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This study investigates the influence of polypropylene (PP) fiber content on the mechanical properties of lightweight foamed concrete (LFC). Four LFC mixtures with a target dry density of 1000 kg/m3 were designed with different PP fiber volumes of 0%, 0.25%, 0.5%, and 0.8%. The fresh unit weight (UW), dry density, compressive and flexural strengths, water absorption, thermal conductivity, ultrasonic pulse velocity (UPV), and scanning electron microscopy (SEM) of the LFC were examined. The results indicate that the fresh UW, dry density, UPV, and thermal conductivity decreased when the PP content varied from 0% to 0.8%. At 28 days, the compressive and flexural strengths of the LFC increased approximately 11.85% and 41.8% when the PP fiber amount varied from 0% to 0.8%, respectively. The result implies that the PP fiber content had a higher influence on the flexural strength content than the compressive strength. Furthermore, the results of SEM could explain well the obtained mechanical properties. The findings of this study indicate that PP fiber could be used up to 0.8% by volume to reduce the self-weight of the LFC and enhance the mechanical strength as well as thermal isolation characteristics of the LFC.

As a large amount of steel is produced for the industrialization and modernization of Vietnam, a correspondingly large quantity of steel slag is also released annually. Besides, the demand for mortar is increasing due to urbanization, especially for the high-strength and durability mortar used for important constructions and structures in aggressive environmental areas. This study aims to carry out further research into high-strength mortars incorporating ground granulated blast furnace slag (GGBFS). The control mixture was designed with a water-to-binder ratio of 0.2, and the amount of silica fume used was equal to 25% of the total binder amount by mass. Four other mixtures were designed using GGBFS to substitute for 15, 30, 45, and 60% of cement by mass. The engineering properties of fresh and hardened mortars were comprehensively investigated, especially the durability properties. The microstructure of these mortars was also examined using scanning electron microscopy. Test results show that replacing 15 or 30% of cement with GGBFS yields an improvement in mortar's strength and durability properties. All the mortars in this study show excellent qualities with high strength, low water absorption, and high resistance to chloride attack. Moreover, the presence of GGBFS reduces the shrinkage of mortar caused by the drying process. Doi: 10.28991/CEJ-2022-08-05-07 Full Text: PDF

The combined utilization of fly ash and ground granulated blast-furnace slag as a partial cement substitution in the production of lightweight foamed concrete (LFC) incorporating different polypropylene (PP) fiber was investigated in this study. The LFC was prepared with a target dry density of 1200 ± 50 kg/m3 and the influence of PP fiber contents (e.g., 0, 0.3, 0.6, and 1.0% by volume) on the characteristics of LFC was examined in terms of fresh unit weight, dry density, water absorption, thermal conductivity, compressive strength, flexural strength, ultrasonic pulse velocity (UPV), and microstructural analysis using scanning electron microscopy (SEM) technique. Results show that the inclusion of PP fiber affected all of the studied characteristics of LFC. Increasing PP fiber percentages resulted in reducing dry density, thermal conductivity, and UPV. Whereas, both the mechanical strength and water absorption were found to be increased with PP fiber content. The result of the SEM analysis also supported these findings. At 28 days, all of the LFC obtained the target dry density of 1200 ± 50 kg/m3, satisfying the requirements of TCVN 9029:2017. The water absorption, thermal conductivity, UPV, compressive strength, and flexural strength values of the LFC specimens were recorded at the respective ranges of below 10%, 0.394 – 0.461 W/mK, 2955 – 3019 m/s, 15.98 – 17.33 MPa, and 2.31 – 4.07 MPa. Furthermore, the results suggested that 1.0% PP fiber was the most suitable level for the production of LFC.

