Cement: What is it and What is it Made of?

Cement has been an essential component of buildings for thousands of years, from the Colosseum of Rome to modern skyscrapers. A fine binding powder, it is used within both concrete and mortar, both of which will be used in the production of almost every type of building. In this overview from Building Materials Nationwide, we’ll explore everything you need to know about cement, looking at what it’s made from, where it’s used, and answering some of the popular questions about pricing and associated dangers.

What is Cement?

Cement is a binding agent, sold as a powder, that hardens to create a powerful seal, giving it a wide range of uses within a building project. Cement is commonly mixed with aggregates to form other substances like mortar or concrete, meaning it can be used to bind objects together like the mortar connecting the bricks in a wall or to create a solid structure itself in the case of concrete, which can either be poured into a shape or produced as brick-like blocks.

What is Cement Made of?

Cement is chiefly made from limestone, mixed with sand, clay, and other components. For instance, Portland Cement, a popular cement option, is made from limestone, clay, shale, iron oxide, and silica sand. Different types of cement will have slightly different mixtures within them, with modern commercial cement produced in laboratory conditions to ensure an exact chemical blend. This exact mix is crucial, allowing cement to be fluid enough after mixing that it can be applied, while also setting to gain the necessary strength for a construction project.

What is the History of Cement?

The use of lime as a building material dates back to ancient Greece and Rome, with the Romans in particular constructing a huge range of buildings that remain standing today, such as the Colosseum and the Pantheon. Modern technical knowledge of cement was developed in the 18th century, with many innovations in products and admixtures since then.

Are There Different Types of Cement?

Cement is broken into two main categories, with a range of specific types available within these. Cement will either be hydraulic or non-hydraulic, with hydraulic cement hardening through the addition of water, and non-hydraulic cement not requiring water to harden. When shopping for cement there will be a few options available, usually defined by their mix of ingredients:

• Portland Cement (OPC): A general-purpose cement used in the production of most concrete, mortars, and renders, portland cement has become the standard cement type. Named after its visual similarities to Portland stone from Dorset, it is a hydraulic cement made from limestone mixed with clay or shale.
• Portland Pozzolana Cement: This cement will be mixed with pozzolana, gypsum, or calcium sulphate. This is typically used for underwater work.
• Mastercrete Cement: Mastercrete cement boasts improved resistance to freezing and thawing, making it a great choice for wet or cold environments. Mastercrete is not regularly used for concrete.
• Rapid Hardening Cement: This cement is produced with an increased lime content which helps it to become stronger faster, hence rapid hardening. This allows for the formwork around concrete to be removed more quickly.
• Quick Setting Cement: Produced with a small amount of aluminium sulphate to speed up the setting process. This can provide benefits in wet conditions where fast setting is crucial.
• Blast Furnace Slag: Slag cement will be a mixture of Portland cement and ground blast furnace slag, an industrial by-product. There are a few benefits to this, increasing the strength of concrete, lowering water permeability, offering resistance to chemical attacks, and reducing the corrosion of rebars installed within concrete.
• Fly Ash: Fly ash is a coal by-product that can be added to cement. Fly ash will reduce the water requirements for concrete, offering a lubricating effect that keeps it usable. Once set, fly ash can help to offer increased strength and durability in concrete mixes

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Where is Cement Used?

Cement is involved in almost every building produced across the world today, as both a building material and as a quality binder. While cement is rarely used on its own, the various mixtures that can be produced within it will be found in everything from brick houses to skyscrapers, to pavements.

How is Cement Used?

Cement will be mixed with sands or aggregates to produce mortar or cement, which serves a huge range of purposes within manufacturing:

• Mortar: Mortar is a mixture of cement and sand, which will be combined with water to make a paste that can be used for several purposes, offering strength and water resistance. Mortar is used for binders between the bricks in any brick structure. This can be walls, brick paths, and houses. Cement-based mortars will be used to create strong, durable brick structures. Mortar will also be used for plastering, as it can be spread over a surface to create a smooth finish. This is called rendering, and the mortar is sometimes called render. Floor levelling can also be accomplished with mortar. Mortar will normally be mixed on-site by builders, with ratios of cement to sand varying depending on needs. Soft sand, or builders' sand, should be used for mortar.
• Concrete: Concrete is one of the key building materials of the modern world, due to its strength, cost, and variety of uses. Concrete will be produced from a mixture of cement, fine aggregates, coarse aggregates, and water. Portland cement is typically used for the production of concrete. Concrete can be used for things like foundations, or can be made into solid blocks which can be used to make buildings and other structures. The strength of concrete will come from the aggregate mixes, containing gravel, crushed stones, and often recycled concrete. Different concrete mixes can use aggregates of a larger diameter. Ready-mixed concrete is available to purchase.

