Composites: Concrete
- artandscienceofmat
- Apr 2, 2023
- 3 min read
ASSIGNMENT
Read the following brief historical overview of concrete.
Concrete is a material that has been used for centuries - starting with the Egyptians who made mortars. Egyptians used a combination of mud and straw to bind bricks together.
They used a combination of gypsum and lime as a mortar in building the great pyramids.
Then came the Greeks and Romans - The Romans developed a special type of concrete that was so strong it is still found in many of their buildings, bridges and roads today — over 2000 years later! This concrete combined hydraulic cement with lime and volcanic ash.
For 2000 years the Pantheon has withstood the test of time including earthquakes, Barbarian invasions and mother nature - without the benefit of steel structural supports. You can read more about why here.
Over time, concrete has been engineered to offer more stability and applications to a wide range of structures. It was initially reinforced with rocks, it was’t until more recent centuries that man began reinforcing concrete with rebar and other metals for construction purposes. The process of reinforcing concrete consists of embedding steel reinforcing bars, also knows as rebar, in concrete before it sets, in order to support the concrete from tensile stresses.
Fun fact:
How can concrete float? Any object, including concrete, will float if it’s less dense than the water it’s placed in.
Ferro-cement rowing boat, designed by Joseph Louis Lambot, 1848 Image source: www.beton.org
The invention of reinforced concrete gave the material a new life. It was pioneered in France in the mid-19th century, but was popularized by California-based engineer Ernest Ransome, who poured over iron (and later steel) reinforcement bars (rebar) to improving its tensile strength. Tensile strength is the maximum amount of tensile stress a material can withstand before it fails or breaks. Ransome himself was not involved in the construction of the world’s first concrete skyscraper, the 16-story Ingalls Building in Cincinnati in 1903, but it would not have been possible without his rebar (reinforcing bar) method.
The Ingalls Building is still in existence - in 1974 was added to the National Register of Historic Places and is currently getting new life as a custom Courtyard by Mariott hotel. You can read more about the project here.
It took architect Frank Lloyd Wright to realize the potential of reinforced concrete to create completely new forms. His first concrete building – the 1908 Unity Temple in Oak Park, Illinois – is widely considered the world’s first modern building. He used the material in many of his designs, including perhaps his most famous work – Fallingwater in Mill Run, Pennsylvania – whose hanging cantilevers project out over the stream’s small waterfall in a way which would have been impossible without the tensile strength of reinforced concrete. You can read more about it here.
The concept of using fibers as reinforcement is not new. Fibers have been used as reinforcement since ancient times. Historically, horsehair was used in mortar and straw in mud bricks. In the 1900s, asbestos fibers were used in concrete but once the health risks associated with asbestos were discovered, there was a need to find a suitable replacement.
In Europe, developments focused on the need to make the glass itself alkali resistant, and at the end of the 1960’s a suitable glass formulation was identified containing zirconia (Zr02), and after exhaustive trials the zirconia content was optimized at approximately 17%. In the 1970’s the technology was developed to produce alkali resistant (AR) glass fibres and the GFRC industry was born.
For almost 50 years of ongoing development, the industry now presents better quality glass fibers with a wider variety of sizing, new pozzolans (Pozzolans are defined as siliceous or siliceous and aluminous materials that have little or no cementitious properties in themselves but, when finely ground, will chemically react with calcium hydroxide in the presence of water to form compounds that have cementitious properties) to enhance the overall GFRC properties, low alkali cement to reduce the attack on the fibers, improved and diversified equipment, and more manufacturing methods. During this time, the market has witnessed continual growth in the volumes and the range of products manufactured. Today GFRC has become one of the most versatile building materials available to architects and engineers.
Ultimately, fiberglass enables us to make lighter, thinner pieces and create different textures that retain strength.
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