Fresh and mechanical performance and freeze-thaw durability of steel fiber-reinforced rubber self-compacting concrete (SRSCC)

The self-compacting concrete (SCC) with the replacement of recycled rubber aggregates is limited for the field application due to high-performance requirements. The steel fiber was introduced to the rubberized SCC (RSCC) to enhance its performance and promote its application. The fresh and mechanical properties and durability performance of steel fiber-reinforced rubber self-compacting concrete (SRSCC) were evaluated. The SRSCC samples were prepared with replaced rubber aggregate based on fine aggregate volume percentages of 10%, 15%, and 25% and a consistent steel fiber ratio of 0.2%. The plain SCC and rubberized SCC samples were also produced for comparison. The fresh performance was evaluated with slump flow, J-ring flow, V-funnel, and U-box tests. The results showed that both filling and passing ability could be affected by the added steel fiber and rubber aggregate. However, the SRSCC could still meet most of the recommended criteria for passing and filling abilities when the rubber content is lower than 25%. Regarding the hardened properties, the compressive strength was reduced in rubber SCC samples with increased rubber contents by comparing with the control SCC samples. Nevertheless, SRSCC samples with 10% rubbers have higher splitting tensile strength than RSCC and plain SCC. Also, the SRSCC specimens showed excellent freeze-thaw resistance after 600 F-T cycles. The relative dynamic modulus of elasticity slightly increased without any dimensional expansion in SRSCC samples. In summary, the proposed SRSCC can meet required flowability, filling and passing abilities along with good mechanical and freeze-thaw performance. This study will provide lab test data for the applications of recycling waste tire aggregates in steel fiber-reinforced SCC

Evaluation of cathode ray tube (CRT) glass concrete with/without surface treatment

Using the crushed waste Cathode Ray Tube (CRT) glass as fine aggregate to produce concrete can be an efficient method to resolve the recycling issue. However, the mediocre mechanical properties of CRT concrete obstructed its wide application. This study aims to resolve this issue based on the study on concrete/mortar specimen incorporating with an innovated surface treatment method. Specifically, a two-step surface treatment method was proposed to improve the performance of CRT concrete by modifying the surface layer of CRT glass sands with NaOH solution and Al(NO3)3 solution. About 30% of the portland cement was replaced with class-F fly ash to mitigate possible ASR damage by the reactive CRT aggregate. The mechanical performance (Compressive/flexural strength, dynamic modulus of elasticity, and flexural fracture energy) and the durability performance (Drying shrinkage and ASR expansion) was examined and compared among different specimens. In addition, the leaching levels of lead in different concrete specimenswas evaluated by toxicity characteristic leaching procedure (TCLP). The results showed that the surface treatment method of CRT glass sands could obviously improve both the mechanical properties and durability performance. Particularly, the leaching of lead (Pb) level in all concrete specimens was much lower than the TCLP heavy metals limit of 5 mg/L. This experimental study will facilitate the production of CRT glass concrete for secondary structural applications

Flexural and shear bond performance of polyurethane-mortar interface under micro- and macroscale

Polyurethane materials have been widely applied in the mending of cementitious materials, and the mending efficiency is highly impacted by the bond strength between the polyurethane materials and the cement base. This paper aims to evaluate both the shear and flexural bond strength between cement mortar and polyurethane with different water and modifier contents. The shear and flexural bond strengths were examined using a slant shear test and three-point bending test on mortar samples prepared with a polyurethane interface. The effect of the polyurethane/water ratio on the bond strength was first examined, and both the highest shear and flexural bond strength were achieved for the samples with a 30% polyurethane/water ratio. To further enhance the bond strength, ethylene-vinyl acetate (EVA) was further added to the polyurethane, and the effect of the replacement ratio on the bond strength was further examined. The macro-size strength tests indicated the highest strength was achieved for the polyurethane samples that had a 10% EVA replacement ratio. The mechanism behind the effect of water and EVA content was further examined with a scanning electron microscope (SEM) and atomic force microscope (AFM). The examined relationship between water and EVA content and bond strength can provide useful information for the field application of polyurethane materials

Biological analysis on extractives of bayberry fresh flesh by GC–MS

Bayberry has been largely planted in China, and the waste of fresh flesh of bayberry was still abandoned. Therefore, the extractives of fresh flesh of bayberry were studied to further utilize the bio-resources. Through the Foss method, the result shown that ketone, aldehyde, ester and acid compounds were accounted for 1.30, 92.61, 0.54 and 6.09% of the extractives which were extracted from fresh flesh of bayberry by methanol solvents. Aldehyde, bicyclic sesquiterpenes, acid, ester and alcohol compounds accounted for 53.74, 9.95, 28.49, 6.79 and 1.05% of the extractives which were extracted from fresh flesh of bayberry by ethanol solvents. Ketone, aldehyde, carbohydrate, acid and ester compounds accounted for 4.77, 77.95, 12.06, 4.77 and 0.44% of the extractives which were extracted from fresh flesh of bayberry by ethyl acetate solvents. The extractives of fresh flesh of bayberry were rich in rare drug and biomedical activities and the ethanol is more better to extract the fresh flesh of bayberry. Keywords: Bayberry, Extractives, Chemical composition, GC–M

Atomic force microscope study of the aging/rejuvenating effect on asphalt morphology and adhesion performance

© 2019 Asphalt aging is one of the most severe threats to the asphalt pavement durability and rejuvenation with cooking oil can help to resolve this issue. Currently, the influence of aging/rejuvenation on the bonding performance of asphalt binder has not been fully understood. This study aims to unveil the influence of aging/rejuvenation on the adhesion performance under both micro and macro scale tests. Three type asphalt binders were examined in this study, including the original, aged and rejuvenated samples. The atomic force microscope (AFM) was first applied to examine the surface morphology and adhesion performance of the three type asphalt samples. It is found that the aging effect can increase the adhesion between asphalt binder and silica particles and the adhesion force can be further enhanced through rejuvenation. Then the three-point bending was further conducted to examine adhesion performance at the macroscale, and the obtained results are in accordance with those obtained at the microscale. However, the slant shear test indicated the shear bond strength can be reduced due to the rejuvenation with vegetable oil, which can be generated due to the lubrication effect of the oil. The results in this study can help to better understand the influence of aging and rejuvenation on the bond performance between asphalt binder and mineral aggregate

A critical review of corrosion development and rust removal techniques on the structural/environmental performance of corroded steel bridges

Corrosion is one of the most severe threats to the stability of steel bridges and regular rust removal techniques is needed for the maintenance of steel bridges. Currently the correlation between rust development/removal process and the structural/environmental performance of the steel bridges has not been fully understood. This study intends to fill this knowledge gap through critically reviewing. The characteristic analysis of the rust on the corroded steel bridges was first introduced, which provided information that was needed to understand the corrosion mechanisms and classify the rust type. Then the related rust removal techniques (chemical and physical methods) are analyzed by considering the environmental impact and cleaning efficiency. Based on the discussion, the laser cleaning method is proposed due to its cleaning efficiency and environmentally friendliness. After that, the influence of developed rust (uniform and pitting) on the structural performance (static and dynamic) of steel members were summarized. Through the discussion, the potential environmental impact of the corroded steel bridges was identified, including runoff of heavy metal and bacteria growth caused by iron rust. Besides that, an improved kinetic model was proposed by considering the influence of rust removal on the corrosion rate. Furthermore, the structural impact of laser cleaning was simulated with the finite element analysis. This study will serve as solid base for the future studies of corrosion development and rust removal on steel bridges, and the proposed technical routes can be proceeded during future studies to better understand the environmental and structural performance of the steel bridges