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.

Self-healing concrete with microencapsulated calcium nitrate was investigated. The compressive strength of concrete admixed with microcapsules (as a percentage of the weight of the cement) was tested and compared with that of control specimens of the same mix design without microcapsules. Surface resistivity tests were conducted to quantify the surface permeability of the concrete specimens with and without microcapsules. The self-healing potential was measured by the modulus of elasticity test (ASTM C469), with measurements being taken before and after damage after 14 days. After the concrete was damaged by application of 80% of its ultimate load, all specimens were incubated by immersion in water. The results showed that the concentration of microcapsules added and the size of the microcapsules had a direct impact on the compressive strength of the concrete. Furthermore, the concrete specimens into which microcapsules were incorporated had greater surface resistivity than the control specimens. The recovery of the modulus of elasticity was analyzed according to the increase from the modulus of elasticity recorded after application of 80% of the sample’s ultimate load and the increase relative to the initial modulus of elasticity of the concrete in the virgin state. Overall, the results of this study indicated that although microcapsules caused a decrease in the compressive strength of the concrete, they enhanced the self-healing capability of the concrete that was produced. To take advantage of the benefits of microcapsules, the authors recommend that future work evaluate the use of a dispersing agent to reduce the amount of microcapsules needed in the mix.

The objective of this study was to evaluate the feasibility of a cost-effective Engineered Cementitious Composite (ECC) with low fiber content (1.5% volume fraction) for pavement application. The ECC material studied was evaluated in compression, uniaxial tension and bending. In addition, flexural fatigue performance was evaluated. The cost-effective ECC material evaluated in this study exhibited a compressive strength of 37.6 MPa, a tensile ductility of 2.61%, and a flexural strength of 9.58 MPa. Moreover, the ECC material exhibited an equivalent flexural fatigue life to that of concrete at approximately two times the applied stress. Based on the experimental findings, it was shown that the cost-effective ECC materials with low fiber content can be promising for pavement application.

Previous studies have shown the possibility of successful implementation of Sugarcane Bagasse Ash (SCBA) as a Supplementary Cementitious Material (SCM) in concrete production. However, its use has been constrained in the construction industry due to lack of a suitable largescale processing methodology of SCBA. In this study, the pozzolanic performance of SCBA produced using three different methodologies (i.e., uncontrolled burning, controlled burning, and post-processing of uncontrolled burning) was investigated. Experimental findings suggested that SCBA obtained from uncontrolled burning (raw SCBA) is not suitable for concrete application due to high carbon content. However, post-processing of raw SCBA yields a material with an adequate pozzolanic performance for concrete applications, which is comparable to SCBA produced under controlled burning conditions.

Implementation of self-healing concrete technologies is a promising approach to enhance the durability of the transportation infrastructure. Among these technologies, bacterial concrete has the potential to seal microcracks through microbial-induced calcite precipitation (MICP). To ensure the viability of this technology, bacterial protection is essential given concrete’s harsh environment. Additionally, the success of this technology depends on the presence of an adequate mineral precursor compound and nutrient for the bacteria. As such, the main objective of this study was to optimize the healing efficiency of bacterial concrete in subtropical climates through the vacuum impregnation of bacteria into a lightweight aggregate (LWA). To achieve this objective, mortar samples were prepared while incorporating different combinations of precursors (magnesium acetate, calcium lactate, and sodium lactate) and alkali-resistant healing agent Bacillus pseudofirmus bacteria (with and without). In addition, a control sample was prepared without bacteria or precursors for comparative purposes. For each sample, three mortar cubes and three mortar beams were cast and used to evaluate the compressive strength, crack healing efficiency, and flexural strength recovery. Additionally, the morphology of healing products was observed in bacteria-containing samples under scanning electron microscopy with energy x-ray dispersive spectroscopy using a scanning electron microscope (SEM) with EDAX Pegasus energy dispersive spectroscopy (EDS). Results showed that self-healing bacterial concrete could be optimized (without significant reduction in mechanical properties) if Bacillus pseudofirmus bacteria at a concentration of 10⁸ cells/ml and sodium lactate precursor at a concentration of 75 mM/l were impregnated into lightweight aggregate.

This study investigates the mechanical and physical properties of engineered geopolymer composites (EGCs) consisting of metakaolin (MK) based geopolymer (GP) binder, microsilica sand (MS) or river sand (RS), and polyvinyl alcohol (PVA) fiber. Plain GP matrices and fiber-reinforced composites were studied. Aspects of the material composition evaluated here included binder composition, aggregate type, and fiber content. Compressive strength test results revealed that GP mortars presented greater compressive strength than pure GP binders. Moreover, the addition of PVA fibers produced an important increment in compressive strength while increases in fiber content generally enhanced compressive strength. MS composites tended to produce higher compressive strength than RS composites. While exhibiting low densities (i.e., 1.80–1.94 g/cm³), the composite materials evaluated exceeded the compressive strength of regular concrete (i.e., 30 MPa). Furthermore, the best performing composite presented a compressive strength of 57.5 MPa, thus falling in the category of high-strength concrete. The EGC-like tensile pseudo strain-hardening (PSH) behavior of MK-based GP composites was confirmed by a uniaxial tensile test with MS-composites exhibiting greater tensile strength and ductility compared with RS composites; yet, robust PSH behavior was not achieved mainly because of a lack of proper fiber dispersion. Scanning electron microscopy (SEM) revealed unreacted metakaolin particles in some areas within the geopolymer gel of both GP binders evaluated in this study, suggesting incomplete geopolymerization in the binder. Furthermore, energy dispersive X-ray spectroscopy (EDS) microchemical analysis of a geopolymer gel encountered close agreement between the target composition of the GP binders produced and the actual chemical composition encountered in the specimens evaluated.