I’d like to thank Michael Whisonant for being a guest blogger this month. Mike is Director of Technical Services for GCC America. In this capacity, he oversees multiple plants across the U.S. If it has to do with concrete QC, Mike has done it. Since it is football season here in the U.S., I think you will enjoy his perspective on concrete QC. For the benefit of our non-U.S. readers, I have added a few comments in [brackets] to explain some of the terms. – Jay Shilstone
The X’s and O’s of Concrete Quality
- Michael A Whisonant PE FACI
Historically our industry, in terms of quality, has put its efforts into making cylinders and testing air. This is what I call “playing defense” when it comes to quality. When you play defense your goal is to prevent people from scoring against you, or preventing the other team from moving downfield. Sure you can score playing defense, and as the saying goes, “defense wins championships”. Though to follow the same saying, how many teams have won championships when their offense never even took the field?
With the current economy, and especially with the ever increasing demands of more technical specifications and more demanding criteria to meet, Ready Mix companies need to be able to be play offense and defense in terms of their quality effort. No longer can a company purely rely on someone stationed at a job site to back up trucks, slump loads and save a load of concrete here or there when something goes bad. The effort has to be one of ensuring that you batch the Right Concrete to the Right Job at the Right Time, Safely and, yes, even with a Smile.
Batching the right concrete, can mean a lot of things to a lot of people but when it comes down to it, if you are playing offense you need to be able to spread the field and score from anywhere. That simply means in part:
- Knowing your materials and how they work together
- Knowing your mixes, their abilities as well as their limitations
- Truly understanding the specifications and what mixtures to use
- Being able to sell the right value added products on the job
- Knowing your contractor and their abilities
- Ensuring that your plants are producing concrete accurately and consistently
- Controlling the concrete that leaves the gate ensuring its uniformity
Understanding your materials is one of the most overlooked aspects to making good concrete. By knowing exactly how your materials work together, understanding how each material affects water demand, air content, and slump life, as well as compressive strength can make or break a company’s quality reputation. Substituting materials that are not equivalent because you don’t understand them is simply turning the ball over in the red zone. [Giving the ball to the other team when you are near their goal line.]
Truly understanding your mixes can be an excellent means of not only producing quality concrete, but making money as well. Are your mixes over cemented? Under cemented? Do they have the correct water content for the slump demanded? Will they meet the customer’s needs? In the graph below concrete trials from different parts of the country with similar w/cm ratios but widely varying materials are shown. It is pretty simple to see that a swing of 10, 15, 20 lbs. or more of cementitious materials can be made when choosing the right combinations of materials and knowing that fact is one of the keys to reducing costs. In other words having a solid running game and a good left tackle.
Once you have established what materials to use and what mixes to use on a particular job your offensive planning is only part way done. Any coach will tell you that you need to be able to adapt to the opponent at hand, you need to design your offense to best take advantage of the situation. If your mixes are good for general use but the contractor wants to do something special in placement, or the structure itself doesn’t lend itself to normal methods, are you prepared for that? Choosing the right mixtures for the job can be a big factor in a successful job. In short, are you using the right game plan offensively?
Will the contractor be able to take advantage of using a HRWR on the job? Is the application right for shrinkage reducing admixtures? Are you missing out on the use of fibers? The value added opportunity is often talked about but are we missing opportunities? Are we missing the open receiver in the end zone? Is this job going to result in a touchdown? A field goal? Or another 3 and out, value added sales and knowing your materials and customers can make your red zone percentage soar. [Scoring often]
One thing that is very often overlooked is, just how accurately you are producing the concrete that you wanted to produce. Whenever I walk into a plant the first time I ask the plant manager how accurately they batch their materials. In most cases the response is “pretty good” or “right on”. Once it is measured that is not always the case. Finding out the Cost of Poor Accuracy or COPA reveals just how much money is not staying in the company’s pocket. Some might consider this a holding call or a false start [penalty] on first down. This kind of thing puts you in a hole before you even start moving the ball. In the case below this company is losing $0.06 per yard on average before the truck even leaves the gate.
The final point here in this overstretched analogy is to test your concrete as it leaves the plant. How many times do we “think” we batched good concrete but don’t really know until it shows up at the jobsite? How many times are we counting on the last bit of quality just to happen? There are numerous things that can happen to the best designed concrete that can ruin it. Are you really confident enough to think it won’t happen? Do you think that the ball won’t get turned over unexpectantly? We need to be sure that we at least have a plan to at least randomly test loads, to make sure that we have produced what we wanted to produce.
From this point simply taking the results, monitoring your standard deviation and adjusting your mixes accordingly seems an easy step but is very easily forgotten. A simple reduction of 100 PSI in your standard deviation can not only provide better and more consistent concrete to your customers but also save money by reducing the overdesign requirements of concrete mixtures thus reducing the cement content demand of the mixture itself. The example below for a 4000 PSI mix would indicate reducing the standard deviation from 500 to 300 could mean a savings of about 25 pounds of cement per yard. How much money is that worth to you?
Can you finish the drive? Can you run an effective two minute drill? This is where you can become a champion or just another team in the league. Which one are you?