14

Where concrete is exposed to water, the water is going to permeate concrete no matter what you do (for the most part). The voids introduced by air entrainment allow the water some place to expand into when it does eventually freeze, thereby reducing the pressure on the concrete to crack. Edit 2021/02/17 to add some supplementary information: ACI 201-16, &...


11

Background Before explaining why this type of Roman concrete is different, let me explain what typical concrete is. Concrete is composed of 4 primary materials: Fine aggregate (sand) Coarse aggregate (gravel) Water Cement In typical concrete, the cement is Portland cement therefore it is typically referred to as Portland Cement Concrete (PCC) to ...


11

Any limit is going to be hard to quantify. There are a lot of factors that have to be weighed when choosing the basic material type. The short answer is that the limit has already been chosen for each building. This was done during the design by the architects and engineers that worked on the building. Some of these decisions might have depended on the ...


10

Design life can be one of two different things, and they aren't interchangeable. A reference to '100 years design life' might mean that it's designed for a '1-in-100-years' loading case (wind load, or tidal surge, or whatever). This is solely about a means of quantifying the magnitude of loading. It is actually nothing whatever to do with the durability of ...


9

This is going to depend a great deal on what you want to achieve with the reinforcement. I'm not aware of any ultimate strength increase for using welded wire mesh allowed by Eurocode 2 or ACI318. I had a quick look and couldn't find anything. I'm also sceptical that welded wire mesh is mandated for all slabs in Germany. However, it is common in Germany. I ...


9

I suspect that the reason to use it is that the cans and the associated empty space is cheaper than actually having solid concrete (and may be partly necessary to reduce the weight of the concrete and thus associated stresses with it). You're probably (mostly) correct. For beams, reducing the weight of the beam itself will reduce stresses in the beam and ...


8

There are two methods to test flexural strength, three point and four point method. Three point method: and the corresponding moment line: four point load: and its moment line: The maximum flexural stress happens to concentrate only in a point in three point test, if you are testing a non-homogeouse material as it's always so in reality, it's not ...


7

The air entrained in the concrete causes discontinuous voids, which will not cause water to penetrate the concrete. Water will permeate through the bleeding pores which are continuous cavities. The entrained air bubbles are small and will only allow space for the freezing water to expand.


6

It looks like a typical precast concrete "hollow-core" or "voided" slab. A quick Google image search reveals the variety of void shapes employed by manufacturers. The image on the left (from Oldcastle Precast, incidentally) nicely shows the variation of void shape with increasing slab thickness. As noted in the other answers, we care about the concrete ...


5

The flat "table" area in the middle of the curve indicates that particles of roughly 1–4 mm diameter are not well-represented in your aggregate. This gap in your particle size distribution is why it's called gap-graded. Basically, you want to look at the slope of the curve in different regions to tell whether particles are accumulating in the sieves of ...


5

Per ACI 318 13.2, two-way slabs are designed based on "column strips" and "middle strips". To paraphrase the code: A Column strip is a design strip with a width on each side of a column centerline equal to 0.25L1 or 0.25L2, whichever is less. Column strip includes beams if any. L1 and L1 are the span lengths in the two slab directions. A Middle strip ...


4

Short answer: No. Longer answer: The code equations (e.g. ACI) relating modulus of rupture with compressive strength cannot be mathematically derived. It is an empirical relationship based on curve fitting to extensive experimental data. The ASTM test for flexural strength (i.e. Modulus of rupture) is ASTM C78/C78M. In essence, the most common test ...


4

You can build this wall as you would any other. Given its size, the fact that it's a ring becomes irrelevant, which means that for all intents and purposes, it can be designed and constructed with the same concepts as that of a linear wall. This can be demonstrated thusly: the wall is 1000 meters in diameter, which gives it a perimeter of approximately 3141 ...


4

Yes, Underground Detention is a thing. That Wikipedia article even mentions placing them under parking lots. The exact method that you propose is a little different than preconstructed vaults, but it is the same in the end. Pervious concrete on top of gravel with voids serves the same purpose but with much lower capacity. It is not really speeding up the ...


