This study focuses on evaluating the mechanical, microstructural, and durability properties of 3D printing mortar (3DPM), with a specific emphasis on the influence of incorporating recycled fine aggregates (RFA). These RFA are produced from construction and demolition waste (C&DW) in Belgium and are sieved to a maximum particle size of 2 mm [0.08 in].

Cast and printed samples of mortar containing 100% RFA, with a sand-to-cement ratio of approximately 1:1 and a water-to-cement ratio of 0.29, were subjected to mechanical tests, including flexural, compressive, and tensile strength, at 2, 7, 28, and 56 days. The possible anisotropic behavior of the printed material was also investigated. The results show that using RFA does not significantly affect the mechanical properties of the mortar, and some anisotropic behavior was observed based on the compression test results. The end goal of the project is to print non-reinforced urban furniture; in order to assess its durability, only freezing and thawing (F-T) behavior was investigated. The F-T behavior was analyzed based on the quantity of spalling particles after 7, 14, 28, 56, and 91 F-T cycles. The results show that up to 91 F-T cycles, no significant surface damage occurred.

Achieving low carbon emissions in the concrete industry necessitates a multifaceted approach, which includes maximizing the efficacy of supplementary cementitious materials (SCMs). In this respect, this paper investigates fly ash-concrete made of fly ash from distinct burning technology, benefited by different pieces of equipment. Several aspects of fly ash-concrete performance were assessed, including hydration, mechanical properties, and eco-efficiency. The results showed that the burning technology plays an important role in fly ash reactivity. Although both approaches to mechanically activating fly ashes provide interesting results, there is an intriguing difference in the performance of the fly ash concrete. Furthermore, the lifecycle analysis underscores the potential for considerable reduction in global warming potential through the incorporation of fly ash in concrete, making it a promising avenue for reducing the industry's environmental footprint. These findings offer valuable insights for optimizing fly ash utilization and advancing the sustainability of the concrete sector.

The 16th International Symposium on Fiber-Reinforced Polymer (FRP) Reinforcement for Concrete Structures (FRPRCS-16) was organized by ACI Committee 440 (Fiber-Reinforced Polymer Reinforcement) and held on March 23 and 24, 2024, at the ACI Spring 2024 Convention in New Orleans, LA. FRPRCS-16 gathers researchers, practitioners, owners, and manufacturers from the United States and abroad, involved in the use of FRPs as reinforcement for concrete and masonry structures, both for new construction and for strengthening and rehabilitation of existing structures. FRPRCS is the longest running conference series on the application of FRP in civil construction, commencing in Vancouver, BC, in 1993. FRPRCS has been one of the two official conference series of the International Institute for FRP in Construction (IIFC) since 2018 (the other is the CICE series). These conference series rotate between Europe, Asia, and the Americas, with alternating years between CICE and FRPRCS. The ACI convention has previously cosponsored the FRPRCS symposium in Anaheim (2017), Tampa (2011), Kansas City (2005), and Baltimore (1999). This Special Publication contains a total of 52 peer-reviewed technical manuscripts from 20 different countries from around the world. Papers are organized in the following topics: (1) FRP Bond and Anchorage in Concrete Structures; (2) Strengthening of Concrete Structures using FRP Systems; (3) FRP Materials, Properties, Tests and Standards; (4) Emerging FRP Systems and Successful Project Applications; (5) FRP-Reinforced Concrete Structures; (6) Advances in FRP Applications in Masonry Structures; (7) Seismic Resistance of FRP-Reinforced/Strengthened Concrete Structures; (8) Behavior of Prestressed Concrete Structures; (9) FRP Use in column Applications; (10) Effect of Extreme Events on FRP-Reinforced/Strengthened Structures; (11) Durability of FRP Systems; and (12) Advanced Analysis of FRP Reinforced Concrete Structures. The breadth and depth of the knowledge presented in these papers is clear evidence of the maturity of the field of composite materials in civil infrastructure. The ACI Committee 440 is witness to this evolution, with its first published ACI CODE-440.11, “Building Code Requirements for Structural Concrete with Glass Fiber Reinforced Polymer (CFRP) Bars,” published in 2022. A second code document on fiber reinforced polymer for repair and rehabilitation of concrete is under development. The publication of the sixteenth volume in the symposium series could not have occurred without the support and dedication of many individuals. The editors would like to recognize the authors who diligently submitted their original papers; the reviewers, many of them members of ACI Committee 440, who provided critical review and direction to improve these papers; ACI editorial staff who guided the publication process; and the support of the American Concrete Institute (ACI) and the International Institute for FRP in Construction (IIFC) during the many months of preparation for the Symposium.

Although the 28-day concrete compressive strength is often used as a quality control indicator, early-age mechanical properties are becoming more critical to optimize construction scheduling. Numerous advanced techniques have been proposed in this regard and among those, electrical resistivity (ER), a non-destructive and inexpensive technique able to characterize the microstructure development of cementitious materials has been showing promising results. Yet, recent literature data have evidenced that ER might be significantly influenced by a variety of parameters, such as the binder type/amount and aggregates nature used in the mix. These factors can hinder the practical benchmark of concrete mixtures proportioned with distinct raw materials. Thus, six concrete mixtures incorporating two types of aggregates (granite and limestone) and two ground granulated blast furnace slag cement replacements (e.g. 0%, 35%, and 70%) were manufactured for this research. Moreover, three distinct ER techniques (e.g. Bulk, Surface, and Internal) and compressive strength tests were performed at different concrete ages. Results show that the binder replacement may significantly affect ER results over time, whereas the aggregate type presented a less significant impact.

Reducing Normal Portland Cement (NPC) has been a major concern of concrete industry and research community over the last 2-3 decades. As much as 8% of the global CO₂ emissions stem from clinker production. Hence, a wide number of research projects have been focusing on reducing NPC in cementitious materials using numerous strategies such as the use of supplementary cementing materials (SMC’s), limestone fillers (LF) and/or advanced mixproportioning techniques. Yet, the impact of these procedures on the overall behaviour of materials with low NPC content, especially in the fresh state and long-term durability, is still not fully understood. This work aims to understand the influence of the distance between the fine particles, the so-called Inter-Particle Separation (IPS), on the fresh state behaviour of cement-base pastes designed through the use of Particle Packing Models and incorporating LF. Evaluations on the fresh (i.e. rheological behaviour and setting time) and hardened states (compressive strength) were conducted in all mixtures. Results show that IPS directly correlates with the viscosity of cementbase pastes for all shear rates appraised. Moreover, the use of LF increases the hydration rate of NPC pastes. Finally, it is clear that the water-to-cement ratio keeps being the main factor controlling the compressive strength of cement pastes with reduced NPC content and high levels of LF replacement.