Olive oil is concentrated in the Mediterranean basin countries. Since the olive oil industries are incriminated for a high quantity of pollution, it has become imperative to solve this problem by developing optimized systems for the treatment of olive oil wastes. This study proposes a solution to the problem. Burned olive waste ash is evaluated for using it as clay stabilizer. In a laboratory, bentonite clay is used to improve olive waste ash. Before the laboratory, the olive waste is burned at 550°C in the high temperature oven. The burned olive waste ash was added to bentonite clay with increasing 1% by weight from 1% to 10%. The study consisted of the following tests on samples treated with burned olive waste ash: Atterberg Limits, Standard Proctor Density, and Unconfined Compressive Strength Tests. The test results show promise for this material to be used as stabilizer and to solve many of the problems associated with its accumulation.
Although olive trees are distributed over all continents, 97% of the world production of olive oil is concentrated in the Mediterranean basin countries: Spain, Portugal, Italy, Greece, Turkey, Tunisia, and Morocco [
Olive waste is the by-product after olives have been pressed and olive oil extracted. Olive oil waste has always been one of the biggest problems associated with the industry. For a long time, the olive oil industry has been troubled with the disposal of their waste. The most important use of olive waste is for fuel owing to the extremely high cost of energy. Recently, there has been an increased rate of interest in olive cake residue by power stations for the high temperatures it generates with minimum ash. Some countries (Greece, Italy, Tunisia, and Turkey) plan to develop the uses for olive waste in energy producing. Some small coal power plant could be reset to burn olive waste. Olive oil residue can also be used in some construction applications. In America, the olive waste has been mixed with bitumen as a component of road construction material. Olive bricks, although lighter than that of traditional bricks, are also manufactured [
On the other hand, especially clayey soils required treatment. In this treatment, waste can be used. In this way, the waste is stabilized, and clayey soil is improved. This study evaluates the use of the burned olive waste ash as a soil stabilizer. In the literature, various additives such as lime, cement, and fly ash were used to stabilize expansive soils [
In this study, bentonite clay was used to improve. The bentonite was dried in an oven at 105 ± 5°C. Properties of the bentonite are given in Table
Properties of the bentonite.
Chemical analysis | |
| |
L.o.I. (%) | 7.50 ± 1.00 |
SiO2 (%) | 71.00 ± 1.00 |
Al2O3 (%) | 14.00 ± 1.00 |
Fe2O3 (%) | 0.70 ± 0.10 |
TiO2 (%) | 0.05 ± 0.01 |
CaO (%) | 1.10 ± 0.30 |
MgO (%) | 3.20 ± 0.20 |
Na2O (%) | 0.25 ± 0.05 |
K2O (%) | 1.00 ± 0.10 |
| |
Mineralogical analysis | |
| |
Montmorillonite (%) | 80 |
Cristobalite-opal C (%) | 17 |
K-feldspar (%) | 3 |
Plagioclase (%) | Trace |
| |
Properties | |
| |
Cation exchange capacity (meq/100 gr) | 85.0 ± 5.0 |
CaCO3 (%) | 0 |
Swelling (mL/2 gr) | 8.0 ± 2.0 |
Sedimentation (72 hours) (mL) | 10 |
Sintering point (°C) | 1200 |
Bulk density (gr/lt) | 800 ± 30 |
Clumping test | Positive |
Clump weight (gr) | 55 ± 5 |
Water absorbtion (%) | 90 ± 5 |
Water absorbtion duration (sec) | max. 65 |
NH3 adsorption (ppm) | 40 |
Bleaching—original(Tonsil equivalent) | 0.6 |
Bleaching—Acid activated (Tonsil equivalent) | 0.7 |
pH (8% solid) | 8.5 |
Grit content (+75 |
<4 |
Color | White |
Lightness | 93 ± 1 |
Moisture (%) | <30 |
The experiments were done by adding the olive waste ash at weight percentages of 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10% accordingly. When every sample was prepared, bentonite was initially mixed with the olive waste ash and was then kept under curing conditions for one hour for chemical process [
First, Atterberg Limit Tests were performed. The tests were conducted in accordance with ASTM 4318. Then Specific Gravity Tests were performed according to ASTM D854, and the Modify Proctor Tests were performed for determining optimum water content. The Modify Proctor Tests were conducted in accordance with ASTM D1557.
Samples which were used at The Unconfined Compressive Strength Test were prepared at the optimum water content. Every ash weight percentage sample was cured for 0, 1, 7 and 28 days. After curing, The Unconfined Compressive Strength Test was performed. The Unconfined Compressive Strength Tests were conducted in accordance with ASTM D2166.
Figure
Effect of olive waste ash on the Atterberg limits.
The effect of burned olive waste ash on the specific gravity of the bentonite is showed in Figure
Effect of olive waste ash on the specific gravity.
Figure
Compaction test results due to the addition of burned olive waste.
Effect of olive waste ash on the maximum dry unit weight.
On the other hand, Figure
Effect of olive waste ash on the optimum water content.
Figure
The effect of burned olive waste on the unconfined compressive strength of the treated soil.
Also, CaCO3 present in the burned olive waste has been converted to CaO and CO2, CaO, or Ca(OH)2. The addition of water can react with the amorphous silica remaining after burning the olive waste or clay in the soil to form calcium silicate hydrate, which is cementitious (or, in other words, the ash of the olive waste is pozzolanic). This would also contribute to the increase in the unconfined compression strength. The decrease of the unconfined compressive strength at a high percentage of burned olive waste is due to a decrease in the density and an increase of the noncohesive material in the samples [
The plasticity index of the treated soils decreases with the increase in percent olive waste.
When 1% by weight the olive waste ash was added, specific gravity had maximum value. To increase the percentage is caused to decrease specific gravity.
The highest maximum dry unit weight value was obtained for the addition of 1% by weight olive waste ash. On the other hand, the lowest optimum water content value was obtained by the addition of 1% by weight olive waste ash.
The unconfined compressive strength of the all cure times of specimen is maximum value when the burned olive waste ash was added 1% by weight.
At the cure times of 0, 1, and 7 days, all specimens acted same. At the cure times of 28 days, unconfined compression strength decreases strongly when the addition of higher percentages.