![]() ![]() You can then tell him what your application is, when you plan to place, and what the specification requires and he can develop the ideal mix. One way to get the right mix for your application is to have a great relationship with your ready mix supplier. Best Stamped Concrete Inc., Huntsville, AL. Properly proportioned mixes will remain beautiful for many years. Use this handy concrete calculator to quickly calculate how many yards or bags of concrete you'll need for your project. Related: How to Color Concrete Mix HOW MUCH CONCRETE MIX DO I NEED? With decorative concrete, surface hardeners will provide a higher strength, more wear resistant and less permeable surface layer, the overall concrete strength can be less. ![]() With slabs, shrinkage is the number one concern and lower strength concrete (with less cement paste) will often shrink and curl less. Nothing sours a client more than a beautiful floor that is cracked or spalled, or a decorative wall that is honeycombed. Durable concrete must resist freeze-thaw action and prevent chloride from penetrating to the reinforcing steel to contribute to corrosion.Īppearance issues are obviously more important for decorative concrete than other applications. Durability is achieved by getting a low-permeability, low-shrinkage concrete that has the proper amount and distribution of entrained air. Long-term durability is at least as important as placeability and strength, but it is sometimes sacrificed if there are compromises to be made. (See Using Fibers for Secondary Reinforcement.) Fibers will not provide structural reinforcement, however. However, synthetic fibers, like Re-Bind, have proven to be beneficial as a way to reduce shrinkage cracks. For flatwork, though, strength is seldom the controlling factor, because higher-strength concrete mixes that produce very stiff concrete can result in more shrinkage which shows up as curling and cracking. In structural concrete applications, strength is indeed critical, since that's what the designer is counting on to hold up the building. The International Residential Code, for example, specifies that interior slabs have a minimum compressive strength of 2500 psi. Strength is nearly always specified for a concrete mix. The classic way to measure placeability is slump, although two different mixes can have the same slump and behave very differently depending on the aggregates, the air content, and the admixtures. The ability to be pumped is another consideration. Placeability includes a mix that doesn't segregate but that can be consolidated. Placeability is simply the traits that the wet or plastic concrete has that allow it to be placed and finished. Placeability is an important attribute of a good mix design. ACI 211.1 notes that the "selection of concrete proportions involves a balance between economy and requirements for placeability, strength, durability, density, and appearance." Finding the right balance to achieve all these requirements comes mainly from experience. The right ratio of concrete mix materials can solve problems and the wrong mix can create them. The type of concrete work you do will determine the type of mix you need: Rather than only specifying how much cement is in the mix, we should be considering things like permeability, shrinkage, workability, pumpability, stampability, and stainability. That mix could be completely wrong for your application and could even be inferior concrete. A bag is 94 pounds of cement, or about 1 cubic foot but if you order a 6-sack mix, all that tells you is how much portland cement is in the mix. When most contractors think about concrete mix design-if they think about it at all-the first thing that comes to mind is "bags" or "sacks." In the old days, when most concrete was mixed on site, cement was purchased in bags. It is everything that makes the concrete work well for your application: What slump do you need? What strength? Do you need entrained air? What happens if the day is particularly cold or hot? What size of aggregate is best? Should you ask for fly ash in the mix? Just what is concrete mix design? The American Concrete Institute doesn't even use the term, preferring mix proportioning, but mix design is really more than simply coming up with the proportions of each mix constituent. Learn about which mixes should be used for stamping, staining, and overlays. ![]()
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