Questions tagged [concrete]
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.
119
questions
13
votes
1
answer
1k
views
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 ...
- 10.6k
11
votes
2
answers
925
views
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 ...
- 857
11
votes
3
answers
648
views
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 ...
user348
10
votes
2
answers
13k
views
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 ...
- 10.6k
10
votes
1
answer
291
views
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 ...
- 203
9
votes
2
answers
3k
views
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?...
- 224
7
votes
1
answer
3k
views
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,...
- 179
7
votes
2
answers
18k
views
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?
...
- 225
7
votes
2
answers
355
views
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 ...
- 2,099
7
votes
1
answer
747
views
(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 ...
- 13k
6
votes
3
answers
3k
views
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 ...
- 571
5
votes
3
answers
23k
views
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 ...
5
votes
2
answers
246
views
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 ...
- 153
5
votes
2
answers
466
views
How much does the elasticity (Young's Modulus) of concrete and asphalt change with ambient temperature?
I'm assuming here that all materials will have a change in elasticity due to thermal expansion/contraction and a resultant reduction/increase in the strength of the bonds of the atoms leading to a ...
- 176
5
votes
2
answers
135
views
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 ...
- 725
5
votes
1
answer
132
views
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 ...
- 857
5
votes
1
answer
325
views
Can concrete lose strength during curing?
We cast a bridge's concrete deck and kept samples for concrete strength tests at 7 and 28 days.
We took a test at 7 days, and the test result were over the design strength (designed for 30 MPa, ...
- 53
5
votes
1
answer
69
views
How does infill material affects the capacity of a tubular section with H-section inside?
How does one consider the moment capacity of a combined pipe plus H-section if the infill material is:
Sand, friction angle 30 degree
Grout, C20
Concrete, C45
Eurocode has a section on composite ...
- 271
4
votes
3
answers
105
views
Design Roller Compacted Concrete Pavement Section
I have been asked to consider using RCC instead of traditional PCC on an upcoming project. For a rough order of magnitude estimate, can I assume that the pavement section design will be similar? I ...
- 41
4
votes
2
answers
147
views
The design of precast concrete-- are they the same with cast-in situ design?
I am curious as to how different is precast concrete design than conventional cast-in situ reinforced concrete design as far as structural engineering is concerned.
To my mind, they should be the ...
- 1,264
4
votes
2
answers
128
views
Got to pour outdoor concrete next week, but forecast is cold. What are my options?
I have to pour outdoor concrete next week. The pour is in two main parts - a 100 mm cover / 2nd pour over a 6 x 3 m area of existing concrete from a 1st rough pour, and the bottom ...
- 571
4
votes
1
answer
191
views
Is the order of operations in jacking a cable relevant?
If you have a prestressed concrete beam or slab and are jacking a cable from both ends, does the order of operations alter the result?
For a symmetric curve, the tension diagram along the cable's ...
- 13k
3
votes
1
answer
234
views
What methods are there to test the flexural, tensile and compressive strength of concrete?
The only one I know is the three point bending test for flexural strength.
- 257
3
votes
1
answer
2k
views
Classification of aggregates
I have this aggregate gradation curve in hand, how can I say whether its gap, well or uniformly graded?
- 147
3
votes
3
answers
330
views
Trapping heat by curing of concrete under plastic sheets
Although curing of concrete under plastic sheets is a recognized technique, I have some doubts about it.
I think that the plastic sheets may trap heat coming from the exothermic reaction, which will ...
- 317
3
votes
1
answer
154
views
Why is the frustum of a cone used to slump test of concrete and not a cylindrical tube?
While performing the slump test for knowing the workability of a concrete mix one uses a tube having the shape of frustum of a cone in order to conduct the test. Why is not a cylindrical tube used ...
3
votes
3
answers
1k
views
Why is the stress distribution on concrete approximated like this?
I'm reading here on reinforced concrete. It is explained there that in calculations, the actual stress distribution is replaced by a constant stress distribution over some limited distance from the ...
- 2,209
3
votes
2
answers
105
views
Tiled/block pavement used to pave high traffic roadway?
We're normally paving the high-traffic road with concrete or asphalt. While for sidewalk/garden, we use pave block/tiles (either concrete or else)
Common reason is because pave block/tiles doesn't ...
- 83
3
votes
1
answer
141
views
What are those objects of the top of this building called?
Does anyone know what these things on the ceiling of this building are called?
I am referring to those objects with semicircle shape that act as a ceiling on the
top of the building.
- 133
3
votes
1
answer
88
views
How monolitic is concrete when falsework is being crafted for parts of future structure only?
Suppose we craft a reinforced concrete pylon for a cable-stayed bridge. It's very tall and rather thin. No one builds falsework for the entire pylon - it'd be very impractical. Instead, a part of ...
- 2,099
3
votes
1
answer
85
views
Can plasticizer leach out of cured concrete?
About 6 months ago I have poured concrete in a plastic mould. The mould was plastic plinth for sun umbrella. It is usually filled with water but it cracked so I filled it with concrete. Before pouring ...
- 31
3
votes
0
answers
69
views
Any Idea of This China's "Transparent Concrete"?
