International Concrete Abstracts Portal

Phosphogypsum (PG) is often used to produce α-Hemihydrate gypsum (α-HH), but the impurities in PG, including intercrystalline phosphorus (IP), limit its reutilization. The objective of this paper is to study the effect of IP on the morphology, hydration, and hardening properties of α-HH, using XRD, XPS, SEM, FTIR, and the test of setting time, hydration heat, and strength. The results revealed that IP dissolved out from dihydrate gypsum (DH) and entered the lattice of α-HH during the preparation of α-HH, while there was little difference in the morphology of α-HH. When α-HH hydrated, IP dissolved and converted into Ca₃(PO₄)₂, absorbed on the surface of DH. 0.04% IP had no effect on the hydration, setting time, and strength of α-HH, with 0.1% or more IP significantly prolonging the hydration of α-HH and deteriorating microstructure of hardened paste, thus reducing strength. Based on the results, IP content in PG should be controlled to less than 0.04%.

This research establishes a systematic methodology for selecting a migratory corrosion inhibitor (M-CoI) as a repair strategy for reinforced concrete structures exposed to aggressive environments. Conducted in two phases, Phase 1 involves corrosion testing in pore solutions to evaluate inhibitor efficacy, while Phase 2 examines the percolation ability of M-CoIs in different concrete systems and the performance of M-CoI in RC with corroded reinforcing bars. The findings reveal that the efficiency of the compounds as repair measures is significantly lower than their preventive performance, primarily due to the presence of corrosion products on the steel surface. Additionally, the effectiveness of the M-CoIs is influenced by their concentration and form at the reinforcing bar level; specifically, 4-Aminobenzoic acid (ABA) achieved maximum concentration in its purest form, whereas Salicylaldehyde (SA) and 2-Aminopyridine (AP) reached the reinforcing bar in lower concentrations. Importantly, the study highlights that compounds effective in pore solution may not perform well in concrete, underscoring the necessity of considering the intended application, preventive or repair, when selecting inhibitors. Thus, a comprehensive approach involving both pore solution testing and migration ability assessments is essential for optimal corrosion protection in reinforced concrete.

Engineered cementitious composites (ECC), a prominent innovation in the realm of concrete materials in recent years, contain a substantial amount of cement in their composition, thereby resulting in a significant environmental impact. To enhance the environmental sustainability of ECC, it is plausible to substitute a large portion of cement in the composition with fly ash, a by-product of coal-fired power plants. In recent years, there has been increased research in ECC containing high-volume fly ash (HVFA) binders and its wider application in construction practices. In this particular context, it becomes imperative to review the role of the HVFA binder in ECC. This review first examines the effects of incorporating an HVFA binder in ECC on fiber dispersion and fiber/matrix interface behavior. Additionally, mechanical properties, including the compressive strength, tensile behavior, and cracking behavior under loading, as well as durability performances of HVFA-based ECC under various exposure conditions, are explored. At last, the review summarizes the research needs pertaining to HVFA-based ECC, providing valuable guidance for future endeavors in this field.

A capsule phase change material (CPCM) was synthesized using n-tetradecane as the core, expanded graphite as the shell, and ethyl cellulose as the coating material through a controlled assembly process. The results demonstrate that the infiltration of n-tetradecane significantly enhances the density of the expanded graphite, while the ethyl cellulose coating effectively prevents the desorption and leakage of the liquid phase change material during phase transitions. As a result, the CPCM exhibits a compact structure, chemical stability, and excellent thermal stability. The incorporation of this CPCM into cement-based materials endows the material with an autonomous heat-release capability at temperatures below 5°C. When the CPCM content reaches 20%, the thermal conductivity of the cementitious matrix increases by 24.66%. Moreover, the CPCM significantly improves the freeze-thaw resistance of the cement-based materials, reducing the compressive strength loss by 96% and the flexural strength loss by 65% after freeze-thaw cycles. This CPCM fundamentally enhances the frost resistance of cement-based materials, addressing the issue of freeze-thaw damage in concrete structures in cold regions.

The production of carbonated aggregates from Class F fly ash (FA) is challenging due to its low calcium content, typically less than 10%. This study investigates the production of carbonated alkali-activated aggregates using FA and calcium carbide sludge (CCS). Sodium hydroxide was used as an activator and examined the effects of autoclave treatment on the properties of these aggregates. The optimal mixture, comprising 70% FA and 30% CCS, achieved a single aggregate strength of >5 MPa in autoclave carbonated (AC) aggregates, comparable to the strength obtained after 14 days of water curing in without autoclave carbonated (WAC) aggregates. Both AC and WAC aggregates exhibited a bulk density of 790 to 805 kg/m³ and CO₂ uptake of 12.5% and 13.3% in AC and WAC aggregates, respectively. FE-SEM and FT-IR analysis indicated the formation C-A-S-H gel in noncarbonated aggregates, while calcite and vaterite, along with N-A-S-H gel, formed in carbonated aggregate. Concrete incorporating AC and WAC aggregates exhibit compressive strengths of 39 and 38 MPa, with concrete density of 2065 kg/m³ and 2085 kg/m³, respectively. Furthermore, AC and WAC aggregate concrete showed a reduction in CO₂ emission of 18% and 31%, respectively, compared to autoclave noncarbonate (ANC) aggregate concrete. These findings highlight the potential of producing carbonated alkali-activated aggregates from FA and CCS as sustainable materials for construction applications.