When planning a construction project, it helps to understand the types of cement you may use, and methods of shipping it to a job site. Although many general contractors use the services of a cement mixer to deliver premixed concrete to a worksite, companies with larger operations will ship concrete ingredients including cement to the site and mix it themselves. This saves money, time, and increases control over quality systems.
Concrete vs. Cement
Concrete is the substance formed when cement is mixed with water, gravel and other fine rock particles to form a hardened building material. Cement is the chemically designed powder which hardens into a rock-like substance when combined with water.
As seen in the following types of cement, building uses for cement include several uses which do not involve turning it into concrete. For most construction companies, though, cement is always a component part of creating concrete.
Type I – General Purpose
Like all general purpose things, Type I cement is designed to be used in most situations but not be the best option for many significant situations. For building sites with no sulfates to degrade the quality of the cement, with adequate time to set the cement, and no need for long-term slow setting, this is the type of cement to use.
General purpose cement gives affordable and consistent sets for various concrete and cement mixtures.
Type II and Type V – Moderate to High Sulfate Resistance
There are two types of normal cement (called Ordinary Portland Cement, OPC) which is designed to prevent cracking caused by a hydration reaction that happens when sulfate ions enter a concrete mixture from the outside environment.
Both of these types (II and V) reduce the amount of tricalcium aluminate and keep higher levels of tetracalcium alluminoferrite. Although the chemistry of this cement is rather complicated, the purpose is relatively simple. One mineral (the cement industry calls it C3A) produces water molecules that stay in the concrete. This water causes damage to the structure of the concrete. The other mineral (C4AF) does not release as much water into the crystalline structure of the concrete.
Type III – High Early Strength
This cement is one of the most important innovations in the construction industry, especially for fast-moving projects and cold-weather setting of the concrete. Early strength cement reacts faster when combined with water. This enables companies to swiftly move on to the next stages of construction after pouring concrete.
The drawbacks to Type III cement is a slightly lower final strength, higher heat of hydration and the fact that it sets so quickly. The vast majority of construction builds do not use the limits of concrete’s final strength, and heats of hydration also rarely affect a construction build. The main issues that a company faces are the cost differences, the time for construction, and the time for pouring the on-site concrete or concrete molds.
Type IV – Slow Setting
This type of cement is not used very often in construction any more, because the same long-setting results can be created using different blends of concrete. The purpose of slow setting concrete is to reduce the heat of hydration caused in extremely large concrete pours like building dams.
Whether used through the cement or the concrete mixture, slow setting concrete is designed to provide the highest final strength and least amount of heat released during the setting process.
Decorative cement removes some of the minerals that cause concrete to maintain its characteristic gray color. This cement has no C4AF and little MgO which takes the color out of it to make it white.
Decorative cement can be mixed with other minerals like iron oxide to create different tones and colors of the final concrete. In using decorative cement and concrete, the selection of aggregates is important as well as the color of the cement. The above link is a good primer on decorative concrete for more information.