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One of the outstanding questions regarding use of alternative cements in concrete infrastructure systems is the corrosion potential of these systems. This study investigated a variety of commercially available alternative concrete systems, including two calcium sulfoaluminate-based systems, tracking changes in conductivity, microcell current, chloride infiltration, and initiation and propagation of corrosion through cracked and uncracked concrete and mortar specimens to provide a comparison of corrosion-related behavior between ACM and OPC systems.

Alternative cementitious materials (ACMs) such as calcium sulfoaluminate cement (CSA) have the potential to be successfully used in a variety of new structural applications. However, there is a significant concern about their ability to resist carbonation, which can result in accelerating the ingress of chloride and the corrosion of the steel reinforcement. In the same vein, the presence of cracks could drastically reduce the chloride threshold for the corrosion initiation of steel hence exacerbating the corrosion of steel reinforcement. In this study, the susceptibility to corrosion due to chloride ingress was accessed on several concrete mixtures produced with four different CSA based systems and one ordinary portland cement (OPC). Six samples were fabricated from each mix per ASTM G109 and subjected to three different pre-conditions prior to chloride exposuer: 1) two samples out of the six samples had cracks of a depth of 10 mm and width of 0.04 mm introduced in them during casting using a plastic shim inserted at the top of the mold; 2) another two out of the six were exposed to accelerated carbonation at 4% CO2 concentration and 57% RH for 28 days; and 3) the remaining two samples of the six were left without cracks or exposure to accelerated carbonation. The six samples for each mix were ponded with 3% NaCl (30g/liter of de-ionized water) for 2 weeks after which they were allowed to dry for another 2 weeks before the process is repeated. Microcell corrosion monitoring was conducted with Gamry testing equipment and software using the linear polarization resistance (LPR) technique. Whereas, microcell corrosion monitoring was done using a volunteer.

The serious CO2 footprint pertaining to the production of Portland cement has necessitated the development of alternative cementing materials with lower CO2 emission (Mo et al. (2015)). Calcium sulfoaluminate (CSA) cement represents an ecofriendly alternative to Portland cement owing to less CaCO3 input than Portland cement and hence has been drawing attention as a potential replacement of Portland cement (Chen and Juenger (2021)). Meanwhile, the characterization of cementitious materials exposed to weathering carbonation is of critical importance since most of these materials are typically jeopardized by the ambient atmosphere (Han et al. (2013)). In addition, the carbonation behavior of cementitious materials is a significant issue in relation to the concrete durability given that the carbonic reaction induces neutralization of the matrix and depassivation of reinforcing steel (Puertas et al (2005)). In particular, the carbonation-induced microstructural evolution of the reaction products in CSA cements is known to be significantly different from that in Portland cement (Seo et al. (2021)). In this regard, earlier works on the characterization of CSA cements exposed to accelerated weathering carbonation conditions will be summarized and presented.

Reducing CO2 emission is now extremely urgent. At the current level of emission in only 7 years we will exceed the level of CO2 in the atmosphere deemed to lead to warming of 1.5°C. LC3 is a technology which can make a major contribution to reduction. In this presentation I will describe how we came up with this innovation, how we went about implementing it in the field and what remaining barriers we need to overcome to realize the full potential.

Wet curing improves OPC concrete durability and strength by increasing total hydration, densifying microstructure and decreasing concrete permeability. In general, wet curing is recommended for ordinary portland cement (OPC) concrete curing until it gains >70% of the designed compressive strength, typically at least 7 days. Calcium sulfoaluminate (CSA) cement may allow for decreased curing time requirements due to its rapid hydration, hardening, and strength gain. This study investigated a variety of curing durations and curing solution compositions to understand their effects on CSA hydration, strength development, and shrinkage. The results demonstrate that curing for 2 days promotes adequate strength gain and completion of hydration reactions and that CSA can be cured using similar methods as used for OPC, including application of fog or limewater. Additionally, curing CSA samples even for 1 day in 100% RH led to lower shrinkage than 7-day cured OPC samples, and may reduce cracking in concrete pavements.