In Pursuit of the Perfect Shot
We ask three industry-leading companies about innovation in concrete spraying, equipment and formulations for underground mining

By Carly Leonida, European Editor


Putzmeister’s Wetkret 5 shotcrete rig in action underground. (Photo: Putzmeister)
Shotcrete, also known as sprayed concrete, plays a critical role in ground support systems for underground mining operations, from a safety, efficiency and time saving perspective. It’s a flexible, relatively cheap and proven method of rock stabilization which has stood the test of time. However, that doesn’t mean that the field is standing still.

“There have been numerous important developments in shotcreting over the past 10-20 years that have contributed to both mine safety and performance,” Rodolfo Ramos Bravo, product line director, Concrete Spraying Mining at Normet, told E&MJ.

“For example, in spraying equipment, reduction in pulsation through innovative concrete pump developments have improved application consistency, spraying booms have evolved enabling large coverage areas through improved kinematics, and ‘in-cab’ spraying capabilities — which is a safe zone for operators due the capacity of the structure to withstand the loads of falling objects and provide filtered air free of particles and fumes — have all made a big difference.”

He added that today, improved spray nozzle and injector configurations provide better mixing of air and accelerants into the concrete stream. Robotic assisted spraying booms are also available, simplifying the sprayed concrete application and providing an even layer along the substrate.

Bastian Dreher, senior director, special applications, and Bob Harmon, national sales manager – shotcrete and mortar at Putzmeister, also joined the discussion. According to Harmon, machine ergonomics have drastically improved during this time, resulting in better health and safety for employees.

“Overall, shotcrete equipment has become smarter and therefore easier to handle,” he said. “In addition, quality control has become simpler with the addition of LiDAR technology for material placement. The machines themselves are also more robust for challenging terrain and the trend towards electrification is ongoing.”

“Another big development was the shift from dry to wet shotcrete, as this greatly reduces dust in already difficult to ventilate areas,” said Dreher. “The pre-bagged materials themselves have evolved greatly over recent years, improving strength while still being able to use conventional shotcrete machines.” Additionally, there’s now a heavy focus on optimizing aggregate, sand grading and conforming mix designs for specific performance capabilities.

“Introducing state-of-the-art concrete admixtures provides improved rheological performance, retention and assists with early-stage strength development,” said Ritchard Hood, director, sprayed concrete process at Normet. “Additionally, the use of steel and macro-synthetic fibers in sprayed concrete can enable the reduction of wire mesh installations in many cases. In turn, this improves shotcrete strength and safety, reduces excavation and support cycle times, and improves flexural strengths, bending moments and energy absorption.”

Designing for Deeper Mines
The current trend towards larger, deeper mining operations creates several challenges in shotcrete design and logistics. For instance, deeper mines tend to have higher ambient rock temperatures and increased groundwater ingress compared to shallower excavations. Ramos Bravo explained: “Stressed rock conditions challenge the current paradigm of mining operations, forcing them to find new ways with ground support in order to minimize the operator’s exposure to operational hazards.”

The increase in underground rock stresses requires improved/increased rock support classes which necessitates the use of more rock bolts, as well as dynamic bolts and cable bolts, shorter blasting lengths and faster closure of open faces. Hood added: “Improved overall performance of sprayed concrete is vital in geotechnically challenging operations. Longer transportation times in declines can require longer rheology retention of the concrete, and there’s also the question of whether longer or multiple drop pipes should be used.”

Dreher agreed: “The logistics involved with getting the machines and material to the right location at the right time are getting more difficult. The shortage of skilled labor is another a big challenge the industry is facing today.”

Putzmeister Optimizes Wetkret Range
To help alleviate these challenges, Putzmeister has designed its latest generation of machines to be modular. This means that they can be disassembled and reassembled quickly and easily to maneuver through tight drifts and narrow shafts.

“Over the past three years, Putzmeister has re-designed the Wetkret 3, Wetkret 4, Wetkret 5 shotcrete machines and adapted them to the North American market,” Harmon told E&MJ. “At the same time, we’re re-focusing on that market and continue to increase our team to support our customers.”

The Wetkret 4 is particularly well suited to underground mining applications thanks to its robust and compact chassis, reduced turning radiuses and crab-mode that allow a wide range of movements. The Putzmeister Wetkret 4 pump guarantees a homogeneous shotcrete application to ensure the required quality and thickness, as well as reducing rebound. Its concrete flow of 20-m3/h allows for increased productivity.


The tunnelling and civil construction markets continue to develop technologies
that have cross-over applications for underground mining and there is much
we can learn from these industries. (Photo: MAPEI)
The spraying arm is adapted to mine galleries requirements with a maximum vertical reach of 8.5-m. Wetkret 4 also comes equipped with automatic synchronization of the additive dosage with the concrete flow, hydrostatic transmission without gear to change, an integrated air compressor as option and optimal weight distribution. Dreher added: “Putzmeister Iberica is continuously researching and developing for its entire product line. Collaborations with material suppliers are being expanded locally and across the globe.”

Normet Brings SmartSpray to Mining
In 2017, Normet launched a robotic assisted spraying boom called SmartSpray that provides different levels of operator assistance. This ranges from assisted boom control that offers simplified controls, up to fully assisted boom control where the operator defines the tunnel profile, and the system generates the spraying pattern. The boom then executes the pattern of movements, ensuring an even layer of concrete along the substrate and also making the operation and quality less dependent upon the operator’s skills. Ramos Bravo told E&MJ: “This technology is available at the moment for the tunnelling market, and we’re now working to make it available for our mining customers too.”