4

In structural situations, portland cement concrete is what is used. The properties of asphalt change with temperature and it never really "sets". It is a viscous liquid that cannot support long-term loads. There really shouldn't be any confusion as to what is being described in that chart as "concrete".


4

What you see is temporary support, only till the time the floors attain their design strength. Then all these will be removed. The rate of progress of the project must be faster than the time required for the concrete to be strong enough. As far as using rebars, just looking at the spans and proportion of cantilevered area's it seems they are using some of ...


4

Note that the curing process for ordinary concrete is a chemical reaction between the ingredients of the cement mix and water which is stirred into that mix. Water is sprinkled onto the curing concrete to make sure that enough water is available to make the curing reaction go to completion and also to cool the concrete, since the reaction releases heat. In ...


4

These are left over from concrete ties which are used to hold the formwork together ready for pouring concrete. They are usually called tie holes. After the concrete is cured and forms need to be removed their ends protruding out are bent and snapped.


4

You haven't specified any material parameters, so for calculation purposes, I am going to assume a reinforcement yield strength of 500MPa and a cylinder compression strength for both concrete and mortar of 25MPa. As I am basically just guessing these values, you will have to adjust the conclusion accordingly, if I haven't been so lucky as to guess correctly. ...


4

Prestress creates an upward deflection on the beam due to the combination of elastic strain, creep and shrinkage in the unloaded beam. This negative deflection will bend back to a straight stance or at least minimize much of the deflection of the beam after the loading. The equations of the deflection of a prestressed concrete beam depend on the curvature ...


4

What is the technical term for this? Bending downwards is called sagging. (Technically "sagging" isn't moving downwards; it's bending in a shape that looks like the mouth on a smiley face). One thing you'll see with concrete structures is creep. This is where under constant load, the deflection increases over time. Is this a problem or not? Why? Sagging ...


4

structural ceramic does have some applications in things like engine parts, but its cost and manufacturing difficulty makes it a less ideal choice for something as large as a building foundation The thing about concrete is that you can mix it with water, and pour it into a space to make a foundation. Ceramics have to be kiln fired at 1300 + C for hours. It'...


4

One of the foundational principles of structural engineering is obviously safety. And one of the foundational aspects of safety is the ability to show warning signs prior to any accidents. In the case of structural engineering, that means designing structures to crack or sway or groan or what-have-you prior to collapse. In fact, when designing beams, one of ...


4

The generation of heat during concrete cure is a significant issue. There are whole books written about it - see for example CIRIA C766 - 'Control of cracking caused by restrained deformation in concrete'. The primary cause of the cracking it discusses is so-called 'early thermal cracking', where the heating and subsequent cooling of the concrete sets up ...


4

Figure 1. A concrete sleeper mould with reinforcing steel. Concrete sleepers are reinforced with pre-stressed steel. Image source: BFT-International. The sleepers will act as heat sinks during the day soaking up heat from the ground. At night this heat is let off. The steel will conduct heat to the ends of the sleepers warming the end-plates and supplying ...


4

No, they are usually fitted once and left. If you need to remove them then you need to drill new holes. Or you should consider fitting a wooden framework to the concrete and attaching to that so it can be easily removed and refitted, without disturbing the concrete fixings.


3

Questions 1 + 3: Your first question is unanswerable. Any design is theoretically safe. Just create a massively thick slab with high-strength concrete and massive reinforcement and you can do just about anything. That being said, your two stories are completely different. The first floor can be best described as four different slabs, all of which are fixed-...


3

With the exception of anything extremely unusual: the concrete will continue to gain strength until 28 days. In fact, it will continue to gain strength for something like 50 years, but the main strength gain happens early on. The motivation for waiting for the 28-day test is therefore nothing to do with strength. Far more likely: the later you are paid, the ...


3

In all references I saw so far it was claimed that this technology has no limits on the height of the buildings. This statement is more or less true. hazzey's answer has already done a good job of summarizing the actual limitations of building height - i.e., the factors that, in any real application, control the decision of how many storeys to build a ...


3

The inclusion of cans was almost certainly to reduce the volume of (expensive) concrete and had nothing to do with any weight savings by including voids. This type of practice has been seen throughout the world when building standards are lax. The quote about this type of construction not being illegal before 1999 may be due to confusion on the part of the ...


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