The manufacture of concrete is relatively simple: Aggregates like sand or gravel, chemical additives, fiber and water are combined with Portland cement. Yet, such a seemingly simple manufacturing process is, according to experts, fraught with environmental challenges.

Specifically, the parts of the process that involve the burning of fuel and the processing of chemicals reportedly produce significant amounts of carbon dioxide, which is a potent greenhouse gas.

As such, researchers the world over have been investigating methods for reducing the environmental impact of this industry and have subsequently arrived at some unexpected material solutions.

Follow along as GlobalSpec examines some of the unusual materials being used in the manufacture of concrete in part 1 of this two-part series.

Diapers

One somewhat unexpected ingredient used in the making of concrete: diapers. Researchers from the University of Kitakyushu in Japan are transforming used disposable diapers into a replacement for sand in the concrete and mortar used in the construction of low-cost housing.

Source: Siswanti Zuraida et al.

To create the new concrete and mortar mix, diapers, which are generally composed of wood pulp, cotton, viscose rayon and plastics like polyester, polyethylene and polypropylene, are washed, dried, shredded and then combined with cement, sand, gravel and water. This mixture is then left to cure for roughly 28 days.

The team determined that for a three-story house, up to 10% of sand can be replaced with the diaper mixture to create columns and beams. In a single-story house, the proportion can reportedly increase to 27%. Further, disposable diapers can potentially be used to replace up to 40% of the sand used in the manufacture of mortar in partition walls, while just 9% of the construction material could be used in the creation of floors and garden paving.

In total, the researchers reported that an estimated 8% of sand in all concrete and mortar materials required for the construction of a 388 ft² single-story house can be substituted with the disposable diaper waste mixture.

Shrimp

Along the lines of diapers in terms of unexpectedness, scientists from Washington State University and the U.S. Pacific Northwest National Laboratory are using the waste from shrimp shells to fortify cement.

According to the researchers, nanocrystals and nanofibers of chitin from waste shrimp, lobster and crab shells added to cement reportedly made the material 40% stronger and delayed the set time for the cement by more than an hour, which benefits long-distance transport and hot weather concrete applications.

Source: Washington State University

Researchers managed to improve the strength of cement using chitin from crab, shrimp and lobster shells based on chitin’s additional set of atoms that enabled researchers to control the charge on the surface of the molecules and their behavior in the cement slurry.

“The chitin nanoparticles repel individual cement particles enough so that it changes the hydration properties of the cement particle within the system,” the researchers asserted.

While adding the processed nanocrystals of chitin to the cement, researchers managed to improve and target its properties, including the material’s consistency, setting time, strength and durability.

By reducing the amount of cement used to achieve the same mechanical or structural function, while doubling its lifetime, the researchers suggest that the carbon emissions from the built environment can be dramatically reduced with the addition of chitin.

Food

Another unexpected solution for fortifying concrete has been discovered by a team of researchers from the University of Tokyo who are transforming food waste into edible cement for building and construction applications.

To develop the edible cement, researchers experimented with various types of food waste — tea leaves, coffee grounds, orange and onion peels, and Chinese cabbage, for example — drying, pulverizing and then compressing the ingredients with simple mixers and compressors. To bind the cement, researchers would have to adjust the temperatures and pressures used according to the food waste source.

Source: The University of Tokyo

The result was edible cement that demonstrated tensile strength quadruple that of traditional cement. Additionally, the researchers coated the cement pieces in Japanese lacquer to both waterproof the cement and prevent it from being eaten by rodents and pests when used to erect a structure.

To eat the cement, which has been flavored with different spices to adjust the taste, the University of Tokyo team suggests that the cement can be broken into pieces and boiled.

Construction waste

Researchers from the School of Building at Universidad Politécnica de Madrid (UPM) have demonstrated that mineral wool from construction and demolition waste (CDW) could potentially be used as an alternative to the reinforced fibers commonly used in building materials.

Using mineral wool waste recovered from insulating materials following construction demolition and adding it to cement mortar in place of sand resulted in cement mortar with improved flexural strength.

Check back with GlobalSpec for part 2 of the series: These unexpected ingredients are being used to fortify concrete, which will look at how manufacturers of concrete are using volcanic ash, PPE, plastic and even vegetables to strengthen concrete.