Buy the best types of Rubber Asphalt at a cheap price
Investigating the relationships between rubber size, rubber content, and binder content will help determine the ideal binder content for an open-graded friction course (OGFC).
Bitumen Crumb Rubber Asphalt
In this article, we have tried to see why crumb rubber is a new and impressive binder for asphalt. In this study, mix gradation type B according to the Road Engineering Association of Malaysia's (REAM) Specification for Porous Asphalt was used.
Four different rubber sizes—20 mesh size [0.841 mm], 40 mesh [0.42 mm], 80 mesh [0.177 mm], and 100 mesh [0.149 mm]—were used to create the Marshall specimens, along with varying amounts of rubberized bitumen (4%, 8%, and 12%) and binder content (4%–7%).
The results of the air voids, binder drain down, and abrasion loss tests are then used to determine the appropriate optimal binder content. The optimal binder content for OGFC can be influenced by crumb rubber particle size, according to test results.
The 1930s saw the introduction of OGFC, also known as porous asphalt when the Oregon Department of Transportation implemented the open graded design in an effort to increase the road's resistance to skidding.
However, at that time, issues with durability and drain down limited its continued use. This kind of surface course was used by the California Department of Transportation (CALTRANS) in the 1940s as a drainage interlayer and an alternative to chip seals and slurry seals.
The Federal Highway Administration agency issued the first design manual for porous asphalt mixes in 1974, and The Franklin Institute in Philadelphia issued a design manual for porous pavements in 1978 that takes into account the soil's properties, its capacity to support weight, and its hydrological implications.
This pavement type's popularity can be attributed to a number of benefits, including a decrease in splash and spray, a decreased risk of wet skidding and hydroplaning, and a reduction in noise from traffic friction.
Due to these advantages, the system has grown in popularity over time and is now being used by more governments. Open-graded pavement systems can be very helpful in tropical nations like Malaysia, where the average monthly precipitation can be as high as 314 mm.
The benefits also have a number of drawbacks, including increased construction and maintenance costs and decreased structural and functional durability.
This necessitates ongoing research in this area to address the design's flaws.
A layer of porous asphalt, a layer of granular subbase, and a layer of crushed stone base course that serves as a reservoir make up an open-graded friction course or porous asphalt system.
This enables water to accumulate at the base of the surface course before penetrating the subgrade.
Because of its high porosity, porous asphalt may experience issues like a quicker rate of binder oxidation and loss of adhesion when it comes into contact with water.
This quickens the process of disintegration, which adds to the raveling issue. This necessitates the use of a modified binder, which can enhance the pavement's durability properties.
Bitumen Crumb Rubber Asphalt
Currently, the majority of authorities who use open-graded asphalt in their roads have chosen to modify the pavement with either rubber or polymer to increase its durability.
It has been demonstrated that adding crumb rubber through the wet process or the dry process can increase the resilience modulus, fatigue cracking resistance, and rutting resistance of asphaltic mixes.
This is because the bituminous binder's viscosity, softening point, loss modulus, and storage modulus properties have changed.
The process by which rubber particles that had interacted with bitumen swelled, however, is what controls the improvement.
Due to the bitumen's maltenes component being absorbed, rubber crumbs can swell up to three to five times their original size. As a result, the number of asphaltenes in the binder increased, which raised its viscosity.
The crumb rubber modified bitumen (CRMB) mixing process, which is influenced by internal and external bitumen, crumb rubber quantity, size, and type variables, as well as mixing temperature, duration, and type is a major determinant of the final properties of CRMB.
The secret to successful CRMB production is a careful selection of the processing factors, such as bitumen type, rubber particle size and content, mixing temperature, and duration.
In this study, the optimal binder content of an open-graded friction course made in accordance with the Road Engineering Association of Malaysia (REAM) Specifications for Porous Asphalt modified with crumb rubber by the wet process is compared to the crumb rubber content and particle size.
Research institutes, as well as road and transport authorities, have all published a number of guides for creating open-graded friction courses. The best binder content for porous mixes can typically be determined using one of three methods.
The first type uses a compacted asphalt specimen to determine the ideal binder content, the second uses an oil absorption test, and the third type uses visual observation.
In the first method, compacted specimens with specific physical properties are used to determine the ideal binder content of OGFC.
The design must generally strike a balance between the mix's abrasion loss and the binder drain down values while maintaining a sufficient amount of air void in the mix to ensure good permeability, according to the guidelines that use compacted specimens to determine the optimum binder contents. The ideal bitumen content is determined by producing samples that satisfy all the necessary requirements.
In addition to the aforementioned primary parameters, some guidelines demand that mix samples be examined for aged abrasion loss.
Following ASTM D6926: Practice for Preparation of Bituminous Specimens Using Marshall Apparatus, samples were prepared in a precise manner.
The air void in the compacted mix (D2041 and D 3203), the binder drainage test (BS EN 1297-18:2004), and the mix's Cantabro abrasion test (D7064) must all be determined in order to determine the best binder content.
Abrasion loss must be less than 15%, void content must be between 18% and 25%, and binder drain down must be less than 0.3%, according to the Malaysian Standard for Porous Asphalt (REAM SP 5/2008).
