Accurately measuring the working stress of concrete through the stress release method is a crucial foundation for assessing the operational condition of building structures and formulating maintenance and reinforcement strategies. The slotting method, employed within the stress release technique, not only addresses the limitations associated with the core drilling and hole drilling methods but also offers a practical solution for engineering detection. This paper presents a novel multi-step slotting method employing a stress release rate model as its foundation. The fundamental equations governing space-related issues are introduced, and a theoretical model of the stress release rate is derived. By employing a multi-step slotting process instead of the conventional one-step slotting approach, the limitations of the traditional drilling method are overcome. The stress release rate model is calibrated using numerical simulation outcomes, followed by both numerical simulation and experimental verification. With a relative error of 3.5% between theoretical and simulated values, and 9.4% with experimental values after excluding the initial slotting data, it is evident that the stress release rate model demonstrates notable accuracy and applicability. This reaffirms the effectiveness and convenience of the multi-step slotting method for measuring concrete working stress.

To study the damage characteristics and failure mechanism of reinforced concrete damaged beams under cyclic load, the load-strain curve and stiffness degradation curve of reinforced concrete (RC) beams strengthened by adding stirrup, longitudinal reinforcement, and high ductile concrete (HDC) under repeated load were compared, as well as the flexural ability before and after strengthened. The results show that: compared with the original beam, the strengthened method with longitudinal strengthened at the bottom of the beam has the most obvious improvement in the flexural capacity of the beam. When the longitudinal strengthened is added, the flexural capacity can be increased by 86.25%. According to the actual failure mode of the reinforced beam, the stress reduction coefficient and height reduction coefficient are theoretically derived, and the bending capacity of the reinforced beam under each strengthened method is calculated. The theoretical value is in good agreement with the test value.

Ultra-high-performance concrete (UHPC) is considered a sophisticated concrete construction solution for infrastructure and other structures because of its premium mechanical traits and superior durability. Fibers have a special effect on the properties of UHPC, especially as this type of concrete suffers from high autogenous shrinkage due to its high cementitious content, so the properties and volume fraction of fibers are more important in UHPC. This study will describe previous related works on the mechanical behavior of UHPC specimens reinforced with micro- and nanoscale fibers, and compare of the behavior of UHPC reinforced with microfibers to that reinforced with nanofibers. The compressive strength, flexural behavior, and durability aspects of UHPC reinforced with nanoand/or microscale variable types of fibers were studied to highlight the issues and make a new direction for other authors.

Inconsistencies in standards and codes result in confusion, increased costs, and do not promote the efficient use of concrete. In addition to inconsistencies, the lack of science-based approaches and data used for defining criteria in these standards and codes can limit the reliability and trust of these requirements. A review of industry documents indicates that inconsistencies and lack of science-based approaches exist across many documents, both throughout the industry and within ACI, relating to the corrosion of steel reinforcement embedded in concrete. This paper proposes to address five key issues to promote science-based standardization of requirements necessary for reinforced concrete systems exposed to corrosive conditions. These five issues include the need for: 1) standardization of chloride testing methods and requirements; 2) standardization of chloride reporting units; 3) standardization of terminology for specifying chlorides in cementitious systems; 4) standardization of exposure classifications for corrosive conditions; and 5) standardization of allowable chloride limits. This paper presents current inconsistencies in guide documents and codes for each of the items listed previously and then proposes an approach to standardize each using either available data and/ or a scientifically based approach. Recommendations for testing, reporting, definition of exposure classifications, and allowable chloride limits are then proposed. It is hoped that the systematic approach used herein will lead to standardization and consistency, less confusion, and will promote the efficient use of durable and economical concrete.

A reliable compressive stress-strain model was established for concrete with varying densities reinforced with either steel fibers alone, or a combination of steel fibers and micro-synthetic fibers. Moreover, a simple equation was presented to determine the compressive toughness index of fiber-reinforced concrete in a straightforward manner. The fiber reinforcing index was introduced to explain the effect of various parameter conditions of fibers on the enhancement of the concrete properties under compression. Numerical and regression analyses were performed to derive equations to determine the key parameter associated with the slope at the pre- and post-peak branches and compressive toughness index through extensive parametric studies. The proposed models are promising tools to accurately predict the stress-strain relationships of fiber-reinforced concrete with different densities, resulting in less-scattered values between experiments and predictions, and reasonably assess the efficiency of fiber reinforcements in enhancing the compressive response of concrete.