Cement FAQs
Frequently Asked Questions About Cement
Have questions about cement and CEMEX cementitious products? Check out our list of frequently asked questions and how it is used to find the answer you're looking for.
What does "setting time" mean?
When cement is mixed with water, the paste that is formed is fluid, or 'plastic', for a short period of time. During this time the paste material may be reformed or remoulded. As the chemical reaction between water and cement continues, the paste becomes stiffer and ultimately hardens. The early period of hardening is referred to as the setting time.
How does the fineness of Portland cement affect its performance?
Typically, cement is ground to very fine particle sizes to enhance its ability to react with water and to increase fluidity in its plastic state. To a point, a smaller particle size improves the mixing characteristics, and strength development of the paste. Finer ground cements tend to set or develop strength quicker than coarser ground products.
How is Portland cement made?
Raw materials (chalk/limestone, clay and sand) are finely ground and proportioned for the desired chemistry. The material is then blended and heated to about 1400 degrees Celcius in rotary kilns. The heated product, called clinker, is allowed to cool, and is then ground to a fine powder along with a small quantity of a mineral called gypsum which present to control setting time.
What is Portland cement?
Portland cement is a fine, powder material produced by heating, at high temperatures, a mixture of minerals containing of lime, alumina, iron, and silica in defined proportions and then grinding the resultant material (clinker) into fine powder. The material is typically mixed with water, sand, and gravel to produce concrete. Cement reacts with water to harden into calcium silicate hydrates resulting in stone-like properties.
Is all Portland cement the same?
Although all Portland cements are governed by standard specification, all cements are not the same. Cement specifications allow for many different combinations of constituent materials, which each give different performance criteria allowing concrete to be produced to meet different performance requirements. This can include sulphate resistance, longer setting, resistance to chemical attacks etc.
Second, even the same classes of cement will vary from manufacturer to manufacturer and there may even be variation from a given manufacturer depending upon when the material was made. Items which can cause cement variation include raw material variations, chemical variations in kiln feed, variations in processing and variations in grinding and grinding additives used. Because consistency is one of the most important criteria for cement manufacturing, producers of cement invest ££millions in plant equipment and quality control to provide the most consistent product possible.
Is concrete and cement the same thing?
No - cement is actually an ingredient of concrete. Concrete is basically a mixture of sand, gravel and cement.
Can I use cement on its own?
Cement on its own is not very strong but when it's combined with other materials it takes on a new form and is commonly used to create mortar, render and concrete.
What happens when cement is mixed with water?
The water causes cement to harden through a process called hydration. Hydration is a chemical reaction in which the major compounds in cement form chemical bonds with water molecules and bind themselves together to form a hardened structure.
Why is it called Portland cement?
When Joseph Aspdin patented the process for making Portland cement in 1824, it was said to resemble a limestone that was found off the coast of Dorset at a place called the Isle of Portand, which is the location of the famous Portland Bill Lighthouse.