Why concrete strength tests are performed after 28 days

Concrete cylinders for strength tests

Contractors often rely on the strength test result of concrete conducted at the age of 28 days. The strength results at 28 days are considered standard and contractors rely on these to determine the integrity of the resultant structure.

Concrete gains strength over time. It can take anywhere from a few weeks to a few years for different concrete mixes to reach almost 100% strength. Contractors generally perform strength tests four weeks after pouring – or 28 days. During this time, all concrete batches will have cured and strengthened rapidly. After 28 days, the rate of strengthening slows down.

How concrete gains strength over time

Standard grades of concrete will generally gain 16% of its strength after the first day, 40% after three days, 65% after seven days, 90% after 14 days and almost 100% after 28 days. This is why compressive strength tests are performed after 28 days. The concrete will be near-optimal strength and is unlikely to change much more after four weeks of curing.

The figures above clearly show how rapidly concrete sets and cures during the first four weeks. After this time, the rate of strengthening slows down considerably, gaining just one more percent of strength in a number of months after being poured. After the first two weeks, concrete only gains nine percent strength in the next two weeks, so the slowing of the rate begins after 14 days.

Concrete takes about 12 months to reach almost 100% strength

Most concrete will reach 100% strength about a year after pouring. Contractors only need to wait for 28 days before performing strength tests as it is close enough to maximum strength to form reliable results. The basis for evaluation is so close to perfect after four weeks that there is no point waiting for another 11 months to do the strength tests.

Although all concrete mixes are different in terms of how rapidly they cure, 28 days has become the standardised length of time to wait. Some rapid-setting concrete mixes may cure within half the time, contractors should still wait for four weeks to perform tests on the structure unless time is extremely limited and deadlines are threatening the project.

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LafargeHolcim is a leading building materials and solutions company that has been operating in international markets for decades. We produce cement and aggregates for construction projects, ranging from small affordable housing developments to large-scale infrastructure projects such as high-rise buildings, dams and bridges. 

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LafargeHolcim Tanzania has been supplying the country and neighbouring countries with our world-class Tembo cement brand for over 30 years. Our head office and fully-integrated plant are located in Mbeya, Southwest Tanzania.

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At LafargeHolcim Tanzania, we believe customers come first. We listen to your specific requirements to supply and develop the best solutions for your needs. As the new leader in building materials, you can also rely on our cutting-edge research and development capabilities that have resulted in the finest materials for your construction projects, whether large or small.

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How to waterproof concrete structures

How to waterproof concrete structures

Waterproofing concrete structures can help to protect them from the weather and keep them in optimal condition. This is especially important in areas prone to flooding, heavy rainfall and constant ocean vapour. Water can penetrate concrete over time and affect its strength, so waterproofing is a good way to keep a building strong.

There are numerous ways to waterproof a concrete structure. Contractors can apply paints and bitumen felts to the exterior of the building, or they can use concrete admixtures to prevent water from penetrating the surface of the structure. For optimal waterproofing results, the design, workmanship and building materials should conform to the correct standards and codes of construction.

Concrete waterproofing admixtures

Certain admixtures make concrete impermeable to water and moisture. These chemicals can be added to the concrete or plaster batch during mixing. They reduce water permeability in the concrete by reducing the size and number of pores in the surface. They also line the surface with hydrophobic materials that prevent the absorption of water.

These admixtures react with the calcium hydroxide in the cement to create a hydrophobic layer. Examples of waterproofing admixtures include animal fats, stearic acid and some vegetable oils. These admixtures can also be mixed with plaster to line the surface of a wall. This acts like a layer of waterproof paint that repels rain, standing water and mist in the air.

Waterproofing concrete with bitumen coating

Another way to make concrete structures waterproof is to place a layer of bitumen on the exterior surface. The concrete first needs to be cleaned and sanded to give the bitumen a rough surface to stick to. Contractors should pour hot bitumen (about 1.5kg per square metre of concrete) onto the surface and spread it evenly. 

Once the first coat had dried and cooled, the second coating (1.25kg per square metre) is applied in the same manner. Immediately after the application of the second coating, contractors should spread sand over the surface. This is then left to dry and cool. The sand will give the surface a non-slip texture and improve the durability of the bitumen.

Certain concrete structures need to be waterproofed internally, such as concrete tanks and reservoirs that will store certain chemicals and liquids. Waterproofing a concrete structure will maintain its strength in the face of exposure to water and other liquids. It will prevent concrete rot and protect a building from heavy rains, flooding and salt moisture from the ocean.

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LafargeHolcim is a leading building materials and solutions company that has been operating in international markets for decades. We produce cement and aggregates for construction projects, ranging from small affordable housing developments to large-scale infrastructure projects such as high-rise buildings, dams and bridges. 

___

LafargeHolcim Tanzania has been supplying the country and neighbouring countries with our world-class Tembo cement brand for over 30 years. Our head office and fully-integrated plant are located in Mbeya, Southwest Tanzania.

