section_path: Important technological developments/Concrete
section_name: Concrete
paragraph_text: Concrete
  
  In 1824 Joseph Aspdin, a British bricklayer turned builder, patented a chemical process for making portland cement which was an important advance in the building trades. This process involves sintering a mixture of clay and limestone to about 1,400 °C (2,552 °F), then grinding it into a fine powder which is then mixed with water, sand and gravel to produce concrete. Portland cement concrete was used by the English engineer Marc Isambard Brunel several years later when constructing the Thames Tunnel. Concrete was used on a large scale in the construction of the London sewer system a generation later.