Ultrasonic Mixing For High-Performance Concrete

The use of micro- and nanosilica or nanotubes leads to improvements in the compressive strength of high-performance concrete. Ultrasonication is an effective means for the mixing, wetting and dispersing of nanomaterials in cement or concrete.
 

Micro silica is widely used in concrete today, leading to higher compressive strength or water and chemical resistant concretes. That can reduce material costs and energy usage. New nanomaterials, such as nano silica or nanotubes lead to further improvements in resistance and strength. But in order to exhibit the full potential of nanomaterials, a reliable and efficient dispersion technique is required. Probe-type sonicators are the most reliable and efficacious technique to produce nano-dispersion, even in highly viscous and paste-like slurries such as cement and concrete.

Microfine Cement Grout Dispersion with Ultrasonic Mixers

The research team of Draganović present research article, the authors investigate the dispersion of microfine cement grout using ultrasound technology and conventional laboratory dissolvers. The study aims to compare the performance of ultrasound – in the study specifically the sonicator UP400St – with traditional methods of grout dispersion.

The researchers conducted a series of experiments using different dispersion techniques to evaluate the particle size distribution (PSD) and zeta potential of the microfine cement particles. The dispersion techniques include ultrasound treatment using the UP400St sonicator, high-speed laboratory dissolvers, and the combination of both methods.

The results showed that ultrasound dispersion using the sonicator UP400St achieved significantly better particle size distribution compared to conventional laboratory dissolvers. The sonicator UP400St effectively reduces the agglomeration of microfine cement particles and produces a more homogenous and stable grout suspension. The ultrasound treatment improves the distribution of smaller particles, resulting in a narrower particle size distribution range.
 

Compared Dispersion methods: Vma-Getzmann Dispermat CV-3 dissolver equipped with a 90-mm disk and a rotor-stator system. Hielscher UP400St ultrasound device equipped with an H22 sonotrode.
(Study and pictures: ©Draganovic et al., 2020)

 
Additionally, the use of ultrasound in combination with conventional laboratory dissolvers further improves the dispersion efficiency, achieving an even finer particle size distribution compared to ultrasound treatment alone. When combined, sonication provides the micro-mixing and nano-dispersion, whilst the dissolver contributes to the macro-mixing ensuring that all particles into the ultrasonic cavitation zone. This allows for better control over the particle size distribution (PSD) and zeta potential of the microfine cement grout in batch operation. When using a flow cell reactor, the particles suspension passes automatically the cavitational hot spot zone so that the additional stirring is superfluous.

Overall, the study highlights the superior performance of the sonicator UP400St in dispersing microfine cement grout. The ultrasound treatment, especially when combined with conventional laboratory dissolvers, offers a highly effective and efficient method for achieving a uniform and stable suspension of microfine cement particles.

It is worth noting that the article provides a comprehensive comparison between ultrasound and conventional dispersion methods highlighting the superior performance of sonication in grout dispersion.
(cf. Draganović et al., 2020)
 

The ultrasonic homogenizer UP400St is compared regarding dispersion efficiency of cement grout with an ordinary laboratory mixer equipped with a disk, and using the rotor-stator technique. The study showed that ultrasonic dispersion is not only an effective method but is even better than a mixer using the rotor-stator technique.
(study and graphic: © Draganović et al., 2020)

Concrete Research And Development

Concrete research looks for materials and processes to:

• reduce material costs and energy costs
• obtain high initial and final resistance
• improve density and compressive strength
• improve workability, pumpability and finishability
• improve durability and reduce permeability
• reduce shrinkage cracks, dusting and delamination problems
• chemical resistance, e.g. sulfate resistance

Cement And Concrete Mixing

When it comes to improvements in concrete properties, mixing technology is as important as concrete composition. Mixing is an essential step in the production of uniform, high quality concrete. Although numerous guidelines and regulations, e.g. DIN EN 206 cover the composition of concrete and its components, the actual process of cement mixing and concrete mixing is left to the user.
It is decisive, that water, cement and admixtures are evenly dispersed and distributed down to a fine scale and that agglomerates are sufficiently dispersed. Insufficient dispersing or deagglomeration results in inferior concrete properties. Due to the low water content and the high dosage of admixtures, the mixing of self-compacting concrete (SCC) and ultra high strength concrete (UHPC) requires a longer mixing time or a more effective mixing technology.

Nanomaterials In Concrete

During the hydration of the cement nanoscale hydration products, such as calcium hydrates form in the hardening concrete. Nano particles of silica or nanotubes turn into nano particles of cement during the solidification of the concrete. Smaller particles lead to shorter particle distance and a denser and less porous material. This increases the compressive strength and reduces the permeability.

A major disadvantage of nanosize powder and materials, though, is the tendency to form agglomerates during wetting and mixing. Unless the individual particles are well dispersed, agglomeration reduces the exposed particle surface leading to inferior concrete properties.

Ultrasonic Mixing Of Nanomaterials

Ultrasonication is a very effective means for the mixing, dispersing and deagglomeration. The picture below shows a typical result of ultrasonic dispersing of fumed silica in water.

Starting (green curve) at an agglomerate particle size of more than 200 micron (D50) most of the particles were reduced to less than 200 nanometers.

Ultrasonic Mixing At Any Scale

Hielscher offers ultrasonic mixing devices for use in research and full scale processing.

Sonicators for Laboratory Research And Development

Hielscher ultrasonic laboratory homogenizers are the perfect mixing tool for research and development on lab scale. Hielscher lab sonicators are typically used for the ultrasonic mixing of small batches. Hielscher ultrasonic homogenizers offer an accurate parameter control and excellent reproducibility for the preparation of the scale up. This makes it easy to mix different formulations and determine the impact of ultrasonication intensity and duration of sonication.

Ultrasonic Inline Mixing In Production

The ultrasonic mixing equipment needed for scale up can be determined exactly based on the laboratory test. For processing large volume streams of cement or concrete, high-performance ultrasonicators are usually operated in continuous flow mode using flow-through reactors. This allows for highly uniform mixing and the flawless processing of pastes and slurries – even with very high viscosities.

The table below gives you an indication of the approximate processing capacity of our ultrasonicators depending on the batch volume or flow rate to be processed: