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• A lab-scale optical microscopy technique was developed for loaded crack measurement. • Resolution achieved 0.3 µm by optical scan and photogrammetric analyses. • Conventional DIC was found to overestimate crack width for subpixel cracks. • The proposed technique may combine with DIC for accurate and holistic crack measurement. Concrete cracks accelerate the ingress of harmful species and must be gauged accurately for durability evaluation and prediction. As a novel class of ultra-ductile concrete, Engineered Cementitious Composites (ECC) develops multiple sub-hairline cracks that are difficult to visualize using conventional techniques. In this study, a semi in-situ laboratory approach is proposed based on optical microscopy and photogrammetric analysis to enhance the accuracy of crack width measurement in ECC. Microscopic images scanned from the material surface were reconstructed and analyzed to extract the statistics of crack width, location, number, and spacing. Results suggested that general portable microscopes can effectively identify cracks smaller than 2 µm in loaded condition and provide magnified high-resolution crack images that are hardly achieved by regular digital cameras. Crack openings can be isolated via 2D FFT filtering and binarized to attain the datasets of crack spacing and crack width distribution. In contrast to microscopy, conventional digital image correlation (DIC) as an indirect method was found to overestimate sub-pixel crack widths particularly when the crack width and spacing are substantially smaller than the image resolution. In these scenarios, it is recommended to combine optical microscopy with DIC to ensure simultaneously accurate and holistic crack width characterization. The proposed technique can be used for general materials with multiple fine cracks. [ABSTRACT FROM AUTHOR]

The production of cement mortar has resulted in significant environmental issues. Many scientists have attempted to reduce environmental pollution by using agricultural waste as a substitute for mortar raw materials. This study creatively investigated the physical and mechanical properties of the new green cement mortar made from macadamia nutshell(MN), including compressive strength, flexural strength, and apparent density of 7d, 14d, and 28d. The effects of cement-sand ratio (c/s), nutshell particle size, and MN substitution rate on cement mortar's physical properties were studied using three-factor and three-level orthogonal test design methods. The digital image correlation (DIC) technique was used to analyze the crack development of macadamia nutshell cement mortar (MNM) at different loading stages. The analysis of variance (ANOVA) showed that the cement-sand ratio was the most significant factor affecting the strength of MNM. In addition, adding MN can increase the compressive strength of the mortar compared to the control group. The apparent density of the mortar decreases with the increase of MN addition. • The influence of adding varying particle sizes of the nutshell on the strength of mortar was studied. • The density and flexural strength of mortar decreased with the increase of macadamia nutshell addition. • Macadamia nutshell could be used as an eco-friendly supplementary natural aggregate material. [ABSTRACT FROM AUTHOR]

The indirect design method for concrete pipes, which estimates the bearing capacity of concrete pipes in a buried environment based on the D-load determined from a three-edge bearing test (TEBT), is a common method for designing concrete pipes. D-load is determined by the load corresponding to the first 3-mm crack, which has been used from the 1930s until today. To explore the potential of modern laboratory techniques as an alternative to the traditional vision method. This study discusses the application and cost-effectiveness of several technologies for detecting D-load, including strain gauges, displacement sensors, acoustic emission, digital image correlation, and infrared thermography, based on TEBT on full-scale double-cage reinforced concrete pipes with internal diameters of 1000, 1500, and 2000 mm. The consistency between D-load values obtained by these approaches along with the predicted value by Heger's model is compared with the D 0.3_visual determined by conventional visual observation in terms of the developed relative reliability. It is found that the method based on acoustic emission techniques is more consistent with the D 0.3_visual than others, but is costly and time-consuming. Also, D e , identified by the load corresponding to the end of the elastic phase of the force–time curve, is a reliable alternative and cost-effective method. This study will provide new insights into the aspect of performance design and evaluation for concrete pipes. • Modern laboratory methods are used to attempt to identify the D-Load of concrete pipes. • The D-load values obtained by the new methods were compared with that from the traditional method. • The cost-effectiveness and reliability of the new methods are discussed. [ABSTRACT FROM AUTHOR]