Lime Bloom in Concrete – How to Prevent it – Sort Of.

Recently I’ve been driving about and am noticing lime bloom or efflorescence cropping up everywhere I look.

I know its very hard to avoid lime bloom – well almost impossible, but there are a few steps you can take to try and minimize it from happening rather than having to hear from your customer complaining months down the line as your concrete is ‘faulty’.

Here is my booklet ‘How to reduce Lime Bloom’ which can be downloaded (along with a lot more booklets) by following the link.

 

How to Reduce Lime Bloom / Efflorescence:

 
Top Tips
· Use a water proofer in your mix
· Use insulating blankets to help the concrete cure properly
· Allow the concrete time to cure
· Use a plasticising agent
· Seal the finished product

 
Overview:

 
Efflorescence produces a white stain white-ish discolouration that can appear to be like a powder or like the soapy scum that appears on your paving or other new concrete products.

It is a problem that has been affecting producers of concrete ever since it has concrete has existed. The white staining is a carbon carbonate (or salt) that is produced with the mixing of the cement in the paving, fencing etc and the environment. This salt then makes its way to the surface of the concrete producing the staining.

Lime bloom or efflorescence does not have always look the same. The stain is sometimes powdery, sometimes milky, sometimes very strong and visible. It can cover a large area as well as being in  between the bricks (mortar). Efflorescence or lime bloom is a natural phenomenon resulting from the reaction between cement and water which produces calcium hydroxide ‘lime’. Although the lime  bloom or efflorescence is not harmful and is unattractive, the effect is temporary. How temporary is the big question – There is no way of knowing how long the effect will last, only know that it will pass
eventually – this could be a week, or it could be 3 years, it really depends on the concrete. Once it has finished, it has finished.
The best way of preventing lime bloom is in the manufacturing process of the concrete.

 
Preventing Lime bloom:

 
Once lime bloom is taking effect there are ways to improve its appearance, however lime bloom is best solved by a good mix for the concrete in the first place. The best way to reduce lime bloom, which  is not helped by water retention in the concrete, is to use a water reducing plasticiser, this will reduce the amount of water in your mix making the concrete stronger (whilst using the same amount of  cement) and more flowable.
Also using a water proofer will help and protect against the water getting into the concrete.
Once the concrete has been produced use a good sealer to seal the product. This will go some way to helping the lime bloom. Unfortunately lime bloom cannot be completely prevented as the salt crystals come from the lime that is used to produce cement. Your best bet is try to follow the above tips and hope that your concrete will not succumb to lime bloom.

For more booklets click downloads

Admixtures in your concrete

Happy new year everyone! 2013!!! I know, its sad that I’m blogging on New Years day, but what can I say, precasting talk always helps me clear my head! (and I may have written this last year…)

So, New start and all, thought it would be a good chance to talk about admixtures, maybe creating a new mix for a new year 🙂 . Which one should I use, how do they help and what do they do? I get asked this all the time. I still can’t believe some people don’t use them! Its crazy, the advantages that admixtures give is too large to ignore! So as a new years resolution, I don’t care what you do as long as you try out atleast 1 new admixture!

So I thought i would explain the different types of admixtures with an extract from my booklet what are admixtures – get it here

In regards to concrete, what is Admixture?
Often referred to as the 5th ingredient, admixtures are formulated from various chemicals – generally in liquid form – but can be powders – and are added to concrete to improve the physical properties in the wet / plastic & hardened state.
POTENTIAL IMPROVEMENTS: Depending on admixture type

In the plastic (workable) state:
· Better mix workability
· Easier to place
· Easier to compact
· Improved cohesion
· Reduced segregation
· Bleed water reduced

In the hardened (set) state:
· Denser concrete
· Increased strength
· Improved durability
· Better frost resistance
· Volume stability
· Reduced permeability
· Reduced efflorescence
· Brighter colours

So these are some of the benefits admixtures can bring to wet cast concrete.

Below is  an extract on my book talking about admixtures in concrete, this part is only focusing on the superplasticiser part: get the full booklet here

Superplasticiser offers a number of significant benefits to the pre-caster.

More effective use of cement results in increased strength allowing a reduction in cement content. Have a look at the following diagrams which illustrate how this works.

Here we see the cement particles are only partly whetted when they mix with the water. As you can see the red area has no water/cement contact at all and will not fully hydrate the cement.

With the addition of superplasticiser the cement particles are dispersed allowing the water to coat the whole of each particle ensuring complete hydration resulting in increased concrete strength.
The economics speak for themselves:
Say you are using a 300kg/m³ cement content to achieve a 28 day strength of 35 N/mm².
Cement cost £24.60 at £82.00/ton If you used superplasticiser you could expect a 30% increase in strength giving 45.5N/mm² or an extra 10N/mm² strength. Typically we need to use 6kgs cement per 1N/mm² strength and so that 10N/mm² we have gained is equivalent to 60kgs cement (6kgs x 10). It follows that we could safely reduce the cement content to say 240kgs/m³ Cement cost £19.68 at £82.00/ton = £4.92 saving in cement. To do this you would add 0.9 litres per 100kg cement. The cost of admix is £3.91/m³ to do this making a saving of £1 per m³ concrete.

If you do nothing else this new year with your concrete but try out an admixture like a super plasticiser, the difference will be immediately noticeable.

So good precasting in the new year, oh and anybody at the precast show or world of concrete in the states, we are there as always this year!

See you soon.

Happy New Year 🙂