Polyethylene Terephthalate (PET) is commonly used to manufacture plastic products such as beverage bottles, food packaging, and clothing fibers. It is the most widely used plastic in the world and ...accounts for about 60% of all plastics. Being non-biodegradable, the accumulation of waste PET presents a significant environmental challenge. Conversely, recycling PET has long been recognized as an optimal strategy for mitigating these environmental concerns. In recent years, recycled PET has gained attention as a potential additive in construction materials, including asphalt mixtures and cement concrete. This paper provides a comprehensive literature review on incorporating waste PET in asphalt mixtures, examining its utilization as an asphalt binder modifier, a partial or complete aggregate substitute, and a partial asphalt binder replacement. The focus is on investigating the mechanical properties of these mixtures, including moisture susceptibility, fatigue resistance, rutting performance, and fracture resistance. The findings from the reviewed studies indicate that the inclusion of PET in asphalt mixtures enhances the mixture's stability, improves resistance to moisture susceptibility, increases resistance to rutting deformation, and improves the asphalt mixture’s fracture resistance. However, certain studies have highlighted a decline in the mechanical properties of asphalt mixtures when PET is used in large quantities.
•PET Incorporation Methods in Asphalt Mixtures: There are three primary methods in which PET can be added into asphalt mixture namely wet, dry, and modified dry methods. Wet and dry techniques are most commonly used, offering versatility based on the melting points of the plastics involved.•PET utilization in asphalt mixture: PET can be utilized in asphalt binder, either by modifying the binder's properties or by partially replacing the asphalt binder. It can also be used as a substitute for traditional aggregates in asphalt mixtures.•Enhanced Performance PET-modified asphalt mixtures: PET inclusion in asphalt mixtures significantly improves resistance to moisture-induced damage, rutting deformation, fracture resistance, and fatigue cracking, contributing to longer-lasting and more durable pavements.•Form and sizes of the PET utilized: The sizes and forms of PET utilized play a crucial role in determining the properties of the asphalt mixture. Fine-grade PET particles increase moisture resistance, coarser particles increase bulk density, and longer PET fibers increase fracture and fatigue resistance.•Economic and environmental benefits. Economically, it reduces material costs by recycling readily available PET waste, cutting expenses associated with virgin materials. Environmentally, it diverts plastic waste from landfills and incineration, conserving natural resources and reducing environmental pollution.
Rheological curves of cement–fly ash (C–FA) paste incorporating nanomaterials including nano-SiO2 (NS), nano-CaCO3 (NC) and nano-Al2O3 (NA) at different resting times (hydration time of 5 min, 60 ...min, and 120 min) were tested with a rheometer. The rheological behaviors were described by the Herschel–Bulkley (H–B) model, and the influences of these nanomaterials on rheological properties of C–FA paste were compared. Results show that the types, content of nanomaterials and resting time have great influences on the rheological properties of C–FA paste. Incorporating NS and NA increases yield stress and plastic viscosity, and decreases the rheological index of C–FA paste. When the content of NS and NA were 2 wt%, the rheological index of C–FA paste was less than 1, indicating rheological behavior changes from shear thickening to shear thinning. Meanwhile, with rising resting time, yield stress and plastic viscosity increased significantly, but the rheological index decreased evidently, showing paste takes on shear thinning due to the rise of resting time. However, incorporating 3 wt% NC and the rising of resting time did not change the rheological properties of C–FA paste. These differences are mainly that the specific surface area (SSA) of NS (150 m2/g) and NA (120 m2/g) are much larger than that of NC (40 m2/g). The huge SSA of NS and NA consume lots of free water and these tiny particles accelerate the hydration process during resting time.
Direct electric curing (EC) is a new green curing method for cement-based materials that improves the early mechanical properties via the uniform high temperature produced by Joule heating. To ...understand the effects of EC and steam curing (SC) on the mechanical properties and microstructure of cement-based materials, the mortar was cured at different temperature-controlled curing regimes (40 °C, 60 °C, and 80 °C). Meanwhile, the mechanical properties, hydrates and pore structures of the specimens were investigated. The energy consumption of the curing methods was compared. The results showed that the EC specimens had higher and more stable growth of mechanical strength. The hydration degree and products of EC samples were similar to that of SC samples. However, the pore structure of EC specimens was finer than that of SC specimens at different curing ages. Moreover, the energy consumption of EC was much lower than that of SC. This study provides an important technical support for the EC in the production of energy-saving and high early-strength concrete precast components.
