Performance Evaluation of the Polyurethane-Based Composites Prepared with Recycled Polymer Concrete Aggregate

Study on Temperature-Dependent Uniaxial Tensile Tests and Constitutive Relationship of Modified Polyurethane Concrete

Modified polyurethane concrete (MPUC) is a new material for steel deck pavements. In service, the pavement is often cracked due to excessive tensile stress caused by temperature changes. In order to study the tensile properties of MPUC in the diurnal temperature range of steel decks, uniaxial tensile tests of MPUC were carried out at five temperatures. Three kinds of specimens and a novel fixture were designed and fabricated to compare the results of four different tensile test methods. The deformation of the specimen was collected synchronously by two methods: pasting strain gauge and digital image correlation (DIC) technique. Based on the experiment, the tensile mechanical properties, failure modes, and constitutive relations of MPUC were studied under the effect of temperature. The research results show that the novel fixture can avoid stress concentration. By observing the fracture surface of the specimens, the bonding performance is great between the binder and the aggregate at different temperatures. The tensile strength and elastic modulus of MPUC decrease with increasing temperatures, while the fracture strain, and fracture energy increase with increasing temperatures. The formulas of temperature-dependent tensile strength, fracture strain, and elastic modulus of MPUC were established, and the constitutive relationship of MPUC is further constructed in the rising stage under uniaxial tension. The calculation results show good agreement with experimental ones.

Preparation and Properties of Bio-Based Attapulgite Copolymer (BAC) Sand-Fixing Material

Desertification, one of the world's most pressing serious environmental problems, poses a serious threat to human survival as well as to social, economic, and political development. Nevertheless, the development of environmentally friendly sand-fixing materials is still a tremendous challenge for preventing desertification. This study developed a bio-based attapulgite copolymer (BAC) by grafting copolymerization of attapulgite, starch, sulfomethyl lignin, and biological mycelia. Water retention, anti-water erosion, and anti-wind erosion tests were conducted to assess the application performance of the BAC. Scanning electron microscopy (SEM) was then employed to determine the morphology of the attapulgite and attapulgite graft copolymer sand-fixing material (CSF). The intermolecular interactions in CSF were revealed using Fourier transform infrared spectrum (FT-IR). The role of sand-fixing materials on soil physicochemical properties and seed germination was then discussed based on the germination rate experiments, and 16S rDNA sequencing technology was used to analyze the differences in microbial communities in each sample group. The results demonstrated that the BAC not only has superior application properties and significantly increased seed germination (95%), but also promotes soil development by regulating the structure of the soil microbial community. This work provides novel insights into the design of sand-fixing material for preventing desertification while improving soil fertility.

Fatigue Properties and Its Prediction of Polymer Concrete for the Repair of Asphalt Pavements

Polymer concrete (PC) is considered a promising repair material for asphalt pavement, since it has excellent paving performance and water stability. Although the mechanical properties of PC have been widely researched, the fatigue behavior of PC under traffic loads was still poorly understood. To predict the fatigue life and optimize the material design of PC, the semi-circular bending (SCB) tests were performed, considering different polymer content, sand ratio, aggregate features and stress condition. Two typical polymer materials were applied to prepare PC specimens, including epoxy resin (ER) and polyurethane (PU). The aggregate features were analyzed by the aggregate image measurement system. The mechanical behavior under repeated loads was investigated by the displacement, fatigue life and stiffness modulus. Results show that the flexural strength increases nonlinearly with the increasing polymer content, rapidly at first, and then slowly. The optimized polymer content and sand ratio were respectively 15% and 30%. As the loading number increases, the vertical displacement of PC shows three stages, i.e., undamaged stage, damage development stage, and fatigue failure stage. The stiffness modulus of the specimen is stress-dependent. An empirical model was developed to predict the fatigue life of PC, which can effectively capture the effects of the polymer content, sand ratio and stress level (or nominal stress ratio). It suggests that the fatigue life has a strong correlation with the mixing gradation, and the optimal sand ratio of PC can be determined by the proposed function. Moreover, the effect of aggregate shapes cannot be neglected.

