What is exposed aggregate concrete

What is exposed aggregate concrete

Exposed aggregate concrete serves two purposes; it is both decorative and functional. It is a term used to describe a concrete surface, such as a floor, path, pavement or parking lot, that has exposed gravel. This method is used to create flat surfaces that not only look good, but they also provide extra grip in wet conditions.

Exposed aggregate concrete is made by removing the top layer of cement and fine aggregate from freshly-poured concrete. This leaves the large aggregate particles (crushed stone or gravel) exposed and sticking out the top of the surface slightly. It is a durable and skid-resistant surface that is often used to make driveways, paths, pool decks and floors safer.

Methods for creating exposed aggregate surfaces

There are many ways to create these types of surfaces, but contractors generally use four methods.

  1. Standard – The standard way to create exposed aggregate surfaces is by mixing a normal batch of concrete; cement, sand, water and crushed stone. The concrete is then poured and left for an hour or so to harden slightly. A broom is then used to vigorously sweep the surface, removing the fine concrete particles and leaving behind the exposed gravel and stone particles.
  2. Seeded – This method involves placing the gravel or crushed stone, by hand, into the surface of freshly-poured concrete. It is similar to planting seeds in the ground, except that just the surface of the stone is left sticking out the top of the concrete.
  3. Topping – Also known as a concrete overlay, this method is used to upgrade and existing concrete surface into a slip-resistant one. A fresh concrete batch is mixed and poured thinly on top of an old floor or path. The thin layer of concrete leaves the thicker stones exposed along the surface.
  4. Polished – This method is often used inside homes and is more decorative than functional. Instead of leaving the aggregate exposed with a textured surface, a grinder or sander is used to flatten the surface and make it level. Several layers of clear coat sealer are applied to create a shiny, polished surface.

As a general rule, the exposed gravel should always be at least two-thirds embedded in the concrete. This will prevent the stones from lifting and being removed from the surface, which would leave holes and large pits in the concrete. These pits can then collect dirt, water and soil, which can affect the durability of the floor.

Benefits of using exposed aggregate concrete surfaces

There are a number of reasons why people choose to use exposed aggregate surfaces in their homes and gardens. Firstly, it can look really nice if you use stones of various shapes and colours. Some homeowners like to match the colour of the exposed stones with the rest of their furniture. This makes it a customisable and aesthetic feature of a house.

Exposed aggregate surfaces are also very durable. They have the structural integrity of concrete and can last for 40 years or more. These surfaces are also highly-resistant to wear and tear and heavy traffic use. They can also handle exposure to the elements really well – sun, rain and hail have little impact on the strength and durability of these surfaces.

As with concrete floors, exposed aggregate surfaces require little maintenance besides sweeping and hosing with water. This makes them a cost-effective solution for floors and driveways. They don’t cost too much to install and they are certainly not expensive to maintain.

The main benefit, however, is the skid-resistance and added grip of the exposed aggregates. These surfaces are useful in wet conditions or around swimming pools. They ensure the safety of users, preventing slips and falls which could lead to serious injuries. Exposed aggregate concrete surfaces are safer than many other flooring materials, especially when wet.

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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 expose aggregate on concrete floors

How to expose aggregate on concrete floors

Some concrete projects call for smooth gravel stones to be exposed for textural and decorative purposes. There are several ways of exposing aggregate on concrete floors. It all depends on the desired appearance and size of the project. Only the top of the stone is revealed, while the rest remains permanently embedded in the concrete. Usually, surface mortar is removed to a depth of no more than one-third of the diameter of the aggregate particle.

1. Brushing and washing

This method doesn’t require special tools or chemical retarders and is the oldest and simplest way of exposing aggregate on concrete surfaces. The thin layer of surface mortar covering the aggregate is simply washed away by spraying with water and scrubbing with a broom until the aggregate is exposed to the desired depth. 

The timing of doing this is very important. Begin as soon as the surface mortar can be removed without overexposing or dislodging the aggregate – the concrete will need to have started setting already, so wait an hour or so after pouring. You can do a test by lightly brushing the surface mortar away in a small area with a stiff-bristled broom.

2. Using a surface retarder

Most contractors use a chemical surface retarder to expose the aggregate. They do this by spraying the retarder onto the slab surface immediately after placing and finishing the concrete. Doing this delays the setting of the concrete and allows them to remove the cement paste a day or so later. This can be done by either pressure washing or scrubbing the concrete surface. Exposing the stones this way can be very useful when working in hot weather or working on large jobs such as pavements and long pathways.

