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The purpose of this study was to evaluate the mechanical properties of concrete specimens produced with recycled aggregate (RA) from construction demolition waste (CDW) based on alkaline activated slag-fly ash (AASF). The recycled aggregate concrete mixtures (RAC) were designed using DMDA method, with RA used as a 30%, 40%, and 50% partial replacement for natural aggregate (Category 1) and with Na2O doses of 4%–8% and modulus ratios of 0.6–1.4 (Ms = SiO2/Na2O; Category 2). The results showed that the inclusion of RA negatively affected the mechanical properties of RAC specimens, with recycled coarse aggregate exhibiting less of a negative effect than recycled fine aggregate. The concrete mixtures exhibited mechanical strength values of 20.7–35.9 MPa and UPV values of 3692–4200 m/s at 28 days of curing age. Concrete characteristics were significantly better in the mixtures produced using higher alkaline concentrations than in those produced using lower alkaline concentrations.

This research presents the engineering performance and the microstructural characterization of ecofriendly construction bricks that were produced using a binder material made from a mixture of class-F fly ash (FA) and residual rice husk ash (RHA). Unground rice husk ash (URHA) was used as a partial fine aggregate substitute (0–40%). The solid bricks of 220 × 105 × 60 mm in size were prepared by mixing FA and RHA with an alkaline solution and fine aggregates, formed by compressing the mixture in a steel mold under 35 MPa of forming pressure, and then cured at 35°C and 50% relative humidity until the required testing ages. The tests of compressive strength, water absorption, and bulk density were conducted in accordance with relevant Vietnamese standards in order to estimate the effect of the URHA content on the engineering performance of the hardened bricks. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) were performed to determine the microstructure and the phase composition of the brick samples. The results show that properties of these bricks conformed to relevant Vietnamese standards. Therefore, FA and RHA are potential candidate materials for producing ecofriendly construction bricks using geopolymerization technology.

Thin-film transistor liquid-crystal display (TFT-LCD) waste glass can be used as a raw material for producing geopolymers, because it contains large amounts of silicon and aluminum in its amorphous structure. The setting time and compressive strength were evaluated to determine the quality of the geopolymer product with various amounts of nano-SiO2 (0%-3%) and TFT-LCD waste glass replacement (0% - 40%). The microstructures of the samples were characterized using mercury intrusion porosimetry (MIP), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The highest compressive strength and compact microstructure of the geopolymer was attained by adding 10% waste glass and 1% nano-SiO2. The results demonstrated that adding nano-SiO2 to the geopolymer substantially enhances compactness, improves uniformity, and greatly increases compressive strength. This work offers a low-cost route for fabricating geopolymers, because TFT-LCD waste glass can be used to partially substitute metakaolin in the composition of the geopolymer. [ABSTRACT FROM AUTHOR]

This study investigates the engineering and durability properties of self-consolidating concrete (SCC) specimens that were produced using various types of foamed lightweight aggregate (FLWA). Further, the effects of FLWA on the engineering and durability properties of SCC are assessed on the basis of related international standards. All of the fresh SCC mixtures exhibited exceptional flowability with uniform composition. The use of surface-treated FLWA improved significantly the compressive strength and the dynamic elastic modulus of SCC and reduced the drying shrinkage at later ages. The lowest thermal conductivity of 0.79 W/mK was achieved for SCC incorporating 80% fly ash (FA) and 20% ground blast furnace slag (GBFS) aggregate that produced with a foaming agent concentration of 7%. Furthermore, the electrical resistivity and the ultrasonic pulse velocity values for all of the 28-day specimens exceeded 20 kΩ-cm and 3,660 m/s, respectively, satisfying the minimum requirements of the referenced concrete durability indices. Finally, the 91-day passing charges for all specimens ranged between 1,500 and 566 C, indicating either low or very low chloride permeability. [ABSTRACT FROM AUTHOR]

