Loadout & Weighing | P&Q University Handbook

Loadout is one of the most critical stages in an aggregate operation, representing the point where material leaves the yard and revenue is realized. But it can also be a point of delay, congestion and wasted cost if not managed carefully. 

From the time the quarry’s gates open each morning to the end of the day, materials are on the move. Every interaction between loaders, trucks, scales and stockpiles affects efficiency – and every unnecessary touch adds cost in fuel, tires, wages and machine hours.

Well-designed loadout systems save time, reduce operating expenses and improve customer satisfaction. Operations that streamline these processes can handle more loads in a day, keep customer trucks turning and minimize bottlenecks at the scale house or stockpile.

Conversely, inefficient loadout costs operators directly in lost productivity and indirectly in customer loyalty, as delays cause haulers to lose revenue and look for faster service elsewhere.

Reducing loadout cycle times

Loadout cycle time is the measure of how quickly a truck is loaded, ticketed and released from a site.

Long waits erode customer profitability because they reduce truck utilization and daily haul capacity. For the producer, poor cycle times create dissatisfaction and increase the risk of losing customers to faster competitors.

Matching mobile equipment correctly to the scale of demand is essential. Trained employees, consistent processes and clearly communicated procedures help ensure cycle times are repeatable and efficient. When loadout operations suffer mismatches – between loaders, trucks, scales or staff – problems creep in and profits decline.

Truck productivity

Hauling is most profitable when trucks are full and moving. 

In reality, backhauls aren’t always available and empty return trips increase costs. When delays occur at the quarry, customers can lose multiple loads across a shift, jeopardizing already slim margins.

Because most projects are priced on a set number of loads per day, quarries must minimize avoidable yard delays. Producers should establish key performance indicators (KPIs) that measure time spent at each stage – from weighing tare, traveling to stockpiles, waiting in queue, loading, tarping and returning to the scale – and develop strategies to reduce these times wherever possible.

Stockpile and scale layout

Effective stockpile and scale layout can greatly reduce congestion and improve truck flow. 

Fast-moving products should be placed in the most accessible positions, while slower-moving products can be located further away. The goal is to minimize travel and reduce bottlenecks.

Adequate space should be provided so trucks and mobile equipment can operate without conflict. Pinch points should be eliminated wherever possible, and one-way traffic systems can help reduce congestion and improve safety. Clear signage, visible traffic rules and layout maps available at the scale house all contribute to smoother flow.

At the scales, design choices also matter. Crossroads where trucks merge should be minimized, and drive-up ticketing windows allow drivers to remain in their vehicles, speeding turnaround and reducing pedestrian activity near the scale house.

Remember: Loadout is more than just the last step in material processing. It is a central element of profitability, customer service and operational safety. By focusing on cycle times, truck productivity and site design, aggregate producers can unlock efficiencies that pay off in lower costs and happier customers.

Truck Scales

The truck scale is a critical link between the stockpile and the customer, serving as the final checkpoint that verifies weights and ultimately determines accuracy, efficiency and profitability in loadout. 

Because every transaction depends on its performance, the scale is one of the most important investments a quarry can make. While a truck scale may appear simple from the outside, it relies on many complex components working together to deliver precise and timely measurements.

Interior of a truck scale

To understand how a truck scale works, it’s important to know what’s happening inside the scale:

1. Load cell. The load cell is a delicate piece of a truck scale. Multiple load cells are placed throughout the scale to accurately detect weight. Load cells flex when a truck passes over. This flexing impacts the electrical signal traveling to the strain gauge inside the load cell, and the resulting signal is sent to the junction box.
2. Junction box. Electrical signals from load cells are transmitted to the junction box. The junction box calculates the truck’s weight by equalizing load cell signals. Depending on the instrumentation, the load cells or the indicator can calculate the weight.
3. Indicator. Typically wired near the truck scale, the indicator will display the final weight. The indicator is the control terminal, which can manage in/out truck programs and printers with additional programming.

