Construction Materials

In recent decades, the need to embrace the concepts of the circular economy and ecological transition has become increasingly apparent, especially in the civil engineering sector. This research aims to study a Cement-Bound Granular Material (CBGM) pavement layer using the industrial by-product Anhydrous Calcium Sulphate (ACS) as a partial replacement for Portland Cement (PC) by weight. The dual objective is to reduce environmental impact and ensure long-term high mechanical performance. Mechanical tests conducted at different curing periods (7, 28, 96, and 120 days) showed compressive strength gains of up to 180%. The evolution of the mechanical behavior was correlated with the formation of the gypsum dihydrate and ettringite hydrated phases, found by quantitative XRD analysis, to reinforce the cement matrix. Finite element simulations and fatigue life predictions using Miner’s rule over pavement lifespans of 15, 20, and 30 years indicated an increase in durability by a factor of 4.68 for the ACS-enhanced mixture compared to traditional PC-only formulations. Leaching tests show the material performs within acceptable environmental thresholds, even if its classification and acceptance may differ across regulatory systems, suggesting a solid basis for its application in sustainable practices.

Concrete remains one of the most widely utilized construction materials, valued particularly for its exceptional compressive strength. However, exposure to fire can compromise both its internal microstructure and external integrity. This research investigates the behavior of concrete manufactured with recycled concrete coarse aggregate (RCA) derived from construction waste, aiming to establish experimental evidence of fire’s impact on compressive strength. We employed the Optimal Density Method to design mix proportions targeting 24 MPa compressive strength. The experimental program comprised 45 cylindrical samples distributed across three replacement levels: 0%, 15%, and 30% natural aggregate substitution with RCA. Following 28 days of curing, samples underwent direct fire exposure in a melting furnace. Temperature progression was monitored using a pyrometer, ranging from ambient (0 °C) through 250 °C, 400 °C, 600 °C, to 800 °C, with controlled exposure duration at each level. Three samples were tested at each temperature. After fire exposure, samples were cooled for 24 h at ambient temperature before compression testing. The densities of the fresh specimens were determined to be 2254.06 kg/m³ for HS-0AR%, 2210.09 kg/m³ for HS-15AR%, and 2180.85 kg/m³ for HS-30AR%, with a percentage density variation with respect to HS-0AR% of 1.95% and 3.25%, respectively. Finally, in relation to the compressive strength of concrete, a reduction of 4.34% was observed for 15% AGR and 5.72% for 30%, suggesting that the variations may be due to factors such as the water/cement ratio, the quality of the aggregate, and the curing conditions of concrete. In addition, several pathologies were observed, such as cracking, fissures, color changes, and spalling.

The ongoing concern about sustainable infrastructure has driven the development of cement-based adhesives (CBAs) for fibre-reinforced polymer (FRP)-based concrete retrofitting. Nevertheless, traditional CBAs usually have low bond strength, low crack resistance, and low long-term durability that undermine the performance of FRP–concrete systems. To address these limitations, this focused review examines the potential of nanomaterial-modified CBAs to enhance interfacial bond behaviour and overall structural performance. A systematic assessment of recent experimental studies was used to analyze CBAs modified with nanosilica, carbon nanotubes, graphene oxide, and other nanomaterials. The roles of these nanomaterials in improving adhesion mechanisms, stress transfer efficiency, crack control, and resistance to environmental stressors are critically discussed. We also contrast the performance of neat and nano-modified CBAs in FRP-based retrofitting systems, with particular emphasis on bond behaviour, mechanical response, and durability-related performance. Particular emphasis is put on innovative high-strength self-compacting cementitious adhesives (IHSSC-CAs), which are identified as an emerging class of sustainable bonding materials combining high mechanical performance with improved environmental compatibility in relation to traditional bonding systems. The paper concludes with the identification of key research gaps, a discussion of practical implementation challenges, and an outline of future research directions for the development of next-generation sustainable and resilient concrete retrofitting technologies.