Fundamentals · 6 min
Lightweight concrete weight: how many kg is 1 m³?
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One cubic metre of dry lightweight concrete weighs roughly its density class. For the Redblok lightweight concrete block, the design targets are about 300 kg for KB300, 500 kg for KB500 and 1,000 kg for KB1000, and the typical wall block band is 500–800 kg/m³. The same volume of normal concrete weighs about 2,400 kg. The fresh mix is heavier than the dry block, because part of its water has not yet dried out.
How does density class set weight?
Lightweight concrete is a broad family; the values in this article apply to the Redblok lightweight concrete block classes. The number in the class code is the target dry density in kg/m³. One cubic metre of KB400 weighs about 400 kg when dry, and one cubic metre of KB800 about 800 kg. The arithmetic is simple: volume × dry density = mass. Half a cubic metre of KB600 is about 300 kg; 10 m³ of KB400 is about 4,000 kg, or 4 tonnes.
The wall's job decides the class. Typical bands are 300–500 kg/m³ for light partitions where thermal and acoustic insulation come first, 500–800 kg/m³ for non-loadbearing partition and infill wall blocks, and 700–1,000 kg/m³ for non-loadbearing walls that need higher strength. These are design targets, and every class is verified by trial mixes and laboratory testing. The final weight is therefore calculated from the dry density in the project-specific test report.
Why do fresh and dry density differ?
Fresh density is measured when the mix is prepared, and it includes all of the mixing water. Part of that water reacts with the cement and becomes bound in the material. The rest evaporates over time. Dry density is the value after that drying, so the fresh mix is always heavier than the dry block.
The gap is not a fixed number. It depends on the mix design, the density class and the curing conditions. We use a separate mix design for each density class; the admixtures and their proportions are specific to our company. So we do not guess the gap. For each mix design, we measure the fresh density and the dry density of the specimens together during trial mixing. Fresh density is used in production and handling. The wall's permanent dead load is assessed from dry density together with in-service moisture. The structural engineer decides which value enters the calculation.
How is density checked in each batch?
What sets the weight of a lightweight concrete block is the amount of air added to the paste. That amount is calculated from the target fresh density. Even a small drift changes the fresh density, so we run the check on the production line.
We measure fresh density on every mix by filling a container of known volume and weighing it. If the value falls outside the target band, we correct the amount of air before the mix goes into the mould. Specimens are taken from the same batch, and dry density and compressive strength are measured on them. ASTM C495 can be used for the compressive strength of lightweight insulating concrete. We record every batch and, on request, add the records to your project file.
Cellular lightweight concrete falls outside the scope of TS EN 206, the Turkish adoption of the European concrete standard, so its performance is defined by the project specification and laboratory testing. Acceptance criteria for density and strength are also written into the project specification and documented by test results.
How much mass does a building save?
Example assumptions: a five-storey building whose interior partition and infill walls total 1,500 m² of surface area, at an average wall thickness of 15 cm. The wall volume is 1,500 × 0.15 = 225 m³. Cutting waste is not included.
Built in KB600 lightweight concrete block, those 225 m³ weigh 225 × 600 = 135,000 kg, or about 135 tonnes. The same volume in normal concrete (2,400 kg/m³) would weigh about 540 tonnes. The block is roughly a quarter of the weight of the same volume of normal concrete. On a real project, areas, thicknesses and the class come from the architectural and structural drawings; this example uses dry density.
The horizontal forces a building feels in an earthquake come from the inertia of its mass as the ground moves. For the same structural system, less mass means smaller forces. In an analysis to TBDY 2018, the Turkish Building Earthquake Code, partition and infill walls count towards the building's mass. Still, this difference alone does not decide how the building behaves in an earthquake; the layout of the structural system, material strengths and ground conditions are assessed together. A lighter block is not a substitute for strengthening an existing building. The responsible structural engineer decides, under TBDY 2018, how the block is reflected in the design.
How do you estimate volume and weight?
For preliminary design, you can use the free lightweight concrete calculator on this site (currently in Turkish). Enter the wall area and thickness, or the volume directly, and choose a target density class. The tool shows the required volume and the approximate weight. It also works out the dead load saved compared with the same volume in normal concrete, including a waste allowance.
The result is for preliminary design only. Final quantities come from the wall areas and thicknesses in the drawings; where sections differ in thickness, an average is used. For a quotation we need the wall type and area, the wall thickness, the target density class, the site's province and district, and the scope of testing required.
Frequently asked questions
- How much does 1 m³ of foam concrete weigh?
- When dry, roughly its density class. For the Redblok lightweight concrete block, the design targets are about 300 kg for KB300, 500 kg for KB500 and 1,000 kg for KB1000. Fresh material is heavier because of mixing water that has not yet dried out. The exact value comes from the test report for the mix.
- How much lighter is lightweight concrete than normal concrete?
- Normal concrete weighs about 2,400 kg/m³. A lightweight concrete block at 500 kg/m³ weighs roughly a fifth of that for the same volume, and one at 300 kg/m³ roughly an eighth. For example, 10 m³ of normal concrete weighs about 24 tonnes, while the same volume of KB500 lightweight concrete block weighs about 5 tonnes.
- Why is fresh lightweight concrete heavier than dry?
- The fresh mix contains all the water added to it. Part of that water reacts with the cement and is bound; the rest evaporates over time and the density falls. The gap varies with the mix design, the density class and the curing conditions, so it is measured during trial mixing rather than estimated with a fixed ratio.
- Does a lightweight concrete block get heavier when wet?
- Yes. Its porous structure takes up water and the weight rises. Redblok's water absorption design target by volume for KB500, for example, is 10–14%. That means a saturated 1 m³ specimen under test conditions holds about 100–140 kg of water. Blocks are therefore stored covered on their pallets, walls are not built with wet blocks, and external faces are protected by render or cladding.
Sources and standards
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