Natural peat is considered incapable of supporting built structure due to its poor engineering properties. Chemical stabilization is one of the peat soil improvement methods which has been studied by many researchers. This study describes an investigation of water additive (
A mixture of fragmented organic material formed in wetlands under suitable climatic and topographic conditions is called peat. Peat is derived from vegetation that has been chemically changed and fossilized as described by Dhowian and Edil [
In civil engineering, peat is classified as a problematic soil due to its weak characteristic related to its ability to support the civil structures. Peat consists of water and decomposed plant fragment with no measurable strength in its natural state. Peat has a high natural moisture content, high compressibility including significant secondary and tertiary compression, low shear strength, high-degree spatial variability, and potential further decomposition as a result of changing environmental conditions [
Ground improvement method has to be done prior to construction on peat. Chemical stabilization such as cement-peat stabilization is considered the effective method for peat stabilization especially for deep peat which can reach up to 10 meters deep. There are some factors that influence cemented-soil mixture [
Summary of tropical peat chemical stabilization study by some researchers.
Reference | Origin and sampling depth | Peat classification | Stabilizer | Stabilization method | Curing method and curing period |
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Banting, Bukit Changgang and Dengkil, Selangor | H4–H7 | OPC 5–15% | Compaction with MDD and OMC | Water curing 7, 14, 28 days |
0.5–1 m | lime 5–25% | ||||
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[ |
Kampung Jawa, Malaysia | H4–H5 | OPC 15, 30, 50% and polypropylene fibers 0.1, 0.15, 0.25% (of natural wet soil) | Amount additive added is percentage additive of wet soil hand-mixed | Air-curing 28, 90, 180 days |
0.05–0.6 m | |||||
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[ |
Kampung Sri Nadi, Klang, Selangor Darul Ehsan, Malaysia | H4 | Cement and slag 300, 250, 200 kg/m3 (25–75%, 50–50%, 75–25%) + 950 kg/m3 siliceous sand | Amount additive added is percentage additive of wet soil mixer mixed | Water curing with pressure 9 kPa 7, 14, 28 days |
1 m | |||||
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[ |
Sri Nadi Village, Klang, Selangor, Malaysia | Fibrous peat | 300 kg/m3 binder + 25% sand, w/o and w/4% accelerator (of wet soil mass) | Amount additive added is percentage additive of wet soil | Water curing with pressure 100 kPa 7 days |
OPC specially manufacture cement: Walcrete, Avancrete, Phoenix, Mascrete | Kitchen mixer mixed | ||||
Cement accelerator: Sodium chloride and calcium chloride | |||||
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[ |
Matang, Sarawak, Malaysia | H3–H4 | OPC 5–40% | Compaction with MDD and OMC | Water curing 7, 14, 28 days |
0.4–0.8 m | FA 5–30% | ||||
QL 2–8% | |||||
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[ |
Matang, Sarawak | H3 | OPC 5–20%, quick lime 5–20%, fly ash2-8% (of soil dry mass) | Compaction with MDD and OMC | Water curing |
0.4–0.8 m | 7, 14, 28 days | ||||
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[ |
Tropical peat | H4 | 85% cement, 15% bentonite (5%, 10%, 15%) | Compaction with MDD and OMC | Water curing 7 and 14 days |
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[ |
Kp Tumbuk darat, Sepang, Selangor, Malaysia | H5–H6 | 10, 20, and 40% OPC (of soil dry mass) | Compaction with MDD and OMC | Air-curing 3 and 28 days |
1 m |
MDD, maximum dry density; OMC, optimum moisture content; OPC, ordinary Portland cement; FA, fly ash; QL, quick lime.
When cement is added into the soil, there occur two chemical reactions. First is primary hydration where water reacts with cement, forming a binding gel called tobermorite/CSH. The second reaction is called secondary pozzolanic reaction. It happens by the reaction of calcium hydroxide [Ca(OH)2], formed in primary hydration and water and pozzolan (silica and alumina) in the soil, which then forms more binding agents.
