Cement and concrete are fundamental materials in construction, indispensable for creating durable and resilient structures. Cement acts as the binding agent, while concrete is a composite material made from cement, water, and aggregates like sand, gravel, or crushed stone. Together, they form the backbone of modern infrastructure, enabling the construction of buildings, bridges, roads, and dams.
Economically, the cement and concrete industries are vital contributors to construction. The cost-effectiveness and widespread availability of these materials make them essential for both small-scale residential projects and large-scale infrastructure developments. The cement industry is adapting to changing conditions and is on the verge of massive changes in the coming years, but it still has difficulties, like a fragmented market and an underdeveloped marketing strategy.
The history of cement dates back to ancient civilizations, with evidence of its use found in structures built by the Egyptians and Romans. The Romans, in particular, developed a sophisticated form of concrete using volcanic ash, lime, and aggregates. Modern cement, known as Portland cement, was developed in the 19th century by Joseph Aspdin, who patented the process of burning finely ground limestone and clay materials to create a strong, hydraulic binder.
Creating cement with minimal tools requires resourcefulness and an understanding of the basic chemical processes involved. Limestone and clay, which can be located via general geological knowledge, must be crushed and ground into a fine powder. A fire pit or rudimentary kiln, built from clay bricks or stones, is needed to heat the mixture to high temperatures (approximately 1450°C) for calcination. After burning, the resulting clinker must be ground again, potentially using stones, and mixed with gypsum to control setting time. As with basic plastic creation, the resulting cement quality would be limited compared to modern production.
Here’s the main process using modern techniques:
Cement Manufacture
The cement-making process consists of two basic steps:
1. Clinker Production: Clinker, the main constituent of cement, is made in a kiln. The kiln simultaneously burns a fuel source and heats the raw materials to about 1,450 degrees Celsius[1]. The raw materials usually consist of a mixture of calcium carbonate (limestone), silica, alumina, and iron oxide[5].
2. Cement Grinding: Clinker is ground into a fine powder[5]. Around 4-5% gypsum is added to control the setting time. The resulting powder is Ordinary Portland Cement (OPC)[1]. Other materials, such as slag, fly ash, or limestone, can be added[1][3]. These blended cements have a lower clinker content[3].
The cement manufacturing process involves four stages:
1. Crushing and grinding raw materials[5][7].
2. Blending the materials in the correct proportions.
3. Burning the prepared mix in a kiln.
4. Grinding the burned product (clinker) with gypsum.
There are three processes of cement manufacture: wet, dry, and semidry. These terms refer to how the raw materials are ground and fed into the kiln. In the wet process, the materials are ground wet and fed to the kiln as a slurry. In the dry process, they are ground dry and fed as a dry powder. In the semidry process, they are ground dry and moistened to form nodules[5].
Ancient Technology, Better Than Current Cement
The ancient Romans developed a remarkably durable form of concrete, opus caementicium, which has proven to be more resilient than much of modern concrete[18]. The ancient Romans created their durable concrete by mixing volcanic ash (pozzolana), lime, and water to form a mortar[10]. This mortar was then combined with aggregates, such as rock fragments, ceramic tiles, or brick rubble[11]. For structures exposed to seawater, the Romans used seawater in the mixture, triggering a chemical reaction with the volcanic ash that resulted in the formation of tobermorite, a mineral that strengthens the concrete over time[10][13]. Recent research suggests the Romans used quicklime instead of, or in addition to, slaked lime in the mixing process[14][16]. This “hot mixing” technique created lime clasts within the concrete, which, when exposed to water from cracks, would dissolve and recrystallize, effectively self-healing the concrete[11][14]. The Romans also discovered that using as little water as possible in the formula also allowed them to create more durable concrete[12].
How To Make Opus Caementicium
To create concrete inspired by the Romans, begin by sourcing high-quality volcanic ash (pozzolana), quicklime (calcium oxide), small stones or broken bricks for aggregate, and fresh water or seawater (depending on the intended use). The key to the Roman technique is “hot mixing”: Combine the quicklime directly with the pozzolana, aggregates, and minimal water, as the heat produced prevents the lime from fully dissolving, creating lime clasts within the mixture. During construction, mix components like lime and volcanic ash in a mortar box, then transport the mixture to the site, tamping it over a prepared layer of rock pieces. It’s crucial to use as little water as possible to avoid weaknesses and to allow the materials to bond fully. This process enables the concrete to self-heal, as the lime clasts react with any water that enters cracks, creating a calcium-rich solution that recrystallizes and seals the cracks. Finally, be sure to source materials and apply techniques according to what would have been available and achievable in the Roman world.
Modern Tests of Hot Mixing to Make Self-Healing Cement
Researchers at MIT created samples of “hot-mixed” concrete using both ancient and modern formulations[19][3]. They deliberately cracked these samples and ran water through the cracks[19][20][21][22]. Within two to three weeks, the cracks in the hot-mixed concrete had completely healed, and water could no longer flow through[19][20]. In contrast, concrete made *without* quicklime *never* healed[19][20].
