Effect of CaSO4 Incorporation on Pore Structure and Drying Shrinkage of Alkali-Activated Binders

This present study investigates the effects of CaSO4 incorporation on the pore structure and drying shrinkage of alkali-activated slag and fly ash. The slag and fly ash were activated at a 5:5 ratio by weighing with a sodium silicate. Thereafter, 0%, 5%, 10%, and 15% of CaSO4 were incorporated to investigate the changes in phase formation and internal pore structure. X-Ray Diffraction (XRD), thermogravimetry (TG)/derivative thermogravimetry (DTG), mercury intrusion porosimetry (MIP), nuclear magnetic resonance (NMR), and drying shrinkage tests were carried out to find the correlation between the pore structure and drying shrinkage of the specimens. The results showed that CaSO4 incorporation increased the formation of thenardite, and these phase changes affected the pore structure of the activated fly ash and slag. The increase in the CaSO4 content increased the pore distribution in the mesopore. As a result, the capillary tension and drying shrinkage decreased.

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Mitigating the Drying Shrinkage and Autogenous Shrinkage of Alkali-Activated Slag by NaAlO2

Materials ◽

10.3390/ma13163499 ◽

2020 ◽

Vol 13 (16) ◽

pp. 3499

Author(s):

Bin Chen ◽

Jun Wang ◽

Jinyou Zhao

Keyword(s):

Autogenous Shrinkage ◽

Drying Shrinkage ◽

Nitrogen Adsorption ◽

Partial Substitution ◽

Hydration Reaction ◽

X Ray Diffraction ◽

Na2o Content ◽

Alkali Activated Slag ◽

Activated Slag ◽

Alkali Activated

The shrinkage of alkali-activated slag (AAS) is obviously higher than ordinary Portland cement, which limited its application in engineering. In this study, the effects of NaAlO2 in mitigating drying shrinkage and autogenous shrinkage of AAS were studied. To further understand the shrinkage mechanism, the hydration products and microstructures were studied by X-ray diffraction, scanning electron microscopy and nitrogen adsorption approaches. As the partial substitution rate of NaAlO2 for Na2SiO3 increased, the drying shrinkage and autogenous shrinkage reduced significantly. The addition of NaAlO2 could slow down the rate of hydration reaction and reduce the porosity, change the pore diameter and the composition of generated paste and cause more hydrotalcite and tetranatrolite generated—which contributed to reduced shrinkage. Additionally, raising the Na2O content rate caused obvious differences in drying shrinkage and autogenous shrinkage. As the Na2O content elevated, the drying shrinkage decreased and autogenous shrinkage increased. A high Na2O content would cause complete hydration reactions and provoke high autogenous shrinkage. However, incomplete hydration reactions left more water in the paste, and the evaporated water dramatically influenced drying shrinkage. The results indicate that addition of NaAlO2 could greatly mitigate the drying shrinkage and autogenous shrinkage of AAS.

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A Systematic Study on Polymer-Modified Alkali-Activated Slag–Part II: From Hydration to Mechanical Properties

Materials ◽

10.3390/ma13153418 ◽

2020 ◽

Vol 13 (15) ◽

pp. 3418 ◽

Cited By ~ 1

Author(s):

Zichen Lu ◽

Jan-Philip Merkl ◽

Maxim Pulkin ◽

Rafia Firdous ◽

Steffen Wache ◽

...

Keyword(s):

Mechanical Properties ◽

Pore Structure ◽

Analytical Techniques ◽

Hydration Products ◽

Ion Diffusion ◽

X Ray Diffraction ◽

Alkali Activated Slag ◽

Activated Slag ◽

Alkali Activated ◽

Polymer Latex

The effect of styrene-acrylate (SA) polymer latex on alkali-activated slag (AAS) was systematically studied in the aspects of hydration, hydration products, pore structure and mechanical properties through the combined analytical techniques including calorimetry, X-ray diffraction, thermogravimetric analysis, mercury intrusion porosimetry, and mechanical measurement. It was found that the addition of SA does not retard the AAS hydration, but slightly accelerates it, possibly due to the increasing ion diffusion through the loosely structured hydration products. Pore structure analysis indicates that the addition of polymer increases the cumulative pore volume and the portion of pores with size >100 nm in the hardened AAS paste. The addition of SA latex results in a continuous decrease of the compressive strength, but the flexural strength firstly increases and then decreases with the increase of polymer dosage. The polymer dosage of 2.5 wt % is optimal when applying polymer latex in the AAS system in this study.