Axelsson et al. [
Unlike clay, peat has a humic acid that can retard the strength development of cement-stabilized peat. However, Huttunen et al. [
Compaction method greatly contributes to the effectiveness of stabilization. However, it is difficult to compact peat soil because of its high moisture content and organic particles which make a slurry-like and sticky texture. Many of chemical-stabilized peat studies [
Axelsson et al. [
Curing time has an important role for cement-stabilized peat to gain strength since cement needs time for reacting with water and pozzolan materials. Many researchers had proved the strength increase over curing time in peat stabilization [
Several studies of peat stabilization show the increment of engineering characteristics of peat after stabilization. The pozzolanic activity in stabilized specimens leads to the increase in its density due to the reduction of the amount of interparticle voids [
Many researchers agreed with the finding that unconfined compressive strength of cement-stabilized peat is increased compared to the untreated peat. The unconfined compressive strength was found to increase with the increase of cement content and curing time [
The disturbed peat sample was collected in Kampung Meranek, Sarawak, Malaysia, from 0.5–1 m depth below the surface. The peat sample transported to the laboratory was kept in a sealed container. Before the tests were performed, the peat sample was screened through 6.63 mm (0.3″) sieve to remove larger objects. Leaving in the larger objects would introduce an inconsistency in the test result.
For the UCS test, peat soil with three different moisture contents were prepared, which are peat with moisture content of 1210% as the field moisture content (later referred as peat A), moisture content of 803% (later referred as peat B), and moisture content of 380% (later referred as peat C). The last two moisture contents are the result of air-dried peat. The stabilizer used was the ordinary Portland cement (OPC).
The physical properties tests carried out were Von Post classification (degree of decomposition), moisture content (BS 1377), organic content (ASTM 2974), fiber content (ASTM D 1997), specific gravity (BS 1377), liquid limit (BS 1377), linear shrinkage (BS 1377), and pH test (BS 1377). There are some adjustments for peat soil tests due to their distinct characters compared to other inorganic soils. For the specific gravity test, kerosene was used as the standard liquid instead of water due to the lightness of peat material. For the liquid limit test, the reversed method was used. Peat was tested from wet to dry condition using a dryer, instead of adding water to the dry peat. The reversed method was applied because peat will unlikely return into its natural state once dried.
A PVC pipe was used as a split mould for UCS specimens. The sample size was 38 mm in diameter and 76 mm in length. Both ends of PVC were covered with Styrofoam and PVC cover. Plastic wrap was used around the PVC mould to prevent water leakage. The inside part was lubricated with grease to prevent the specimen adhering to the mould surface.
The
Cement dosage for peat A of various
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% cement in wet soil | Cement dosage (kg/m3) |
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2.0 | 1210.497 | 500.000 | 38.153 | 461.847 | 230.923 | 46.185 | 472.282 |
2.5 | 1210.497 | 500.000 | 38.153 | 461.847 | 184.739 | 36.948 | 377.825 |
3.0 | 1210.497 | 500.000 | 38.153 | 461.847 | 153.949 | 30.790 | 314.854 |
3.5 | 1210.497 | 500.000 | 38.153 | 461.847 | 131.956 | 26.391 | 269.875 |
4.0 | 1210.497 | 500.000 | 38.153 | 461.847 | 115.462 | 23.092 | 236.141 |
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2.0 | 803.920 | 500.000 | 55.315 | 444.685 | 222.343 | 44.469 | 459.402 |
2.5 | 803.920 | 500.000 | 55.315 | 444.685 | 177.874 | 35.575 | 367.521 |
3.0 | 803.920 | 500.000 | 55.315 | 444.685 | 148.228 | 29.646 | 306.268 |
3.5 | 803.920 | 500.000 | 55.315 | 444.685 | 127.053 | 25.411 | 262.515 |
4.0 | 803.920 | 500.000 | 55.315 | 444.685 | 111.171 | 22.234 | 229.701 |
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2.0 | 380.606 | 500.000 | 104.035 | 395.965 | 197.982 | 39.596 | 421.350 |
2.5 | 380.606 | 500.000 | 104.035 | 395.965 | 158.386 | 31.677 | 337.080 |
3.0 | 380.606 | 500.000 | 104.035 | 395.965 | 131.988 | 26.398 | 280.900 |
3.5 | 380.606 | 500.000 | 104.035 | 395.965 | 113.133 | 22.627 | 240.772 |
4.0 | 380.606 | 500.000 | 104.035 | 395.965 | 98.991 | 19.798 | 210.675 |
w, moisture content; W, wet soil mass;
Peat and cement were weighed according to the mix design calculation and mixed well with a putty knife. Therefore, the mixture was put inside the mould and pressed with a plastic spoon by three layers. Since the mixture was a kind of slurry, the standard compaction method cannot be used. After the mould had been covered, the air-curing procedure was done by keeping the specimens at a normal temperature and without any water intrusion. The air-curing procedure was carried for 28 and 56 days for peat A, B, and C specimens. To prevent water accumulation, the specimens were turned over every day for the first 3 days and then every 3-4 days.
