The main functions of geogrid are as follows:
1. Slow down reflection cracks
Reflective cracks are caused by the stress concentration in the asphalt overlay above the old concrete surface due to the large displacement of the old concrete surface near the joints or cracks. It includes horizontal displacement due to changes in temperature and humidity, and traffic loads. The vertical shear displacement caused by the action. The former leads to a relatively concentrated tensile stress in the asphalt overlay above the joint or crack; the latter causes the asphalt overlay above the joint to experience greater flexural tensile stress and shear stress.
Because the modulus of the geogrid is very large, reaching 67Gpa, it is used as a hard interlayer with high rigidity in the asphalt overlay. Its function is to restrain stress and release strain. Tensile and shear resistance, so as to achieve the purpose of reducing cracks. Practice has shown that the corresponding crack energy of a horizontal crack that has changed its direction can move 0.6 meters from its starting point, and reinforcements with a width of more than 1.5 meters help to ensure that the energy is completely dissipated on both sides of the crack.
2. Anti-fatigue cracking
The main function of asphalt overlay on old cement concrete pavement is to improve the use function of the pavement, but it does not contribute much to the bearing effect. The rigid concrete pavement under the overlay still plays a key bearing role. The asphalt overlay on the old asphalt concrete pavement is different, and the asphalt overlay will carry the load together with the old asphalt concrete pavement. Therefore, in addition to reflection cracks, fatigue cracking will also occur due to the long-term effect of load when asphalt overlay is applied on asphalt concrete pavement. We do a stress analysis on the load condition of the asphalt overlay on the old asphalt concrete pavement: because the asphalt overlay is a flexible surface with the same properties as the asphalt overlay, when subjected to load, the road surface will bend. Shen. The asphalt surface layer directly in contact with the wheel is under pressure, and in the area other than the wheel load edge, the surface layer is subjected to tensile force. Since the force properties of the two stressed areas are different and they are close to each other, the two parts are affected by tension. The junction of the force area, that is, the sudden change of force, is prone to damage. Fatigue cracking occurs under long-term loading.
In the asphalt cover layer, the glass fiber geogrid can disperse the above-mentioned compressive stress and tensile stress, and form a buffer zone between the two stressed areas, where the stress changes gradually instead of abruptly, which reduces the impact of sudden stress on the asphalt. Destruction of the overlay. At the same time, the low elongation of the glass fiber geogrid reduces the deflection of the pavement and ensures that the pavement will not undergo transitional deformation.
3. High temperature rutting
Asphalt concrete has rheological properties at high temperature, which is manifested in: the asphalt road surface becomes soft and sticky in summer; under the action of vehicle load, the stressed area is dented, and the asphalt surface cannot be completely restored to before the load after the vehicle load is removed. Under the action of repeated rolling of the vehicle, the plastic deformation continues to accumulate, forming ruts. our asphalt
After analyzing the surface layer structure, it can be known that due to the rheological properties of asphalt concrete under high temperature, there is no mechanism in the surface layer that can restrict the movement of aggregates in the asphalt concrete when it is loaded, resulting in the movement of the asphalt surface layer. The main reason for the formation of ruts.
Fiberglass geogrids are used in the asphalt overlay, which acts as a skeleton in the asphalt overlay. The aggregate in the asphalt concrete runs through the grids to form a composite mechanical interlocking system, which restricts the movement of the aggregate and increases the lateral restraint force in the asphalt surface layer. move, so as to play a role in resisting rutting.
4. Resist low temperature shrinkage cracking
For asphalt roads in severe cold areas, the surface temperature in winter is close to the air temperature. Under such temperature conditions, asphalt concrete shrinks when cold, resulting in tensile stress. When the tensile stress exceeds the tensile strength of asphalt concrete, cracks will occur, and cracks will occur in the places where the cracks are concentrated, resulting in diseases. From the perspective of the causes of cracks, how to make the strength of asphalt concrete resist the tensile stress is the key to solving the problem.
The application of glass fiber geogrid in the asphalt surface layer greatly increases the tensile strength of asphalt concrete, which can resist large tensile stress without damage. In addition, even if the stress at the place where the crack occurs is too concentrated because of the crack in the local area, it gradually disappears through the transmission of the glass fiber geogrid, and the crack will no longer develop into a crack. In the selection of glass fiber soil
When the grid is used, in addition to its performance indicators should meet the requirements of the above table, special attention should be paid to ensure that its width is not less than 1.5m, so that it has enough cross-sectional area to fully dissipate the crack energy when it is used as an interlayer for controlling reflection cracks. At the same time, the mesh size should be 0.5 to 1.0 times the maximum particle size of the asphalt surface material on it, which will help to achieve the best shear adhesiveness and promote aggregates.
Interlocking and restraining.
