A BRIEF LESSON FROM HISTORY.
We've all heard the stories about what happens when history repeats itself, but in our case, we intented to repeat what the Romans figured out more than 2000 years ago. Everyone knows that water is needed to make concrete, but there is a lot of confusion as to why. There is a general misconception that the water is added just to start the cement reacting, and once the concrete is in place the hardening process will be "helped along" by drying it out. Nothing could be further from the truth! Water is an integral part of the reactionary products that give cement paste and concrete its strength, and just about the worst thing that can happen to young concrete is drying out. In fact, cement paste and concrete will harden and gain strength underwater with time.
There are two primary reasons that drying is bad for concrete. First, the reactions between cement and water (hydration) continue for many days and weeks after initial mixing. If the water is removed by drying, these reactions stop and the concrete can't gain any more strength. Second, concrete shrinks when it dries. More specifically, the cement paste component of concrete shrinks, due to its pore system. This shrinkage is related primarily to the surface tension of water, and the same process is easily observed when a kitchen sponge dries out and shrinks to half its wet size. Why is this so bad for concrete? Unlike a sponge, a large section of concrete cannot shrink uniformly due to its larger size and weight . Instead, the surface dries out first while the interior remains moist. As the surface dries it tries to shrink, but cannot because the concrete next to in the interior is not shrinking with it. This puts the surface layer of concrete into a state of tension. When this tensile stress exceeds the strength of the concrete, it cracks. Cracks reduce the strength of concrete, make it less durable by offering easy access to water and corrosive ions, and of course are unsightly. For this reason, good contractors take careful steps to keep the surface of freshly placed concrete moist, often by covering it with plastic or moist burlap. This is particularly important on hot, windy days. Once concrete is older and stronger, it is able to resist the stress of drying without cracking. However, concrete at any age is better off moist than dry. Drying of cement paste, and the associated shrinkage, are an important aspect of the science of concrete and are discussed in more detail later in the monograph.
Another important issue associated with the mix water is the amount that is added in relation to the amount of cement. This important parameter is called the water/cement ratio, or "w/c", and it always refers to the weights of water and cement.... Although there are many aspects of the concrete mix design and the curing process that affect the final properties of the concrete, the w/c is probably the most important. If the w/c is too low, the concrete will be stiff and clumpy and will be difficult to place. However, the lower the w/c, the stronger and more durable the final concrete. This is easy to understand when one realizes that any space in the fresh concrete that is originally occupied by the mix water will end up as porosity in the hardened concrete. Porosity lowers the intrinsic strength and makes it easier for the concrete to corrode, crack, and spall. For this reason, the w/c should be a low as possible, meaning just high enough so that the concrete can be placed properly. This will depend on many factors, such as the amount, size, and shape of the aggregate, the fineness of the cement, the type of form or mold the concrete is being placed into, and the type of reinforcement. There are also special chemicals called water-reducers or plasticizers that can be added to the mix that will improve the workability and thus reduce the amount of water needed, but these additives are chemical based and are therefore not appropriate for use in NewRomanStone's 100% natural concrete. This is what drove us to learn the ancient ways of the Romans and rediscover an old method to make new concrete for our wine fermentation containers.
Specifically, Roman style concrete has withstood the test of time, both above and below the sea, as a material of near magical qualities, comprised of simple ingredients created by mother nature. Concrete is lime, an aggregate such as sand, clean water and volcanic ash commonly referred to as Pozzolan, named for the region in Italy where the ash in Roman concrete is believed to have originally been been sourced. When these basic materials are mixed with water, a process of crystalization and hardening begins and proceeds to grow in strength over time. Until the 1950's, all modern concrete was made with volcanic ash, but as modern roads and demand grew, a new source emerged called fly ash, which put volcanic ash mines out of business. Fly ash is derived primarily from the remains of coal burning plants and became the standard for the next 65+ years, until now. With a growing global awareness of the impact of toxic metals and chemicals that exist in modern materials, such as concrete, a new demand is emerging for natural, healthy products that will not leech into our soil, food and bodies. In our case, this has spawned a rebirth of natural volcanic ash mining for the creation of non-toxic concrete that our team at NewRomanStone is at the forefront of rediscovery, mastery and the recreation of pure, natural concrete like the Romans developed for winemaking and construction over 2000 years ago.
NewRomanStone worked for the better part of a year to recreate this ancient process, in partnership with some of the world's foremost experts in concrete who share our enthusiasm for recreating ancient Roman style concrete that will not alter the flavor of wine, and will withstand the test of time.
Sources:
http://iti.northwestern.edu/cement/monograph/Monograph2_2_2.html