This study examined the characteristics of geopolymer with solar panel waste glass. After 28 days of curing, the compressive strengths of the geopolymer samples containing 10 mass % and 20 mass % solar panel waste glass were 63.3 ± 1.8 and 49.1 ± 2.2 MPa, respectively. The geopolymer sample with 10% solar panel waste glass exhibited a stronger reaction than that with 20% solar panel waste glass, and the strength decreased as the amount of solar panel waste glass increased. Thermo-gravimetric and differential thermal analysis (TG/DTA) results showed that the mass loss of geopolymer after heating declined as the amount of solar panel waste glass increased. The principal peaks in the Fourier transformation infrared spectroscopy (FTIR) spectra correspond to the Si-O-Al bond in geopolymer. Scanning electron microscopy (SEM) observations indicated that the microstructures of the stronger samples were more homogeneous, and the microstructures of geopolymer with 10% solar panel waste glass did not exhibit substantial deterioration. The experimental results indicate that solar panel waste glass has the potential to serve as a partial replacement of metakaolinite and exhibits favorable mechanic characteristics. [ABSTRACT FROM AUTHOR]

Effects of polypropylene (PP) fibers, steel fibers (SF) and hybrid on the properties of high-strength fiber reinforced self-consolidating concrete (HSFR-SCC) under different volume contents are investigated in this study. Comprehensive laboratory tests were conducted in order to evaluate both fresh and hardened properties of HSFR-SCC. Test results indicated that the fiber types and fiber contents greatly influenced concrete workability but it is possible to achieve self consolidating properties while adding the fiber types in concrete mixtures. Compressive strength, dynamic modulus of elasticity, and rigidity of concrete were affected by the addition as well as volume fraction of PP fibers. However, the properties of concrete were improved by the incorporation of SF. Splitting tensile and flexural strengths of concrete became increasingly less influenced by the inclusion of PP fibers and increasingly more influenced by the addition of SF. Besides, the inclusion of PP fibers resulted in the better efficiency in the improvement of toughness than SF. Furthermore, the inclusion of fibers did not have significant effect on the durability of the concrete. Results of electrical resistivity, chloride ion penetration and ultrasonic pulse velocity tests confirmed that HSFR-SCC had enough endurance against deterioration, lower chloride ion penetrability and minimum reinforcement corrosion rate. [ABSTRACT FROM AUTHOR]

Solid waste management is becoming a sustainability issue in highly industrialized societies. Recycling or reuse of solid waste is desirable to reduce the adverse impact of this material. The vast annual production of printed circuit board (PCB) waste in Taiwan creates environmental concerns because of the leaching of toxic chemicals into landfills. This study assessed the feasibility of utilizing resin powder and glass fiber recycled from PCB waste as a partial replacement of fine aggregate (natural river sand) in concrete. It also established a comprehensive test program to promote the use of recycling waste for waste reduction. The crushed powder of PCB mixed with standard mortar in fixed volumetric mix proportion, as sand:cement:water = 2.75:1:0.485 was the control group to test the fresh and hardened properties of the material. The test results of hardened specimen properties showed that the addition of PCB resin powder should be less than 10 %, and the addition level of glass fiber should be less than 2 %. The engineering properties and durability matched those of the cement mortar of the standard control group. Because toxic chemicals released from PCB powder and hardened concretes were found to be less than the tolerance limit in the local ordinances, waste PCB can be used in cement mortar, providing an alternative for recycling industrial waste PCB. [ABSTRACT FROM AUTHOR]

This paper focuses on the application of Fuller's ideal gradation curve to theoretically design blended ratio of all solid materials of high performance contrete (HPC), with the aid of error function, and then to study the effect of rice husk ash (RHA) on the performance of HPC. The residual RI-IA, generated when burning rice husk pellets at temperatures varying from 600 to 800°C, was collected at steam boilers in Vietnam. The properties of fresh and hardened concrete are reviewed. It is possible to obtain the RHA concrete with comparable or better properties than those of the specimen without RHA with lower cement consumption. High flowing concrete designed by the proposed method was obtained without bleeding or segregation. The application of the proposed method for HPC can save over 50% of the consumption of cement and limit the use of water. Its strength efficiency of cement in HPC is 1.4-1.9 times higher than that of the traditional method. Local standards of durability were satisfied at the age of 91 days both by concrete resistivity and ultrasonic pulse velocity. [ABSTRACT FROM AUTHOR]