In order to study the synergistic effects of organic and inorganic thickening agents on the rheological properties of cement paste, the rheological parameters, thixotropy cement-paste containing ...limestone powder (LP), re-dispersible polymer powder (RPP), and hydroxypropyl methylcellulose ether (HPMC) were investigated using the Anton Paar MCR 102 rheometer at different resting times. The early-age hydration process, hydration products, and microstructure were also analyzed with scanning electron microscopy (SEM) and thermogravimetry analyses (TGA). The results showed that the addition of LP, RPP, and HPMC affected the rheological properties of cement paste, but the thickening mechanism between organic and inorganic thickening agents was different. The small amount of LP increased the plastic viscosity but decreased the yield stress of cement paste due to its dense filling effect. Adding 1% of RPP improved the thixotropic property of cement paste by 50%; prolonging the standing time could improve the thixotropic performance by as much as two times. Only 0.035% HPMC added to the cement paste increased the plastic viscosity by 20%, while the yield stress increased nearly twice. The more HPMC added, the more significant effect it showed. Cement paste compounds with LP, RPP, and HPMC balanced the yield stress and plastic viscosity and improved the thixotropy. The C-L6-R1.0-H0.035 paste presented as a pseudoplastic, its rheological indexes were close to one, and it was hardly affected by the resting time. The composite superposition effect of organic and inorganic thickening agents reduced the impact of resting time for all pastes. As the organic thickening component inhibited the hydration more than the LP promoted the hydration of the cement paste, indicating that the C-L6-R1.0-H0.035 paste remained in the particle fusion stage after curing for three days, as shown by the SEM images.
In order to explore the applicability of different cementitious paste systems used for massive concrete structures, the hydration characteristics and mechanism of the binary and ternary cementitious ...paste systems in Portland cement pastes containing fly ash and slag were investigated in this work. The hydration heat release rate and cumulative heat release of each cementitious paste system at 20 ℃ and 60 ℃ were measured by an isothermal calorimeter. The characteristic parameters of each cementitious paste system hydration process were calculated and analyzed using the Knudsen equation and Krstulović-Dabić hydration kinetic model. Besides, the hydration mechanism was analyzed. It was obtained that the cement-fly ash (C-F) binary system is not effective in reducing the early reaction rate but its overall heat release is lower; while, the cement-slag (C-S) binary system is more effective in reducing the reaction rate but its overall heat release is higher, and the cement-fly ash-slag (C-F-S) ternary system has the advantages of both above binary systems. Probably, the C-F-S ternary system is more consistent with the heating characteristics of massive concrete structures, and it is more applicable. There are few studies on the hydration characteristics of C-F-S ternary systems from the perspective of hydration kinetic, and this work provides theoretical basis for the selection of cementitious paste systems for massive concrete structures.
•Premature deterioration mechanism of steam-cured concrete track slab was investigated.•Steam-cured heat damage (SCHD) makes track slab concrete surface layer loose, porous and more micro ...cracks.•3.Long-time dynamic load and moist environment acting on track slab enlarges micro cracks and results in water penetration into concrete easily.•Ingression of water into concrete causes the formation of alkali-silica gel and delayed ettringite.
Deterioration mechanisms of some premature damaged steam-cured concrete track slabs (CTS) in Chinese railway less than 4 years were investigated. Field investigation, raw materials test and suspicious products analysis were carried out. Results show that steam-cured heat damage (SCHD) of concrete takes place in steam-cured process. Expansion products are ettringite in hydrated products and alkali-silica gels between the interface of hydrated products and coarse aggregate. SCHD makes CTS surface layer loose, porous and more micro-cracks. Long-term fatigue load from high-speed train acting on CTS enlarges concrete microcracks, leading to water penetrating into concrete easily in moist and rainy environment. In the process of water ingression, alkali-silica reaction (ASR) and delayed ettringite formation (DEF) take place, hence resulting in CTS cracking and premature deterioration.
