This paper brings a new insight into understanding the influence of macrocapsules in packing systems, which can be useful in designing the inert structure of self-healing concrete. A variety of ...tubular macrocapsules, in terms of types and sizes, was used to assess the capsules' effect in the packing, together with various aggregate types and fractions. The voids ratios (
) of aggregate mixtures were evaluated experimentally and compared with the prediction via the particle packing model of Dewar. The packing of coarse particles was found to be considerably affected by the presence of macrocapsules, while no capsules' effect on the packing of fine particles was attained. A higher capsule dosage and capsule aspect ratio led to a higher voids ratio. In the formulation of the inert structure, the packing disturbance due to capsules can be minimised by increasing the content of fine aggregates over coarse aggregates. Dewar's model showed a good compatibility with experimental results in the absence of capsules. However, the model needed to be upgraded for the introduction of tubular macrocapsules. Accordingly, the effect of macrocapsules was extensively analysed and a '
model' for capsules (with some limitations) was finally proposed, offering a high predicting accuracy.
The use of macrocapsules in self-healing applications offers a potential benefit by carrying a larger amount of healing agent in comparison with microcapsules. However, the application of ...macrocapsules is still limited to paste and mortar levels on lab-scale. This is due to a concern that most capsules might be broken when mixed with concrete components. In this study, cementitious tubular capsules were used and they were considered as a partial replacement of coarse aggregates (2 vol% gravel). The capsules have a dimension of 54 mm and 9 mm in length and outer diameter, respectively. A water-repellent agent (WRA) was entrapped in the capsules as a proposed agent to seal the crack. Initial results revealed high survivability of capsules during concrete mixing: 100% survival ratio when tested in a drum mixer and 70–95% when tested in a planetary mixer. The mechanical and self-sealing properties of concrete containing embedded capsules were evaluated. With the addition of capsules, around 8% reduction of compressive strength was noticed, but no further effect on splitting tensile strength was detected as compared with concrete without capsules. Ultrasonic pulse velocity (UPV) tests confirmed that the presence of capsules also did not significantly affect the compactness of the hardened concrete. Furthermore, the embedded capsules were able to break when a crack was introduced and it was found that 90% sealing efficiency was achieved by capsule-based concrete as a result of the successful release of sealing agent into the crack.