___

At LafargeHolcim Tanzania, we believe customers come first. We listen to your specific requirements to supply and develop the best solutions for your needs. As the new leader in building materials, you can also rely on our cutting-edge research and development capabilities that have resulted in the finest materials for your construction projects, whether large or small.

___

Follow us on Facebook, Twitter, LinkedIn and Pinterest for the best tips on construction, handy projects and the latest industry news. See our Instagram channel for more insights into our products.

Concrete for roads and driveways

Concrete can be used to build roads

Concrete is becoming a more popular choice for civil engineers and road builders. Previously, asphalt was the favoured material for building roads but concrete has some unique qualities and benefits that make it a good choice. The three main benefits of using concrete to build roads and driveways are its strength, durability and sustainability.

Another major reason why concrete is becoming a popular road material is its cost-effectiveness over the long-term. Concrete roads will cost a similar price to tar roads, but they will need less maintenance and are less susceptible to potholes over a long period of time. Concrete is a good investment for roads, driveways and parking lots. 

Benefits of concrete for roads and driveways

1. Strength

On average, a road will last between 20 and 25 years before it needs to be completely resurfaced. Roads often need major repairs within the first seven years of their life. Concrete, on the other hand, is a much stronger building material. Concrete roads can last up to 50 years before needing major repairs.

This is due to the strength of concrete. These roads often outlast their initial lifespan. Concrete is designed to last long and withstand lots of wear and tear. This is important for road that need to support heavy vehicles and the friction of rubber tyres.

2. Durability

This brings us to our next point; concrete is durable enough to withstand years of punishment from daily traffic. It is a highly durable material that does not crack or crumble under the weight of vehicles. Concrete can also withstand rain and hot weather, which means fewer potholes.

Concrete has the ability to spread the weight of traffic evenly, which minimises the pressure on the internal structures of the road. Normal roads cannot do this as easily, which is why they are less durable and more susceptible to cracks and potholes. This leads to earlier repair and maintenance needs for normal roads.

3. Sustainability

Concrete is highly sustainable and 100% recyclable. Old concrete structures can be broken down into rubble, which is then reused on new building sites. Concrete is the most widely-recycled construction material. It is also environmentally-friendly, for a number of reasons.

Concrete roads have a light grey colour which is highly reflective. Unlike black road surfaces, concrete roads reflect the sun’s radiation which helps to cool the surface temperature of the road. This is better for vehicle tyres and surrounding buildings – it helps to keep cities and towns cool. Concrete is also manufactured from recyclable natural materials, such as fly ash from coal-fired power stations.

4. Affordability

Concrete is an affordable building material – that is why it is so popular. During its lifetime, a concrete road will cost the government and taxpayer less to maintain and use.

These reasons highlight why concrete is a better building material for roads and pavements. Concrete is relatively inexpensive, but it offers far more advantages over its lifetime. It is strong, durable, sustainable and affordable – ideal for any construction project, including roads.

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LafargeHolcim is a leading building materials and solutions company that has been operating in international markets for decades. We produce cement and aggregates for construction projects, ranging from small affordable housing developments to large-scale infrastructure projects such as high-rise buildings, dams and bridges. 

___

LafargeHolcim Tanzania has been supplying the country and neighbouring countries with our world-class Tembo cement brand for over 30 years. Our head office and fully-integrated plant are located in Mbeya, Southwest Tanzania.

___

At LafargeHolcim Tanzania, we believe customers come first. We listen to your specific requirements to supply and develop the best solutions for your needs. As the new leader in building materials, you can also rely on our cutting-edge research and development capabilities that have resulted in the finest materials for your construction projects, whether large or small.

___

Follow us on Facebook, Twitter, LinkedIn and Pinterest for the best tips on construction, handy projects and the latest industry news. See our Instagram channel for more insights into our products.

The importance of aggregates in concrete

Three different aggregates

Concrete consists of three core ingredients; cement, aggregates and water. Aggregates play a major role in holding the concrete together and adding to the durability of the finished product. Using the right aggregates is important when it comes to the performance of the concrete – they make up between 60% and 80% of concrete, after all.

The main types of aggregate are sand and gravel. These both come in a variety of forms, such as fine river sand, small gravel chips or larger crushed stones. A combination of aggregates can be used to create the perfect concrete texture for your project.

Choosing the right aggregates

The size, weight and moisture content of aggregates will directly affect the quality of the final concrete mix. Aggregate choice can also affect the cost, workability and durability of the concrete, so it is a major factor to consider when starting a construction project.

Aggregates should be clean, hard and strong. Choose aggregates that are free of clay coating, soil impurities, additional chemicals and organic material. Sand and gravel should not contain any mud, seeds or leaves.

Other factors to consider when choosing aggregates

The moisture content of aggregates is also important. It can affect the water-cement ratio in the concrete mix and either cause the concrete to be too dry (by absorbing the water) or too wet (by adding additional moisture to the mix).

Ideally, the aggregates should be in a saturated surface dry (SSD) condition. This means that they are dry on the outside but have internal moisture. In turn, the aggregates will not absorb any moisture from the concrete mix and leave it too dry.

