Power, Precision and Performance: Selecting Batch Plants for UHPC

Ultra-High-Performance Concrete (UHPC) is an advanced class of concrete known for its exceptional strength, durability and resilience compared to conventional mixes. UHPC boasts compressive strengths above 22,000 psi (150 MPa), more than double the performance of high-strength concrete.

UHPC is dense and impermeable, thanks to a mix-design that includes fine powders such as silica fume and quartz flour, a very low water-to-cement ratio, high range-water reducers, and steel or polymer fibers. So, it may come as no surprise that UHPC producers require a specialized approach when investing in mixing technology and batch plants.

In this article, Mixer Systems, Inc., experts weigh in on the unique specifications and options producers should consider when UHPC production demands power, precision and performance.

High Shear Mixing Technology

At the heart of UHPC production is high shear mixing technology. Because UHPC is typically used in large infrastructure and complex architectural applications, high volume is an important factor as well. Traditional drum mixers simply cannot provide the energy or precision required to thoroughly combine dry powders with water and superplasticizers, or to evenly disperse fibers throughout the mix. Furthermore, traditional drum mixers or concrete mixing trucks producing UHPC can be very difficult to clean, making it an undesirable product to supply.

Planetary mixers, horizontal shaft and twin shaft mixers are the most common mixers used to mix UHPC. Planetary mixers from Mixer Systems, Inc. produce a unique counter current mixing action, resulting in fast, homogenous mixes. Horizontal mixers from Mixer Systems, Inc. are typically used on smaller applications, including on-site UHPC production.

Mixer Systems, Inc., Twin Shaft mixers are high volume, high shear with mixing times from 60-90 seconds. Intermeshing paddles to rapidly blend materials while maintaining consistent flow and distribution and have been successfully used on major UHPC projects such as the Delaware Memorial Bridge resurfacing project.

High-shear energy is especially important during the addition of water and superplasticizers. The extremely low water content of UHPC means that even slight inconsistencies can lead to clumping, reduced workability, or strength losses.

Advanced mixers often incorporate variable speed controls and multiple mixing phases – dry blending, liquid introduction and high-energy homogenization – to achieve the required paste fluidity and particle dispersion. All of these systems can be equipped with automatic washout systems making maintenance significantly easier.

Batch Plant Automation and Accuracy

Beyond the mixer itself, the batch plant plays a vital role in successful UHPC production. Precision is paramount at every step, from weighing powders to testing aggregate moisture. UHPC mix designs have small tolerances compared to conventional concrete, and errors in batching can have serious impacts on performance and can be very costly.

UHPC producers should look for batch plants that provide:

• Automated powder handling systems for cement, silica fume and quartz powder.
• High accuracy weighing systems capable of handling fine powders and micro-additions.
• Specialized liquid dosing equipment for superplasticizers and other admixtures that must be delivered within tight tolerances.
• Fiber feeders that meter and introduce steel or polymer fibers without clumping.
• Temperature control to manage heat generated from mixing, including a cooling system or chilled water dosing.

The BatchMaster plant from Mixer Systems, Inc., is a top-of-the-line plant capable of producing up to 250 yards per hour. Mixer Systems load cells feature an aggregate weighing accuracy within +/-2% and cement/water weighing accuracy within +/-1% of the batch size. Proprietary automated controls run a high-volume batch plant from start to finish-batching, mixing, moisture control, even automated concrete delivery of different mix designs to multiple locations.

The Path to Scalable UHPC Production

As demand for UHPC grows in infrastructure, precast, and architectural applications, the importance of advanced mixing and batching systems will only increase. High-shear mixers and precisely engineered batch plants are essential to unlocking the full potential of this specialty mix.

Mixer Systems, Inc., pours more than 45 years of experience into the design, manufacturing and construction of every mixer system we produce. We build every mixer, batch plant and batch control system from the ground up to meet customer specifications.

For producers, investment in the right equipment enables not only superior material quality but also improved efficiency and repeatability, ensuring UHPC can be scaled to meet the needs of tomorrow’s most ambitious projects.