Troubleshooting Concrete Problems

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By G. Terry Harris Sr.

Using a detailed process to analyze an issue in the plant, report the error and quickly determine corrective action.

No matter how much concrete you batch in your precast plant, at some point you will have problems with its performance – whether it’s due to low strength, slump loss, inconsistent entrained air or another issue. While quick action is critical when these problems occur, it is also important to have a process to follow for solving these problems and avoiding a reoccurrence.

Troubleshooting or problem solving

Before taking any action, be clear about what you want to accomplish. Troubleshooting can occur on the plant floor or during production and is often referred to as “putting out the fire.” Some problems must be solved immediately to continue production. For example, with a batch of concrete that has excessive slump, you likely won’t take the time to determine the exact cause of the high slump, but will reduce the water or admixture content so the next batch is within the specified limits. Thus, you’ve solved the immediate problem and production can continue. Using this same example, a detailed process can be followed to determine why that particular batch was wet and what steps can be taken to prevent future slump problems.

Problem solving steps

There are a number of tools available to help with the problem-solving process. Part of Six Sigma is the DMAIC cycle: define, measure, analyze, improve and control.

• Define the problem – Concrete problems are seldom simple or one-dimensional. Is the slump inconsistent because the air is fluctuating, or is the air fluctuating because the slump is inconsistent? An accurate problem statement is key.
• Measure performance – Anecdotal data is often useful in problem solving, but hard data is required to determine current performance and improvement over time. For example, slump measurements are required to accurately gauge performance. It may be necessary to increase the frequency of testing temporarily to collect more data.
• Analyze the data – Once collected, analyze the data to assess if the root cause can be determined or if more information is needed.
• Improve the process – Once you have determined the root cause, you can then make changes in procedures or materials to eliminate or reduce the frequency of the problem.
• Control – Develop new control procedures to ensure the improved process is followed.

Finding the root cause

After you have a defined problem statement – which is often more difficult than it sounds – and have collected sufficient data, you can determine the root cause of the problem. One of the first steps to take in any problem-solving investigation is to talk with the people involved in the process. Continuing with the example of excessive slump, at a minimum you need to interview the batch technician, loader operator, delivery vehicle operator and quality control technician.

While you review and analyze the data, the additional information collected from those involved in the process is often invaluable. There are times when you can easily identify the root cause of an issue through the interview process. For example, in looking at the data and interviewing the key production staff, you may learn that the first batch after the lunch break always has a high slump. You can then determine the difference of the after-lunch batch and take steps to correct the issue. In addition, here are two tools that are easy to use in a root cause investigation:

5 Whys

This is a very simple tool, but the answers may be difficult to determine. The purpose of the 5 whys is to dig deeper into each answer that is given during your investigation. Continuing with our slump example, here is an interview scenario using the 5 whys.

Q: Why was the batch rejected?
A: Slump was too high.

Q: Why was the slump too high?
A: There was too much water in the mix.

Q: Why was there too much water in the mix?
A: The aggregate moistures were incorrect.

Q: Why were the moistures incorrect?
A: The moisture probes were turned off.

Q: Why were the moisture probes turned off?
A: They needed to be calibrated.

In this example, the rejected high-slump batch resulted from aggregate moisture probes that were turned off because they needed to be calibrated.

Fishbone diagram

The fishbone diagram is another tool that can be used to determine the root cause of a problem. The problem is the head of the fish. In this case, it’s rejected batches. The major components of the mix are on the bottom and on the top are production processes. Each of the “fish bones” can be filled in with possible rejected batch causes for each step or material.

Have a process

Regardless of the problems you encounter while producing concrete, having a process that you follow to solve each problem is important. Using the tools like 5 whys and the fishbone diagram can make solving problems easier, but you can also develop your own tools and processes. The key is having a formalized process that you can follow when problems occur to make solving problems easier and to improve and create controls to reduce them.

G. Terry Harris is director of technical services at GCP Applied Technologies, Cambridge, Mass. He has 37 years of experience in the concrete industry, including ready mix, precast, prestress, masonry and admixtures, and is an active participant in ACI, ASTM, NRMCA and NPCA.