scholarly journals Effect of CaO on the Autogenous Shrinkage of Alkali-Activated Slag Mortar

2021 ◽  
Vol 2021 ◽  
pp. 1-9
Author(s):  
Dengdeng Zheng ◽  
Tao Ji ◽  
Guojie Wang
Keyword(s):  
Autogenous Shrinkage ◽  
Magic Angle Spinning ◽  
Partial Replacement ◽  
Hydration Reaction ◽  
Magic Angle ◽  
Promising Alternative ◽  
Alkali Activated Slag ◽  
Angle Spinning ◽  
Activated Slag ◽  
Alkali Activated

The autogenous shrinkage of alkali-activated slag (AAS) is significantly higher than that of ordinary Portland cement (OPC). The higher risk of concrete cracking due to autogenous shrinkage is a critical drawback to wider use of this promising alternative binder. The effect of CaO content on the autogenous shrinkage of AAS mortar was investigated. The autogenous shrinkage of AAS mortars was determined by comparator. The pore structure of the pastes was determined by mercury intrusion porosimetry. The hydration products of the pastes were determined by Fourier transform-infrared, thermogravimetric analysis, X-ray diffraction, and 29Si solid-state magic-angle spinning nuclear magnetic resonance. The results show that the amount of portlandite increases as CaO content increases. CaO in the paste causes the partial replacement of C-S-H(I) (low stiffness) by C-S-H(II) (high stiffness). The hydration reaction of AAS is inhibited by the addition of CaO. The increase of polymerization degree of C-(A-)S-H and rearrangement of C-S-H(I) during hydration are inhibited by the addition of CaO, and micropores closure is also inhibited. Therefore, the autogenous shrinkage of AAS mortar decreases with the increase of CaO content.

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

Materials ◽  
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.

Experimental Study of Alkali-Activated Red Mud Cement Material

2013 ◽  
Vol 357-360 ◽  
pp. 705-709 ◽  
Author(s):  
Min Zhou ◽  
Yong Sheng Ji ◽  
Zheng Chang ◽  
Chan Zhang ◽  
Xing Tong Yan
Keyword(s):  
Experimental Study ◽  
Flexural Strength ◽  
Red Mud ◽  
Hydration Reaction ◽  
Cement Material ◽  
Alkali Activated Slag ◽  
Strength Variation ◽  
Activated Slag ◽  
Alkali Activated ◽  
Sem Test

In order to use the alkaline ingredient in red mud, this paper studied the strength variation law of alkali-activated red mud and lime cement material combined with slag. When the content ranged from 0 wt% to 20 wt%, the experiment showed that the flexural strength increased when the content increased, and the compress strength increased when the content increased with the content ranging from 0 wt% to 15 wt%. When the content reached 25 wt%, the strength of alkali-activated red mud cement material was equal with alkali activated slag cement. The SEM test of alkali-activated red mud cement material showed that red mud and lime both participated in hydration reaction fully.

scholarly journals Effect of Sodium Aluminate Dosage as a Solid Alkaline Activator on the Properties of Alkali-Activated Slag Paste

2021 ◽  
Vol 2021 ◽  
pp. 1-13
Author(s):  
Bin Chen ◽  
Jun Wang ◽  
Jinyou Zhao
Keyword(s):  
Mechanical Properties ◽  
Compressive Strength ◽  
Setting Time ◽  
Sodium Aluminate ◽  
Hydration Reaction ◽  
Hydration Products ◽  
Alkali Activated Slag ◽  
Alkaline Activator ◽  
Activated Slag ◽  
Alkali Activated

