Handling the raw ingredients of concrete such as aggregates, admixtures and cement requires careful selection of plant equipment where bucket sizing a
Handling the raw ingredients of concrete such as aggregates, admixtures and cement requires careful selection of plant equipment where bucket sizing and horsepower play an equally important role has hydraulic capability and mobility around the site.
Getting either one of these wrong can lead to an uncomfortable and often less profitable outcome for concrete manufacturers and construction contractors alike. Whether it be a 30-ton excavator, loader or a small TLB (tractor-loader-backhoes) or skidsteer, the right decisions need to be made based on the weight and density of the product being handled otherwise known as specific gravity of the material.
Based on specific material gravity and an understanding of how those materials behave during transfer, mixing and batching are the most important consideration followed by reach requirements and mobility on the specific site. Get it wrong and you’re either under-delivering on productivity or overworking your machine which are potentially expensive mistakes.
The backbone of accurate sizing starts with a fundamental concept: specific gravity. This simple number tells you how dense a material is relative to water and when applied to earthmoving it quickly determines the weight your machine is lifting with each bucket load. For instance, sand typically has a specific gravity of about 2.65 while fly ash is lighter at around 2.3 and cement heavier at 3.15. Loaders and excavators don’t measure buckets in ton but rather move materials in volume so unless you know how dense the material is you won’t know the real payload weight. Multiply the specific gravity by 1,000 kg/m³ and you’ll get the bulk density. That’s the figure that matters.
Let’s put that into a working example. A typical 2 m³ loader bucket filled with sand (SG 2.65) weighs about 5.3 tons. But fill the same bucket with dry Portland cement (SG 3.15) and you’re looking at over 6.3 tons or a full ton heavier. This could easily exceed the lift capacity of smaller machines. For an experienced fleet operator it is therefore no wonder that concrete batch plants and precast yards often run different machines for different tasks for example one for aggregates, another for admixtures and a third for stacking and palletising. This can help larger plants to get the most out of their equipment by controlling, accuracy and avoiding unnecessary wear.
In a precast yard where consistency and cycle times are king, mid-sized wheel loaders such as the Caterpillar 950, Komatsu WA380 or Bell L2606E are popular choices. With bucket sizes ranging from 2.5 to 4.5m³ they’re ideal for loading hoppers, feeding batch plants or transferring stockpiles. Admixtures like slag and silica fume which are finer and more flowable often require smaller more precise buckets to avoid overloading and spillage. A machine with a 1.5 m³ bucket like a JCB 437 or LiuGong 856H provides enough capacity without overshooting dosing accuracy.
At a building materials supplier yard the requirements may be very different with machines required to be nimble and versatile as well as capable of navigating confined stock areas and loading customer trucks. Compact loaders or TLBs are a staple here in this type of environment especially those with quick couplers that switch between forks, buckets and hoppers. Front-end buckets are typically around 0.8 to 1.2 m³ in size which is ample to handle aggregate without exceeding axle limits on paved yards. The Kubota range, JCB 3CX, Terex TLB890 and Bell 315SK all offer respectable capacities with good road manners and serviceability.
On construction sites machine selection depends on the scope of concrete works. For major civils or roadworks where large volumes of concrete are poured daily a dedicated 20–35-ton class excavator with a 1.8 to 3.5 m³ bucket is ideal for aggregate management, mixing pad loading and handling recycled materials. Contractors using excavators like the Komatsu PC300, Caterpillar 345C or LiuGong 925E typically pair them with heavy-duty rock buckets when handling crushed stone or slag. These attachments are often reinforced with side-cutting edges and wear plates to extend service life in abrasive conditions.
This brings us to a critical component that’s often overlooked: ground engaging tools or GET. The teeth, cutting edges and wear plates on a bucket are a machine’s point of contact with hard reality and some of these materials are brutally abrasive. Silica, for example, while fine and seemingly benign becomes an aggressive wearing agent over time especially when dry and airborne. Slag is even more punishing with coarse angular edges that chew through standard-grade steel. Machines operating in these environments benefit from hardened GET whether it’s a Cat HD rock bucket with bolt-on edges or Komatsu’s KVX system using segmental cutting plates.
There’s also a balance to be struck in productivity. Bigger buckets might seem better but overfilling adds stress to hydraulics, frames and tyres and shortens the lifespan of equipment. Instead, the use of specific gravity as a sizing guide is a better option: if your operator is scooping a 3 m³ bucket full of slag (SG 2.9), that’s an 8.7-ton payload not something every loader can handle on repeat. In many cases it’s safer and more productive to opt for a slightly smaller bucket, load a few more cycles and avoid mechanical stress and safety risks.
And what about fly ash and silica fume those light, dusty by-products that can be challenging to handle? Despite their lower density these materials often require special handling equipment like sealed buckets, low-dust hoppers or even vacuum loaders in sensitive environments. This isn’t about brute strength it’s about finesse and containment.
Across the board, manufacturers like Caterpillar, Komatsu, JCB, LiuGong, Terex and Bell provide extensive documentation and application guidelines for their machines. Most include cycle time estimates, fuel burn rates and volumetric efficiency charts based on material density. The trick is to build your machine spec backwards from the material you’re handling not the other way around. Start with the specific gravity do the maths on the bucket size and then find the machine that lifts that weight safely, efficiently and consistently.
📌 Concrete Material Specific Gravity Reference Table
Material Approximate Specific Gravity (SG)
Portland Cement 3.15
Ground Granulated Slag 2.85–2.95
Silica Fume 2.2–2.3
Fly Ash (Class F/C) 2.3–2.5
Fine Sand 2.65–2.77
Coarse Aggregate 2.65–2.84
🔍 Understanding Specific Gravity in Metric
Specific Gravity (SG) is a unitless number that tells you how dense a material is compared to pure water which has an SG of exactly 1.
Since the density of water is 1,000 kg/m³, the specific gravity of a material multiplied by 1,000 gives you its bulk density in kilograms per cubic metre (kg/m³).
Here’s the basic formula:
Material Density (kg/m³) = SG × 1,000
So, when you see:
Material Specific Gravity Meaning in kg/m³
Cement 3.15 3.15 × 1,000 = 3,150 kg/m³
Sand 2.65 2.65 × 1,000 = 2,650 kg/m³
Fly Ash 2.4 2.4 × 1,000 = 2,400 kg/m³
This means a 1 m³ bucket of dry Portland cement weighs about 3,150 kilograms, or 3.15 tons in metric.
How to Use It for Equipment Sizing
Let’s say you’re using a wheel loader with a 2.5 m³ bucket to move sand (SG = 2.65):
• Payload = 2.5 m³ × 2.65 × 1,000 = 6,625 kg or 6.6 tons
Now compare that to cement:
• Same 2.5 m³ × 3.15 × 1,000 = 7,875 kg or 7.9 tons
So you need to ensure the machine’s tipping load or lifting capacity exceeds the heaviest bucket weight not just the volume. You can quickly see why heavier materials require smaller buckets or beefier machines.
