Engineered cementitious composites (ECCs) are a type of micromechanically-designed cementitious composite reinforced with a moderate volume fraction of short fiber, typically 2% by volume. ECCs form steady-state multiple cracking that considerably improves the tensile strength and ductility of traditional concrete. In this study, the properties of matrix and the interface of ECCs were tailored through the use of crumb rubber, different types of sand, and different replacement levels of cement with fly ash. The study examined the effect of sand replacement with crumb rubber (20% by volume), two types of river sands (coarse and fine), increasing the content of class F fly ash (up to 75% cement replacement), and low fiber content (1.75%) on the mechanical properties of ECCs. Compressive strength, uniaxial tensile, and third-point bending tests were performed to characterize the properties of ECC mixes. Experimental results demonstrated that increasing fly ash content and using crumb rubber favored ductility of the composites. However, higher fly ash contents and a low water-to-binder (W/B) ratio produced lower strengths as these limited the pozzolanic reaction of fly ash making it act partially as a filler. While incorporation of crumb rubber showed adverse effects on the tensile strength of ECC materials (up to 26% decrease), the tensile ductility of ECC materials improved significantly (up to 434% improvement). Moreover, the implementation of different types of sand produced minor effects on the mechanical properties of ECCs. Overall, a tradeoff between the strength and ductility of the composites was detected, which highlights the implications of matrix/interface tailoring in the overall performance of ECC.

This study investigates the effects of raw sugarcane bagasse ash (SCBA) used as a partial or complete replacement for silica sand in engineered cementitious composites (ECCs). ECC mixtures with five different replacement levels of sand with SCBA were produced (i.e., 0%, 25%, 50%, 75%, and 100% by volume). The SCBA utilized in this study was comprehensively characterized. Furthermore, the fresh and hardened properties of the produced ECC materials were thoroughly evaluated. The characterization of SCBA revealed that raw SCBA consisted mainly of small (i.e., 256 μm average particle size), porous, and irregularly shaped particles with carbon and silica as the main constituents. Furthermore, the SCBA met the pozzolanic component requirement for Class C pozzolans; however, it did not meet the minimum strength activity index requirement to be classified as a pozzolan; however, it did not meet the minimum strength activity index requirement to be classified as a pozzolan. In terms of ECC fresh properties, the incorporation of SCBA produced an important loss in workability, which was mitigated with increasing dosages of high-range water reducer for increasing amounts of SCBA, which also resulted in a substantial increase in the air content. In the case of hardened material properties, the incorporation of SCBA as sand replacement produced a slight decrease (up to 11%) of the compressive strength of ECCs. However, the tensile strength and especially the tensile ductility of the composites were substantially enhanced (up to 22.3% and 311%, respectively). The tensile strength improvements were credited to the pozzolanic and/or filler effect of SCBA. On the other hand, enhancements in the tensile ductility were associated to the combined effect of the reduction of crack-tip matrix toughness (credited to the decrease in aggregate particle size), reduction in ECC cracking strength (due to increase in air content), and increase in the complementary energy (attributed to the potential decrease in the chemical bond of the fiber/matrix interface and an enhanced fiber dispersion). The surface resistivity of ECC materials was negatively affected by the addition of SCBA. Furthermore, the length change of all SCBA-ECC materials, at all ages of curing, was higher in comparison with that of the control mixture, except for the mixture with 25% replacement at 28 days of curing.

Engineered Cementitious Composites (ECC) are considered a promising alternative for the construction of durable pavements. The objective of this study was to evaluate the effects of plasticity and flexural fatigue behaviour of ECC on pavement performance. A low-cost ECC using low fibre content (1.5% volume fraction), locally-available river sand and a high level of cement replacement with class F fly ash (75% by weight) was investigated. The ECC demonstrated a pseudo-strain-hardening (PSH) behaviour at all curing ages. Furthermore, as curing progressed, the tensile and flexural strengths increased; yet, ductility decreased. The flexural fatigue performance of the ECC was significantly superior to that of regular concrete. Finite Element Analysis (FEA) was integrated with flexural fatigue experimental results to establish a thickness vs. cycles to failure (T-N) relationship. In developing the T-N relation, the effect of ECC plasticity was accounted for by proposing a stress equivalency function to convert plastic stress into an equivalent linear elastic stress. From the T-N curves, it was determined that the original ECC T-N curve (without implementing the stress equivalency function) greatly overestimated the numbers of the cycle to failure for thicknesses below ~60 mm as this curve starts exhibiting an asymptotic behaviour with respect to N.

The objective of this study was to evaluate the feasibility of developing practical and cost-effective ultra-high-performance engineered cementitious composites (UHP-ECCs) using natural river sand and no silica fume (SF). Fresh and hardened properties of composites utilizing river sand, with and without SF, and incorporating 1.5 and 2 vol% (volume percent) ultra-high-molecular-weight polyethylene fibers were evaluated. Furthermore, matrix and fiber/matrix interface properties were investigated. Experimental results showed that the inclusion of SF generally produced negative impacts in the mechanical strength (i.e., compressive, tensile, and flexural) and ductility of the composites, which was mainly attributed to a worsening fiber dispersion. This was supported by the loss in workability observed when increasing fiber content or implementing SF. Clear tendencies in the effect of fiber content on the mechanical strength of the composites were not observed. However, increment in fiber content decreased the tensile ductility of the materials, presumably because of poor fiber dispersion. All the mixtures evaluated exhibited pseudo strain-hardening (PSH) behavior and ECC-like ductility, which was supported by the PSH strength and energy indexes obtained, which exceeded the minimum recommended values for robust PSH behavior. Practical and cost-effective UHP-ECC materials (i.e., cementitious composites simultaneously exhibiting compressive strength >120 MPa and tensile strain capacity >2%) using natural river sand and no SF were successfully developed, which to the authors’ knowledge was achieved for the first time.

Automated and seamless integration of reinforcement is one of the main unresolved challenges in large-scale additive construction. This study leverages a dual-reinforcement solution consisting of high-dosage steel fiber (up to 2.5% by volume) and short vertical reinforcements as a complementary reinforcement technique for 3D-printed elements. The mechanical performance of the printing material was characterized by measuring the compressive, flexural, and uniaxial tensile strengths of mold-cast specimens. Furthermore, the flexural performance of the plain and fiber-reinforced 3D-printed beams was evaluated in the three main loading directions (X, Y, and Z-directions in-plane). In addition, short vertical threaded reinforcements were inserted into the fiber-reinforced 3D-printed beams tested in the Z-direction. The experimental results revealed the superior flexural performance of the fiber-reinforced beams loaded in the longitudinal directions (X and Y). Moreover, the threaded reinforcement significantly increases the flexural strength and ductility of beams loaded along the interface, compared to the control. Overall, the proposed dual-reinforcement approach, which exhibited notably less porosity compared to the mold-cast counterpart, holds great potential as a reinforcement solution for 3D-printed structures without the need for manual operations.