Concrete is today’s most widely used construction material, and one of the most widely used of any material, second only to water! Ever wonder how it got that way? The use of concrete dates way back to the time of ancient Egyptians and has a rich history. This blog post highlights major milestones in the history of concrete. Be sure to scroll down to view the infographic!
Before we map out dates in concrete’s history, it’s important to define what we mean by concrete. In ancient times, concrete-like substances were made from crude cements, produced by crushing and burning gypsum or limestone. When sand and water were added to these cements, they became mortar, a plaster-like material used to bond building stones together. Over the course of thousands of years, these early materials evolved into what we now recognize as modern concrete.
Today, concrete is made using water, fine and coarse aggregates, modern Portland Cement and a variety of performance enhancing admixtures. This engineered material offers many advantages including:
- A strong, versatile building material with a long service life
- Easily mixed, transported and placed in dimensionally controlled forms
- Readily usable in wet or completely submerged environments
- Ideal choice for road pavements with difficult subgrade conditions and heavy loading
- Low long-term costs with minimal maintenance
- Stable and predictable estimates for material costs
6500-700 BC - Bedouins in southern Syria and northern Jordan discovered the advantages of hydraulic lime, or cement that hardens underwater. By 700 BC, they were building kilns to supply mortar for the construction of homes, concrete floors and underground cisterns. The Bedouins understood the need to keep the concrete mix as dry or low-slump as possible, since excess water introduces voids and weakness into the concrete. Their building practices even included tamping the freshly placed concrete with special tools.
3000 BC - Ancient Egyptians used gypsum and lime mortars in building the pyramids. The Great Pyramid at Giza required about 500,000 tons of mortar, which was used as a bedding material for the casing stones that formed the visible surface of the finished pyramid. Around the same time, the Chinese were using a cement-like mixture based on sticky, glutinous rice for boat-building and later for mortar in construction of the Great Wall of China.
200 BC -The Romans learned to manufacture two types of artificial pozzolans, or cementitious materials that hydrated when combined with water, -- calcined kaolinitic clay and calcined volcanic stone. For grander and more artful structures, and for infrastructure requiring more durability, Roman cement was made from a naturally reactive volcanic sand called harena fossicia. For structures exposed to fresh water, such as bridges, docks, storm drains and aqueducts, they used a volcanic sand called pozzuolana. These two materials probably represent the first large-scale use of a truly cementitious binding agent. Both react chemically with lime and water to hydrate and solidify into a rock-like mass that can be used underwater. The Romans also used these materials to build large structures, such as the Roman Baths, the Pantheon, and the Colosseum, and these structures still stand today.
1824 - Joseph Aspdin developed Portland Cement by burning finely ground chalk and clay in a kiln until the carbon dioxide was removed. Today, it’s manufactured by heating a limestone and clay mixture in a kiln to temperatures between 1,300° F and 1,500° F. Up to 30% of the mix becomes molten but the remainder stays in a solid state, undergoing chemical reactions that can be slow. Over time, the mix forms a clinker, which is then ground into powder. A small proportion of gypsum is added to slow the rate of hydration and keep the concrete workable longer.
1891 - George Bartholomew poured the first concrete street in Bellefontaine, Ohio and it still exists today. The concrete used for this street showed compressive strengths at about 8,000 psi, about twice the strength of modern concrete used in residential construction.
1913 - the first load of ready-mix was delivered in Baltimore, Maryland. Four years later, the National Bureau of Standards (now the National Bureau of Standards and Technology) and the American Society for Testing and Materials (now ASTM International) established a standard formula for Portland cement.
1930 – Air entrainment was an important step in improving the durability of modern concrete. Water enters pores in the surface of hardened concrete and turns to ice with freezing weather. As the freezing water expands, small cracks are created and grow larger as the process is repeated, eventually resulting in damage to the concrete. Air entraining agents added during mixing create small, tightly spaced air bubbles. The bubbles compress slightly under the forces of expansion and absorb some of the stresses. Entrained air also improves workability because the bubbles act as a lubricant between aggregate and cement paste.
Today – Research has demonstrated the importance of not just total air content, but also the size and spacing of air bubbles in the matrix when predicting long-term resistance of concrete mixes to freeze-thaw cycles. Small, well dispersed bubbles are a sign of a quality air void system and spacing is a better indicator of freeze-thaw durability than air content alone. The Super Air Meter, or SAM, measures total air content by conventional methods as well as air void spacing in fresh concrete. Test results provide a new value known as the SAM number, proven to correlate with air void spacing.