In reinforced concrete (RC) structures, a proper bond between the reinforcement and the concrete is key for appropriate composite action. To date, limited studies exist that evaluate the bond of fiber-reinforced polymer (FRP) bars in concrete members under flexure and its effect on the development length required to ensure a full stress transfer. In this paper, the bond strength developed by glass FRP (GFRP) and steel rebars is evaluated and compared by testing 16 RC beams under three-point bending. The beams were 1.83 m long and had a section of 150 x 360 mm. Different embedment lengths were evaluated as a function of the bar diameter (db): 30 db, 40 db, and 50 db for GFRP reinforced specimens, and 20 db, and 30 db for steel reinforced beams. Two different GFRP rebar types (six beams for each) and conventional steel (four beams) were used as reinforcement; all the rebars had a nominal diameter of 12.7 mm. Based on the results presented herein, GFRP rebars have a lower bond capacity than steel rebars. Also, the development lengths as suggested by actual code provisions for GFRP rebars (ACI 440.1R-15) appear to be over-conservative: the theoretical development length values were around 110% - 188% higher than the experimental results for the tested GFRP rebars, while the predicted development length for steel rebars according to ACI 318 was about 83% higher than the experimental results.

The recycling of waste materials from the construction sector represents an opportunity for environmental protection, to save expensive landfill costs, and promote sustainability. The increased interest in the use of recycled materials is seen in several European countries with the production of concrete using granulates from demolition material. In Switzerland, the SIA 2030 standard defines recycled concrete based on a minimum percentage of 25% recycled aggregates to be added. This research focuses on the possibilities of producing high-quality recycled concrete, starting from high-quality cementitious material, i. e. concrete. The original material with known properties was demolished and used as aggregates to replace the natural aggregates. Fresh, hardened, and durable properties of concrete were evaluated on blends containing 25, 50, and 100% recycled aggregates. At early stage (2 days), the lowest value of compressive strength was already above 15 MPa for the blend with 100% recycled aggregates. Most of the recycled concrete satisfies the main mechanical and durability features, in particular with the addition of 25 respectively 50% of the recycled aggregate component.

The application of a novel superabsorbent polymer (SAP) as a multifunctional chemical admixture for concrete properties is expected to contribute to the overall durability and sustainability of concrete structures. SAPs are well known to quickly absorb and retain a significant amount of water within the concrete matrix as a means of providing internal curing. However, the rate of water uptake can significantly affect the rheology of fresh concrete such as reduced flowability. This paper introduces a novel SAP that features slow water absorption and swelling behavior, and its resulting impact on both fresh and hardened concrete properties. The novel SAP has been shown to delay swelling for several hours in cement filtrate, followed by a predictable absorption of water over a 24-hour period comparable to conventional SAP. The delayed swelling effect observed with the novel SAP eliminates the need for additional water to obtain a similar flowability, but with a very slight increase in viscosity, compared to a concrete mixture without SAP. Moreover, the internal curing capability of the novel SAP can result in an increase in both early age and long-term compressive strengths, improved freeze-thaw resistance, and a reduction in autogenous shrinkage under sealed and air curing conditions.

Performance-based specifications (PBS) may increase concrete quality and sustainability by facilitating innovations in material selection and proportioning. This is particularly relevant now with increased interest in a broader set of minimally processed minerals for use as supplementary cementitious materials (SCMs) or fillers; these are often industrial and agricultural byproducts and with limited performance history in concrete. This study compares traditional largely prescriptive concrete design, following practices currently allowed by the Georgia Department of Transportation, with three new concrete designs which do not comply with current specifications but offer increased sustainability. Three metrics are assessed for each mixture: the associated cradle-to-gate CO₂ emissions, a metric that incorporates the environmental burden of concrete, compressive strength at 28 days, and surface resistivity measurements taken weekly from 28 to 56 days. A framework is proposed to statistically analyze compressive strength data to pre-qualify mix designs, which can be broadly applied to reduce time-consuming iterative testing and to help meet sustainable development goals. The aim is to foster innovation in material use and mixture design towards an increased durability and performance, while reducing environmental impact and minimizing risk.

High purity lithium hydroxide and lithium carbonate for use in lithium-ion batteries are produced by the processing of spodumene ore from the Whabouchi mine (Northern Quebec, Canada). The main byproduct of this treatment is an aluminum silicate waste stream, which is produced in very large quantities and should be recycled to avoid its storage in landfills, which is not environmentally friendly. Previous research work by the authors on the characterization of this aluminum silicate waste stream showed its potential as a pozzolanic material and hence that it could be used by the cement and concrete industry, which would contribute to the sustainability of these industries. The purpose of this study was to assess the pozzolanic activity of this new material and its effects on the properties of concrete in its fresh and hardened states in order to evaluate the effects of replacing part of the cement with this aluminum silicate waste stream in various classes of concrete. Series of air-entrained and non-air entrained concrete mixtures were produced and tested in this study. Results from fresh state testing, mechanical and durability properties of the concrete made with this material were similar to those obtained with conventional supplementary cementitious materials and equal or superior to those obtained with reference concrete mixtures made with plain and ordinary portland cement.