Are you using the right cement?

Cement is the bond that holds all construction together. 
Photo | Tony Mushoborozi.

What you need to know:

  • Cement is the most widely used construction material after water. It is the main component in the construction and production of infrastructures for building and development of buildings.

Cement is one of the most fundamental elements in the construction industry.

Whether it is the nuclear power plants or the hydropower dams that produce electricity to run global economies, or the factories and the financial institutions that make production possible, or the lofty palaces that house the princes that run the world, or the highways, railways, sea ports and airports that connect the world, cement is the bond that holds it all together.

Even if it is a primary construction material, we never give cement much thought until something has gone terribly wrong. When a building collapses during construction for instance, that is when people talk about cement.

We would do ourselves a great favour to know the basics about cement, especially if we are planning on a construction project.

What is cement?

Cement is a chemical substance used in construction that sets, hardens and bonds materials together to form sturdy structures. It is produced by mixing burnished limestone and clay after which they are ground up together to form a fine powder.

Cement is one of most widely used building materials in the world for good reason. Not only is it a comparatively cheaper and very durable material, it can also be used in all sorts of applications.

It is also weather resistant and can be used in the construction of at least one stage of most structures. It is used in foundations, floors, beams, columns, interior or exterior walls, ceilings and even roofs.

Types of cement

There are several types of cement, some of which are rapid-set cements, waterproofing cements (hydrophobic) and normal binder cements.

Rapid-set cement

 This type of cement sets and hardens faster than ordinary cement. Whereas traditional concrete will harden within 48 hours, some rapid-set cements will harden within an hour. According to experts at Hima Cement Limited, a cement manufacturer in Uganda, rapid-set cement is designed mainly for use in manufacture of precast concrete products such as building blocks, paving blocks, fencing poles, culverts, road kerbs, pre-fabricated concrete slabs and many more.

 It is packaged in a dust free hybrid bag and brings about extra value in form of strength, speed, quality and low cost. Rapid-set cement allows for the removal of formworks shortly after casting so they can be used again.

Waterproof or hydrophobic cement

This cement contains a water-repellent agent or film-forming substance. It is suitable for use in underwater constructions such as bridges and dams and other water-logged applications. This particular cement is used to reduce the rate of structural deterioration due moisture exposure. 

Normal binder cement

This is the commonest used cement in the construction industry. It is the most available on the market and is used in normal construction works that need no special application cements.

According to Mark Itenga, a construction manager with Thorn Impex Construction Company, different types of cement have different applications in construction and a basic knowledge of this will help you get better results from your mason.

“Most of the builders in Uganda only trained on the job. They got their skills from spending time at building sites and many only know cement on a surface level. If you have more knowledge about cement, then you will for instance insist on waterproofing cement for your foundation if it is in a lowland and so on,” he says.

Here are some of the commonest types of cement

Ordinary Portland cement (OPC)

This is the commonest and most readily available cement on the market in Uganda. Ordinary Portland cement is not only the commonest in Uganda but across the world because it is suitable for all general construction needs. It is made from primary cement materials; limestone with clay.

It is called ‘Portland’ because when it was first made and used in the early 19th century in England, it resembled a building stone from the Isle of Portland off the British coast.

Uses

This cement is for general use. It is suitable for binding all sorts of materials together such as bricks and building blocks in the construction of walls, plastering and making of concrete. What should be noted however is that this type is suitable in normal situations where there is no special attention is needed.

Pozzolana cement

Pozzolana cement is prepared by grinding pozzolanic clinker with Portland cement. It is also produced by mixing pozzolana with gypsum or calcium sulfate or by intimately and uniformly blending Portland cement and fine pozzolana.

Uses

Pozzolana cement is not only extremely water resistant but also resistant to several other chemicals. It is therefore suitable for underwater construction, waterlogged foundations, and slabs for flat-roofed houses. It is used in marine structures, sewage works, and for laying concrete underwater in such construction works as bridges, piers, dams, etc.

It is also used in masonry mortars and plastering as it gives better surface finish. Pozzolana is used in decorative and art structures.

Rapid hardening cement

This is perfectly suitable in the production of prefabricated concrete works. Rapid hardening cement attains high strength in a short time and for that, it is used in works where formworks need to be removed at an early stage, for instance in the making of concrete blocks, culverts, etc.

The advantage of this cement is that formwork can be removed early, which increases the rate of construction and decreases the cost by using much less formwork.

Quick setting cement

This is suitable for situations where you have to build concrete in water. This cement sets very quickly.

The difference between the quick setting cement and rapid hardening cement is that quick-setting cement sets earlier but gains strength later. 

This cement would work perfectly in the construction of protected wells, water channels in water logged places, etc.

Sulfates resisting cement

This type of cement is manufactured to resist sulfate attack in concrete. Sulfate attack is one of the most damaging causes of concrete deterioration, causing either softening and decay of the concrete matrix.

This cement is designed for the mining industry to counteract the reaction of chemical attack in aggressive underground environments. It can also be used in concrete surfaces subjected to alternate wetting and drying such as bridge piers. In the construction industry, this cement is perfect for use when building retaining walls, basements and dump-proofing works.

White cement

It is a type of ordinary Portland cement, which is white. It is produced from carefully chosen raw materials that are free from iron oxide. It is mostly used for aesthetic purposes and decoration in architecture. Some of the applications where white cement is used include facing panels, terrazzo surfaces, external renderings of buildings, facing slabs, floorings, ornamental concrete art, paths of gardens, swimming pools, etc. It is one of the more expensive types of cement.

This type of cement is especially suited to improve the workability with a smaller water-cement ratio and to improve frost resistance of concrete.

Cement additives

According to Itenga, cement has its weak points and to solve these challenges, one sometimes needs special additives. These additives are also termed as construction chemicals or admixes. They are added in cement to make it more waterproof, to prevent rapid weathering, or to accelerate setting and hardening, etc.

“Some admixes act as water reducers, others are for waterproofing and others are for weather protection while others prevent rapid weathering.  They are applied depending on the need at hand. Other admixtures come in to curb issues such as efflorescence (the white puffs that come out of concrete in moist conditions). They also remove the excess chlorine and enable the reaction of excess calcium hydroxide,” he says.

He adds, “There are admixtures that are high range water reducers which reduce the amount of water you are required to use in the process of absorption. On the market here we have Sika visco crete as the main product that can be accessed locally. These increase the overall strength of the concrete.”

These admixes transform ordinary cement into what your needs are during construction. There are admixes that make cement more waterproof, more dusting-proof, stronger, smoother, etc. There are other admixes that cause cement to set faster, to set slower, to self-compact, and many other needs.

Cement shelf live

In general, the shelf life of a cement bag is three months. When fresh cement is stored for a longer period of time, it gradually loses its strength.

Never use expired or outdated cement to construct a house or any important structure.

Always check the shelf life of cement before using it. To ensure high-quality construction, use lump-free and fresh cement. Good cement results in a safer and longer-lasting house. It will also save money that would otherwise be spent on repairs and maintenance.

Origin

The cement that we use today was discovered by a British stonemason called Joseph Aspdin, in the 19th century. He simply heated up some ground limestone and clay in his own kitchen and then broke it down into a fine powder.

Thus, the cement we know and love was born.

While Aspirin perfected cement mix as we know it, cement and concrete were used by ancient civilisations such as the  Egyptians to help build pyramids.