how ancient romans built concrete walls?

• Using rebar
  • Rebar makes our concrete 2x stronger and allows it to take tensile loads in addition to compression
  • Rebar can deteriorate over time with repeated exposure to moisture, so it only lasts 75 years or so
  • Coating rebar is a potential solution being looked at to extend its lifespan
  • Rust-free rebar is used in some 100 year projects like dams and bridges
• Reducing environmental impact
  • Roman concrete has been proposed as an alternative to modern concrete, as it would have a substantially smaller environmental impact
  • There are a variety of concrete recipes tailored to specific performance needs, including those designed to reduce environmental impact
  • Companies are looking for ways to reduce the amount of cement in the concrete used
• Increasing durability
  • Roman concrete is far more durable, surviving thousands of years in harsh conditions nearly unscathed
  • Increasing the thickness of the concrete or sealing layers being applied can increase the durability of the concrete
• Other contributions
  • Roman Law has been hugely influential
  • Romans brought peace to the region
  • Roman concrete is used in lower levels of skyscrapers and rebar is used in almost all concrete structures

• The Romans used pozzolanic material such as volcanic ash from the area of Pozzuoli, on the Bay of Naples
  • This ash was shipped all across the Roman empire to be used in construction
  • It was described as a key ingredient for Roman concrete by architects and historians at the time
• The Romans also incorporated small, distinctive, millimeter-scale bright white mineral features, known as “lime clasts”
  • It had been assumed that these features were merely evidence of sloppy mixing practices, or poor-quality raw materials
  • However, the new study suggests that these tiny lime clasts gave the concrete a self-healing capability
  • The lime clasts were formed at extreme temperatures, as is expected from the exothermic reaction produced by using quicklime instead of, or in addition to, the slaked lime in the mixture
  • Hot mixing was key to the super-durable nature of Roman concrete
  • The lime clasts develop a characteristically brittle nanoparticulate architecture, creating an easily fractured and reactive calcium source
  • As soon as tiny cracks start to form within the concrete, they can preferentially travel through the high-surface-area lime clasts
  • This material can then react with water, creating a calcium-saturated solution, which can recrystallize as calcium carbonate and quickly fill the crack, or react with pozzolanic materials to further strengthen the composite material
  • These reactions take place spontaneously and therefore automatically heal the cracks before they spread

• Ancient Romans used a combination of volcanic ash and lime mortar to build concrete walls
  • Volcanic ash was mixed with water and lime to form a mortar-like material which was used to bind the stones together
  • This mixture was applied between layers of stones and then allowed to dry, forming a durable and waterproof wall
• Ancient Romans also used a technique called opus caementicium, which involved pouring a mixture of aggregate and a lime-based cement into wooden frames
  • This cement was stronger than the mortar and allowed for the construction of large and complex structures
  • It was also used as a waterproofing material, protecting walls and buildings from the elements

• Romans used “hot-mixing” to make their famously durable concrete
  • MIT has discovered how Roman engineers used “hot-mixing” to make their famously durable concrete
  • Self-healing concrete can be created using a variety of different “ingredients”
• Roman concrete is designed to be in compression everywhere and doesn’t rely on rebar for tension reinforcement
  • In modern construction, rebar corrosion is what drives the service life of a structure down
  • We could easily build what the Romans built today and it would be as, if not more, durable
• Is it cheaper to build roads from concrete in a regional climate that sees 150+ days of freeze-thaw cycles per year?
  • When we get a service life requirement for 100 years we prescribe w/c ratio and concrete cover so that carbonization and chloride initiated corrosion should not initiate before 100 years
  • Customers specify the design life time in the order, if they want longer they can get longer but it costs more so usually they don’t specify excessively long design life

• Ancient Romans built concrete walls by adding volcanic ash to the concrete mix.
  • This is similar to modern concrete that has fly ash added to it.
  • Pozzolan (Roman volcanic ash) may be superior to modern fly ash for a couple of reasons related to cement chemistry.
• Ancient Romans also mixed clay pots into their concrete mixes to make it less dense.
• Modern concrete can have a variety of other “pozzolanic” additives added such as silica fume and metakaolin which can improve compressive strength and durability, but can delay curing time and strength gain.
• Ancient Romans did not have a secret concrete mix - modern concrete could be made with the same ingredients, but it is not advantageous or economical to do so.

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What are the challenges to reviving the Roman approach to construction?

