Case Studies in Construction Materials最新文献

Due to significant population concentration and capital influx in Guangdong-Hong Kong-Macao Greater Bay Area, the construction of cross-sea tunnels with significant consumption of various resources and materials, has been frequently witnessed. However, there is a lack of knowledge regarding how carbon emissions of cross-sea transportation infrastructure are generated across its life-cycle stages. This study proposes a life cycle assessment (LCA) approach for quantifying the carbon emissions and exploring the carbon reduction potentials with a case study of a world-renowned cross-sea tunnel project in Guangdong-Hong Kong-Macao Greater Bay Area. The results find that this project contributes approximately 849 kilotons CO₂eq of carbon emissions with an emission intensity of 1.1 kilotons CO₂eq per meter. The materialization stage is the largest contributor of carbon emissions (474.9 kilotons CO₂eq), followed by service stage (248.3 kilotons CO₂eq, accounting for 29.2 %). Some carbon emissions of raw materials can be offset by using recycled materials. The discarded concrete, block, stone, and sand, occupying over 90 % of the total recycled waste in weight could achieve a 93.5 % of carbon reduction potentially. It provides the opportunity to reveal the engineering details and carbon emission for a world-class super complex cross-sea transportation infrastructure. This study makes one of the first attempts to quantify life-cycle carbon emissions of cross-sea transportation infrastructure, which enriches foundational dataset for environmental impact assessment in this emerging field. The findings of this study can provide scientific references for formulating targeted low-carbon strategies for cross-sea transportation infrastructure across its different life-cycle stages.

Bamboo scraps/magnesium oxychloride composites (BS/MOC) is a new low-carbon and eco-friendly building material, which is composed of magnesium oxychloride cement (MOC) as the matrix and bamboo scraps as the reinforcing materials. However, the poor strength and durability of BS/MOC under special environmental conditions seriously restrict its application range. To solve the above problems, citric acid (CA), D-gluconic acid sodium salt (GS), and styrene-acrylate emulsion (SAE) were used as modifiers to improve BS/MOC properties. The effect of modifier addition on the mechanical strength and durability of BS/MOC was investigated under dry-wet cycling environments. The phase composition, microstructure, pore structure, and Clˉ concentration of BS/MOC were characterized by XRD, TGA, SEM, MIP, and ICS-600. The results showed that CA and GS improved the interface adhesion between bamboo scraps and MOC matrix, and both inhibited the hydration reaction of the residual MgO and the hydrolysis of phase 5 crystals, resulting in good mechanical properties and microstructural stability of BS/MOC under dry-wet cycles. GS outperformed CA in refining pore structure, improving mechanical properties and durability of BS/MOC under identical dry-wet cycles. Conversely, the addition of SAE increased initial defects and interfacial transition zones in the BS/MOC matrix, and increased the total porosity and the harmful pores content, which negatively affected the mechanical properties and durability of BS/MOC.

Against the backdrop of saline soil solidification and the resource utilization of solid waste and aeolian sand in cold and arid regions, this study employs locally accessible fly ash and aeolian sand to solidify saline soil. By combining unconfined compressive strength tests, X-ray diffraction analysis, scanning electron microscopy, orthogonal experiments, and single-factor analysis, the strength characteristics, mineral composition, and interfacial structure changes of saline soil solidified with different freeze-thaw cycles and varying amounts of fly ash, aeolian sand, and alkali activators were investigated. The effects of each factor were analyzed to determine the optimal mixture ratio and to explore the solidification mechanism.The results indicate that the unconfined compressive strength of saline soil is most significantly enhanced when solidified with a combination of fly ash, aeolian sand, and alkali activators. The optimal mixture ratio was found to be 24 % fly ash, 7 % aeolian sand, and 4.5 mol/L alkali activator. With the incorporation of these solidifying materials, the failure mode of saline soil transitions from plastic to brittle, and the stress-strain curve exhibited a strain-softening behavior. The combined solidification method demonstrated the most pronounced effect in mitigating freeze-thaw damage, with the unconfined compressive strength of the solidified soil reaching 7.01 MPa after seven freeze-thaw cycles, compared to 0.03 MPa for the untreated soil, an increase by a factor of 234.This significant enhancement is attributed to the formation of substantial gel substances, which mitigate the strength loss caused by freeze-thaw cycles. The gel locking mechanism between particles in the solidified soil far exceeds the detrimental effects of freeze-thaw cycles, effectively inhibiting freeze-thaw deterioration. Additionally, the reaction pathways involving AFt and AFm phases reduce the content of SO₄^2- and Cl^- in the solidified soil, effectively suppressing salt expansion and significantly improving the soil's strength.

