Experimental Program Research Articles

Effect of Guar Gum Content on the Mechanical Properties of Laterite Soil for Subgrade Soil Application.

Using biopolymers for soil stabilization is favorable compared to more conventional methods because they are more environmentally friendly, cost-effective, and long-lasting. This study analyzes the physical properties of guar gum and laterite soil mixes. A comprehensive engineering study of guar gum-treated soil was conducted with the help of a brief experimental program. This study examined the effects of soil-guar gum interactions on the strengthening behavior of guar gum-treated soil mixtures using a series of laboratory tests. The treated laterite soil's dry density increased marginally, while its optimum moisture content decreased as the guar gum increased. Treatment with guar gum significantly enhanced the strength of laterite soil mixtures. For laterite soil with 2% guar gum, the unsoaked CBR increased by 148% and the soaked CBR increased by 192.36%. The cohesiveness and internal friction angle increased by 93.33% and 31.52%, respectively. These results show that using guar gum dramatically improves the strength of laterite soil, offering a more environmentally friendly and sustainable alternative to traditional soil additives. Using guar gum in T8 subgrade soil requires a 1395 mm pavement depth and costs INR 3.83 crores, 1.52 times more than laterite soil. For T9 subgrade soil, the depth was 1495 mm, costing INR 4.42 crores, 1.72 times more than laterite soil. This study introduces a novel approach to soil stabilization by employing guar gum, a biopolymer, to enhance the physical and mechanical properties of laterite soil. Furthermore, this study provides a detailed cost-benefit analysis for pavement applications, revealing the financial feasibility of using guar gum despite it requiring a marginally higher initial investment.

An Experimental Investigation Replicating the Surface Behavior of Ground Steel Gears in Mixed Lubrication Using Twin-Disk Testing Part 1: Running-in

ABSTRACT The surface of ground gear teeth is changed during the initial period of operation through a process termed running-in. During this process asperity peaks are plastically deformed and removed to better distribute the load across the surface, resulting in modification of the surface finish. In this work the influence of pressure, slide-roll ratio, and entrainment velocity on two-dimensional surface roughness parameters is evaluated through the running-in process using a full-factorial experimental programme. Hardened steel disks are used to simulate gear tooth contacts via the use of a twin-disk rig. Results showed that all three variables strongly influence the change in surface geometry, both individually and through both two- and three-factor interactions.

Impact of virgin and recycled polymer fibers on the rheological properties of cemented paste backfill

The addition of polymer fibers to cemented paste backfill (CPB) has shown promise in enhancing mechanical properties, although it also introduces changes in rheological characteristics. This study aimed to investigate the influence of different types of polymer fibers, namely virgin commercial polypropylene fiber (CPPF), recycled tire polymer fiber (RTPF), and recycled tire rubber fiber (RF), on the rheological properties of CPB mixtures through an experimental program, and provide design references for CPB pipeline transport. The results revealed consistent reductions in bulk density upon the incorporation of polymer fibers into CPB, alongside varying impacts on slump. Specifically, the addition of CPPF had a mild effect, while RTPF caused a continuous decrease in slump, and RF exhibited minimal influence up to a 4% concentration, with substantial effects thereafter. Moreover, the inclusion of fibers led to increases in apparent viscosity parameters, with RTPF inducing the most significant changes, followed by varying responses from CPPF and RF. When using RTPF for CPB reinforcement, emphasis should be placed on enhancing technical indicators related to viscosity such as energy consumption and pipeline wear during pipeline transport. Furthermore, adjustments were necessary to account for flow curve instability resulting from interactions between fibers and the paddle, with the data aligning well with the Bingham model. The addition of fibers, particularly CPPF and RF, primarily influenced plastic viscosity rather than yield stress, underscoring the limitations of slump tests in assessing rheology.

