Effect of silica fume substitution by limestone powder and cement kiln dust on the shrinkage, durability, and sustainability of UHPC.

Silica fume is usually used in UHPC, three times more than that for normal concrete, to enhance mechanical properties and durability. However, silica fume (SF) is an expensive material and has high production costs. This work is aimed at investigating the shrinkage and durability performance of previously developed UHPC mixtures utilizing the two calcareous waste materials, namely limestone powder (LSP) and cement kiln dust (CKD), by partially replacing the silica fume. The optimally selected mixtures of UHPC, having flow and strength above the minimum required, were used for detailed investigation in terms of shrinkage and durability characteristics. The results showed that by replacing SF with up to 20% of LSP and up to 20% of CKD, the mechanical properties of UHPC remained satisfactory compared to the control mixture with 100% SF. However, the ultimate shrinkage was higher for mixtures incorporating LSP or CKD, indicating the need for more volume of steel fibers to compensate for the shrinkage strains. The developed UHPCs also exhibited high resistance against reinforcement corrosion and sulfate attack, making them suitable for use in aggressive exposure conditions. However, special attention needs to be paid to the CKD content, where it is recommended to limit the content of CKD to about 15% or less to control the durability performance of the UHPCs. In addition, the sustainability analysis of developed UHPC mixtures was carried out using the life-cycle assessment and eco-strength intensity index. The results indicated that the UHPC mixtures possess a higher life-cycle and are therefore more sustainable.

A universal hydro-mechanical coupled behavior model for clay-bearing strata-Molecular-level simulation approach.

Clay minerals in soils and rocks exhibit large volume change upon interaction with water and this behavior becomes even more complex when the strata are being stressed by the engineering and environmental loads. Therefore, a realistic prediction of the hydro-mechanical behavior of the clay-bearing strata is always a challenge due to their coupled swelling-mechanical response in the cases of geotechnical and geoenvironmental engineering problems, nuclear waste storage in clay-bearing rock repositories, shale gas extraction, and other uses of clay in the manufacturing industry. All the existing behavior models have restricted applications in the engineering and other fields of practice mainly due to the partial consideration of the structure and fabric of clay-bearing strata in the model formulation. In this study, a hydro-mechanical behavior model has been formulated using the parameters acquired from the molecular-level simulations and modeling of the volume change and stress-strain behavior of the clay-bearing structure. The Molecular Mechanics and Molecular Dynamic simulations were performed on the natural structure of the clay-bearing strata formulated using Monte Carlo technique. The mathematical model, developed from the simulation results, can predict the overall hydro-mechanical behavior of clay-bearing strata for all possible combinations of clay minerals, non-clay minerals, salts causing cementation of the soil/rock structure, confining pressures, and the induced strain levels. The developed model has successfully been validated through laboratory and field testing on the clay-bearing strata in both the elastic and elasto-plastic regions of the stress-strain behavior and also from the data of two (02) swelling clays (MX-80 and FEBEX Bentonite) from the existing literature, supporting the universal nature of the developed behavior model.

Investigating the Soil Unconfined Compressive Strength Based on Laser-Induced Breakdown Spectroscopy Emission Intensities and Machine Learning Techniques.

Laser-induced breakdown spectroscopy (LIBS) is a remarkable elemental identification and quantification technique used in multiple sectors, including science, engineering, and medicine. Machine learning techniques have recently sparked widespread interest in the development of calibration-free LIBS due to their ability to generate a defined pattern for complex systems. In geotechnical engineering, understanding soil mechanics in relation to the applications is of paramount importance. The knowledge of soil unconfined compressive strength (UCS) enables engineers to identify the behaviors of a particular soil and propose effective solutions to given geotechnical problems. However, the experimental techniques involved in the measurements of soil UCS are incredibly expensive and time-consuming. In this work, we develop a pioneering technique to estimate the soil unconfined compressive strength using artificial intelligent methods based on the spectra obtained from the LIBS system. Decision tree regression (DTR) and support vector regression learners were initially employed, and consequently, the adaptive boosting method was applied to improve the performance of the two single learners. The prediction power of the established models was determined using the standard performance evaluation metrics such as the root-mean-square error, CC between the predicted and actual soil UCS values, mean absolute error, and R2 score. Our results revealed that the boosted DTR exhibited the highest coefficient of correlation of 99.52% and an R2 value of 99.03% during the testing phase. To validate the models, the UCS values of soils stabilized with lime and cement were predicted with an optimum degree of accuracy, confirming the models' suitability and generalization strength for soil UCS investigations.

