Effect of mixing geopolymer and peat on bearing capacity in Ogan Komering Ilir (OKI)by California bearing ratio (CBR) testDanang S. Raharja, Sigit P. Hadiwardoyo, Wiwik Rahayu, and Nasuhi Zain

Citation: AIP Conference Proceedings 1855, 030009 (2017); doi: 10.1063/1.4985479View online: http://dx.doi.org/10.1063/1.4985479View Table of Contents: http://aip.scitation.org/toc/apc/1855/1Published by the American Institute of Physics

Effect of Mixing Geopolymer and Peat on Bearing Capacity in Ogan Komering Ilir (OKI) by California Bearing Ratio

(CBR) Test

Raharja, Danang S.1,a), Hadiwardoyo, Sigit P.1,b), Rahayu, Wiwik1,c), Zain, Nasuhi1,d)

1Civil Engineering Department, University of Indonesia, New Campus Depok, West Java, 16424, Indonesia

a) Corresponding author: danang.setiya@ui.ac.id b)sigit@eng.ui,ac,id

c)wrahayu@eng.ui.ac.id d)nasuhi.zain@ui.ac.id

Abstract. Geopolymer is binder material that consists of solid material and the activator solution. Geopolymer material has successfully replaced cement in the manufacture of concrete with aluminosilicate bonding system. Geopolymer concrete has properties similar to cement concrete with high compressive strength, low shrinkage value, relatively low creep value, as well as acid-resistant. Based on these, the addition of polymers in peat soils is expected to improve the bearing capacity of peat soils. A study on the influence of geopolymer addition in peat soils was done by comparing before and after the peat soil was mixed with geopolymer using CBR (California Bearing Ratio) test in unsoaked and soaked conditions. 10% mixture content of the peat dry was used, weighted with a variety of curing time 4 hours, 5 days, and 10 days. There were two methods of mixing: first, peat was mixed with fly ash geopolymer activators and mixed solution (waterglass, NaOH, water), and second, peat was mixed with fly ash and mixed geopolymer (waterglass, NaOH, water, fly ash). Changes were observed in specific gravity, dry density, acidity (pH), and the microscopic structure with Scanning Electron Microscope (SEM). Curing time did not significantly affect the CBR value. It even shows a tendency to decline with longer curing time. The first type mixture obtained CBR value of: 5.4% for 4 hours curing, 4.6% for 5 days curing and 3.6% for 10 days curing. The second type mixture obtained CBR value of: 6.1% for 4 hours curing, 5.2% for 5 days curing and 5.2% for 10 days curing. Furthermore, the specific gravity value, dry density, pH near neutral and swelling percentage increased. From both variants, the second type mixture shows better results than the first type mixture. The results of SEM (Scanning Electron Microscopy) show the structure of the peat which became denser with the fly ash particles filling the peat microporous. Also, the reaction of fly ash with geopolymer is indicated by the solid agglomerates that are larger than normal fly ash particle size.

INTRODUCTION

Peat soil is a top soil layer which is formed from the precipitation of food residual that decays. Therefore, peat has some characteristics, such as high water content, high permeability, high compressibility low shear strange, and acidity. Those characteristics make peat soil have low bearing capacity. So, it needs improvement or stabilization. Certain addictives need to be added to change the physical and mechanical behaviors. Some experiments on peat stabilization had be done using addictive, such as supercement [1], peatsolid [2], geosynthetics [3], cement type V [4], lime + pozzolan [5], and potential cellulolytic microorganism [6-7]. Almost all of these have not shown good results in stabilizing peat soil especially in bearing capacity. In the other study, geopolymer cement that is environmentally friendly had succesfully substituted Portland cement with better pressure strength.

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THEORETICAL CONSIDERATION

Based on ASTM D 4772-92 [8], peat is a natural layer of soil with a high organic matter content which is mainly derived from plant materials. Soepandji et al. [9] in his research report on the stabilization of peat with a clean set cement mentioned that peat is a soil that has a high organic content, formed from a mixture of organic materials from plants that have fossilized.

