Drying shrinkage behavior of hybrid alkali activated cement (HAAC) mortars

Nowadays, alkali-activated cements (AACs) are the most promising alternatives to ordinary portland cement (OPC). Such cements characterized by better strength and corrosion resistance that determine improved durability of materials based on them. However, the shrinkage of AAC systems is noticeably higher compared with OPC. The purpose of this work was to study the shrinkage behavior of alkali-activated slag cement (AASC) pastes. To improve early age performance of AASCs – OPC and Ca(OH)2, as mineral additives, were added to the designed cement mixtures. The properties, like, flexural and compressive strength of cement mortars, chemical shrinkage, autogenous shrinkage and drying shrinkage of cement pastes were studied. The results showed that the chemical shrinkage, autogenous shrinkage and drying shrinkage at 28 days were between 0.064 – 0.074 ml/g, 4.5 – 7.9 mm/m and 3.3 – 4.9 mm/m, respectively. The relationship between the nature of alkaline components, the type of mineral additives and the shrinkage behavior of cements were discussed.

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Investigation of drying shrinkage of alkali-activated cement paste

IOP Conference Series Earth and Environmental Science ◽

10.1088/1755-1315/567/1/012035 ◽

2020 ◽

Vol 567 ◽

pp. 012035

Author(s):

Yukun Kong

Keyword(s):

Cement Paste ◽

Drying Shrinkage ◽

Alkali Activated ◽

Alkali Activated Cement

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Effects of Expansive Additives on the Shrinkage Behavior of Coal Gangue Based Alkali Activated Materials

Crystals ◽

10.3390/cryst11070816 ◽

2021 ◽

Vol 11 (7) ◽

pp. 816

Author(s):

Xu Gao ◽

Chao Liu ◽

Zhonghe Shui ◽

Rui Yu

Keyword(s):

Mechanical Properties ◽

High Performance Concrete ◽

Early Stage ◽

Drying Shrinkage ◽

Coal Gangue ◽

Reaction Process ◽

Activated Coal ◽

Activated Coal Gangue ◽

Alkali Activated ◽

Shrinkage Behavior

The suitability of applying shrinkage reducing additives in alkali activated coal gangue-slag composites is discussed in this study. The effect of sulphoaluminate cement (SAC), high performance concrete expansion agent (HCSA) and U-type expansion agent (UEA) on the reaction process, shrinkage behavior, phase composition, microstructure and mechanical properties are evaluated. The results show that the addition of SAC slightly mitigates the early stage reaction process, while HCSA and UEA can either accelerate or inhibit the reaction depending on their dosage. The addition of SAC presents an ideal balance between drying shrinkage reduction and strength increment. As for HCSA and UEA, the shrinkage and mechanical properties are sensitive to their replacement level; excessive dosage would result in remarkable strength reduction and expansion. The specific surface area and average pore size of the hardened matrix are found to be closely related with shrinkage behavior. SAC addition introduces additional hydrotalcite phases within the reaction products, while HCSA and UEA mainly result in the formation of CaCO3 and Ca(OH)2. It is concluded that applying expansive additives can be an effective approach in reducing the drying shrinkage of alkali activated coal gangue-slag mixtures, while their type and dosage must be carefully handled.

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Understanding the Role of Metakaolin towards Mitigating the Shrinkage Behavior of Alkali-Activated Slag

Materials ◽

10.3390/ma14226962 ◽

2021 ◽

Vol 14 (22) ◽

pp. 6962

Author(s):

Bo Fu ◽

Zhenyun Cheng ◽

Jingyun Han ◽

Ning Li

Keyword(s):