Study on the Yield Surface of a Fibre-Reinforced Stabilised Soil – Effect of the Number of Loading Cycles

Cyclic loading may induce changes in the geomechanical behaviour of materials that should be characterised. This work studies the impact of the number of loading cycles on the mechanical behaviour of a fibre-reinforced stabilised soil focusing on its behaviour before failure (yield surface). To this end, an experimental testing program based on triaxial tests was performed on samples not subjected to a cycling loading stage, as well as on samples previously subjected to a cycling loading stage varying the number of loading cycles from 1,000 to 100,000. The results were studied in terms of the accumulated permanent axial strain and the yield surface of the composite material. It was observed that increasing the number of loading cycles led to a rise in the accumulated permanent axial strain and in the undrained resilient modulus. The results also showed an expansion of the yield surface during the first 1,000 loading cycles (the yield occurs later due to the partial mobilization of the tensile strength of the fibres during the cyclic stage) but its shape is maintained. The results also showed a progressive reduction in the yield loci with the increase in the number of loading cycles, reflecting the greater degradation of the solid matrix induced by the accumulated permanent axial strains.

Experimental Program of the HL-LHC Inner Triplet String Test at CERN

Experimental Program of the HL-LHC Inner Triplet String Test at CERN

Predicting the compressive strength of engineered geopolymer composites using automated machine learning

Engineered Geopolymer Composites (EGC) offer a sustainable and high-performance alternative to traditional concrete and Engineered Cementitious Composites, boasting reduced environmental impact and enhanced mechanical properties. However, optimising EGC mix design for specific applications requires an accurate prediction of its compressive strength. This study investigates the application of Automated Machine Learning using the PyCaret library to develop reliable predictive models for EGC compressive strength. A comprehensive experimental program was conducted, testing 132 EGC specimens with varying mix design parameters, including binder ratio, silica fume content, activator ratio, water content, superplasticizer dosage, and curing method. The collected data was used to train and evaluate twenty different machine learning models. Model performance was assessed using various metrics. The top six models were shortlisted and optimised using Random Search algorithm. The models were assessed through a detailed analysis of their residual plots and learning curves. Additionally, Feature importance and SHAP analysis were employed to understand the influence of each input parameter on the predicted compressive strength. The results demonstrate the effectiveness of AML in accurately predicting EGC compressive strength, with the Gradient Boosting Regressor and CatBoost Regressor models exhibiting superior performance, achieving Mean Absolute Error (MAE) below 1.2 MPa and R² exceeding 0.96. The study highlights the potential of AML as a valuable tool for optimising EGC mix design and promoting the wider adoption of this sustainable construction material.

Horizontal shear behavior of self-compacting lightweight concrete composite beams with dry joints and unbonded reinforcements

This study aims to investigate the horizontal shear behavior of self-compacting lightweight concrete (SCLC) composite beams with dry joints and unbonded transverse reinforcement. For this, the experimental program included different concrete types, joints configurations, and the use of unbonded high-strength bars with varying levels of prestressing and transverse reinforcement ratios in composite beams. Two precast beams were fabricated using a match-cast method and integrated horizontally to form composite beams, utilizing unbonded transverse reinforcements. The composite beams incorporating lightweight aggregates (LWA) instead of normal weight aggregates (NWA) exhibited a decreased ultimate shear strength of 19.5 %; however, the addition of steel fibers into the mixtures mitigated this decrease, resulting in a 22.8 % increase in strength compared to mixture without steel fibers. The vertical prestressing level significantly influenced the horizontal shear behavior and failure mode of composite beams, with adequately prestressed composite beams exhibiting similar ductile behaviors to the monolithic beam. Composite beams with keyed joints exhibited higher horizontal shear strength, up to 65.3 % more than the beam with flat joint, attributed to the interlock provided by the shear keys. Increased slip between two precast beams activated the dowel action of unbonded reinforcements, effectively resisting horizontal shear. Predictions of the horizontal shear strength, as per current codes, were compared to the experimental results. The results indicate that the design approach in Eurocode 2 provides reasonable estimations of the strengths of composite beams with dry joints and unbonded reinforcements.

