There are two types of concrete batching plants: dry batching and wet batching. While wet plants are generally considered to produce a higher level of consistency, in Australia, the predominant method of producing concrete is dry batching.
Dry batching involves combining fine and coarse aggregates with cementitious material in a truck-mounted transit mixer, before adding a predetermined amount of water.
Horst Hendrich, National Key Account Manager Gough Industrial Solutions, says each variant of concrete has a specific formula based on its application.
“Water is an important ingredient in the making of concrete, plus the other materials used do not have the decency to remain completely dry,” Mr. Hendrich says.
“Moisture probes are not often used and as a result, determining the moisture content of the aggregates, both fine and course, is never going to result in an accurate reading.”
Mr. Hendrich says once a mixture is dry batched, the agitator is parked under a load bay, with a volume of water added based on an educated guess of existing moisture content.
“The barrel is sped up to 14 to 18 revolutions per minute, before the combined aggregates and cementitious material is dropped into the now speeding bowl,” he says.
“This is the messy part where cement dust fills the air.”
According to Mr. Hendrich, once this process is complete, the agitator makes its way to a slump stand, where the driver spends 10 minutes checking the slump or “wetness” of the concrete.
“Ask three different people to gauge the slump of concrete and you will have three different results, which determines the ultimate strength of the product,” he says.
According to Mr. Hendrich, for every 10 litres of water added to a cubic metre of concrete, there is a 2.5-megapascal reduction in strength.
“There are many significant and costly effects of too much water, from the inconvenience of streaks, flaking or cracking, to total loss of a slab,” he says.
“Dry batching therefore has few draw backs including environmental dust and noise issues and inconsistent batches of concrete.”
The alternative, wet batching, is used less widely by concrete and pre-mix companies in Australia. Mr. Heinrich says however that the process is steadily gaining traction.
“Wet batching was tried many years ago, perhaps with some apathy – but technology has advanced and we now have more efficient mixer designs, batching systems and software,” Mr. Heinrich says.
“I’m now asked to quote on wet batch plants quite regularly.”
At a wet batch plant, the concrete mixture, including water, is mixed at one central location.
“Wet batch does away with guess work and inconsistency by removing the slump stand and as a consequence, the possibility of human error,” Mr. Heinrich says.
“The dangerous dust issue also becomes non-existent, noise is reduced and any issue with batch consistency is solved.”
According to Mr. Heinrich, Italian construction and engineering company Simem is a leader in the wet batch space. He adds that Gough Industrial Solutions is Simem’s exclusive Australian and New Zealand distributor.
“Wet batch plants are especially useful for large infrastructure and commercial projects, where thousands of cubic metres of concrete can be batched identically,” he says.
“Simem wet batch plants utilise moisture probes at the aggregate gate, so moisture is measured as the aggregates are dosed and not from the front of the storage stock pile.”
Mr. Heinrich says while Simem plants have multiple mixers, he suggests the MSO Twin Shaft series for general pre-mix or ready-mix concrete. He adds that Simem mixers have large top openings, which allows combined cementations and aggregates to be fed directly into the mixer.
“Without the rotating blades of an agitator getting in the way, the load time of an MSO mixer is half that of an agitator,” he says.
“It also solves the dust issue. The finer cementitious mix is not displaced as dust by the air being expelled out of the agitator barrel.”
Mr. Heinrich says with a Simem wet batch plant, the mixing time is measured in seconds.
“The intensity of the mixing action thoroughly blends the ingredients and uniformly coats the aggregate particles with cement paste,” Mr. Heinrich says.
“The plant becomes cleaner, quieter and more efficient and truck utilisation improves significantly with less fuel consumption and quicker turn arounds.”
According to Mr. Heinrich, Gough Industrial Solutions, in conjunction with Simem, can design and deliver wet batch plants in accordance with all relevant Australian Standards.
“Simem has a range of mobile, semi-mobile and fixed wet batch plants suitable for local supply, commercial, infrastructure and precast projects,” he says.