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Explosive tested at highest density, increased energy


Boral Quarries has successfully executed a trial blast in the Sunshine Coast hinterland utilising an emulsion explosive which is formulated for high fragmentation in rock. Karen Normanton, of Orica, discusses the basis of the trial and its outcomes.

Boral agreed to conduct a trial blast on a Queensland site to demonstrate the performance of Orica’s Centra Gold bulk emulsion at the highest average in hole density of 1.25 grams per cubic centimetre (g/cm3). The Boral Moy Pocket quarry site was selected due to its geological conditions, large area available for a trial, the site’s ability to measure specific key performance indicators (KPIs) and the team’s strong environmental track record.


In 2018, Orica launched a reformulated range of Centra Gold bulk emulsion products for the Australian quarry and construction market. The average in hole density of the new products is between 1.15 and 1.25 g/cm3. The purpose of this trial was to measure the performance of the product at the highest density: 1.25 g/cm3. 

The trial used a “matched pair” design (Figure 1). Halves of the blast were loaded with 1.15 g/cm3 and 1.25 g/cm3 Centra Gold, while all other design parameters were held constant. The half with the higher density was designated as “Side A”. Side A therefore had a 15 per cent higher design powder factor than Side B.

Boral and Orica determined the KPIs that could be measured on site and recorded these in the project charter. Table 1 refers to the KPIs showing the measures and the values that are desirable from the implementation of the higher energy bulk emulsion.

Table 1. KPIs used in the trial.


Fragmentation is an important and direct indicator of blast performance. Quarries are interested in this as it directly affects the cost and efficiency of downstream processes, and the yield of saleable material from the resource. Fragmentation is often presented as a single number, such as P80, representing the size of the sieve that 80 per cent of the rock mass would pass through. As a single number, it can be compared to other blasts analysed by the same method. 

Figure 2. Side A produced better fragmentation.

The fragmentation measurements (Figure 2) show 25 per cent improvement in fragmentation, P80, on Side A.

Oversize material was set aside during excavation. Figure 3 shows the oversize material set aside in stockpiles. The stockpile volume was measured using aerial photography. Figure 4 shows that Side A produced less than half of the oversize of Side B, a 55 per cent reduction.

Excavation productivity was measured using Orica’s video analysis software, CyclePro. The analysis showed loading was five per cent faster on Side A. The average dig time per bucket for Side A was 25 seconds and the average dig time per bucket for Side B was 28 seconds (Figure 5).

Figure 3. Oversize was set aside in stockpiles and measured.

As the blast was fired as one single event, it was not possible to distinguish vibration levels from each side of the blast at the normal monitoring location. The measured vibration was compliant with the site’s licence conditions and within the normal range for standard production blasting on site. Extra vibration monitors installed in the near field1 indicated that the vibration was 14 per cent higher from Side A. Face velocity measurements showed that Side A had a 15 per cent higher face velocity than Side B. Despite this, the measured overpressure from each side was not significantly different.

Figure 4. Side A produced less oversize.


Other measured results showed that Side A had, compared to Side B:

Six per cent higher VoD.

Similar crusher throughput (one per cent higher).

15 per cent less scalps.

No observable difference in back-break and side break.

No discernible post-blast fume.

This trial sought to verify the performance of Centra Gold at a density of 1.25 g/cm3 by comparing VoD and blast outcomes in a side by side blast with Centra Gold at a density of 1.15 g/cm3. The results were mostly in line with expectation for a 15 per cent increase in energy.

Figure 5. Loading time was measured using video analysis.

Karen Normanton is the senior technical services engineer for quarries and construction at Orica.


Offering higher strength base emulsion, with an increased density range, Orica’s capability to deliver higher throughput and lower cost is better than ever before.

With Centra Gold, you can tailor density and blends to match your site’s unique geology. Its improved maximum in-hole density also means you can increase fragmentation and dig rates, or expand drill patterns, depending on your site’s operational objectives. 

Combined with Orica’s robust and responsive supply chain, and industry‑leading service and support, Centra Gold provides increased power from every angle.

More information: Orica, orica.com/centragold


“Boral Quarries are continuously searching for ways to improve how we operate, whether this be from a safety and environmental perspective, or in a commercial sense. The trial of the higher density Centra Gold at Moy Pocket Quarry was performed in a professional manner – Orica personnel and Boral site staff worked together to scope out and risk assess the trial, determine the methods for capturing and assessing outcome data and performance, and implement the appropriate processes to conclude the data was representative of the outcome. The Centra Gold high energy project has been an excellent example of supplier and customer working together to yield a result that has value for both parties.”

Neil Bellamy, Drill and Blast Manager, Boral 

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