It’s been a work in progress for four years but a longstanding dust control company has devised an innovative alternative to conventional rock stemming in blasting. Mason Trouchet, of Rainstorm Dust Control, spoke to Damian Christie about the company’s new stem gel product.
Rainstorm Dust Control has operated for more than three decades across Australia, providing solutions in dust control, materials handling, rehabilitation and erosion control, coatings and contracting for the mining, civil construction, and quarrying sectors.
Rainstorm’s dust control solutions have traditionally addressed haul roads and stockpiles and open areas but have now expanded to encompass the dual challenges of dust and noise generated by blasting. In late August 2018, the Perth-headquartered company announced – in partnership with PWS Shockwave Gel Systems – that it would begin trialling and eventually distributing Stem Gel – a new patented technology as an alternative to the conventional rock stemming method. The product was first developed in 2015 by an inventor and licensed to PWS but it wasn’t until Rainstorm Dust Control engaged with PWS that the first steps were initiated to bring Stem Gel to the market.
“Rainstorm became involved because over the 30 years that we’ve been in business doing roads and open areas, we’ve always been challenged about what we do with dust that comes from a blast,” Rainstorm’s Mason Trouchet explained. “Blasting was a bit of an outlier in terms of dust control because it was a high impact dust event in a relatively short period of time in a relatively small area. It didn’t necessarily have a big impact on the overall dust of a site like a truck driving up and down a road all day long does.
“So we looked at this technology, and what we found with the blasting and the gel was two things: one, that some of the test work we did showed a greater than 50 per cent reduction in noise, and two, a lot of the quarries operate close to local communities and public areas, so we could comfortably bring about a reduction in dust in all the blasting.”
He added that a lot of the dust that flies out of the hole in a blast is generated by the rock aggregate that is put down the hole. “If you don’t have that stemming aggregate, you’re reducing that kind of rock by blowing it up in little dusty bits.”
Trouchet explained Stem Gel is a “super absorbent polymer” that, once pumped into a blasthole or used in above ground stemming, will stabilise water as a solid containment system for the explosive. When the blast is initiated, Stem Gel attenuates 98 per cent of the energy of the pressure wave (Pw) and diverts it into surrounding rock to increase fragmentation during the initial moments of the explosion (see Figure 1).
“When you blow things up, the pressure wave actually moves three to five milliseconds (m/s) in front of the plasma gases,” Trouchet said. “And what we’ve validated is that the pressure wave hits the gel and attenuates in front of that energy, and then a millisecond later, the plasma gases hit the gel and vaporise the first section of the stem.
“The principle of the energy as it comes up the hole and hits the top of the bench is like a balloon bursting and the energy is immediately dispersed in all directions,” he added. “If you can bring that energy higher than the hole – which is what we call stemming above the hole – you actually don’t disperse that balloon, it won’t burst until it hits the stemming material above the hole, which in turn brings the energy right to the surface of the bench.
“The problem with stemming is that if it’s not effective when the blast energy comes up, you get oversize material in that space above the explosive. But because we can [with Stem Gel] use far less stemming horizon or depth, you can bring the explosive higher up the hole and get away with a small amount of stemming in the hole, like a little mushroom, and with a little bit of stemming above the hole, you’re able to get the energy higher up the bench and therefore have less oversize.
“The subsequent benefit of that powerful containment,” he added, “is a sizeable reduction in noise and dust. As the gel is expressed from the blast and becomes airborne, dust particles flocculate in mid-air and fall to the ground. The gel itself acts like an aerial flocculant, and you can see it on the actual muckpile afterwards, the little grains of aggregated particles that have fallen to the ground, as opposed to flying off into neighbouring areas.”
In addition to greater fragmentation and less oversize, Stem Gel, combined with optimal blasthole design and drill patterns, leads to lower powder factors, smaller holes, increased safety (with reduced oversize risk areas) and significant cost savings, particularly for mines and quarries.
“The big factor for quarries is that it will give them better fragmentation at the higher part of the bench,” Trouchet said. “Stem Gel has enough ramifications for the crushing plants and a ripple effect for the throughput of the plant. So that’s where the actual cross-benefits will come for the quarries and the miners, they will be able to dig faster and crush faster.”
