Influence of off-spec fly ash and surfactant-coated nano-iron-oxide on the fresh and hardened properties of cement pastes: An exploratory study

AbstractNatural gypsum can degenerate into hemihydrate during cement clinker grinding which changes the physical and chemical properties of cement hydration, affecting therefore the fresh and hardened properties of cement based materials. Cement systems containing a constant total amount of calcium sulfate (4%) with relative proportions of hemihydrate and natural gypsum were considered. Rheological measurements were executed on an Anton Paar MCR51 rheometer to evaluate the flow properties of cement pastes. Results show that, the yield stress and the plastic viscosity of cement pastes were affected when the degeneration of natural gypsum exceeded 50%. Above this concentration, the yield stress remarkably increased and a variation in plastic viscosity of about 50% was observed. Using TG-DSC techniques, it was shown that, the amount of formed ettringite could not explain these rheological changes. However, centrifugational packing and SEM-SE measurements confirmed that, more than the amount of ettringite precipitated, ettringite morphology plays a major role in controlling the yield stress and plastic viscosity of fresh cement pastes.

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Zeolite-iron oxide nanocomposite from fly ash formed a ‘clubbell’ structure: integration of cardiac biocapture macromolecules in serum on microelectrodes

Microchimica Acta ◽

10.1007/s00604-021-04834-w ◽

2021 ◽

Vol 188 (6) ◽

Author(s):

Zhiqiang Liu ◽

Subash C. B. Gopinath ◽

Zhifang Wang ◽

Yibo Li ◽

Periasamy Anbu ◽

...

Keyword(s):

Iron Oxide ◽

Fly Ash

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New Approach for the Determination of Radiological Parameters on Hardened Cement Pastes with Coal Fly Ash

Materials ◽

10.3390/ma14030475 ◽

2021 ◽

Vol 14 (3) ◽

pp. 475

Author(s):

Ana María Moreno de los Reyes ◽

José Antonio Suárez-Navarro ◽

Maria del Mar Alonso ◽

Catalina Gascó ◽

Isabel Sobrados ◽

...

Keyword(s):

Fly Ash ◽

Activity Concentration ◽

Gamma Ray ◽

Coal Fly Ash ◽

Cementitious Materials ◽

New Method ◽

Supplementary Cementitious Materials ◽

Hardened Cement ◽

Cement Pastes ◽

Activity Concentrations

Supplementary cementitious materials (SCMs) in industrial waste and by-products are routinely used to mitigate the adverse environmental effects of, and lower the energy consumption associated with, ordinary Portland cement (OPC) manufacture. Many such SCMs, such as type F coal fly ash (FA), are naturally occurring radioactive materials (NORMs). 226Ra, 232Th and 40K radionuclide activity concentration, information needed to determine what is known as the gamma-ray activity concentration index (ACI), is normally collected from ground cement samples. The present study aims to validate a new method for calculating the ACI from measurements made on unground 5 cm cubic specimens. Mechanical, mineralogical and radiological characterisation of 28-day OPC + FA pastes (bearing up to 30 wt % FA) were characterised to determine their mechanical, mineralogical and radiological properties. The activity concentrations found for 226Ra, 212Pb, 232Th and 40K in hardened, intact 5 cm cubic specimens were also statistically equal to the theoretically calculated values and to the same materials when ground to a powder. These findings consequently validated the new method. The possibility of determining the activity concentrations needed to establish the ACI for cement-based materials on unground samples introduces a new field of radiological research on actual cement, mortar and concrete materials.

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Effect of Chopped Basalt Fiber on the Fresh and Hardened Properties of Fly Ash High Strength Concrete

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.567.381 ◽

2014 ◽

Vol 567 ◽

pp. 381-386 ◽

Cited By ~ 1

Author(s):

Nasir Shafiq ◽

Muhd Fadhil Nuruddin ◽

Ali Elheber Ahmed Elshekh ◽

Ahmed Fathi Mohamed Salih

Keyword(s):

Compressive Strength ◽

Fly Ash ◽

High Strength Concrete ◽

Basalt Fiber ◽

High Strength ◽

Progressive Increase ◽

Test Results ◽

Strength Concrete ◽

Hardened Properties ◽

Chopped Basalt Fiber

In order to improve the mechanical properties of high strength concrete, HSC, several studies have been conducted using fly ash, FA. Researchers have made it possible to achieve 100-150MPa high strength concrete. Despite the popularity of this FAHSC, there is a major shortcoming in that it becomes more brittle, resulting in less than 0.1% tensile strain. The main objective of this work was to evaluate the fresh and hardened properties of FAHSC utilizing chopped basalt fiber stands, CBFS, as an internal strengthening addition material. This was achieved through a series of experimental works using a 20% replacement of cement by FA together with various contents of CBFS. Test results of concrete mixes in the fresh state showed no segregation, homogeneousness during the mixing period and workability ranging from 60 to 110 mm. Early and long terms of compressive strength did not show any improvement by using CBFS; in fact, it decreased. This was partially substituted by the effect of FA. Whereas, the split and flexural strengths of FASHC were significantly improved with increasing the content of CBFS as well as the percentage of the split and flexural tensile strength to the compressive strength. Also, test results showed a progressive increase in the areas under the stress-strain curves of the FAHSC strains after the CBFS addition. Therefore, the brittleness and toughness of the FAHSC were enhanced and the pattern of failure moved from brittle failure to ductile collapse using CBFS. It can be considered that the CBFS is a suitable strengthening material to produce ductile FAHSC.

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Assessment of Hydration Degree of Cement in the Fly Ash-Cement Pastes Based on the Calcium Hydroxide Content

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.875-877.177 ◽

2014 ◽

Vol 875-877 ◽

pp. 177-182 ◽

Cited By ~ 2

Author(s):

Xiang Li ◽

Hua Quan Yang ◽

Ming Xia Li

Keyword(s):

Fly Ash ◽

Calcium Hydroxide ◽

Cement Hydration ◽

Ash Content ◽

Content Increase ◽

Hydration Degree ◽

Equilibrium Calculation ◽

Cement Pastes ◽

Cement Ratio ◽

Water Cement Ratio

The hydration degree of fly ash and the calcium hydroxide (CH) content were measured. Combined with the equilibrium calculation of cement hydration, a new method for assessment of the hydration degree of cement in the fly ash-cement (FC) pastes based on the CH content was developed. The results reveal that as the fly ash content increase, the hydration degree of fly ash and the CH content decrease gradually; at the same time, the hydration degree of cement increase. The hydration degree of cement in the FC pastes containing a high content of fly ash (more than 35%) at 360 days is as high as 80%, even some of which hydrates nearly completely. The effect of water-cement ratio to the hydration degree of cement in the FC pastes is far less distinct than that of the content of fly ash.

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