Peatlands in Indonesia are the largest in the tropics; the width is about 20.6 million hectares, or approximately 10.8% of Indonesia's land area [10]. There are many variations of peat soil classifications. This study will use the classification of ASTM D 4772-92, where peat is classified based on the fiber content, ash content, acidity, the ability to absorb water, and biological composition.

Based on research on peat land in Indonesia, particularly Sumatra, Borneo, and Java during the last 20 years, it is known that Indonesian peat soil has a natural water content ranging between 190-770%. The dry weight and water content were dominant in the range of 500 -800%. Based on the classification of ASTM, peatlands of Indonesia are regarded as moderately absorbent. The value specific gravity in the range of 1.4 to 1.8 indicates that the density of peat is quite small or not dense than the mineral soil which usually ranges from 2.5 to 2.8. The value of the liquid limit ranges from 80% to 440% and the plastic limit value ranges from 110% to 380%. The acidity level is high with the range of pH values from 3 to 6.5. Ashes content varies from low to high depending on the location of these peat soils.

In general, there are two methods of soil improvement, mechanically and stabilization. An example of mechanical repair is done by mixing the native soil that has certain technical characteristics with soil from other locations that has good technical properties so that the resulting mixture of soil could qualify the desired strength. Meanwhile, stabilization is solidification, the addition of additives (either in fact or just contained of a material) into a mass of soil to improve the mechanical properties [4]. Soil stabilization materials commonly used are lime, cement, and asphalt. For the application on mineral soils, it generally produces good results if the use of a stabilizing agent in accordance with the provisions of the soil property to be stabilized. However, when applied to the special soil such as peat, it produces unsatisfactory results.

One of the studies used as a reference in this study is Ilyas, et al. [4] who studied the stabilization of Bereng Bengkel peat, Central Kalimantan by mixing Portland cement type-V (PC-V) which has the property of being more resistant to acids, showed by the increase of shear strength and CBR values, although it is not significant. The more levels of PC-V were added and the longer the period, the more ripened ride the CBR value, while the value of soil expansion (swelling) gets down. Viewed microscopically using Scanning Electron Microscope (SEM), it shows that more and more levels of PC-V is given, the closer the gap between the particles of soil porosity due to compaction. It is caused by clot formation of particles (flocculation) due to cement hydration reaction that causes the substitution of positive ions on the soil surface grain by ion Ca++. This shows the cementing process on the ground stabilized.

This study has successfully developed geopolymer cement which can replace Portland cement with almost the same quality that the early strength is high, shrinkage is low, freeze thatresistance, resistance to sulfates, corrosion resistant, resistant to acids, resistant to fire, and alkali aggregate reaction that occurs harmless [11]. In general, inorganic geopolymer is a two-component system consisting of solid components and activator components which are formed through a process of polycondensation. Solid component is a natural material containing enough SiO2 and Al2O3 so that it can form compounds. The examples of materials containing silica and alumina are fly ash, pozzolan, copper slag, and iron blast furnace. Activator component is a liquid alkali chemical that contains alkali hydroxides, silica alumina, carbon and sulfate or a combination of both.

RESEARCH METHODOLOGY

Peat soil samples used in this study obtained from Ogan Kemiring Ilir (OKI), South Sumatra. There were three

things observed in this study, namely: Physical changes, which include specific gravity, dry density, and acidity (pH) Mechanical changes which are CBR value in an unsoaked condition and the CBR value in a soaked condition for

96 hours for the native peat soil and once stabilized with geopolymer Microscopic changes, which were observed with photos Scanning Electron Microscope (SEM)

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It only used one type of geopolymer cement mix levels, namely 10% of the dry weight of peat. There are two types of data used in this study, secondary data from previous research and primary data directly from the laboratory.

FIGURE 1. SEM Photo of stabilization peat with PC-V [4]

SAMPLE PREPARATION

The samples of peat used were peat with moisture content in the range of 80% to 150%. So, we need to dry the original peat soil in the sun to obtain the desired moisture content. The geopolymer cement used consists of material fly ash, waterglass, NaOH, and water with certain compositions according to Table 1. The fly ash used is classified as Type F according to ASTM.

