Ferrock is a carbon-negative sustainable concrete made from iron dust obtained from industrial byproducts that would otherwise be dumped in landfills. When exposed to carbon dioxide in the air, the iron dust solidifies through a process called cementation by iron carbonation, forming solid iron carbonate called ferrock. Unlike cement production, ferrock production does not emit carbon dioxide and instead consumes carbon dioxide during its curing process, making it more environmentally friendly. Optimal mixtures for ferrock include 60% iron powder, 12-20% fly ash, and other components that are cured for 7 days with carbon dioxide and 7 days with air to achieve desired strength and durability properties.

1. Modified Blended Ferrous Concrete:
Iron carbonation as novel structural binding mechanism
Shaik Sana
Department of Civil Engineering, VJIT, Hyderabad, India

2. Ferrock: A Carbon Negative Sustainable Concrete
• Iron dust obtained from industries as byproduct which is of little use is dumped in landfills shall causes various
health hazards. This byproduct can solidify when exposed to carbon dioxide present in air. This solidification
process may take time depending on the availability of the carbon dioxide. This process is called cementation by
iron carbonation and solid formed is called ferrock, the term promoted by David Stone, the professor of Arizona.
• This process indirectly consumes carbon dioxide from the atmosphere by gaining strength to the iron
carbonate. This mechanism can be one of the ecofriendly solutions to replace cement in concrete.
• Unlike cement, ferrock is formed by curing the iron dust product with carbon dioxide and then air-cured till it
achieves the desirable strength and durability properties.
• The duration of carbon dioxide and air curing depends on the composition of iron dust and powder along with
the nature of formation of iron carbonate’s microstructure.
• This iron-based product can be a suitable substitute for cement-based products in which cement is the energy-
intensive and artificially manufactured product which releases carbona dioxide during its manufacturing process.
• It was reported that the greenhouse gases release during the production of cement contributes to nearly 7-8% of
the total gases release into the environment. Contrary to cement which is a carbon positive material, the product
ferrock is a carbon negative in nature because it takes away carbon dioxide from the atmosphere to boost its
carbonation process.
• The process of gaining strength with cement using the water is called hydration whereas the process of
acquiring strength with iron particles using carbon dioxide is called carbonation. David stone in the year 2017
produced this iron carbonate product ‘ferrock’ which has constituent materials such as Iron powder, metakaolin,
fly ash, lime stone and oxalic acid.

3. Ferrock
• Ferrock is a more environmentally friendly product since it dont emit
carbon dioxide in the entire production process.
• According to Das, Hendrix, Stone, & Neithalath (2015), Das, Souliman,
Stone, & Neithalath (2014), Das, Stone, Convey, & Neithalath (2014), and
Widera, & Stone (2016), the raw materials for ferrock are iron powder, fly
ash, metakaolin, limestone, and oxalic acid. Iron powder makes up most of
the material in ferrock.
• Since ferrock serves as a substitute for cement, its other components are
evaluated considering that comparison as well as how well it works with
other building materials. By consuming carbon dioxide, which reacts with
the iron to generate iron carbonate, which adheres grimly to the substrate,
ferrock gains strength.

4. Chemical reactions
• Cementation process in cement is called hydration where as in ferrock it is called
carbonation.
• Calcium silicate hydrates are the hardened products formed after hydration whereas iron
carbonate is the formation product in ferrock. The following are the chemical reactions
involved in hydration and carbonation:
• Cement Hydration: C+H2O→CSH+CH
• Iron carbonation: Fe + CO2 + H2O → FeCO3 + H2↑
• Unlike cement, which needs water throughout the curing process to gain strength, here water
is only required for raw material transfer and mixing.

5. Iron particles
• Iron powder, a major component of ferrock, is derived from the wastes of steel mines and
industries, particularly the dust left over from steel shot blasting and electric arc furnace
manufacture. Due to the impracticality of recycling this waste and removing its iron concentration,
it has been dumped in landfills across the globe at significant financial expense.
• The iron particles used for the study is made up of iron dust (size less than 1.18mm) and iron
powder (less than 90 microns).
• The fineness modulus of iron particles procured is 3.28 which means that the size of the iron
particles used are in between 600 microns and 1.18mm.
• The specific gravity (sp. Gr) of iron particles is 7.84. After assessment, iron powder indicated that
they have an angular and elongated shape. However, its significant surface area leads to its
increased reactivity.

14. Curing Process
The curing process starts by demoulding the cubes immediately after the compaction, later the 70.6 mm cube
specimens were kept for carbon dioxide curing in plastic drum with 5g–10g of marble chips or baking soda
and add 5M hydrochloric acid. The chemical process releases gaseous carbon dioxide.
Various optimal combination of carbon curing duration and air curing durations are tried for optimum curing
regime. Seven days carbon curing duration and seven days of air curing duration found to be optimal for
attaining the desired properties of ferrous concrete.
It was observed that air curing was effective only with the increase in carbon curing duration, as the average
pore size decreased with increased carbonation duration. This is due to the fact that larger pores in initial days
of carbonation exert less internal moisture pressure under compression test and thus loss of moisture in air
curing after lesser carbonation duration does not have a larger effect on internal pressure and in turn on the
compressive strength.
In increased carbonation duration, pore size is reduced and thus more sensitive to compressive strength and
loss of moisture during the air curing.

15. Conclusions
• It has been also concluded that the solids composition of ferrous concrete as 60% iron
powder, 12-20% fly ash, 6-10% GGBS, 7-8% metakaolin, 7-8% limestone, 2%
gypsum and 2% oxalic acid.
• Water to solids ratio is maintained at 0.4.
• Carbon curing duration and air curing duration was finalized to 7 days and 7 days
respectively for ferrous blended concrete for better compressive strengths.
• The experimental works conducted on ferrous concrete are majorly focusing on
complete replacement of cement by supplementary cementitious materials with carbon
and air curing.

16. References
1. Barcelo, L., Kline, J., Walenta, G., & Gartner, E. (2014). Materials and structures, 47(6), 1055-1065
2. Niveditha M et al., International Journal of Sustainable Construction Engineering and Technology Vol. 11 No.
4 (2021) p. 90-98
3. Das, S., Hendrix, A., Stone, D., & Neithalath, N. (2015). Construction and Building Materials, 93, 360-370
4. Das, S., Souliman, B., Stone, D., & Neithalath, N. (2014). ACS applied materials & interfaces, 6(11), 8295-
8304
5. Das, S., Stone, D., Convey, D., & Neithalath, N. (2014). Materials characterization, 98, 168-179
6. Gao, J. M., Qian, C. X., Liu, H. F., Wang, B., & Li, L. (2005). Cement and concrete research, 35(7), 1299-
1304
7. Khatib, J. M., & Hibbert, J. J. (2005). Construction and building materials, 19(6), 460-472
8. Lanuza, A., Achaiah, A. T., Bello, J., & Donovan, T. (2017). ISE 576-Industrial Ecology, 2-24
9. Li, C., Gong, X. Z., Cui, S. P., Wang, Z. H., Zheng, Y., & Chi, B. C. (2011). Materials Science Forum (Vol.
685, pp. 181-187). Trans Tech Publications Ltd
10.Mouli. P, Gokul.V and Shanmugasundaram. M, (2019), International Research Journal of Engineering and
Technology, 467-469

17. Thank you