Durability of Geopolymer Concrete Under Chemical Attack: A Review of Acid, Sulfate, Chloride, and Multi-Exposure Resistance

Green and Bio-Based Corrosion Inhibitors for Reinforced Concrete: Recent Advances, Mechanisms, Durability, and Future Perspectives

Corrosion of reinforcing steel remains a major cause of premature deterioration in concrete infrastructure, motivating the development of inhibitors with lower toxicity and reduced environmental impact. This review critically examines recent advances in green and bio-based corrosion inhibitors for reinforced concrete, including plant extracts, agro-industrial residues, naturally occurring organic compounds, proteins, polysaccharides, bio-based coatings, hybrid formulations, and microbial systems. The available evidence is synthesized in terms of chemical functionality, delivery route, adsorption and film-forming mechanisms, electrochemical response, compatibility with cementitious materials, and durability under chloride- and carbonation-related exposure. Many formulations provide substantial inhibition under optimized laboratory conditions through interfacial adsorption, coordination with iron species, passive-film stabilization, suppression of anodic and cathodic reactions, and restriction of aggressive-species transport. However, reported efficiencies are not directly comparable because experimental scale, exposure conditions, dosage, steel preparation, and calculation methods vary considerably. Moreover, long-term reinforced-concrete and field studies remain scarce, while extract standardization, cement compatibility, toxicity, biodegradability, and life-cycle performance are frequently insufficiently addressed. Green and bio-based inhibitors therefore represent a promising but heterogeneous technology class. Their practical implementation requires chemically reproducible formulations, complementary electrochemical and surface evidence, concrete-scale durability assessment, environmental validation, and stage-gated progression toward monitored field applications.

Durability assessment of bio-modified geopolymer concrete in simulated sewage environments

Sewer infrastructure worldwide is ageing beyond its designed lifespan, rendering it increasingly vulnerable to biogenic sulphuric acid corrosion, cracking, and structural collapse. Geopolymer concrete represents a promising sustainable alternative to ordinary Portland cement in such aggressive environments; however, its durability under acidic conditions remains insufficiently characterised, particularly when combined with microbial modification. This study evaluated the sulphuric acid resistance and microstructural integrity of two fly ash-based geopolymer concrete formulations—a control mixture and a Shewanella oneidensis species-enhanced bio-modified mixture (Bio)—subjected to 1% H₂SO₄ immersion at 30 °C for 10 days to simulate sewer conditions. A multi-technique analytical framework comprising mechanical testing, capillary water absorption, SEM–EDS, XRF, FTIR, and XRD was employed to elucidate degradation mechanisms and quantify the effect of bacterial modification. Bio-modified specimens exhibited a denser, more homogeneous microstructure and markedly superior acid resistance, including an 82% increase in splitting tensile strength following acid exposure, in contrast to a 13% decrease recorded in control specimens. SEM–EDS analysis confirmed reduced cracking and enhanced retention of Ca and Fe in bio-modified specimens. XRD revealed the preservation of acid-resistant crystalline phases, including quartz and andradite, in bio-modified specimens, whereas the control specimens showed greater phase decomposition and decalcification. FTIR analysis indicated greater stability of Si–O–T bonds in bio-modified specimens, consistent with reduced silicate depolymerisation. These findings confirm that Shewanella-based bio-modification significantly enhances the durability of geopolymer concrete under sulphuric acid attack, supporting its application as a resilient and sustainable material for sewer infrastructure.

Corrosion-Resistant Compounds Based on Polymer Matrices and Inorganic Additives

Corrosion of metal and reinforced concrete structures remains one of the most serious problems affecting strength and durability of products. It is primarily caused by environmental factors such as chloride, sulfate, and carbon dioxide exposure. Various methods are widely used to apply corrosion-resistant coatings onto metal surface. Purpose:  The aim of this work is to synthesize corrosion-resistant compounds based on polymer matrices and inorganic additives and investigate their corrosion-resistant properties. Methodology/approach:  It is shown that proposed compositions can be used as a complex protective coating. The introduction of a mixture of iron oxides with variable valence into the polyurethane polymer matrix significantly reduces the corrosion rate in chloride-containing environments due to secondary redox processes in the protective layer. The contact angle, adhesive strength are calculated, and the Pourbaix diagram is analyzed. Research findings:  Synthesized are corrosion-resistant compounds based on metal-phosphate binders incorporated into polyurethane, polyvinyl acetate or alkyd polymer matrix. Practical implications:  Polymer matrices combined with chemical additives and fillers have advantages in the protection efficiency, cost-effectiveness, and environmental sustainability, and such compounds can be used for corrosion protection.

