For questions about the material concrete, or its application in an engineering context. Concrete is a composite material composed mainly of water, aggregate, and cement.
Questions tagged [concrete]
120 questions
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Can Zinc/Aluminum coated anchor rods be used in concrete?
Bolts and anchor rods that are very high strength ($F_u$ > 150ksi) are not supposed to be galvanized. This is because of concerns about hydrogen embrittlement. This includes ASTM A 490 bolts and ASTM A 354 Gr. BD anchor rods.
The project in…
hazzey
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How different is using styrofoam rather than empty cans when pouring concrete?
In the recent 6.4 earthquake that hit Taiwan, it was seen in a newswire photograph of rubble that metal cans were embedded in the concrete.
The quote from an official regarding this practice:
For such purposes in construction, it was not illegal…
user348
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Why do air entrainment admixtures improve the freeze-thaw resistance of concrete?
It is stated on here that:
Air-entraining admixtures cause small stable bubbles of air to form uniformly through a concrete mix. The bubbles are mostly below 1 mm diameter with a high proportion below 0.3 mm. The benefits of entraining air in the…
egg
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Developing a stochastic differential equation model for concrete fibers
I am working on modeling concrete fibers (metallic fibers) as a mathematical model. My work is for my thesis. I am a PhD student of numerical analysis, but I am working on a real tunnel project.
I have had issues with the distribution of fibers in…
Khosrotash
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How is the design life of a reinforced concrete structure calculated?
The specifications for large structural projects typically call for the structure to have a specific design life. This can be 50 years, 100 years, etc.
Accommodating the design life for steel can be as simple as adding additional thickness to…
hazzey
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What is the practical limit on the number of storeys in residential buildings built with monolithic reinforced concrete?
I have recently bought a flat in a 25-storey building. I wonder what is the practical limit for the number of storeys in a mass-produced residential buildings built from monolithic reinforced concrete?
Can we expect the number of storeys in typical…
Anixx
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7
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Recipe for Roman concrete
I recently read in an online article, that researchers have found the recipe of concrete used by imperial Roman architects. The cited article however uses a recipe described by Vitruvius, which is 2,000 years old. So how exactly is this finding the…
DaPhil
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(Non)simultaneous prestressing anchorage slip losses
Post-tensioned prestressed concrete beams suffer from a multitude of losses. When jacked, they suffer friction losses and their tension diagram is, for example (to simplify the drawing, I'm using the linearized version of the friction loss equation…
Wasabi
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What's the name and purpose of this specific shape of hollows in a reinforced concrete slab?
Below is a stack of reinforced concrete slabs with hollows (camera is positioned along the hollows' axis). Such slabs are used for floors - you build walls of the next floor, then lay such slabs such that they rest onto walls with the end shown on…
sharptooth
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Relative strength of wire mesh vs rebar for reinforcing a concrete slab
I have a friend who is German and he says that wire mesh is much stronger than steel bars (rebar) and is mandated in Germany for reinforcing concrete slabs.
The question is, is that true, and why?
Here's a typical concrete reinforcement here (in…
thelawnet
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Concrete formwork - best approach to counter uplift forces, for a freestanding pour?
I'm casting a 4m long triangular-profile reinforced gravity retaining wall against soil movement due to a 1 metre jump in ground level.
The lateral forces and moments on the formwork have been easy to handle, but I'm trying to find a good approach…
Stilez
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Why railroad concrete tie tips become dry first after a rain?
I've witnessed this phenomenon:
Why are only the tie tips dry? Why are only the stones around the tips dry? This is a railroad in Ukraine in the morning after a rain at night. Around 80% of observed tips looked like that, slightly elevated tips…
Sashko Lykhenko
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Typical flatness of Portland cement
Does anyone have a feel for the flatness of Portland Cement when poured in a standard/typical way? Say, for example, that I wanted to pour a cement "cube" (20"x 18"x 19.25") in a mold. How flat would the top surface be without any special…
willpower2727
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Why is there this perforated pipe inside this vertical construction joint in a reinforced concrete wall?
The picture below shows a veritcal construction joint of an approximately 50 years old reinforced concrete industrial structure. The expansion joint was likely originally sealed with a flexcell which due to age and water ingress has deterioriated…
egg
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How to determine reinforcement design strip widths and locations
When designing reinforced concrete slabs it is common to divide the slab into 'design strips', which are then used to rationalise the reinforcement design along (typically orthogonal) lengths of the slab (also known as the Hilleborg Strip Method).
I…
thomasmichaelwallace
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