What You Need to Know About the Quality of CementKen Thayer | February 01, 2018
Cement is an integral component of concrete and mortar, and is a primary building material found in structures, sidewalks and roads all over the world. It is critical that the cement is of proper quality to prevent cracks, premature failure and allow the project to be safe, strong, and durable for as long as possible.
Many people incorrectly use the terms cement, concrete and mortar interchangeably. Concrete is a composite material, formed by mixing aggregates such as sand, gravel or crushed stone with a paste made of water and a cement. Mortar is a mixture of a cement and a fine aggregate and is used for bonding bricks or other components in structural applications. Rarely used on its own, cement is a binder that sets and hardens. When mixed with aggregates cement forms concrete or mortar and is used to adhere and bind other materials together.
The term cement is a generic term that can refer to one of many different formulations. The common thread for all of them is that they serve as binder materials to be combined with an aggregate to form a concrete or mortar.
(See How Cement is Made on the Portland Cement Association website.)
Portland cement is based on calcium silicate (CaSiO3) and made from a combination of calcium, silicon, aluminum and iron oxide minerals. It is the most common cement for general concrete applications today and is the type most people think of when they hear the term concrete. Other cement types including calcium aluminate, carbon bond, phosphate, slag, polymer bond, epoxy and several others.
Portland cement is a hydraulic cement, meaning it sets and bonds due to a chemical reaction between water and the dry ingredients of the cement. Unlike hydraulic cement, non-hydraulic cements will not set in wet conditions. They set and dry based on other technologies. Other non-hydraulic cure technologies include air setting, chemical setting, heat setting, hot melt and two- or multi-component.
(For additional information on these binder types and setting methods, see the IEEE GlobalSpec SpecSearch® help content, located here, below the product search filter.)
How do you go about determining the quality of cement to ensure the project has a successful outcome? There are several items to check, including some that can be conducted on-site.
Ordinary Portland cement (OPC) is available in standard grades. These grades can be specified at the time of purchase.
For general construction jobs in normal environmental conditions, 33 Grade OPC is an appropriate choice. 43 Grade OPC is primarily used for brickwork, foundations, plastering and compound wall applications in home construction. 53 Grade OPC provides early high strength and durability for structures such as skyscrapers, bridges, runways, concrete roads and other heavy-duty construction applications.
The following standards have been set for OPC grades:
Once you have selected the appropriate cement grade for your application, make sure to source the cement from a reputable seller. Purchase bags that have been machine stitched from a brand-name manufacturer.
Even if all of the pre-purchased items seem satisfactory, you can and should still check the quality once the cement has arrived. Most of these quality checks can be done on-site.
If purchased in a bag, verify the stitching is intact and the bags do not have holes in them. Look for certification marks, such as CE or ISI, to make sure the cement conforms to manufacturing standards. Check the date of manufacture that is printed on the bag. The strength of cement degrades over time and should be used as close to the date of manufacture as possible, ideally within 90 days. After three months cement strength is reduced by 20-30 percent, 30-40 percent after 6 months, and as much as 40-50 percent after 12 months.
2. Look and Feel
Scoop up a handful of cement. You can make some quality judgments just by feeling and looking at the cement. The cement should be lump- and dust-free and feel cool to the touch, indicating no hydration reaction is taking place. Look at the color. Cement for building construction should be a uniform greenish-gray, while cement for decorative applications is white.
3. Water Tests
When tossed into a bucket of water, quality cement that is free from impurities should float on the surface for a while before sinking. To ensure that the cement will harden correctly, mix some cement with water to form a paste. Form the paste by hand, place it in a bucket of water and let it sit for 24 hours. The cement should harden and retain its shape.
If the cement has an earthy smell, it may contain too much clay and silt.
Form an 8 in. by 1 in. by 1 in. block and immerse it in water for seven days. Then place the block on supports that are about 6 in. apart and place under a 75 lb. load. The block should not show any signs of failure.
If you are diligent about following these simple inspection tips, you can be sure your cement-based structure will be strong and last for years to come.
For additional information on cement and concrete basics, visit the FAQ page on the Portland Cement Association website.