International Concrete Abstracts Portal

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.

The paper presents a comparative study on the seismic behavior of circular columns reinforced with glass fiber-reinforced polymer (GFRP) and steel. The study specifically investigates the influence of replacing steel bars with GFRP bars on columns’ seismic response. All the studies summarized in this article were conducted at the University of Toronto. Results from the tests of 24 columns (all having 356 mm diameter and tested in a similar manner) from three different studies are closely analyzed to compare their responses. Based on the experimental results, it is found that replacing steel spirals with GFRP spirals did not result in substantial variation in the seismic performance of columns. Both types demonstrated similar ductility parameters and drift ratios when similar amounts of spirals were used at comparable pitches. Likewise, columns with steel longitudinal reinforcement and GFRP longitudinal reinforcement achieved similar displacement ductility, energy dissipation, and drift ratio.

Adding fibers, especially steel fibers, to cementitious composites is one of the most commonly used methods to improve the mechanical properties of cementitious composites. The high price is the most concerning factor in the use of steel fibers. This study aims to investigate the influence of the content of multiscale fibers, including nanocellulose, sisal fibers, and steel fibers, on the fracture properties of cementitious composites. The fracture properties will be evaluated using the initial fracture toughness, unstable fracture toughness, and fracture energy through notched-beam bending tests. The results demonstrate that replacing steel fiber with an appropriate amount of sisal fiber effectively improves fracture properties, indicating a balancing point between fracture- impeding properties and price/environment. Specifically, under total macrofiber volume fractions of 1 and 1.5%, the 0.2% sisal fiber replacement for the steel fibers exhibits the best fracture- impeding properties. Additionally, the incorporation of nanocellulose (2% optimal in the research) enables the formation of a multiscale crack resistance system at the nano-micro level, further enhancing the fracture-impeding properties of cementitious composites. Moreover, the research found that adding the fibers collaboratively can cultivate a better enhancement in fracture-impeding properties than adding them separately.

The reduction in shear capacity when using recycled coarse aggregate (RCA) made from crushed concrete is evaluated in terms of tensile cracking and fracture-surface characteristics. An experimental investigation into the fracture and flexure-shear behaviors of recycled aggregate concrete (RAC) is presented. Replacing natural aggregate in concrete proportioned for 30 MPa (4350 psi) compressive strength with RCA results in lower compressive and tensile strengths. The tensile fracture-surface characteristics vary between RAC and natural aggregate concrete (NAC). While the surface area created in the tensile fracture of RAC is larger than that of NAC, the fracture surface profile in RAC has a smaller roughness than NAC. In the flexure-shear response of reinforced concrete beams, the dilatancy determined from the slip and crack opening displacements measured across the shear crack is smaller in RAC than in NAC. The failure in the reinforced beam is due to the frictional stress transfer loss across the primary shear crack. There is a larger decrease in the shear capacity with the use of RAC than indicated by the reduction in compressive strength. The reduced shear capacity of reinforced RAC is due to the combined influences of reduced tensile strength and crack surface roughness. The design provisions require calibration for crack surface roughness when using RAC in structural applications.

As global demand for concrete has been forecasted to keep rising, one of the approaches towards more sustainable constructions is the adoption of mix designs replacing conventional ones. The current study contains a comparison between concrete mixes that constitutes only Ordinary Portland Cement (OPC) and mixes incorporating 25% OPC with a 75% replacement by supplementary cementitious materials (SCM). The major experimental hypothesis circles around investigating whether it is effective to use thermal treatment under moderately elevated temperatures to enhance the physical and mechanical properties of concrete. Comparisons were performed using mechanical tests such as: compressive strength, tensile strength, flexural strength, and through several non-destructive physical experiments as well as microstructural investigation using SEM and EDS. In conclusion, the experimental results have shown a mostly positive influence observing significant enhancements after thermal treatment. However, treated concrete mixes that constitute only OPC seem to excel in overall performance compared to those incorporating SCM.