What Concrete Buildup Costs a Ready-Mix Fleet

Cured concrete in a mixer drum is weight your trucks haul on every trip and never bill for. This guide works out the concrete buildup cost for a ready-mix fleet in plain arithmetic: what an inch of buildup weighs, how much payload it takes off each load, what that adds up to in a month, and what getting it out costs on top. You also get a way to measure the buildup on your own trucks, a routine that keeps it thin, and what to order.

Where the cost comes from

Every discharge leaves a little concrete behind on the fins, the head, and the shell. Whatever is not rinsed out before it sets cures in place, and the next load bonds to it. Over weeks it becomes a lining of old concrete, and that lining costs you in 4 places.

• Payload. When a truck is loaded to its legal weight limit, every pound of cured concrete in the drum is a pound of fresh concrete it cannot carry. When the truck fills by volume first, the lined drum holds less than its rating.
• Fuel and wear. The buildup rides out with the load and back with the empty truck, every trip. The engine, tires, brakes, and drum drive handle that weight each time, and it earns nothing.
• Mixing and discharge. Buildup rounds off the fins and then buries them. The drum mixes and discharges more slowly, and a load that hangs up leaves more behind to cure, so the buildup feeds itself.
• Cleaning. Once it is thick, it comes out with a chipping hammer or a dissolver routine, and either one takes the truck off the schedule for a while.

Payload is the easiest to put a number on, so start there.

How to work out the concrete buildup cost for your ready-mix fleet

The arithmetic needs 3 numbers: how thick the buildup is, how much steel it covers, and how many loads the truck runs. This guide assumes normal-weight concrete at 150 pounds per cubic foot for cured buildup and fresh concrete alike. An inch is 1/12 of a foot, so each inch of buildup adds about 12.5 pounds for every square foot of steel it covers.

The example assumptions

For example, take a truck with a 10-yard drum. The numbers below are assumptions for the arithmetic, not measurements of any particular truck:

• The buildup covers 200 square feet of fins, head, and shell at an even thickness. Real buildup is uneven, and your coated area will differ.
• The truck is loaded to its legal weight limit on every trip, so each pound of buildup comes off the payload.
• It runs 4 loads a day, 5 days a week: 20 loads a week.
• A month is 4 weeks, or 80 loads, and a ton is 2,000 pounds.
• A cubic yard of fresh concrete weighs about 4,050 pounds: 27 cubic feet at 150 pounds each.

The arithmetic

At 1 inch, the buildup is 200 square feet × 1/12 foot = about 16.7 cubic feet of cured concrete. At 150 pounds per cubic foot, that is 2,500 pounds, or 1.25 tons, of dead weight in the drum. On a truck loaded to its weight limit, those 2,500 pounds come off every load: about 0.62 cubic yards of concrete (2,500 ÷ 4,050) that stays at the plant. At 20 loads a week, that is 50,000 pounds, or 25 tons, a week, and 100 tons, about 49 cubic yards, over a 4-week month. That is close to 5 full loads for a 10-yard drum.

The table runs the same arithmetic for 4 thicknesses.

Buildup thickness	Cured concrete in the drum (200 sq ft × thickness)	Added dead weight per drum (× 150 lb per cu ft)	Payload lost per load (at the weight limit)	Loads per week	Payload lost per month (80 loads)
1/4 inch	4.2 cu ft	625 lb	625 lb, about 0.15 cu yd	20	25 tons, about 12 cu yd
1/2 inch	8.3 cu ft	1,250 lb	1,250 lb, about 0.31 cu yd	20	50 tons, about 25 cu yd
1 inch	16.7 cu ft	2,500 lb	2,500 lb, about 0.62 cu yd	20	100 tons, about 49 cu yd
2 inches	33.3 cu ft	5,000 lb	5,000 lb, about 1.23 cu yd	20	200 tons, about 99 cu yd

Every row scales in a straight line: double the coated area or the loads per week and the loss doubles. For a fleet, add up the trucks. For example, 5 trucks each carrying 1 inch would give up about 500 tons of payload, roughly 247 cubic yards, in a 4-week month.

If your trucks fill by volume

If a truck fills its drum before it reaches the weight limit, the buildup costs room instead of pounds: in the example, 16.7 cubic feet of the drum is taken up by old concrete. The fuel, wear, and mixing costs do not go away, because the weight still rides along and the fins are still buried.

Measure it on your own trucks

The example is a starting point. Your own numbers are better, and most of them are already in the yard.