There are two kinds mixing process. First, peat was mixed with a correct amount of fly ash and mixed with a solution of geopolymer activators (waterglass, NaOH, and water). Second, peat was mixed with a correct amount of fly ash and then mixed with geopolymer cement (fly ash, waterglass, NaOH, and water). Mixing was done manually using a container. There are two steps of mixing stabilization measures, namely: Type X: fly ash material and peat were mixed and stirred evenly using a container, then ripened for 24 hours.

Meanwhile, other geopolymer materials (waterglass, NaOH, and water) were mixed with different containers and left in an open-air condition at room temperature for 24 hours. After that, both were mixed in one container and stirried until they were evenly distributed. In short, it can be called (G + Fa) + Activator Solution.

Peat 10% PC-V compacted

Peat 30% PC-V compacted

a) magnification 500x b) magnification 1000X c) magnification 2000x

a) magnification 500x b) magnification 1000X c) magnification 2000x

Micro Crack

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Type Y: geopolymer cement activator in the form of waterglass, NaOH, and water were mixed until homogeneous, and then left in an open condition at a room temperature for 24 hours. Meanwhile, peat was mixed with fly ash with a composition according to the calculation and left in a closed bag for 24 hours. After that, the solution (waterglass, NaOH, and water) was mixed with fly ash, then mixed with peat soil mixed with fly ash. In short, it can be called (G + Fa) + Geopolymer. Curing was applied to the sample results for 4 hours, 5 days, and 10 days. Curing was done in a closed condition

and at a room temperature. After the curing period, the samples were tested in accordance with the plan. Compaction was done following the ASTM D 689-78 standard proctor [12]. The compaction of the mold 6 "to CBR test was done in unsoaked and soaked conditions and swelling test. Most of the remaining samples were tested in the oven for SG and acidity level (pH).

RESULT AND ANALYSIS

Secondary Data for Peat without Stabilization

Peat Soil compaction test data without stabilization OKI were taken from research conducted by [7]. Compaction was carried out using a mold of 4" with hammer standard proctor. Testing was done in the water content which ranged from 75% to 150% and dry density values obtained which ranged between 0.37 to 0.41 g/cm3. Optimum moisture content of peat was in the range of 100% to 120%. Specific Gravity value of OKI peat without stabilization was 1.39 and the value of the level of acidity (pH) was 4.43. CBR value in penetration 0.2" tend to be bigger than penetration 0.1" for the third variation of moisture content. The highest CBR value was at 114.89% moisture content, which is in accordance with the maximum dry density value of compaction results.

TABLE 1. CBR value of peat without stabilization [7]

Moisture CBR US (%) CBR S (%)

(%)

97.26 4.30 5.48 4.85 6.16

114.89 4.85 6.26 5.87 6.52

134.88 2.50 4.07 1.72 3.24 Peat soil does have a unique property because the value of CBR soaked conditions tends to be larger than the

unsoaked condition. Whereas, mineral soils, such as clay, silt, sand, and others, have a CBR unsoaked value greater than the condition of CBR soaked condition due to moisture conditions which are bigger after a soaking. The uniqueness of this is possible because the structure of the peat comprised of organic fibers which were not yet completely decomposed and the presence of micro pores and macro pores thereby making inter-particle holding capacity which has been compacted; peat is getting stronger with the inclusion of water which filled pores in an unsoaked condition.

Primary Data from Laboratory Testing of Stabilized Peat

CBR value generated for stabilization with a mixture of type X was still not good enough. CBR value for the penetration of 0.1" in unsoaked conditions ranged from 2.7% to 4.3%. For the soaked condition, the average increased to a value ranging from 2.9% to 5.4% except on the type X- 5 days-100 that declined. CBR value for the penetration of 0.2 " in unsoaked conditions ranged from 4% to 5.3%. The average soaked condition increased with values ranging from 4.5% to 6.15%, except on the type X-5days-100 that declined. The difference value is far below the water content of the sample for X-5 days-100 which is too dry (96.08%). Dry density value of all samples variations tends to be equal to the average value of 0.44 g/cm3. Thus, an increase of 11.5% was compared to the dry density value of the original peat. For the specific gravity, the value increase to 1.98, which increased as much as 42.4% of the original peat. The value of the level of acidity (pH) was in the range of 5.6 to 6.12 with an average value of 5.85.

