The theoretical life of concrete is very long, which can reach hundreds of years.
But since everything in our lives has the potential to corrode these houses, such as rain from the sky, which may contain acids that can corrode stones. Or it has encountered a severe natural disaster such as ** strong winds. External factors can easily affect the longevity of these building materials. Therefore, in order to ensure the personal safety of the occupants inside the building, a service life of the building materials will be set.
The general life span of concrete is about 100 years. However, typically, the design life in concrete codes is between 50 and 100 years. 50 years for ordinary residential construction.
But this is the theoretical design life, not that the life of the concrete will come to an end after 50 years.
The demise of concrete is all formed little by little. Large amounts of moisture and salt erode the surface and form a crack. Water and salt enter through the cracks, corroding the concrete reinforcement, which is infiltrated by the water and salt little by little, and over time, some of these substances will react with each other to form precipitation, and gradually the concrete will be weathered.
The earliest concrete of ancient Roman concrete in the 3rd century BC.
Around the 3rd century B.C., the ancient Romans discovered the water hardness of natural volcanic ash, and the mortar mixed with it had a high strength after hardening. In the remnants of ancient Rome, we see that the collapsed blocks are firmly connected together, and if the blocks are compared to coarse aggregates, this is the rudimentary form of ancient concrete.
Due to the use of natural pozzolana cement, ancient Roman concrete is more durable than modern concrete, and it is still strong and intact even after 2,000 years of weather, frost, rain and snow.
Portland Cement 1824.
Modern concrete uses cement as the cementitious material, and cement is the soul of concrete materials, which affects all aspects of the performance of concrete.
In 1756, the British engineer John Smeaton Smeaton accidentally discovered that a high strength could be achieved by mixing clay and limestone in the right proportions and calcining (similar to the process of volcanic ash formation). Smithton's approach soon spread across Europe, and everyone followed suit.
From 1824 to 1840, Joseph Aspldin and William Asptin worked out a method of calcining "cement" with lime, clay, slag and other mixtures. Because the cement is similar in color and strength to natural stone on the island of Portland in the United Kingdom, it is called "Portland cement" (i.e. ordinary Portland cement).
Reinforced concrete, 1849.
In 1849, the French gardener Joseph Monier combined iron wire with concrete to make flower pots, which solved the problem of low tensile strength of concrete, and presented his new invention at the Paris Exposition in 1867. After that, he successively invented iron-reinforced concrete pipes, water tanks, curtain wall panels, and designed the first iron-reinforced concrete bridge in 1875.
Prestressed concrete 1888.
Shortly after the application of steel (iron) reinforced concrete in the field of construction, in 1888 the American engineer Ph.Jackson came up with the concept of prestressed concrete, but the initial attempts were unsuccessful. The low-strength steel (iron) reinforcement defines the prestress value, while the small prestress is quickly lost after the creep and shrinkage of the concrete.
In 1956, Mr. Lin Tongyan completed the classic book "Design of Prestressed Concrete Structure", and proposed the theory of "load balance method", which regarded prestress as another load on the component that tries to balance with the external load, and simplified the analysis of the prestressed structure. He put the theory of prestressing into practice in many bridge works, and won the reputation of "Mr. Prestress".
Prestressed reinforced concrete technology is considered one of the most important advances in the development of concrete, creating an ideal material bond.
The concrete structure form also determines the different service life.
Concrete itself has high compressive strength and low tensile strength, and early concrete buildings often used arch shell systems derived from masonry structures. With the development of reinforced concrete and prestressing technology, the flexural and tensile properties have been greatly improved, and since then more concrete has appeared in the form of frames derived from timber structures.
Robert Maillart Mayar (1872, 1940) was a pioneer in the practice of concrete structures. In the early days of concrete, he designed beamless roofs, mushroom-shaped column caps, and perfect concrete three-hinged arch bridges that gave concrete structures a sense of spirituality and vitality.
In 1933, Ove Arup's Penguin Pond had two intersecting concrete spiral ramps, presenting a very light and free form. In terms of structure, a prestressed concrete construction surface is used, and the root of the spiral ramp is staggered up and down, resulting in a stress effect similar to that of a truss cantilever.
Concrete can also increase its service life by improving its material properties.
By changing the proportion and characteristics of concrete components, or adding other admixtures, concrete with different characteristics can be prepared. For example, commonly used high-strength concrete, impermeable concrete, micro-expansion concrete, low-hydration thermal concrete, low-activity concrete, aerated concrete, lightweight concrete, early-strength concrete, ultra-high pumped concrete, etc.
High-strength concrete.
At the beginning of the 20th century, theories such as water-cement ratio initially laid the theoretical foundation for concrete strength. Since the 60s of the 20th century, the application of high-efficiency superplasticizers, polymer materials, and various fibers has led to the development of concrete materials with higher and higher strength. High-performance concrete HPC is a direction for the development of concrete materials, and the so-called high performance refers to high strength, high durability, high fluidity, etc.
In the actual project, the super high-rise of Two Union Square in Seattle, USA, requires the elastic modulus of pumped concrete to reach 50GPA and the standard value of compressive strength to 131MPa. The standard value of 56d compressive strength of concrete measured by the project reached 1335mpa。
Fiber-reinforced concrete.
In order to improve the tensile properties and ductility of concrete, fiber-reinforced concrete was developed. Common ones include steel fiber, alkali-resistant glass fiber, carbon fiber, aramid fiber, polypropylene fiber or nylon synthetic fiber concrete. Studies have shown that the volume fraction of steel fiber content is about 1% 2, the tensile strength of concrete can be increased by 40% 80, and the plastic deformation capacity is greatly improved.
At the Federal Garden Exhibition in Stuttgart, the 26-metre-long shell structure made of fiberglass concrete with an average thickness of only 15 mm demonstrated the potential of fiber-reinforced concrete.