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.

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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 ...
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11 votes
2 answers
786 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 ...
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11 votes
3 answers
614 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 ...
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10 votes
2 answers
12k 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 ...
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10 votes
1 answer
282 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 ...
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8 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?...
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7 votes
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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,...
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7 votes
2 answers
17k 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? ...
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337 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 ...
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7 votes
1 answer
736 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 ...
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6 votes
3 answers
2k 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 ...
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3 answers
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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 ...
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5 votes
2 answers
241 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 ...
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5 votes
2 answers
438 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 ...
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5 votes
2 answers
131 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 ...
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5 votes
1 answer
120 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 ...
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5 votes
1 answer
288 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, ...
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5 votes
1 answer
67 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 ...
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4 votes
1 answer
210 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.
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4 votes
3 answers
98 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 ...
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4 votes
2 answers
124 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 ...
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4 votes
3 answers
808 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 ...
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4 votes
2 answers
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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 ...
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4 votes
1 answer
70 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 ...
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4 votes
1 answer
186 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 ...
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4 votes
0 answers
31 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 (...
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3 votes
1 answer
1k views

Classification of aggregates

I have this aggregate gradation curve in hand, how can I say whether its gap, well or uniformly graded?
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3 votes
3 answers
229 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 ...
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3 votes
1 answer
223 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.
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3 votes
2 answers
95 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 ...
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3 votes
1 answer
125 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.
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3 votes
1 answer
87 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 ...
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3 votes
1 answer
80 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 ...
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3 votes
0 answers
67 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 ...
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3 votes
0 answers
45 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 (...
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3 votes
0 answers
384 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 ...
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2 votes
2 answers
396 views

Why is this structurally sound?

While visiting Vancouver, Canada recently, I noticed there is a lot of construction for apartments and condos. Attached is a photo of one of many of those sites, and at these sites, I noticed ...
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2 votes
1 answer
96 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 ...
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2 votes
2 answers
288 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 ...
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2 votes
1 answer
167 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 ...
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2 votes
1 answer
392 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 ...
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  • 364
2 votes
1 answer
107 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 ...
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  • 225
2 votes
2 answers
201 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 ...
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2 votes
1 answer
55 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 ...
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2 votes
2 answers
236 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 ...
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  • 364
2 votes
2 answers
552 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 ...
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  • 225
2 votes
2 answers
35 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 ...
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2 votes
1 answer
143 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 ...
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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 ...
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2 votes
1 answer
163 views

How is prestressing with losses self-balanced?

By definition, prestressing is a self-balanced load. This is because it is in fact merely an applied state of internal stresses. This can also be demonstrated mathematically (in this case for a ...
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