Geopolymers are environmentally friendly substitutes for Portland cement; in many applications, geopolymers not only reduce green- house gas emissions but also are recyclable. The hardening mechanism of geopolymer polymerization differs from that of ordinary Portland cement. In the present research, two methods are used to evaluate the microstructure of this inorganic material. In the first method, complete polymerization was observed by means of scanning electron microscopy (SEM) to reveal the foundations of strength establishment. The SEM results show that the synthesized geopolymer maintained a layer structure of metakaolinite particulates. Therefore, it was thought that the geopolymeric reaction mainly occurred at the surface of microflakes of metakaolinite particulates. In order to further investigate the polymerization process of the material, two Raman spectrum frequency ranges--875 nm and 325 nm--were used in the study because of their capability to characterize the mineral/hydrated phases under a thick post-treatment layer. Also, in order to facilitate quality control of the production and explore the extreme compressive strengths of metakaolin cement, the polymerization mechanism and microstructures of the products were monitored step by step using Raman spectroscopy. The lessons learned in the research program can be used to advance the research methodology needed for further investigation of the strength enhancement of the geopolymer. [ABSTRACT FROM AUTHOR]

This paper presents the way durability has been introduced to steel fiber reinforced concrete in Taiwan. It is generally acknowledged that steel fibers are added to improve the toughness, abrasion resistance, and impact strength of concrete. However, a locally developed mixture design method, the densified mixture design algorithm (DMDA), was applied to solve not only the entanglement or balling problem of steel fibers in concrete or to produce steel fiber reinforced self-consolidating concrete (SFRSCC) with excellent flow-ability, but also to increase the durability by reduction in the cement paste content. By dense packing of the aggregates and with the aid of pozzolanic material and superplasticizer (SP), concrete can flow honey-like with less entanglement of steel fibers. Such SFRSCC has already been successfully applied in several projects, such as construction of a low radiation waste container, bus station pavement, road deck panel, and two art statues. So it is recommended that the SFRSCC can be used for improving the performance of ordinary steel fiber reinforced concrete in many ways and should be considered for increasing the lifecycle of a concrete structure. [ABSTRACT FROM AUTHOR]

Two series of column specimens were tested to investigate the behavior of self-consolidating concrete (SCC) columns under concentric compression. The first series contained 16 columns made with normal concrete (NC), and the second 16 columns were made with SCC. The test variables included the concrete strength, amount of longitudinal reinforcement, volumetric ratio of transverse reinforcement, strength of transverse reinforcement, and arrangement of transverse reinforcement. Comparisons were made between the SCC and NC specimens. Behavior of the SCC used in this study was also compared with that of high-flowability concretes in other studies. The results show that SCC can have better structural performance than NC, as long as the concrete is properly proportioned. The ductility and crack control ability of SCC columns are better than NC columns. Stiffness of SCC is also higher than that of NC. Mechanical behavior of the SCC in this study was better than other SCC compared due to the larger amount of coarse aggregate used. [ABSTRACT FROM AUTHOR]

The objective of this study was to investigate the recycling of the fine sediments of Shih-Men Reservoir to manufacture lightweight aggregate. By qualitative and quantitative analysis of the fine sediment and sintered aggregate through soil test, X-ray fluorescence, X-ray diffraction and scanning electron microscopy, a strategy of recycling fine sediment as aggregate for other similar material is proposed. The test results indicate that such fine sediment can be classified as low plastic clay, and clay of such chemical composition is located in the Riley's 'area of bloating'. The particle density of sintered light-weight aggregate decreases when the sintering temperature increases especially above 1200°C due to phase transformation and formation of a vitrified layer on the surface through subsequent dehydration, bloating and collapsing stages. Our findings show that the fine sediment of Shin-Men Reservoir could be a suitable raw material for making expanded light-weight aggregate sintered at 1200 to 1300°C for 10 to 12 min by a programmable furnace and a diffusion process. [ABSTRACT FROM AUTHOR]

An abstract of the article "Self-Consolidating Concrete Columns Under Concentric Compression" is presented.