ᐅ Concrete slab, insufficient cement content in the concrete mix
Created on: 14 Jun 2020 15:06
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Eriwan2
Hello, I am quite inexperienced with construction and very worried about the following issue:
I want to build a swimming pool in my garden, measuring 3x5x1.5 meters (10x16x5 feet), using Styrofoam formwork blocks that will be filled with concrete.
A friend who works in construction helped me pour the base slab (20cm (8 inches) thick) over the weekend, and for various reasons, we had to mix the concrete ourselves from cement and gravel.
I read online that the ideal mix ratio is 1 part cement to 4 parts gravel by weight, and this is exactly what my friend had told me before. He mixed the concrete, and I did the pouring.
Now that the slab is finished, I checked the delivery notes. When I calculate everything, we used exactly 8 tons of gravel and 1.25 tons of cement. But for a 1:4 ratio, we should have used 2 tons of cement.
He says this is not a problem and gave me explanations I don’t fully understand. (For example, there was some water in the gravel, so we actually used less gravel than was delivered. The gravel was indeed damp, but as a layperson, I am still very concerned if this will truly hold.
Does anyone have experience with this and could please share some advice?
I want to build a swimming pool in my garden, measuring 3x5x1.5 meters (10x16x5 feet), using Styrofoam formwork blocks that will be filled with concrete.
A friend who works in construction helped me pour the base slab (20cm (8 inches) thick) over the weekend, and for various reasons, we had to mix the concrete ourselves from cement and gravel.
I read online that the ideal mix ratio is 1 part cement to 4 parts gravel by weight, and this is exactly what my friend had told me before. He mixed the concrete, and I did the pouring.
Now that the slab is finished, I checked the delivery notes. When I calculate everything, we used exactly 8 tons of gravel and 1.25 tons of cement. But for a 1:4 ratio, we should have used 2 tons of cement.
He says this is not a problem and gave me explanations I don’t fully understand. (For example, there was some water in the gravel, so we actually used less gravel than was delivered. The gravel was indeed damp, but as a layperson, I am still very concerned if this will truly hold.
Does anyone have experience with this and could please share some advice?
M
Matthew0315 Jun 2020 09:27Eriwan2 schrieb:
Probably not compacted.That’s unusual; typically, using a shaking tool on the bottle once should be enough... but regarding the mixing ratio, I wouldn’t worry too much, since it was reinforced properly.
What exactly is a "construction expert"? If the concrete hasn’t properly set, you will definitely notice because it becomes porous. However, I don’t assume that is the case.
Missing proper compaction, on the other hand, is really frustrating. Recently, we built a small garden wall foundation and were able to compress it quite well just using a wooden board on a handle. With the right equipment, even more could have been achieved.
Make sure to do this especially with the bricks.
Missing proper compaction, on the other hand, is really frustrating. Recently, we built a small garden wall foundation and were able to compress it quite well just using a wooden board on a handle. With the right equipment, even more could have been achieved.
Make sure to do this especially with the bricks.
Eriwan2 schrieb:
then we used exactly 8 tons of gravel and 1.25 tons of cement.
With a ratio of 1:4 there should have been 2 tons of cement. Hello Eriwan
A reasonable concrete mix would have been 1:4. I would even lean towards 1:3 for something like that.
You now have about 1:5. That is "lean concrete."
20cm (8 inches) with proper reinforcement inside. Nothing will happen to it. Provided the concrete was well wet so it consolidated properly. Then the reinforcement will not rust. What is supposed to happen to the slab? It can’t move sideways or downwards. And neither bending nor tensile forces will act on it. Don’t worry about that.
Having starter bars is good. Also put horizontal and vertical reinforcement into the formwork blocks. Use a mix of about 3.5:1.
So, when mixing, 3.5 shovels of gravel to 1 shovel of cement. Approximately. Make it well wet. The mix should flow like batter. Tamp it slightly with a batten and your pool will be fine.
Steven
Yes, and this is confusing for me because the ratios actually refer to weight. So 1:4 means 1 kg (2.2 lbs) of cement to 4 kg (8.8 lbs) of aggregate. However, aggregate is much heavier than cement, so using the number of shovels doesn’t work. A 1:4 ratio would be more like 2 shovels of cement to 4 of aggregate, right? So I have approximately 1:6.25 (estimated).
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