Effective foundation reinforcement treatment is essential for modern large and complex infrastructure, while it is significant for developing new green high-performance materials for foundation ...reinforcement. This study investigates a new green concrete by using high volume fly-ash and coal gangue aggregates, which is expected to apply for foundation treatment of modern infrastructure with high loading-bear ability. In this experiment, 12 mix proportions of fly ash coal gangue mixture (the material name, abbreviated FGM) were designed, and its mechanical properties and durability performance were investigated. The mechanical properties of FGM include compressive strength, dynamic elastic modulus, dynamic shear modulus, Poisson's ratio, and the stress-strain behaviors. The durability performance was evaluated by the parameters of acid resistance, which simulated an acid circumstance. After that, the environmental effects about carbon emission of this material were also investigated. Results show that the FGM with 84.6% wastes utilizing rate is a cost-effective material for foundation reinforcing treatment. Its compressive strength at 28 days and 60 days can reach more than 8 MPa and 10 MPa, respectively. After being immersed in the acid environment for 140 days, the mass loss (%) of the material could be under 3.5%. The greenness shows that the e-CO
indices of FGM are lower than 20 kg/MPa·m
, and the e-energy indices are at below 150 MJ/MPa·m
. FGM has the advantages of acid resistance, waste recycling, and lower carbon emissions than the previous methods for foundation improvement.
The concrete hydration heat and different construction methods directly affects the early crack resistance of massive concrete structures and may lead to concrete cracks. In this work, the hydration ...heat test and finite element simulation were conducted to investigate the early cracking resistance and the main influencing factors of the massive concrete bridge pier. The size of the bridge pier was 8 m (length) × 4 m (width) × 22.5 m (height), and the pier was poured in two layers (8.5 m/14 m) with an interval of 37 h. The internal temperature of the pier was tested 16 days after the concrete pouring using pre-buried temperature sensors, and the crack expansion on the surface of the pier was continuously observed during the test period. The test obtained a maximum concrete temperature of 64.25 °C after 100 h after the concrete pouring, and 3 cracks were found on the surface of the pier. The pier simulation model is established according to the actual situation in the test, The maximum temperature inside the bridge pier obtained from the simulation is 61.73 ℃, and the temperature field development pattern and the crack expansion on the pier surface were basically consistent with the test, which confirmed the reliability of the simulation method. Besides, the simulation process found that the maximum main tensile stress on the surface of the bridge pier was 2.77 MPa, which was mainly distributed near the interface of the 2 layers, indicating that the layered pouring scheme adopted in the test was improper. The effect of layered casting schemes on the early cracking resistance of massive concrete has rarely been discussed, and further simulations revealed that: the maximum main tensile stress can be reduced by gradually improving the number of layers, layer height and interval between each layer. By changing the original layered pouring scheme to 3 layers with an interval of 3 days between each layer, the maximum principal tensile stress is reduced to 1.50 MPa, and early cracking of the bridge pier can be avoided. This work provides a general numerical analysis method with high accuracy, parameterization and quantification for early crack control of massive concrete structures in a multi-factor complex environment.
Along with the construction industrialization degree, precast concrete is being utilized more and more frequently in construction to speed up the process and guarantee the quality of structural ...concrete. In order to make the precast concrete reach the required strength quickly and speed up the turnover of formwork, various rapid concrete curing methods emerged. Currently steam curing, direct electric curing, and microwave curing are the widely studied rapid curing methods. Rapid curing methods could promote early strength growth by changing the internal and external temperature and humidity of concrete, but may lead to late strength shrinkage, increased internal micro-cracks, coarsening of pore structure and other problems. Based on the comprehensive analysis of the curing principles of the three rapid curing methods, this paper reviews the effects of the three rapid curing methods on the hydration process, properties, and microscopic pore structure of concrete. The shortcomings of different rapid curing methods, and the topics of future researchs are also included.
PDF
