Reinforced Concrete Structures

• UNCCD COP17 will take place in Ulaanbaatar, Mongolia in 2026.

Reinforced Concrete

• Reinforced concrete (RC) structures contain steel bars.
• Steel reinforcement is used because concrete is weak in tension, meaning it's poor at resisting stretching forces.
• Steel is strong in tension, allowing reinforcing bars to overcome concrete’s weakness.
• Formwork (or shuttering) is used to form different parts of structures
• Formwork consists of steel or timber molds of the required size and shape that contain the concrete until it sets.
• Wet concrete cast or placed in its final position is called in situ concrete.
• Reinforced concrete elements may be precast at a factory and then delivered to the construction site for assembly.
• Pre-cast concrete can also be pre-stressed, where tension is applied to the reinforcing bars usually before the concrete is poured.
• The bars are held in tension while the wet concrete is poured, becoming "trapped" in tension after the concrete sets.
• This increases the concrete's ability to resist bending forces.

Pre-stressing Techniques for Concrete

• Pre-stressing usually involves holding the reinforcement in tension while pouring the concrete.
• This form of pre-stressing is called pre-tensioning where tension is applied before the concrete is poured
• Pre-tensioning is often used for floor components small enough to fit on a truck for transport.
• This occurs at a factory.
• Post-tensioning is a less common technique where tension is applied after the concrete has set.
• Post-tensioning is more suitable for large elements like long beams that can't be transported and must be poured in situ.
• Ducts, usually plastic tubes, are placed inside the formwork along the beam's length before pouring concrete.
• These ducts contain steel cables.
• After the concrete has been cast and gained sufficient strength, the cables are put in tension using jacks at either end of the beam.
• Post-tensioning is only possible because the cables can move within the ducts, unlike pre-tensioned reinforcing bars held fast by the surrounding concrete.
• The ends of the cables are then permanently anchored at either end of the beam.

Vocabulary

• To teem (with) means to be full of, filled with.
• To synthesize is related to the production of chemical compounds by reaction from simpler materials.
• Gelatin is a food ingredient, often from collagen taken from animal body parts like cartilage, and is rubbery when moist.
• Nutrients are substances that provide nourishment for life and growth.
• Regeneration is the formation of something new.
• Humid means having a high level of water vapor in the air.
• Viable means capable of surviving or living successfully, especially under particular environmental conditions.
• To grind up means to reduce something to small particles or powder by crushing it.

Bacteria-Based Living Concrete

• A new kind of concrete developed at the University of Colorado teems with life.
• Unlike traditional concrete, this new material uses photosynthetic bacteria and gelatin.
• The so-called "living concrete" bricks are made by mixing the ingredients in a mold, as published in the journal Matter.
• Researchers created arches, two-inch cubes, and shoebox-sized bricks that start green due to the bacteria's photosynthetic abilities and fade to brown as the material dries.
• The bacteria uses gelatin and nutrients to hold the sand together in a web of minerals.
• Two-inch cubes of living concrete can hold the weight of a person, although the bricks are weaker than traditional concrete.
• A beneficial advantage is their ability to regenerate.
• Mixing half a brick with additional nutrients, sand, gelatin, and warm water allows the bacteria in the original piece to grow into the added material.
• This process results in two bricks instead of one in seven days.
• The bacterial bricks can be used for exponential brick reproduction, creating eight bricks from the original.
• Generating new bricks requires viable bacteria and a humid environment.
• After 30 days in a humid environment, about 9 to 14 percent of the bacteria in the brick remain viable, which is better than previous attempts.
• This new concrete may not be suitable for the desert due to humidity needs.
• Waste materials like ground up glass or recycled concrete could be used, eliminating the need to transport cement.