How Long Does It Take For Cement to Dry?

For concrete, you’ll be looking at 1 to 2 days before the forms can be removed, 7 days before it will be set enough for vehicles and equipment to be used on it, and around 4 weeks before it should be fully cured. There are specialist types of cement intended to either dry or set faster. Similarly, mortar will be around 60% dried within the first 24 hours, but will take approximately 4 weeks to reach its maximum strength.

Is Cement Waterproof?

As cement will not be used on its own, the real question to ask is whether concrete and mortar are waterproof. Concrete is not waterproof, but offers long-term protection from water. In the longer term, while water will not be forced through concrete by pressure, it will seep through gradually. 

While mortar performs well in wet environments it is also not waterproof in its standard form. For both options, waterproof cement is available, to which a water-repellent agent is added during production. Some options can be used as an alternative to water in a concrete mix to give it waterproofing.

Are There Any Drawbacks to Cement?

Concrete structures need reinforcement to work within stronger structures, with concrete often poured around steel rebars. The largest concrete buildings will therefore contain other elements to support their weight.

Concrete is also difficult to change once installed, as it is produced in huge pieces. While it can be repaired, it cannot be easily altered. As we’ll explain later there are also some severe environmental impacts from cement as a building material, alongside dangers to health from contact with wet cement and inhaling cement dust, both of which are worth keeping in mind.

How is Cement Sold?

Traditional cement will usually be sold in 25kg bags in the UK, with other specialist types sometimes coming in smaller bags or tubs. As of writing, Building Materials offers standard Portland Cement 25kg bags for £5.67 before VAT.

How Many Bags of Cement Do You Need?

An estimate for traditional brickwork is 1kg of mortar per brick, to build each required 10mm join. If building mortar with a 4 to 1 ratio of sand and cement this would mean that each bag of cement could be used for 125 bricks. In terms of concrete, the standard ratio in the UK would be for 1 part cement, 2 parts fine aggregate (sand), and 3 parts coarse aggregates (such as gravel), mixed with .5 parts water. This will therefore produce 162.5kg of concrete from one bag.

Does Cement Go Off?

Cement will typically have a use-by date on it, after which the strength can degrade and there can also be potential issues with allergens. Over time cement will react to moisture in the air which will cause it to degrade. The reason for issues with allergens is that some of the harmful elements of cement can become more of a threat when the mix is out of date.

Is Cement Dangerous?

There are some dangers associated with cement, both from contact and from inhalation, alongside environmental factors to consider.

Is Cement Eco Friendly?

Between 4 and 8% of global CO2 emissions are thought to come from concrete. While this pales in comparison to fuels like coal and oil, it is still a considerable factor in the ongoing climate crisis. Cement also uses a huge amount of water, which can cause issues in areas with drought issues. There have been some reductions in the level of emissions from cement production, and concrete debris that would once have been disposed into landfills is now often recycled.

Is Cement Contact Dangerous?

Skin contact from cement can cause dermatitis, causing itchy, cracked, and painful skin. In situations where those using cement are allergic to hexavalent chromium, an element of cement, this can be more severe. Skin can also become burned by wet concrete, due to the interaction between chemicals in the mix reacting to your skin. These can be dangerous and will require medical care at times.

Is Cement Dust Dangerous?

As cement is powdered it can be inhaled by those using it, risking nose and throat irritation. Cement can also contain silica which can cause Silicosis, a lung disease, when inhaled in large amounts. There is evidence to suggest cement manufacture contributes to air pollution in areas near mines and construction sites.

Is Cement Poisonous?

As stated, cement that contains silica can cause serious health issues. Wet cement burns can also cause serious injuries to someone.

Our Range of Cement and Other Building Materials

Building Materials Nationwide aims to provide builders and contractors with everything they could need, delivered to them at a great price. We stock high-quality cement for sale, alongside a huge range of aggregates, perfect for mixing mortar or concrete. We stock quality rebars for reinforcing larger concrete structures, alongside a range of clay bricks and concrete blocks. 

For customers within the industry, we offer trade accounts, giving access to our huge network of suppliers, our express delivery options, and the services of a dedicated account manager, who’ll be there to assist you with advice or complex orders. Sign up for a trade account today.