Material selection while starting a trailer based concrete mixer company
It’s true that concrete is nothing more than sand, gravel, water and cement. However, the ratio of these ingredients is critical to making good concrete. Specifically, the ratio of sand to gravel. Too much sand makes for easy finishing, but weak concrete. Too much rock and there’s not enough sand to finish the mud at all.
When filling a concrete mixing trailerthe ratio isn’t as tightly controlled as it is for a truck at a ready-mix plant. Ready-Mix companies often pour spec mixes called out by an engineer. Some of these mixes have standards that locations using mixing trailers can easily match, such as for a house foundation or a long driveway. The size of the job, however, wouldn’t be suitable to do with small loads.
Other mixes need to be very tightly controlled, like for a bridge or dam and don’t lend themselves to concrete coming from a mixing trailer. When calibrating one of Cart-Away’s CBL Automated Loaders, we hold to a 56% rock/gravel and 44% sand ratio. With this ratio, we have tested concrete core samples at over 5400 psi at 28 days.
This ratio alone isn’t the only key to good concrete, though. It’s very important to have good material with a proper mix of different size particles within the rock and sand. Technically speaking rock and sand are both aggregates. In good concrete, these aggregates are actually a carefully measured mix of different-sized stones. The idea is to make a mixture of aggregates that will pack tightly together with small sand pieces filling the gaps between larger stones. Cement is the “glue” that holds this sand-and-stone stew together. The better the aggregate mix the better the concrete.
Too often, aggregates are looked upon as being merely inert filler materials. Yet, aggregates can greatly affect the quality of the finished product. Concrete with well-graded aggregates, properly proportioned, will require less cement paste for particle coating. In the long run, the quality aggregate can turn out to be the most important and economical material in the finished product.
Finding out how suitable your aggregates are can be done by looking at the sieve analysis of the materials. Most quarries are able to provide the analysis for their products. We at Cart-Away help our customers read the results an choose the best aggregates for their mixing trailer businesses. This is why we place material selection as a step in getting ready to start a concrete mixer trailer company.