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Chitin is the second most abundant biopolymer after cellulose and is found in many species, including crustaceans. The nanofiber structure of chitin in shrimp shell waste was extracted in this study by mechanical and chemical methods, producing chitin nanofibers (ChNF) and nanocrystals (ChNC), respectively. Their surface functional group, size, morphology, and zeta potential were characterized. Testing of a range of dosages in mortar showed that ChNF (0.05%wt) with a larger aspect ratio than ChNC resulted in the greatest improved flexural strength and fracture energy by 24% and 28 percent. In addition, elastic modulus increased by up to 91% and 43% with ChNC and ChNF. With their anionic surface charges, both chitin nanomaterials induced electrostatic interactions with cement particles and caused a delay in setting time and increased the viscosity of the fresh cement slurry. Findings so far indicate chitin is a viable biomass source for powerful structural nanofibers to strengthen cementitious materials and reduce cement demand in concrete.

As the supply of conventional supplementary cementitious materials (SCMs) continues to fall behind concrete industry’s demand, new sources must be identified and evaluated to allow production of high-quality and durable concrete. This session reports on the latest research related to the use of harvested fly ash (HFA) and ground bottom ash (GBA) as concrete SCMs. The presentations will include studies on the chemical and physical characteristics of these ashes, their pozzolanic reactivity, and their performance in concrete in terms of their impact on fresh, mechanical, and durability properties of concrete mixtures. The audience will become familiar with this potentially valuable new SCM source.

Understanding chloride penetrability and corrosion performance is one of the key issues hindering the advancement and continued adoption of belitic calcium sulfoaluminate (BCSA) cements and composites. There has been little work to address the suitability of existing standardized test methods or the correct interpretation of test results for these materials. In this work, we use a wide variety of electrical (rapid chloride penetrability, surface resistivity, and bulk resistivity) and diffusion-based (ponding, bulk diffusion, non-steady-state migration) test methods to measure the chloride penetrability of a range of BCSA and portland cement concretes. Results suggest that there is a need to recalibrate chloride penetrability classifications based on electrical test methods to better align with ground truth results from diffusion-based tests. Furthermore, there is a need to recalibrate the chloride concentration threshold for color change with silver nitrate indicator, which is a critical factor in interpreting the results of the non-steady-state migration test. Finally, we applied the ASTM G109 corrosion test to the same concrete mixtures. Results indicate corrosion of rebars in BCSA concretes at early ages, but further analyses show this to be a function of the test conditions rather than a shortcoming of the material. The ASTM G109 testing age is not consistent with the time period required for steel passivation in BCSA systems.

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The diminishing supply of traditional fly ashes opens up potential for utilization of alternative types of supplementary cementitious materials (SCMs), such as ground bottom ashes (GBAs) and fluidized bed combustion ashes (FBCAs). This talk will present the results of a comprehensive study involving 3 GBAs and 2 FBCAs, including evaluation of such characteristics as chemical and mineralogical composition, particle size distribution, LOI and grain morphology. The pozzolanic reactivity of these materials was assessed using the R3 test. Moreover, reactivity of both types of these ashes in cementitious systems was evaluated on pastes with various levels of replacement of cement by these alternative SCMs. The evaluation involved quantification of the heat of hydration and the Ca(OH)2 consumption capacity. In addition, mortar samples with different replacement levels of cement by these ashes were tested for workability, setting time and compressive strength. The least reactive ash from each of these two groups of materials was chosen for evaluation of mechanical (compressive and flexural strength) and transport (water absorption, formation factor and freezable water amount) properties in concrete specimens.

This presentation will compare the long-term changes in the porosity and diffusion coefficient of belite CSA cements and compare the results to portland cement, calcium sulfoaluminate, and alkali activated binder. The results will also show that the addition of a pore blocking admixture will greatly reduce the diffusion coefficient with only minor impact on the porosity. The findings suggest that early age durability testing of belite CSA cements may not be appropriate.