This study uses densified mixture design algorithm (DMDA) to design the mixture proportions green mortars incorporating fly ash and ground granulated blast furnace slag (GGBFS). Three green mortar mixtures with various paste contents were designed using the DMDA method while a control cement-based mortar mixture was designed using the conventional method for comparison. The effect of different paste contents (n = 1.1, 1.3, and 1.5) on the changes of porosity, thermal conductivity, compressive strength, chloride ion penetration, resistance to sulfate attack, and ultrasonic pulse velocity (UPV) of both the green and control mortars was studied. The procedures of DMDA mix design for green mortar mixtures were also presented in this study. Test results reveal that all three green mixtures show a better performance than the control mixture, especially for long-term properties. On the other hand, increasing paste content increased porosity and compressive strength, however, it reduced thermal conductivity and UPV of the green mortars. All of the green mortars exhibited good performance with low porosity and compressive strength values of above 40 MPa after 28 days of curing. Moreover, the green mortars also demonstrated excellent ability to resist chloride (with RCPT values significantly lower than the threshold of 1000 coulombs) and sulfate attacks. As a result, the quality of these mortars was classified as very good level with UPV values of above 4000 m/s. This study proves the effectiveness of using the DMDA method to design the green mortar mixtures in the combination of using fly ash and GGBFS.

This paper presents the results of the experimental works to investigate the use of waste limestone from water treatment industry as fine aggregate in green concrete. Two concrete mixtures with a constant water-to-binder ratio of 0.3 were prepared for this investigation, in which, the normal concrete mixture was designed following the guidelines of ACI 211 standard, while the green concrete mixture was designed using densified mixture design algorithm (DMDA) technology. For comparison, both types of concrete samples were subjected to the same test program, including fresh properties, compressive strength, strength efficiency of cement, drying shrinkage, electrical surface resistivity, ultrasonic pulse velocity, and thermal conductivity. Test results indicate that both concrete mixtures showed the excellent workability due to the round-shape of waste limestone aggregate and the use of superplasticizer. In addition, the green concrete mixture exhibited a better performance in terms of engineering properties and durability in comparison with the normal concrete mixture. The results of the present study further support the recycling and reuse of waste limestone as fine aggregate in the production of green concrete.

This paper investigates both fresh and hardened properties of concrete produced with different particle sizes of coarse aggregate (CA). The CAs with the maximum sizes (Dmax) of 25 mm, 19 mm, 15 mm, 12.5 mm, and 9.5 mm were used to produce concrete samples with a water-to-binder ratio of 0.4. The workability, fresh unit weight, compressive strength, and ultrasonic pulse velocity (UPV) of the concrete were tested. Additionally, some concrete samples were fully immersed in 5% sodium sulfate solution in order to assess the performance of the concrete under sulfate attack condition. The experimental results show that the workability of fresh concrete increased with increasing the particle size of CA used, while the particle size of CA insignificantly affected to the unit weight of fresh concrete mixtures. The concrete mixture produced with Dmax of 12.5 mm obtained the highest compressive strength and UPV values in comparison with those of other mixtures. This study also found that the compressive strength values of concrete samples that fully immersed in sulfate solution reduced about 15% as compared with those of the concrete samples cured in lime-saturated water. All of the concrete samples prepared for this investigation exhibited good durability performance with ultrasonic pulse velocity values of above 4300 m/s. Test results also indicated that the concrete properties can be enhanced if the CA sizes were appropriately selected.

Controlled low-strength material (CLSM) is a self-compacting, flowable, and low-strength construction material that is used widely in variety construction applications. The present study evaluates the properties of CLSM that was prepared using a mixture of class-F fly ash (FA) and ground granulated blast-furnace slag (GGBFS) with the addition of three different ratios (0%, 10%, and 20% as calculated by combined FA and GGBFS weight) of waste water treatment sludge (WTS). A sodium hydroxide (NaOH) solution was used to activate these powder materials in the mixture in order to produce the alkali-activated CLSM. The effects of adding WTS on the properties of both fresh and hardened CLSM are evaluated using workability, setting time, drop ball time, unit weight, compressive strength, and toxicity characteristic leaching procedure (TCLP) tests. Moreover, a scanning electron microscope (SEM) coupled with an energy dispersive spectrometer (EDS) and X-ray diffraction (XRD) is used to examine the microstructural properties of the CLSM. Results show that adding WTS to the CLSM samples reduces workability and increases fresh unit weight and compressive strength. Additionally, initial setting time and drop ball time are both associated positively with level of WTS content. Moreover, the liquid-to-solid (L/S) ratio and the alkali equivalent (AE) are shown to affect the properties of the CLSM significantly. The TCLP assessed leaching concentrations of heavy metals are all significantly below the regulatory thresholds that are currently allowed by the Environmental Protection Administration (EPA) in Taiwan. Finally, the properties of the CLSM sample with an L/S ratio of 0.9, WTS of 10%, and AE of 9% are found to conform well to the requirements of the Public Works Department, Taipei Government in terms of design principles and provisions.

