 312.8 148.7 149.6 312.8 168.7 168.6 342.8 145.7 168.6 326.8 168.7 188.6 346.80.25 143.5 145.4 173.5 387.4 165.4 173.5 397.4 175.4 172.5 447.4 166.4 182.5 467.4 185.4 192.5 547.40.3 147.7 149.0 185.8 414.3 169.0 185.8 424.3 188.0 195.8 484.3 178.1 205.8 464.1 198.8 215.8 494.10.35 149.8 149.9 185.8 465.3 189.1 191.8 468.3 199.7 201.8 508.3 189.7 212.8 508.3 209.7 222.8 568.30.4 154.4 159.3 197.4 512.4 199.9 207.4 522.4 200.9 237.4 602.4 212.9 237.4 522.4 210.9 257.4 622.40.45 158.5 160.1 202.1 521.3 200.1 209.1 529.9 210.1 309.1 859.9 224.1 348.1 766.8 222.1 349.1 866.90.5 159.9 161.8 206.3 532.3 211.8 226.3 542.3 220.8 426.3 882.3 234.8 436.3 792.3 234.8 446.3 892.30.55 162.7 163.4 211.3 603.2 243.4 251.3 603.2 249.4 451.3 903.2 248.4 448.3 883.2 249.4 451.3 983.20.6 168.0 169.8 219.4 673.4 285.8 299.4 663.4 275.8 509.4 1063.4 282.8 517.5 964.4 280.8 529.5 1164.40.65 171.5 175.8 232.4 712.3 298.8 332.4 702.3 308.8 532.4 1702.3 319.1 612.4 1002.4 318.9 632.4 1602.30.7 175.6 189.3 238.2 789.4 301.3 338.2 779.4 311.3 738.2 1779.4 324.3 727.8 1479.4 334.3 767.2 1879.40.75 178.9 189.9 256.4 832.2 311.9 356.1 837.2 341.9 856.1 1837.2 411.9 816.1 1737.2 441.9 916.1 1937.20.8 180.6 195.0 267.4 894.4 321.8 367.4 898.4 366.8 997.4 1898.4 434.8 981.4 2008.4 467.8 987.4 2098.40.85 183.5 198.9 269.5 1104.3 345.9 369.8 1114.3 375.9 999.8 2114.3 515.7 1012.8 2114.8 555.9 1009.8 2214.80.9 184.6 199.8 286.4 1432.4 354.8 386.4 1432.4 394.8 1006.4 2432.4 668.8 1106.8 2238.4 664.8 1106.7 2338.40.95 185.9 201.1 367.6 1782.3 355.1 407.6 1782.9 405.1 1117.6 2482.9 715.1 1167.1 2382.9 755.1 1166.1 2482.91.00 196.6 208.8 414.3 1893.2 368.8 414.9 1896.2 428.8 1114.9 2496.2 815.9 1234.8 2496.2 828.0 1244.8 2486.2

0 0.2 0.4 0.6 0.8 10

500

1000

1500

2000

2500

3000

Strain (%)

Com

pres

sive

str

engt

h (k

N/m

2 )

0% NBA 5% NWPA 10% NWPA 15% NWPA

5% NPBA10% NPBA

15% NPBA

5% NSSA10% NSSA15% NSSA

5% NQD10% NQD15% NQD

5% NPSA10% NPSA15% NPSA

Figure 8.  unconfined compressive strength behaviour of nBa additive 5% cemented lateritic soil.

5 10 15 2065

70

75

80

85

90

95

100NWPANPBANSSANQD NPSA

NBA Materials (%)

Dur

abili

ty R

atio

(%

)

(a)

(b)

5 10 15 20100

200

300

400

500NWPANPBANSSANQD NPSA

NBA Materials (%)

Los

s of

Str

engt

h du

e to

imm

ersi

on (

kN/m

2 )

Air curingImmersed curing

Figure 9. ucS loss of strength vs. nBa materials (a), and (b) durability index vs nBa materials.

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8 K. C. ONYELOWE AND B. V. DUC

strength of the stabilized soil and agrees with the findings of Das and Sobhan (2012). These values satisfy the ‘very stiff ’ and ‘hard’ materials at 10% and 15% by weight addition of additive material, condition for use as a sub-base material for pavement construction (Das and Sobhan 2012). Additionally, increase in the additives (nanostructured biomass) concentration resulted in increasing of compressive strength and decreasing of strain. By addition of NBA, the cemented soil samples became denser by filling some voids in the soil samples structure. Also, the good dispersion of the cement particles by addition of NBA led to a better filling of free spaces between the soil particles and more resistant soil samples. By increasing the NBA concentration, the soil samples became more dense and resistant in the cemented soil. Additionally, the increase in NBA concentration increased the interconnection between soil particles and produced more homogenous compressible material. Therefore, the NBA had a considerable effect on increasing the unconfined compressive strength of the cemented soil samples.