Choosing the right gradation is also important. Aggregates that are too fine will need more water and will result in a sticky concrete mix – such as ultra-fine river sand. Aggregates that are too coarse will make the concrete harsh, hard to work and more difficult to place. The key is to find the right balance with aggregate gradations.

Aggregates make up the majority of concrete and are a vital factor to consider. Depending on the project and the final finish of the concrete, choose the right aggregate for your needs.

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LafargeHolcim is a leading building materials and solutions company that has been operating in international markets for decades. We produce cement and aggregates for construction projects, ranging from small affordable housing developments to large-scale infrastructure projects such as high-rise buildings, dams and bridges.

___

LafargeHolcim Tanzania has been supplying the country and neighbouring countries with our world-class Tembo cement brand for over 30 years. Our head office and fully-integrated plant are located in the Mbeya Region at Songwe in Southwest Tanzania.

___

At LafargeHolcim Tanzania, we believe customers come first. We listen to your specific requirements to supply and develop the best solutions for your needs. As the new leader in building materials, you can also rely on our cutting-edge research and development capabilities that have resulted in the finest materials for your construction projects, whether large or small.

___

Follow us on Facebook, Twitter, LinkedIn and Pinterest for the best tips on construction, handy projects and the latest industry news. See our Instagram channel for more insights into our products.

The importance of concrete forms

Wooden forms holding wet concrete path in shape

Concrete forms are temporary frames that hold wet concrete in shape until it dries and hardens. They can be made out of wood or steel and allow the builders to easily pour concrete into certain shapes.

Concrete forms also allow the wet mix to retain its strength and cure properly, giving the structure durability. The forms need to have tight joints to prevent wet concrete from seeping through the frame.

They also need to be strong enough to support the weight of the concrete – small household projects, such as driveways, use wooden forms but larger projects need to use steel forms. The forms should have enough bracing and support to help them keep their shape once the cement is poured in.

They also need to be able to withstand the weather without bending or warping. You can guarantee that your projects will be strong and durable if you have used proper concrete forms.

Concrete forms can be made from various materials

The most common material used to make concrete forms is wood. These forms are usually constructed on-site from plywood or timber. Wooden forms are cheap and are ideal for flat concrete structures such as floors, steps or driveways.

Metal is another common material for creating forms. These steel moulds are usually used on larger construction sites, such as commercial buildings and skyscrapers. They are ideal for creating vertical columns and pillars for tall structures.

Some forms are created from fibreglass, reinforced plastic, ceramic or aluminium. All of them have their benefits and disadvantages but their purpose remains the same – to create moulds for concrete structures.

Two types of concrete forms

Construction projects are three-dimensional and, as such, need vertical and horizontal forms. Vertical forms are needed for building concrete walls, columns, pillars and stairs. These forms need to support the lateral pressure of the concrete, so they should be anchored or bolted to the soil or floor to keep them in place.

Horizontal forms are used to build beams, ceilings, floors and paths. They need to support the weight of wide concrete structures, so should be reinforced with braces, struts or metal pegs.

Components of concrete forms

Concrete forms are made up of various components. The form that comes into direct contact with the concrete is called the formwork sheeting. This mould is responsible for the precise look and shape of the finished concrete surface. It needs to be water-resistant or have its own moisture content so as not to suck water out of the concrete and leave it too dry.

The elements that support and connect the formwork sheeting are known as the formwork bearers. These include steel or wooden beams and clamps that connect and support the formwork sheeting. They provide structural strength to the form and support the weight of the heavy concrete.

Lastly, formwork ties are the steel wire components that bind two forms together. The ties are usually wrapped around the formwork bearers then guided through drilled holes in the formwork sheeting. The wires are then tightened by twisting.

Concrete is then poured into the formwork structure and left to cure for a few weeks. The formwork can then be stripped and deconstructed once the concrete has set properly. Avoid using too many ties or nails in the formwork as this will make it hard to deconstruct later.

Concrete forms are a vital component of any construction project. When assembled properly, the forms will hold concrete in shape for up to four weeks while the concrete cures. This allows the concrete to reach its optimal strength and durability.

___

LafargeHolcim is a leading building materials and solutions company that has been operating in international markets for decades. We produce cement and aggregates for construction projects, ranging from small affordable housing developments to large-scale infrastructure projects such as high-rise buildings, dams and bridges.

___

LafargeHolcim Tanzania has been supplying the country and neighbouring countries with our world-class Tembo cement brand for over 30 years. Our head office and fully-integrated plant are located in the Mbeya Region at Songwe in Southwest Tanzania.

___

At LafargeHolcim Tanzania, we believe customers come first. We listen to your specific requirements to supply and develop the best solutions for your needs. As the new leader in building materials, you can also rely on our cutting-edge research and development capabilities that have resulted in the finest materials for your construction projects, whether large or small.

___

Follow us on Facebook, Twitter, LinkedIn and Pinterest for the best tips on construction, handy projects and the latest industry news. See our Instagram channel for more insights into our products.