6. Mixture Delivery
6.2 PLANNING
Watch Video
The planning process for a paving job includes determining the number of trucks needed and ensuring the truck drivers are properly trained. The size and types of available trucks, the time to make one trip from the plant to the paver and back (known as cycle time), the planned hourly plant production rate, the length of the paving shift, and any mixture stored at the start of the workday are all details that should be considered by the paving contractor to properly plan their trucking needs. Also, drivers should be trained in their proper role in loading at the plant, hauling, and unloading at the paver to minimize segregation, ensure safety, and promote continuous paving.
The cycle time includes all steps that are a part of a complete cycle. This may include time to load and ticket the truck, tarp the load, haul it to the paving site, wait onsite to unload, dump and clean, and return to the plant.
If a shift begins with paving material stored in a silo, that material effectively adds production capacity for the contractor. The amount of added capacity is determined by the amount stored and the shift length. For example, if a 10-hr shift begins with 250 tons of mixture in a silo, this equates to 25 tons/hr (250 tons/10 hr) of additional production capacity. Thus, the true production will be the tons/hour produced by the plant plus the added tons/hour supplied from the silo.
Determination of the required minimum number of trucks is an important aspect of planning for an asphalt paving project. The items stated above are needed to properly estimate this requirement. The minimum number of trucks needed can be calculated by the following equation:
Where:
T = tons
hr = hours
min = minutes
The answer is always rounded up. For example, if the equation yields 13.1 trucks, a minimum of 14 trucks will be needed.
EXAMPLE
Determine the minimum number of trucks for a job with the following information:
| Plant Production = | 250 T/hr (227 tonnes/hr) |
| Silo Charge at Start of Day = | 200 T (180 tonnes) |
| Shift Length = | 10 hr |
| Truck Capacity = | 20 T (18 tonnes) |
| Load Time and Ticketing = | 4 min |
| Tarping Time = | 2 min |
| Haul to Jobsite = | 35 min |
| Time on Site = | 4 min |
| Dump and Clean = | 4 min |
| Return Haul = | 35 min |
Step 1: Determine True Plant Production Rate
This will be the added production rate from the use of the materials stored in the silo at the beginning of a shift plus the plant production rate. In this example, 200 tons are stored that will be used over a 10-hour workday.
Step 2: Determine the Total Cycle Time
The total cycle time will be the sum of each of the steps encountered from the loading to the return of a single truck: 84 min in total.
Step 3: Calculate the Total Trucks Needed:
This number should always be rounded up. Therefore, 19 trucks will be needed to maintain a proper flow of mix to the jobsite.
The time interval between each delivery should be consistent, and the trucks should not be allowed to bunch up at the paver or at the plant. If a break in the delivery of material occurs, the paver contractor should stop the paver using a rapid stop technique and then use a rapid start when enough trucks are on the jobsite. This method will promote continuous paving. Starting and stopping the paver for each truck as it arrives on the project will reduce the smoothness and quality of the finished pavement and negatively affect the density of the mat.
Starting and stopping the paver for each truck as it arrives on the project will reduce the smoothness and quality of the finished pavement and negatively affect the density of the mat.