Exterior of a truck scale

1. Foundation. The scale is installed on top of a foundation to keep it level and steady. Foundation designs such as pier, floating slab and pit are most common. The best foundation depends on the needs of the application and environment.
   
   Pit-type scales are more expensive to construct but sit flush with grade, eliminating the need for ramps and providing easier access to components. They are common in colder climates but require sump pumps or drainage systems to handle water accumulation.
   
   By contrast, above-grade or “low-profile” scales are generally more economical and popular. These require ramps and level approaches and need more frequent cleaning beneath the deck, but they are less costly and easier to relocate.
2. Weighbridge. The weighbridge is the large steel or concrete deck that trucks directly drive over. It houses the load cells and wiring. Ease of installation and access points to load cells depend on the manufacturer.
   
   Platform size is a critical choice because it cannot be changed after installation. Common sizes range from 10 to 14 ft. wide and up to 200 ft. long, with 11 ft. x 70 ft. among the typical specs. Operators should consider not just current fleet sizes but also potential future vehicle requirements when choosing a deck.
   
   Material choice also matters. Steel platforms are less expensive and easier to relocate, but they can be slippery and corrode over time. Concrete decks cost more upfront, require curing and are difficult to move. But they provide better long-term durability in high-traffic operations.
3. Finish. The scale’s finish protects it from the elements. This is typically done with urethane liquid paint or powder coating. The color varies depending on the manufacturer or customization opportunities.

Alternative truck scale designs

Stationary truck scales function with these components. However, different site conditions or mobility requirements may call for alternate configurations:

• Portable scale. A portable truck scale uses wireless wheel pads positioned under each truck wheel. The weights from each pad are sent to a remotely paired indicator to calculate the nonlegal for trade weight. Large, single-draft portable truck scales are another alternative. These are suited for temporary applications but can be moved using equipment. These scales are legal for trade.
• Axle scale. An axle scale is a smaller device, so it weighs each axle individually. Then, the junction box calculates the overall weight. This is known as axle weighing. Single-draft weighing, meanwhile, occurs when a whole truck is weighed at once. Scales that use axle weighing are not legal for trade.
• In-motion weighing system. In-motion weighing relies on an indicator with in-motion software and a speed sensor. Using a single-draft in-motion weighing system, vehicles are weighed while crossing the scale at low speeds, reducing the time trucks spend idling.

Calibrating scales

There are four common calibration methods that can be used to check or verify the accuracy of a scale: using calibration weights, using an object from a calibrated scale, using material to substitute for weights, and calibrating with a simulator or theoretical calibration.

1. Using calibration weights. Using certified calibration weights, or test weights, is the most accurate method for calibrating a scale – and it should be a first choice. This is also the only legal-for-trade method that can be used to calibrate scales. 

It’s essential to review “NIST Handbook 44” to ensure you’re using the correct class and amount of weight for the capacity of your scale during calibration procedures. Generally, you’ll need weights that equal at least 12.5 percent of the scale’s capacity, though some lower-capacity scales may require weights equal to the total capacity. 

For example, if you have a scale with a 50-lb. capacity, “Handbook 44” recommends using calibration weights equivalent to 50 lbs. to calibrate the scale.

While it is recommended you use certified calibration weights to calibrate your scales – and it is necessary to do so in legal-for-trade applications – there are some instances when calibration weights may not be available. Still, perform a scale calibration through this primary method with certified calibration weights whenever possible.

2. Using an object from a calibrated scale. If you have a scale known to be accurately calibrated, you can use it to help calibrate another scale if calibration weights are not available. 

To compare the scales, place an object on the calibrated scale and record the exact weight. Then, place the same object on the uncalibrated scale to ensure it produces the same weight reading. The object works as a temporary substitution for calibration weights to check accuracy quickly.

This method is helpful for heavy-capacity scales, such as truck scales. A truck could drive into a calibrated scale, record the weight and then drive onto an uncalibrated second scale to check the accuracy.

3. Using material to substitute for weights. This method isn’t as accurate as using certified calibration weights, but it can be used if you don’t have enough weights to meet the minimum requirement of 12.5 percent of the scale’s capacity. 