Shear strengthening of self-compacting lightweight concrete beams with steel fibers and unbonded prestressing bars

This study aims to investigate the shear behavior of self-compacting lightweight concrete (SCLC) beams strengthened with steel fibers and unbonded prestressing bars. For this, the experimental program included the use of hooked-end steel fibers with volume fractions of 0.5 %−0.75 %, and high-strength prestressing bars with varying prestressing forces and transverse reinforcement ratios. The addition of steel fibers in SCLC significantly increased the normalized shear capacity of beams, reaching up to 2.50 times higher values, whereas the substitution of normal coarse aggregates with lightweight aggregate resulted in a decrease of up to 10.1 %. The shear strengthening of SCLC beams with unbonded prestressing bars provided a substantial increase in the ultimate shear capacity up to 2.06 times higher than that of beam without reinforcement. Increasing the prestressing force of bars effectively restrained the occurrence of critical shear cracking, consequently enhancing the shear capacity. Utilizing hybrid reinforcement with fibers and prestressing bars resulted in a transition of failure mode from shear to flexural, attributed to the improved shear capacity. For the SCLC beams reinforced with steel fibers, the shear strengths were predicted by previous prediction models. When modifier for lightweight concrete was considered, the Imam’s model most precisely predicted the shear strengths with an average vu/vn ratio of 1.00 and SD of 0.07. The fib model Code, based on the modified compression field theory, provided accurate predictions for the shear capacities of SCLC beams with unbonded prestressing bars, exhibiting an average Vu/Vn ratio of 1.00 and SD of 0.09. The fiber-resisting component was reasonably considered in the model with an average Vu/Vn ratio of 1.02 and SD of 0.07.

Tests, simulations and web crippling design of S690 and S960 high strength steel unlipped channel sections under end-one-flange loading

This paper presents experimental and numerical investigations into the web crippling behaviour and structural design of high strength steel unlipped channel sections under end-one-flange loading. An experimental programme including six grade S690 and four grade S960 steel test specimens was firstly carried out, and the corresponding test set-up, procedures and results were reported. The web crippling test results were subsequently used in a finite element programme to validate developed finite element models, which were then adopted to perform parametric studies to cover wider parameter ranges of the bearing length, web slenderness and inside bend radius. It is found that the ultimate web crippling strength of high strength steel unlipped channel sections increases with increasing bearing length but decreasing web slenderness and inside bend radius. Considering that relevant codified design provisions are absent, the design rules of normal strength steel unlipped channel sections, as prescribed in EN 1993-1-3, EN 1993-1-5 and AISI S100, were assessed for their suitability to high strength steel unlipped channel sections. The codified design methods provide inaccurate and scattered resistance predictions for high strength steel unlipped channel sections under end-one-flange loading. Thus, an improved AISI S100 design method and a novel slenderness-based design method were proposed, which can outperform the codified design methods.

Dematerialization of Concrete: Meta-Analysis of Lightweight Expanded Clay Concrete for Compressive Strength

The construction industry is responsible for a significant share of global material consumption, including natural resources. Therefore, the United Nations Sustainable Development Goal 12.2 on sustainable management and efficient use of natural resources cannot be achieved without significant advances and contributions from the construction sector. Furthermore, various materials used by the construction industry contribute to the development and expansion of the LEED (Leadership in Energy and Environmental Design) system. LECA (Light Expanded Clay Aggregate) is one such material that enhances LEED performance through its key benefits, including lightness, thermal insulation, sound insulation, and fire resistance. One of the most effective methods for reducing the weight of concrete is the incorporation of lightweight aggregates, and the advantages of LECA include lessening loads and enabling reduced cross-sections, directly improving the sustainability of the built environment via reduced materials consumption. This study aims to develop a prediction model for the compressive strength of LECA-incorporated concrete through a meta-analysis. More than 140 data points were compiled through literature via 15 separate studies, and results were analyzed to conduct the meta-analysis. Moreover, an experimental program was carried out to verify the model and evaluate its accuracy in predicting compressive strength. Results from the developed model and the experimental program were in accordance with concrete having lower compressive strengths compared to those at high strength values. Likewise, more accurate results were obtained for concrete mixes that have w/b ratios of 0.5 or higher. Concrete mixes that have higher amounts of LECA by volume of concrete yielded more accurate results when using the prediction model. A sensitivity analysis was carried out to quantify the impact of several parameters on the compressive strength of LECA concrete.