Characterization and Applications of Red Mud, an Aluminum Industry Waste Material, in the Construction and Building Industries, as well as Catalysis.

The disposal of red mud (RM), a waste material generated by the aluminum industry, remains a global environmental concern because of its high alkalinity and smaller particle size, which have the potential to pollute air, soil, and water. Recently, efforts have been made to develop a strategy for reusing industrial byproducts, such as RM, and turning waste into value-added products. The use of RM as (i) a supplementary cementitious material for construction and building materials, such as cement, concrete, bricks, ceramics, and geopolymers, and (ii) a catalyst is discussed in this review. Furthermore, the physical, chemical, mineralogical, structural, and thermal properties of RM, as well as its environmental impact, are also discussed in this review. It is possible to conclude that using RM in catalysis, cement, and construction industries is the most efficient way to recycle this byproduct on a large scale. However, the low cementitious properties of RM can be attributed to a reduction in the fresh and mechanical properties of composites incorporating RM. On the other hand, RM can be used as an efficient active catalyst to synthesize organic molecules and reduce air pollution, which not only makes use of solid waste but also lowers the price of the catalyst. The review provides basic information on the characterization of RM and its suitability in various applications, paving the way for more advanced research on the sustainable disposal of RM waste. Future research perspectives on the utilization of RM are also addressed.

Optimum design and performance of a base-isolated structure with tuned mass negative stiffness inerter damper.

In order to increase the efficiency of the structures to resist seismic excitation, combinations of inerter, negative stiffness, and tuned mass damper are used. In the present work, the optimum tuning frequency ratio and damping of the tuned mass negative stiffness damper-inerter (TMNSDI) for the base-isolated structure were determined by employing the numerical searching technique under filtered white-noise earthquake excitation and stationary white noise. The energy dissipation index, the absolute acceleration, and the relative displacement of the isolated structure were considered as the optimum parameters, obtained by their maximization. Evaluations of base-isolated structures with and without TMNSDI under non-stationary seismic excitations were investigated. The efficiency of the optimally designed TMNSDI for isolated flexible structures in controlling seismic responses (pulse-type, and real earthquakes) were evaluated in terms of acceleration and displacement. A dynamic system was used for deriving the tuning frequency and tuned mass negative stiffness damper inerter (TMNSDI) for white noise excitation by using explicit formulae of the curve fitting method. The proposed empirical expressions, for design of base-isolated structures with supplementary TMNSDI, showed lesser error. Fragility curve results and story drift ratio indicate reduction in seismic response by 40% and 70% in base-isolated structure using TMNSDI.

Synthesis of waste limestone powder-based alkali-activated binder: experimental, optimization modeling, and eco-efficiency assessment.

More than half of the CO2 emissions during the manufacturing of ordinary Portland cement (OPC) occur due to the calcination of calcium carbonate in addition to burning of fossil fuel to power the process. Consequently, there is a concerted effort to decrease the carbon footprint associated with this process, by minimizing the use of OPC. In line with this trend, an attempt was made in the reported study to synthesize a novel alkali-activated binder using CaCO3-rich waste limestone powder (WLSP) as a precursor. Utilizing the Taguchi method, four important parameters were varied at three levels to optimize the alkali-activated mixture. Analysis of variance (ANOVA) of the obtained results was performed to assess the impact of each of the factors on the properties of the developed binder. To enhance the strength further, OPC was added as a partial replacement of WLSP. The binder was characterized using scanning electron microscopy. The results have indicated that alkaline activator to binder ratio, Na2SiO3 to NaOH ratio, and sand to binder ratio of 0.575, 1.57, and 2.5, respectively, were the optimum to obtain satisfactory strength and workability with a 13.7-M NaOH activator solution. The incorporation of a small quantity of OPC in the mixture remarkably improved the density and strength of the alkali-activated-WLSP binder. Pirssonite (CaCO3.Na2CO3.2H2O) and C/N-A-S-H were the dominant mineral phases formed in the developed binder, particularly in the ones alkali-activated WLSP/OPC. In addition, the eco-efficiency assessment revealed that the WLSP is a promising low-carbon binder that can be used in developing more sustainable alkali-activated binder. The results have shown that the WLSP can be potentially utilized in developing binder that can be potentially used in the structural applications.

