Case Studies in Construction Materials最新文献

Using advanced materials to optimize designs and make structures resilient is becoming of crucial importance. Advanced rapidly growing materials with superior mechanical properties, like ultra-high performance concrete (UHPC), can make structures better in terms of strength and service life when compared to conventional concrete. Behind the excellent performance of UHPC stands its dense packing theory and usage of steel fibers or even carbon nanofibers (CNF) in emerging UHPC mixtures. UHPC is mostly used in small-scale applications like bridge field joints and overlays, but research is extending UHPC to full structural applications such as girders and columns. To expand existing knowledge on UHPC columns and add new results from emerging and recently commercialized UHPC mixtures, this study uses, for the first time, two new UHPC mixtures with white cement and CNF enhancement to investigate axial behavior of nine full-scale columns with varying confinement. An extensive experimental program considers two groups of columns from two different mixtures with several other variables such as transverse reinforcement detailing, cross-section, and percentage of steel fibers. The paper presents results from companion material tests along with a detailed discussion of the global and local behavior of the columns, i.e. force, axial strains, reinforcement strains, and stiffness. Test results are interpreted in light of existing ACI 318 Code provisions and guidance is provided for axial design capacity estimation and transverse reinforcement detailing.

Salt-induced erosion from de-icing salts in Northern China and sea salt in Eastern coastal areas significantly compromises asphalt pavement integrity. A selection was made of four different types of foamed asphalt with different levels of water content, two types of aged asphalt, and three typical minerals (α-quartz, calcite, and bauxite), in addition to three chloride salt solutions (NaCl, CaCl₂, MgCl₂). It was found that (1) in dry conditions, the moisture level of foamed asphalt noticeably influences the adhesive performance at the juncture between asphalt and aggregates. Unlike acidic minerals, the bond strength between alkaline and neutral minerals and foamed asphalt increases as the water content of the foamed asphalt rises; (2) chloride salt solutions presence and increased levels significantly reduced the bond strength between asphalt and aggregates, particularly impacting neutral and alkaline minerals (in the presence of 10 % NaCl solution, the work of adhesion was reduced by 83.82 % and 87.48 %, respectively); (3) the influence of diverse chloride salts on the interfacial adhesive performance of asphalt mixtures varied, with the three chloride salts reducing the asphalt-aggregate interfacial adhesion work by 44.52 %, 21.90 %, and 34.94 %, respectively. (4) the investigation determined that the mineral composition considerably influences the hygroscopic sensitivity of asphalt mixtures. Minerals of an acidic nature exhibit superior moisture resistance when juxtaposed with alkaline counterparts, recommending the adoption of acidic aggregates in scenarios demanding elevated mixture stability.

Bituminous mixtures containing various defects, such as cracks and voids, exhibit ductile behavior in hot environments and brittle behavior in cold environments. Such materials can only be simulated realistically with the criteria of nonlinear fracture mechanics. In this investigation, the semi-circular bending (SCB) specimens, which have commonly been used to measure linear elastic fracture toughness parameters and fracture energy of asphalt and rock materials up to now, are studied to estimate several nonlinear fracture parameters of bituminous composites such as nonlinear fracture toughness, effective crack extension, critical crack tip opening displacement and brittleness. For this, the compliance functions of SCB specimens based on crack mouth opening displacement and load line displacement are derived by the finite element method at first. Subsequently, eight series of SCB tests in the literature, which were experimented with at low and room temperature environments, are examined by using two different compliance methods in fracture mechanics of quasi-brittle materials. This study's findings reveal that the crack extension in the pre-peak regime for mixes with bituminous at both low and normal temperatures is not statistically negligible and the use of nonlinear fracture toughness is, therefore, a necessity.

The Kahramanmaraş earthquakes that struck the Antakya downtown resulted in significant structural damage, highlighting the need to understand the underlying causes and develop effective mitigation strategies. This experimental study aims to investigate the reasons behind the observed structural damage by examining defects in building materials. Through comprehensive laboratory testing, a detailed analysis was conducted to identify the factors contributing to the vulnerability of structures in the affected area. To simulate the conditions experienced during the earthquake, various building materials, including concrete and reinforcement steel, were subjected to rigorous testing. The results revealed variations in concrete quality, with some samples exhibiting lower compression strength, incorrect aggregate mixing ratios, deepening of carbonation over time and higher permeability, indicating potential weaknesses in the structural integrity. Furthermore, the examination of reinforcement steel samples revealed the presence of corrosion and inadequate bond strength, compromising the load-bearing capacity of the structures. These defects significantly affected the performance of reinforced concrete elements during the earthquake, leading to localized failures and increased vulnerability. In addition to these tests, cylindrical concrete elements with the same properties were reproduced to examine the concrete-steel adhesion interface. Ø8 reinforcements collected from the field was placed in the concrete elements during the production phase. Tensile tests were carried out on 48 test samples produced. In particular, pull-out tests of test elements without ribs and with low concrete compression strength, simulating the field, were completed at very low loads. The experimental results provide valuable insights into the causes of structural damage observed in the Hatay region following the Kahramanmaraş earthquakes. The identified defects in building materials, such as concrete and reinforcement steel, highlight the importance of stringent quality control measures during construction.

