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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2 answers
159 views

Reinforced mesh at different distance in a concrete slab?

Trying to determine some information regarding the reinforced concrete slabs (reinforced with mesh) in an apartment, by looking through the holes in the middle of the rooms for lights, I've come ...
0 votes
1 answer
26 views

Is there a substance i could treat concrete with to make it not scratched by steel?

Is there a substance i could use that would harden the surface of concrete enough to make it resist scratching by steel?
0 votes
2 answers
73 views

Is there a standard formula available to calculate lateral concrete pressure from the measurements of lateral concrete strain?

As shown in the image, I have done a vibrating wire type strain gauge and pressure cell (not shown in the image) instrumentation on full scale form. the objective is to measure the lateral pressure of ...
1 vote
3 answers
75 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? ...
-1 votes
2 answers
38 views

Question on plastic limit theorems and reinforced concrete

The lower plastic limit theorem is stated in Wikipedia as follows: If an equilibrium distribution of stress can be found which balances the applied load and nowhere violates the yield criterion, the ...
2 votes
2 answers
52 views

Once stopped, is it possible to achieve full cement hydration?

Several sources state that if hydration is stopped during cement curing, is not possible to resume it, and final strength will be compromised. But so far, I haven't found a reliable explanation. I ...
0 votes
1 answer
94 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 ...
0 votes
0 answers
17 views

How could these 2 concrete pours affect algae build up?

Here's the image: https://ibb.co/12kJCg8 First off, I live in a third world country with little standards for home building. My family's driveway ended up like this as the laborers somehow didn't ...
0 votes
2 answers
51 views

Modeling of a strap beam/foundation tie beam

The purpose of a strap beam (or tie beam - i'm not sure of the exact expression on english) as far as I know, is to enable foundation (horizontal) stifness. So my question is: how to model them ...
7 votes
2 answers
327 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 ...
0 votes
1 answer
48 views

Live and dead loads on lift core (passenger and cargo)

According to Eurocode or even better - JUS standards (if there is someone from EX-JU countries here), what are the dead and live load values and schemes for reinforced concrete lift core for both ...
0 votes
0 answers
25 views

Building Engineering - Lightning Conductor [duplicate]

I went on a new building, for installing many "details" before people relocating inside. On the roof, I saw a very intriguing things about lightning conductor : they are inside walls, packed ...
1 vote
5 answers
206 views

Reinforced concrete by steel, poor durability, why?

I've been reading up about reinforced concrete, as it is one if not the cheapest way how to build (with some solid foundation). I found out that it actually has quite poor durability (50-100 years or ...
0 votes
3 answers
116 views

How does Gypsum Concrete work?

When mixed with water how does gypsum act as a binder in creating concrete?
1 vote
1 answer
88 views

installing swing hook before concrete is poured

I want to place a swing hooks in place before the concrete is poured so that , i dont have to drill a hole later. My contractor is not ready to make these bolts with TMT bars itself.. what kind of ...
0 votes
0 answers
37 views

where did the concrete splitting test calculated stress formulat come from?

In compression test of cylindrical concrete sample we get the normal stress easily by dividing failure force by sample cross section, but how we can explain the formulat used to determine tensile ...
0 votes
3 answers
87 views

Why we say prestressed concrete is "more efficient"?

In my class my teacher said that prestressed concrete is more efficient, and when asked why he talk because of the constructing process. I believe because you have no cracked section hence you can use ...
1 vote
5 answers
142 views

Exactly what makes steel-concrete composite beam better than pure steel?

A composite action beam may have a concrete section the top, carrying the compression load, and steel at the bottom, carrying tension. But I have always thought that concrete had lower strength for a ...
0 votes
1 answer
64 views

Are there any ways to know whether the element has failed under loading, while knowing only limited properties?