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Investigation of the Effects of Magnesium-Sulfate as Slag Activator

Materials ◽

10.3390/ma13020305 ◽

2020 ◽

Vol 13 (2) ◽

pp. 305 ◽

Cited By ~ 2

Author(s):

Choonghyun Kang ◽

Taewan Kim

Keyword(s):

Compressive Strength ◽

Pore Structure ◽

Magnesium Sulfate ◽

Great Influence ◽

Hydration Products ◽

X Ray Diffraction ◽

Binder Ratio ◽

Mechanical And Microstructural Properties ◽

Activated Slag ◽

Alkali Activated

This study is about the mechanical and microstructural properties of alkali-activated slag (AAS) paste using magnesium sulfate (MS) as an activator. MS is 2%, 4%, 6%, 8% and 10% contents of binder weight and water-binder ratio is 0.35. Compressive strength, X-ray diffraction, mercury-intrusion porosimetry, and thermal analysis were performed for analysis. The MS contents at which the maximum compressive strength appeared varied according to the measurement age. Hydration products affecting compressive strength and pore structure were ettringite and gypsum. As a result, the changes of ettringite and gypsum depending on the contents of MS have a great influence on the pore structure, which causes the change of compressive strength. The high MS contents increases the amount of gypsum in the hydration products, and the excess gypsum causes high expansion, which increases the diameter and amount of pores, thereby reducing the compressive strength.

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High strength fiber reinforced one-part alkali activated slag/fly ash binders with ceramic aggregates: Microscopic analysis, mechanical properties, drying shrinkage, and freeze-thaw resistance

Construction and Building Materials ◽

10.1016/j.conbuildmat.2020.118129 ◽

2020 ◽

Vol 241 ◽

pp. 118129 ◽

Cited By ~ 6

Author(s):

Z. Abdollahnejad ◽

M. Mastali ◽

B. Woof ◽

M. Illikainen

Keyword(s):

Mechanical Properties ◽

Fly Ash ◽

Microscopic Analysis ◽

Drying Shrinkage ◽

High Strength ◽

Alkali Activated Slag ◽

Freeze Thaw ◽

Activated Slag ◽

High Strength Fiber ◽

Alkali Activated

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Rheology, shrinkage and pore structure of alkali-activated slag-fly ash mortar incorporating copper slag as fine aggregate

Construction and Building Materials ◽

10.1016/j.conbuildmat.2020.118029 ◽

2020 ◽

Vol 242 ◽

pp. 118029 ◽

Cited By ~ 6

Author(s):

Nanqiao You ◽

Yongchao Liu ◽

Dawei Gu ◽

Togay Ozbakkaloglu ◽

Jinlong Pan ◽

...

Keyword(s):

Fly Ash ◽

Pore Structure ◽

Copper Slag ◽

Fine Aggregate ◽

Alkali Activated Slag ◽

Activated Slag ◽

Alkali Activated

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Waste glass as binder in alkali activated slag–fly ash mortars

Materials and Structures ◽

10.1617/s11527-019-1404-3 ◽

2019 ◽

Vol 52 (5) ◽

Cited By ~ 2

Author(s):

G. Liu ◽

M. V. A. Florea ◽

H. J. H. Brouwers

Keyword(s):

Fly Ash ◽

Glass Powder ◽

Reference Sample ◽

Drying Shrinkage ◽

Waste Glass ◽

Reaction Products ◽

Alkali Activated Slag ◽

Carbonation Resistance ◽

Activated Slag ◽

Alkali Activated

Abstract This paper illustrates the application of waste glass powder as part of the binder in slag–fly ash systems activated by NaOH and NaOH/Na2CO3 activators. To evaluate the reaction kinetics, reaction products, mechanical properties, and durability performance of glass powder modified alkali activated slag–fly ash systems, calorimetry test, X-ray diffraction, FTIR, strength test, drying shrinkage tests, and carbonation test were conducted. From the isothermal calorimeter results, glass powder shows a higher reactivity compared to fly ash but still lower than slag. The reaction products of glass power modified samples exhibit an enhancement of polymerization degree of Si–O–T, observed in FTIR. As a consequence, higher drying shrinkage exists in glass modified mortars. The mechanical performance of different samples is mostly controlled by the Ca/Si of dry mixtures and activator type. After the slag–fly ash binder system was modified by the waste glass, a significant enhancement of resistance to carbonation was identified, especially for NaOH/Na2CO3 activated mortars, which show an increase of 300% on the carbonation resistance ability compared to the reference sample. The Na/(Si + Al) ratio of dry mixtures exhibits a positive correlation with carbonation resistance.

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