Bitumen Crumb Rubber Asphalt mix
For the abrasion loss and air void samples, the chosen binder content ranges from 4% to 7%, while for the binder drainage test, the chosen binder content ranges from 5% to 9% at an incremental 1%.
Each sample's rubber content, percentage, and particle size were duplicated three times. The samples are categorized based on the amount of rubber, the size of the rubber mesh, and the amount of binder.
For instance, 20# 8R 5B denotes samples that had 20 mesh crumb rubber sizing at 8% binder content added to them.
Crumb Rubber
For samples made with 20 mesh rubber crumbs, the abrasion loss exhibits an exponential trend of 4% to 7% BC. Abrasion loss for all samples is very high at 4% BC, reaching 55.6% loss for 12% RC, 51% loss for 8% RC, and 41.2% loss for 4% RC.
The average abrasion loss at 5% BC is 14.8%, which is within the acceptable range set forth in the REAM Porous Asphalt design guide. At 5% BC, the abrasion loss for samples with 12% RC is 23%.
With the exception of samples with 12% RC and 6% BC, all samples with 6% and 7% BC and all RC have acceptable abrasion loss values. This is likely the result of an insufficient binder in a mixture that was altered with a lot of crumb rubber.
Binder drain down tests for samples made with 8% and 9% binder content reveal very high drain down values.
At 7% BC, samples with 12% RC display an acceptable drain down value of 0.27%, while at 5% and 6% BC, all samples display an acceptable drain down value with the exception of samples modified with 4% RC. The mix has enough void space for all of the rubber and binder components.
Due to the added strength provided by higher binder content, all samples exhibit satisfactory abrasion loss at 6% and 7% binder content for samples modified with 40 mesh rubber crumbs.
Only samples with 4% RC exhibit an adequate abrasion loss value of less than 15% at 5% BC, while none of the samples do so at 4% BC. Once more, this is the result of a high rubber content that is not offset by a higher binder content. The mixture becomes fragile as a result and breaks upon impact.
As expected, binder drain down at 8% and 9% is too close to the acceptable limit, whereas samples modified with 8% and 12% show drain down values at 6% and 7% BC that are within the designated limit. All samples produced acceptable drain down values at 5% BC.
Binder drain down value will rise when lower RC is applied to samples with higher BC, in contrast to the factors that affect abrasion loss.
As a result, binders have a low viscosity and have a propensity to drain down quickly. For every tested binder and rubber content, void in mix still displays satisfactory results.
The 80 mesh crumb rubber modification offers an acceptable abrasion loss for samples at all binder contents except at 4% BC due to the finer nature of the rubber crumb.
Greater surface area in finer rubber crumbs allows them to absorb more of the bitumen's lighter oils. This makes the binder more viscous, which strengthens the mixture as a result.
crumb rubber asphalt pavement
On the other hand, drain down characteristics produce adequate results for BC levels of 5%, 6%, and 7%. Only samples with 12% RC offer an adequate drain down value at 8% and 9% BC.
This is to be expected, as with coarser mesh size, as 8% and 9% BC lower RC cannot provide the higher viscosity necessary to provide an acceptable drain down value.
Results for void in mix exhibit a marginally distinct pattern from those of earlier results. The amount of void in the mix does not meet the specification's requirement at 4% binder content.
This demonstrates that bitumen with a viscosity that is low enough to completely coat the aggregate but not so low that it drains down easily would be needed in order to create rubber crumb with a finer texture.
Lower binder content combined with rubber crumb modification would result in a too-thick binder that would not adequately cover the aggregates, leading to more void in the mix.
The results of samples modified with 100 mesh crumb rubber are comparable to those of their 80 mesh counterpart. This is probably because there is probably not much of a size difference between the two mesh sizes.
Following an analysis of the test results, the conclusions listed below can be made.
Mixtures modified with a lower bitumen content and coarser rubber crumb typically have a higher abrasion loss. This is because there isn't enough binder to balance out the addition of rubber crumb, resulting in a mix that is fragile and breaks on impact.
The optimal binder content window is smaller for coarser rubber crumb. Higher binder and crumb rubber content can be used as the mesh size decreases.
It's important to keep in mind that the rubber crumbs used in this study were sheared at low shear rates and at low mixing temperatures.
As a result, it is possible that higher shear rates and higher mixing temperatures will alter the characteristics of the coarser rubber crumbs since higher blending temperatures and high shear rates tend to cause swelling and shrinkage of the crumb rubber.
Higher bitumen content increases strength, but mixes with more binder have a higher binder draindown value. Higher rubber content also makes bitumen more viscous, which thickens the film and reduces the amount of void in the mixture.
However, it appears that finer rubber crumbs are less sensitive to changes in the content of rubber and binder. As a result, there is a larger window for choosing the ideal binder content.
A wider range of ideal binder contents can be chosen thanks to the flexibility in the range of optimum binder content offered by bitumen modified with finer rubber crumb (80 and 100 mesh size).
However, the minimum and maximum allowable void contents of 18% and 25% are close to the lower and upper limits of the optimal binder content (5% and 7%, respectively).
Therefore, to ensure a high-quality product while still allowing for some tolerance in the production of rubberized bitumen, it is advised to use an intermediate value between 6% and 6.5% as the ideal binder content.
How useful is this article to you?
Average Score
5
/
Number of votes:
1
