International Concrete Abstracts Portal

Infilled cementitious composite (ICC) is produced by infilling cementitious paste into a designed aggregate skeleton. This approach enables the incorporation of both coarse aggregate and fibers while maintaining adequate fresh and hardened performance at minimal paste volume. In this study, ultra-high-performance concrete (UHPC) pastes incorporating supplementary cementitious materials were infilled into fiber-aggregate skeletons (FAS) with macro steel fiber volumes ranging from 0 to 2.0%, yielding a total of 16 ICC mixtures. The FAS packing density, UHPC infilling ability, and the fresh, mechanical, and microstructural properties of both UHPC paste and the resulting ICC were evaluated. The 28-day compressive strength of ICC ranged from 96.0 (13.9 ksi) to 121.6 MPa (17.6 ksi), while the first-cracking flexural strength increased by up to 61.8% at a fiber volume of 2.0%. The cement content of ICC ranged from 229 to 1116 kg/m3 (14.3 to 69.7 lb/ft3). Relative to the corresponding conventional UHPFRC without coarse aggregate, ICC reduced material cost by up to 50% and embodied CO2 by up to 55%. These findings demonstrate that ICC can provide a low-carbon, material-efficient pathway for sustainable structural concrete.

The interference between steel fiber and coarse aggregate reduces the homogeneity of fiber distribution and orientation, which may compromise the expected reinforcing effectiveness of steel fibers in concrete. Traditional destructive testing techniques constrain the quality control of steel fiber distribution in prefabricated concrete segments; developing an inductance-based technique contributes to non-destructive characterization of steel fiber distribution. This work uses a Helmholtz coil to solve the magnetic field non-uniform distribution, thereby designing an inductor device to improve the accuracy of steel fiber distribution monitoring within concrete. On this basis, a multi-parameter experiment was designed to study the coupling effect of coarse aggregate and steel fiber, with key variables including water-to-binder ratio, coarse aggregate gradation, steel fiber mixing sequence, vibration duration, and casting flow distance. The C50 concrete mixture incorporates fly ash (75 kg/m³) as a supplementary cementitious material to improve workability and particle packing density. The primary findings are as follows: the induction-based method enables non-destructive evaluation of steel fiber content and orientation in steel fiber‑reinforced concrete containing coarse aggregate (SFRC‑CA), demonstrating high detection efficiency. The larger the aggregate size and water-binder ratio, the worse the steel fiber distribution uniformity. Improper vibration will lead to steel fiber thickness-related settlement, while the longer the flow distances, the more uneven the orientation of the fiber. These results offer important reference for material design and quality control of precast SFRC-CA components.

The growing generation of construction and demolition waste necessitates the development of effective recycling strategies to address environmental concerns. This study investigated the replacement of natural fine aggregate (NFA) with recycled fine aggregate (RFA) at 0, 50, and 100% using two treatment methods: 1) sodium silicate (SS)-silica fume (SF) presoaking treatment (SS-T); and 2) organic treatment (OA-T) with bio-additives derived from Persea macrantha, Haritaki, and Cissus glauca Roxb. A quantitative comparison of the aggregate and mortar quality was conducted for each method. The combined application of SS-T and OA-T demonstrated an 85% improvement in workability and a 68% reduction in water absorption for RFA. Mortar experiments revealed up to 76% improvement in compressive and flexural strengths compared with untreated RFA mortar. Microstructural analyses (scanning electron microscopy [SEM], energy-dispersive spectroscopy [EDS], X-ray diffraction [XRD], and Fourier-transform infrared spectrometer [FTIR]) confirmed the enhanced bond strength and mineral composition. This study highlights the potential of SS-T and OA-T to produce durable, high-performance RFA mortars using locally available, economical bio-additives.

Several approaches are currently used to proportion recycled aggregate concrete (RAC), each having limitations. An effective and universal way to proportion RAC is not only an important tool for developing high-quality concrete but also a critical milestone for promoting the wider use of recycled concrete aggregate (RCA) in concrete. A mixture design method based on particle packing and excess paste theory is proposed in this study. Given the focus on pavement concrete, the modified Box Test was used to quantify RAC workability. RAC mixtures with five different RCAs of varying quality, developed using the proposed method, showed excellent workability (Box Test Rating E1-S1), whereas mixtures developed with conventional mixture design methods failed to achieve adequate workability. Mechanical properties of optimized RACs were either comparable or improved. The adverse effect of RCA on concrete resistivity and shrinkage appeared negligible and was mitigated by the mixture design approach developed in this study. Compared with conventional direct weight replacement (DWR)/direct volume replacement (DVR) mixtures, the proposed design achieved a reduction of surface voids by more than 80%, up to 25% higher compressive strength, and 20% lower shrinkage at 28 days, while maintaining comparable resistivity.

As recycled concrete reaches the end of its service life, a new generation of coarse recycled aggregate (CRA) is created. Although the variables influencing the physical properties of CRA are well understood, the performance of multi-recycled concrete aggregate (MRCA) remains insufficiently explored, and it is essential to study how the modified properties could affect the performance of recycled concrete. This research involved five recycling cycles to evaluate the properties of MRCA and its impact on the mechanical and durability performance of concrete made with 75% MRCA. The findings indicate that water absorption, porosity, and abrasion of MRCA increase with each recycling cycle. Although the mechanical behavior of the concretes appears to be unaffected by the number of recycling cycles, the elastic modulus is negatively impacted when MRCA is used. Furthermore, while some permeability properties are significantly influenced by each recycling cycle, both water penetration depth and resistance to sulfate attack remain largely unchanged.