Analysis of Shear Resistance and Mechanism of Construction and Demolition Waste Improved by Polyurethane

A large amount of construction and demolition waste (CDW) is generated during the construction of projects. In this paper, polyurethane foam adhesive (PFA) was used to improve the mechanical properties of CDW. The large-scale direct shear tests, California bearing ratio (CBR) tests and Scanning electron microscope (SEM) tests were carried out to study the variation regularities of mechanical properties of treated CDW during the laboratory tests. The test results show that the shear strength of CDW increases with the increase of PFA content, vertical pressure and the shear rate. However, the increase of vertical pressure on the shear strength of CDW is smaller than that of PFA, and the improvement of the shear rate is relatively small. The California bearing ratio (CBR) test also proves that PFA can effectively improve the bearing capacity of CDW and reduce the loss of CBR caused by the 4-day soaking. Scanning Electron Microscope (SEM) finds that polyurethane wraps multiple particles and enhances the internal connection, which results in the cohesion between the particles being greatly increased. The study presented in this paper will better assess the shear resistance of improved CDW with PFA as a substitute for pavement base materials in practical engineering applications.

Study on Mechanical Properties of Modified Polyurethane Concrete at Different Temperatures

The objective of the present research was to study the effect of temperature on the mechanical properties, failure mode and uniaxial compression constitutive relationship of a modified polyurethane concrete. A total of 24 cube and 27 prism specimens were fabricated, and the uniformity of the polyurethane concrete was checked. The compressive test, splitting tensile test and static uniaxial compression test were carried out at 0, 15, 40 and 60 °C. The failure mode, cube compressive strength, splitting tensile strength, axial compressive strength, elastic modulus and the compressive stress–strain curves of the modified polyurethane concrete were obtained. Based on the experimental results, a uniaxial compression constitutive model of the modified polyurethane concrete considering temperature characteristics was proposed. The results show that the elastic modulus, cubic compressive strength, splitting tensile strength and axial compressive strength of the modified polyurethane concrete decrease with the increase of temperature, and the peak strain and ultimate strain increase significantly. When the temperature rises from 0 to 60 °C, the cubic compressive strength, splitting tensile strength and axial compressive strength are decreased by 67.1%, 66.4% and 73.3%, respectively. The calculation results of the proposed constitutive model are in good agreement with the test results. The results are expected to guide the application of the modified polyurethane concrete in bridge deck pavement.

Preparation and Mechanical-Fatigue Properties of Elastic Polyurethane Concrete Composites

In order to solve issues related to bridge girders, expansion devices and road surfaces, as well as other structures that are prone to fatigue failure, a kind of fatigue-resistant elastic polyurethane concrete (EPUC) was obtained by adding waste rubber particles (40 mesh with 10% fine aggregate volume replacement rate) to conventional engineering polyurethane concrete (PUC). Based on the preparation and properties of EPUC, its constitutive relation was proposed through compression and tensile tests; then, a scanning electron microscope (SEM), an atomic force microscope (AFM) and a 3D non-contact surface profilometer were used to study the failure morphology and micromechanisms of EPUC. On this basis, four-point bending fatigue tests of EPUC were carried out at different temperature levels (-20 °C, 0 °C, 20 °C) and different strain levels (400 με~1200 με). These were used to analyze the stiffness modulus, hysteresis angle and dissipated energy of EPUC, and our results outline the fatigue life prediction models of EPUC at different temperatures. The results show that the addition of rubber particles fills the interior of EPUC with tiny elastic structures and effectively optimizes the interface bonding between aggregate and polyurethane. In addition, EPUC has good mechanical properties and excellent fatigue resistance; the fatigue life of EPUC at a room temperature of 600 με can grow by more than two million times, and it also has a longer service life and reduced disease frequency, as well as fewer maintenance requirements. This paper will provide a theoretical and design basis for the fatigue resistance design and engineering application of building materials. Meanwhile, the new EPUC material has broad application potential in terms of roads, bridges and green buildings.

Polymeric composite materials for radiation shielding: a review

The rising use of radioactive elements is increasing radioactive pollution and calling for advanced materials to protect individuals. For instance, polymers are promising due to their mechanical, electrical, thermal, and multifunctional properties. Moreover, composites made of polymers and high atomic number fillers should allow to obtain material with low-weight, good flexibility, and good processability. Here we review the synthesis of polymer materials for radiation protection, with focus on the role of the nanofillers. We discuss the effectivness of polymeric materials for the absorption of fast neutrons. We also present the recycling of polymers into composites.