I opt to check whether a precast concrete wall (no reinforcements, only concrete) withstand both vertical and lateral loading condition but the only properties I know are the Young's Modulus, density, ...
2 votes
2 answers
140 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 ...
1 vote
1 answer
43 views

Jointed reinforced concrete tie-bar smoothness

We know that in Jointed Reinforced Concrete pavements we use dowels and tie bars. Why are dowel bars Smooth and tie bars are deformed? Dowels are used to transfer about 40% of the load from one slab ...
1 vote
2 answers
45 views

Where to place air, water and electric cables in a composite beam [closed]

If water, gas and electrical cables have to pass through three (3) openings provided in the cross section shown in Figure 2, with tangible and scientific arguments specify the adequate opening for ...
0 votes
2 answers
108 views

Creep coefficient over time

I came across 2 creep coefficient diagram. First one is from Eurocode, second one is from elsewhere. I think the second one make sense, As the time progress, the creep coefficient shall increase, ...
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 ...
1 vote
2 answers
126 views

Dependency between load capacity for reinforced concrete slab and thickness

How does the load capacity for a reinforced concrete slab depend on the thickness of the slab? Example: Let's suppose that we have the following constants: concrete quality (including the maximum ...
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 ...
0 votes
4 answers
2k views

Why does a beam in shear crack at 45 degrees?

Why does a beam in shear like in this picture crack at 45 degrees instead of vertically? This is called "Punching shear", and requires concrete reinforcement at an angle: Assuming that the ...
11 votes
2 answers
750 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 ...
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 ...
0 votes
2 answers
42 views

Can anyone help me with the concept of bearing stresses in steel reinforcement in Reinforced Concrete?

When there is tension reinforcement(steel) embedded in concrete, does it not also undergo bearing stresses on account of the weight of the concrete and other forces which are acting above the steel? ...
0 votes
1 answer
42 views

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

I have been talking to some structural engineers trying to find one to design foundations for my contemplated bespoke building based on hi-cube 40-ft shipping containers. The initial concept is just ...
5 votes
2 answers
434 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 ...
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 ...
1 vote
0 answers
32 views

How to calculate load bearing capacity of a floating pavement?

Given tire load of a vehicle, how do I calculate load bearing capacity of a non-reinforced concrete pavement floating on a layer of heat insulation material, which is on the RC base? I can't figure ...
0 votes
0 answers
30 views

Modern equivalent concrete strength to 'Class Ws 3/4" '

Consider the following extract from a UK reinforced concrete detail drawing dated 1970: What is the modern equivalent to this concrete class?
4 votes
3 answers
713 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 ...
1 vote
0 answers
67 views

Is it possible to measure the concrete workability by a mobile app one day? [closed]

After studying all methods that can measure the concrete slump, I found 62 devices that service this purpose at the same time these devices are expensive and not practical enough, for this reason the ...
5 votes
2 answers
240 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 ...
1 vote
2 answers
1k 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 ...
0 votes
2 answers
289 views

Concrete pad over filled, in-ground pool better with or without wall support?

We are currently having a project done in our backyard to: (1) fill an in-ground pool and (2) build a "sport court" (with a large concrete pad and some tiles) over top. The pool demolition ...
3 votes
3 answers
193 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 ...
-1 votes
1 answer
72 views

How to choose the dimensions for a prestressed I-beam?

I need to design a simply supported symmetric I-beam (for a school problem). However, I can't find much information about the selection of the section or if there exist any standards for that. the ...
3 votes
2 answers
90 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 ...
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 ...
0 votes
1 answer
38 views

Control joint and contraction joint in concrete

What is the difference between a control joint and a contraction joint in concrete? I mean, a control joint is to control the cracks in concrete due to temperature or shrinkage etc... I understand it. ...
3 votes
0 answers
40 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 (...
-1 votes
3 answers
158 views

can ceramic be used as a building material?

From what I read, concrete has much lower compressive strength than ceramics. So why aren't we using ceramics to build? Is it because ceramic failure is difficult to predict? Because it's hard to ...
5 votes
1 answer
115 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 ...
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 ...
4 votes
2 answers
117 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 ...