What does concrete density have to do with anything? It’s essential and one of the defining qualities of good concrete. Density is a measurement that tells us how much object x (mass) is in size y (volume), so it can help us measure structures and their qualities.
So, what is concrete density about? Concrete consists of cement and fine and coarse aggregates (sand and gravel), and it’s mixed with water for the hardening/curing process to start. The low water-to-cement ratio makes the most demanding concrete, while too much water-to-cement will weaken it.
Average concrete density per cubic foot is reportedly from 143 lb/ft³ (2300 kg/m³) to 150 lb/ft³ (2400 kg/m³). The actual density varies depending on mixing conditions and materials used.
So, suppose you’re wondering how much concrete weighs. In that case, you must calculate how much concrete you need and use the information above to multiply it.
How about wet concrete? Is the density of fresh concrete different from the hardened one?
Concrete loses around 5% of its weight when water evaporates. So, the density of wet concrete can be calculated with that in mind. One of the properties of concrete is that it shrinks when it hardens/cures. For more concrete math, here is about concrete yardage calculations.
Lightweight concrete density
Lightweight concrete is different from “normal” because the aggregates used are of lighter density. Lightweight concrete aggregates include shale, clay, volcanic pumice, scoria, tuff, perlite, and slate.
Lightweight concrete density is around 90 to 115 lb / ft³ (1440 to 1840 kg/m³). There is more than one way to make lightweight concrete besides lighter aggregates. It can also be caused by voids in the concrete, resulting in aerated concrete. The third type is leaving fine aggregates like sand away.
The density of sand can be higher than the lightest lightweight concrete (from 90 lb/ft³(1442 kg/m³) to 100 lb/ft³ (1602 kg/m³)), so that isn’t all that surprising. Average weight concrete aggregate density is around 75-110 lb / ft³ (1200-1750 kg / m³)
Lightweight concrete mixes that can be done at home depend on what aggregate is used and the amount of sand. Glass fiber could also strengthen its structure. One way to test it at home could be a 1:1:1 ratio of cement, sand, and lightweight aggregate and mix it with a little over 0.5 water.
Regarding lightweight concrete vs normal-weight concrete, everything has its uses. Lightweight will help to lessen structure weight load, but on the other hand, the structure will make it less resistant to moisture. For the same reason, it takes longer for lightweight concrete to dry.
Reinforced concrete density
Concrete can take a lot of pressure but needs to be more decisive regarding pulling force. That’s why the concrete structures are almost always reinforced with steel. Reinforced concrete density would depend on how much steel has been used on the structure. Steel density is multiple times higher, 484 to 503 lb/ft³ (7750 and 8050 kg/m³).
How is concrete testing done?
Concrete testing is one way of controlling quality and an excellent way to check if the building material is appropriate. I listed a few of them here. Density is one of the points.
Some ways to test fresh concrete are slump test, density (unit weight), and the air content of new concrete by pressure. There is a Schmidt Rebound Hammer, pull-out, ultrasonic pulse velocity, and compression test for hardened concrete.
Fresh concrete measuring
The slump test is done with fresh concrete to test its flow. The tool used is an inverted cone that has no top or bottom. It’s held against a platform-wide side down and filled from the top with concrete. The concrete is pushed with tools now and then, so it’s as dense as possible. When the cone is complete, it’s lifted, and the concrete “slumps” due to gravity. Then, it’s measured how much the concrete sunk from the top; 4-5 inches is ideal.
Density is easy to measure as we know how much it should ideally weigh. We take a bucket and calculate how much it should weigh full of concrete. Then we fill it and consider it, and after we take off the container weight, we know how close we are to the ideal.
Air pressure tests can also be done with fresh concrete on the construction site. Concrete is placed on a circular container, tamped with something like in the slump test, to be as dense as possible. Then, the container is closed with a device that has a dial, and air is hand-pumped into it. The result can be read from the dial.
Hardened concrete measuring
Concrete can be measured when it has hardened as well. The rebound hammer test is one way to measure it. To be short, the device launches a mass on springs and measures the rebound from concrete. The best thing is that it’s non-destructive.
The pull-out test is done with a metal rod placed within the concrete structure during the cast. Then, it’s pulled with straight pull force, showing how much the concrete can handle. The wrong side is that concrete is damaged during the process.
Ultrasonic pulse velocity test is to measure density and elastic properties. The device sends acoustic waves through material that can tell about those qualities. Here, the problem might be metal in the structure and other issues with the material, like cracks.
A compression test is done by extracting concrete samples of the existing structure. Then, it’s put on compression to see how much pressure it can take. This is a reliable method to measure strength, but the downside is that it is also destructive.
Density might not seem too important at first, but it’s one of the most essential factors of concrete. It defines its strength (with other factors), so we know how to use it.
The weakness of concrete is that it can’t handle pulling forces well. That can be taken care of with proper reinforcement. It’s not only building houses but also helpful to know, even with smaller structures and hobby projects.
Testing concrete in fresh form and hardened is good for knowing how well we succeeded. Testing is also an easy way to oversee concrete projects, and usually, we aim for the best results in the casting phase.
The easiest way is to follow ready mix instructions and remember that the amount of water needed varies a little from bag to bag. If you’re working with concrete materials separately, try taking even measures to keep quality the same.