Samuel Ramírez-Arellanes

The production and use of Portland cement (PC) are essential to modern infrastructure but remain among the most environmentally intensive industrial activities, accounting for approximately 8% of global CO2 emissions due to limestone decarbonation and high thermal energy demand (1,2). In this direction, supplementary cementitious materials (SCMs) represent an effective strategy to lower the environmental footprint of PC-based materials (3). Industrial and agro-industrial by-products, such as fly ash, blast-furnace slag, silica fume, and sugarcane bagasse ash have been adopted due to their pozzolanic reactivity and durability benefits (4). More recently, attention has shifted toward postconsumer waste streams, particularly waste glass (WG), which, when finely ground, exhibits high amorphous silica content and can partially replace PC (5).Although WG has been shown to improve fresh-state behavior, refine microstructure, and maintain or enhance long-term mechanical and durability performance (7), reported results remain inconsistent across different mix designs, glass sources, and particle sizes. Contradictory trends in early-age strength, alkali-silica reaction (ASR), and long-term durability further complicate its implementation (8). These inconsistencies suggest that WG performance is often interpreted as system-dependent rather than mechanism-driven. In this context, this work does not aim to provide a comprehensive review. Instead, it presents a critical opinion arguing that WG behavior in PC-based materials is governed by coupled physicochemical and processing variables, with particle size acting as a key controlling parameter.Recent studies show that WG has evolved from a recycling alternative into a viable SCM. Finely ground soda-lime glass, particularly below 45 μm, exhibits pozzolanic reactivity due to its amorphous silica content (9,10). In fresh-state behavior, WG often reduces water demand and improves flowability, especially when combined with chemical admixtures (11). Microstructural studies indicate a dual mechanism involving filler effects and pozzolanic reaction, characterized by Ca(OH)2 consumption and the formation of secondary C-S-H and C-A-S-H phases, leading to pore refinement and reduced transport properties (12). Advances in quantifying the reacted WG fraction have improved the distinction between physical and chemical contributions (13). These microstructural changes generally translate into satisfactory mechanical performance. Low-tomoderate replacement levels preserve or enhance long-term strength, while higher substitutions require finer grinding or extended curing to compensate for clinker dilution (14)(15)(16)(17). Durability studies report improved resistance to permeability and chemical attack, and finely ground WG has been shown to mitigate (ASR), in contrast to the deleterious behavior of coarse glass particles (18)(19)(20). However, longterm data on carbonation, chloride ingress under marine exposure, and reinforcement corrosion remain limited. From a sustainability perspective, life-cycle assessments indicate that environmental benefits depend primarily on clinker substitution, provided that grinding energy and transport distances remain controlled (21,22). Durability improvements may further enhance these benefits by extending service life. Despite these advances, the literature remains characterized by apparent contradictions. While WG may improve workability at low dosages, higher replacement levels can reduce consistency (23).Similarly, mechanical performance is often enhanced at later ages but reduced at early ages, and WG may either mitigate or promote ASR depending on particle size (16,17). These inconsistencies are reported as isolated observations, reflecting the absence of a unifying framework. Key variables such as particle size, dissolution kinetics, and processing energy are often treated independently, despite governing multiple coupled phenomena. This limitation highlights the need for an integrated perspective. In this context, the following section proposes a conceptual framework in which particle size is identified as a governing parameter that simultaneously controls reactivity, durability, and sustainability in PC-based materials with WG.The current literature on WG as a SCM remains fragmented, as it typically evaluates reactivity, mechanical performance, durability, and environmental impact as independent variables. However, this work argues that these aspects are intrinsically coupled and governed by a single controlling parameter: particle size. From a mechanistic perspective, particle size defines the transition between different reaction regimes. Coarse WG particles behave predominantly as inert fillers or may even promote ASR. As particle size decreases, particularly below approximately 45 μm, the system shifts toward a dissolution-controlled regime in which the high alkalinity attacks the amorphous silicate network, leading to the rupture of Si-O-Si bonds. The above enables the pozzolanic reaction and formation of secondary C-S-H and C-A-S-H phases, which contribute to microstructural densification and improved performance. Therefore, the commonly reported threshold of ~45 μm should not be interpreted as an empirical boundary, but rather as a mechanistic threshold at which dissolution kinetics become sufficiently rapid to sustain pozzolanic reactivity. This particle size-dependent transition also provides a basis for resolving apparent contradictions reported in the literature. For instance, the dual role of WG in either mitigating or promoting ASR, where coarse particles tend to induce localized expansive reactions, whereas sufficiently fine particles promote homogeneous pozzolanic behavior (20). Similarly, inconsistencies in mechanical performance, particularly at early ages, can be understood as the result of competing effects between clinker dilution and the rate of pozzolanic reaction, both of which are...

The manufacture of Portland cement (PC) emits a significant amount of CO₂ into the atmosphere. Therefore, the partial replacement of PC by supplementary cementitious materials (SCMs) possessing pozzolanic properties is considered a viable strategy to reduce its environmental impact. Recently, waste glass (WG) has been explored as a potential SCM. However, due to the wide variety of glass types and their differing physical and chemical properties, not all WG can be universally considered suitable for this purpose; therefore, this study investigates the use of recycled WG as an SCM for the partial replacement of PC. Two types of WG were evaluated: green waste glass from wide bottles (GWG) and laboratory waste glass (LWG), and their performance was compared to that of fly ash (FA). The physical, mechanical, and pozzolanic properties of the materials were assessed. Results show that both types of WG exhibit particle size distributions comparable to PC and have contents of SiO₂, Al₂O₃, and Fe₂O₃ exceeding 70%. Chemical, mineralogical, and pozzolanic analyses revealed that both GWG and LWG presented higher pozzolanic activity than FA, particularly at later ages. Notably, LWG demonstrated the most significant contribution to mechanical strength development. These findings suggest that recycled waste glass, especially LWG, can serve as a viable and sustainable SCM, contributing to the reduction of the environmental footprint associated with Portland cement production.

Portland cement (PC) is a material that is indispensable for satisfying recent urban requirements, which demands infrastructure with adequate mechanical and durable properties. In this context, building construction has employed nanomaterials (e.g., oxide metals, carbon, and industrial/agro-industrial waste) as partial replacements for PC to obtain construction materials with better performance than those manufactured using only PC. Therefore, in this study, the properties of fresh and hardened states of nanomaterial-reinforced PC-based materials are reviewed and analyzed in detail. The partial replacement of PC by nanomaterials increases their mechanical properties at early ages and significantly improves their durability against several adverse agents and conditions. Owing to the advantages of nanomaterials as a partial replacement for PC, studies on the mechanical and durability properties for a long-term period are highly necessary.