How to accurately test the water damage of asphalt pavement and extend the service life of highway?
Release time: 2017-06-27
According to relevant research, more than 70% of the early destruction of asphalt pavement is directly or indirectly related to the water stability of the pavement, which is caused by water damage. Water damage has become one of the most severe forms of asphalt pavement damage in China. Whether in the hot and humid south or the cold north, shortly after opening to traffic, water damage problems occurred to varying degrees. Therefore, it is of great economic and social significance to evaluate and analyze the water damage test of asphalt pavement.
Overview of Asphalt Pavement Water Damage
The water damage of asphalt pavement is that in the presence of moisture, the asphalt pavement will gradually fall off the aggregate under the repeated action of water and vehicle load, and then the asphalt mixture will loosen and fall, and gradually develop into pits. It may even cause diseases such as pulping and mud. Common forms of water damage and damage include: potholes, network cracks, cracks, and rutting.
Residual stability reflects the ability of asphalt pavement to resist spalling when damaged by water, that is, water stability. With the rapid development of expressways, domestic and foreign countries have paid more and more attention to the problem of asphalt pavement water damage, and conducted a systematic study on the asphalt pavement water stability index.
Domestic testing status
At present, the determination of water stability of asphalt pavement in China is mainly based on the three methods specified in "JTG E20-2011 Highway Engineering Asphalt and Asphalt Mixture Test Regulations": submerged Marshall test, vacuum saturated Marshall test and freeze-thaw split test. The comparison of the three methods is as follows:
The true water damage mechanism of the pavement is: under the dual action of water and repeated wheel loads, the internal adhesion (asphalt and aggregate) and cohesion (asphalt and asphalt) of the asphalt pavement are destroyed.
The three domestic water stability tests mainly focus on the loss of internal adhesion (asphalt and aggregate) of asphalt pavement under static water under the action of water, while neglecting the anti-adhesion of wheel load pressure and void water pressure Destruction of cohesion (asphalt and asphalt).
Adhesion damage: As the aggregate has a greater attraction to moisture than asphalt, moisture can enter between the asphalt and the aggregate, reducing the contact area between the asphalt and the aggregate surface, and reducing the bonding force, which results in the peeling of the asphalt film and making the aggregate The material is exposed and damaged.
Cohesive force destruction: As a result of moisture intrusion, the asphalt becomes soft and the viscosity decreases, which leads to a decrease in the internal cohesion of the asphalt, which leads to the overall destruction of the asphalt mixture.
Note: Gray represents aggregate and black represents asphalt
In summary, the current domestic main methods of testing the water stability of asphalt pavement can not fully restore the true damage mechanism of asphalt pavement water damage.
New technologies abroad
The MIST water sensitivity tester developed by the US INSTROTEK company innovatively adds the function of dynamic scouring in the saturated water process of the test piece. It is used to simulate the pore water pressure and hydraulic scouring phenomenon formed by the tire load on the site. It is consistent with the mechanism of water damage on the road surface. The test pieces in the test chamber will be subjected to three effects of water immersion, high temperature and cyclic pressure at the same time, which can not only reduce the adhesion between the asphalt and the aggregate and cause damage, but also soften the asphalt and reduce the internal The cohesion between them is reduced and damage occurs.
MIST water sensitivity tester
Successfully developed and applied in 2010
Asphalt pavement water damage environment simulation system
In the United States, mainly used for experimental research tools
In the United States, as an alternative to the traditional test method AASHTO T-283 (TSR)
In 2013, it became the test method stipulated by ASTM specification, ASTM D7870
Principle of MIST water sensitivity tester
Mist uses a pressurized tank to simulate the destruction mechanism of the road surface under wheel load
Mist uses hydraulic pumps and pneumatic pistons to simulate the failure mechanism of road surfaces under wheel load
The asphalt mixture test piece is put into the Mist simulation silo, filled with water
After the lid is closed, set the temperature, air pressure, and air pressure cycle times in the chamber. All three parameters can be adjusted.
Simulate the water pressure of the voids in the test piece through the air pressure cycle (pressure and no pressure), destroy the internal adhesion (asphalt and aggregate) and cohesive force (asphalt and asphalt) of the test piece
MIST water stability judgment standard
Before and after the test, the gross volume density change rate of the test piece is <1.5%, and the water stability is considered to be good
The split strength ratio of the test piece before and after the test is more than 80%, and the water stability is considered to be better
For more information about MIST products, please contact INTROTEK China exclusive agent service provider Europe and the United States.