3. Abrasive blasting

Abrasive blasting allows the aggregate to be exposed after the concrete has set and hardened. Either shot blasting or sandblasting can be used. A disadvantage of this method is that it can dull the aggregate’s appearance due to fracturing the surface of the smooth stones. If you want to preserve the shape and full color intensity of the aggregate, this is not the best method to use. 

These three methods of exposing aggregate on a concrete surface allow contractors to create textured and decorative structures. The most common application of this building method is on concrete pathways, parking lots and pavements where the stones give added grip and a pleasing look to the grey concrete.

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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.

Finding the right size of crushed stone for your construction project

Finding the right size of crushed stone for your construction project

Crushed stone aggregate comes in a variety of sizes and shapes that are suited to various applications in a construction project. Contractors cannot assume that any sized stone will work for their structures. They need to understand the key differences between the various types and sizes of aggregate needed for construction.

For example, you should use large stones for a smooth path, otherwise, the stones would make the surface bumpy and difficult to walk on. Likewise, using large stones were small stones are actually needed could increase the overall building costs unnecessarily. Large stones are heavier and more expensive to transport, so they are less practical for certain building projects.

Choosing the correctly-sized stone for the job will ensure that a concrete structure is finished to a higher quality and standard. These buildings will be stronger, more durable and keep their value for longer. When planning a project, be sure to choose the right size of crushed stone aggregate.

Types of crushed stone

  • Crushed and screened – This is the most basic type of crushed stone that you can get. Large granite rocks are crushed and the various chipped stones are fed into a screen filter that separates them into specific sizes. These stones are not cleaned or treated, so may carry some excess rock dust.
  • Washed clean – These are crushed and screened stones that are fed into a washer to remove the rock dust and any additional mud or debris. These stones are clean and do not have any contaminants that could affect dam projects or a concrete batch.
  • Gravel – This is a smoother form of crushed stone that is often used for landscaping projects and to make stone pathways. Gravel comes in a variety of sizes and is more suited to decorative purposes than functional building applications.
  • Quarry process – This type of crushed stone is also known as ‘dense-grade aggregate’. It is a combination of stone dust and crushed stone aggregate of various sizes. The stone dust makes the batch more dense as it fills the spaces between the stone chips.
  • Riprap stone – This is one of the largest types of coarse aggregate. Some of the pieces can be as large as 23 centimetres in diameter. These mini-boulders are often used in heavy concrete applications, such as high-rise foundations and bases for large roads.
  • Stone grits – These are fine particles of stone that are a by-product of the crushing process. They are 5 millimetres or less in diameter and are technically the smallest size of coarse aggregate available (before being classified as rock dust).

Crushed stone sizes and their uses

Small crushed stone (5mm or less) is often used as a functional surface layer on top of a compacted base for landscaping and decorative purposes. This size of stone is ideal for paths, driveways, patios, parking lots, water features and concrete pots.

Medium crushed stone (5mm to 2cm) is ideal for use as a layer on top of a larger crushed stone foundation. The medium stones will settle into the gaps between the larger stones and provide a stable and supportive layer for concrete. Medium crushed stone is also used in most general concrete applications for buildings.

Large crushed stone (2cm to 6cm) is ideal for foundations and filling sub-bases for roads, pavements and airport runways. These large rock particles give a strong and durable base support for concrete and bricks. Sometimes large crushed stone is used for decorative landscaping purposes or to build retaining walls with mortar.

Mixed crushed stone (variety of the sizes above) is often used to build solid foundations for most buildings. It can also be used to build semi-permanent roads and driveway surfaces, such as dirt roads to remote villages and walking trails. Mixed crushed stone is a dense and compact mix that creates solid surfaces as the smaller particles settle into the gaps between the larger particles.

These guidelines should help contractors to choose the right size of crushed stone for their needs. Not all crushed stone is the same, and certain structures call for a certain size of particle. Most general concreting jobs require medium crushed stone. The right size of aggregate can improve the quality and durability of concrete and building projects.

___

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.

How fine aggregate affects the mix design of concrete

Fine aggregate concrete mix design

When it comes to aggregate in a concrete mix, contractors can choose to use fine sand or coarse stone. This decision depends on the application of the concrete mix – whether they want a smooth and binding concrete mix or a sturdy and durable structure. Concrete mix design depends largely on the size of the aggregate used.

Fine aggregate can affect the water content of the concrete mix – it determines how much water needs to be added to the mix to create a workable texture. Other factors, such as the specific gravity of fine aggregate and its silt content, will affect the mix design of concrete. These factors are outlined below.

Fineness of aggregate

The fineness or particle size of aggregate is one of the biggest variables that contractors need to consider. It determines how much sand will be needed in the concrete mix to achieve a strong and workable mix. This affects the overall ratios of the cement to sand to water.

