Summary Reader Response: Concrete that Grows

According to Corless, in the article "Scientists create living concrete from bacteria and sand" (2020) researchers from the University of Colorado Boulder have created living concrete from bacteria and sand. They have introduced a new living material, by combining sand, hydrogel and bacteria.

The article explains that photosynthetic cyanobacterium was biomineralized with a 3D sand-hydrogel scaffold, which produces new bricks from the original brick. Corless explains that additives are incorporated for enhancement because biological viability and mechanical performance cannot coincide. Corless claims that the new material possesses properties that are comparable to cement-based mortar, which carries biological purposes. Corless interviewed Srubar (2020), the director of Living Materials Laboratory, and he said that this process will change people's thinking about the manufacturing industry and reusable materials. Despite this technology still being in its infancy, it represents a new era in material manufacturing: a new grade of responsive materials “in which structural function is complemented by biological functions.”

Alternative cement for concrete production are being researched today is illustrated by the article, “Sustainable concrete: Building a greener future,” which focuses on more sustainable construction materials.

Some of the alternatives are, using microsilica (silica fume, or SF) for partial cement replacement, 3D concrete printing, and sugarcane bagasse ash. The environment benefits from these alternatives because they can curb the dangerous carbon emissions produced by long-term concrete production.

Firstly, silica fumes have been used as partial cement replacement. Silica fume is a by-product of high-purity quartz after reduction with coal in an electric furnace. Many researchers (Moozlam, 2002; Wong, 2010) have been studying the effect of replacing cement with silica fume on the strength and durability aspects of concrete. Scholars from Arni University, for example, replaced up to 15% cement with SF, by weight increment. The test results from the study concluded that “The strength of concrete increases rapidly as we increases the silica fume content and the optimum value of compressive strength is obtained at 10% replacement.” (Kumar et al., 2016) Thus, silica fume is suitable to be a substitutional cement material as there is an increase in the compressive strength of the concrete.

Another innovative method of producing concrete is 3D concrete printing (3DCP). While 3D printing techniques have been successfully implemented in a multitude of sectors, including aerospace and automotive, concrete construction is still in its infancy (Nematollahi et al., 2014). An article from the Swinburne University of Technology, Melbourne, explains how 3D concrete printing allows for freeform construction without the necessity of costly formwork, which has numerous advantages over the traditional method of pouring concrete into a formwork. (Nematollahi et al., 2014). This emerging technology is rapidly progressing in such a way that 3D printing of large-scale concrete structures may become a reality in near future.

Lastly, the use of waste products’ ashes to substitute cement. Some waste products that are being utilised in the construction sector are such as sugarcane bagasse, rice husk and seashells. Scholars of Iqra National University substituted cement with sugarcane bagasse ash (SCBA) in concrete production. (Afridi et al., 2019) SCBA can partially replace the clinker in cement production and in the process, it reduces the emission of CO² into the atmosphere.

In addition to this, researchers from Malaysia also reviewed seashell ash as partial cement replacement. (Wan et al., 2017) Utilizing the waste products to produce the ashes and replacing cement, partially solves the environmental pollution problems. Optimising the different wastes products’ ashes will possibly decrease the carbon emissions with a reduction of cement production.

Even with today’s modern technology, there are qualities of traditional concrete that outperform the new alternatives. For instance, the geopolymer material from 3DCP has drawbacks in its post-production. Manual inspection and application of bacteria on cracked areas of concrete structures are labour-intensive during the service life (Nematollahi et al., 2017). This is costly as compared to conventional concrete that can be produced in abundance whilst ensuring minimal to no cracks. Furthermore, humid conditions are not available in all parts of the world, so the scope of living concrete is not in the entire world. (Dashore, n.d.) Dashore explained that the living material matches properties with mortar which is not as strong as concrete.

To summarise, there are innovative researchers attempting to find alternative methods of cement production and what has been described above are just a few. The construction industry may even have an unprecedented invention such as living concrete. The mixture of sand, hydrogel and cyanobacteria produces a concrete material that is able to reproduce from itself when segregated. This creation pushes beyond the structural boundaries of construction. Nevertheless, there is a never-ending search for new possibilities for alternative concrete production or substitute materials.

References:

Afridi, A. (2019). Use of Sugarcane Bagasse Ash as a Partial Replacement of Cement in Concrete. Journal of Mechanics of Continua and Mathematical Sciences, 14(2). https://doi.org/10.26782/jmcms.2019.04.00006

Assi, L., Carter, K., Deaver, E., Anay, R., & Ziehl, P. (2018). Sustainable concrete: Building a greener future. Journal Of Cleaner Production, 198, 1641-1651. https://doi.org/10.1016/j.jclepro.2018.07.123

Dashore, A. (n.d) Living Concrete: Advantages and Problems. The Constructor. https://theconstructor.org/building/living-concrete-advantages-and-problems-pdf/37822/

Nematollahi, B., Xia, M., & Sanjayan, J. (2017). Current Progress of 3D Concrete Printing Technologies. 34th International Symposium on Automation and Robotics in Construction (ISARC 2017) http://dx.doi.org/10.22260/ISARC2017/0035

Singh, L., Singh, A., & Kumar, A. (2016). Study of Partial Replacement of Cement by Silica Fume. International Journal of Advanced Research http://dx.doi.org/10.21474/IJAR01

Wan Mohammad, W., Othman, N., et al. (2017). A review on seashells ash as partial cement replacement. IOP Conf Series: Materials Science And Engineering, 271, 012059. http://dx.doi.org/10.1088/1757-899X/271/1/012059