Engineered and green natural pozzolan-nano silica-based alkali-activated concrete: shrinkage characteristics and life cycle assessment.

Alkali-activated concrete (AAC) or binders (AABs) have emerged as a substitute to conventional ordinary Portland cement (OPC)-based concrete owing to their techno-ecological merits. Saudi Arabia has vast resources of natural pozzolan whose impact on some fresh and hardened properties was encouraging; however, the long-term shrinkage behavior of AABs and life cycle assessment (LCA) of the developed product is yet to be explored. Therefore, this study evaluates shrinkage characteristics and LCA of Saudi natural pozzolan (NP)-based AAC. The synergistic impact of admixing nano-silica (NS) up to 7.5% dosage was also observed on the properties of engineered AABs in comparison with OPC-based concrete. The shrinkage properties were correlated with the microstructure and pore structure. The study revealed that the shrinkage properties of both NP-based AABs and OPC-based concrete are comparable. However, adding NS increased the drying shrinkage strain because of the finer pore structure than AABs without NS, which was confirmed through nuclear magnetic resonance (NMR). The maximum average drying shrinkage strain of 510 µÎµ was recorded in the OPC concrete, whereas in the engineered AAC with 0, 1, 2.5, 5, and 7.5% NS, it was 486, 537, 568, 601, and 651 µÎµ, respectively. It is postulated that the NP can be beneficially valorized in the production of green AABs without compromising the shrinkage characteristics, while the NS is favorable for enhancing the strength and refinement of the pore matrix. Besides, the LCA indicated the feasibility of recycling the high volume of natural waste by AAB technology, which significantly lowers the carbon footprints and minimizes the environmental implications in infrastructural applications.

Evaluating Rutting Resistance of Rejuvenated Recycled Hot-Mix Asphalt Mixtures Using Different Types of Recycling Agents.

Growing environmental pollution worldwide is mostly caused by the accumulation of different types of liquid and solid wastes. Therefore, policies in developed countries seek to support the concept of waste recycling due to its significant impact on the environmental footprint. Hot-mix asphalt mixtures (HMA) with reclaimed asphalt pavement (RAP) have shown great performance under rutting. However, incorporating a high percentage of RAP (>25%) is a challenging issue due to the increased stiffness of the resulting mixture. The stiffness problem is resolved by employing different types of commercial and noncommercial rejuvenators. In this study, three types of noncommercial rejuvenators (waste cooking oil (WCO), waste engine oil (WEO), and date seed oil (DSO)) were used, in addition to one type of commercial rejuvenator. Three percentages of RAP (20%, 40%, and 60%) were utilized. Mixing proportions for the noncommercial additives were set as 0−10% for mixtures with 20% RAP, 12.5−17.5% for mixtures with 40% RAP, and 17.5−20% for mixtures with 60% RAP. In addition, mixing proportions for the commercial additive were set as 0.5−1.0% for mixtures with 20% RAP, 1.0−1.5% for mixtures with 40% RAP, and 1.5−2.0% for mixtures with 60% RAP. The rutting performance of the generated mixtures was indicated first by using the rutting index (G*/sin δ) for the combined binders and then evaluated using the Hamburg wheel-track test. The results showed that the rejuvenated mixtures with the commercial additive at 20 and 60% RAP performed well compared to the control mixture, whereas the rejuvenated ones at 40% RAP performed well with noncommercial additives in comparison to the control mixture. Furthermore, the optimum percentages for each type of the used additives were obtained, depending on their respective performance, as 10%, 12.5%, and 17.5% of WCO, 10%, 12.5−17.5%, and 17.5% of WEO, <10%, 12.5%, and 17.5% of DSO, and 0.5−1.0%, 1.0%, and 1.5−2.0% of the commercial rejuvenator, corresponding to the three adopted percentages of RAP.

