question: how is concrete + steel so strong? What makes them a strong combo?
comment: Concrete has very high “compressive” strength, which basically means it can handle a heavy load pressing on it. However, it can easily snap like pieces of a Hershey’s bar. The steel inside the concrete increases the “sheer” strength of the pour, which basically prevents the snapping. Each part absorbs those dynamics of the load making the part’s job a little easier and the whole structure stronger as a whole. This synergy makes them a strong combo, but it is also that the thermal coefficient of both steel and concrete are nearly the same. This means that they will expand and contract at the same rate. If one expands or contracts faster than the other, their forces acting on each other can cause cracks, breaks, and voids.
passages: Concrete is a very strong and economical material that performs exceedingly well under compression. Its weakness lies in its capability to carry tension forces and thus has its limitations. Steel on the other hand is slightly different; it is similarly strong in both compression and tension. Combining these two materials means engineers would be able to work with a composite material that is capable of carrying both tension and compression forces.
  
  Eurocode 2 is intended to be used in conjunction with:
  
  BULLET::::- EN 1990: Eurocode - Basis of structural design;
  
  BULLET::::- EN 1991: Eurocode 1 - Actions on structures;
   BULLET::::- Bonding agents are used to create a bond between old and new concrete (typically a type of polymer) with wide temperature tolerance and corrosion resistance.
  
  BULLET::::- Corrosion inhibitors are used to minimize the corrosion of steel and steel bars in concrete.
   Section::::Steel vs. concrete.:Combining steel and reinforced concrete.
   BULLET::::2. When the cement paste within the concrete hardens, this conforms to the surface details of the steel, permitting any stress to be transmitted efficiently between the different materials. Usually steel bars are roughened or corrugated to further improve the bond or cohesion between the concrete and steel.
   Steel is the strongest commonly available fiber, and comes in different lengths (30 to 80 mm in Europe) and shapes (end-hooks). Steel fibers can only be used on surfaces that can tolerate or avoid corrosion and rust stains. In some cases, a steel-fiber surface is faced with other materials.
   BULLET::::- The bond created by utilizing rebar and concrete can also be attributed to the ridged rebar surface. This allows stresses to transfer from the concrete to the steel, and from the steel to concrete.
  
  BULLET::::- Concrete and steel have similar thermal expansion coefficients. Upon freezing or heating, they contract and expand in a similar manner, maintaining the structure needed.
  
  Section::::Guidelines.
  
  National codes also specify minimum cover requirements based on their respective local exposure conditions.
  
  Section::::Paradox.
   Section::::Steel plate construction.
  
  In steel plate construction, stringers join parallel steel plates. The plate assemblies are fabricated off site, and welded together on-site to form steel walls connected by stringers. The walls become the form into which concrete is poured. Steel plate construction speeds reinforced concrete construction by cutting out the time-consuming on-site manual steps of tying rebar and building forms. The method results in excellent strength because the steel is on the outside, where tensile forces are often greatest.
  
  Section::::Fiber-reinforced concrete.
   Section::::Peculiarities of Concrete.:Material Properties.
   All concrete structures will crack to some extent. One of the early designers of reinforced concrete, Robert Maillart, employed reinforced concrete in a number of arched bridges. His first bridge was simple, using a large volume of concrete. He then realized that much of the concrete was very cracked, and could not be a part of the structure under compressive loads, yet the structure clearly worked. His later designs simply removed the cracked areas, leaving slender, beautiful concrete arches. The Salginatobel Bridge is an example of this.
   BULLET::::- Increased ultimate strength in flexureWith bonded post-tensioning, any flexure of the structure is directly resisted by tendon strains at that same location (i.e. no strain re-distribution occurs). This results in significantly higher tensile strains in the tendons than if they were unbonded, allowing their full yield strength to be realised, and producing a higher ultimate load capacity.
   UHPC is also characterized by its constituent material make-up: typically fine-grained sand, silica fume, small steel fibers, and special blends of high-strength Portland cement. Note that there is no large aggregate. The current types in production (Ductal, Taktl, etc.) differ from normal concrete in compression by their strain hardening, followed by sudden brittle failure. Ongoing research into UHPC failure via tensile and shear failure is being conducted by multiple government agencies and universities around the world.
  
  Section::::High-performance concrete.:Micro-reinforced ultra-high-performance concrete.
   Ducon was the early developer of micro-reinforced UHPC, which has been used in the construction of new World Trade Center in New York.
  
  Section::::Self-consolidating concrete.
   BULLET::::- Improved crack-controlIn the presence of concrete cracking, bonded tendons respond similarly to conventional reinforcement (rebar). With the tendons fixed to the concrete at each side of the crack, greater resistance to crack expansion is offered than with unbonded tendons, allowing many design codes to specify reduced reinforcement requirements for bonded post-tensioning.
  