I am currently make an attempt to make miniaturized version of this China's solar highway on my garage
https://www.youtube.com/watch?v=zK8FvzI3yDA
Just so i can re-evaluate the performance
However, I ...
3
votes
0
answers
57
views
water leak through subterranean cable penetrations in concrete
See the image below for the detail of 4 no. cable ducts that run from a trench in a raft foundation (on the left) through an approximately 1 m square penetration in the raft foundation, through soil (...
- 857
3
votes
0
answers
444
views
Why do we use the strain-controlled test for the compressive strength of concrete?
As you all now, a typical stress-strain curve for concrete under compression can be seen in any reinforced concrete design textbook. The decreasing part of the curve (post-peak) can be obtained by ...
- 31
3
votes
0
answers
32
views
Waste Foundry Sand as an aggregate for concrete mixes. I have a question regarding grain diameter and it's possible applications
I'm working on a project with a company that uses sand casts during moulding processes and they provided us with samples of the sand they use before it's involved in the procedure and afterwards (...
2
votes
1
answer
115
views
Are concrete screws suitable for repeated removal and reinstallation?
Is a concrete screw like the HILTI HUS3 removable?
I.e. can it be repeatedly unscrewed and reinstalled as required? Will this damage the fixing or the hole in the concrete?
We're thinking about using ...
- 857
2
votes
2
answers
318
views
Concrete Slab Deformation
The concrete slab (?) supporting the swimming pool (≈ 10 x 10m x 1m) of my building has clearly a 'belly':
I'm not sure whether this was built this way or evolved over time, however, my best guess is ...
- 153
2
votes
1
answer
179
views
What is the preferred composition for modern concrete bridges?
It seems that most bridge are composed of concrete, e.g in Latvia
However, concrete encompases a lot of bridge types:
Most concretes used are lime-based concretes such as Portland cement
...
- 123
2
votes
3
answers
115
views
Concrete Strut and tie- modeling: Why can a tie and a strut cross at a point without forming a node?
I'm reading this source about concrete strut and tie design.
Here is a picture from the site:
I'm curious, why isn't there a node at the point where the lower tie crosses the middle diagonal strut? ...
- 2,209
2
votes
1
answer
232
views
What is the curing process for polymer concrete if it doesn't use any water?
The curing process for regular cement concrete is sprinkling water fog or using a moisture retaining fabric. I was wondering what the process is for polymer concretes because they don't use any water.
- 257
2
votes
1
answer
488
views
How can the shear capacity of a concrete slab be determined for effective depths under 200mm? [Eurocodes]
All,
I'm designing a minor slab to Eurocode 2. It's purpose is more for show than any real structural purpose however I need to justify it's ability to resist it's own self weight and possibly the ...
- 364
2
votes
1
answer
109
views
Do beams in a structure transmit to piers?
Sorry if the question is confusing as such, here's an image that makes it hopefully clearer:
So let's say this building consists of two elevated concrete slabs. The first elevated slab is supported ...
- 225
2
votes
2
answers
428
views
How to calculate the required prestressed jacking pressure to apply to a pre-tension concrete beam?
How does the fabricant of prestressed pre-tensioned beams calculate the equivalent pressure in the hydraulic jack (in bars) to the design prestress force (in kN)? Are there factors to multiply like a ...
2
votes
1
answer
57
views
How does concrete perform in an Insulated Concrete Form (ICF) house?
From: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4033560/
I can see that concrete can really go bad after a few hundred freeze and unfreeze cycles:
If an ICF house has insulation from the inside ...
- 21
2
votes
2
answers
241
views
Assessment of a concrete beam being strengthened by an additional steel member
Hi there (from Europe),
I am completing what should be a relatively quick assessment for the client, but I have started to second guess my self and would like some reassurance.
Essentially the job ...
- 364
2
votes
2
answers
568
views
Does a concrete slab (deck) cause compressive load in a wall beneath it?
Let's say you build a square reinforced concrete deck at height of, say, 3 meters, with the deck supported by its own steel reinforcement and by four reinforced concrete piers (call them, A, B,C, and ...
- 225
2
votes
2
answers
36
views
Small building basement foundation moisture: permeable vs impermeable
I understand that moisture is the enemy of interiors. I know that the standard basement foundation for a house-sized building uses moisture barriers on the outside of concrete retaining walls to ...
- 21
2
votes
1
answer
148
views
What's the difference between Creep and Dynamic Viscous Damping?
What's the mechanism behind each phenomenon and what's the difference between them?
Why is Creep considered in the Constitutive Equation (taken as an inelastic strain) while damping is considered in ...
user26705
2
votes
1
answer
39
views
Can aggregate gain almost 200 grams of water when submerged in water for a day?
I'm doing this special project where I have to make concrete using a Martian simulant provided from a commercial source.
I measured it as 500 grams initially, then submerged it in water for a day. It ...
- 257
2
votes
1
answer
83
views
How to resolve the interruptions in the screw pump operation due to air trap?
In one of my application, there is a requirement to dispense the concrete paste at the required rate continuously. some technical details of the application given below
Dispense rate 5-50 LPM
...
- 163