In order to meet the requirements of concrete filling, vibration, and pumping during the construction of the concrete-filled steel tube (CFST) arch bridge, the C80 expansive self-compacting concrete (SCC) is prepared using the absolute volume method. This research investigates the effects of MgO-based expansive agent (EA) and water-to-binder ratio (w/b) on the fresh properties, mechanical properties, autogenous shrinkage, and creep behaviors of expansive SCC. The microstructure of expansive SCC is analyzed by scanning electronic microscopy (SEM) and nuclear magnetic resonance (NMR). Results show that, as the MgO-based EA content increases from 5 % to 10 %, its effect on fresh properties of SCC is negligible. The addition of EA retards the hydration reaction of cement at early ages, thus delaying the strength development. However, the long-term mechanical strengths of the SCC are enhanced, due to the expansion product refines the microstructure at later ages. Moreover, the 14-day autogenous shrinkage of SCC with 10 % EA content is eliminated and shows the micro expansion (155.3 με). The microstructural analysis shows that the porosity of SCC with 10 % EA content is 1.8 % while the pore throat below 0.1 μm accounting for 55 % and the pore size above 30 μm is negligible. This research reveals the mechanism of the effects of MgO-based EA and w/b on the volume stability of the SCC, facilitating the application of expansive SCC in CFST composite structures.

The extensive use of cement exacerbates the greenhouse effect by increasing carbon dioxide (CO₂) emissions. So, many standards recommend using Portland-composite cement in construction as one of the methods for reducing CO₂ emissions, especially cement CEM II/A-P. This paper presents an extensive experimental and numerical study to investigate the effect of micro and nano-silica on the flexural behavior and mechanical properties of Self-Compacted High-Performance Concrete (SCHPC) produced by cement CEM II/A-P. The extensive experimental work consisted of eight mixtures: three with micro-silica (MS), four with nano-silica (NS), and a reference mixture without silica. For both MS and NS, different percentages of adding or replacement content were tested to study their effect on the following: (a) the workability of fresh concrete, (b) concrete compressive strength, (c) splitting tensile strength, (d) flexural behavior including flexural tensile strength, and (e) the optimum percentage of each of the MS and NS to get the maximum structural and economic benefits of using for SCHPC with CEM II/A-P. Also, through a statistical program, these experimental results were used to obtain accurate formulae that could predict both the splitting tensile strength (f_sp) and modulus of rupture (f_ctr ) for SCHPC with adding nano-silica. In addition, the numerical study verified the experimental results based on the finite element program ANSYS. The flexure behavior of SCHPC beams is verified using the Microplane model (recently added to ANSYS). The experimental results showed that adding NS is more effective than replacing or adding MS for SCHPC mixture with CEM II/A-P to increase the concrete compressive strength, splitting tensile strength, and flexural tensile strength, especially for the mixture with adding NS content of 4 %. The numerical results showed the ability of the coupled damage-plasticity microplane model to simulate the flexural behavior of the tested SCHPC beams with MS or NS well. This research confirms nano-silica's structural and economical efficiency in the behavior of SCHPC beams. It was found that the optimum percentage of adding NS is 4 % for SCHPC mixtures with CEM II/A-P.

Freeze–thaw cycles could easily cause the structural damage and mechanic performance deterioration of clay. In order to prevent the freeze–thaw cycles problem in the core-wall zone of the high core-wall rock-fill dam in cold regions, gravel-clay mixed with phase change material (GC-PCM) can be used as damming material and present a certain level of anti-freezing performance during winter construction. However, GC-PCM construction work area is still likely to run a risk of freezing under the severe cold and strong wind weather. In order to solve the freezing problem of GC-PCM, this study developed an infrared radiant heating device without interfering with the original construction procedure and conducted an indoor test to investigate the temperature rising performance of GC-PCM after receiving infrared radiation. Also, a numerical simulation method was proposed for the temperature rising and anti-freezing performance of the GC-PCM construction work area and the effects of different factors (including radiant pass, moving speed of infrared device and wind speed) on the anti-freezing performance were analysed subsequently. Main results show that: (1) the effectiveness of proposed numerical simulation method is validated by the indoor test; (2) after receiving 8-pass infrared radiation, the GC-PCM construction work area at 4 % PCM content remains unfrozen in 24 hours under the typical weather in December; and (3) instead of increasing radiant passes, reducing the moving speed of infrared device can better improve the anti-freezing performance of GC-PCM. This study validates the feasibility of applying infrared radiant heating method on GC-PCM, providing a potential technical means for gravel-clay anti-freezing during winter construction.

