Manufactured sand differs from natural sea and river dredged sand in its physical and mineralogical properties. These can be both beneficial and detrimental to the fresh and hardened properties of concrete. This paper presents the results of a laboratory study in which manufactured sand produced in an industry sized crushing plant was characterised with respect to its physical and mineralogical properties. The influence of these characteristics on concrete workability and strength, when manufactured sand completely replaced natural sand in concrete, was investigated and modelled using artificial neural networks (ANN). The results show that the manufactured sand concrete made in this study generally requires a higher water/cement (w/c) ratio for workability equal to that of natural sand concrete due to the higher angularity of the manufactured sand particles. Water reducing admixtures can be used to compensate for this if the manufactured sand does not contain clay particles. At the same w/c ratio, the compressive and flexural strength of manufactured sand concrete exceeds that of natural sand concrete. ANN proved a valuable and reliable method of predicting concrete strength and workability based on the properties of the fine aggregate (FA) and the concrete mix composition.

This paper presents a new form of biomimetic cementitious material, which employs 3D-printed tetrahedral mini-vascular networks (MVNs) to store and deliver healing agents to damage sites within cementitious matrices. The MVNs are required to not only protect the healing agent for a sufficient period of time but also survive the mixing process, release the healing agent when the cementitious matrix is damaged, and have minimal impact on the physical and mechanical properties of the host cementitious matrix. A systematic study is described which fulfilled these design requirements and determined the most appropriate form and material for the MVNs. A subsequent series of experiments showed that MVNs filled with sodium silicate, embedded in concrete specimens, are able to respond effectively to damage, behave as a perfusable vascular system and thus act as healing agent reservoirs that are available for multiple damage-healing events. It was also proved that healing agents encapsulated within these MVNs can be transported to cracked zones in concrete elements under capillary driving action, and produce a recovery of strength, stiffness and fracture energy.

Microbially induced carbonate precipitation (MICP) is increasingly being explored as a potential ground improvement mechanism, both for improved mechanical performance and groundwater control. However, the formation of a brittle cemented monolith will produce structures susceptible to chemical or physical deterioration over time, requiring potentially costly maintenance in the future. We present a demonstration of the potential for a simple and durable self-healing mechanism to be incorporated within the MICP process that allows the monolith to automatically respond to and heal damage. By selecting a bacterium capable of both causing MICP and surviving long periods and harsh conditions as a spore, it is demonstrated that such an organism can be entombed within calcium carbonate precipitates of its own making, survive in a senescent state, and ultimately germinate upon damage to the encapsulating precipitate matrix. The organism is then capable of producing further calcium carbonate to heal the damage. It has further been shown that this mechanism can be used to initially cement a mass of sand, survive damage and deterioration, and respond to restore the functionality of the stabilized mass, exhibiting the potential for such a system to provide “smart” autonomous stabilized soil structures that offer enhanced durability and reduced maintenance.

The success of self-healing cementitious materials relies on their ability to repeatedly heal over the lifetime of the material. Vascular networks have a distinct advantage over other self-healing techniques whereby the healing agent in the network can be routinely replenished. The aim of this study was to develop a multiuse vascular network that can be reused over the lifetime of a structure to enable repeated self-healing events in cementitious materials. The feasibility and self-healing efficacy of novel two-dimensional (2D) vascular networks in concrete beams were tested on laboratory-scale specimens before being trialed in situ on larger, structural-scale elements. The vascular networks were formed via linear interconnecting hollow channels filled with a healing agent that is delivered to zones of damage under an externally supplied pressure. This technique was reproducible at large scale and channels were refilled over a test period of 6 months. Of the two healing agents used in this study, sodium silicate (SS) proved easier to handle and supply into the vascular network, but cyanoacrylate (CA) offered greater strength recovery (up to 90%) in a relatively short time scale. The presence of flow networks in the cover concrete tended to act as a crack initiator and this was particularly evident in the larger-scale specimens. Nevertheless, the potential to enhance and enable multiscale healing in cementitious materials has been demonstrated.

Capillary flow through discrete cracks is the main mechanism by which healing agents embedded in cementitious matrices travel to zones of damage to afford the host matrix a healing ability. However, the nature of the interaction between the healing agents in their fluid state and the host matrix is unknown and may limit the ability to predict the behavior and efficacy of self-healing systems. This study considered the capillary flow characteristics of a low-viscosity cyanoacrylate and ground granulated blast furnace slag in a water suspension using glass capillaries and channels formed from a range of concrete mixes. Both healing agents conformed closely to Poiseuille’s law and experienced increases in viscosity over the 40-min period that they were exposed to a cementitious environment. Numerical simulations of the capillary rise response of the healing agents in a discrete crack confirmed that the rate of damage and degree of saturation of the concrete element have a significant influence on the choice of healing agent in the design of self-healing systems.

Property owners are facing increasing threats from flooding and in response are likely to turn to products designed to waterproof or ‘seal’ the outside of the building in an effort to prevent the...