State-of-the-art review: mechanical and durability properties of cement concrete with metakaolin and fiber over two decades

Current State of Research on Geopolymer Materials

Ordinary Portland cement (OPC) production generates substantial carbon emissions and imposes considerable ecological burdens, thereby driving global research on low-carbon alternative cementitious binders. Geopolymers, formed through the alkali activation of aluminosilicate industrial solid wastes, have emerged as promising sustainable materials for replacing OPC. This narrative review integrates the research framework of geopolymer materials, covering core definitions, classification systems, four-stage geopolymerisation and polycondensation mechanisms, and microscopic characterisation techniques. Representative precursor systems, including metakaolin, fly ash, blast furnace slag and multi-solid waste composites, and three major categories of alkali activators are summarised, with attention to the regulation of workability, mechanical strength, volume stability, multi-scale durability, high-temperature resistance and heavy metal immobilisation capacity. A comparative table distinguishes the strengths and limitations of four typical geopolymer precursor systems. This paper also discusses six major industrial application scenarios, including green prefabricated components, refractory and anti-corrosion materials, hazardous waste stabilisation, geotechnical solidification, 3D printing feedstock and multifunctional intelligent geopolymer composites. Key bottlenecks restricting large-scale industrialisation are identified, including unstable raw material composition, corrosive liquid activators, excessive drying shrinkage, insufficient long-term field service data and the absence of unified international testing standards. Targeted future research directions are proposed, including low-corrosion single-component solid activators, multi-waste synergistic blending, fibre/nano toughening, functional integrated geopolymers, full life-cycle environmental assessment and global standard development.

Low-Carbon Cementitious and Alkali-Activated Materials for Roadbed Stabilization: A Review from Microstructural Mechanisms to Engineering Adoption

Problematic subgrade soils degrade pavement performance, while conventional cement/lime stabilizers generate excessive carbon emissions. Unlike earlier reviews that focus on single-material systems—such as industrial by-products, alkali-activated binders for expansive soils, or geopolymers for pavement applications—an integrated framework spanning reaction mechanisms, microstructural evolution, engineering parameterization, and life-cycle validation is proposed The work offers three distinctive contributions: (i) a four-level evidence chain hierarchy (strength → microstructure → durability → leaching/LCA) to grade research completeness; (ii) repositioning resilient modulus, permanent deformation, and pore-connectivity evolution as core engineering outputs bridging material design and structural response; and (iii) a comparative assessment of alkali-activated geopolymers, low-clinker calcium-based composites, and multi-scale reinforcement strategies under consistent durability and environmental boundaries. Quantitative synthesis reveals the following: strength retention after 12 wet–dry/freeze–thaw cycles ranges from 60% to 85%; resilient modulus improvements over untreated soils reach 30%–120%, yet stress-dependent characterization remains essential; leaching concentrations of hazardous elements (Cr, Ba, Pb) can increase by 50%–200% after durability cycling if pore connectivity rebounds. Life-cycle carbon comparisons are boundary-sensitive—geopolymer advantages shrink from 60% to ≤20% when activator transport and pre-treatment are included. We conclude that the primary barrier to engineering adoption is not the absence of high-strength formulations, but the lack of extrapolatable design parameters and closed-loop evidence chains. A decision-support framework incorporating durability retention, leaching safety, carbon footprint, and field validation is proposed to guide robust design and industrial scaling. Critically, the review identifies that engineering adoption is constrained not by the absence of high-strength formulations, but by the lack of standardized construction protocols, quality control procedures, and long-term field performance data—gaps that must be addressed through coordinated field-scale demonstration projects.