Case study of permeability-reducing admixture use in anti-flotation slabs: building in Brasilia, Brazil

On effects of freezing and thawing cycles of concrete containing nano-[Formula: see text]: experimental study of material properties and crack simulation

Construction during cold weather can lead to freezing accidents in concrete, causing significant hidden threats to the project's performance and safety by affecting the mechanical properties and durability reduction. This study aims to deduce the compressive strength and durability of the concrete containing nano-[Formula: see text] under freezing-thawing cycles with the Caspian seawater curing condition. The specimens were subjected to freezing-thawing cycles according to ASTM C666. Furthermore, crack propagation in the concrete after freezing-thawing cycles is simulated. The results reveal that adding until nano-[Formula: see text] until 6% improved compressive strength before and after freezing-thaw cycles. The water permeability experiences a substantial reduction as the amount of nano-[Formula: see text] increases. Furthermore, the water permeability exhibits a positive correlation with the number of cycles, resulting in significantly higher values after 150 cycles compared to the initial sample. Moreover, adding 8% nano-[Formula: see text] reduced the depth of water permeability and chloride ion penetration after 150 cycles by 57% and 86%, respectively. The crack simulation results indicate that concrete containing 6% nano-[Formula: see text] shows an optimal resistance against crack formation. Concrete with 6% nano-[Formula: see text] requires 13.88% less force for crack initialization after 150 freezing and thawing cycles. Among different nano-[Formula: see text] percentages, 6% shows the best crack resistance and 8% the minimum water permeability and chloride ion penetration.

Development of a novel method for the in-situ dechlorination of immovable iron elements: optimization of Cl- extraction yield through experimental design

The conservation of iron objects exposed to marine aerosol is threatened by the formation of akaganeite, a highly unstable Cl-bearing corrosion phase. As akaganeite formation is responsible of the exfoliation of the rust layer, chlorides trigger a cyclic alteration phenomenon that often ends with the total consumption of the iron core. To prevent this degradation process, movable iron elements (e.g. archaeometallurgical artefacts) are generally immersed in alkaline dechlorination baths. Aiming to transfer this successful method to the treatment of immovable iron objects, we propose the in-situ application of alkaline solutions through the use of highly absorbent wraps. As first step of this novel research line, the present work defines the best desalination solution to be used and optimizes its extraction yield. After literature review, a screening experimental design was performed to understand the single and synergic effects of common additives used for NaOH baths. Once the most effective variables were selected, an optimization design was carried out to determine the optimal conditions to be set during treatment. According to the experimental work here presented, the use of 0.7 M NaOH solutions applied at high temperatures (above 50 °C) is recommended. Indeed, these conditions enhance chloride extraction and iron leaching inhibition, while promoting corrosion stabilization.