How to fix common concrete slab problems

How to fix common concrete slab problems

When working with concrete, contractors may encounter a few different problems. The following issues can sometimes occur when pouring concrete slabs. While some aspects of working with concrete slabs have changed over the years, many issues have not. Here are three common problems that come with pouring concrete slabs, and their possible solutions.

1) Excessive Bleeding

Bleeding occurs when the heavy ingredients in concrete (aggregate and sand) settle and push the extra water to the top of the slab. Concrete that bleeds for too long or too fast can cause problems like sand streaks in walls; weak horizontal construction joints; rock jams in pump lines; etc. Finishing a concrete slab before bleed water has evaporated can cause cracking, dusting, scaling and low-wear resistance.

Excessive bleeding can be avoided by not adding too much water to the concrete; placing concrete at the lowest possible slump (if you need a higher slump to speed placement, consider using a superplasticizer); using a more finely ground cement; adding more cement to the mix; blending in a fine blow sand or fly ash.

2) Curling

Curling happens when a slab rises up at corners and edges – or sometimes at a mid-panel crack. It happens when the top section of a concrete slab dries or cools faster than the bottom section. Curled concrete slabs can be fixed, but it is expensive. 

Grinding can level out the edges, and grout can be used to restore support to the slab. The best way to avoid curling is to control it before it happens. There are a number of material choices, construction practices and design decisions that will help prevent curling from happening in the first place.

3) Thin slab

All concrete slabs have varied thicknesses – some parts of the slab are thicker than others. When it comes to thin slabs, the thinnest sections may be too thin to retain their strength and may be prone to crumbling. In such cases, the contractor needs to decide how thin is too thin.

They must decide whether to make the slabs thicker for the sake of giving additional strength and durability to the concrete slab. Contractors should also pour thin slabs very carefully and ensure that the depth of concrete is even throughout the slab.

These are three of the most common problems that can arise when working with concrete slabs. They are easy to fix; taking care while pouring the concrete and being precise with measurements is the best way to avoid these problems in the first place.

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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.

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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.

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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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 to prevent dampness in a building

How to prevent dampness in a building

Dampness in a building may occur due to faulty construction, the use of poor-quality building materials or bad architectural design. Dampness affects the lifespan of a building or structure, but it also creates unhygienic conditions. Mold and fungi love to grow in damp conditions, so it is best to fix any signs of wet concrete as soon as possible.

The measures taken to prevent water from leaking into a roof is usually called waterproofing. The treatment given to a structure to keep its basement, floor and walls dry is called damp proofing. Some of the problems caused by dampness in a building include the disintegration of bricks, stones, tiles; the softening and crumbling of plaster; the corrosion of metals; the warping, buckling and rotting of timber; the presence of termites; deterioration to electrical fittings and the bleaching and flaking of paint with the formation of coloured patches.

What causes dampness in a building?

The absorption of moisture by building materials is one of the main causes of dampness. This can be caused by faulty structure design, bad workmanship or the use of defective structures or materials.

Sources of dampness in buildings include the rising of moisture through the foundation walling; splashing rainwater which rebounds after hitting the wall surface; penetration of rainwater through unprotected tops of walls, parapets or compound walls; gutters which allow rainwater to descend through the top supporting wall. In the case of buildings with flat roofs, inadequate roof slopes, improper rainwater pipe connections and defective junctions between roof slabs and parapet walls can also cause dampness.

How to prevent dampness in a building

1. Membrane Damp Proofing

This involves placing layers of water-repellant materials between the source of dampness and the structure. This type of material is commonly known as damp proof course (DPC). It could be made from materials like plastic or polythene sheets, cement-based concrete, bituminous felts or asphalt. Applying DPC in a basement is usually referred to as tanking and can prevent ground moisture from seeping into the concrete walls.

2. Integral Damp Proofing

This form of damp proofing involves adding certain waterproofing compounds to the concrete mix to increase its impermeability (resistance to absorbing moisture). The compounds made from sand, clay or lime help to fill the voids in concrete and make it waterproof. Compounds such as aluminium sulfate, calcium chlorides and alkaline silicates chemically react when mixed with concrete, producing waterproof concrete.

3. Surface Treatment

This type of treatment involves filling up the pores of the surfaces subjected to dampness. Water repellent metallic soaps such as calcium and aluminium oleates and stearates are often used for this purpose. Cement coating, transparent coatings, paints, varnishes and bituminous solutions also fall under this category. Another economical option for damp surface treatment is lime cement plaster. This effectively prevents dampness in walls as a result of rain.

