VALVE GP-RELIEF 3102221 - Caterpillar

Rolling Procedures
The operator should first determine the proper frequency at which to operate the machine. As the drum vibrates, it travels in an up and down motion. The vertical distance the drum moves is called amplitude. It is this vertical movement that creates the compactive effort of vibratory compactors.Amplitude is governed by the weight of the drum, the weight of the eccentrics and the distance to the center of gravity of the weights from the center of rotation. The frequency of impacts combined with the travel speed of the compactor determines the surface smoothness of the asphalt.The higher the frequency of impacts, the closer the spacing. The mat will be smoother and greater travel speed will be possible. On asphalt, 25 mm (1 in) spacing will usually result in a satisfactory smooth finish. In addition to the vibratory variables, drum diameter and drum length must be considered since they determine the contact area of the compactor on the asphalt.This is of prime importance because the total applied force of the compactor is distributed over this area.It is recommended to use the maximum frequency allowed for a given amplitude setting. However, due to the nature of the mix, thickness or other variables, it may be necessary to vary the frequency. Once the frequency of vibration has been selected, the maximum travel speed is determined by the 25 mm (1 in) impact spacing requirement. This chart represents the maximum travel speed of the roller to achieve 25 mm (1 in) impact spacing at various VPM's.Of all the variables in asphalt compaction, the temperature of the mix at the time of compaction is probably the most significant.If the temperature is too high, the mix will disperse easily under the force of the compactor causing waves and creases.If the temperature is too low, the mix will be difficult to compact. Such things as ambient air temperature, base temperature, wind conditions, aggregate size, viscosity of the asphalt and the thickness of the mat all are factors influencing the proper mix temperature. What is desired is a temperature high enough to allow time to achieve compaction before it cools too much for further rolling to be effective.The cooling time of the asphalt mix must be kept in mind as this will partly determine the speed required of the compactor. For efficient compaction, it is generally agreed upon that density must be reached before the asphalt mix cools to 79°C (175°F).Factors such as aggregate size, laydown temperature, mat thickness, ambient temperature and wind condition all influence cooling time. If at all possible, set up a test strip before the actual job starts. The test strip will verify the proper amplitude frequency, roller speed and rolling pattern. It will assure the density will be reached while maintaining a proper finish surface. The test strip will also confirm if the proper compactor has been selected or whether additional units will be required to meet production.If the test strip does not meet density requirements, slow the roller down.