Warm-mix asphalt (WMA) has been gaining popularity in sustainable road engineering due to its reduced environmental impacts. However, uncertainties remain regarding its long-term pavement performance compared to hot mix asphalt (HMA). Especially, the critical factors influencing the field performance of WMA are yet to be determined. Hence, this study analyzes the long-term field performance of pavement overlaid with WMA, using data from the Specific Pavement Studies 10 (SPS-10) of the long-term pavement performance (LTPP) program. The evaluation includes 58 field sections from nine projects across the United States, encompassing two WMA types (foaming processing and chemical additive) and their corresponding HMA control sections. Performance indicators such as alligator cracking, longitudinal cracking in the wheel path, transverse cracking, rutting, and roughness (measured by the international roughness index, IRI) were considered. Per-state and per-climate region Bayesian multilevel models were built to account for site- and region-level heterogeneity. The study results demonstrated that pavement with WMA performed equally well to the HMA counterparts under similar conditions, indicating that their potential for widespread application in meeting both performance standards and environmental conservation requirements. Also, WMA technologies did not differ in pavement performance, and thus the field performance of WMA was not a dominant factor in deciding WMA technology types. Furthermore, Bayesian multilevel models proved highly effective in performance data varying across construction sites and regions.

Recent research have highlighted the potential of hybrid confinement, combining high tensile strength fiber-reinforced polymers with large rupture strain confinement. This study presents experimental findings on 64 cylindrical and square-shaped specimens tested under axial compression, introducing a novel hybrid confinement method utilizing low-cost fiberglass chopped strand mat sheets and cotton ropes (COFS confinement). The experimental and analytical results yielded several key conclusions. Firstly, circular specimens exhibited significant peak strength increases in various subgroups, with enhancements ranging from 97.5 % to 285.5 %, and ultimate strain improvements ranging from 588.6 % to 1650.0 %. Similarly, square specimens under COFS confinement also demonstrated notable enhancements in ultimate strength and strain, with increases up to 244.7 % and 1083.0 %, respectively, particularly evident with higher levels of confinement. The influence of cross-sectional shape on compressive strength, strain, and energy dissipation was noted, with COFS confinement notably improving these factors for circular sections. Additionally, the study found that as the unconfined compressive strength increased, the enhancement in compressive strength, ultimate strain, and energy dissipation decreased. Moreover, the confinement ratio positively affected axial behavior improvement, with a proportional enhancement observed. However, the efficacy of the confinement ratio was influenced by cross-section type and plain concrete strength, emphasizing the need for considering these factors in COFS-based confinement design. Lastly, an analytical design-oriented model proposed for approximating stress vs. strain curves of COFS-confined concrete showed close agreement with experimental results, providing valuable insights for future design considerations.

This paper investigates the shear strengthening of simply supported deep beams using welded wire mesh and glass fiber mesh filled with strain-hardening cementitious composites (SHCC) concrete. Nine reinforced concrete (RC) deep beams were tested in this study to investigate different shear-strengthening techniques including the type of mesh (glass fiber mesh and welded steel wire mesh), number of layers (single and double), and the effects of additional anchor using high-strength bolts on the shear performance of RC deep beams. The results showed the SHCC-mesh jackets increased the ultimate load of the deep beams by up to 82 %, cracking load by up to 73 %, elastic stiffness by up to 457 %, and energy absorption by up to 380 % compared to the unstrengthen control beam. Furthermore, the welded wire mesh provided greater enhancements of strength, stiffness, and energy absorption than the glass fiber mesh. In addition, anchoring the jackets further improved the strengthening efficiency. Advanced nonlinear three-dimensional finite element models were also simulated to capture the structural responses of the RC deep beams strengthened using welded wire mesh and glass fiber mesh. It was found that the numerical models accurately predicted the behavior of the beams upon validation against the experimental results.

Owing to the large viscosity and mixing temperature of crumb rubber modified asphalt (CRMA), possesses high construction costs, the addition of warm-mix agent can reduce the viscosity and mixing temperature of CRMA. In this study, the Sasobit or DWMA-1 warm-mix agent was added into CRMA to prepare the warm-mix crumb rubber modified asphalt (WRMA). Rotational viscosity (RV) measurement revealed that viscosity of WRMA reduced significantly with the increasing temperature. Dynamic shear rheometer (DSR) showed that Sasobit and DWMA-1 have similar effects on the viscoelasticity of WRMA at the actual pavement temperature (64 °C). Phase separation test showed that the addition of warm-mix agent enlarged the softening point difference, and DWMA-1 had better anti-segregation effect than Sasobit. Fourier transform infrared spectroscopy (FTIR) analyses revealed that there was a chemical reaction after mixing the warm-mix agent and produced new functional groups at 1368 cm⁻¹∼735 cm⁻¹. Fluorescence microscope (FM) and polarizing microscope (PM) analyses indicated that warm-mix agents could improve the solubility between rubber and asphalt. DWMA-1 had a lesser impact on the surface roughness of WRMA compared to another warm-mix agent or composite agent. In addition, preparation method and viscosity reduction mechanism of WRMA was elaborated. This study could be of potential interest for engineering applications of WRMA.