In this study investigate laboratory scale evaluation of rheological characteristics for three different types of natural hydrocarbons; the GILSONITE; ASPHALTITE and the SYRIAN Al_Beshery region natural asphalt , were added into the Bitumen samples at five different ratios.
RHEOLOGY is the study of the flow of matter. It is a branch of physics which deals with the deformation and flow of materials, both solids and liquids.
These modified binders were evaluated with some tests like; softening point, dynamic viscosity and penetration.
Viscoelastic properties of the modified binders were determined with dynamic mechanical analysis and were presented in the form of temperature and frequency dependent rheological parameters.
It was determined by the results obtained from the tests that; with increased natural asphalt content, the softening point and the viscosity increased and the penetration and the thermal sensitivity decreased.
Dynamic shear rheometer test results indicated that the temperature and the frequency had a significant effect on the complex modulus of natural asphalt modified binders.
Investigation of the types of various additives yielded that the most effective additive was Gilsonite powder in all experiments and the least effective additive in all experiments was the Syrian NA.
Flexible pavements are resilient surfaces that distribute loads down to the sub base in a radiant manner.
Flexible pavements generally have thin wearing surfaces and thick
Bases. Asphalt is an example of a flexible pavement. Hot mix
Asphalt (HMAs) has more strength than cold mixes therefore it can be laid in thinner layers.
Flexible pavement surfaces includes two important parts: bitumen and aggregates.
The bituminous binders are strong binders for flexible pavement surfaces
And the aggregates provide the internal shear strength and the stability of the mixture.
Bitumen binders also bind the aggregate particles together preventing their breakdown under the traffic load. They also fill the voids in the mixture and increase the stability of the mixture b cohesion and enabling its impermeability.
Although bituminous binders are used in pavement mixtures in low amounts (5-7% by weight), they have a considerable effect on the mixture efficiency.
Flexible pavement surfaces could be prepared in different ways, but the highest strength among these methods is hot mix asphalts and this used in the flexible pavements of highways, various deformations such as permanent deformation, moisture damage and cracks because of low temperature and fatigue regularly occur.
In this study we employed different modifier materials to raise the resistance of hot mix asphalt against deformation
The modifiers can be added into the bituminous binder as well as into the mixture directly.
- These were used in the bitumen modification:
- Styrene-butadiene-styrene (SBS)
- These were used in mixture modification:
- carbon black
In this way, there are some positive attributes that exist to prevent deformation in the HMA.
Natural hydrocarbons is other type of modifiers that are used in HAMs. Pay attention to this diagram:
Trinidad Lake asphalt and Gilsonite are the often used natural hydrocarbons in the modification of HMAs.
The natural hydrocarbons mined from in the Southeastern Anatolian Region are classified to be in between asphaltite and pyrobitumens in terms of their solubility in carbon disulfide, they are collectively named as asphaltite.
The rheological properties of bitumen shows in table.1 and the physical properties of Gilsonite and asphaltite are in table2.
Syrian natural asphalt including asphalt and aggregate, with the extraction test we found that it contains 17% fraction of bitumen and an 83% fraction of mineral. The elemental analysis of this material exist in table.3 and in figure.1 shows the appearance of that.
figure1: Appearance of the Syrian NA, Gilsonite and asphaltite
To produce different mixtures of asphalt binders with the modifiers we have chosen, we can use the device shown in the figure below. This is a laboratory scale mixing device which has four blades impeller.
Conditions in which the blends is prepared:
- Temperature =180ºC
- Rotational speed =1000 rpm
- During a period =1h
Gilsonite and asphaltite were used in 5 different concentrations in the range of
0-10% by weight of natural bitumen increasing in 2% increments and the Syrian natural asphalt was used in 5 different concentrations in the range of 0-25% by weight of bitumen increasing in 5% increments.
Figure2: Apparatus and the setup for the preparation of the modified binder
The penetration test at 25 ̊C and the softening point test were performed on the neat.
This test is performed to determine the softening point based on the ASTM D5 and for penetration is ASTM D36.
Penetration Index (PI), calculates with this relationship:
Consider, lower values of PI indicate higher temperature susceptibility.
Most commonly used method for rheological testing of bitumen is oscillatory test. That carry out using dynamic shear rheometers (DSR). In the tables above two parameters G* and δ have been defined; G* parameter obtained from the DSR is complex shear modulus that is defined as the ratio of maximum stress to maximum strain. δ parameter is phase angle, that is the phase or the time or the lag between the applied shear stress, and shear strain response phase angle range is 0-90. If this parameter equals 90, the bituminous material can be considered to be purely viscous in nature.