An Experimental Investigation Replicating the Surface Behavior of Ground Steel Gears in Mixed Lubrication Using Twin-Disk Testing Part 2: Micropitting

Tooth surfaces in heavily loaded power-transmission gearing can often suffer from surface fatigue on the surface roughness scale, known as micropitting. In this paper, the influence of three variables (pressure, slide-roll ratio, and entrainment velocity) on micropitting is investigated using a full-factorial experimental program using a twin-disk test rig. The results showed that pressure was most influential on micropitting growth during the latter phases of the test, with slide-roll ratio being a more important factor during micropit initiation. The full-factorial nature of these tests allowed two- and three-factor effects to be investigated, demonstrating that micropitting is a complex phenomenon influenced by a network of interconnected effects.

Performance assessment of alko-amine corrosion inhibitors for use as an admixture in reinforced concrete structures: Experimental investigation and mechanism of action

Corrosion in reinforced concrete (RC) is a major issue in the construction industry, giving rise to structural failure, huge repair costs, and safety concerns. To mitigate RC corrosion, chemical corrosion inhibitors (CCI) are commonly used. This study aims to investigate the performance of different alko-amine CCIs for corrosion control in reinforced concrete (RC) structures subjected to chloride-rich conditions. The experimental program was divided into two levels: investigations comprised of quick testing on bare rebars, suitable for industries, and analysis which comprised of electrochemical investigation in simulated concrete pore solution and testing on rebar embedded in concrete, suitable for research labs. The interaction between inhibitors and steel was examined through surface analytical techniques such as AFM and XPS. Finally, the inhibition mechanism for the CCI was proposed. The alko-amines were found to show a strong dependence on their molecular structure for the formed film integrity. Monoethanolamine (MEA) and methyl ethanolamine (MeEA) formed a denser and more uniform film compared to dimethyl ethanolamine (DMeEA) and ethyl monoethanolamine (EMEA). MeEA showed the highest inhibition efficiency in both simulated pore solution environments and when used as an admixture in RC.

Utilization of High-Performance Concrete Mixtures for Advanced Manufacturing Technologies

The presented experimental program focuses on the design of high-performance dry concrete mixtures, which could find application in advanced manufacturing technologies, for example, additive solutions. The combination of high-performance concrete (HPC) with advanced or additive technologies provides new possibilities for constructing architecturally attractive buildings with high material requirements. The purpose of this study was to develop a dry mixture made from high-performance concrete that could be distributed directly in advanced or additive technologies of solutions in pre-prepared condition with all input materials (except for water) in order to reduce both financial and labor costs. This research specifically aimed to improve the basic strength characteristics—including mechanical (assessed using compressive strength, tensile splitting strength, and flexural strength tests) and durability properties (assessed using tests of resistance to frost, water, and defrosting chemicals)—of hardened mixtures, with partial insight into the rheology of fresh mixtures (consistency as assessed using the slump-flow test). Additionally, the load-bearing capacity of the selected mixtures in the form of specimens with concrete reinforcement was tested using a three-point bending test. A reference mixture with two liquid plasticizers—the first based on polycarboxylate and polyphosphonate and the second based on polyether carboxylate—was modified using a powdered plasticizer based on the polymerization product Glycol to create a dry mixture; the reference mixture was compared with the developed mixtures with respect to the above-mentioned properties. In general, the results show that the replacement of the aforementioned liquid plasticizers by a powdered plasticizer based on the polymerization product Glycol in the given mixtures is effective up to 5% (of the cement content) with regard to the mechanical and durability properties. The presented work provides an overview of the compared characteristics, which will serve as a basis for future research into the development of additive manufacturing technologies in the conditions of the Czech Republic while respecting the principles of sustainable construction.

