THE IMPACT OF SUBSTANDARD AND INCONSISTENT AGGREGATES ON THE READYMIX PRODUCER

1
THE IMPACT OF SUBSTANDARD AND INCONSISTENT
AGGREGATES ON THE READYMIX PRODUCER
Author Matthew Barker Date 22 April 2016
2
CONSISTENCY

• All manufacturing processes depend on consistency
  to quality control and cost their products.
• For the readymix industry aggregates are their
  biggest source of inconsistency.
• Admixtures and cement work on less than 2
  variance
• Cement plants have huge stock piles that are
  constantly being mixed
• I challenge any of you here to go back to your
  sand grading files and just look at the changes
  in the Fineness Modulus F.M.
• A change from 2.7 to 2.8 can mean as much as 10
  litres of water
• Or 20 kg of cement, or R20.00 per m3
• QC systems monitor the changes in strength where
  they should be watching the consistency of the
  aggregates

3
AGGREGATES

• You can make concrete out of any aggregates.
• True but poor aggregates make poor concrete
• That concrete is costly and will not perform its
  function
• We have been making aggregates from this quarry
  for years and nothing has changed
• Ja Sure
• However the truth is that 70 of the concrete is
  made up of aggregates

4
Raw materials aggregates

• Definition
• There are different types of aggregates
• fine aggregates (sands)
• coarse aggregates
• Different physical natures
• rolled
• crushed
• Different chemical natures
• limestone
• granite
• silica
• etc.

5
Raw materials aggregates

• Definition
• Main use in following application fields
• Concrete
• Driveway bases
• Railway bases

6
Raw materials aggregates

• Differentiation between

7
AGGREGATE GRADING

• Aggregates are the cheap filler of the volume of
  concrete
• Water and cement are the expensive glue
• Admixtures reduce the water content to attain the
  flow or slump required therefore reducing the
  cement requirement.
• Surface area. Which has the most surface area
  per volume a stone or a grain of sand.
• The finer the particle the more surface area.
• THE MORE GLUE REQUIRED TO COAT THE PARTICLE
• The more water and cement

8
Aggregate Grading

• So the more larger stones in the mix the cheaper
  the concrete will be
• Sizes 75, 37, 26, 19, 13, 9.5, 6.7mm
• The finer the sand the more expensive
• Sizes 4.75, 2.36, 1.18, 0.60, 0.30, 0.15 mm
• The really expensive stuff is the DUST, silt and
  clay
• 0.075 and lower
• Clay Contents - very thirsty, very expensive
• Only certain admixtures work with clays. Ask your
  friendly CHRYSO rep
• To fill the volume you need a portion of all the
  sizes to fill the voids or gaps

9
RELATIVE DENSITY

• Relative Density (R.D.) or Specific Gravity
  (S.G.) is the weight of the aggregate relative to
  water.
• 1 litre of water 1 kg
• 1 litre of your rock 3.15 kg Norite (2.9 3.3)
  Others 2.5 3.5 kg
• 1 litre of concrete 2.4 kg or 2400 kg/m3
  Norite 2.8kg or 2800kg/m3
• If you change R.D. from 2.8 to 2.9 you change the
  volume by 24 litres or 2.4
• Loose Bulk Density loosely placed stones 1900
  kg/m3
• Compacted Bulk Density compacted placed stones
  2000 kg/m3
• Bulking Factor Sand bulks when wet.
• This means you are buying water or additional
  volume

10
Cleanliness and Shape

• Round is great. Rolls and allows the concrete to
  flow

• Angular and flaky is horrible, the concrete will
  not flow

• The aggregates must be sound - strong, wearing
  and the same geological activity
• No alkali reactivity
• A heap of stones with sand and dust in it is
  expensive as you will not get consistency when
  loading. Sand goes to the bottom.
• Dust is a killer as its very thirsty. The dust
  needs washing away.
• Where do the piles of dust go when cleaning under
  conveyor belts?

11
Dont tell me they are always the same

• Natural product Different parts of the
  quarry, the overburden is moved but what about
  the weathered layer on the surface of the rock.
• Dykes Faults
• Deleterious Materials Wood
• Detonators, plastic, paper , metals all cause
  surface defects
• Wearing sieves Holes allow larger particles
  through
• Wet sieves can clog and the holes become smaller
  and thus the sand becomes finer and the water
  demand goes up. (40 litres/m3 at Karee 4)
• Natural Sands Need sieving and washing to
  remove dust and silt

12
Adsorption

• Some materials will adsorb moisture.
• Most in SA are less than 0.5 adsorption so this
  is not considered.
• The rest of the world experience up to 5
  regularly.
• 5 of 1000 kg 50 litres of water.
• Can take 30 minutes to be adsorbed, in doing so
  what is happening to your slump?
• Pre wet aggregates. Saturated surface dried

13
Wearing Surface

• The aggregates give the concrete its wearing
  properties.
• They are harder than the glue.
• If not they will probably crumble while mixing
  and push up the water demand. A quarry at
  Hartebeesport battled with 30 MPa concretes with
  their stone.
• You need enough stone close to the surface of the
  concrete to provide these properties.
• Never just look at concrete and think its stony,
  compact it first then feel how deep the
  aggregates are. If more than a few mm deep you
  are giving away money and you are asking for
  problems.
• Concrete has to be compacted. Compact properly
  first , then decide.
• Contractors are paid to compact, without this
  compaction the concrete will fail. And as always
  you will be blamed because you did not point this
  out to them.

14
Curing

• Otherwise the complaints will be shrinkage
  cracks, dusting etc.
• It is also your duty to point out that Curing is
  not a place in China.
• Admixtures can assist with solving some of the
  minor problems
• Admixtures make good concrete better not bad
  concrete good
• Admixtures make bad concrete better

15
Thank You

• Any Questions
• Thank You