By Del Williams
For ready-mixed concrete plants, any delay in washouts—whether due to truck operators driving long distances or the complexity of the process itself—can reduce productivity and profitability. After each delivery, washing out the trucks and equipment is essential to meet mix specifications, reclaim unused material, and keep equipment clean. Ideally, washouts should be fast and efficient, with all reusable material reclaimed.
The challenge is that traditional washout techniques can be time-consuming and labour-intensive, often involving multiple steps. As a solution, industry innovators have created systems that dramatically streamline the washout process, which saves considerable time, labour, and money. These systems can recover sand, stone, and cement for re-sale or reuse using recycled water in a closed-loop system.
Inefficient waste material handling
For ready-mixed operations, washing out concrete trucks and equipment is essential to reclaim unused material. It also prevents buildup on the equipment and makes meeting mix specifications easier. However, the typical practices are inefficient, involving multiple processing and material handling steps.
The washout process for concrete trucks involves several steps to manage the residual materials effectively. After a concrete truck has finished its delivery, the driver fills the truck’s tanks with water from the plant’s supply to rinse out the mixing barrels. The truck is then driven to a designated washout pit where high-pressure water is used to clean the truck and equipment, allowing excess concrete to wash into the pit. The washout water, containing suspended cementitious solids, is allowed to settle at the bottom of the pit or settling pond. Once the solids have settled, they can be removed and disposed of properly, while the clarified water may undergo further processing or disposal as needed.
Another concrete reclamation method, concrete curing, involves spreading the leftover concrete on the ground. Once the concrete has dried and hardened to a certain extent, it is typically broken into manageable pieces using heavy machinery or equipment. Crushing machines then process the broken concrete pieces further for use as recycled aggregate. This material can sometimes be used as a substitute for natural aggregates in new concrete mixes or other construction applications.
In all these conventional methods of concrete reclamation, truck drivers do not make deliveries during the time they travel to washout pits, settling ponds, or concrete curing sites. The extra material handling steps slow the process, increase labour costs, add to equipment wear and tear, and reduce the plant’s profitability.
In washout ponds and pits, the cost to replace make-up water, often purchased from a local utility or pumped from wells, can also add up quickly. The ponds and pits usually require continual maintenance to remain functional. Ponds typically need continual sludge cleanup. As pits fill with washout material, they must be excavated and carted to a facility that charges for recycling. It is a messy job that coats equipment with cement and can cause serious maintenance headaches. Pond liners can also become torn and require additional maintenance and repair.
In the case of a ready-mixed concrete company, about every three months, they had to excavate the pit of washout material, put it in a stockpile, and let it dry out. The material was mixed with clays, fines, stone, and hydrated cement. Deemed as a useless product, they had to pay to have it hauled to a concrete recycling facility a few miles away. Previously, it would cost about $200 per load to dump the material (not counting the truck rental); today, it would cost about $500 per load.
The cost of water was also an issue, as using metered city water meant paying for any wasted water. As the company offered about 25 different concrete mixes, the wasted water at the end of each quarter was excessive. Additionally, space was constrained with the onsite pit and stockpiles since the company operated on a 0.6 ha (1.5 acre) site.
Faster, more efficient washout
Rather than have concrete truck operators waste time driving to remote locations for washout as this machine is conveniently located at the plant. Water is also readily available at the washout system. There is no running back and forth from one site to another, and a significant amount of time is saved compared to the previous washout pit. There is also no water wastage to wash out the trucks, only to have it evaporate or hydrate into the ground.
The driver backs up the concrete truck to the machine to perform a washout. The machine adds recycled water to the truck’s rotating cylinder, which mixes the water with any remaining concrete for a couple of minutes. The truck then dumps the washout water and concrete into the machine, which processes and reclaims it. This one-stop approach allows for faster washing out of concrete trucks.
Further, unlike traditional reclamation-only units, the concrete washout system does not require settling ponds, washout pits, or filter presses because it has a built-in water clarification capability.
The washout system provides concrete reclamation and water handling within one self-contained, closed-loop unit. The machine separates and discharges the sand and stone, enabling complete recovery of these items. Sand is not washed out of the aggregate. Spent cement is discharged separately, and a loader can easily handle this cement as a dry, clay-like product. The water is directed into a separate area of the machine, where it is clarified and reused for washouts.
One unique aspect of this approach is that there is no need to “dribble” or “slowly meter” the washout material into the machine. The system is designed to take in 9 m3 (8 yd3) in four minutes or less.
With high-speed washouts, the concrete plant can run fewer trucks with less labour and material handling while still delivering the same or more material. Regarding jobsite conditions, the machines are moveable/semi-mobile and can be installed at individual jobsites, but most installations are permanent installations at the batch plant.
Further, the system separates the clays and cement from the sand and gravel. Since the machine recycles the water, this approach eliminates the cost of replacing makeup water in ponds and pits, which lose water constantly due to seepage and evaporation. There is also no pond sludge to clean up and no pit to excavate and maintain.
The approach also saves concrete plants considerable space since one compact unit accomplishes the truck washout. Without settling ponds or pits, the plant can use the space more productively as storage for concrete products and inventory or other needed applications.
For concrete plants where settling ponds or pits are still in use, the reclamation and water-handling system works similarly as an efficient washout material reclamation solution because it can still separate sand, aggregates, and cement. However, this system directs washout water to the plant’s existing settling ponds or pits to be clarified.
Conclusion
The most advanced units allow a driver to complete a washout in minutes at a single onsite location without a washout pit, settling pond, or presses. Water usage is also reduced significantly because of the reuse process.
The systems support washout standards by providing fast, efficient, complete washouts while recovering all materials for re-use and/or disposal. This is all done while maintaining clean worksites and helping to meet Environmental Protection Agency (EPA) and the Department of Natural Resources (DNR) requirements— equivalent of the Canadian Environmental Protection Act (CEPA) in Canada.
Although washout pits and ponds are common, concrete producers who use innovative options can streamline the washout process and boost their productivity. With the sophisticated systems available today, plants can reclaim any leftover concrete materials faster and more profitably than ever before.
Author
Del Williams is a technical writer based in Torrance, Calif. He writes about health, business, technology, and educational issues, and has an M.A. in English from California State University (CSU) Dominguez Hills.
The post From hours to minutes: Streamlining the concrete reclamation process appeared first on Construction Canada.