One of the most present types of concrete in buildings is ultra-high-performance concrete. In contrast, large quantities of cement are consumed to achieve the required strength. To minimize the quantity of cement utilized in manufacturing ultra-high-performance concrete, this research aims to look at the usage of a unique agricultural waste as an alternative to cement. This study focuses on using agricultural waste as a partial cement alternative to reduce the amount of cement used in the production of ultra-high-performance concrete. This study employed basil plant ash as a partial substitution for ordinary Portland cement at 5 %, 10 %, 15 %, 20 %, and 25 % by mass. basil plant ash was heat-treated at temperatures of 300 °C, 500 °C, 700 °C, 900 °C. The compressive strength, splitting tensile strength, and sorptivity coefficient of ultra-high-performance concrete were investigated using 21 different mixes. In addition, microstructure characteristics as assessed using X-ray diffraction, thermal gravimetric analysis, and scanning electron microscope. The results showed that treating basil plant ash at 700 °C contributed to achieving the best mechanical properties when it was utilized as a partial substitution for 20 % of the weight of ordinary Portland cement. The compressive strength and splitting tensile strength were enhanced by 15.07 % and 20.39 %, respectively, compared with the control mix at 28 days. The thermo-gravimetric analysis, X-ray diffraction, and scanning electron microscope analyses are consistent with the obtained mechanical and durability characteristics. The outcomes of this investigation help shed light on the use of basil plant ash as a partial substitution at a level of 20 % of the weight of cement to produce ultra-high-performance concrete with high performance and lower cost.

Due to worldwide water scarcity, especially in arid regions, and the substantial use of drinking water in concrete production, the consideration of gray water usage is growing. However, wastewater contamination adversely affects concrete's mechanical strength and durability, with Chemical Oxygen Demand(COD) as one of the indicator. In the present work, the effect of COD of different types of domestic wastewater on workability, mechanical, and durability properties of self-compacting concrete (SCC) with 400 kg/m³ and 440 kg/m³ of cement, and water-to-cement ratios of (w/c) 0.36 and 0.5 for 12 different SCC mixture designs were investigated. The results of the experiments indicated that increasing the COD of domestic wastewater negatively impacts the workability of fresh concrete. Additionally, as the COD of the wastewater increases, the compressive strength of SCC decreases at 7 and 28 days when using raw sewage, sewage sludge, and artificial wastewaters. However, by 90 days, the compressive strength showed no significant difference compared to SCC made with tap water. With increasing COD of wastewater, the 28-day tensile strengths of SCC decreased by 6–10 %. The COD of wastewater did not significantly affect the flexural strength. However, the fracture toughness, at a water-cement ratio (w/c) of 0.5, decreased with increasing COD, reaching a reduction of 36 % at a COD of 940 mg/L. As the COD concentration rises, water absorption increases. In SCC samples containing sludge water and raw sewage, capillary water absorption was at its maximum due to the presence of impurities, as well as organic and mineral materials.

This study evaluated the uniaxial tensile strength and bond performance of natural hybrid reinforcement bars. Hybrid FRP combines multiple fibers and matrixes, resulting in a desirable performance. Two types of hybrid bars were tested: one with natural fibers surrounded by glass fiber, and the other with a steel core surrounded by natural fiber and then glass fiber. Thirteen samples were used to assess tensile behavior, with four groups including glass fiber, flax, sisal, and jute fibers. Pull-out behavior testing was conducted on twelve samples, divided into four groups of fiberglass, flax, sisal, and jute. Each group used three types of concrete: normal, high strength, and ultra-high-performance concrete (UHPC). The results refer to flax samples that had a higher tensile strength and elastic modulus of 143 MPa and 38 GPa, respectively, than samples made of sisal and jute fibres. The hybrid bars with a steel core exhibited a significant improvement in elastic modulus of 206 % in compared to samples made solely from glass, sisal, and jute fibers. On the other hand, the samples with UHPC showed the highest bond strength. The sample U-GFRP with ultra-high-performance concrete showed the highest bond strength 9.32 MPa, while the sample N-GFRP with normal concrete showed the lowest bond strength 5.87 MPa, respectively. However, this study suggests that hybridizing natural fibers can be a cost-effective and eco-friendly alternative to synthetic fibers.