The overall particle size of sand is determined by the fineness modulus, which is found by sieve analysis. The fineness modulus of sand varies between 2 and 4 – these numbers allow contractors to determine the size of the average grain of sand in a batch. Fine aggregate requires more water in a concrete mix than coarse aggregate as it has a larger surface area.

Moisture content of fine aggregate

The moisture content of sand is a crucial factor in determining the water to cement ratio. All aggregates contain some moisture, but sand is able to retain more moisture than crushed stone, for example. Contractors often keep their aggregates damp so that they do not absorb too much water from the concrete mix.

Fine aggregate can be purchased with different moisture conditions; oven-dry (OD), air-dry (AD), saturated-surface dry (SSD) and wet. Only OD and SSD sand correspond to a specific moisture state and can be used as reference points for calculating the moisture content of fine aggregate.

Fine aggregate is frequently sold in a wet state with a moisture content of up to five percent. This is known as ‘bulking’ and needs to be taken into consideration when proportioning the cement and water to the sand. Wet aggregate will absorb less water from the concrete mix, so less water will be needed to achieve a workable mix.

Specific gravity of fine aggregate

Specific gravity is the ratio of the solid density of sand particles to the density of water. Bulk specific gravity is the measure of the volume occupied by the aggregate and the voids between the particles in the concrete mix. This determines the proportioning or ratio between cement, aggregate and water. A high specific gravity means that the sand particles are heavier and more densely packed, resulting in a dense concrete mix. On the other hand, a low specific gravity of sand will result in a low-density concrete mix.

Silt content of fine aggregate

The silt content of sand affects its fineness, and in turn, the amount of water needed in the concrete mix. The silt content can be determined by wet-sieving the sand. Any particles that pass through a 75-micron sieve are classified as silt. These are super-fine particles that can give concrete a smooth and silky texture, but they also require more cement and water in the concrete mix. Silt also lowers the strength of concrete – it makes for better screeds and plaster but is not suitable for high-strength concrete applications.

These properties of fine aggregate will determine the final quality and strength of a concrete batch. The fineness, moisture content, specific gravity and silt content of the aggregate all influence the final concrete mix in various ways, so contractors need to keep an eye on these variables.

___

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.

How coarse aggregate affects the mix design of concrete

Coarse aggregate concrete mix design

When it comes to aggregate in a concrete mix, contractors can choose to use coarse stone or fine sand. This decision depends on the application of the concrete mix – whether they want a sturdy and durable structure or a smooth and binding concrete mix. Concrete mix design depends largely on the size of the aggregate used.

Coarse aggregate, such as crushed stone and gravel, occupies a large portion of a concrete mix but it also adds strength to the final concrete batch and reduces its water demand. The properties of the coarse aggregate, such as angularity and strength of the material, can affect the concrete in numerous other ways, which we will outline below.

Size of coarse aggregate

The maximum size of the coarse aggregate dictates how much water will be needed in the concrete mix. It also determines how much fine aggregate will be needed to produce a workable mixture and cohesive concrete batch. The bigger the size of the aggregate, the smaller its bondable surface area becomes for cement, sand and water. This means that less water and fine aggregate is needed with concrete mixes that contain coarse aggregate.

The size of the coarse aggregate determines the cement to water ratio. Less water means a stronger mix, but it also becomes less workable. One important factor that contractors need to consider when it comes to the size of aggregate used is the spaces between steel rebar. The aggregate needs to be smaller than the space between internal reinforcements. This will allow the aggregate to pass between the rebar and settle evenly throughout the structure.

Grading of coarse aggregate

The grading of aggregate is the average size of the particles, from the smallest to the largest. It is important that the grading is kept constant for concrete batches with the same application. The aggregate particles need to be a consistent size for an even grading and a cohesive and dense concrete mix.

Grading is directly linked to aggregate size, so it also determines the workability, pumpability and durability of concrete. Proper grading of coarse aggregate will minimise the possibility of segregation of the concrete mix. By using aggregate particles that are similar in size, the concrete is more cohesive and uniform throughout.

Shape of coarse aggregate

Coarse aggregate may be round, angular or completely irregular in shape. Rounded aggregates, such as gravel, have the lowest water demand due to their lower surface area. They also have the lowest cement requirement. This makes rounded aggregates more economical, however, the bonds formed are not as strong as angular aggregate.

Angular coarse aggregate requires more water and cement because they have a higher surface area. This can make a concrete batch more expensive, but it is also stronger and more durable. Irregularly-shaped aggregate has similar properties to angular aggregate, but if the particles are too flaky or elongated, it can result in segregation in the concrete.