After the curing process, the unconfined compressive strength test was conducted for the peat specimens according to ASTM D 2166 guidelines. The specimens were loaded axially using UCS testing equipment with 2 kN load proving ring until the load values decreased, the sample failed, or the strain has reached 15%.
The test result of the physical properties of the peat is shown in Table
Physical properties of Kampung Meranek peat.
Properties | Values |
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Degree of decomposition | H7-H8 |
Moisture content (%) | 1210.497 |
Specific gravity | 1.408 |
Liquid limit (%) | 458 |
Linear shrinkage (%) | 27.338 |
Organic content (%) | 95.793 |
Fiber content (%) | 32.333 |
pH | 3.31 |
The peat sample had a dark brown color. The consistency was very pasty and amorphous with faintly recognized plant remains. When squeezed, about two-thirds of peat escaped between the fingers. Therefore, the degree of decomposition of Kampung Meranek peat by Von Post classification was classified as H7-H8 or sapric (amorphous) peat [
Peat should be contained by organic content more than 75% [
Figures
Stress vs. strain of peat A specimens after 28 days air-cured.
Stress vs. strain of peat A specimens after 56 days air-cured.
Stress vs. strain of peat B specimens after 28 days air-cured.
Stress vs. strain of peat B specimens after 56 days air-cured.
From the result of the UCS test, peak strength is found in peat A specimens. From the graphs, it can be inferred that UCS values increase as the decrease of
In contrary with the stress,
The pattern of the graphs from peat B specimens is relatively the same with peat A specimens. The peak strength is found, and strength from
Aside from peat A and B, peat C shows a different response with
Stress vs. strain of peat C specimens after 28 days air-cured.
Stress vs. strain of peat C specimens after 56 days air-cured.
The strength obtained by peat C specimens is a lot greater than peat A and B specimens. The greater availability of soil particle in peat C specimens might affect the greater strength compared to peat A and B specimens. Nevertheless, it is interesting that the strength of peat A specimens, which has fewer soil particles and higher moisture content compared to peat B specimens, is greater than that of peat B specimens. Therefore, the secondary pozzolanic reaction might occur in the stabilization of peat C specimens, while primary hydration took a more dominant role for peat A and B specimens since both have a high moisture content that exceeds the liquid limit and has fewer soil particles.
Figure
UCS value vs. curing time for peat A specimens (
UCS value vs. curing time for peat B specimens (
For peat C specimens graph as shown in Figure
UCS value vs. curing time for peat C specimens (
From Figure
UCS value vs.
Peat C specimens, otherwise, have a different condition from peat A and B specimens, to begin with. The moisture content of peat A and B which exceeds the moisture content of the liquid limit (Table
As discussed above,
Figure
UCS value increase factor vs.
Peat A and B, which had given the same variations of
From the investigation of the various water additive ratio application on the unconfined compressive strength of cement-stabilized amorphous peat at different natural moisture contents, several conclusions are made: UCS values increase with the increase of cement dosage (decrease of water additive ratio). UCS values increase with the increase of curing time. Even though the increase is not really significant between 28 and 56 days, but compared to the original peat strength, it gives increase factor of 9–40 folds (from varied The insignificant results in For the same The application of Cement hydrolysis reaction is evident in the specimens, despite the presence of humic acid content of peat, proved by the higher strength values achieved by the higher moisture content of peat.
The data used to support the findings of this study are included within the article.
The authors declare that they have no conflicts of interest.
This research was funded by Zamalah Postgraduate Scholarship of Universiti Malaysia Sarawak (UNIMAS/NC-30/04–30/01 Jld. 3 (93)). The project was also supported by the Faculty of Engineering and Research Innovation Management Centre of Universiti Malaysia Sarawak and the Ministry of Education of Malaysia (FRGS/TK07 (01)/1055/2013(1)). The authors would like to express their gratitude to Zamalah Postgraduate Scholarship of Universiti Malaysia Sarawak (UNIMAS/NC-30/04–30/01 Jld. 3 (93)), Faculty of Engineering and Research Innovation Management Centre of Universiti Malaysia Sarawak, and Ministry of Education of Malaysia (FRGS/TK07 (01)/1055/2013(1)) for financial support. The authors also wish to acknowledge Cream-CIDB CoPS (Construction on Peat Soil) of UNIMAS and UNIMAS Geotechnical Engineering lab technicians for their assistance throughout this research.