Bio-Based Admixture (Black Tea Extraction) for Better Performance of Metakaolin Blended Cement Mortars

Investigation the effect of nanocarbon tube prepared from tea waste on microstructure and properties of cement mortar

Environmental contamination and the massive high cost of waste disposal have been a huge concern for scholars throughout the globe, prompting them to alternatives of recycling waste materials in various implementation fields. The rising expenditure on disposal and the shortage of naturally main resources such as aggregate have increased interest in reusing recycled waste materials to manufacture concrete and mortar. The annual consumption of a country's population of hundreds of tons of black tea results in considerable numbers of discarded teabags. These huge quantities are disposed in landfills without being recycled or otherwise used. Moreover, such landfills are considered one of the country's biggest global issues. Therefore, the aim of this experimental work is to investigate the influence of nanocarbon tube produced from tea waste as cement replacement materials in mortar mixtures. Cement mortar mixes contain four replacement levels (1%, 2%, 3%, and 4%) of cement with nanocarbon tube produced from tea waste. The compressive strength, ultrasonic pulse velocity, and water absorption were tested to demonstrate the effect of the nanocarbon tube made from recycled tea waste on the mechanical properties of the mortar mix. The fresh properties such as flow rate were evaluated in accordance to specific standards. Scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDX) analyses were performed to demonstrate the microstructure of the mixtures. The results show that the fresh properties (flowability) of mortar containing nanocarbon tubes from tea waste were improved with the increase of the replacement ratio. In addition, the compressive strength was improved by substitution of up to 2%. For the other levels of substitution, it decreased with an increasing replacement percentage. In contrast, the density had increased with the increase of substitution levels of the tea waste. Based on the results of the experiments, it seems that the suggested biomixture could increase the compressive strength of the material by up to 2% of the replacement at 28 days of curing.

Effect and Mechanism of Metakaolin Powder (MP) on Rheological and Mechanical Properties of Cementitious Suspension

The effects of metakaolin powder (MP) on the microscopic rheological properties and macroscopic flow parameters of cementitious suspension under various water-cement ratios were investigated. By analyzing the changes in the bonding strength coefficient and water film thickness (WFT), the mechanism of MP on flow and rheological parameters can be explored. Further, the effect of MP on mechanical properties was explained from the perspective of water absorption kinetics and hydration activity contribution rate. The incorporation of MP can reduce the flow rate and flow spread and increase the compressive strength, plastic viscosity, yield stress and thixotropy, and the effects of MP were distinctive under various W/CM ratios. The bonding strength coefficient and WFT increased and decreased with increasing MP replacement content, respectively. The regression analysis results revealed that the bonding strength coefficient and WFT were the most important factors influencing the macroscopic flow parameters and rheological parameters, which indicated that MP influenced the rheology and flowability of cementitious suspension by affecting the flocculent structure and particle distance. Compared with WFT, the bonding strength coefficient had a stronger effect on these parameters. The MP improved the compressive strength by reducing the average pore size and porosity and increasing the pore uniformity and hydration activity contribution rate of hardened paste, and this improvement was enhanced by increasing curing age.

Assessment of Pozzolanic Activity of Ground Scoria Rocks under Low- and High-Pressure (Autoclave) Steam Curing

Two sources of natural scoria rocks were procured and ground for use in concrete as natural pozzolans (NP1 and NP2). The evaluation of their pozzolanic reactivity is carried out using different techniques and approaches. The primary goal of employing these techniques is to monitor the amount of portlandite (CH=Ca(OH)₂) consumed during steam curing at low or high pressure. The pozzolanicity of NP powders is determined either directly by monitoring CH variation or indirectly by compressive strength and microstructure development. Autoclave curing is known to stimulate the pozzolanicity of the inert siliceous and aluminosiliceous materials under its high-pressure steam conditions. Both steam-curing conditions were applied in this investigation. In this study, X-ray diffraction, scanning electron microscope, thermogravimetric, Fourier transform infrared, and isothermal analyzers were used. It is concluded that the nature and types of minerals in SR determine their pozzolanic reactivity as either low-pressure steam-reactive or high-pressure steam-reactive cementitious materials. Due to the nature of their silicate structures, notably single-chain or 3D-framework structures, plagioclase feldspars (albite-anorthite) minerals are high-pressure steam-reactive minerals, whereas pyroxene (enstatite and diopside) minerals are low-pressure steam-reactive minerals. Using high-pressure steam curing, varied replacement levels of up to 60% were achieved in NP1, with a consistent strength activity index (SAI) of 99%, while an SAI of 79% was obtained with NP2. During low-pressure steam curing, NP1 and NP2 consumed around 72 and 80% of portlandite, respectively, demonstrating their relative pozzolanic reactivity. When compared to the control concrete mix, the strength activity indices of NP1, NP2, and class F fly ash in their normal concrete mixes reached 74.3, 82, and 73.7%, respectively, after 56 days of normal curing conditions.