Fatigue Properties and Damage Characteristics of Polyurethane Mixtures under a Stress Control Mode

Abstract

A polyurethane mixture (PUM) is an energy-saving and emission-reducing pavement material with excellent temperature stability; however, the fatigue properties and fatigue damage models of PUM still require further research. Therefore, four-point bending static load tests, fatigue tests, and digital speckle correlation method (DSCM) tests with different load levels of PUM and styrene butadiene styrene (SBS)-modified asphalt mixture (SMA) were carried out. The fatigue life, stiffness, midspan deflection, and maximum tensile strain were obtained and compared. The fatigue damage factor calculation method of PUM based on stiffness degradation was proposed, and the fatigue damage function of PUM at different load levels was fitted. The results show that the fatigue life of PUM was much larger than that of SMA, and the static loading failure and fatigue failure modes of PUM were both brittle. The fatigue damage of PUM exhibits an obvious three-stage damage law: the rapid development stage (accounting for about 10–20% of the fatigue life), the deformation stability expansion stage (accounting for about 70–80% of the fatigue life), and the instability development stage (accounting for about 10–20% of the fatigue life). The fatigue damage factors (DB) were calculated based on stiffness, according to DB=EI0−EInrEI0−EINr, and the fatigue damage functions of PUM were fitted based on the stiffness degradation, according to fnN=1−1−(n/N)a(1−n/N)b. The fatigue damage fitting curves have good correlation with the calculation results of the damage factor based on test data, which can predict the stiffness degradation of PUM at different load levels. The results can help further the understanding of the fatigue characteristics and damage mechanism of PUM, which will provide theoretical support for the application of PUM in pavement structures.

Mechanical Properties of Polyurethane Mixture and Load Response Behaviour of Polyurethane Composite Pavement

“…The bending stresses of PUM-20 and PUM-25 mixtures increase rapidly under loading, and the mixture fails after bending for about 3 s, while the time–stress curves of PUM-20 and PUM-25 mixtures are relatively flat, and the mixture fails after loading for 15 s. In addition, the bending failure stress of PUM-20 and PUM-25 is about four times larger than that of SMA-13, AC-20, and AC-25, while the maximum deformation of SMA-13, AC-20, and AC-25 is about 15 times larger than that of PUM-20 and PUM-25. This indicates that the PU mixture has a strong ability to resist loading; however, its plastic deformation under loading is small, easily leading to brittle failure [ 12 ].…”

“…When the stress level of SMA-13, AC-20, and AC-25 mixtures increases to 0.5, the fatigue life is only 1000–2000 cycles, while the fatigue life of the PUM-20 and PUM-25 mixtures at the 0.7 stress level can still reach 2000–3000 cycles; that is, PU mixtures still have good fatigue resistance at high stress levels. At the 0.5 stress level, the fatigue life of PUM-20 and PUM-25 mixtures is more than 25 times that of the SMA-13, AC-20, and AC-25 mixtures, indicating that the PU mixture has a strong ability to resist fatigue load [ 12 ]. The four-point bending fatigue test shows that the PU mixture has strong fatigue resistance and can be applied at higher stress levels.…”

“…At present, there is an increasing body of research on polyurethane (PU) mixtures in pavement engineering [ 6 , 7 , 8 , 9 , 10 ]. Compared to traditional mixtures, PU mixtures have better durability, temperature stability, waterproof properties, and crack resistance, which can reduce maintenance frequency [ 11 , 12 , 13 , 14 , 15 ]. However, as a new type of road construction material, the conventional pavement structure design method is not applicable [ 16 , 17 , 18 , 19 , 20 ].…”

Preparation of Mullite/PU Nanocomposites by Double Waste Co-Recycling

“…The German chemist Otto Bayer invented polyurethane (PU) in the 1930s, which is a class of polymeric materials with -NHCOO-as a repeating group [20,21]. Polyurethane can be in the form of elastomers, adhesives, paints, or foams (PUF), of which polyurethane foam is the most used polyurethane product [22][23][24][25][26].…”