Since late 2018, Rainstorm Dust Control has partnered with numerous companies in the mining and quarrying segments to test and perfect the Stem Gel and substantiate the cost savings and benefits it offers. Indeed, major conclusions from a trial of Stem Gel in a Western Australian limestone quarry with 102mm holes was that:
• Its performance was comparable to that of aggregate stemming.
• No poor detonation was measured at the interface of the gel and ammonium nitrate/fuel oil (ANFO), indicating there was no degradation of the ANFO.
• There was no measurable pressure pulse in the gel stemming due to the detonation-induced shock wave (indicating an attenuation of the Pw by the gel).
• There was somewhat less fine material at the hole collar than the aggregate stemming.
• There was no discernible difference in the performance of weighted and unweighted gel.
• There was an ability to remediate a misfired hole through removal of the stem gel.
• It was possible for the gel to solidify water at the bottom of the blasthole and then load ANFO on the gel.
Rainstorm also partnered with Holcim Australia’s quarry division in WA in trialling the product. Trouchet said he was bound by confidentiality with regards to the finer details of the Holcim trial but that the quarrying business was nonetheless “happy with the results, particularly as the trial validated the reduction in noise and dust, which was the primary purpose. The fragmentation was also very successful”.
He added there have been successful trials in the mining sector, with global iron ore miner First Quantum Minerals and gold miner Newcrest Gold. The latter installed sensors in the hole to measure the pressure wave of the blasts and to validate the attenuation.
Most importantly, some of the global explosives suppliers – MAXAM and Dyno Nobel – have also been running what Trouchet described as “sleep tests” with the Stem Gel, using combinations of both ANFO and emulsion explosives across different sites.
“Dyno Nobel is testing the stemming gel not just against specific products for a trial but every single product or explosive type in their inventory. It means that for any client who says ‘I’m using a Dyno product’, we already have the sleep test, so they can go straight to trial. It removes this delay to market that each individual company needs to worry about before they do a trial.
“It’s also particularly important for medium to smaller quarries that are working with lesser known explosives groups because they use more local suppliers than the major companies. It means there’s a fast track to doing the trials without having to do the sleep tests.”
While the principles of the Stem Gel have been validated across many trials by quarries, mines and the explosives groups, the next problem that the product presented for Rainstorm was the method of delivery. Rainstorm ultimately settled on several means, depending on the sector it is servicing:
• LR2, the liquid reagent that is pumped into the holes, loading the stem gel on top of the explosive.
• A down the hole dewatering agent (DHDA).
• Dosing rigs for above ground and underground stemming.
• Blast mats for surface stemming, fly rock containment and dust control.
Trouchet said that for the quarrying industry, some of the methods for delivering the Stem Gel are either quite complex or very expensive.
“The DHDA is a powder – or ‘free particle’ flour-size polymers – that coats little granules of rock that are literally tipped down the hole,” he explained, “and because it’s attached to these granules of rock – which aren’t much bigger than three or four one hundreds and thousands altogether – the polymer is pulled through the column of water to the bottom and it instantly solidifies the down hole water into a solid gel and a stemming gel. And what happens is that one litre of water is the equivalent of 1.7 litres of plasma gas energy – it’s like making more explosive out of the stemming gel.
“The LR2 is a liquid reagent that is pumped into holes that are then loaded with stem gel on top of the explosive,” he continued. “We use this for the big mines that are filling the big holes and require trucks and dosing rigs.”
Neither the DHDA nor the liquid reagent are particularly expensive – but the costs rise when it comes to the additional resources required to implement them.
Trouchet said that dosing rigs are the most ideal way of dispensing the LR2 and the DHDA. “The breakthrough of this technology is that you can actually perform what is called a ‘one-pass lead-in’, so you could load the hole with the explosives and then the same truck could effectively load the stemming gel. The Stem Gel is able to be pumped vertically in a blasthole to six metres, and in this capacity opens up stemming for underground and contour work.”
COST-EFFECTIVE BLAST MAT PANELS
For now, the best, most cost-effective method of delivering Stem Gel to a quarry’s blast site is through rolls of 250mm by 400mm blast mat panels cut to fit the hole. While rubber and recycled tyre mats or steel plates have been used over the years to suppress dust and noise emissions on blast sites, Trouchet said Rainstorm’s blast mat panels actually contribute to the stemming gel process.
