Cutting the Carbon Cost of Concrete

Concrete is the most popular construction material on the planet due to its impressive mechanical properties. However, it is responsible for around 8% of global CO2 emissions, arising primarily from generation of cement powder. Cement acts as the binder in concrete composites, which typically include both coarse (gravel) and fine (sand) aggregates as fillers. Cement powder is manufactured using an energy-intensive process (~1 kg CO2 generated per 1 kg cement). Because of this, alternatives for cement powder in concrete are of great interest from an environmental standpoint.

CT reconstruction of zeolite cement. The microporous nature of the composite is apparent. When viewed in an SEM, the reaction products (needles and platelets) can be seen.

Exothermic reactions with water densify and strengthen cement by producing components such as calcium hydroxide and calcium silicate hydrate (CSH). Pozzolans are materials that participate in a separate series of reactions to further densify cement via production of calcium silicate hydrate. Zeolite is a natural pozzolanic mineral composed primarily of silica and alumina that forms when layers of ash and rock from volcanic eruptions react with groundwater. Particles of zeolite are micro- and nano-porous, which increases the relative surface area and thus the reactivity. The combination of zeolite’s aluminosilicate and microporous nature make it a promising pozzolanic material for concrete materials.

A challenge to using pozzolans in concrete is that only limited amounts can be added before the material performance decreases below acceptable levels. However, zeolite has the potential to be used in substantial concentrations, reducing the amount of cement (and in turn carbon emissions) needed. To fully realize natural zeolite as a pozzolan, many aspects of the material need further understanding. In collaboration with Zeolite Composites, LLC, we are conducting studies to observe the impact of zeolite additions on various properties of hardened cement composites, characterize the pozzolanic activity of natural zeolite, understand the effect
of zeolite on the hydration reactions and strength development of concrete over time, and assess the durability of cement composites as a function of zeolite.

Durability is an important consideration since concrete structures are often subjected to challenging (e.g. marine or coastal) environments for long durations. Finally, the microporous nature of zeolite also introduces a potential mechanism for capturing ions or molecules, such as greenhouse gases. We therefore implement a carbonation chamber to study the accelerated exposure of carbon dioxide on cement composite samples with increasing zeolite content. Current efforts are also dedicated to conduct freeze/thaw testing and saltwater exposure experiments for more extensive durability characterization.

Select Publications

 K. Deng, R. Song, B. Lou, D. Uhm, D. Arola, Improving the strength and reliability of mortar composites with zeolite substitution, Case Stud. Constr. Mater. 21 (2024). https://doi.org/10.1016/j.cscm.2024.e04037.