After performing an initial calibration with the weights you have, remove the weights and replace them with products or material – and then add the calibration weights back to see if the scale is returning the expected amount of weight.

4. Calibrating with a simulator or theoretical calibration. The final method is using a simulator, or theoretical calibration, to calibrate a scale only when you don’t have any calibration weights. This is the least accurate calibration method and should never be used in a legal-for-trade application. 

After using this method, you should return to the scale with test weights to perform a full calibration.

This is a complex process with room for error because numerous calculations are involved. You will also need additional information about the system, such as excitation voltage from the indicator and millivolt output of the load cells. 

Because you’re using a simulator connected to the weight indicator, you won’t be able to properly exercise the scale or account for environmental factors during calibration. You will also need to “re-zero” the system after the calibration to account for the weight of the scale’s top plate on the load cells, further adding to the inaccuracy of this calibration method.

Scale maintenance

Routine maintenance is essential to keep truck scales accurate, reliable and in service. The following five tasks should be part of every scale maintenance program, regardless of season:

1. Regular cleaning. Keep truck scales free of debris, dirt and other obstructions that interfere with weighing accuracy.

Every scale’s weighing will be affected if something external is touching the platform. With truck scales, debris building up between the scale bridge and end or pit walls – or underneath the scale around the foundation – can become problematic. 

Daily visual inspections are recommended to ensure the platform is clean. Check beneath the weighbridge for debris buildup between the foundation and weighbridge, as well as between the weighbridge and end or pit walls. Check all load cells, too, and clear debris around them. 

Additionally, wash out around the base and end walls, as needed, to keep the scale platform free and clear of obstructions. 

Some truck scales utilize axis load cell stands that position the load cells up high within the load cell pocket. In these cases, debris buildup around the base won’t affect weighing performance, and there are no moving parts below the scale deck.

2. Mechanical checks. Inspect components such as load cells, junction boxes and cables for signs of wear, damage or corrosion. Regular checks help identify issues before they lead to significant problems.

Many truck scales include rodent protection that encloses load cell cables in metal conduit and features metal trays above and below the load cell pocket to prevent rodents from chewing on wires. Check the ground connections to make sure the cables are tight and free of corrosion. This helps to protect your scale from lightning strikes, which can cause serious electrical damage. 

Also, some truck scales do not require junction boxes because the load cells daisy-chain to one another and the home run cable runs from the last load cell to the weight indicator in the scale house. This type of digital scale provides individual load cell diagnostics.

3. External check rod adjustments. Some truck scales require external check rods to limit the movement of the scale platform to ensure accurate weight readings from the load cells. Check rods help to maintain platform alignment and prevent excessive side-to-side or end-to-end movement, which affects the accuracy of the measurements.

Some truck scales employ axis frictionless load cell stands that provide gravity-driven dynamic centering, because the entire scale platform rests on durable ball suspension that restrains deck movement and vibration. With these scales, no external checks or maintenance are required.

4. Weatherproofing. Seasonal weather changes can affect truck scale performance, so ensure all weatherproofing measures are in good condition to protect scales from rain, snow and temperature fluctuations.

Remember that some load cells are completely encapsulated within the load cell body to protect them internally and externally against moisture ingress, which is the most common factor affecting load cells in truck scales.

5. Scale calibrations. High-traffic truck scales performing 150 or more weighments per day may require calibration multiple times a year due to high volume. They are typically calibrated at least two to three times per year by an authorized scale service company using a test weight truck or cart.

For lower volume use, an annual calibration is typically sufficient. But environmental factors and specific operational demands may necessitate more frequent calibration. 

Additionally, any time a scale component such as a load cell, junction box or check rod is replaced or adjusted, a scale calibration is necessary using a test truck or cart. 

Some truck scales do not have junction boxes or check rods, which are common points of failure that can cause downtime and costly calibrations.

By prioritizing these maintenance tasks, aggregate producers can ensure their truck scales remain accurate and reliable, minimizing downtime and maximizing productivity.

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