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• The Roman concrete mixture was composed of lime and volcanic ash to bind with rocks.
  • The elements within the volcanic material reacted with sea water to strengthen the construction.
  • It contains a rare mineral called aluminium tobermorite.
  • Elements within the mixture react with sea water to form crystals, which reinforce the concrete and prevents cracks from forming.
• The modern concrete mixture differs from the Roman substance in that modern concrete erodes over time while the Roman substance gains strength from exposure.
  • Modern buildings are constructed with concrete based on Portland cement, which involves heating and crushing a mixture of several ingredients.
  • The process of making cement has a heavy environmental penalty.
• Roman concrete could be used to create more environmentally friendly building materials.
  • Marie Jackson from the University of Utah is testing new materials using sea water and volcanic rock.
  • The Roman technique was based on building massive structures that are environmentally sustainable and long-lasting.
  • However, there are a number of limiting factors that make the revival of the Roman approach challenging, such as the lack of suitable volcanic rocks and the lack of the precise mixture that the Romans followed.

• Opus quadratum
  • Technique used around the 6th century BC
  • Consisted of blocks of similar and uniform sizes, arranged in rows
  • Used limestone blocks or volcanic tuff
• Opus caementicium
  • Mix of stones, limestone, water and pozzolana
  • Walls were between 60 and 90 centimeters wide
  • Built using wooden shapes filled with the mixture
• Opus incertum
  • Introduced around the end of the 3rd century BC
  • Used small pyramidal blocks placed outside the wall
  • Consisted of a more careful placement of the caementa
• Opus reticulatum
  • Successor of Opus incertum
  • Network of small square blocks cut in the form of truncated pyramids
  • Seated in diagonal lines ordered on thin layers of mortar
• Opus latericium
  • Main building material in the 1st century AD
  • Bricks of thick structure used to face a core of opus caementicium
• Opus mixtum
  • Hybrid walls, usually with Opus reticulatum at the angles and sides of Opus latericium
  • Reinforced Opus Reticulatum with horizontal bands of bricks or flat tiles
• Opus craticium
  • Technique related to half-timbering
  • Timber framework with the wall infill of stones in mortar called Opus incertum

• The Romans used volcanic rock and ash to build strong concrete walls
  • The Roman concrete was stronger than modern concrete
  • The secret was a mixture of lime and volcanic rock, placed in seawater
  • This created a mortar and volcanic tuff, and formed a strong calcium-aluminum-silicate-hydrate
  • Examples of Roman concrete that has lasted 2,000 years include sea walls and the Colosseum
• The Romans invented a hypocaust system to efficiently distribute heat
  • This system used a series of interconnected flues and ducts beneath the floors and walls of buildings

• Ancient Romans built concrete walls by hot mixing
  • Hot mixing involves combining lime, pozzolanic material such as volcanic ash, and water in a process known as slaking, as well as using quicklime in its more reactive form
  • Hot mixing produces high-temperature-associated compounds that would not otherwise form, and significantly reduces curing and setting times since all the reactions are accelerated, allowing for much faster construction
  • Lime clasts give the concrete a self-healing capability, wherein tiny cracks can preferentially travel through the high-surface-area lime clasts and be filled with a calcium-saturated solution
  • Tests were conducted to prove that this was the mechanism responsible for the durability of the Roman concrete, wherein two weeks after cracks were formed, they had completely healed
• Ancient Romans built concrete walls by using lime clasts
  • Lime clasts are small, distinctive, millimeter-scale bright white mineral features
  • They are formed at extreme temperatures, as would be expected from the exothermic reaction produced by using quicklime instead of, or in addition to, the slaked lime in the mixture
  • The lime clasts develop a characteristically brittle nanoparticulate architecture, creating an easily fractured and reactive calcium source, which can provide a critical self-healing functionality and quickly fill the crack
  • Calcite-filled cracks in other Roman concrete samples provide additional evidence of this hypothesis

• They used hot mixing
  • This involved the use of quicklime in the mixture, which produced an exothermic reaction
  • This enabled the formation of a dense network of hydration products, which made the concrete more durable
  • It also provided a self-healing function that sealed cracks and reduced the risk of further damage
• They over-engineered the structures
  • The walls were 6m thick on the street level
  • The structures were built with more vertical supports for horizontal spans
• They utilized lime clasts
  • This was the key to the ultradurable concrete used by ancient Romans
  • The lime clasts were formed at high temperatures
• They used special concrete
  • For dams, they used special concrete that lasts longer
  • For plastered facades, they used concrete that doesn’t need replacing or touch ups every 20 years or less

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What was the best method the Ancient Romans used to build concrete walls?