Extensive research on fiber-reinforced concrete (FRC) has led to a solid understanding of its structural behavior, enabling the development of design codes. Initially dominated by steel fibers, FRC has progressively incorporated macro synthetic fibers, particularly in Latin America, where it is widely used in tunnel linings. More recently, hybrid FRC, combining different fiber types, has attracted increasing attention due to its improved performance throughout the different stages of crack development. Although its short-term behavior is well established, its response under sustained loading (creep) and its influence on post-creep behavior remain insufficiently understood. This paper presents an experimental evaluation of the post-creep behavior of hybrid FRC, conducted in accordance with RILEM recommendations. The results are compared with those obtained for concrete reinforced with steel fibers and macro synthetic fibers.
The aim of this study is to evaluate the mechanical properties of self-compacting concrete (SCC) containing two types of brick aggregate (discarded and demolition brick aggregate) with a 100% replacement of both fine and coarse natural aggregates, besides incorporation of 10% tire crumb rubber as a replacement by volume of fine aggregate. Slump flow was evaluated for fresh state. Density, ultrasonic velocity (UPV), compressive strength, and dynamic modulus of elasticity were measured at 28, 56 and 90 days. The results showed significantly reductions in densities and UPV depending on the aggregate type and presence of rubber. Likewise, the dynamic modulus of elasticity decreased up to 63.2% at 90 days by inclusion of brick aggregate and by 22% with the rubber incorporation. A proposed equation to estimate dynamic modulus of elasticity at late ages was introduced with reasonable error and comparable values with experimental data obtained in this study.
Ultra-high-performance fiber-reinforced concrete (UHPFRC) exhibits outstanding mechanical and durability performance, strongly influenced by fiber orientation. This study evaluates the fiber orientation coefficient considering casting methods, element geometry, and thickness effects. Beams (100×100×500 mm3 and 150×150×600 mm3) and slabs (1000×50×1000 mm3) were analyzed. Beams were cast horizontally (with fixed and moving pouring points) and vertically (at different casting speeds). Slabs were cast using fixed and moving pouring points and later cut into longitudinal and transverse specimens. A total of 84 prisms were tested in flexure to determine tensile properties. Results show that casting procedures, structural typology, and thickness significantly affect fiber distribution and tensile behavior. Horizontal beams displayed lower variability, whereas slabs showed marked differences associated with their bidirectional configuration. Fiber orientation was found to influence constitutive law parameters. A good correlation was found between UNE 83519 results and UHPFRCMat app simulations. Reference orientation coefficients are proposed to support structural design.
This research explores the usability of reactive MgO (RM)-based materials as sustainable, low-carbon alternative binders for 3D concrete printing. Specifically, RM was substituted with 25 wt% of diverse silica sources to assess their potential: micro-silica (MS), metakaolin (MK), fly ash (FA), and basalt powder (Bst). By evaluating rheology, buildability, and 28-day compressive strength under a constant initial consistency, results reveal that the MK blend exhibited optimal rheological behavior. It combined low initial dynamic yield stress for smooth extrusion with substantial time-dependent viscosity build-up, completely preventing filament deformation. All mixtures demonstrated excellent buildability, successfully sustaining 20-layer structures without collapse. Furthermore, XRD analysis confirmed that highly amorphous silica in MS and MK facilitated extensive precipitation of magnesium silicate hydrate (M-S-H) gels. This microstructural improvement yielded the highest compressive strengths of 16.5 MPa and 13.9 MPa, respectively. Ultimately, RM-SiO₂ systems emerge as highly promising, low-carbon materials for digital construction.
The fresh and hardened state performance of conventional and self-compacting concrete (SCC) is affected by multiple factors. Supplementary cementitious materials (SCMs), chemical admixtures, the maximum aggregate size or the grading of aggregates influence how the mix is designed to specified performance requirements. Cohesiveness and workability can influence the hardened state properties of any mix, self-compacting or not. A large dataset compiled from routine industrial testing has been analysed to develop a tool that predicts the workability from the mix design. The dataset includes SCC and conventional mixes, incorporating SCMs and water reducers or superplasticisers at different dosages. Machine learning techniques have been employed to develop a classifier which estimates the slump class of mix designs. This paper describes how the challenges posed by analysing such a broad range of mix designs has been overcome and in what ways the knowledge obtained can be applied.