Extensive research into alkali-activated slag as a green gel material to substitute for cement has been done because of the advantages of low-carbon dioxide emissions and recycling of industrial solid waste. Alkali-activated slag usually has good mechanical properties, but the too fast setting time restricted its application and promotion. Changing the composition of alkaline activator could optimize setting time, usually making it by adding sodium carbonate or sodium sulfate but this would cause insufficient hydration reaction power and hinder compressive strength growth. In this paper, the effect of sodium aluminate dosage as an alkaline activator on the setting time, fluidity, compressive strength, hydration products, and microstructures was studied through experiments. It is fair to say that an appropriate amount of sodium aluminate could obtain a suitable setting time and better compressive strength. Sodium aluminate provided enough hydroxyl ions for the paste to promote the hydration reaction process that ensured obtaining high compressive strength and soluble aluminium formed precipitate wrapped on the surface of slag to inhibit the hydration reaction process in the early phase that prolonged setting time. The hydration mechanism research found that sodium aluminate played a key role in the formation of higher cross-linked gel hydration products in the late phase of the process. Preparing an alkali-activated slag with excellent mechanical properties and suitable setting time will significantly contribute to its application and promotion.

scholarly journals A Low-Autogenous-Shrinkage Alkali-Activated Slag and Fly Ash Concrete

2020 ◽  
Vol 10 (17) ◽  
pp. 6092
Author(s):  
Zhenming Li ◽  
Xingliang Yao ◽  
Yun Chen ◽  
Tianshi Lu ◽  
Guang Ye
Keyword(s):  
Fly Ash ◽  
Portland Cement ◽  
High Performance ◽  
Structural Engineering ◽  
Autogenous Shrinkage ◽  
Portland Cement Concrete ◽  
Alkali Activated Slag ◽  
Cracking Potential ◽  
Activated Slag ◽  
Alkali Activated

Alkali-activated slag and fly ash (AASF) materials are emerging as promising alternatives to conventional Portland cement. Despite the superior mechanical properties of AASF materials, they are known to show large autogenous shrinkage, which hinders the wide application of these eco-friendly materials in infrastructure. To mitigate the autogenous shrinkage of AASF, two innovative autogenous-shrinkage-mitigating admixtures, superabsorbent polymers (SAPs) and metakaolin (MK), are applied in this study. The results show that the incorporation of SAPs and MK significantly mitigates autogenous shrinkage and cracking potential of AASF paste and concrete. Moreover, the AASF concrete with SAPs and MK shows enhanced workability and tensile strength-to-compressive strength ratios. These results indicate that SAPs and MK are promising admixtures to make AASF concrete a high-performance alternative to Portland cement concrete in structural engineering.

scholarly journals A Review of Durability and Strength Characteristics of Alkali-Activated Slag Concrete

Materials ◽  
2019 ◽  
Vol 12 (8) ◽  
pp. 1198 ◽  
Author(s):  
Osama Ahmed Mohamed
Keyword(s):  
Rapid Development ◽  
Setting Time ◽  
High Rate ◽  
Alkali Activation ◽  
Promising Alternative ◽  
Alkali Activated Slag ◽  
Granulated Blast Furnace Slag ◽  
High Alkalinity ◽  
Activated Slag ◽  
Alkali Activated

Alkali-activated slag (AAS) is a promising alternative to ordinary Portland cement (OPC) as sole binder for reinforced concrete structures. OPC is reportedly responsible for over 5% of the global CO2 emission. In addition, slag is an industrial by-product that must be land-filled if not re-used. Therefore, it has been studied by many investigators as environmentally friendly replacement of OPC. In addition to recycling, AAS offers favorable properties to concrete such as rapid development of compressive strength and high resistance to sulfate attack. Some of the potential shortcomings of AAS include high shrinkage, short setting time, and high rate of carbonation. Using ground granulated blast furnace slag (GGBS) as an alternative to OPC requires its activation with high alkalinity compounds such as sodium hydroxide (NaOH), sodium sulfate (Na2SO3), sodium carbonate (Na2CO3), or combination of these compounds such as NaOH and Na2SO3. The mechanism of alkali-activation is still not fully understood and further research is required. This paper overviews the properties, advantages, and potential shortcomings of AAS concrete.

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