Key Engineering Materials Vol. 986

Abstract: Shotcrete and compressed air are often utilised for providing temporary support in tunnel excavation. On occasions of concurrent application of shotcrete and compressed air, there would be concerns of the quality of concrete sprayed within pressurised space, as well as the strength development of shotcrete in pressurised environment. To address these concerns, field experimentation of the shotcrete strength development under compressed air pressure was conducted, and the results are reported in this paper.

Abstract: This research investigated the influence of phosphogypsum (PG) addition to mortar mixture and determined the possibility of utilizing PG in soil stabilization. Originally, the chemical composition and mineralogy of the PG were determined using X-ray fluorescence (XRF) and X-ray diffraction (XRD) tests. The principal constituent of PG becomes calcium sulfate hemihydrate with the presence of some impurities. A total of 9 mixes have been developed: A plain mortar mix is a comparative base, and the other 4 mixes are with 5, 10, 15, and 20 % cement replacement with PG for each type (fresh and stockpiled PG called PGF and PGS, respectively). The experimental program focuses on analyzing the effects of PG on setting time, hardened density, compressive strength, and water expansion of mortar mixtures before its soil stabilization application. Test results indicate that with higher PG, the setting time of the mortar mix is delayed except for the mixture with 20% PG, which experienced an early false set. The results of the compressive strength tests revealed that the 5% PG mixes exhibited higher values compared to the control mix, starting from the 28-day curing period, regardless of PG type. Although the higher PG content and compressive strength lowered, the expansion levels were very low based on the ASTM C 1260 limits for all mixtures, excluding heaving risks.

Abstract: Concrete-filled steel tubes (CFSTs) have better application in the application of beams and columns. This application form has obvious advantages, mainly because they are not restricted by the forming process, and the filled concrete does not need long-term maintenance. However, the design and analysis of steel-concrete beam-columns is a complex task involving many factors. In the design of CFSTs, it is essential to understand the influence of these factors on the behavior of steel-concrete members. In particular, the cross-sectional shape of the member has a significant impact on its bearing capacity, stiffness, and buckling behavior. However, there is relatively little research on the influence of member slenderness on the strength of CFSTs. Therefore, this study conducted an in-depth analysis of the stability of the member, and explored in detail the influence of the member slenderness ratio on the section properties and the overall bending strength of the beam. This study provides a basis for the application of CFSTs in beam-column design and analysis. In the bending strength analysis, the member slenderness ratio has an important influence. Smaller slenderness ratios have better strength performance, but the attenuation is also relatively significant. The larger the slenderness ratio, the slower and more stable the strength change becomes. In terms of section properties, when the slender section is reached, the influence of effective section reduction will be greater, and the strength reduction may exceed the engineering allowable error range. Therefore, special attention should be paid when using slender sections.

Abstract: This study is to propose time-variant probabilistic models of surface chloride and diffusion coefficient based on the survey data of 16 concrete bridge decks with the attack of de-icing salts. These models are developed, because there is no study that simultaneously considers both time-variance and probabilistic descriptors in the model for concrete bridge decks. From the study, it can be found that long-term surface chloride and its time-variant development are fitted with Log-normal and Weibull distributions, respectively. In addition, the 28-day diffusion coefficient and age factor are fitted with Log-logistic and Triangular distributions, respectively. Considering only the mean value in the models, the corrosion-free residual life of concrete bridge decks is equal to 18.3 years based on the target value of critical chloride of 1.2 kg/m³, whereas their cracking-free residual life is equal to 29.5 years based on the target value of critical chloride of 2.0 kg/m3. In comparison with the probabilistic analysis, it was nevertheless found that at year 18.3, there are 38% and 20% probabilities to have rebar corrosion and concrete cracking, respectively. However, at year 29.5, there are 63% and 42% probabilities to have rebar corrosion and concrete. Specifically, there are 6 and almost 7 out of 16 bridge locations having rebar corrosion in the year 18.3 and concrete cracking in the year 29.5, respectively.

