International Concrete Abstracts Portal

CO2 mineralization in concrete enhances cement hydration by reacting with calcium-rich materials, forming nano-scale calcium carbonate that fills micro-pores. This study explores CO2-mineralized concrete performance, produced using a two-step mineralization process. Concrete with 0.2% CO2 by cement weight exhibited significantly higher compressive strength, increasing by 18.78%, 19.27%, and 20.63% at 7, 28, and 56 days, respectively. Isothermal calorimetric analysis confirmed increased heat evolution in CO2-mineralized cement paste, while X-ray diffraction and scanning electron microscopy revealed calcium carbonate formation and more ettringite volume. The higher strength gain due to CO2 mineralization is used to leverage the cement content. A comparative study reveals that CO2-mineralized concrete with 7.5% reduced cement content achieves equivalent strength and durability to conventional concrete, reducing carbon emissions by 8% while significantly lowering cost per unit strength and enhancing sustainability and performance.

The cement industry´s strategy in many countries is to reduce its CO2 emissions to diminish greenhouse effects. This strategy is to reduce these emissions by decreasing the clinker content in their new formulations, replacing it by using supplementary cement materials or inert fillers. One of the most used additions in Latin America´s cement industry is inert limestone fillers, which is the most inexpensive one. In North America, there are restrictions on using this inert addition in Portland cement, defining as 15% the maximum allowable content as limestone cement (LSC). Nevertheless, in Latin America and other countries, this limestone filler content restriction is not that strict, allowing contents as much as 35%. This investigation includes experimental results obtained from Portland cement mortars where inert limestone fillers used were between 20% and 30% by clinker replacement, and only 24-hour curing was considered. Results obtained include mechanical (compressive strength), physical (electrical resistivity, total void content, capillary porosity), and chemical (carbonation after one-year natural exposure) performance of such mortars. The carbonation coefficients (kCO2) obtained after 1-year exposure in a natural urban environment were 17.3, 22.9, and 24.5 mm/y½ for 23%, 27%, and 29% LSCs, respectively. These results were comparable higher than typical kCO2 values of ~ 4 mm/y½ obtained from ordinary Portland cement-based mortars having 90 to 95% clinker content.

Crack densities obtained from on-site surveys of 74 bridge deck placements containing concrete mixtures with paste contents between 22.8% and 29.4% are evaluated. Twenty of the placements were constructed with a crack-reducing technology (shrinkage-reducing admixtures, internal curing, or fiber reinforcement) and 54 without; three of the decks with fiber reinforcement and nine of the decks without crack-reducing technologies involved poor construction practices. The results indicate that using a concrete mixture with a low paste content is the most effective way to reduce bridge deck cracking. Bridge decks with paste contents exceeding 27.3% had a significantly higher crack density than decks with lower paste contents. Crack-reducing technologies can play a role in reducing cracking in bridge decks, but they must be used in conjunction with a low paste content concrete and good construction practices to achieve minimal cracking in a deck. Failure to follow proper procedures to consolidate, finish, or cure concrete will result in bridge decks that exhibit increased cracking, even when low paste contents are used.

The durability of reinforced concrete is often compromised by chloride penetration, leading to corrosion of reinforcing steel and reduced structural strength. To improve the sustainability and longevity of concrete structures, it is crucial to model and predict chloride permeability (CP) accurately, thereby minimizing the time and resources required for extensive experimental testing. This paper presents a proof-of-concept study applying Artificial Neural Networks (ANN) to predict CP in concrete structures. The model was trained on a small but carefully controlled experimental dataset of 10 concrete mixtures, considering four key parameters: water-to-cementing materials ratio, silica fume content, cementing materials content, and air content. Despite the limited dataset size, which constrains generalizability and statistical robustness, the ANN captured nonlinear relationships among the input parameters and CP. The comparison between experimental and simulated CP values showed reasonable agreement, with errors ranging between –242 and 420 Coulombs. These results establish the trustworthiness and reliability of the proposed model, providing a valuable tool for predicting CP and informing the design of durable and sustainable concrete structures.

Building resilient infrastructure in chloride-rich environments presents significant challenges. This study examines the impact of nanosilica (NS) and ground granulated blast furnace slag (GGBFS) on chloride ingress in cement composites exposed to seawater, NaCl solution, and a combined NaCl-Na₂SO₄ solution. Analysis using microcharacterisation, BSE-EDS hypermaps, and thermodynamic modelling reveals that GGBFS enhances chloride binding by forming Friedel's salt (FSS) across all environments, effectively immobilizing chloride ions. NS further refines the cement matrix by densifying the calcium silicate hydrate (C-S-H) structure and generating additional C-S-H gels, improving physical chloride binding. This combined effect reduces porosity and strengthens resistance to chloride diffusion. Sulfate ions significantly influence hydration products and chloride binding, with excessive sulfate reducing FSS formation, thereby weakening chloride resistance. Sulfate may also convert FSS into monosulphate (AFm) and ettringite (AFt), altering chloride immobilization. Cement composites containing both GGBFS and NS demonstrated superior resistance to chloride and sulfate exposure, as confirmed by thermodynamic modelling. These findings provide insights into sulfate-chloride interactions and offer guidance for developing durable cementitious materials in aggressive environments.