4. Guniting

For this type of damp-proofing, a cement gun machine is used to deposit a layer of rich cement mortar over the surface. The surface must be completely cleaned of dirt, dust, grease or loose particles by wetting it properly. Cement and sand (or fine aggregates) are then fed into the machine. This mixture is finally shot onto the prepared surface under a pressure of 2 to 3 kg per square centimetre by holding the nozzle of the cement gun at a distance of 75 to 90 cm from the working surface.

5. Cavity Wall Construction

This form of damp-proofing consists of protecting the main wall of a building by an outer wall, leaving a cavity between the two walls. The cavity prevents moisture from spreading from the outer to the inner wall.

These five methods of damp-proofing will help to protect concrete structures from excess moisture, which can lead to mold, fungus, rot and damage to buildings. Contractors and homeowners must always inspect their buildings for any signs of stress and damage, such as dampness, which could affect the integrity and durability of the structure.

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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.

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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.

What is concrete bleeding?

What is concrete bleeding?

Concrete bleeding is a problem that can affect any batch of concrete that has been improperly measured and mixed. It is the movement of water to the surface of the concrete after it has been poured. Water collects on the surface of a concrete slab or structure when the water-to-cement ratio of the mix is too high (when too much water has been added to the batch). 

Bad proportioning of materials in a concrete batch is the main cause of bleeding. Too much water causes the concrete to segregate – a phenomenon where the heavy aggregates sink to the bottom of the mix, leaving the cement, sand and water at the surface of the structure. The water then seeps to the surface of the slab or structure, which creates big problems on the resultant integrity of the concrete.

When the water travels to the surface of the structure, it carries the fine particles of cement with it. This leaves a deficiency of cement within the rest of the structure. Since cement is the main binding material, the rest of the structure dries without much bonding between materials. Bleeding causes a weak, crumbly and dry concrete structure that cannot support any weight.

Bleeding affects the workability of concrete

There are two categories of concrete bleeding; normal and excessive bleeding. These are determined by the amount of water lost through the surface of the concrete structure. Both normal and excessive bleeding can affect the final quality of the concrete and the overall durability of the structure.

Normal bleeding is that which often occurs in all concrete projects. When you see freshly-poured concrete, it will often have a very thin layer of water on its surface. This is nothing to worry about and can actually enhance the workability of the mixture. The improvement in workability makes it easier to pour and work with before it sets. It also gives the concrete a smooth finish.

Excessive bleeding is an abnormal amount of water loss through the surface of the concrete. The mixture is usually too wet before it is poured. Contractors should keep an eye on their concrete batch and add more cement or dry aggregate if they think the mixture is too runny. Excessive bleeding leads to a high loss of water and a dry, brittle concrete structure.

Concrete that has suffered from excessive bleeding may also have large voids in the centre of the structure where heavy aggregates have moved the fine particles out of their way as they sink. This creates air bubbles and empty pockets that can severely affect the strength and durability of the concrete.

The best way to prevent concrete bleeding is to use the required amount of water, as printed on the bag of cement. Contractors can also carry out a slump test to check the mixture has the correct ratio of dry to wet ingredients. Bleeding is a normal occurrence with concrete, but excessive bleeding creates long-term problems that cannot be easily repaired.

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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.

Types of inspection for concrete structures

Inspection of concrete bridge

Inspecting concrete is a necessary step in the proper maintenance of buildings and  structures. It allows contractors to find any faults, such as cracks and salt damage, before they become bigger problems. Inspections will provide assurance that the concrete is structurally safe at any given period, so they need to be performed once every couple of months at least.

During inspections, any defects or problems need to be recorded. This allows contractors to keep an accurate record of when issues occur and how they are resolved. This information can also help engineers and architects to plan the repair work and strengthen the concrete structure.

Types of concrete inspection

There are three main types of inspection that need to be performed on concrete structures. These are; routine, detailed and special inspections.