Aligned with customer’s decarbonization roadmaps, Normet also recently launched a battery-electric sprayer for mining applications called the MF 050 VC SD. “We have successfully delivered units to Australia, India and Chile,” said Hood. “The machine is the perfect mix between our proven spraying technology and our latest developments in battery-electric drivelines. These help our customers to improve the health of the users by eliminating diesel particulates and reducing noise and heat at the source.”

The machine is fully equipped for battery-operated spraying, and features Normet’s latest low pulsation concrete pump technology as well as the possibility to spray from the cabin. Hood said: “As overall rock support requirements increase, sprayed concrete technology is continually evolving, and in the future we will see new concepts in equipment, spraying concepts and chemical abilities.”

He added that greater investment and collaboration is needed to accelerate research and development (R&D) in ground support systems and their key components, including shotcrete. “Normet is already collaborating/partnering with mining and tunnelling companies and specialist applicators to jointly drive R&D initiatives in this field,” Hood said. “The cost of this doesn’t come cheap and buy-in from clients and contractors is a must looking ahead.”

Innovation in Admixtures
The use of admixtures in concrete systems has become standard practice in multiple construction applications, including underground mining operations. To learn more about their role and evolution, E&MJ spoke to Peter Collins, market specialist within MAPEI’s Underground Technology Team (UTT).

“Admixtures can be used in concrete for belt conveyance foundations, cemented rock fill, cementitious injections and shotcrete,” he explained. “They’re one of the essential parts of ensuring the proper performance of any shotcrete system. Having a proper concrete mix design is critical to the final system and admixtures are a piece of the puzzle that can adjust the fresh and hardened properties of concrete. Shotcrete can be utilized in underground mining operations for ground control in hard-rock mining and as an anti-weathering, skin-control device in soft-rock mines.”


The cement and concrete industry will continue to evolve with more innovative and environmentally friendly
products for shotcreting. (Photo: MAPEI)
Admixtures can also help to address some of the issues associated with shotcreting in underground mining operations. For instance, Collins said that operations in very remote locations or those that that entail long-distance pumping tend to be unique to the underground mining world. Often a combination of admixtures is necessary to meet the needs of these operations. “Some of the most commonly used chemical admixtures include high-range water-reducers (HRWR), hydration-controlling admixtures, alkali-free accelerators and viscosity modifiers,” he told E&MJ. “Each admixture can help solve a piece of the puzzle. For example, HRWR allow a level of workability to be maintained at a lower water-to-cement ratio, which results in increased strength.”

Hydration-controlling admixtures allow for a controlled and delayed set time which can be critical to underground mining operations in remote locations. Alkali-free accelerators lead to rapid setting and have become essential in ensuring rapid strength development of the concrete and allowing for faster re-entry times. Viscosity modifiers allow for a reduction in bleeding and segregation which is important for long-distance pumping operations. Collins said: “The use of admixtures is often tailored to the unique environment of underground mining operations as often a combination of admixtures is needed to ensure proper shotcrete performance.”

Cutting-edge Chemistry
The cement and concrete industry is continually evolving with improved products and operations to ensure a safer working environment with higher performance. According to Collins, one major developments has been the increased use and improved formulas of alkali-free accelerators over sodium silicate-based accelerators. Alkali- free accelerators come in both liquid and powdered form and result in a rapid hardening of the concrete with minimal impact on compressive strength and durability.

“The other key development in the admixture space has been on hydration- controlling admixtures that allow for a controlled and substantially delayed set time,” he said. “The hydration-controlling admixtures influence on the concrete can be nullified by the alkali-free accelerators allowing for rapid setting when desired. Other types of additives, such as fibers and supplementary cementitious materials, have been making strides in the industry as well. Macro-synthetic fibers have been introduced as an alternative to steel fibers and serve to improve the toughness of the concrete. This allows for increased strength of permanent shotcrete and concrete structures, such as ramps, adits, slopes, etc.”

Micro-synthetic fibers can help with plastic shrinkage and reduce spalling under high temperatures. Supplementary cementitious materials can also be used in a shotcrete system to reduce CO2 emissions, supplement the fines in a mix for improved pumpability, and improve the strength and durability of the mix.

MAPEI Expands in North America
MAPEI reinvests a considerable percentage of its annual profits back into R&D. Collins said this commitment ensures that the company’s UTT product line comprises the most innovative and technologically advanced products available. MAPEI also continues to expand its footprint and now has over 20 production facilities throughout the U.S. and Canada.


Shotcrete equipment has become smarter and therefore easier to handle over the past 10-20 years. (Photo: Putzmeister)
“MAPEI UTT offers a full range of admixtures and synthetic fibers,” Collins said. “Of note are the alkali-free accelerators which come in the form of liquid solutions, liquid suspensions and powders. Mapequick AF 701 S is the latest liquid-solution product in North America. Liquid solutions are advantageous from an end-user perspective in that they do not need to be agitated like a liquid-suspension product to maintain homogeneity. The product is designed to work with the latest admixtures and cements.”

Mapequick AF 100 RP is another new UTT offering in North America and is a powdered alkali-free accelerator that is meant to be dissolved in water before use. This is an ideal alkali-free accelerator for colder climates where freezing and storage of materials may be of concern.

Collins added: “The cement and concrete industry will continue to evolve with more innovative and environmentally friendly products, such as Type 1L cement, alternative cementitious materials and even cement-free systems. Continual innovation of admixtures for the shotcrete market will allow for deeper and more challenging underground mining operations.

As featured in Womp 2024 Vol 11 - www.womp-int.com