Effect of coarse aggregate size and matrix quality on ITZ and failure behavior of concrete under uniaxial compression

Effects of coarse aggregate size and water/cement (w/c) ratio of the matrix on the formation of interfacial transition zone (ITZ) and subsequently on the failure process of concrete under uniaxial compression were studied. For this purpose, a series of experiments were designed and carried out on mortars with two different w/c ratios containing single spherical steel aggregates of different sizes. The ITZ properties and the failure process of concrete were investigated through tensile strength tests both before and after compressive preloading, stress-axial strain, stress volumetric strain and stress-lateral strain measurements. It was observed that ITZ becomes critical for larger aggregates and lower w/c ratio mortar matrices. The negative effect of smooth surface texture of the aggregate and the large difference between aggregate and matrix moduli of elasticity on the properties of ITZ is of paramount importance for low w/c ratio composites. The effect of reduced bond properties of ITZ relative to its matrix was reflected in the lower critical stress levels for the low w/c ratio composites with larger aggregates

Effect of coarse aggregate size on interfacial cracking under uniaxial compression

The effects of aggregate type and size are important parameters in the formation of interfacial transition zone (ITZ) structure and subsequently in the failure process of concrete. The influence of surface, rigidity and size of aggregates and water/cement (w/c) ratio of the matrix on bond strength at the ITZ and the interrelationship between the bond and the matrix in the failure process of concrete under uniaxial compression were studied. For this purpose a series of experiments were designed and carried out on mortars (with two different w/c ratios) containing single spherical steel aggregates. The ITZ properties and the failure process of concrete were investigated by means of tensile and compressive strength, and stress-volumetric strain measurements. It was observed that the effect of aggregate properties (high modulus of elasticity, smooth surface texture and size) on the weakness of ITZ and the failure process of concrete are of paramount importance for low w/c ratio composites. The effect of reduced bond properties was reflected in lowered critical stress levels for the low w/c ratio composites with larger aggregates

Assessing the ITZ microcracking via scanning electron microscope and its effect on the failure behavior of concrete

The influence of aggregate size and water-to-cement (w/c) ratio of the matrix on the structure of interfacial transition zone (ITZ) and the interaction between the ITZ and the matrix on the failure process of concrete under uniaxial compression were studied. The ITZ microcracking and the failure process of concrete were investigated experimentally by means of compressive and indirect tensile testing, stress-volumetric strain measurements and microscopic analyses on the model concrete containing single spherical steel aggregate with three different w/c ratios. At low w/c ratios, the rigid and smooth surface texture aggregates made by the ITZ have a significant structural difference compared to the mortar. This was more pronounced for larger aggregates. Higher structural differences between the mortar matrix and ITZ in low w/c ratio composites resulted in accelerated ITZ microcracking at high stress level. The effect of condensed microcracking in a narrower ITZ was reflected in the lower critical stress levels for the low w/c ratio composites with larger aggregates

Teaching systems thinking through game design

In this mixed-methods study, we examined if students benefitted from a game design course offered during an enrichment hour in terms of gains in their system analysis and design skills. Students at a rural middle school in Southeast US (n = 19) attended a 1-hour game design course offered weekly during an academic enrichment class period, for the duration of a school year, learning basics of digital game-design and practicing system design skills such as making flowcharts. The results of quasi-experimental data indicated that the treatment group’s pretest–posttest system analysis and design skills, compared to the control group, which did not receive any training, further improved, F(1,33) = 16.516, p \u3c 0.001. Results from the interviews showed that the participants were able to verbalize how they applied system analysis and design skills developed during the course to problem-solving in different contexts. We discussed the instructional aspects of learning game-design that align with systems thinking. We also explored the possible influence of initial cognitive skills on student learning outcomes from such interventions

Body mass index and complications following major gastrointestinal surgery: a prospective, international cohort study and meta-analysis.

AIM: Previous studies reported conflicting evidence on the effects of obesity on outcomes after gastrointestinal surgery. The aims of this study were to explore the relationship of obesity with major postoperative complications in an international cohort and to present a meta-analysis of all available prospective data. METHODS: This prospective, multicentre study included adults undergoing both elective and emergency gastrointestinal resection, reversal of stoma or formation of stoma. The primary end-point was 30-day major complications (Clavien-Dindo Grades III-V). A systematic search was undertaken for studies assessing the relationship between obesity and major complications after gastrointestinal surgery. Individual patient meta-analysis was used to analyse pooled results. RESULTS: This study included 2519 patients across 127 centres, of whom 560 (22.2%) were obese. Unadjusted major complication rates were lower in obese vs normal weight patients (13.0% vs 16.2%, respectively), but this did not reach statistical significance (P = 0.863) on multivariate analysis for patients having surgery for either malignant or benign conditions. Individual patient meta-analysis demonstrated that obese patients undergoing surgery for malignancy were at increased risk of major complications (OR 2.10, 95% CI 1.49-2.96, P < 0.001), whereas obese patients undergoing surgery for benign indications were at decreased risk (OR 0.59, 95% CI 0.46-0.75, P < 0.001) compared to normal weight patients. CONCLUSIONS: In our international data, obesity was not found to be associated with major complications following gastrointestinal surgery. Meta-analysis of available prospective data made a novel finding of obesity being associated with different outcomes depending on whether patients were undergoing surgery for benign or malignant disease