  1. Routine inspection – This is the examination of concrete structures at regular intervals. Routine inspections are usually quick and they only look at the general condition of the structure. Each examination is recorded in a book. The inspector will make a visual assessment and use simple tools to determine the condition of the concrete. The purpose of routine inspections is to find cracks, chips, delamination, spalling, salt build-up, rust streaks and deformation in the concrete.
  2. Detailed inspection – This is a thorough examination of a concrete structure that takes longer than a routine inspection. A detailed inspection requires the assessor to closely examine the concrete and use specialised tools to accurately determine the state of the structure. These inspections need to be carried out by trained engineers who can plan comprehensive repairs.
  3. Special inspection – These examinations are done in special circumstances or after unusual events. They are usually performed when a building is being extended vertically, when reinforced concrete pillars show signs of stress, when a foundation starts to collapse, after earthquakes or ground tremors, after a fire, after a flood and after accidents. Any of these circumstances or events will require an engineer to perform a special inspection, which looks at very specific aspects of a structure’s integrity.

These three inspections ensure that buildings and other load-bearing concrete structures remain in perfect condition. Routine inspections must be carried out regularly, white detailed and special inspections are more needs-based – they are carried out as and when necessary. All concrete inspections must be recorded and performed by trained engineers and contractors.

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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.

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.

The role of calcium chloride in concrete

The role of calcium chloride in concrete

Admixtures are chemicals that are mixed in with the cement, aggregate and water in a concrete batch. These chemicals have various effects on concrete; some make it waterproof, others make it more workable. Calcium chloride is an admixture that speeds up the hydration process and makes the concrete set quicker with high initial strength.

This can have various benefits. By speeding up the initial setting time, building projects can progress at a more rapid pace. It also allows contractors to build on top of new concrete within a number of days. This is ideal for load-bearing structures, such as columns and beams.

How to add calcium chloride to concrete

Calcium chloride can be purchased as flakes, pellets, granules or as a liquid. All forms of this chemical are soluble; they can dissolve in water, so it is recommended to use the liquid form. No more than two percent of a concrete batch should be calcium chloride. 

The chemical reacts directly with cement, not the other ingredients in a concrete batch, so it cannot come into direct contact with cement until a concrete batch is being mixed. Contractors should dilute the calcium chloride in the water for the concrete batch and then mix it with the sand and crushed stone. The cement can then be added to the mix.

Effects of calcium chloride on concrete

As mentioned before, calcium chloride speeds up the setting time of concrete and allows it to develop high initial strength. This admixture can be used in low-temperature conditions where concrete would normally take a few days to set. When using calcium chloride, contractors need to make sure that the concrete does not set before they have finished working with it.

Calcium chloride does not affect the water ratio required for a concrete batch. However, it can cause the mix to become stiff, so contractors may need to add a bit more water to keep the mix workable. This admixture also reduces bleeding in concrete once it has been poured, which can sometimes increase drying shrinkage. Contractors need to keep the surface of the concrete damp to prevent it from cracking.

In some cases, calcium chloride can cause a white deposit to form on the surface of the cured concrete. This efflorescence does not happen in every case, but it is not the same as salt damage – contractors do not need to be concerned. These white deposits cannot be washed away with water, so contractors must dilute hydrochloric acid with water and pour it over the surface of the concrete. Brush the diluted acid away with a broom and always wear rubber gloves.

Advantages of using calcium chloride in concrete

  • Development of high initial strength.
  • Reduced initial and final setting time.
  • Reduced bleeding.
  • Improved workability in cold conditions.
  • Fast work turnaround.
  • Cost-effective

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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.

How to test the workability of concrete on-site

How to test the workability of concrete on-site

There are a few ways to test the workability of concrete at a construction site, but three of the most common methods are the Vee-Bee test, slump test and compaction factor test. Different concrete mixes will have various values for these tests, depending on their applications. So, what is the workability of concrete?

The workability describes the ease or difficulty of the handling of a concrete mix. It is the dryness or liquidity of concrete that determines how easy it is to mix, transport, pour and place in formwork. The workability is an important factor for a concrete mix for a couple of reasons.

If the mixture is too wet, the coarse aggregates will sink and settle at the bottom of the concrete structure. As a result, the concrete will be non-uniform and have weakened integrity. If the concrete mixture is too dry, it will be hard to mix and place in position. It will also be prone to cracking.

Tests for the workability of concrete

As mentioned before, there are three common tests for concrete workability. These include:

  • Vee-Bee consistometer test
  • Slump test
  • Compaction factor test

The slump test is the only one that can be performed on-site. The Vee-Bee test and compaction factor test are usually performed in a laboratory or specialised facility.

