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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3
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1answer
73 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 ...
4
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1answer
58 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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0answers
29 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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7 views

What degree of open span/narrow support can rigid PIR thermal insulating foam sustain under the short term load of setting concrete?

I've found data related to the deformation and shear performance of typical PIR (polyisocyanurate) foams such as Celotex/Kingspan, but I'm not sure how to use these figures in my own situation. I am ...
3
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1answer
181 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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1answer
153 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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2answers
336 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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0answers
138 views

Bonding steel plate to fiber cement sheet effectively

I've been trying to produce a cheap panel using fiber cement and zincalume sheet. There is a research paper that I read about bonding steel plate to concrete to increase their tensile strength by ...
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0answers
26 views

Difference Between minimum steel required in Slabs and Shear Walls

My question is very simple, I need to know why the minimum reinforcement for slabs is less than the minimum reinforcement required in Shear walls? What are the criteria and reasons to set minimum ...
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0answers
42 views

Will screed on plywood do instead of beam and block, to replace a floor?

I'm gutting and redoing an older house (early 20th C, ordinary suburban terrace house, London UK). I'd planned beam and (dense) block for the upstairs structural floor, for a few reasons, and already ...
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1answer
72 views

Base Support for a Tree house

I am building a tree house in my backyard and it is going to be relatively simple. There are no parts that require drilling into the tree. The whole house is propped up by four 4x4 wood supports. I'm ...
3
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1answer
101 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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2answers
647 views

Why is desert sand not processed to make it suitable for concrete?

The shape of the sand grains from our planet's deserts is too round to be used in concrete (1, 2, 3). This is why we are drawing the last sand resources from natural beaches for making concrete for ...
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0answers
68 views

How to consider shear forces in CEB/fib 2010 three-layer model for concrete slab design?

I have a question about design of concrete shells with three-layer method described in p.7.3.2.2 fib Model Code for concrete structures. The main idea of method is that we divide shell on three layers....
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2answers
273 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 ...
5
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1answer
61 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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0answers
308 views

Shift Concrete Column by few inches

While building the foundation of a house, the concrete columns were built 15cm (6 inches) from the planned position, which is reducing the space for a door. The position that should have been there ...
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0answers
145 views

Why do we dig holes and fill them in with concrete?

I'm watching construction of a new building across from my office. The old building has been demolished and the demo team has completed taking everything away and a new company has come in to start ...
2
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1answer
290 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 ...
2
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2answers
232 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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2answers
400 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 ...
4
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2answers
115 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 ...
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1answer
152 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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3answers
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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2answers
15k 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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1answer
93 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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2answers
136 views

Why do lvdt sensors give us different results?

We take a cylindrical concrete sample and apply compression load on it, perpendicular to its head. To measure its strain we use 2 Lvdt(strain measurement devices)on both sides of the concrete sample . ...
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1answer
621 views

Shear strength of reinforced concrete filled PVC pipe

BACKGROUND: I'm burying a 3 foot x 4 foot drainage box (2 foot tall) in my driveway to hold/distribute excess gutter flow (1" of rain produces ~21cuft). I've constructed the walls with brick, laid on ...
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2answers
1k views

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

Retention/Detention Ponds are often added to a site-design to mitigate storm-water runoff. Enhanced Porosity Concrete (EPC), aka Pervious Concrete, can be used as a parking-lot pavement that allows ...
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1answer
237 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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2answers
525 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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1answer
56 views

What effect does the weight of a wall have on the steel in the reinforced concrete below?

Considering the two options build internal wall on top of 10 cm deep concrete slab reinforced with 7.7 mm smooth steel wire mesh build internal wall on top of 30 cm deep concrete floor ...
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1answer
1k views

Is there a way to derive a formula of modulus of rupture vs compressive strength?

Is there a way to derive a formula of modulus of rupture (flexural strength) vs compressive strength? I want to know is there any mathematical reason for the $\sqrt{f_{c} ^{'}}$ placed somewhere in ...
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1answer
148 views

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

Here's the situation: a thin concrete wall needs to go up, but it's a very large diameter, say 1 km. The wall thickness is on the order of 20 cm. The wall only needs to be maybe 3 meters high. I'm ...
7
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1answer
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,...
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3answers
564 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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1answer
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 ...
2
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1answer
130 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 ...
6
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1answer
706 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 ...
5
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2answers
128 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 ...
4
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1answer
169 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 ...
10
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1answer
268 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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1answer
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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2answers
11k 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 ...
13
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1answer
922 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 ...
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2answers
2k views

What is the best insulation wall for a house? ACC wall, Cavity wall, etc

Normally, people use Autoclaved Aerated Concrete (AAC) to build a concrete house because ACC is a good thermal insulation brick that easy to buy and not expensive ...
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2answers
2k 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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3answers
21k 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 ...

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