14

Where concrete is exposed to water, the water is going to permeate concrete no matter what you do (for the most part). The voids introduced by air entrainment allow the water some place to expand into when it does eventually freeze, thereby reducing the pressure on the concrete to crack. Edit 2021/02/17 to add some supplementary information: ACI 201-16, &...


7

The air entrained in the concrete causes discontinuous voids, which will not cause water to penetrate the concrete. Water will permeate through the bleeding pores which are continuous cavities. The entrained air bubbles are small and will only allow space for the freezing water to expand.


4

Figure 1. A concrete sleeper mould with reinforcing steel. Concrete sleepers are reinforced with pre-stressed steel. Image source: BFT-International. The sleepers will act as heat sinks during the day soaking up heat from the ground. At night this heat is let off. The steel will conduct heat to the ends of the sleepers warming the end-plates and supplying ...


4

The generation of heat during concrete cure is a significant issue. There are whole books written about it - see for example CIRIA C766 - 'Control of cracking caused by restrained deformation in concrete'. The primary cause of the cracking it discusses is so-called 'early thermal cracking', where the heating and subsequent cooling of the concrete sets up ...


4

No, they are usually fitted once and left. If you need to remove them then you need to drill new holes. Or you should consider fitting a wooden framework to the concrete and attaching to that so it can be easily removed and refitted, without disturbing the concrete fixings.


3

Foundation's task is not just to support gravity loads, it should resist lateral loads, wind and earthquake, as well. Wind loads are dependent on the geometry of the building and seismic loads are dependent on the mass distribution throughout the buliding. For example of you will show access to the roof of your third floor container for its use as a deck, ...


2

They're the same thing. See the link below for an article by the Portland Cement Association. Just different vocab from different regions of the country. Another common example of this in structural engineering is mat slab versus raft slab. They're synonyms. https://www.cement.org/learn/concrete-technology/concrete-construction/contraction-control-joints-...


2

Using conditions given in the sketch above, let's do a parameter study. M = AsFy(d - a/2) a = Asfy/0.85fc'b, note, since As, b, fc' and fy are constant throughout this exercise, "a" is constant as well. Let's assume a = 50mm. d = 65, M1 = AsFy(65-50/2) = 40Asfy d = 115, M2 = AsFy(115-50/2) = 90Asfy d = 165, M3 = AsFy(165-50/2) = 140Asfy M2/M1 = ...


2

Engineering decisions are fundamentally about problem solving. Thus, when asking, "Why not do [x] instead of [status quo]?" an answering question is: "What problem does [x] solve or what benefit does [x] provide versus existing designs?" If no satisfactory answer is forthcoming to the second question then that's the answer to the starting ...


2

Concrete crack is essentially caused by the diagonal tension stresses that acting normal to the crack plane. The tension stress is a maximum on a plane that is 45 degree to the analytical axes. You need to review the "Principal Stresses and Maximum Shear Stresses" in the engineer mechanics textbook.


2

In simple tension , the maximum resolved shear stress is 45 degrees to the tensile force . That is why a tensile test bar makes a "cup and cone" fracture face ; the cup edges are 45 degrees to the tensile force . This if for ductile materials that can deform in shear.


2

There have been many attempts to simplify the stress distribution in reinforced concrete beams. In 1937, Whitney proposed the use of a rectangular compressive stress distribution to replace the parabolic stress distribution. After many tests, he chose average stress of 0.85f'c, with a rectangle of depth $a = \beta c.$ Whitney determined that $\beta$ should ...


2

Some other answer have touched upon this, but I think it needs to be made explicit: Your mistake is in thinking that civil engineering is about making the lightest structure possible. It's not. Instead, it's about making the most cost-effective structure possible. Give me a material that weighs a billion tons per cubic centimeter but is cheap enough to let ...


2

I will make a slight add to the answers given here already, as follows. Take the case of a bridge. When loaded, some parts of it will be in compression, other parts will be in tension. The designer's job is to manage the stress levels in the most cost-effective manner. If a certain amount of concrete is capable of handling the compressive stresses less ...


1

You are looking at a diagram for an infinite duration of loading, which is noted by the $\infty$-symbol. For a limited duration of loading, refer EN 1992-1-1 annex B.1. Just for clarity, the time shown on the first diagram, $t_0$, is the concrete age when loading starts, which is why the creep coefficient decreases with increasing $t_0$.


1

You are missing seepage with humidity. Seepage is the infiltration of water into the living space (basement) and makes the space wet or moist. It does cause concern about humidity, but seepage alone won't cause the humidity to reach the extent that is uncomfortable (for humans) and harmful for building materials. It needs to work with the elevated ...


1

A partial listing ( in addition to the previous answer) ; for reinforced concrete only simple generic shapes are needed ( bars) while steel only needs "I" , "H" beams, gussets, fasteners, welding . Careful inventory control of the previous steel items. Coating of these shapes to reduce rust during construction. Inspection to verify the ...


1

The most important advantage of reinforced concrete over pure steel structure is availability. Many countries/regions on earth rely on imports for general goods production needs, the cost of steel can run prohibitively high compared to concrete. The next advantage is weight. In certain types of structure weight counts, such as underwater powerhouse. However, ...


1

Why only on the compressive side: Concrete has an unpredicable tensile behaviour. It is strongly recommended to avoid any tensile stresses on a concrete beam. So, what happens in this case, is that only the section of the beam which is in compression contributes to the load carrying capacity of the structure. That is why the rectangular section is limited to ...


1

Creep in concrete is when under sustained load, strain increases without an increase in the load. Excessive creep can lead to unacceptable deformation, redistribution of the stresses, even collapse of the structure. Creep is generally recoverable after removing the load. It has to do with the structural deformation of the Concrete matrix under constant long ...


1

By definition, bearing stress is the resulting stress between two rigid bodies in contact. It is relevant to concrete only because of its brittle nature, and prone to crack (weak in shear). On the other hand, reinforcing steel does not have such weakness, while it shares/feels the stress, the result rarely be meaningful and detrimental. So for all practical ...


1

They have collected heat during the day . And being solid they conduct heat better than the loose gravel. So they collect more heat and when cool the heat is conducted back to the surface better than the loose gravel. Under some humidity and temperature conditions the few degrees of temperature causes faster evaporation from the solid concrete. You ...


1

If the backfill material is not sand, it is difficult to get proper compacted density of the backfill on top of the concrete slab. If the backfill material is sand, then it is easier to compact. The wall of the pool will act as retainer of the sand backfill. If the sport court does not cover the whole area of the pool, it is not recommended to keep the pool ...


1

CONCERNS It is not only water peculating from the new deck that needs to be drained, there may be hydrostatic pressure from under the pool floor during the rainy season trying to come up that needs to be relieved. The floor of the pool is an obstacle to maintain hydraulic continuity. And from the viewpoint of geotechnical engineering the better uniform, ...


1

The reason tiles or flagstone or any other finishing is not used for heavy trrafic areas is lack of strength and toughness. Even in the decks you have attached photos these tiles/ stones will crack and dislodge due to differential heat expansion, vibration and water penetration to adhesive layer. They require a much higher level of maintenance. For roads and ...


Only top voted, non community-wiki answers of a minimum length are eligible