An approach to develop printable strain hardening cementitious composites

New additive manufacturing methods for cementitious materials hold a high potential to increase automation in the construction industry. However, these methods require new materials to be developed that meet performance requirements related to specific characteristics of the manufacturing process. The appropriate characterization methods of these materials are still a matter of debate. This study proposes a rheology investigation to systematically develop a printable strain hardening cementitious composite mix design. Two known mixtures were employed and the influence of several parameters, such as the water-to-solid ratio, fibre volume percentage and employment of chemical admixtures, were investigated using a ram extruder and Benbow-Bridgwater equation. Through printing trials, rheology parameters as the initial bulk and shear yield stress were correlated with variables commonly employed to assess printing quality of cementitious materials. The rheology properties measured were used to predict the number of layers a developed mixture could support. Selected mixtures had their mechanical performance assessed through four-point bending, uni-axial tensile and compressive strength tests, to confirm that strain hardening behaviour was obtained. It was concluded that the presented experimental and theoretical framework are promising tools, as the bulk yield stress seems to predict buildability, while shear yield stress may indicate a threshold for pumpability

Validation of self-healing properties of construction materials through nondestructive and minimal invasive testing

When studying the self-healing properties of construction materials, a plethora of destructive and nondestructive testing (NDT) techniques can be used. In this review, the applicability of different nondestructive test methods is discussed in detail. The methods can be categorized whether they are used to study the encapsulation and/or protection mechanism of the healing agent, the sequestered healing agent itself, the distribution of healing agents, the trigger mechanism for healing, the healing efficiency, or healing performance. Based on this categorization, nondestructive techniques found in literature are discussed. In this way, a robust understanding of the different techniques can be used for future research on self-healing construction materials