• Weigh the truck empty. On a truck scale, with the fuel and water tanks at a known level, compare today’s empty weight with the truck’s empty weight after its last full cleaning. The difference is a close reading of the buildup.
• Log it. A weekly or monthly empty weight shows which trucks are gaining, before anyone looks inside.
• Look through the hatch. Fins with clean, sharp edges are carrying little. Rounded fins, or fins you cannot see, have been carrying weight for a while.
• Count the loads. Dispatch or ticket records give loads per truck per week.

Then run the same formula on your numbers:

• Pounds lost per load = inches of buildup × square feet covered × 12.5, or the weight difference from the scale
• Pounds per month = pounds lost per load × loads per week × 4
• Tons per month = pounds per month ÷ 2,000
• Cubic yards per month = pounds per month ÷ 4,050

Multiply the cubic yards by what a delivered yard earns your operation and you have the payload side of the cost in dollars. Fuel, wear, cleaning, and the time the truck spends out of service come on top.

What getting it out costs

Cured buildup does not come off with the rinse hose. Once it has bonded to the steel, the usual choices are a chipping session or a dissolver routine that softens it first.

Chipping

Chipping puts a person inside the drum with a hammer, and the truck earns nothing until the job is done; the thicker the deposit, the longer the job. Each blow that breaks concrete loose also hits the fin or shell under it, and a gouged, rough fin gives the next load a better grip.

The dissolver routine

An acid-based concrete dissolver goes onto the cured buildup and stays there until it softens and loosens; then the softened material pressure-washes off. Heavy deposits get another application. The cost is the product, the wash-bay time, and the labor to spray or foam it on and rinse it off, in the PPE the SDS calls for. No hammer touches the fins.

Thin buildup is the cheap case twice over: it comes off in fewer passes, and it has taken less payload in the meantime. In the example above, a truck carrying 1 inch gives up about 49 cubic yards of payload in a 4-week month. Set that against the cost of a treatment; that comparison is the case for treating on a schedule.

A routine that keeps the cost down

The cheapest buildup is the kind that never cures. Most of the routine is habit.

• Rinse after every load. Wash the drum out before anything sets. Fresh concrete comes off with water; cured concrete does not.
• Watch the empty weights. Treat a truck when its empty weight starts to climb, not when the fins are gone.
• Treat on a schedule. Slide Off, used as supplied, or Slide Off+, foamed on at 5:1, on a set interval keeps the deposit thin.
• Keep the heavy-duty product for heavy buildup. Blaster, the strongest cement dissolver in the line, is for drums that have gone too long between cleanings. Bring a drum back with it, then hold it with the regular routine.
• Include the chutes and hopper. Buildup there rides along too, and all 3 concrete products list chutes, hoppers, and discharge steel among their uses.

The outside of the truck is a separate job: see the Fleet wash category.

What to order

For mixer drums, chutes, and hoppers on a regular schedule, start with Slide Off or Slide Off+. Slide Off is an acid-based concrete dissolver, pre-blended and ready to use straight from the drum, with no mixing step. Slide Off+ is a concentrate of acids, surfactants, wetting agents, foaming agents, and corrosion inhibitors: diluted 5:1 with water, the foam clings to drum fins, blades, and vertical steel while it works, and the inhibitors protect the metal underneath. Both list steel, painted steel, rubber, and plastics as their surfaces.

For drums that have gone too long between cleanings, Blaster is the hydrochloric acid concrete remover concentrate, diluted 5:1, for the buildup a milder dissolver leaves behind. Its surfaces are steel and rubber; test painted and aluminum surfaces first. All 3 are in the Concrete category.

Slide Off comes in a 55-gallon drum or a 330-gallon tote, and Slide Off+ and Blaster in a 55-gallon drum or a 275-gallon tote. At 5:1, a drum of either concentrate makes 330 gallons of use solution and a tote makes 1,650. Prices are on each product page and exclude freight, which is calculated at checkout on the pallet count. Tote quantities, standing orders, and fleet programs can be quoted by phone from the Kirkwood sales office.

All 3 are acid-based. Read the label and the SDS before use, and wear the PPE the SDS calls for. Slide Off and Slide Off+ call for gloves and eye protection; Blaster calls for acid-rated gloves, eye protection, and a face shield. When diluting a concentrate, add the product to water, never the reverse. A Safety Data Sheet ships with every order, and a technical data sheet is available on request.

Run the numbers on 1 truck this week: weigh it empty, count its loads, and multiply. If the answer is more payload than you want to give away, call 314-266-4600 (toll-free 888-556-0502) or request a free sample and try it on your own buildup before you order for the fleet. Samples are for fleets, plants, and crews evaluating a product for purchase, 1 per product per company.