Every year, the construction industry consumes 20 billion tons of raw materials to produce concrete, a vital component in building infrastructure. Unfortunately, the production of concrete, particularly Portland cement, is associated with high carbon dioxide emissions.
This significant environmental impact has spurred research into alternative materials and methods to reduce the carbon footprint of concrete. A recently studied process by researchers at Idaho State University’s Department of Civil and Environmental Engineering focuses on the utilization of precipitated calcium carbonate (PCC), which came from waste created during sugar production, and upcycled recycled concrete aggregates (UCA) to help lower the impact of the building material.
In the pursuit of achieving net-zero emissions, sustainability has become a global priority, especially in the construction sector. Concrete, the second most consumed material worldwide, contributes significantly to carbon emissions due to the use of Portland cement. This study aims to explore innovative approaches to reduce cement usage in concrete and replace fresh aggregates with upcycled recycled concrete aggregates. By utilizing waste products from the sugar beet and concrete demolition industries, this research contributes to a sustainable future by reducing carbon emissions.
Research into the substitution of cement and aggregates in concrete with alternative materials has yielded mixed results.
Some studies show the benefits of replacing portions of cement with materials like fly ash, silica fume, or slag cement, as well as substituting aggregates with steel fibers, shredded tires, and recycled concrete aggregate (RCA). However, conflicting viewpoints exist, making it uncertain whether these substitutions offer overall benefits or drawbacks.
While many new materials are being explored to reduce carbon emissions from concrete, limited options are available to replace cement or aggregates effectively. Despite this, cement remains essential for providing the necessary bond strength in concrete, necessitating further investigation into new materials and treatment methods for RCA.
The Idaho State research focuses on the use of waste products from the agricultural and demolition sectors in concrete. It introduces an upgraded version of recycled concrete aggregates known as UCA. Small-scale laboratory tests on concrete containing PCC and UCA were conducted, including compressive strength, split tensile strength, and flexural strength tests following ASTM procedures.
The PCC used in this study is a waste product obtained from the sugar beet industry. It differs from commercially produced PCC or marble powder from carbonate rocks. The sugar beet industry generates significant waste, and utilizing these by-products, including lime sludge containing calcium carbonate, can partially replace cement. Nanoplatelets of PCC enhance the mechanical properties of concrete, and sugarcane bagasse ash (SCBA) from cane sugar can also replace a portion of cement. Studies have shown that replacing 10% of cement with SCBA increases concrete's compressive strength by 15.67%.
While this study is an initial effort to reduce carbon emissions, it recommends further large-scale tests, including durability assessments and analytical approaches.
The primary objectives of this research are:
The precipitated calcium carbonate used by the researchers from Idaho State University is a waste product from sugar beet processing. PCC, chemically identical to natural limestone, offers a promising alternative to conventional cement production, which contributes significantly to global carbon emissions. Laboratory tests demonstrated that up to 30% of cement in concrete can be replaced with PCC while meeting ASTM standards.
In addition to investigating PCC, the research team explored the use of upcycled concrete aggregate as a substitute for conventional aggregates. Upcycled concrete aggregate involves crushing previously used concrete pieces to the desired sizes for construction projects. The results showed that up to 100% of conventional aggregates can be replaced with upcycled concrete without compromising strength.
While this eco-friendly concrete shows promise, further testing is required to assess its resistance to freeze-thaw conditions, surface hardness, and overall durability in real-world applications. Collaboration with industry partners to identify practical applications for these concrete mixes is also on the horizon.
In conclusion, the utilization of PCC and UCA presents a significant step towards achieving sustainable concrete production. By addressing carbon emissions and waste reduction, this research contributes to a more environmentally friendly construction industry.
