The fracture process in reinforced concrete structures is complicated because it is associated with the development of both micro cracks and major cracks. The fracture behavior is also connected to other phenomena including strain localization and crack bridging and depends on the heterogeneity of concrete, the type of reinforcement, and the concrete and reinforcement properties. The purpose of this study is to investigate the mode I crack propagation in reinforced concrete using Digital Image Correlation (DIC). DIC is a robust, non-contact and precise tool for fracture measurements. Digital images are taken at different loading stages and by comparing the images it is possible to infer the deformation of an object subjected to external loads. In this paper, the relationship between the fracture properties and the properties of the concrete and steel reinforcement is investigated experimentally. Tests were performed on small-scale reinforced concrete specimens in three point bending. By means of the DIC technique the visualization and quantification of the fracture properties of reinforced concrete could be determined. The DIC technique was found to be an effective mean to measure the crack opening displacements.

Relatively few fracture-oriented experimental studies have been conducted on concrete that is reinforced. An experimental investigation was therefore undertaken to explore the cracking process in lightly reinforced concrete (RC) beams and to observe the details of the localised fracture process zone development. More specifically, the aims were to investigate the relationships between beam height (120 mm, 220 mm and 320 mm), steel reinforcement ratio (0.1%-0.5%), ductility and the onset of crack branching. RC beams were tested in three-point bending and experimental surface strains and crack openings were inferred using digital image correlation (DIC). It was found that the presence of the reinforcement prevented premature fracture and led to crack branching where a single crack bifurcated in the region of the compression zone. In the larger beams the branching developed at a lower relative height and a greater reinforcement ratio led to a shallower branching angle. These observations were associated with ductility measures for lightly reinforced concrete beams.

Minimum reinforcement ratios are specified for reinforced concrete structures to provide enough ductility. The aims are to control cracking in the serviceability limit state and to prevent sudden failure by ensuring sufficient ductility after the loss of tensile stress in concrete due to cracking. This can provide a warning before collapse and time to take preventive or remedial measures. A review of past research reveals that there are large variations, and sometimes contradictions, in proposed minimum reinforcement requirements for flexural members. In this paper, a fracture mechanics-based model is used to study different local phenomena such as tensile and compressive concrete softening to more precisely describe the behaviour of reinforced concrete beams. The findings show a decrease in the minimum reinforcement ratio with increasing beam size. This contradicts the provisions of prevailing codes and standards which suggest no change in the minimum reinforcement ratio with size. Therefore, there is a need to review the minimum reinforcement provisions.

There is an opportunity to revisit and generalise classical theories for concrete cracking in light of increased interest in the use of non-conventional reinforcing materials and material efficiency. Fracture-based models to describe concrete cracking have potential but a limitation has been that many variables and different phenomena have to be incorporated to produce realistic material models. In this paper, an integrated fracture-based model (IFBM) is developed to predict the behaviour of lightly reinforced concrete beams. The proposed model is a closed-form solution that integrates different local phenomena to more precisely describe the onset of cracking, crack propagation and crack rotation. The IFBM incorporates post-cracking tensile stresses in the concrete, the bond-slip behaviour between the reinforcement and concrete, and compression softening in the concrete compressive zone. The model can predict parameters such as the crack length development and crack mouth opening displacement in Mode I lightly reinforced concrete flexural specimens subjected to three-point bending. The predictions show a fairly good agreement with experimental results for small-scale reinforced concrete beams with low reinforcement ratios (0.15-0.5%). The ability of the IFBM to identify specific failure modes and to capture the crack propagation and crack rotation stages of behaviour in lightly reinforced concrete beams are particular advantages. Such an approach provides a powerful tool to study the problem of minimum reinforcement requirements.

Presenting a promising option that could be used to encapsulate nuclear waste material for disposal, supersulfated cement (SSC) is, again, receiving wide attention among research community as a cementitious system that has noteworthy properties. It is also an environmentally friendly cement since it is mainly composed of ground granulated blast furnace slag (GGBS) that is activated by a sulphate source such as gypsum, hemihydrate or anhydrite. Although there is some research on SSC, little research work has focused on modelling the effects of the various parameters using a statistical approach which is the aim of this paper. The effect of dosages of GGBS, anhydrite (ANH) and water-to-binder ratio (W/B) on the fresh and rheological parameters, induced bleeding, permeability, compressibility, and compressive strength of supersulfated grouts was investigated. Then, statistical models and isoresponse curves were developed to capture the significant trends of the tested parameters using factorial design approach. The models suggested that that W/B had significantly higher influence on most of the parameters tested while the influence of GGBS and ANH and their interactions varied depending on the parameter in question. . The findings of this study show the importance of understanding the role of and optimising the relevant key factors in producing SSC fit-for-purpose. The statistical models developed in this paper can facilitate optimizing the mixture proportions of grouts for target performance by reducing the number of trial batches needed.