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Coupled FEM-microstructural X-ray examination of a controlled internal damage approach for concrete samples

Sidiq Amir, Robert Dilan, Gravina Rebecca, Giustozzi Filippo

Archives of Civil and Mechanical Engineering

2021

Vol. 21, no. 2

350--369

One of the critical factors that govern the technology of concrete self-healing evaluation at laboratory scale is the crack induction pattern within the concrete sample. Within the various techniques of inducing artificial cracks, such as the flexural testing or splitting testing methods, there are limitations of inducing the microcracks homogenously throughout the entire volume of the concrete sample. In this study, an innovative technique is utilised to induce the microcracks at a controlled damage level to further study the self-healing phenomena in concrete at the laboratory scale. By placing a concrete sample into an ad-hoc fabricated steel mould and applying fractional compressive strength, the axial-circumferential pressure induces microcracks in the concrete sample, homogenously. A Finite Element Model was also built to investigate the hypothesis on the cracking pattern at various damage levels; jointly, experimental work was conducted with X-ray µCT images to reconstruct the three-dimensional sections at the various damage levels. Qualitative analyses in relation to the two test methods were conducted. Furthermore, quantitative analyses on the individual-artificially generated-cracks were conducted in terms of the crack size crack geometry variation and the orientation of the newly formed cracks. Results revealed that the proposed crack-inducing methodology is highly efficient to induce uniform cracks in the sample, assisting for the evaluation of concrete self-healing process. The novel method can be adapted to identify the optimised strategies for enhancing the structural performance of concrete, thus facilitating the safe operation of concrete infrastructure.

Creep, shrinkage and permeation characteristics of geopolymer aggregate concrete: long-term performance

Seneviratne Charitha, Gunasekara Chamila, Law David W., Setunge Sujeeva, Robert Dilan

Archives of Civil and Mechanical Engineering

2020

Vol. 20, no. 4

633--647

The long-term impact on creep, drying shrinkage, and permeation characteristics of an innovative concrete produced with manufactured geopolymer coarse aggregate (GPA) has been investigated and compared with quarried Basalt aggregate concrete. Microstructure and pore-structure development up to 1 year were examined through scanning electron microscopy, nanoindentation, and X-ray computed tomography. Compressive strength and elastic modulus of GPA concrete varied from 34.6 to 50.8 and 18.5 to 20.5 GPa, respectively, between 28 and 365 days. The 1-year creep strain of GPA concrete was 747 microstrain while the calculated creep coefficient was 0.97, which is significantly lower than the creep coefficient predicted by AS 3600 and CEB-FIP models. Moreover, the 365-day drying shrinkage is 570 microstrain, which is also lower than the maximum permissible limit specified by AS3600. The GPA concrete displayed high water absorption, but lower air and water permeability compared to Basalt aggregate concrete. This is attributed to a porous surface layer with large number of capillaries increasing the water absorption of GPA concrete through capillary suction. The discontinuity in the pore network coupled with a condensed interfacial transition zone formed in GPA concrete could be the reason for lower permeability. Overall, the long-term performance of the GPA demonstrates a potential as a lightweight coarse aggregate for concrete, with the added advantage of reducing the environmental impact utilizing fly ash from coal-fired power generation.