TANZANIA - #likelafargeholcim

For building tips and information, follow us on

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

___

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.

Synthetic fibres can increase the durability of concrete

Contractors sometimes add synthetic fibres to their concrete mix. These fibres of man-made polymers are specifically engineered to withstand the long-term alkaline environment within a concrete mix. They are used to minimise cracking, lower the permeability of the concrete and increase the strength of the structure. They act as a secondary reinforcement element; the primary …

The eight types of construction company

There are many different types of construction company. Not all contractors specialise in the same fields and not all companies do the same construction work. Depending on the type of work they do, construction companies can be classified into the following eight types: 1. General contractors A general contractor provides all of the labour, equipment, …

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 …

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 …

The importance of having a schedule for a construction project

Construction projects are delicate operations that need to run on time in order to stay within the allocated budget. As soon as a project is delayed, it costs the contractors and building owners more money. Having a strict schedule is important as it keeps the project on time and allows all workers to know when …

How to prepare a concrete surface for a topping

Sometimes concrete surfaces are given a decorative topping that adds further protection and durability to a floor or carpark. The underlying concrete will need to be prepared properly before any topping is laid on top. This will ensure that a good bond is formed between the two materials and that no cracks or chips will …