Analysis of Unconfined Compressive Strength of Rammed Earth Mixes Based on Artificial Neural Network and Statistical Analysis.

Earth materials have been used in construction as safe, healthy and environmentally sustainable. It is often challenging to develop an optimum soil mix because of the significant variations in soil properties from one soil to another. The current study analyzed the soil properties, including the grain size distribution, Atterberg limits, compaction characteristics, etc., using multilinear regression (MLR) and artificial neural networks (ANN). Data collected from previous studies (i.e., 488 cases) for stabilized (with either cement or lime) and unstabilized soils were considered and analyzed. Missing data were estimated by correlations reported in previous studies. Then, different ANNs were designed (trained and validated) using Levenberg-Marquardt (L-M) algorithms. Using the MLR, several models were developed to estimate the compressive strength of both unstabilized and stabilized soils with a Pearson Coefficient of Correlation (R2) equal to 0.2227 and 0.766, respectively. On the other hand, developed ANNs gave a higher value for R2 than MLR (with the highest value achieved at 0.9883). Thereafter, an experimental program was carried out to validate the results achieved in this study. Finally, a sensitivity analysis was carried out using the resulting networks to assess the effect of different soil properties on the unconfined compressive strength (UCS). Moreover, suitable recommendations for earth materials mixes were presented.

Finite Element Modelling of Corrosion-Damaged RC Beams Strengthened Using the UHPC Layers.

This paper describes a study on finite element modeling (FEM) carried out on the ABAQUS platform for the prediction of flexural strength of corrosion-damaged reinforced concrete (RC) beams strengthened using layers of ultra-high-performance concrete (UHPC). Considering different combinations of the degree of reinforcement corrosion and thickness and configuration of UHPC layers, a total of twenty-two corroded, un-strengthened, and strengthened RC beam specimens were tested to record their flexural behavior. Following the flexural testing, the FEM was carried out considering the degradation in the diameter and the yielding strength of the corroded reinforcing bars. The cohesive surface bonding approach was used to simulate the interfacial bond stress slip between the corroded bars and surrounding concrete. The results of the FEM were validated using the experimental test results of the respective beam specimens. The FEM results (including crack pattern, flexural strength, stiffness, and linear and nonlinear behavior of the strengthened RC beams) were found to be in close agreement with the corresponding experimental test results. This indicates that the proposed FEMs can capture the flexural behavior of the corroded RC beams strengthened using layers of UHPC with high accuracy. Furthermore, a parametric study was carried out using the validated FEMs to investigate the effects of varying the compressive strength and thickness of UHPC layers on the flexural strength of the corroded strengthened RC beams.

Finite Element Analysis of Rubberized Concrete Interlocking Masonry under Vertical Loading.

Fine aggregate and cement have been partially replaced by 10% and 56% crumb rubber and class F-fly ash, respectively, in order to manufacture rubberized concrete interlocking bricks (RCIBs). The newly developed product has been used for masonry construction without the need for mortar (mortarless), and the experimental testing under compression load was investigated by Al-Fakih et al. Therefore, in line with that, this study carried out finite element (FE) analysis for experimental result validation of masonry walls and prisms made of RCIBs. ANSYS software was utilized to implement the FE analysis, and a plasticity detailed micro-modeling approach was adopted. Parametric studies were carried out on masonry prisms to investigate the effect of the slenderness ratio and the elastic modulus of grout on the prism behavior. The results found that the adopted FE model has the ability to predict the structural response, such as compressive strength, stiffness, and failure mechanism, of the interlocking masonry prisms with about a 90% agreement with the experimental results. Based on the parametric studies, the compressive strength for a 6-course prism is approximately 68% less than a 3-course prism and 60% less than a 5-course prism, which means that the slenderness ratio plays a vital role in the behavior of the RCIB masonry prism under the vertical compression load. Moreover, the results showed that the difference between FE and experimental results of the walls was less than 16%, indicating a good match. The findings also reported that masonry walls and prisms experienced higher ductility measured by the post-failure loading under compression. The finite element model can be used for further investigation of masonry systems built with rubberized concrete interlocking bricks.