Compressive Strength ◽

Setting Time ◽

Drying Shrinkage ◽

Activator Concentration ◽

Reaction Products ◽

Alkali Activated Slag ◽

Activated Slag ◽

Alkali Activated ◽

Shrinkage Behavior

This research investigates the mechanism of metakaolin for mitigating the autogenous and drying shrinkages of alkali-activated slag with regard to the activator parameters, including concentration and modulus. The results indicate that the incorporation of metakaolin can decrease the initial viscosity and setting time. Increasing activator concentration can promote the reaction process and shorten the setting time. An increase in the metakaolin content induces a decrease in compressive strength due to reduced formation of reaction products. However, increasing activator dosage and modulus can improve the compressive strength of alkali-activated slag containing 30% metakaolin. The inclusion of metakaolin can mitigate the autogenous and drying shrinkage of alkali-activated slag by coarsening the pore structure. On the other hand, increases in activator concentration and modulus result in an increase in magnitude of the autogenous and drying shrinkage of alkali-activated slag containing metakaolin. The influence of the activator modulus on the shrinkage behavior of alkali-activated slag-metakaolin binary system should be further investigated.

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Improved Reactivity of Volcanic Ash using Municipal Solid Incinerator Fly Ash for Alkali-Activated Cement Synthesis

Waste and Biomass Valorization ◽

10.1007/s12649-019-00604-1 ◽

2019 ◽

Vol 11 (6) ◽

pp. 3035-3044

Author(s):

Sylvain Tome ◽

Marie-Annie Etoh ◽

Jacques Etame ◽

Sanjay Kumar

Keyword(s):

Fly Ash ◽

Volcanic Ash ◽

Alkali Activated ◽

Alkali Activated Cement

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

Materials ◽

10.3390/ma12101673 ◽

2019 ◽

Vol 12 (10) ◽

pp. 1673 ◽

Cited By ~ 3

Author(s):

Hyeongmin Son ◽

Sol Moi Park ◽

Joon Ho Seo ◽

Haeng Ki Lee

Keyword(s):

Fly Ash ◽

Pore Structure ◽

Drying Shrinkage ◽

Phase Changes ◽

X Ray Diffraction ◽

Activated Slag ◽

Capillary Tension ◽

Alkali Activated Binders ◽

Internal Pore Structure ◽

Alkali Activated

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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Efflorescence of microwave-heated alkali-activated cement synthesized with ultrafine coal combustion ashes

Fuel ◽

10.1016/j.fuel.2021.121225 ◽

2021 ◽

Vol 303 ◽

pp. 121225

Author(s):

Huimei Zhu ◽

Pei Qiao ◽

Yuwen Zhang ◽

Jiani Chen ◽

Hui Li

Keyword(s):

Coal Combustion ◽

Ultrafine Coal ◽

Alkali Activated ◽

Alkali Activated Cement

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Alkali-Activated EAF Reducing Slag as Binder for Concrete

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.723.580 ◽

2013 ◽

Vol 723 ◽

pp. 580-587

Author(s):

Wen Huan Zhong ◽

Tung Hsuan Lu ◽

Wei Hsing Huang

Keyword(s):

Portland Cement ◽

Drying Shrinkage ◽

Portland Cement Concrete ◽

Steel Making ◽

Chemical Content ◽

Alkaline Activator ◽

Furnace Slag ◽

Alkali Activated ◽

Better Than

Electric arc furnace (EAF) reducing slag is the by-product of EAF steel-making. Currently, reducing slag is considered a waste material by the industry in Taiwan. Since the chemical content of reducing slag is similar to blast furnace slag (BFS), it is expected that reducing slag exhibits a similar pozzolanic effect as the BFS. This study used alkaline activator consisting of sodium silicate and sodium hydroxide to improve the activity of reductive slag so as to replace Portland cement as binder in concrete. Some BFS was used to blend with the reducing slag to enhance the binding quality of alkali-activated mixes. The results show that a blend of 50% BFS and 50% reducing slag can be activated successively with alkali. Also, the sulfate resistance of concrete made with alkali-activated EAF reducing slag is found to be better than that of concrete made with portland cement, while the drying shrinkage of alkali-activated EAF reducing slag concrete is greater than that of portland cement concrete.

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