ASET Technology Alberta Fall 2020 - 22

P R OJ E C T

AC A D E M I C I N S T I T U T I O N

An alternative to
the conventional
hot mix asphalt

Lethbridge College
E N G I N E E R I N G T E C H N O L O GY D I S C I P L I N E

Civil engineering technology

P R OJ E C T D E S C R I P T I O N
Today's world has become overridden with garbage and materials that deteriorate over time. Our objective was to look
for ways to alter conventional asphalt to reflect a greener
environment while maintaining or increasing the strength
and durability of hot mix asphalt. By using different types
and sizes of crumb rubber and altering the asphalt cement
content respectively, we worked to alter the characteristics
of asphalt mix briquettes.
We used two different crumb rubbers in an attempt to alter
the characteristics of the asphalt mix briquettes. One crumb
rubber sample was a sieved 1.25mm crumb rubber, and the
second specimen was a 30-mesh (0.600um) crumb rubber
received from CRM®. Our process focused on altering mix
design proportions with the two different sizes of crumb
rubber, as well as the percentage of asphalt cement added.
Three briquettes of each of the test crumb rubbers were
tested in relation to one conventional sample. This test included a consistent increase of asphalt cement throughout
the crumb rubber briquettes in order to compensate for the
aggregate volume being increased by the crumb rubbers.
By combining methods from the Marshall mix and Superpave designs, as well as altering the amount of crumb rubber products that were in the test samples, we could see
how the strength and characteristics of the asphalt were affected. To determine if crumb rubber was a viable ingredient
in hot mix asphalt, the briquettes were tested as per ASTM
standards. Once the data was collected, comparisons were
conducted to conclude whether the recycled crumb rubber
would be an applicable ingredient in hot mix asphalt.
The requirements for design based on a medium traffic
pavement were that the stability would be a minimum of
5.338 kN, the flow would be between eight and 16 (0.25mm
units), air void percentage would be between three and five
per cent and voids filled would be between 65 and 78 per
cent. In addition, the minimum voids in mineral aggregate
would need to be above 13 per cent and air voids a minimum
of four per cent. Based on our research findings, approximately half of these standards were met.

22 | FALL 2020 | TECHNOLOGY ALBERTA

The 30-mesh briquettes compared very similarly to the
sieved rubber briquettes. None of the samples met the
standard criteria for air void percentage, percentage of
voids filled and flow. When compared to the conventional
mix design briquettes, we determined that the stability of
the crumb rubber mixtures were much higher, and the densities much lower.
In addition to only meeting half of the design requirements of
a medium traffic pavement, there were several challenges in
the design and methodology of the research. One issue was
the breakdown of briquettes because of a "bounce back"
effect, causing the briquettes to crumble. There was also a
problem with the compaction and lateral stability of the mix
designs containing the crumb rubber. The briquettes would
crumble upon initial removal from the gyratory compactor.
This meant that the briquettes needed to cool for a minimum of 24 hours in a supported environment, supporting a
conclusion that these mixes may only be applicable in a municipal setting. In addition, the overall strength and stability of the briquettes decreased at increased temperatures,
making them extremely fragile. All of these challenges and
limitations also affected the overall conclusion of this research project.
After completing data collection, testing, addressing challenges and final analysis, we determined that the mix design
and process followed in this project may not be applicable
for standard pavement requirements. We believe that an improvement in design and testing is possible with similar processes. We could also consider an environment with cooler
temperatures where the heat would not affect the strength
of cohesion of the briquette. Alterations to the type, size
and content of rubber in the mix designs may change the
outcome of all testing. Additional research and literature review could also provide insight on other methods to improve
results. To combat the breakdown of aggregate while in a
Superpave compactor, the number of gyrations, pressure or
angle could also be altered.



ASET Technology Alberta Fall 2020

Table of Contents for the Digital Edition of ASET Technology Alberta Fall 2020

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ASET Technology Alberta Fall 2020 - Cover3
https://www.nxtbook.com/dawson/aset/ta_fall_2021
https://www.nxtbook.com/dawson/aset/ta_summer_2021
https://www.nxtbook.com/dawson/aset/ta_spring_2021
https://www.nxtbook.com/dawson/aset/ta_winter_2020
https://www.nxtbook.com/dawson/aset/ta_fall_2020
https://www.nxtbook.com/dawson/aset/ta_summer_2020
https://www.nxtbook.com/dawson/aset/ta_spring_2020
https://www.nxtbook.com/dawson/aset/ta_winter_2019
https://www.nxtbook.com/dawson/aset/ta_summer_2019
https://www.nxtbook.com/dawson/aset/ta_spring_2019
https://www.nxtbook.com/dawson/aset/ta_fall_dec2018
https://www.nxtbook.com/dawson/aset/aset55anniversary
https://www.nxtbook.com/dawson/aset/ta_spring_2018
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https://www.nxtbook.com/dawson/aset/ta_fall_2017
https://www.nxtbook.com/dawson/aset/ta_spring_2017
https://www.nxtbook.com/dawson/aset/ta_winter_2017
https://www.nxtbook.com/dawson/aset/ta_fall_2016
https://www.nxtbook.com/dawson/aset/ta_summer_2016
https://www.nxtbook.com/dawson/aset/ta_spring_2016
https://www.nxtbook.com/dawson/aset/ta_winter_2016
https://www.nxtbook.com/dawson/aset/ta_fall_2015
https://www.nxtbook.com/dawson/aset/ta_summer_2015
https://www.nxtbook.com/dawson/aset/ta_spring_2015
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