Rebar and concrete are two different materials, why they work together effectively

Let's start with the following concept: Concrete is made by mixing cement, sand, gravel and water in a certain proportion. After solidification, it is as hard as stone, and has good compression ability, but poor tensile ability, and is easy to break due to tension.

In order to solve this contradiction and give full play to the compressive capacity of concrete, a certain number of steel bars are often added in the concrete tension area or the corresponding part, so that the two materials are bonded into a whole and bear external force together. This type of concrete, which is equipped with reinforced steel, is called reinforced concrete. The fact that two materials with different properties, steel and concrete, work together effectively is due to the cohesion between concrete and steel bar after concrete hardening.

It consists of three parts: molecular force (glue force), frictional resistance, and mechanical occlusion force. Let's talk about why the concrete is not equipped with steel bars and other things: the reason why reinforced concrete can work together is determined by its own material properties.

First of all, steel and concrete have approximately the same linear expansion coefficient, and will not be overstressed due to different environments. Secondly there is good adhesion between the steel bar and the concrete, and sometimes the surface of the steel bar is also processed into a rib with intervals (called deformed steel bar) to improve the mechanical occlusion between the concrete and the steel bar in the construction process, when this is still not enough to transmit the tensile force between the steel bar and the concrete, usually the end of the steel bar is bent up 180 degree hook.

Just like your heart and liver are two different organs, but they are inseparable from each other.

The main reason: there is sufficient cohesion between the concrete and the rebar, and the temperature linear expansion coefficient of the two is similar.

1) There is good bonding performance between concrete and steel bar, and the two can be reliably combined together, under common force and deformed together.

2) The temperature linear expansion coefficient of concrete and steel bar is very close (concrete, rebar, to avoid large temperature stress when the temperature changes, and the cohesion between the two is damaged.

3) The concrete is wrapped on the outside of the steel bar, which can prevent the steel bar from corrosion or softening at high temperatures.

Other than that. The compressive strength of concrete is high and the tensile strength is low (the tensile strength of concrete is generally only about 1 l0 of the compressive strength). The steel bars are highly resistant to compression and tensile strength.

The two materials of steel bar and concrete are combined to work together, making full use of the high compressive strength of concrete and the strong tensile strength of steel bar, so that the two materials can do their best and complement each other to form structural components with good performance.

Why can two materials, steel and concrete, which have very different physical and mechanical properties, work together? This is mainly due to:

1) The hardened concrete has a strong adhesion to the surface of the steel bar;

2) There is a relatively close temperature expansion coefficient between the steel bar and the concrete, and the deformation will not be asynchronous due to temperature change, so that the dislocation between the steel bar and the concrete is generated;

3) The concrete is wrapped on the surface of the steel bar, which can prevent the steel bar from corroding and play a protective role. The concrete itself has no corrosive effect on the reinforcement, thus ensuring the durability of the reinforced concrete components.

There are three main reasons why two materials, steel and concrete, work together effectively:

Due to the induration of the large soil of the concrete bureau, a good bond force is generated between the steel bar and the concrete, so that the two are reliably combined, so as to ensure that the steel bar and concrete in the component are coordinated and deformed under the load, and the common force is stressed.

The coefficient of expansion of the temperature line of steel and concrete is very similarTherefore, when the temperature changes, it will not produce large temperature stress and destroy the bond between the two.

In the reinforced concrete bonded dry structure, the steel bar is wrapped by the concrete, so that it will not be very digging and rusting quickly, thereby improving the durability of the structure

Reinforced concrete properties.

Concrete is a mixture of cement (usually Portland cement) with aggregates. When a certain amount of water is added, the cement hydrates to form a microscopic opaque lattice structure, which wraps and binds the aggregate into a monolithic structure.

However, the tensile strength of concrete is low, usually only about one-tenth of the compressive strength, and any significant tensile bending will cause its microlattice structure to crack and separate, resulting in structural failure.

Compared with concrete, the tensile strength of steel bars is very high, generally above 200MPa, so people usually add stiffening materials such as steel bars to work together with concrete, and the tensile force of steel bars is borne by the steel bars, and the concrete bears the compressive stress part.

In some small cross-sections, in addition to the tensile force, the reinforcement can also be used to withstand the pressure, which usually occurs in the column. The cross-section of reinforced concrete members can be made into different shapes and sizes according to the needs of the project.

The main reason why two different materials, steel and concrete, can work together effectively is that there is sufficient cohesion between the concrete and the reinforcement, and the temperature line expansion coefficient of the two is similar.

The freeze-thaw cycle of steel rust and concrete can cause damage to the concrete structure. When the rebar is corroded, the rust spreads, causing the concrete to crack and causing the bond between the rebar and the concrete to be lost.

When the water penetrates the surface of the concrete and enters the interior, the volume of water condensed by freezing expands, and after repeated freeze-thaw cycles, cracks and deepens the concrete microscopically, so that the concrete is crushed and causes permanent irreversible damage to the concrete.

The main reasons why steel and concrete can work together are as follows:

1. The two have similar linear expansion coefficients.

2. After the concrete is hardened, there is a good adhesion between the steel bar and the concrete.

Steel bar and concrete are important building materials in civil engineering, the tensile and compressive strength of steel bars are very high, and they show good deformation ability when they are damaged, but they are also relatively high; Concrete has a high compressive strength but a low tensile strength. In order to give full play to the properties of the material, the two materials of steel bar and concrete are organically combined to work together in a reasonable way, so that the steel bar mainly bears tensile force and the concrete mainly bears pressure, which constitutes reinforced concrete.

Advantages of reinforced concrete structureSteel key reinforced concrete structure is widely used in civil engineering, and mainly has the following advantages:

1) Local materials. Sand and stone are the main components of concrete, which can be used locally. In addition, industrial wastes such as slag and fly ash can be effectively utilized.

2) Good durability and fire resistance. In a general environment, the steel bar is protected by concrete and is not susceptible to corrosion, thus improving the durability of the structure. When a fire breaks out, the reinforced concrete structure will not be burned like a wooden structure, nor will it be destroyed as quickly as a steel structure can reach a softening temperature.

3) Good modularity (also known as plasticity). Reinforced concrete structures can be poured into a variety of shapes and sizes as required.

4) Good integrity. The cast-in-situ or medium-high assembled integral reinforced concrete structure has good integrity, and can obtain good delayed slag cultivation through suitable reinforcement, which is conducive to seismic resistance and explosion-proof.