This paper is aimed to evaluate the engineering properties of fly ash-based geopolymer bricks. Four geopolymer brick mixtures were designed with a constant solution-to-binder ratio of 0.40 and various concentrations of sodium hydroxide solution. The engineering properties of fly ash-based geopolymer bricks consisting of compressive strength, unit weight, water absorption, water permeability, and ultrasonic pulse velocity were investigated. The microstructure of fly ash-based geopolymer bricks was also investigated by using the scanning electron microscope (SEM). Test results indicated that the compressive strength, unit weight, and ultrasonic pulse velocity (UPV) of geopolymer bricks increased, while the water absorption and water permeability of geopolymer bricks reduced with increasing NaOH concentration. Moreover, brick samples with high NaOH concentration showed a higher geopolymeric reaction of fly ash than brick samples with low NaOH concentration. All geopolymer brick samples produced in this study showed a good quality with compressive strength of above 10.1 MPa, water absorption of below 9.4%, water permeability of below 1.84 L/m2 .h, and UPV of above 2500 m/s.

Based on the actual, discrete locations of interception points between the critical shear crack and transverse reinforcement, this study developed the discrete computational shear strength models for 5-, 6-, and 11-circular-hoop and spiral reinforcement. Moreover, conventional simplified calculation method was revised for use for 5-, 6-, and 11-circular-hoop and spiral reinforcement. Examination of the difference between the discrete computational shear strength models and simplified calculation shows that the error of the simplified calculation increases with increasing ratios of spacing to diameter of circular hoops or spirals. Limiting values of spacing to diameter ratios were proposed to control the error of the simplification calculation to be equal to or less than 10%. Plots of modification factors were proposed to be used with the simplification calculation when the spacing to diameter ratio is large.

Unfired four-hole hollow brick (UFHB) is a type of environmental-friendly brick with low energy consumption. However, the using of ordinary Portland cement (OPC) in UFHB is costly and indirectly affects the environment. This paper focuses on an exploratory study on the use of blended fly ash (FA)-OPC in the production of the UFHB and proposes the application of FA-OPC mixtures as a timely solution for the reduction of OPC in UFHB. The 80×80×180 mm UFHB samples were produced using different proportions of FA and OPC under a constant coupled-static forming pressure. The report exhibited experimental characterizations on physical and mechanical properties of both starting materials and UFHB products. In addition, a scanning electron microscope (SEM) analysis was used to evaluate the microstructure of the final UFHB. Test results show that the inclusion of FA in the UFHB mixtures provided positive effects on brick properties. As a result, 10% FA was found as an optimal content, which resulted in the highest brick’s strength, the lowest water absorption rate, and a denser microstructure. Furthermore, properties of all of the UFHB samples produced for this study satisfied the requirements of the National Vietnamese standard for non-bearing building brick.

This study investigates the behavior of transversely reinforced oblong and rectangular bridge columns under combined axial and flexural loading, including eccentric compression and lateral cyclic loading under constant axial load. The transverse reinforcement schemes include conventional tie and multi-spiral reinforcement. The multi-spiral reinforcement for the oblong column comprises two interlocking spirals and, for rectangular columns, comprises two interlocking large central spirals interlocked with four small spirals at the corners. The amount of transverse reinforcement for all of the columns conforms to the current seismic bridge design specifications. Test results indicate that all of the columns exhibit ductile behavior with ductility capacities significantly higher than the ductility capacity required by the design code. The oblong spiral column with an amount of transverse reinforcement 43% that of the corresponding tied column shows strength, ductility, energy dissipation, and over-str...