How to perform a concrete slump test

A concrete slump test is performed on-site to determine the correct workability of a concrete mix. Contractors will use a cone-shaped mould that is 30cm high with a top diameter of 10cm and a bottom diameter of 20cm. The test is performed in the following steps:

  1. Place the slump mould on a smooth, flat, non-absorbent surface.
  2. Mix the dry ingredients of the concrete and then add the required amount of water, according to the instructions on the bag of cement.
  3. Fill one quarter of the slump mould with the concrete mix.
  4. Compact the concrete 25 times using a tamping rod.
  5. Place some more concrete in the mould, filling it half-way. Compact it again.
  6. Place more concrete in the mould, filling it three-quarters of the way. Compact again, 25 times. 
  7. Fill the mould completely and compact again. The tamping rod should penetrate all the layers to ensure maximum compaction and no lines of separation between layers.
  8. Scrape off any excess concrete from the top of the mould, using a trowel.
  9. Flip the mould over and place the concrete on the flat surface. Remove the mould in an upwards direction.
  10. Watch the concrete slump and settle. Once it has stopped moving, measure the subsidence (or how much the concrete sinks from its original 30cm height) in millimetres. This will tell the contractor how much the concrete will settle and how easy it will be to handle on-site.

Recommended values for the slump test

The slump test should only be used for concrete that is supposed to be of high or medium workability (i.e. stiff or semi-dry mixes, not dry mixes). The following table outlines the recommended slump value for various concrete applications:

Concrete applicationSlump
Road construction20 to 40 mm
Walls, slabs, piers, curbs40 to 50 mm
Normal reinforced cement concrete (RCC) work80 to 150 mm
Mass concrete20 to 50 mm
Concrete to be vibrated and compacted10 to 25 mm

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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.

Eight frequently asked questions about concrete

Eight frequently asked questions about concrete

Concrete is one of the most popular building materials across the globe. It is used in most construction projects, along with other cement-based materials such as plaster and mortar. Here are eight frequently asked questions about concrete that can shed some light on the material for people wanting to know more or become contractors themselves.

1. Are cement and concrete the same thing?

No, cement and concrete are not the same. Cement is a main ingredient of concrete and comes in a dry powder form. Together with water and aggregates (usually rock, gravel or sand) cement is used to make concrete. As a part of concrete, cement is the binding agent that holds the mixture together.

2. How long does it take for concrete to become hard, or set?

It takes 24 – 48 hours for concrete to set. Concrete will achieve 70% of its full strength seven days after it was laid. It will reach its full strength (100%) 28 days after it was laid. Concrete will become increasingly stronger over time because the cement forms bonds with surrounding moisture particles.

3. What are the ingredients of concrete?

Concrete is made up of cement, water and aggregates (sand or crushed stone). Cement is a dry powder made by LafargeHolcim Tanzania. Cement is the binding agent that holds the mixture together. Water is needed to form a chemical reaction with the cement. The water/cement ratio will determine the strength of the concrete. Aggregates can be either gravel, rocks or sand. It gives the concrete its structural volume and strength.

4. Can I lay concrete in wet weather?

Yes, it is possible to lay concrete when it is raining, but proper preparation is necessary. Precipitation (rain, snow, sleet, or hail that falls to or condenses on the ground) can lead to concrete becoming soft, which could reduce its strength. Constructing a protective enclosure of wood and plastic sheeting around the area where the concrete will be laid can prevent this type of damage.

5. What is concrete’s durability?

Concrete is extremely durable. It is a high-strength product and its traits make it suitable to be used in a number of ways, from industrial to domestic. Concrete has a lifespan of 40 years or more and it also hardens with age.

6. Is concrete an eco-friendly material?

Concrete is sourced from natural rock and often extracted on location, which means that minimal resources are needed to transport it to the required work site. At the end of its lifespan, concrete can be crushed and recycled. So, while it is not traditionally classed as an environmentally-friendly material, there are eco-friendly elements to concrete’s creation.

7. Will my floors be cold if they are made from concrete?

While concrete floors can be cold, they are not much colder than other often-used materials like natural stone flooring or ceramic tiles. During hot summer months, cooler floors can be a bonus and contribute to lower air conditioning costs – especially in a country like Tanzania where hot weather can be experienced all year-round.

8. How do I calculate the amount of concrete my project requires?

It is simple to calculate the amount of concrete needed for your project. Here’s an article that outlines the process of estimating the volume of concrete needed for any project, based on its area and volume.  

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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.

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. 

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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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