Strength of coarse aggregate

The strength of the actual material of coarse aggregate will determine the final strength of the concrete mix. Some rocks and stones are stronger than others – they have a higher resistance to cracking and crushing. Granite, for example, is far stronger than limestone. Therefore, it is a common aggregate used by contractors.

Coarse aggregate water absorption

Aggregate absorption is the amount of water that the crushed stone soaks up in the concrete batch. Dry aggregates suck up any water in the concrete, which can lead to a dry and brittle mix. That is why contractors keep their aggregates damp before mixing a batch of concrete. Coarse aggregate can absorb water up to five percent of its weight. This means that contractors need to add extra water to a concrete mix if the aggregate is dry.

These properties of coarse aggregate will determine the final quality and strength of a concrete batch. The size, grading, shape, strength and water absorption of the aggregate all influence the final concrete mix in various ways, so contractors need to keep an eye on these variables.

___

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.

Sand alternatives for sustainable construction

Sand alternatives for construction

The construction industry relies on many raw materials and minerals for its operations – stone, soil, steel and sand are among the most consumed natural elements in the industry. A growing global population means that more buildings need to be constructed, so some contractors have started to look for sustainable alternatives to these materials.

Sand is a natural material that may seem abundant, but it is being depleted quicker than it is formed by the environment. Leading engineering firms and contractors are exploring sand alternatives for use as aggregates in concrete. These efforts are minimising sand depletion and enabling existing sand to be recycled for other construction projects.

The world uses around 44-billion tonnes of sand every year for construction, land reclamation, roadways and to produce concrete. Not all of it is suitable for construction – desert sand is too fine and beach sand can contain unwanted contaminants such as seashells and plastic pollution. Rivers and quarries are the primary sources of sand used in the building industry.

Sustainable alternatives to sand

Some contractors have started to use plastic waste as an alternative. Non-recyclable bits of plastic waste are ground up into small pellets which are then used as the fine aggregate in a concrete mixture. This process has started to gather momentum in India and the United Kingdom.

While the long-term effects of using plastic in concrete are not fully known, researchers have studied its durability, thermal properties and fire resistance. Plastic is a good alternative to sand and also allows contractors to use up non-recyclable plastic waste in the process.

Contractors are also exploring the use of other sand-like aggregates, including crushed glass and quarry dust. Glass bottles can be recycled but small fractions of broken glass cannot. These bits of broken windows, mirrors, tubes and bottles can be crushed into a sand-like texture. Quarry dust from rock blasting and granite excavation also has similar properties to sand and crushed glass.

Where alternatives to sand cannot be found, contractors have started to recycle sand from old construction projects and sites. Recycling old building materials such as sand, concrete and rubble is starting to gain traction around the world. By embarking on sustainable campaigns, engineers, architects and construction practitioners can minimise their impact on the environment and reduce consumption of natural materials.

___

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.

Aggregates: the difference between crushed stone and gravel

Crushed stone and gravel aggregates

Aggregates are an essential part of any concrete mix. Different concrete projects call for different aggregates, so make sure you know what the differences are between the aggregates. Crushed stone and gravel are not the same, even though they come from the same ore and the same quarries.

Crushed stone and gravel have different uses in construction. This is why aggregate suppliers will sell them separately. They have different methods of production and separate applications. Here are some details that you should know.

Production of crushed stone and gravel

Crushed stone is the result of breaking down large rocks in a crushing machine. The most common ore used to make crushed stone includes granite, limestone, trap rock, basalt, dolomite and sandstone.

Gravel is a natural product of weathering and erosion. It can be collected from river beds or harvested from the same quarries that produce crushed stone. The types of ore in the gravel are similar to crushed stone.

Crushed stone usually has more angled surfaces than gravel as a result of the crushing process. Crushed stone can also range in size from fine dust to large rocks. Gravel is more rounded and often smaller than crushed stone. Gravel also comes in various sizes, from 6mm up to 50mm.

Uses for crushed stone and gravel

Both aggregates are most commonly used for construction projects. The angular surfaces of crushed stone make it perfect for forming flat surfaces when compacted or rolled. It makes a stable, interlocking base for concrete foundations, roads and floors.

Crushed stone is also ideal for railway track ballast beds, a filler element, drainage system and retaining walls on shorelines and mountain roads.

Gravel, being smoother, is often used for aesthetic purposes. It also has a wider range of natural colours, which makes it ideal for decorative landscaping on pathways and flower beds. Gravel is also used as a flooring material on patios, paths, stepping stones and driveways.

If you want an aggregate for construction purposes, crushed stone is your best option. If you need an aggregate for decorative purposes, then gravel is the answer. The two aggregates have different purposes so use the right stone for the job.

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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.