In marine structures, concrete requires adequate resistance against chloride ion penetration. As a result, numerous studies have been conducted to enhance the mechanical properties and durability of concrete by incorporating various pozzolans. This research has investigated the curing conditions of samples including zeolite and metakaolite mixed with Micro nanobubble water in artificial seawater and standard conditions. The results indicated that incorporating zeolite and metakaolin mixed with Micro nanobubble water, which was cured in artificial seawater conditions, compared to similar samples that were cured in standard conditions, improved the mechanical properties and durability of concrete samples. The compressive strength of 28 days concrete samples containing 10% metakaolin mixed with 100% Micro nanobubble water and samples consisting of 10% zeolite blended with 100% Micro nanobubble water cured in seawater in comparison to the control sample cured in the standard condition indicated an increase of 25.06% and 20.9%, respectively. The most results were obtained with a compound of 10% metakaolin, and 10% zeolite with 100% Micro nanobubble cured in seawater (MK10Z10NB100CS) which rose significantly Compressive, Tensile and Flexural Strength by 11.13, 14, and 9.1%, respectively, in comparison with to the MK10Z10NB100 sample cured in the standard condition. Furthermore, it decreased considerably 24-hr water absorption and Chloride Penetration at 90 days by 27.70 and 82.89%, respectively, in comparison with the control sample cured in standard conditions.

To reduce construction costs and carbon footprint while maintaining durability, recent research has focused on incorporating supplementary cementitious materials (SCMs) (for example, blast-furnace slag, fly ash, and natural pozzolans) and microaggregates (for example, cenospheres) in the primary cement matrix. Because of their low density and porous nature, these supplementary materials are capable of imparting some desirable properties on structures, such as light weight and reduced thermal conductivity. In this context, this work investigates the rheology, three-dimensional (3D) printability, and mechanical and thermal properties of white portland cement (WPC) containing 25 wt.% cenospheres in comparison with pure WPC. While both compositions were tuned with suitable additives to enhance their 3D printability, significant differences were observed in their rheological properties. Rheological tests revealed that the addition of cenospheres improved the paste extrudability while retaining good buildability. For both mixtures, the same types of structures were 3D-printed and compared in terms of morphology, microstructure, compressive strength, and thermal conductivity. This study paves the way toward the development of 3D-printable WPC-based mixtures with improved structural and thermal properties for modern construction needs.

Recently, alkali-activated cement (AAC) has been studied to partially replace portland cement (PC) to reduce the environmental impact caused by civil construction and the cement industry. However, with regard to durability, few studies have addressed the behavior of AAC. This study aimed to evaluate the performance of AAC made from blast-furnace slag with contents of 4 and 5% sodium hydroxide as an activator (Na2Oeq of 3.72% and 4.42%, respectively) when subjected to alkali-aggregate reaction (AAR). Length variation tests were carried out on mortar bars immersed in NaOH solution (1 N of NaOH, T = 80°C [176°F]) and on concrete bars (T = 60°C [140°F], RH = 95%); compressive strengths tests and scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) analyses were also made. Two types of PC were used as a comparison. The results showed good behavior of the AAC in relation to the AAR, with expansions lower than those established by the norm (34% of the limit) and without the finding of losses of mechanical resistance or structural integrity. The alkaline activator content had a small influence on the behavior of the AACs, in which the lowest amount of NaOH (4%) showed fewer expansions (only 15% of the limit established by the norm). Even for the highest activator content (5%), the results were good and comparable to those of PC with pozzolans, which is recommended for the inhibition of AAR.

Fly ashes with high alkali contents have been observed to be less effective in controlling expansion due to alkali-silica reaction (ASR) in concrete than low-alkali fly ashes, a problem that can be hard to predict using accelerated testing. Many natural pozzolans have high alkali contents, and there is concern that these alkalis may likewise reduce their effectiveness in ASR control and affect accelerated test results. This study examines the performance of natural pozzolans in ASR testing. The mineralogies of the natural pozzolans were determined using Rietveld quantitative X-ray diffraction (XRD), and the compositions of the natural pozzolans were determined using X-ray fluorescence spectroscopy (XRF) and available alkali testing. The results suggest that the available alkalis from fly ashes and natural pozzolans are different, and high-alkali natural pozzolans perform well in both the accelerated mortar bar and concrete prism tests for ASR.

No widely accepted method is available to assess the efflorescence in small-scale mortar specimens. Thus, the analysis and determination of parameters that actually have an influence on the occurrence of efflorescence in cementitious materials become difficult to be accomplished, especially considering that its appearance in natural field conditions can take months or even years to happen. This paper has the objective to compare eight small-scale accelerated test methods for the assessment of efflorescence in lime-cement mortars and then to evaluate their sensibility to variations in the mixture composition. The results show that the method in which a water column introduces pressure produced the highest amount of efflorescence in the smallest time. The method was able to clearly identify the impact of silica fume towards the refinement of the porous microstructure and the efflorescence reduction. This study demonstrates that 28 days is enough time to finalize the accelerated testing proposed.