Concrete has been around for centuries. In fact, some in construction joke that the Parthenon in Greece was the first continuous pour. However, it was not until 1900 that the first concrete blocks were made. Harman S Palmer created a cast-iron machine by which he shaped the concrete into blocks. These blocks created a revolution. "Why should I hew these stones when I could make them in a mould?" asked Nels Peterson, a stone cutter; so he founded the Ideal Cement Stone Company. The concrete blocks of today are used to build skyscrapers, bridges and walls, and these modern blocks contain properties that make them valuable in the building industry.
Concrete blocks share a common size. They are, for the most part, rectangular, and usually 8 inches by 8 inches by 16 inches. This means that it makes it easier for masons to work with, thanks to the lack of variation. However, it is possible to have custom concrete blocks moulded into different sizes and shapes. The design of the block, with its centre channel that makes it look like a flattened figure eight, allows the weight to be distributed in more than one point. This evens the load and makes the blocks stronger.
Concrete blocks are made from Portland Cement, water, sand and gravel. This combination makes the concrete block durable and long lasting. Some concrete blocks may include other ingredients such as colour pigment, air-entraining, or water repellent. Air-entraining is, according to the Federal Highway Administration, "the process whereby many small air bubbles are incorporated into concrete and become part of the matrix that binds the aggregate together."
Concrete blocks are cured rapidly in a chamber built for the purpose. Inside the chamber, the temperature is high. After the blocks are cured, they are stored in a chamber where they are allowed to dry before use. This process of accelerated curing strengthens the concrete blocks and lengthens their life-span.