Summary Reader Response Draft 3

 According to Corless, the article "Scientists create living concrete from bacteria and sand" (2020) mentions that 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. The article states that biological viability and mechanical performance cannot coincide. Thus, additives are incorporated to enhance the quality of the material. The article 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 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.”

The prospect of alternative cements for concrete production are being researched as of today. From the Journal of Cleaner Production, a research article, “Sustainable concrete: Building a greener future” focuses on more sustainable construction.

Some of the alternatives are, using microsilica (silica fume) for partial cement replacement, 3D concrete printing, and sugarcane bagasse ash. The environment benefits from these alternatives because they can curb the generous 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 have been studying the effect of replacing cement with silica fume on the strength and durability aspects of concrete. Scholars from Arni University replaced 0% to 15% of 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.” 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. 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. With abundant carbon emission when producing Ordinary Portland Cement (OPC), geopolymer is a sustainable alternative to OPC. Geopolymer has superior mechanical, chemical and thermal properties and 80% less carbon emissions as compared to OPC. 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 as cement substitutes. Some waste products that are being utilised in the construction sector are such as sugarcane bagasse, rice husk and seashells. Scholars of Mehran University of Engineering and Technology substituted cement with sugarcane bagasse ash (SCBA) in concrete production. Since SCBA can partially replace the clinker in cement production, it reduces the emission of CO² into the atmosphere. The emissions reduction according to UNFCCC was 519.3 kilo tons of CO² per year. In addition to this, researchers from Malaysia also reviewed seashell ash as partial cement replacement. Utilizing the waste products to produce the ashes and replacing cement, partially solves the environmental pollution problems. By consuming different wastes, it 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 other 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 is labour-intensive during the service life. This is costly as compared to conventional concrete that can be produced in abundance whilst ensuring minimal to no cracks. Conventional concrete can source ingredients easily, in contrast to cyanobacteria concrete. The latter requires additives and hydrogel which is an even longer process to obtain. The monolithic character of traditional concrete gives much rigidity to a structure as well, if compared to the newfound 3D concrete printing.

To summarise, there are innovative researchers attempting to find alternative methods of cement production and these are just a few. The construction industry may 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, it should not stop the never-ending search for new possibilities for alternative concrete production or substitute materials.

References:

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

Jonkers, H., Thijssen, A., Muyzer, G., Copuroglu, O., & Schlangen, E. (2010). Application of bacteria as self-healing agent for the development of sustainable concrete. Ecological Engineering, 36(2), 230-235. doi: 10.1016/j.ecoleng.2008.12.036

Nematollahi, B., Xia, M., & Sanjayan, J. (2017). Current Progress of 3D Concrete Printing Technologies. https://www.researchgate.net/publication/318472250_Current_Progress_of_3D_Concrete_Printing_Technologies

Singh, L., Singh, A., & Kumar, A. (2016). Study of Partial Replacement of Cement by Silica Fume. https://www.journalijar.com/uploads/31_IJAR-11086.pdf

Vikas Srivastava, V., Atul, A., Ashhad Imam, A., P. K. Mehta, P., Satyendranath, S., & M. K. Tripathi, M. (2018). Supplementary Cementitious Materials in Construction - An Attempt to Reduce CO2 Emmission. Journal Of Environmental Nanotechnology, 7(2), 31-35. doi: 10.13074/jent.2018.03.182306

Wan Mohammad, W., Othman, N., Wan Ibrahim, M., Rahim, M., Shahidan, S., & Rahman, R. (2017). A review on seashells ash as partial cement replacement. IOP Conf Series: Materials Science And Engineering, 271, 012059. doi: 10.1088/1757-899x/271/1/012059