Reducing Concrete Balling | Production Expert Randy Willaman

Techniques for Reducing Balling in Concrete

This month we will diverge from new and exciting technology to familiar and frustrating challenges and provide practical techniques for loading your trucks at a dry batch plant. My thanks to Tim Schiever of Advanced Batch Consulting, LLC for sharing his experience.

Mechanicals Matter

The ﬁrst technique for reducing balling in your trucks is to ensure that the discharge gates and valves for your dry material scales work well. This means no leaking air hoses or cylinders, no gate creeping, no binding/sticking, and certainly a clean and dry air supply. The key to eliminating lumps is consistent ﬂow and material blending. To start, set up these recommended guidelines for adequate scale discharge gate performance:

Aggregate Scale
Target rate of discharge should range from 100 to 400 lb./second
What	Why
Add speed controls to inching gates that provide a 3-4 second full close to full open and vice-versa.	Less movement by the gates with smooth motion and no jerking provides a faster tuning process. Longer gate pulses from the computer (i.e., 0.05 – 0.10 sec) instead of very short pulses (0.03 sec) push the limits of electric over air mechanisms.
Adjust the gate open/close pulses in the computer to move 1/4” per pulse.	Hopper scale lengths range from 8’ to 15’ (or longer). If the gate moves ¼” per side that is ½” total movement with up to another 100 lb./second leaving the scale. If your target is 200 lb./second, that is a big change.

Cementitious Scale
A 10” butterﬂy can dump 300 lb./second — Target rate of discharge should be between 30 lb./second to 75 lb./second
What	Why
Add speed controls to butterﬂy actuator that provide for a 3-4 second full close to full open and vice versa.	Less movement by the actuator with smooth motion and no jerking provides a faster tuning process. Longer gate pulses from the computer (i.e., 0.10 sec) instead of very short pulses (0.03 sec) push the limits of electric over air mechanisms.
Adjust the gate open/close pulses in the computer to move 1/4” per pulse.	When the butterﬂy moves ¼” per side, that is ½” total movement which increases cement ﬂow out of the scale.
Aeration System	Proper aeration is critical for successful outcomes. Do not assume the aeration system is working properly… conﬁrm it. Start the aeration on the scale either during weigh up or upon weigh complete. Shut off scale aeration when the vibrator is started.

Scale Parameter Setup

The ratio between discharge of aggregate to cement is critical. The goal is to achieve cement discharge throughout the aggregate yet not causing an overﬂow. This can be complicated by different strength mixes and load sizes. The COMMANDbatch system provides for adjustment of material discharge rates by mix type and is a useful technique for reducing balling in concrete in your trucks.

Aggregate Scale
What	Why
All head water and admixes in the front of the load before discharge of aggregate.	Don’t add water when sand is loading into the drum. When sand sticks, so does cement, creating ﬁn buildup.
Set the ‘Start Control After’, ‘Time Between Calcs’ to at least two (2) seconds (three is better)	The ﬂow calculations from E-Z CAL and COMMANDbatch are not accurate unless 2-3 seconds are allowed to pass. Making it quicker only makes it worse.
Set the agg ‘Initial Pulses’ time to achieve the desired ﬂow. Recommend 1.75-2.25 seconds.	This can be difficult if the gate open sticks due to stone in the bottom of the scale. Consider putting sand in ﬁrst.
Set the Adjustment pulses in the range of 0.07-0.09	Look for ¼” to ½” change per pulse.
If you don’t see the hourglass discharge of the aggregate, it conﬁrms the adjustment open/close pulses are correct and the ﬂow rate/adjustment pulses are not too frequent.

Cementitious Scale
What	Why
Set the “Start Control After” and “Time Between Calcs” to at least two seconds (three is better).	The ﬂow calculations from E-Z CAL and COMMANDbatch are not accurate unless 2-3 seconds are allowed to pass. Making it quicker only makes it worse.
Set the ‘Initial Pulses Time’ allows the cement to start but not at full ﬂow. Recommend 0.75-1.25 seconds.	The system will adjust to get to target ﬂow. Too high ﬂow at the beginning will push the cement past the aggregate causing head pack and balling.

If you see “some dusting” from the cement, then confirm the adjustment open/close pulses are correct and the flow rate / adjustment pulses are not too frequent.

Typical Dry Batch Sequencing

Managing the start of the materials into the truck is one of the critical techniques for reducing balling in concrete. While somewhat intuitive, ensuring a ‘slow but steady’ cement ﬂow rate will produce better results and less balling.

What	Why
Add initial water before aggregate starts	Don’t add water when sand is loading into the truck. Wet sand sticks to the ﬁns then cement sticks creating buildup.
Gate Open Timing: Agg Scale First open Cementitious Scale at three to ﬁve (3 – 5%) discharge and 4-7 second delay.	Allow 1 to 3 seconds of aggregate in the truck before discharge of the cement. Blending cement with the aggregate will keep the ﬁns clean. After aggregate and cement are complete add wash water into the truck.
The slower the ﬂow of cement into the truck the faster the overall loading rate can be. Use these numbers to start then increase for your fastest truck. Use the truck rate to slow down for the other trucks that need to go slower. Focus on getting the 5 – 6 bag mixes working ﬁrst before moving onto others.

Typical Flow Rate Values

Normal Aggregates
Cement content /yd.	Target Agg Flow Rate	Target Cem Flow Rate
470- 564	250 lb./second	45 lb./second
564-658	225 lb./second	50 lb./second
658-752	200 lb./second	55 lb./second

Lightweight Aggregates
Cement content /yd.	Target Agg Flow Rate	Target Cem Flow Rate
	160 lb./second	50 lb./second

Grout
Cement content /yd.	Target Agg Flow Rate	Target Cem Flow Rate
	125 lb./second	60 lb./second

1/2” Pea Gravel or Chips
Cement content /yd.	Target Agg Flow Rate	Target Cem Flow Rate
	160 lb./second	60 lb./second

Contributing Factors to Fin Buildup and Concrete Balling

What	Why
A head pack can occur when cement ﬂow starts too early and opens too wide, preventable by not opening the gate too far or all the way.	If the cement ﬂow is too fast the cement will push past the aggregate and pack at the front wall of the mixer.
Not enough head water.	Packing will occur.
Packing of cement on the third ﬁn of the truck.	The cement discharge boot may be too long. The cement boot should end with the aggregate boot in the raised up to 4” inside. The cement is directed to one side. The cement boot should empty in the center of the aggregate boot, which will envelop the cement to pull it into the truck rather than trying to push it in. This will also result in less dust.
Other factors
What	Why
Load size too large	Mix design, not enough room to mix
Too much head water	Too wet in front of load
Worn ﬁns on the truck	Unable to mix properly
Mix Design itself, sometimes split batching will help	Mix designs are designed to make concrete, not loading, easy.
Hot Cement	Increased stickiness

Closing Thoughts

Managing concrete production quality is a continuous process. Material gradation, plant wear, operator training, and mix design variance all have an impact. One of the important questions as a producer is to consider how to internalize the expertise needed so that these techniques for reducing balling in concrete are institutionalized. Invest in training in a batch system specialist within your company or look at outside resources such as Advance Batch Consulting.

As a key architect behind COMMANDbatch and REDI-VIEW, Randy Willaman brings decades of hands- on experience with concrete batching systems. Through his posts on the MARCOTTE Blog, Randy shares his unparalleled expertise and insights with concrete producers looking to maximize their system’s potential. Learn more about his services. Tim Schiever brings 40+ Years of experience making plants (Central Mix, Dry Batch, Horizontal, Dual Alley) run clean and eﬃcient with increased production.