Abstract: Angle steel is commonly used in inclined bracing components such as transmission towers. Due to its inherent section characteristics, unequal angle steel undergoes angular rotation when subjected to eccentric axial pressure, resulting in a change in the direction of action along the X and Y axes. In comparison to equal angle steel, the analysis of unequal angle steel is more complex. In design, particular attention should be given to whether the angle steel section is compact or noncompact, with a significant emphasis on the impact of the width-to-thickness ratio on strength. In study analyzed nine different angle steel sections, revealing that two of them exhibit a phenomenon known as control point transfer. This is especially prone to occur with shorter lengths of angle steel components, leading to Leg Local Buckling. In contrast, longer components are more susceptible to Lateral-Torsional Buckling. Summarizing the research findings, it is recommended to exercise caution when using non-compact section angle steel in design, and a preference for compact sections is advised to ensure the safety of the structure. Furthermore, it is advised to pay attention to the parameter β_w in the AISC unequal angle steel calculation formula and adhere to relevant specifications to enhance the accuracy and reliability of structural design.

Abstract: This study extensively investigates T-shaped axial compression members with varying wing-flange width-to-thickness ratios, focusing primarily on the influence of section width-to-thickness ratio and effective width on the sectional resistance. Based on the AISC 2017 specifications, assuming the overall component is a stable member, the study analyzes the impact of varying the wing-flange width-to-thickness ratio on the sectional stability and resistance of the structure. Especially for slender sections that exceed the width-to-thickness ratio limits specified in AISC 2017, it is necessary to consider the sectional resistance affected by local buckling. Therefore, the concept of reduced section is proposed - effective width constraint, which accurately reflects the actual resistance of the component. As the T-shaped section is a singly symmetric profile, a detailed analysis will be conducted on flexural buckling (FB) and flexural-torsional buckling (FTB) under various wing-flange width-to-thickness ratio conditions. Through the analysis of these two buckling behaviors, a more comprehensive understanding of the stability and resistance of T-shaped section members under different wing-flange width-to-thickness ratio conditions can be achieved. This study contributes to the understanding of the stability and cross-sectional solid of T-shaped members, providing insights for the design analysis of AISC2017-specified T-shaped section components. Particularly, it focuses on research related to section width-to-thickness ratio, slender section considerations, and sectional resistance. Further research is conducted on the issue of reduced resistance due to excessively slender cross-sections. This not only aids in better understanding the resistance of cross-sections but also provides practical design references. Therefore, this study holds research value regarding the analysis of the width-to-thickness ratio design for T-sections in the AISC 2017 specification, particularly when considering factors related to slender sections and cross-sectional resistance.

Abstract: The author analyzed technological solutions for the production of blocks from soil cement. It is proposed to make soil cement blocks from portland cement brand 400 in the amount of 20 % of the mass of soil and water. Experimental addition of fly ash to the solution in different amounts depending on the cement content. It is proposed to add ash removed from the Darnytsya thermal power plant, which was sifted through a 4 mm sieve, because the ash contains a significant amount of impurities. The content of inclusions from 1 to 4 mm was up to 40 %. It is proposed to make blocks from soil cement with the addition of fly ash with the aim of improving the thermotechnical properties. It is proposed to make soil-cement blocks with two voids. To ensure high-quality compaction of products in forms, the moisture content of the content for most soils should be within 14–23 %. The maximum force that the sample can withstand was taken as a destructive load. It was decided that the use of fly ash as part of the mixture in the production of soil cement gives a positive effect. With an increase in the period of exposure of samples in water to 90 days, the average compressive strength of soil cement samples without additives and with the addition of the appropriate percentage of fly ash increases.

Abstract: This study aims to explore the correlation between the dimensions of concrete specimens and their compressive strength. In the field of engineering, it is essential to determine concrete strength. Besides the standard cylindrical compressive strength test, core samples are often required for compressive strength testing to verify the quality of concrete. However, coring requires significant time and energy, and the number of available samples is limited. Some projects may not be suitable for coring, necessitating the use of non-destructive testing methods to assess in-situ concrete strength. This research project aims to investigate the correspondence between various specimen sizes and the compressive strength of concrete, establishing corresponding curves for compressive strength of concrete core specimens of different sizes. The results of this research reveal that smaller specimen sizes tend to exhibit slightly higher compressive strength, provided that the concrete mixture is well-blended, and the specimen diameter and the proportion of the largest coarse aggregate nominal diameter comply with specifications. Regardless of specimen size, representative compressive strength values can be obtained. In lower-strength concrete specimens, the quality control aspects have a more substantial influence on compressive strength than specimen size effects.