Evaluating shear capacity in reinforced concrete deep beams with web openings strengthened using fiber-reinforced polymer and fiber-reinforced cementitious matrix

This research systematically compares the effectiveness of Carbon Fiber-Reinforced Polymer (FRP) and Fabric-Reinforced Cementitious Matrix (FRCM) in shear strengthening of reinforced concrete (RC) deep beams featuring web openings. Through a comprehensive experimental program, six RC beams were subjected to shear tests, considering variations in the number of layers for both FRCM and FRP, employing a U-wrapping configuration. Recorded parameters include load-deflection curves, ultimate strength, cracking patterns, failure modes, and strains in steel bars, allowing a comprehensive comparison between strengthened and un-strengthened RC beams. The study compares observed shear strengths from experiments with shear capacities predicted by proposed models for RC beams strengthened with FRCM and FRP, following codes such as ACI 440.2R-17, CSA S806-12, Eurocode 2, and ACI 549.4R-20. Increasing layers enhanced shear strengths and post-elastic stiffness. The presence of substantial openings led to early shear cracks and reduced strength. CFRP improved shear strength by 13.99% (1-layer) and 18.12% (2-layer), while FRCM strengthened layers by 20.2% (1 layer) and 29.3% (2 layers). FRCM outperformed in strength and stiffness, while FRP excelled in ductility and concrete confinement. Experimental and calculated results varied based on ACI, CSA, and Eurocode, with ACI providing consistent and accurate results. CSA’s calculation surpassed experiments, emphasizing its consideration of effective fabric design strain.

Experimental study and modeling of unidirectional jute FRP for concrete confinement

This study introduces a unidirectional jute fiber-reinforced polymer (UJFRP) composite to examine its application on concrete confinement. The study aims to explore the effect of UJFRP on the strength and ductility of concrete, and to propose a predictive model for the compressive behavior of UJFRP-confined concrete. Firstly, the tensile properties of UJFRP coupons were examined, followed by a series of compression tests conducted on UJFRP-confined concrete. The experimental program considered the effects of the compressive strength of concrete (low- and normal-strength concrete) and the number of UJFRP jackets (ranging from 1 to 4 layers). Experimental results indicated that UJFRP exhibited superior tensile performance compared to conventional bidirectional jute fiber-reinforced polymer. The ultimate compressive stress of UJFRP-confined concrete was significantly enhanced up to 5.0 times for low-strength concrete and 1.7 times for normal-strength concrete, due to the ascending behavior observed in UJFRP strengthening. Moreover, a simplified predictive model for the compressive behavior of UJFRP-confined concrete has been proposed. By substituting the concrete compressive strength and the tensile properties of UJFRP coupons into the simplified model, it is possible to estimate both the ultimate compressive strain and stress of UJFRP-confined concrete. The predictive values from the model showed good agreement with the experimental results. The findings in this study will facilitate the adoption of UJFRP as an eco-friendly alternative material for retrofitting and strengthening concrete structures.

Re-anchoring of failed in-situ grouted post-tension anchor rods with high rod to duct area ratios

An experimental program was conducted that simulated an internal rod failure to review re-anchoring ability, transfer length, and residual bond strength of grouted post-tension anchors with high rod to duct area ratios under in-situ conditions. Additionally, a theoretical model founded on interference fit, initial assumptions, and debris wedging was expanded to include a concrete to pipe interface. The experimental program included three full scale concrete specimens, whose length, annulus space for grout, and anchor diameter were nearly identical to existing anchors within dams in California. The specimens were instrumented along the anchor and concrete to capture strains in the longitudinal and transverse directions, the values of which, were compared against the theoretical model and found to be in good agreement along with the measured transfer length values. The debris wedging ratio found was consistent across the specimens and closely resembles the ratio captured in a similar study by the authors.

Soil-water characteristic curve of expansive soils considering cumulative damage effects of wetting and drying cycles

A novel experimental program was undertaken to explore crack development inside an expansive soil column under cyclic Wetting and Drying (W-D) and its influences on the Soil-Water Characteristic Curve (SWCC). Experimental investigations revealed that in the first drying cycle, fine and evenly distributed cracks developed from initial defects in the upper surface. In the subsequent drying cycles, the unhealed cracks during the wetting cycle further grow in width, length and depth while the initiation zone of new cracks was limited. The crack development characteristics within the soil column were described using fractal dimensions. The cracking degree of soil cross-sections gradually reduced with increasing depth. Also, each W-D cycle process contributed to a similar increment in the crack fractal dimension of soil at the same depth. In addition, the saturated water content, air-entry value and residual suction of cracked expansive soils gradually reduced with an increase in the number of W-D cycles. An obvious bimodal phenomenon was only observed in the SWCC of soil samples after the third W-D cycle. In order to quantify the damage induced by crack development to the soils, the damage variable was proposed based on the crack fractal dimensions. Furthermore, the Damage Impact Factor (DIF), as a function of the volume damage variable and soil plasticity index, was introduced into the traditional Fredlund and Xing (F-X) model to estimate the SWCC of cracked expansive soil. The form of modified F-X model is relatively simple and can be conveniently extended into geotechnical engineering practice applications.