The use of pozzolanic materials as a sustainable partial replacement option for portland cement in concrete has been extensively studied over the last few decades. This study aimed to assess the pozzolanic reactivity of seven different powdered materials: pottery cull, brick powder, lightweight aggregate fines, class C fly ash, silica fume, glass powder, and dolostone. Pozzolanic reactivity was evaluated using seven different direct and indirect methods, including the Frattini test, strength activity index (SAI), ultrasound pulse velocity index (UPVI), thermogravimetric and differential thermal analyses (TG/DTA), calorimetry, electrical conductivity, and pH. Robust correlations and a ranking analysis were performed to evaluate the relationship and efficiency between various direct and indirect test methods. Results of the robust regression analyses showed that Frattini and TGA, SAI and electrical conductivity, SAI and calorimetry, and UPVI and calorimetry were well correlated, suggesting that these methods may be suitable alternatives to each other. According to the ranking method, electrical conductivity and calorimetry are the most rapid and efficient methods for the assessment of different pozzolans in comparison to other longer-duration test methods examined in this study.

In saline-alkali and coastal areas, cement soil faces various threats from salt erosion, and these environmental conditions can significantly impact the mechanical properties of cement soil. To counter external erosion, the addition of graphene oxide (GO) nanomaterials to cement soil is considered an effective solution. This study systematically investigates the strength variations of GO cement soil after erosion in different concentrations of NaCl solution (0 g/L, 4.5 g/L, 18 g/L, 30 g/L), Na₂SO₄ (0 g/L, 4.5 g/L, 18 g/L, 30 g/L), and a composite salt solution of both (0 g/L, 4.5 g/L, 18 g/L, 30 g/L) at different times (7d, 14d, 30d, 60d) through salt immersion tests, unconfined compressive strength tests, and SEM scanning electron microscope tests. Simultaneously, the study analyzes the mass change rate, stress-strain curves, peak stress of unconfined compressive strength, and modulus of elasticity changes in cement soil samples after erosion. The internal erosion mechanism of cement soil samples is explored at the microscopic level. When the GO cement soil was eroded in different concentrations of NaCl solution for 14 days, a consistent trend of mass decrease was observed. However, after 7, 30, and 60 days of erosion in various concentrations of NaCl solution, the mass showed an increasing trend. When immersed in pure water for 7d, 14d, 30d, and 60d, as well as in a 4.5 g/L NaCl solution for 7d and 14d erosion, the peak stress of GO cement soil samples shows an increasing trend, while it decreases under other conditions, especially significantly in Na₂SO₄ solution. Simultaneously, Na₂SO₄ has the greatest impact on the modulus of elasticity of cement soil. SEM test results reveal that due to nucleation effects, GO promotes the generation of hydration product C-S-H, enhancing the resistance of cement soil samples to external erosion. Furthermore, it is observed that under the influence of SO₄^2-, C-S-H undergoes decalcification to generate AFt, while the impact of Cl^- on C-S-H is relatively small.

This work describes the synthesis of geopolymers, a family of amorphous alumino-silicates, employing Silica fume and bauxite waste as precursor materials in an alkali-activated polycondensation reaction and the investigation of their properties. The purpose of the study is to determine the feasibility of producing one-part alkali-activated geopolymer for use in cast-in-place construction. Following calcination of the bauxite residue at 800 °C, different amounts of solid activator Na₂O (10 %, 15 %, and 20 %) were added. Furthermore, Silica fume content ranging between 10 % and 40 % was utilised at intervals of 10 %, in lieu of alkali-thermally treated bauxite residue. The primary objective of the study is to evaluate the fresh properties throughout the first 28 days of geopolymer formation, including consistency, flowability, heat evolution, initial setting time (IST), and final setting time (FST). Scanning electron microscopy (SEM) images are used in conjunction with the 28-day average compressive strength to demonstrate the solidification of one-part geopolymers. Furthermore, these properties are affected by adding Silica fume at regular intervals between 10 % and 40 % as a replacement of the alkali-thermally treated Bauxite residue. The 28-day average compressive strength, with a maximum value of 19 MPa indicating successful geopolymer formation, supports the solidification of one-part geopolymers.