14 votes
Accepted

Why do air entrainment admixtures improve the freeze-thaw resistance of concrete?

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 ...
grfrazee's user avatar
  • 3,587
11 votes

Recipe for Roman concrete

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 ...
Cory Kramer's user avatar
9 votes
Accepted

Relative strength of wire mesh vs rebar for reinforcing a concrete slab

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 ...
atom44's user avatar
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9 votes

How different is using styrofoam rather than empty cans when pouring concrete?

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 ...
grfrazee's user avatar
  • 3,587
7 votes
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What's the name and purpose of this specific shape of hollows in a reinforced concrete slab?

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 ...
CableStay's user avatar
  • 2,760
7 votes

Why do air entrainment admixtures improve the freeze-thaw resistance of concrete?

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 ...
Yesman77's user avatar
5 votes
Accepted

What are the regular holes in poured concrete walls called?

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 ...
kamran's user avatar
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5 votes
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Why does rebar in reinforced pre-stressed conrete reduce in deflection if compressive stress is applied to member?

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 ...
kamran's user avatar
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4 votes
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Is there a way to derive a formula of modulus of rupture vs compressive strength?

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 ...
CableStay's user avatar
  • 2,760
4 votes

How to construct a very large circular wall made of concrete?

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 ...
Wasabi's user avatar
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4 votes

Can a retention/detention pond and a parking-lot be constructed in the same site foot-print?

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 ...
hazzey's user avatar
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4 votes
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What is the preferred composition for modern concrete bridges?

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 ...
hazzey's user avatar
  • 10.7k
4 votes

Why is this structurally sound?

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 ...
kamran's user avatar
  • 22.4k
4 votes

Impact of having flexible electrical hose buried into the reinforced concrete slab

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 ...
ingenørd's user avatar
  • 1,288
4 votes
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Concrete Slab Deformation

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 ...
AndyT's user avatar
  • 3,153
4 votes

can ceramic be used as a building material?

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 ...
Mohammad Athar's user avatar
4 votes

can ceramic be used as a building material?

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 ...
Wasabi's user avatar
  • 13.1k
4 votes
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Trapping heat by curing of concrete under plastic sheets

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 ...
achrn's user avatar
  • 632
4 votes
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Why railroad concrete tie tips become dry first after a rain?

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 ...
Transistor's user avatar
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4 votes
Accepted

How do extra building levels affect the foundation design apart for the extra load?

Foundation's task is not just to support gravity loads, it should resist lateral loads, wind and earthquake, as well. Wind loads are dependent on the geometry of the building and seismic loads are ...
kamran's user avatar
  • 22.4k
4 votes
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Are concrete screws suitable for repeated removal and reinstallation?

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 ...
Solar Mike's user avatar
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4 votes
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Exactly what makes steel-concrete composite beam better than pure steel?

Some other answer have touched upon this, but I think it needs to be made explicit: Your mistake is in thinking that civil engineering is about making the lightest structure possible. It's not. ...
Wasabi's user avatar
  • 13.1k
3 votes

How different is using styrofoam rather than empty cans when pouring concrete?

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 ...
hazzey's user avatar
  • 10.7k
3 votes
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What are those objects of the top of this building called?

This is Kuwait National assembly building designed by Jorn Utzon, Danish architect. In your image the building is under construction. The objects are permanent formwork for roof concrete slab. They ...
kamran's user avatar
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3 votes
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How can the shear capacity of a concrete slab be determined for effective depths under 200mm? [Eurocodes]

As @Wasabi and @AndyT mentioned in the comments, this means the maximum value $k$ can have is $2$, so if $d<200$ then $k=2$. This can be confirmed in the section on shear design for slabs from the ...
atom44's user avatar
  • 2,641
3 votes

How much does the elasticity (Young's Modulus) of concrete and asphalt change with ambient temperature?

For concrete and asphalt, you would be more interested in the properties of creep, which is always a function of temperature. For example, there is an entire wikipedia page about this at this time, ...
Mark's user avatar
  • 5,343
3 votes

Got to pour outdoor concrete next week, but forecast is cold. What are my options?

The absolutely critical factor is that the concrete does not cool to 0C before it has developed enough strength to resist the expansion if any free water in the mix freezes. If it does freeze before ...
alephzero's user avatar
  • 12.5k
3 votes

Do beams in a structure transmit to piers?

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 ...
Wasabi's user avatar
  • 13.1k
3 votes
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Can concrete lose strength during curing?

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 ...
AndyT's user avatar
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