Investigation of Fluidelastic Instability in Parallel Triangular Tube Arrays Subjected to Air Flow

Abstract One of the major considerations in the design and operation of heat exchangers is the flow-induced vibration (FIV). While there are multiple FIV excitation mechanisms, fluidelastic instability (FEI) is by far the most crucial mechanism as it can significantly compromise the structural integrity of the tube arrays. Traditionally, it was assumed that FEI could only happen in the transverse direction. However, recent tube failures in replacement steam generators have demonstrated that FEI can occur in the streamwise direction and be equally devastating. This new phenomenon has sparked intensive research to uncover its nature. An intensive experimental research program was launched to investigate the geometrical impact of various tube array types on the FEI in both the transverse and streamwise directions. To that end, the stability of a single flexible tube and multiple flexible tubes in tube arrays was tested. The study will focus on the stability behavior of parallel triangular arrays at pitch ratios in the range of 1.25–1.70. A comparison between the available experimental data and the current results was presented. The current results reveal that the stability threshold is sensitive to the pitch-to-diameter ratio of the array and the number of flexible tubes, especially in the streamwise direction.

Validation of a Numerical Model for Novel Self-Centring Concentrically Braced Steel Frames

Significant inelastic deformations induced in structural systems lead to structures possibly possessing some degree of permanent lateral deformation following major seismic events. These permanent deformations have led to considerable research being conducted over the past 20 years into developing structural systems that exhibit self-centring behaviour. For a structural system such as the concentrically braced frame (CBF), for which the dissipating mechanism is the tensile yielding and compressive buckling of the diagonal steel tubular members, these residual deformations present a problem when considering the structure’s overall resilience to the seismic loading both during and after an event. This paper describes the numerical modelling of a novel self-centring, concentrically braced frame (SC-CBF) system that combines a conventional CBF with a self-centring arrangement to produce a structure that possesses the desirable lateral load-resisting capacity of the CBF but which also re-centres when subjected to many cycles of large inelastic brace deformation. First, an experimental test programme for the SC-CBF is briefly described, followed by a numerical model to capture the SC-CBF’s characteristics during cyclic loading. This numerical model is validated using the experimental test data, showing that the experimental and numerical simulation data match rather well. This development presents a platform upon which further research through experimental testing and numerical simulation can be conducted. The proposed SC-CBF system can then be developed into a viable lateral load-resisting system that will provide a more resilient system than the current conventional CBF.

Influence of Bio-Additives on Recycled Asphalt Pavements.

The construction and maintenance of asphalt pavements is a resource-consuming sector, where the continuous rehabilitation of the superficial layers demands large volumes of non-renewable resources. The present work focuses on the design and characterization of asphalt mixtures for the binder layer of an asphalt pavement containing 50% reclaimed asphalt (RAP), in which seven different bio-based additives, identified as R1A, R1C, R2A, R2B, R2C, R3A, and R3B, were added to improve the workability, strength, and stiffness properties. The experimental program envisioned the hot mixing of aggregates and RAP with either a 50/70 or a 70/100 bitumen and, in turn, each of the seven bio-additives. The asphalt mixtures underwent the characterization of their densification properties; air voids; indirect tensile strength (ITS); indirect tensile stiffness modulus at 10, 20, 40, and 60 °C; and rutting resistance at 60 °C. The results highlighted that the performance in terms of workability and ITS of the resulting mixtures depends on the type of bio-additive and largely on the fresh bitumen type, while the stiffness at high temperature is not significantly affected by the presence of the bio-additives.