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 effect of the parameters of a model, namely flow ratio (Κ) and angle of friction (β), is analyzed numerically on high-strength concrete (HSC) under a time-dependent pressure load. HSC, with a compressive strength of 120 MPa under static loading, when simulated under a rate of loading of 1100 GPa/s, shows an ultimate compressive strength ranging from 133 MPa to 160 MPa. The dynamic stress and strain of HSC is proportional to the flow ratio and angle of friction. Multiple regression equations have been established to define the relationship between model parameters and dynamic strength, which are applicable for flow ratios between 0.80 and 1.00 and an angle of friction between 50° and 65°.

Cellulose excelsior (CE), sometimes referred to as wood wool, is a shredded wood product with a strand thickness of 0.12 to 0.64 mm, a width that is up to three times the thickness, and a straw-like consistency. CE can be combined with cementitious materials to form cellulose cement composite (C3) materials. The production of C3 materials requires accurate methods to quantify the moisture in the CE. This paper describes a methodology to obtain the surface dry state repeatably by using a centrifuge and an approach to control water content that can be used to provide consistency in C3 production. The mix water absorbed by the CE can be estimated from the desorption isotherm when the relative humidity of the CE is greater than 80%. Isothermal calorimetry was used to confirm the accuracy of using the desorption model to quantify the water uptake.