Knowing the unit weight of concrete is an important step while designing reinforced concrete structures as well as during preparing mix-design. The unit weight of simple concrete (un-reinforced concrete) is different as compared with the weight per cubic foot of a reinforced concrete mass. Similarly, if you’re working on a demolition project, you need a dumpster to suit the size depending on the weight of concrete.
Here’s a detailed guide about weight of concrete:
Why you need to know the weight of concrete?
Here’re different scenarios in which it is pretty helpful to reckon the weight of the concrete:
- You’re placing precast concrete panels and need to determine the capacity of lifting crane or skid-steer loader.
- You’re working on demolition project and have to know the size of the dumpster to put the concrete in properly-sized container.
- Or the know the correct amount of trucking to remove the broken concrete during demolition.
- You’re designing concrete structure and have to estimate the dead weight of the concrete member.
- You’re pouring concrete at site using crane and need to know the size of bucket to carry the weight of the concrete to the pouring site.
Unit weight of concrete
The density or unit weight of normal concrete is 2400 kg/m3 (150 pounds per cubic foot) while the light weight concrete weighs about 1750 kg/m3 or 110 pounds per cubic foot per unit. This means that if you take a block having size of 1 foot x 1 foot with height of 1 foot, it will weigh 2400 kg or 150 pounds.
The weight of reinforced cement concrete (RCC) is 2500 kg/m3 that comes around 156 pounds per cubic foot. So, you see due to reinforcement, the weight of concrete is increased.
Please note that the above figures are for density of concrete. The density of different ingredients like cement or aggregate will be different from this value. The density or unit weight of normal Portland cement is 1440 kg/m3 or 94 pounds per cubic foot (lb/ft3).
In laboratory, civil engineers determine the density or unit weight of the concrete as per ASTM C138 or as per IS 1199. It includes pouring and compacting mass of concrete in a standard jar of known volume. The sample is poured in layers with each layer properly compacted using 25 to 50 strokes each layer. The weight is measured for the concrete and is divided by volume to determine the density of the concrete.
See also: Properties of Hardened Concrete
Weight of concrete for slabs
During estimation, if you’re to find the volume of concrete required for a concrete slab, you have to use the unit weight to determine the quantity of cement. For example, if you have a slab or 24” by 24” the volume of the concrete would be:
Volume of concrete = 2 ft x 2 ft x 0.5 ft (height) = 2 ft3.
Now using density, we can determine the weight of the slab;
weight of concrete = 150 lb/ ft3 x 2 ft3 = 300 lbs.
In some concrete projects you need to batch concrete based on weight while in others they batch concrete per volume (like in m3 or ft3).
If you’re working to know the weight of a slab that’s already poured and is solid, you need to use another approach. Knowing the square footage of the slab is pretty straight forward. The biggest variable is the thickness of the slab. If you can find a side of slab exposed, it will be easy. But that’s not always the case. Now you can either make a guess or if you have equipment you can drill a core and know the exact amount of thickness. For estimation, here’re usual thickness of concrete slabs:
- thickness of patio slab = 5”
- thickness of walkway = 5”
- Driveway slab = 5”
- reinforced concrete slab = 6”
Factors effecting weight of concrete
We know concrete is an amalgam or mixture of different constituents. The most common ingredients of concrete include cement, sand, and aggregate. With such, we call this concrete as plain cement concrete or PCC. So, weight or density of concrete depends entirely on the composition or mixture along with the compaction or densification of concrete components. So, we can say the weight of concrete depends on
- Size of the concrete member
- type of aggregate (normal or light weight)
- type of cementitious material (cement type or slag)
- type of reinforcement (rebar, fibers, or other types)
- compaction or densification (densely packed or loose)
- mode of compaction (Table vibrator, rodding, or no compaction)
Weight of concrete per m3A
A normal concrete weighs about 2400 kg per cubic meter. So, that means if you’re batching a cubic meter of concrete and would be carrying that on a transit mixer, the weight of the concrete is 2400 kg that is 2.4 tons.
Weight of concrete in different units
|1 in3||1.39 oz Weight in ounces per cubic inch|
|1 ft3||150 lb Weight in pounds per cubic foot|
|1 yd3||4050 lb Weight in pounds per cubic yard|
|1 m3||2400 kg Weight in kg per me|
Weight of concrete calculator
Well, I’ve been preparing a lot of concrete calculators. So, just hold on I am still preparing that for you. Once it will be ready, I’ll place that calculator here. Anyhow, I still have prepared one excel sheet to help you in determining the weight of the concrete in different units.
See Also: Advantages of Air-Entrained Concrete
How much weight of concrete I am going to toss up from my old concrete driveway?
As a rule of thumb we normally take weight of concrete for one cubic yard is about one ton. Now start from measuring the square footage of the concrete driveway. You can divide the driveway in different patches if the area is irregular. You can first determine the length of the driveway and multiply that with the width of the driveway. If your driveway doesn’t have any transition or irregular shape, you can determine the length at centerline and multiply that with the width.
Once you have the square footage of the concrete, you can multiply that with the density to know the weight of the concrete you’re going to be tossing.
Weight of concrete kN/m3
Do you know the weight of normal plain concrete in kN/m3 is 23 while for reinforced concrete is 25 kN/m3. Let’s see how:
Actually here you’d need to know the basic concept of mass and weight.
As per basic formula; weight (w) = mass (m) x g (acceleration due to gravity)
2500 kg/m3 = 2500 x 10 N/m3 (taking w = mg)
25000 N/m3 = 25000 / 1000 = 25 kN /3.