This study developed discrete computational shear strength (DCSS) models for two-circular-hoop, two-spiral, seven-circular-hoop, and seven-spiral transverse reinforcement for reinforced concrete columns. The DCSS models show that as a shear crack moves along the column, the reinforcement shear strength varies periodically. The critical shear crack, which yields the smallest shear strength, can be from any of the shear cracks that intercept at least one edge of a hoop series or spiral. The conditions are presented for when a shear crack intercepts the two edges of every hoop series or spiral, which leads to a drastic reduction in shear strength. At the critical shear crack condition, the DCSS models yield shear strength lower than the integral averaging method. To control the error of the integral averaging method, the ratio of the reinforcement spacing to hoop or spiral diameter should be limited. Charts to correct the error are presented for use in practice.

This paper presents the experimental results of an investigation on the engineering properties and durability of high loss on ignition-fly ash concrete fully immersed in 5% sodium sulfate solution. The fly ash used in this study is a raw material with the loss on ignition of 15.8%, which is much higher than the upper limitation of 6% as stipulated by ASTM C618. Eight concrete mixtures were designed with different water-to-binder ratios of 0.35 and 0.45. For each water-to-binder ratio, the fly ash was used to replace 0%, 10%, 20%, and 30% amount of cement. Test results show that the workability of fresh concrete increased, while its unit weight decreased with increasing the fly ash replacement level. In addition, the concrete mixtures with 10% and 20% fly ash content showed the higher compressive strength, especially at long-term ages, than that of the fly ash-free concrete mixture. Further, all of the fly ash concrete mixtures exhibited the good quality with ultrasonic pulse velocity values of higher than 4100 m/s.

This study investigates the feasibility of using raw fly ash with a high loss on ignition in concrete. The fly ash-free concrete samples were prepared with different water-to-binder (w/b) ratios of 0.35, 0.40, and 0.45, whereas the fly ash concrete samples were prepared with a constant w/b of 0.40 and with various fly ash contents (10%, 20%, and 30%) as a cement substitution. The physical properties and durability performance of the concretes were evaluated through fresh concrete properties, compressive strength, strength efficiency of cement, ultrasonic pulse velocity, and resistance to sulfate attack. Test results show that the w/b ratio affected the concrete properties significantly. The incorporation of fly ash increased the workability and reduced the unit weight of fresh concrete. In addition, the fly ash concrete samples containing up to 20% fly ash exhibited an improved strength at long-term ages. Further, all of the fly ash concrete samples showed a good durability performance with ultrasonic pulse velocity value of greater than 4100 m/s and a comparable sulfate resistance to the no-fly ash concrete.

This research proposes innovative seven- and 11-spiral transverse reinforcement to replace two- And six-spiral reinforcement, respectively, to decrease spiral size to address the issue of spiral fabrication in large columns. Moreover, this research proposes using large reinforcing bars or H-shaped steel as longitudinal reinforcement to reduce the potential of reinforcing bar cage failure. The objectives of this research were to investigate the seismic performance of seven- And 11-spiral columns and the effect of using large reinforcing bars and H-shape steel as longitudinal reinforcement. Cyclic tests of columns showed that seven- And 11-spiral columns, even with less amounts of transverse reinforcement, exhibited higher ductility capacities than tied columns. The use of H-shaped steel as longitudinal reinforcement increased ductility and energy dissipation of the column. Among ACI 318, Caltrans BDS, and Caltrans SDC methods to estimate probable moment strength, only the Caltrans SDC method produced conservative results for all columns examined.

An innovative seven-spiral transverse reinforcement is proposed for oblong reinforced concrete bridge columns. Compared to conventional single-spiral or two-spiral transverse reinforcement, the proposed scheme reduces the size of the spirals and hence improves the constructibility of spirals for large bridge columns. Four seven-spiral columns were tested under high shear stress to assess their performance. Comparable conventional tied and two-spiral columns were also tested. Test results showed that spirals in the proposed seven-spiral columns remained interlocked. With less transverse reinforcement, the seven-spiral columns achieved similar or better shear performance compared to the tied columns. The seven-spiral column exhibited the highest effective shear coefficient, followed by the two-spiral column and the tied column. Comparison of shear-strength predictions with the test results shows that the ACI (American Concrete Institute) 318 model generally provides conservative estimates, and the Caltrans SDC (Seismic Design Criteria) and Sezen models provide reasonable estimates of experimental behavior in terms of failure point prediction.