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Alternative binder chemistries, such as calcium sulfoaluminate (CSA) cements, often require admixtures to achieve set-time and workability requirements. A common carboxylate retarder for CSA cement, citric acid, is compared against a series of phosphono-group compounds for both retarding and workability capability. X-ray diffraction, pore solution analysis, and adsorption analysis were analyzed to understand the early hydration phase formation and retardation mechanism by each retarder utilized. While citric acid maintained the longest Vicat set time, it was found through mini-slump experiments that phosphono-based chemistries maintained higher mini-slump spreads compared to citric acid.

Belitic calcium sulfoaluminate cement is a fast setting, fast strength gain alternative cement that has some advantages which make it a good structural material. Because it is a low shrinkage cement it is a great choice for structural repairs. BCSA cement's fast strength gain also makes it a good choice for precast concrete. This presentation details past work on the use of belitic calcium sulfoaluminate cement in structures. The flexural and shear behavior of reinforced concrete beams made with BCSA cement will be described including comparisons with building code equations and with portland cement concrete. Finally, an update on ongoing work on structural concrete repairs made with BCSA cement will be given.

A substantial fraction of fly ash co-mingled with flue gas desulfurization (FGD) products are discarded as off-specification materials due to exceeding the 5.0% SO3 content limit specified in ASTM C618. As such, it is expected that fly ash harvested from some landfills and ponds will have high SO3 content. The behavior of these fly ashes in cementitious systems varies significantly depending on the type of sulfur present in the ash including calcium sulfate, calcium sulfite, and sodium sulfate. As such, a single SO3 content limit specified in ASTM C618 is not sufficient to capture their complexity or performance. Four off-specification FGD co-mingled fly ash products were investigated in this study. This included evaluating their impact on workability, setting time, pore solution pH, compressive strength, and expansion in lime water using paste and mortar mixtures at 20% cement replacement level. Advanced characterization techniques such as X-ray diffraction, isothermal calorimetry, and pore solution analysis using inductively coupled plasma atomic emission spectroscopy were also used to study the hydration behavior of blended systems containing these ashes. The results of this study have been used to identify appropriate beneficiation options and potential modifications to the specifications.

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Achieving the Cement and Concrete Industry net zero goal by 2050 relies significantly in carbon capture as represented in Figure 1. Many of these technologies are not readily available today, and those that exist may not be scalable, or lack efficiency. A scalable carbon removal solution, for direct source emissions capture using photo bio reactors is presented as an innovative solution to reach the net zero goal.

The capture and utilization of carbon dioxide (CO2) is emerging as a potential research area, which offers the advantage of mitigating climate change and generating economically viable products. For CO2 sequestration in cement-based composites, a number of nanomaterials are being investigated, including graphene, graphene oxide, nano-titania, carbon nanotubes, and graphene nanoplates. Graphene-based nanomaterials have been extensively employed to modify cement matrix due to their exceptional surface area, high strength, and modulus. The enhanced adsorption capacity and affordability of these materials are making them a viable alternative for the removal of ambient CO2. In our study, we found that the CO2 absorption capability of cement composites was increased by 30% when very modest amounts of graphene oxide nanosheets (about 0.05 to 0.1%) were added. GO-reinforced concrete offers the ability to store CO2 while maintaining structural integrity in comparison to conventional cement-based materials.