Modern Formulations: Subsequent work tested a new industrial formulation (Mix 2), and found 9% less drying shrinkage after 90 days[22]. After a year of casting, the difference was within 1%[22].
These experiments provide strong evidence that the hot mixing technique with quicklime does indeed contribute to the self-healing properties and durability of Roman concrete[19][20][21][11].
Uses of Cement
Cement is a very useful binding material in construction. Applications include:
* Mortar for plastering and masonry
* Making joints for drains and pipes
* Ensuring water-tightness of structures
* Concrete for floors, roofs, lintels, beams, stairs, pillars[2][8]
* Protecting exposed surfaces from weather and chemicals
* Manufacturing precast pipes, piles, and fencing posts
* Constructing bridges, culverts, dams, tunnels, and lighthouses
* Foundations and footpaths
* Wells, water tanks, tennis courts, lamp posts, telephone cabins, and roads
* Industrial flooring, warehouses, factories, and parking lots[4]
* Repairing and rehabilitating existing structures
* Nuclear power plant structures
Cement is often mixed with aggregates like sand, gravel, or crushed stone to form concrete[8]. Concrete is commonly used for foundations, walls, floors, and roofs in residential buildings[8].
Concrete Applications
* Pavement reconstruction, resurfacing, restoration, or rehabilitation
* State highways, rural roadways, residential and city streets, intersections, airstrips, intermodal facilities, military bases, and parking lots[9]
* Precast concrete elements for bridges, high-rise office buildings, parking structures, stadiums, and schools
* Lightweight cellular concrete for soil or fill replacement[6]
Environmental Considerations
The production of cement results in CO2 emissions[1][5]. Some strategies to reduce these emissions include:
* Increasing energy efficiency
* Replacing fossil fuels with renewable energy[3][5]
* Capturing and storing CO2
* Using alternative formulations that reduce the need for clinker
Despite its versatility and widespread use, cement production contributes significantly to environmental pollution. High-temperature processing of raw materials releases greenhouse gases, particularly carbon dioxide, exacerbating climate change. Addressing these challenges requires adoption of sustainable practices, including using alternative fuels, reducing clinker content in cement, and investing in carbon capture technologies to minimize the environmental footprint of cement and concrete production.
Read More
[1] https://cembureau.eu/media/drylkjo0/manufacturing-process-factsheet_update-jan2021.pdf
[2] https://civiltoday.com/civil-engineering-materials/cement/46-uses-of-cement
[3] https://www.mapei.com/it/en/realta-mapei/detail/top-level-technical-assistance-for-modern-cement-industry
[4] https://www.jkcement.com/blog/basics-of-cement/uses-of-cement/
[5] https://www.britannica.com/technology/cement-building-material/Extraction-and-processing
[6] https://www.cement.org/cement-concrete/applications-of-cement/
[7] https://www.cement-plants.com/how-to-build-a-integrated-cement-plant/
[8] https://www.jswonemsme.com/blogs/blogs-articles/cement-applications-in-residential-construction
[9] https://www.cement.org/cement-concrete/applications-of-cement/uses-in-infrastructure/
[10] https://ancientengrtech.wisc.edu/roman-concrete/
[11] https://en.wikipedia.org/wiki/Roman_concrete
[12] https://www.youtube.com/watch?v=4VVJ9KyFepk
[13] https://www.science.org/content/article/why-modern-mortar-crumbles-roman-concrete-lasts-millennia
[14] https://www.science.org/content/article/scientists-may-have-found-magic-ingredient-behind-ancient-romes-self-healing-concrete
[15] https://www.designboom.com/architecture/ancient-roman-concrete-durable-mit-self-healing-abilities-01-09-2023/
[16] https://news.mit.edu/2023/roman-concrete-durability-lime-casts-0106
[17] https://www.sciencenews.org/article/chemists-long-lasting-roman-concrete
[18] https://riskfrontiers.com/insights/why-is-roman-concrete-more-durable-than-modern-concrete/
[19] https://news.mit.edu/2023/roman-concrete-durability-lime-casts-0106
[20] https://www.labroots.com/trending/chemistry-and-physics/24482/chemists-recreated-long-lasting-roman-concrete
[21] https://riskfrontiers.com/insights/roman-concrete-2-discovery-of-the-chemical-processes/
[22] https://pmc.ncbi.nlm.nih.gov/articles/PMC9821858/
[23] https://www.science.org/doi/10.1126/sciadv.add1602
[24] https://www.researchgate.net/publication/229442009_Mortar_studies_towards_the_replication_of_Roman_concrete
[25] https://engineeringrome.org/development-of-roman-concrete/
[26] https://www.reuters.com/lifestyle/science/scientists-chip-away-how-ancient-roman-concrete-stood-test-time-2023-01-09/