  BULLET::::- Improved fire performanceThe absence of strain redistribution in bonded tendons may limit the impact that any localised overheating has on the overall structure. As a result, bonded structures may display a higher capacity to resist fire conditions than unbonded ones.
   Other materials can also be used as a concrete binder, the most prevalent alternative is asphalt, which is used as the binder in asphalt concrete.
  
  The "mix design" depends on the type of structure being built, how the concrete is mixed and delivered, and how it is placed to form the structure.
  
  Section::::Composition.:Cement.
   Concrete is the most common artificial composite material of all and typically consists of loose stones (aggregate) held with a matrix of cement. Concrete is an inexpensive material, and will not compress or shatter even under quite a large compressive force. However, concrete cannot survive tensile loading(i.e., if stretched it will quickly break apart). Therefore, to give concrete the ability to resist being stretched, steel bars, which can resist high stretching forces, are often added to concrete to form reinforced concrete.
   Concrete fracture analysis
  
  Concrete is widely used construction material all over the world. It is composed of aggregate, cement and water. Composition of concrete varies to suit for different applications desired. Even size of the aggregate can influence mechanical properties of concrete to a great extent.
  
  Section::::Peculiarities of Concrete.
  
  Section::::Peculiarities of Concrete.:Response to tensile and compressive loading.
   Section::::Steel vs. concrete.:Structural steel.
  
  BULLET::::- Characteristics - Structural steel differs from concrete in its attributed compressive strength as well as tensile strength.
  
  BULLET::::- Strength - Having high strength, stiffness, toughness, and ductile properties, structural steel is one of the most commonly used materials in commercial and industrial building construction.
   For individual strand tendons, no additional tendon ducting is used and no post-stressing grouting operation is required, unlike for bonded post-tensioning. Permanent corrosion protection of the strands is provided by the combined layers of grease, plastic sheathing, and surrounding concrete. Where strands are bundled to form a single unbonded tendon, an enveloping duct of plastic or galvanised steel is used and its interior free-spaces grouted after stressing. In this way, additional corrosion protection is provided via the grease, plastic sheathing, grout, external sheathing, and surrounding concrete layers.
   Open Web Composite Steel Joists, CJ-Series, were developed to provide structural support for floors and roofs which incorporate an overlying concrete slab while also allowing the steel joist and slab to act together as an integral unit after the concrete has adequately cured.
  
  The CJ-Series Joists are capable of supporting larger floor or roof loadings due to the attachment of the concrete slab to the top chord of the composite joist. Shear connection between the concrete slab and steel joist is typically made by the welding of shear studs through the steel deck to the underlying CJ-Series Composite Steel Joist.
   SCC is characterized by the following:
  
  BULLET::::- extreme fluidity as measured by "flow", typically between 650–750 mm on a flow table, rather than slump (height)
  
  BULLET::::- no need for vibrators to compact the concrete
  
  BULLET::::- easier placement
  
  BULLET::::- no bleeding, or aggregate segregation
  
  BULLET::::- increased liquid head pressure, which can be detrimental to safety and workmanship
  
  SCC can save up to 50% in labor costs due to 80% faster pouring and reduced wear and tear on formwork.
   Also concrete has a heterogeneous structure due to uneven composition of ingredients in it. This also complicates the analysis of concrete by producing misleading results.
  
  Section::::LEFM and Concrete.
   Reinforced concrete is the most common form of concrete. The reinforcement is often steel, rebar (mesh, spiral, bars and other forms). Structural fibers of various materials are available. Concrete can also be prestressed (reducing tensile stress) using internal steel cables (tendons), allowing for beams or slabs with a longer span than is practical with reinforced concrete alone. Inspection of existing concrete structures can be non-destructive if carried out with equipment such as a Schmidt hammer, which is sometimes used to estimate relative concrete strengths in the field.
   BULLET::::- Constructability - Structural steel can be developed into nearly any shape, which are either bolted or welded together in construction. Structural steel can be erected as soon as the materials are delivered on site, whereas concrete must be cured at least 1–2 weeks after pouring before construction can continue, making steel a schedule-friendly construction material.
   Section::::Overview.
  
  BULLET::::- SCC is measured using the slump-flow test (or "flow table") rather than the usual slump test, as it is too fluid to keep its shape when the cone is removed. A typical SCC mix will have slump-flow of around 500 – 700mm.
  
  BULLET::::- SCC is weakened, not strengthened, by vibration. As vibration is not needed for compacting the mix, all that it achieves is to separate and segregate it.
  
  Section::::See also.
  
  BULLET::::- Concrete slump test
  
  BULLET::::- Flow table test
  
  BULLET::::- Self-leveling concrete
  
  Section::::External links.
   BULLET::::- formula_1, initiation time: from the moment the structure is built, to the moment corrosion initiates on steel rebar. More in particular, it is the time required for aggressive agents (carbon dioxide and chlorides) to penetrate the concrete cover thickness, reach the embedded steel rebar, alter the initial passivation condition on steel surface and cause corrosion initiation.
  