Concrete is simply a blend of aggregates (such as crushed stone, gravel or natural sand) bound together by a fluid hydraulic binder such as cement paste. This is all combined using water. Eventually, when hardened and dried over time, it simulates the properties of rock.
Concrete is actually often referred to as artificial rock. This is because it isn't easily compressed with force or broken. It can be used to create paths and roads, bridges, patios, the base for floors and foundations, and walls and is therefore the most widely used material in construction (and the second most used material on earth after water). It can also be moulded into different shapes which makes it beneficial for all manner of tasks.
Therefore, if you work within construction and building, it is likely you will have to concrete at some point. It is really important to know how to work with concrete and how to stay safe around concrete, too.
How to Make Concrete
Step 1: Mix it
Before you get mixing with your cement mixer, decide on the strength of concrete needed for the job at hand.
High strength concrete needs more cement added to the ratio of cement, sand and stone, whilst more rough applications need more aggregates.
Check out this handy table below to give you an idea of the mix you’ll need to consider for your concreting job.
*35 litres is approximately 6 No.2 shovels – 1m (3) – 1000 litres
Step 2: Poke it
Throughout these concreting steps, context is key. The size of the job and the power supplies available to you will determine the poker you will be using:
- Small jobs, powered by mains electric or a generator – Hand Held Pokers
- Availability of standard site compressors (flexible shaft) – Air Pokers
- Dedicated petrol or diesel drive units (electric) – Flexible Shaft Pokers
- Availability of 230V or 400V 3ph, converted to a safe 24V – Electric High Frequency Pokers
Step 3: Lay it
Now we’re ready for laying! If you’re laying concrete floor slabs, they’ll need to be compacted flat and at the correct level. We call this “Screeding” and there are two different techniques you can follow:
- Traditional Screeding
Use the formwork or screed rails set at the right level to guide the screed machine. Concrete is poured and placed slightly higher than the finished level, the machine is then pulled or winched down so the slab can ‘strike-off’ the concrete at the correct level.
- Free Screeding
Does not use formwork or screed rails. High slump concrete is placed accurately to the right level. On deep slabs a poker should be used, so the action of compaction doesn’t cause levels to drop. The machine is pulled across the surface of concrete to flatten and level small deviations.
Step 4: Finish it
At the end of the screeding process, ripples can be left on the surface of the concrete. For some jobs this may be acceptable, or even desired as the texture increases the plus weight slip resistance on slopes.
If you want to smooth out any ripples or grooves, a float can be used whilst the concrete is still in a plastic state. Using a long handle, wide float blades can be pushed or pulled across the surface of the concrete. You can even incorporate a brush into your float, if you wish to re-introduce your own texture into the concrete surface.
Alternatively, you can use a floor planer to obtain your desired effect.
Safety with Concrete
Because concrete is so commonly used, it is really vital that everyone on site knows how to deal with it safely, both if coming into contact directly or just being on site where concrete is used.
As with many aspects of working on a building site, dealing with cement and concrete is not without its risks.
Wet cement requires safety measures of its own. It is actually caustic for human skin, and can cause chemical burns to exposed skin. Protective equipment is required and workers need to be properly trained to prevent incidents involving both themselves and other employees.
As with cement, dermatitis and respiratory exposure to silica are two of the biggest issues. Exposure through skin contact, eye contact, or inhalation are the most common routes for issues.
When mixing cement, the risk of dried materials can cause dust. Wet cement can also cause slip risks, especially if spilled on the floor or onto work boots.
Mixed, set concrete slabs and blocks are also incredibly heavy, so if being moved in a wheelbarrow or being moved by hand, you need to be cautious of lifting.
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