Effect of biomass ashes on the durability of the stabilized soil

Table 9 shows the loss of strength on immersion test results and the durability index of DOPC + Biomass Ash the treated lateritic soil. This was a test conducted on the DOPC + Nanostructured Biomass materials stabilized soil for use in pavement construc-tion and other geotechnical engineering works because it is a moisture (hydraulically) bound material (HBM). The control test showed that the stabilized natural soil was not durable with a durability index of 76.10% <80% (Das and Sobhan 2012). But on the addition of different rates of different biomass ashes, the durability index increased considerably and consistently. The matrix suction on immersion may have affected the strength of the admixture stabilized cemented soil but the results remained within the limits of durability (i.e. >80%). This may be due to the fact that the nanostructured materials showed strong pozzolanic properties because of the strong cations released at the adsorbed complex as to form strong resistance to the effect of moisture on immersion. Also, the reaction between the soil anion and the nanostructured materials cations at the adsorbed complex contributed to the formation of fluccs and eventual densification and durable strength gain which resisted the effect of suction at the immersion of the test samples. The promotion of the cemen-titious reactions by greater homogenisation of nanostructured ashes and cement (higher degree of pulverisation and reactive surface) promoted strength development in the test specimens at the different rates and hence led to an increase in durability potential.

Concluding remarks

The following concluding remarks held sway during the research work; relevant literature materials were reviewed and observa-tions drawn from previous investigations, (ii) nanostructured biomass materials were prepared by the direct combustion and UV-vis spectrophotometric characterisation and were applied in the research work at the rates of 5, 10 and 15% for each of the materials, which effects on the durability of the cemented lateritic soil were examined, (iii) preliminary examinations and Ta

ble

9. u

cS lo

ss o

f str

engt

h on

imm

ersi

on te

st o

n bi

omas

s ash

 +5%

Do

Pc st

abili

zed

late

ritic

soil.

Test

Cont

rol

NW

PA s

oil t

reat

men

t by

wt (

%)

NPB

A s

oil t

reat

men

t by

wt (

%)

NSS

A s

oil t

reat

men

t by

wt (

%)

NQ

D s

oil t

reat

men

t by

wt (

%)

NPS

A s

oil t

reat

men

t by

wt (

%)

510

155

1015

510

155

1015

510

1528

 day

s air

curin

g (k

n/m

2 )21

9.11

200.

4625

6.45

233.

0121

9.65

295.

7530

0.94

395.

1240

0.15

411.

8540

0.65

425.

2546

5.25

400.

5541

0.50

412.

8514

 day

s air

curin

g +

14

 day

s im

mer

sed

curin

g (k

n/m

2 )

166.

7516

5.45

211.

4821

8.25

145.

4524

5.84

236.

7533

8.78

375.

8640

0.85

356.

4438

6.48

415.

6237

2.88

391.

0840

0.55

Dur

abili

ty ra

tio (%

)76

.10

82.5

482

.46

93.6

766

.22

83.1

278

.67

85.7

493

.93

97.3

388

.97

90.8

889

.33

93.0

995

.27

97.0

2

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INTERNATIONAL JOURNAL OF GEOTECHNICAL ENGINEERING 9

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classification were conducted on the soil and the additive mate-rials and results showed that the soil was an A-2-7 soil according to AASHTO classification system, poorly graded, a highly plastic, frost susceptible and with high swelling properties. The additive materials were observed to be highly pozzolanic materials. (iv) the stabilisation exercise conducted with the nanostructured materials as admixtures showed significant improvement on the strength properties of the cemented lateritic soil, and (v) the erodibility and durability potential tests conducted showed that the addition of the nanostructured additive materials to the cemented soil improved the erodibility and the durability index of the soil. This shows that the soil could be treated with the addi-tive materials to achieve a more durable matrix for construction purposes and a less erodible stabilized matrix for the same pur-pose. ‘The principle aim of a durability test is to assess a material’s performance over its designed life’. In relation to the volumetric stability of stabilised soils, the durability tests investigated have predicted materials suitability for this purpose.

Limitations

The results of the exercises carried out are subjects of the test soil collected from Olokoro and the adaptation of the additive materials. These, though could be related to circumstances and situations which are similar to the ones treated here, will be applied to soils of similar geotechnical properties.

Disclosure statementNo potential conflict of interest was reported by the authors.

ContributorsKCO conceived, designed the study, analyzed the data, provided his per-sonal funding, wrote the article in part and revised the article. BVD wrote the article in part and plotted the graphs in part.

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