Red-bed mudstone from civil excavation is often treated as waste due to its poor water stability and tendency to disintegrate. This study proposes a sustainable approach for its utilization in controlled low-strength material (CLSM) by blending it with cement and water. Laboratory tests evaluated the fresh properties (i.e., flowability, bleeding rate, setting time, and subsidence rate) and hardened properties (i.e., compressive strength, drying shrinkage, and wet-dry durability) of the CLSM. The analysis focused on two main parameters: cement-to-soil ratio (C/S) and water-to-solid ratio (W/S). The results show that increasing W/S significantly improves flowability, while increasing C/S also contributes positively. Flowability decreased exponentially over time, with an approximately 30% loss recorded after 3 h. Bleeding and subsidence rates rose sharply with higher W/S but were only marginally affected by C/S. To meet performance requirements, W/S should be kept below 52%. In addition, the setting times remained within 24 h for all mixtures tested. Compressive strength showed a negative correlation with W/S and a positive correlation with C/S. When C/S ranged from 8% to 16% and W/S from 44% to 56%, the compressive strengths ranged from 0.3 MPa to 1.22 MPa, meeting typical backfilling needs. Drying shrinkage was correlated positively with water loss, and it decreased with greater C/S. Notably, cement's addition significantly enhanced water stability. At a C/S of 12%, the specimens remained intact after 13 wet-dry cycles, retaining over 80% of their initial strength. Based on these findings, predictive models for strength and flowability were developed, and a mix design procedure was proposed. This resulted in two optimized proportions suitable for confined backfilling. This study provides a scientific basis for the resource-oriented reuse of red-bed mudstone in civil engineering projects.

Using precast concrete pipes to develop sewage water transportation systems is important for keeping hygienic, safe, and sustainable urban environments. This study reviews the state-of-the-art knowledge of the manufacturing processes, materials, curing regimes, design philosophies, laboratory and field tests, and various standards for assessing the quality of precast concrete pipes. Data from various sources such as research publications, technical reports, dissertations, and standards code provisions were gathered and presented in tabular/ graphical form to analyze the critical factors that affect concrete pipe behavior. The manufacturing process was found to be an important factor that affects the quality of precast concrete pipes. A review of past failures of pipes showed that cracking, deterioration of concrete, and erosion or voids in concrete pipes were due to biogenic sulfuric acid attack. A comparison of the indirect design and direct design methods for precast concrete pipes was conducted, proving the advantages of the direct design method over the century-old indirect design method. Closed-form equations were presented for the complete distribution of internal forces, i.e., bending moments, shear forces, and thrust forces over the circumference of the pipe. Various challenges including the development of laboratory and field quality assessment tests, and a widely accepted standard of precast concrete pipes were also highlighted. Despite its importance, the field performance of precast concrete pipes was explored in a dearth of previous studies due to its costly procedures. Therefore, long-term monitoring of buried concrete pipes is needed to enhance the understanding of their complex behavior, accounting for the changing soil-pipe interaction, erosion of soil, and deterioration of concrete and steel over time. This study should assist infrastructure stakeholders and operation managers in making informed decisions regarding the choice of materials, design methods, manufacturing, and curing techniques to overcome catastrophic pipe failures and incidents, leading to a safe and sustainable environment and mitigating financial losses due to pipe failures.

This paper describes the relevant research activities that are being carried out on the development of a novel shotcrete technology capable of applying, autonomously and in real time, fibre reinforced shotcrete (FRS) with tailored properties regarding the optimum structural strengthening of railway tunnels (RT). This technique allows to apply fibre reinforced concrete (FRC) of strain softening (SSFRC) and strain hardening (SHFRC) according to a multi -level advanced numerical simulation that considers the relevant nonlinear features of these FRC, as well as their interaction with the surrounding soil, for an intended strengthening performance of the RT. Building information modelling (BIM) is used for assisting on the development of data files of the involved design software, integrating geometric assessment of a RT, damages from inspection and diagnosis, and the characteristics of the FRS strengthening solution. A dedicated computational tool was developed to design FRC with target properties. The preliminary experimental results on the evaluation of the relevant mechanical properties of the FRS are presented and discussed, as well as the experimental tests on the bond between FRS and current substrates found in RT. Representative numerical simulations were performed to demonstrate the structural performance of the proposed FRS -based strengthening technique. Computational tools capable of assuring, in real time, the aimed thickness of the layers forming the FRS strengthening shell were also developed. The first generation of a mechanical device for controlling the amount of fibres to be added, in real time, to the FRS mixture was conceived, built and tested. A mechanism is also being developed to improve the fibre distribution during its introduction through the mechanical device to avoid fibre balling. This work describes the relevant achievements already attained, as introduces the planned future initiatives in the scope of this project.

Tailings volumes continue to collectively increase worldwide, leading to larger dams and tailings management facilities. With numerous high-profile dam failures in the past decade, the risks of these management practices are also growing. A potential shift to waste management practices at mineral mines is to commingle waste rock and dewatered tailings. This blended material should have superior physical strength properties provided by the waste rock together with improved chemical stability characteristics associated with the low permeability of the tailings. Ideally, commingled tailings and waste rock can be used to construct various mined earth landforms that are both physically and chemically stable, which will enhance operational performance and ultimately provide for the sustainable decommissioning and closure of the mining facility. To study these materials, the University of Alberta Geotechnical Centre is working with global industry partners to test commingled materials from several mine sites with varying ore and host rock types and climate regimes. The first stage of this study is described here and is focused on the optimum density, saturated hydraulic conductivity, and soil-water characteristic curves of various blend ratios, performed at laboratory scale.