The DSR test was performed under controlled-stress loading conditions
Using frequency sweeps between 0.01 and 10hz and also the perfect temperature for it 40 and 80°C.
This tests were performed with a test plate with a diameter of 25 mm, a 1 mm gap and parallel plates.
In the figures below has been shown variation in the penetration values, penetration index and softening point with respect to the type and amount of the additive.
The letters denotes in the figures, modified binders with.….
- The letter A denotes the modified binders with 2%
asphaltite or gilsonite, or 5% Syrian NA
- the letter B denotes the modified binders with 4% asphaltite or gilsonite or10% Syrian NA
- the letter C denotes the modified binders with 6% asphaltite or gilsonite, or 15% Syrian NA
- the letter D denotes the modified binders with 8% asphaltite or gilsonite, or 20% Syrian NA
- the letter E denotes the modified binders with 10% asphaltite or gilsonite, or 25% Syrian NA
Figure 2: Variation in the penetration values with respect to the type and the amount of the additive
Figure 3: Relationship between the softening point, and the type and the amount of the additive
Figure 4: Variation in the PI with respect to the type and the amount of the additive
In figure.2, penetration was decreasing with the increase in the content of additive. But the most effective was Gilsonite and the least effective one was the Syrian NA.
Actually the penetration decreased by 56% when 10% wt Gilsonite was used and it decreased by 46% or by 61% when 10% wt asphaltite or 25% Syrian NA were used.
In figure.3 comparison of softening point of the binders with 10% additive content indicated which most effective additive was Gilsonite and the least effective one was the Syrian NA.
the softening point increased by 24% when 10% wt asphaltite was used and by 38% when 25% wt Syrian NA was used and see also 10% wt gilsonite was used, the softening point increased by 36% in comparison to its value for the neat binder.
Figure.4 indicates as the amount of natural additives was increased, PI increase but temperature sensitivity of the binders was decrease.
The highest PI value at 10% additive content with Gilsonite and the lowest PI values at this content was asphaltite.
It was found that PI samples were high not only high resistance to permanent deformation, but also against low temperature fractures.
According to PI, it can be concluded that the use of natural asphalt additives increases resistant lead band against any permanent deformation and low temperature fractures.
In accordance with the results of the penetration and testing of the softening point, the viscosity of all types connections increase with increasing incremental content and their efficiency decreases.
Because the viscosity of all bitumen modified samples was less than 3000cP, the viscosity of the threshold required for Contracts, all receivers are in terms of efficiency.
A comparison of the correction index between the collected values at 135 ̊C and 165 ̊C showed that indicator values were low at 165 °C, indicating that the effect of additives on viscosity decrease with increasing
Among the recipients adding 10% by weight, the highest viscosity for Gilsonite was measured containing receptors at 135 °C and viscosity values were determined for all receptors with any type of additive approximately 165 ̊C.
Table4: Viscosity test results for the neat and the modified binders
The review of Table.5 showed that the increase of the G * value and the devaluation of δ decreases with increasing incremental content and frequency.
The phase angle decreases at frequencies below 1Hz and increases at higher frequencies threshold.
The modification index (MI) increased with increasing incremental content and decreased with increasing frequency.
An additive which causes the greatest increase G * among additives with a 10%wt is Gilsonite. The G* and the δ values of the binders having 10% content of asphaltite or Syrian NA were similar.
Table.5: G*, δ and the modification index values obtained from the master curves at 40°C
Based on the results of this study, the relevant findings and conclusions can be summarized as follows:
- Observed penetration values are gradually reduced by increasing the incremental content that the results show
From penetration experiments. Compare modified bands with the same amount of additives (10%) Showed that the most effective additive in the amount of penetration was Gilsonite and its least side effects was the Syrian NA.
- The values of the softening point factor gradually increase with increasing incremental content by which it is shown with softening point experiment, the most effective additive was
Gilsonite and the least effective additive was Syrian NA.
- The PI values increases with increasing natural additive
the content thus reduces the sensitivity of the temperature of the binders. PI values indicated that Gilsonite was the most effective additive and the least effective additive was Asphaltite.
- Gilsonite is defined as an additive that further increases viscosity, as measured by experiments conducted at 135 ° C using different binders with equal amounts of additives.
- The results of DSR experiments showed that the value of the complex modulus increases substantially
Increased content and frequency.
The most effective additive was Gilsonite whereas asphaltite and the Syrian NA were the additives that were the least effective on G* values.
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