International Concrete Abstracts Portal

The production of carbonated aggregates from Class F fly ash (FA) is challenging due to its low calcium content, typically less than 10%. This study investigates the production of carbonated alkali-activated aggregates using FA and calcium carbide sludge (CCS). Sodium hydroxide was used as an activator and examined the effects of autoclave treatment on the properties of these aggregates. The optimal mixture, comprising 70% FA and 30% CCS, achieved a single aggregate strength of >5 MPa in autoclave carbonated (AC) aggregates, comparable to the strength obtained after 14 days of water curing in without autoclave carbonated (WAC) aggregates. Both AC and WAC aggregates exhibited a bulk density of 790 to 805 kg/m³ and CO₂ uptake of 12.5% and 13.3% in AC and WAC aggregates, respectively. FE-SEM and FT-IR analysis indicated the formation C-A-S-H gel in noncarbonated aggregates, while calcite and vaterite, along with N-A-S-H gel, formed in carbonated aggregate. Concrete incorporating AC and WAC aggregates exhibit compressive strengths of 39 and 38 MPa, with concrete density of 2065 kg/m³ and 2085 kg/m³, respectively. Furthermore, AC and WAC aggregate concrete showed a reduction in CO₂ emission of 18% and 31%, respectively, compared to autoclave noncarbonate (ANC) aggregate concrete. These findings highlight the potential of producing carbonated alkali-activated aggregates from FA and CCS as sustainable materials for construction applications.

Engineered cementitious composites (ECC) represent a significant innovation in construction materials due to their exceptional flexibility, tensile strength, and durability, surpassing traditional concrete. This review systematically examines the composition, mechanical behaviour, and real-world applications of ECC, with a focus on how fiber reinforcement, mineral additives, and micromechanical design improve its structural performance. The present study reports on the effects of various factors, including different types of mineral admixtures, aggregate sizes, fiber hybridization, and specimen dimensions. Key topics include ECC’s strain-hardening properties, its sustainability, and its capacity to resist crack development, making it ideal for high-performance infrastructure projects. Additionally, the review discusses recent advancements in ECC technology, such as hybrid fibre reinforcement and the material’s growing use in seismic structures. The paper also addresses the primary obstacles, including high initial costs and the absence of standardized specifications, while proposing future research paths aimed at optimizing ECC’s efficiency and economic viability.

Prolonged neutron irradiation can damage concrete biological shields, particularly when nuclear power plants extend reactor lifespans. Retrofitting biological shields with thin and highly efficient neutron shields may limit neutron damage. Portland cement mortars amended with boron carbide and polyethylene powders were assessed for neutron attenuation. Shielding performance was compared to concrete with a similar design and coarse aggregate as a biological shield at an operational nuclear plant. Boron carbide enhanced the shielding performance of specimens under the full energy spectrum of the neutron source. Boron carbide and polyethylene synergistically enhanced neutron attenuation under a purely high-energy neutron flux. Engineered thin composite mortars needed 90% less thickness to achieve similar or better shielding efficiency as the concrete in a typical biological shield under the test conditions. Isothermal calorimetry, compressive strength, and thermal expansion results indicate that mixture design parameters of thin shields can be adjusted to achieve adequate structural properties without diminishing constructability or structural performance.

The effects of carbonated aggregate and aggregate replacement ratio on the stress-strain behavior of recycled aggregate concrete (RAC) under uniaxial compression were studied, and based on Lemaitre's strain equivalence hypothesis and Weibull distribution, a damage constitutive model was proposed. The results showed that carbonated aggregate enhanced the peak stress. As the aggregate replacement ratio increased, the slopes of both the ascending and descending sections of the stress-strain curve gradually decreased, resulting in reduced peak stresses and decreased material brittleness. Besides, the damage constitutive model modified using linear regression analysis could describe the stress-strain curves well. As the aggregate replacement ratio increased, the slope of the “S” curve representing the damage variable evolution law gradually slowed down, and the corresponding strain gradually increased when the damage variable was 1. Meanwhile, the shape of the “parabola” curve representing the damage variable evolution rate became wider, and its vertex gradually decreased.

The rapid growth of population, consumption, and economy stimulates the extraction of natural resources at an accelerated rate, directly impacting the environment by generating waste and CO₂ emissions, primarily in the civil construction industry. This research investigates the use of untreated tire waste rubber as a replacement for fine aggregate (sand) in geopolymer mortar, in response to environmental concerns from the civil construction industry. The study uses a Central Composite Design and Response Surface Methodology to optimize the modulus of rupture, modulus of elasticity, and toughness. With a global desirability of 0.73, the optimized values for these variables were 2.85 MPa, 676.3 MPa, and 0.331 kJ/m², respectively, with experimental errors below 10%. The results suggest that tire waste rubber can effectively replace fine aggregate in geopolymer mortar, potentially reducing environmental impact.