The mats, he said, work on the same principles as the DHDA. “We’ve taken the same powder and then put it inside the mat panels which is a tissue paper-style cloth that is permeable with water. So all a quarry professional has to do is wet those panels, the panels swell up over the hole within 30 seconds and you have your stem.
“Water as the stemming material is the novelty,” he continued. “Two things come out of that: one, it’s a lot cheaper just because you have that tissue paper and the polymer in there isn’t that expensive, and two, you add the water, and so water does the work. With traditional rubber blasting mats, the intention is to remove those mats and reuse them over and over again in other blasts. In this case, our blast mat panels are a one-off – you load one up, put it over the hole and that’s the end of it.”
Trouchet said the blast mat panels are a new innovation and have only just come off the production line. “We were initially a little nervous about putting the mats out without having the dosing equipment close behind to do the job properly down the hole. We didn’t want the efficacy of the mats to be the be all and end all when the main focus is on stemming down the hole. However, now that we have that groundwork sorted, we are happy to introduce the blast mats to the market. So people will go out and play with the mats. It’s an opportunity for them to experiment without any major costs, and after they realise it can give them better fragmentation, we can then talk about other, more advanced alternatives for stemming the hole and saving even more costs.”
He added that in adapting the blast mats to their blasting procedures, quarry operators should not have to really change their preparations at all.
“With the mats, we’re not necessarily saying to them, ‘Oh, change what you’re doing!’ We can say to them: ‘Continue with your rock aggregate, do everything that you’re doing every day of the week. However, on top of the holes, build up 200mm of the mats, and then you will have your above ground stemming.’ In other words, you will have explosive, aggregate, rock and then stemming mats on the surface.
“The purpose of this exercise is to come to the quarry market primarily to reduce noise and dust, and to illustrate how easy that can be if the blast mats are laid over the top of the hole just by adding water to those blankets.
“All of a sudden, with nothing more than adding water and laying them out, quarries will get a reduction in noise and dust, which has been a real challenge to that market.
“We’re selling those panels – their configuration is 250mm long and they come in a 40mm wide box – and they can be cut to whatever size and length is desired. The advantage for the quarries is that it’s a low entry cost process to validate or to start experimenting with the stemming gel.”
Trouchet added that, by comparison, it may cost quarries between $5000 and $6000 to hire a dosing rig.
“In our marketing strategy,” he added, “introducing the mats now is a low risk to the quarries that experiment with this material and will lead to more sophisticated applications.
“In the quarries, if they hit an oversize rock, they will drill a hole in that rock, and throw some gel down that, and you could lay these mats over that rock and it would contain that energy in there.
“All of this leads to less explosive use, efficiencies in the drill size diameter of the hole, and the density of the explosives. There’s a number of facets that we are looking at, and we have software that is backing this up.”
Trouchet said that Rainstorm Dust Control, after four years of experimentation, sleep tests, trials and in-field tests, is ready to take Stem Gel to the next stage of commercial development.
“In the development phase, it took some time for the product’s capacity to be a stemming material to be understood and validated,” he said.
“The second part of the equation was how to put it in the hole – how do you actually apply it? Part of the delay in the industry wasn’t so much on the efficacy of the chemistry of the material, that was pretty quickly understood by all the drill and blast professionals. It was about the activity on the bench, to get it down the hole. That was complicated because there was no equipment until we invented and built it and came up with the blast mats to actually get it into the market – where the quarrying and mining people would go: ‘That’s a tool we can use because it’s easy to use’.
“The real interesting part of this is that blasting in all aspects is going through a huge technical revelation at the moment,” Trouchet continued.
“Explosives companies are doing magical things with their timers and detonators, they’re making amazing changes to the density of their explosives as they drop them down the hole.
“The big missing piece in all of this has been how to stem – and there were very few alternatives on the market that were effective. It’s that unique characteristic of Stem Gel to measurably reduce noise and dust output from blasting that makes it such a game-changer.
“So there’s been a paradigm shift in the stemming technology,” Trouchet concluded. “We’re going to launch it, take it to business and I reckon within a year or two we’ll be partnering with one of those explosives groups because it’s up their alley for them to take us global.
“We’ve been focusing on the Australian market first, which is logical to get to where we are based and where the core businesses are. Eventually Stem Gel will be a global thing but for now we’re quite happy to be in Australia as we launch it.”
For more information about Stem Gel, visit rainstorm.com.au/dust-control/blasting