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TABLE 2. Data of Stabilized Peat Sample with X Mixed Method

Type WUS

(%) US US dry

(g/cm3) WS

(%)

S S dry

(g/cm3) pH

Swelling (%)

X-4hr-110 111.43 3.2 4.6 0.449 145.26 5.4 6.15 0.455 5.63 0.95

X-4hr-100 102.7 3.7 5.3 0.438 141.2 3.9 5.2 0.467 5.98 1.79

X-4hr-104 104.5 3.5 4.7 0.45 136.9 4.3 5.7 0.47 6.12 1.3

X-5dy-100 96.08 3.3 4.7 0.429 143.02 2.9 3.6 0.454 5.91 1.8

X-5dy-110 114.3 4.3 5.3 0.437 132.86 4.6 5.16 0.456 5.75 1.28

X-5dy-120 119.4 4.3 4.95 0.445 136 4.3 5.4 0.469 5.86 0.92

X-10dy-100 104.15 3.36 4.75 0.447 150.29 3.75 4.59 0.441 5.87 0.55

X-10dy-110 113.8 2.7 4.07 0.437 153.1 3.6 4.69 0.435 5.83 1.09

X-10dy-120 121.96 2.97 4.07 0.458 143.59 4.3 5.32 0.455 5.75 0.55

CBR value results in stabilization with Y mixed type were already quite well with the largest value of the unsoaked conditions 5.8 for 0. -5dy-120 and soaked conditions greatest value was 7.2

-4hr-110. CBR value average for unsoaked 0.1" was 4.4 and 0.2" was 5.3, while for soaked 0.1" is 5.2 and 0.2" is 6.1. CBR value for the penetration 0.1" of unsoaked conditions ranged from 3.05% to 4.9%, for the soaked condition of the average has increased in value ranged from 3.9% to 6.1% except for samples of type Y-5dy-100 which showed a decline. CBR value for the penetration 0.2" of unsoaked conditions ranged from 4.3% to 5.8%, for an average soaked condition increases with a value ranged from 5% to 7.4%, except on the type Y-5dy-100 which showed decline. The difference value is far enough for sample X-5dy-100 is caused by soil moisture too dry (99%). Dry density value of all the variations is 0.49 g/cm3, higher than the result of mixtures of type X are only 0.44 g/cm3. When compared with peat soils without stabilization, dry density value of Y-type mixture is increased 23.3%. For specific gravity value rise to 2, an increase of 43.8% from the original peat. The value of the level of acidity (pH) is sufficient to rise to near neutral. The average pH value of all the variations of the sample is 5.86.

CBR value peat with geopolymer stabilization for X and Y mixing method, both showed a trend CBR value in soaked conditions greater than unsoaked conditions corresponding to that of the original peat. Increased curing time tends not affect in changes the CBR value, the chart actually shows a decline as increasing of curing time. The water content near optimum moisture (110%) result CBR value relatively largest for any variations sample. Y mixing method gives better results than the X mixing method.

TABLE 3. Data of Stabilized Peat Sample with Y Mixed Method

Type WUS

(%) US US dry

(g/cm3) WS

(%)

