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.
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.
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.
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