Incorporation of High Loss-on-ignition Fly Ash in Producing High-strength Flowable Mortar

A large amount of fly ash with a high loss on ignition (over the maximum allowance value stipulated by ASTM C618) is being released and increasing daily in Vietnam. The recycling of this fly ash is still limited, while a big remaining part is disposed of in storage yards, causing environmental pollution. On the other hand, the demand for high-strength mortar as a repair material is increasing for high-rise buildings and important projects, gradually depleting natural resources. However, the application of this fly ash in the production of mortar is restricted in the literature. In this study, local fly ash with a high loss on ignition is used to replace 0%, 15%, 30%, 45%, and 60% cement content in producing high-flowability and high-strength mortar. Changes in the fresh and hardened mortar properties were systematically investigated using samples produced with various fly ash contents. Test results indicate that the effect of impurities in fly ash on the mortar’s workability can be neglected due to the spherical shape of fly ash. The unit weight, thermal conductivity, and drying shrinkage of mortars decreased with increasing fly ash content. Although some other properties of mortar are reduced due to the use of high loss-on-ignition fly ash, all mortars produced in this study still showed good quality with the presence of silica fume. In addition, the relationships between compressive strength and flexural strength with ultrasonic pulse velocity were established to predict the strength of mortar in a non-destructive method

A Modified Reactive Powder Concrete Made with Fly Ash and River Sand: An Assessment on Engineering Properties and Microstructure

Containing a high quantity of both fine powders and steel fiber makes reactive powder concrete (RPC) a unique kind of ultra-high strength concrete. However, the cost of manufacture, shrinkage, and hydration heat are increased when silica fume and cement are used in significant amounts. To mitigate these negative consequences and the environmental impact, this study assessed the use of fly ash (FA) with high volume combined with natural-fine river sand (NFRS) in the manufacturing of RPC. FA was utilized to partially substitute cement at 0, 20, 40, and 60 wt% in RPC mixtures that had a set water/binder ratio of 0.2. Thermal conductivity, porosity, water absorption, and compressive strength tests were performed. Furthermore, RPC's microstructure was examined using a scanning electron microscope (SEM). This study also included a cost and global warming potential analysis of RPC production. Test results indicated that a modified RPC with a 60 MPa compressive strength value could be created by using NFRS and a large amount of FA. In comparison to the reference mixture, a higher compressive strength, reduced water absorption, and lesser porosity were observed in RPC when the FA replacement amount was less than 40%. Many FA particles did not engage in the hydration reaction when the FA replacement level was more than 40%, which had a detrimental impact on the RPC's characteristics. In general, using FA to produce RPC has certain benefits for the economy and the environment. It is recommended that 40% of FA be used in actual practice

Effect of Coconut Fiber Content on the Properties of Unfired Building Bricks Incorporating Thermal Power Plant Ashes

This study examined the effect of coconut fiber (CF) content on the properties of unfired building bricks (UBBs) using fly ash (FA) and bottom ash (BA) from the Nghi Son coal-fired thermal power plant (CTP). Cement and FA served as binders while BA replaced crushed stone as the fine aggregate. Raw brown CFs were treated with a 5% NaOH solution at 50 °C to increase their mechanical properties. The treated CFs were then cut to a short length of 15 mm and had an average aspect ratio of 103. Brick samples were cast with CF content at ratios of 0%, 3%, 6%, and 9% by binder weight (CF/B) and water-to-binder (W/B) ratios of 0.30 and 0.35. The UBBs were formed under a low pressure of 0.5 MPa and tested to evaluate the effects of CF/B and W/B ratios on brick properties. Results showed that compressive strength (CS) increased with higher CF content, with all samples exceeding 10 MPa after 28 days, classifying them as grade M10 per TCVN 6477:2016. The optimal CF content was 6%, which yielded the highest CS. Increasing CF content reduced unit weight (UW), ultrasonic pulse velocity (UPV), and thermal conductivity (TC), while water absorption (WA) increased. Conversely, a lower W/B ratio improved CS, UW, UPV, and TC, while reducing WA. Microstructural observations revealed that CF acts as a bridge connecting cracks, which helps restrain crack widening and enhance CS

Safety and efficacy of fluoxetine on functional outcome after acute stroke (AFFINITY): a randomised, double-blind, placebo-controlled trial

Background Trials of fluoxetine for recovery after stroke report conflicting results. The Assessment oF FluoxetINe In sTroke recoverY (AFFINITY) trial aimed to show if daily oral fluoxetine for 6 months after stroke improves functional outcome in an ethnically diverse population. Methods AFFINITY was a randomised, parallel-group, double-blind, placebo-controlled trial done in 43 hospital stroke units in Australia (n=29), New Zealand (four), and Vietnam (ten). Eligible patients were adults (aged ≥18 years) with a clinical diagnosis of acute stroke in the previous 2–15 days, brain imaging consistent with ischaemic or haemorrhagic stroke, and a persisting neurological deficit that produced a modified Rankin Scale (mRS) score of 1 or more. Patients were randomly assigned 1:1 via a web-based system using a minimisation algorithm to once daily, oral fluoxetine 20 mg capsules or matching placebo for 6 months. Patients, carers, investigators, and outcome assessors were masked to the treatment allocation. The primary outcome was functional status, measured by the mRS, at 6 months. The primary analysis was an ordinal logistic regression of the mRS at 6 months, adjusted for minimisation variables. Primary and safety analyses were done according to the patient's treatment allocation. The trial is registered with the Australian New Zealand Clinical Trials Registry, ACTRN12611000774921. Findings Between Jan 11, 2013, and June 30, 2019, 1280 patients were recruited in Australia (n=532), New Zealand (n=42), and Vietnam (n=706), of whom 642 were randomly assigned to fluoxetine and 638 were randomly assigned to placebo. Mean duration of trial treatment was 167 days (SD 48·1). At 6 months, mRS data were available in 624 (97%) patients in the fluoxetine group and 632 (99%) in the placebo group. The distribution of mRS categories was similar in the fluoxetine and placebo groups (adjusted common odds ratio 0·94, 95% CI 0·76–1·15; p=0·53). Compared with patients in the placebo group, patients in the fluoxetine group had more falls (20 [3%] vs seven [1%]; p=0·018), bone fractures (19 [3%] vs six [1%]; p=0·014), and epileptic seizures (ten [2%] vs two [<1%]; p=0·038) at 6 months. Interpretation Oral fluoxetine 20 mg daily for 6 months after acute stroke did not improve functional outcome and increased the risk of falls, bone fractures, and epileptic seizures. These results do not support the use of fluoxetine to improve functional outcome after stroke

Assessing the Effect of GGBFS Content on Mechanical and Durability Properties of High-Strength Mortars

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: PD

Lightweight foamed concrete reinforced with different polypropylene fiber contents

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.</jats:p

Discrete computational shear strength models for 5-, 6-, and 11-circular-hoop and spiral transverse reinforcement

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. </jats:p