There have been many innovations for asphalt pavers, since its first development in 1931 that got them to where they are today. In 1933, the independent floating screed was developed. Pavers added electronic leveling controls in the 1950s and automated screed controls in the early 1960s. Extra-wide finishers, capable of paving two lanes at once, debuted in 1968.
The quest to improve mat quality, increase spec density and smoothness, and eliminate segregation have led to many of these paving innovations, as has the push to reduce maintenance costs, boost machine uptime and increase ROI.
The basic asphalt paver configuration was the same as it is today – wheel or track undercarriage, front loading hopper and floating screed. The fundamental principles of the free-floating screed and tractor have not changed a lot. What has changed is the ease of operation, quality of pavement and smoothness and ease of maintenance.
Asphalt pavers have come a long way, but they haven't stopped evolving. Despite their complexity, paving machines are becoming simpler to operate with a high degree of proficiency.
Transformation (advancement) of drive system
Early asphalt pavers had mechanical drive system and so described as Mechanical Pavers where in drive to tracks / wheels for traction, conveyor chain and auger is through mechanical gearboxes, chain and sprocket. This drive system is very complicated and requires high maintenance. Further, mechanical drive system offers limited and fixed operational speeds.
Development of hydraulic drive system eliminated the complexity and service requirements of mechanical drive systems and created a more reliable, automated drive system for pavers that lowered operating costs. Hydrostatic drives are widely recognized as an excellent means of power transmission when variable output speed is required. Typically outperforming mechanical and electrical variable-speed drives and gear-type transmissions, they offer fast response, maintain precise speed under varying loads, and allow infinitely variable speed control from zero to maximum.
Pavers with hydrostatic drive systems can have an unlimited number of speeds within the operating range and once set will automatically maintain the desired speed. These pavers have variable displacement motor and pump for infinitely variable paving and travel speeds. No mechanical shifting either in the paving or travel mode – effortless selection through finger-tip control. Conveyor and augur drive is through variable displacement hydraulic pump and fixed motor for material feed. The steering and transmission are also hydraulically controlled.
Advancement in paving screeds
The first and most important innovation that has aided the advancement of screeds was the introduction of hydraulically extendable screeds. Prior to this innovation, all screeds were fixed width and only able to be adjusted for width with bolt-on blocks of different widths to meet the required paving width. The advantage of the hydraulically extendable screed is the ability to attain infinitely variable paving widths at the touch of button leading to substantial time and labour savings. This screed increased the paving flexibility for the contractor; no longer did they have to stop the paver to mechanically change paving widths.
Another key advancement in screed technology has been the development of electric heat. Prior to its introduction, screeds utilized fossil fuel burners to heat the screed plates. The usage of fossil fuel heat, while cheap and readily available, had serious draw back including uneven heat that lead to warping of screed plates, smoke and fumes, and constant maintenance. Electric screed heating eliminates the common smoky startups with diesel screeds and provides more uniform heat distribution across the entire screed bottom. It also gives screed operator more zonal control over screed temperature.
Automatic Grade and Slope control system
Automatic Grade and Slope control system provides automated control over the screed tow point cylinders in order to maintain precise mat thickness and percent slope or crossfall during paving operations. This system ensures that correct amount of mix reaches across the width of the screed.
Manual control of the screed requires a high level of attention at all times and automatic grade & slope control eliminates some of the “human factor” of fatigue and simply estimating, or “eyeballing” adjustments as opposed to the machine measuring precisely and making adjustments. Automatic grade and slope technology can react to certain surface conditions faster and more accurately than a human being can.
The system increases road smoothness while using less asphalt than with traditional paving methods, especially in complex designs such as transitions, super-elevated curves and frequently changing cross slopes; it also eliminates high and low areas in the area to be paved early in the paving process.
Automatic grade and slope control systems for pavers provide paving companies with a broad range of benefits. These include improving grade and slope accuracy; increasing productivity; helping with smooth transitions, controlling mat thickness and yield; and lowering costs related to grade and slope re-work. In addition, these systems decrease operator fatigue related to manually controlling grade and slope.
Automatic and Independently controlled feeder systems
The material feed system of the paver machine plays a very important part in producing a consistent, high-quality mat behind the laydown machine. Automatic feed systems use sensors to automatically regulate the proper delivery and flow of material in front of the screed to ensure smooth and consistent paving.
Independently controlled feeder systems eliminate
flow gates and improve the homogeneity of the mix, which improves consistency
and reduced segregation. The gateless material handling system promotes hands-free
operation by providing features such as ratio control dials, and independent
control of each auger and each conveyor. Both the augers and dual slat
conveyors offer full automatic control with manual override. This allows the
operator to precisely control the amount of material being sent to the screed
if paving wider or thicker on one side or the other. The independent operation
reduces component wear and minimizes the potential for mix segregation.