Design of Eco-Friendly Concrete Mixtures with New SCMs

Concrete is a fundamental building material used in all manner of construction projects around the world. The primary ingredient in concrete typically being portland cement. Naturally, in an effort to lower their environmental impact and move toward more sustainable options, the industry as a whole is looking for greener alternatives to partially replace the portland cement component of concrete mixes. The goal with our project was to research and develop concrete mixes that incorporate these alternative SCMs with the aim to lower their environmental impact while maintaining the same desirable strength properties.

While utilizing SCMs in concrete mixtures is nothing new, as SCMs like fly ash have been used commonly in industry for decades [2]. Where our design innovates is in the exploration of less common and less well-researched SCMs. In particular, we researched pulverized recycled glass, pulverized pumice, silica fume, Juno XP, and diatomaceous earth. From this list, we conducted an initial research and analysis phase in order to determine which materials we could procure and move forward with to develop our actual test concrete mixtures. Ultimately, we casted mixes using pumice, (one at 25% cement replacement and one at 40%) and diatomaceous earth. In addition to our mixes utilizing the new SCMs, we also cast two control mixtures: a general use portland cement mixture and a fly ash mixture to provide a point of comparison to current common industry practice.

For measuring the sustainability of our concrete mixtures, we considered the three pillars of sustainability: environmental, economic, and social. We researched metrics like carbon footprint, measured in kg CO₂ emitted/tonne produced. Graduate student Vaihedi Pitre also took our mix designs and conducted life cycle assessments, yielding data about our mixture’s energy consumption (MJ/1m³ of Concrete) and global warming potential indicator (kg CO₂ e). We also considered factors like transportation and manufacturing processes for our mixtures in addition to the raw material costs when comparing economic sustainability. Lastly, to address the social aspect of the implementation of our mix designs, we considered sourcing of the materials and how their use may provide additional benefits like greater insulative properties in the case of pumice.

Carbon Emissions Associated with Portland Cement and SCMs

As mentioned above, our goal was to develop concrete mixtures that would be more environmentally friendly, but not compromise the effectiveness of the concrete as a whole. Specifically, we were designing our concrete to meet a strength requirement of 35MPa. We conducted testing throughout the course of our project, doing strength testing at the 7-, 14-, 28-, and 56-day mark in order to measure the strength development of our mixes. Additionally, we conducted electrical resistivity and air entrainment testing to measure the durability and weather resistance of our concrete mixes.

Summary of Compressive Strength Developments

Summary of Air Entrainment Percentages for 1kHz Frequency (56-Day) using ASTM

Summary of Air Void Contents

When considering the feasibility of our mix designs, it is important to consider how they would be utilized in industry. Initially, the team had concerns that because of a potentially greater initial financial cost for incorporating the SCMs the appeal of our mixes would be lessened. However, in discussions with our industry advisor Mr. Tyler Callaghan of Lafarge, he explained that the industry is willing to spend the extra capital in order to facilitate a more eco-friendly design. Indeed, the market as a whole is shifting greatly towards greener construction, with programs like USGBC’s LEED Certification surpassing 100,000 registered commercial projects in the United States alone in 2019 [7]. We believe that concrete mixture designs like the ones that we have developed can help in fulfilling this goal for more eco-friendly design and construction.