S

S dry

(g/cm3) Swelling

(%) pH

Y-4hr-100 100.63 4.5 5.2 0.483 135.4 5.5 6.4 0.498 0.64 5.86

Y-4hr-110 111.64 4.69 5.53 0.502 125.3 6.1 7.4 0.511 0.45 5.88

Y-4hr-112 112.89 3.9 5.2 0.492 120.1 5.7 6.8 0.5 0.44 5.98

Y-5dy-100 99.43 4.5 5 0.474 136 3.9 4.7 0.48 0.73 5.78

Y-5dy-110 111.43 4.9 5.6 0.493 124.1 5.2 6.4 0.498 0.86 5.8

Y-5dy-120 112.14 4.8 5.8 0.497 123.3 5.5 6.7 0.492 0.59 5.8

Y-10dy-100 99.04 3.05 4.3 0.463 134 4.7 5.06 0.47 0.83 5.86

Y-10dy-110 110.15 4.5 5.6 0.492 123 5.2 6.1 0.497 0.39 6.01

Y-10dy-120 113.6 4.5 5.5 0.487 119.1 4.8 6.1 0.5 0.71 5.8

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(a) (b)

FIGURE 2. penetration

FIGURE 3. SEM Photo for Pure peat and stabilized peat

Pure peat

Peat X

Peat Y

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The structure of pure peat still has pores between fibers, which were very clear with the size of 20-60 μm. In the picture with a magnification of 1000x, visible folds around the fiber surface peat soil that indicates the zone is still relatively undisturbed or conserved. In the peat with X-type mixing, it was seen that the soil may be compacted well, observed by only one point of particle shape, which is not compacted well. Peat micro pore fraction has been filled by fly ash, which is shown from their spherical particles at 2500x magnification. However, there are still macro cracks due to the sample used for SEM must be in dried conditions so that the pores initially filled with water became empty and then cracked due to temperatures that were too hot during the drying.

Peat with Y-type mixing is much more compacted well with fewer pores macro as seen at a magnification of 1000x. Cracked macro is also much less, shown by the number of pores which are filled with fly ash, thereby reducing process water infiltration excessively and lost during the drying process. At 2500x magnification, it was also found particle greater than normal fly ash particles as the result of SEM mixture of type X, where the clot is possible a fly ash which has reacted with a geopolymer and clots with peat soil in the vicinity. Micro fibers that look solid in magnification of 2500X and 5000X is more massive and dense.

CONCLUSION

1. Long curing time did not significantly affect the value of CBR. The values would show a tendency to decline as curing time gets longer.

2. The water content during solidification has a very big influence on the value of CBR, the largest value obtained in water levels approaching the optimum moisture content. In the near optimum moisture content, for a X type mixture, the obtained CBR value by cured 4 hours is 5.4%, 5 days is 4.6%, and 10 days is 3.6%. For a Y type mixture, the obtained CBR value by cured 4 hours is 6.1% 5 days is 5.2%, and 10 days is 5.2%.

3. An increase in the value of specific gravity and density dry ( dry), as well as a decrease in the percentage of expansion (swell) in the samples of peat with a Y type mixture stabilization compared with samples of peat with the stabilization X type mixture. But for the level of acidity (pH) is not likely or same.

TABLE 4. Conclusion

Criteria Type X Type Y Spesific grafity 1.98 2 Increasing kering 11.5 % 23.3 % swelling 1.13 % 0.62 % Average pH 5.85 5.86

Condition US S US S CBR Pure peat 485% 5.87

% 4.85%

5.87%

CBR curing 4 hours 3.2 % 5.4 % 4.7 % 6.1 % CBR curing 5 days 4.3 % 4.6% 4.9 % 5.2 % CBR curing 10 days 2.7 % 3.6 % 4.5 % 5.2 %

4. In accordance, Flexible Road Pavement Planning Guidelines book, the CBR value submerged stabilization results can be used as pavement subgrade, but the value is still not good enough.

5. There structure microscopic changes to be more solid or dense in the peat sample by Y type mixture stabilization compared with peat samples with X type mixture stabilization and there are fly ash particles that fill the microporous peat. It is estimated that there is also a reaction of fly ash with geopolymer solution that happened shown by the solid agglomerates that are larger than normal fly ash particle size.

ACKNOWLEDGMENTS

Thanks to Allah so this paper can be finished. Special thanks to Wiwik Rahayu who gives guidance, Nasuhi Zain who gives suggestion and critic, Sigit P. Hadiwardoyo who gives guidance and suggestion for all of process in this research. All of staff of Soil Mechanics Laboratory Civil Engineering Department who give so much support and time.

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