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 improve the added application value of an industrial waste stone powder (SP), the optimizing mechanism of SP for the structure and composition of hydrothermal synthetic hardened cement stone was investigated in this paper. Cement was partially replaced by SP, silica fume (SF), or ground-granulated blast-furnace slag (GGBS), and then the microstructure with different SP content was tested through X-ray diffraction, thermogravimetric analysis (TG-DTG), mercury intrusion porosimetry (MIP), and scanning electronic microscopy. The findings indicate that the incorporation of SP in autoclaved products significantly enhanced compressive and flexural strengths. As the proportion of SP in cement was increased, a corresponding increase in the content of tobermorite within autoclaved cement mortar was observed. This increase in tobermorite concentration results in an initial rise followed by a subsequent decline in both compressive and flexural strengths. The maximum compressive and flexural strengths were achieved at an SP content of 15%. In addition, the mechanical strength was further improved by adding SP+GGBS or SP+SF. The strengthening mechanism of SP reveals that the change in the ratio of calcium and silicon ions (C/S) caused by SP in the sample was conducive to the formation of tobermorite and strength increase. Meanwhile, an increase in the quantity and a decrease in the crystal size of tobermorite were observed with an increase in the content of stone powder, resulting in a more compact microstructure of the sample. Moreover, the mechanical strength of cement composites doping SP+GGBS or SP+SF was further improved through superposition effects of SP and GGBS or SF with high activity. Currently, it is mainly applied to pipe pile products, and the strengthening effect of SP increases its use value. Meanwhile, the study of SP strengthening mechanism has laid a theoretical foundation for its application in high-strength autoclave and improved the relevant theory.

Concrete mixture design is the foundation of cement and concrete research. Innovations in concrete materials could, should, and would inevitably be incorporated into new mixture designs. Thus, a rigorous method for concrete mixture design can better bridge the research community and the construction industry with high reliability and high fidelity. However, current methods for concrete mixture design vary a lot in the literature, thus compromising the accuracy and consistency in interpreting the properties of concrete subject to changes in its raw ingredients. Moreover, the extraneous variables in controlled experiments are not always controlled well. To solve this old but critical problem, this paper summarizes the prevalent concrete mixture design methods in the literature and in practice. By contrast, the volume-based mixture design method is superior to the mass ratio-based mixture design method in terms of simplicity, accuracy, and consistency. Further discussion on packing density measurement and water or slurry film thickness (SFT) as a basis of volume-based mixture design is elaborated. Mathematically, the hardened properties were linked to the particle packing behavior and fresh properties of concrete. This research contributes to a unified volume-based design method to bridge the research community and the construction industry. In the end, it is conducive to upgrading from concrete technology to science.

A new mixture proportioning method is developed for performance-based concrete with supplementary cementitious materials (SCMs). The method is based on the thermodynamic calculations of the properties for concrete and identifying the mixtures that satisfy a predefined set of performance criteria. This new approach considers the chemical composition and reactivity of SCMs while proportioning concrete mixtures. Performance criteria examples are shown for a bridge deck (corrosion and freezing-and-thawing damage), an unreinforced pavement (salt damage), and a foundation (moderate sulfate and alkali-aggregate reaction). The method is used to proportion concrete mixtures satisfying these three performance criteria using four ashes per mixture. Experiments show that these mixtures met the targets. The proposed approach can proportion mixtures that are optimized for predefined performance using a wide range of SCMs, which can be useful in reducing the cost and carbon footprint of concrete.

The appropriate and efficient design of structural components made with ultra-high-performance concrete (UHPC) requires the establishment of key design properties and material models that engage UHPC’s distinct mechanical properties, as compared to conventional concrete. This paper presents the results of an extensive program of compression and tension property assessment executed according to existing testing methods to assess the mechanical characteristics of several commercially available UHPC products. The experimental results are then used to propose suitable mechanical models and design parameters that are foundational for the structural-level application of UHPC. The models rely on a set of experimentally identified mechanical performance properties that distinguish UHPC from conventional concrete and establish the basis of the material qualification for use in structural design. As such, this work constitutes a fundamental step in ongoing efforts to develop UHPC structural design guidance in the United States.