New Cementitious Materials Based on Alkali-Activated Fly Ash: Performance at High Temperatures

Recently, research on alkali-activated concrete that does not use cement as binder has been actively conducted. This alkali-activated concrete is a cement zero concrete which, instead of cement, is activated by alkali solution using fly ash known to be rich of Si and Al and enables to reduce effectively the emission of CO2 gas. This paper presents a basic study for the manufacture of cementless concrete using 100% of fly ash. To that goal, the mechanical characteristics of cementless concrete is evaluated according to the age and the variation of the molar concentration of the alkali activator with focus on the identification of the reaction mechanism. The experimental results show that larger molar concentration elutes larger quantities of Si4+ and Al3+. Specifically, approximately twice larger quantities of Si4+ and Al3+ were eluted for molar concentrations of 9M and 12M than 6M. The formation of gel at the surface of fly ash appeared to be caused by the stronger activation of fly ash in higher alkali environment. The resulting compressive strengths per age indicated that the strength of concrete could be controlled according to the molar concentration of NaOH. Moreover, results also demonstrated that a molar concentration of 9M for NaOH seems to be appropriate to secure a strength superior to 40MPa as the reference for high strength concrete in ordinary concrete.

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A comprehensive overview about the effect of nano-SiO2 on some properties of traditional cementitious materials and alkali-activated fly ash

Construction and Building Materials ◽

10.1016/j.conbuildmat.2013.10.101 ◽

2014 ◽

Vol 52 ◽

pp. 437-464 ◽

Cited By ~ 58

Author(s):

Alaa M. Rashad

Keyword(s):

Fly Ash ◽

Cementitious Materials ◽

Comprehensive Overview ◽

Nano Sio2 ◽

Alkali Activated

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Resistance to Chemical Attack of Hybrid Fly Ash-Based Alkali-Activated Concretes

Molecules ◽

10.3390/molecules25153389 ◽

2020 ◽

Vol 25 (15) ◽

pp. 3389

Author(s):

William G. Valencia-Saavedra ◽

Ruby Mejía de Gutiérrez

Keyword(s):

Fly Ash ◽

Portland Cement ◽

Strength Loss ◽

Cementitious Materials ◽

Sodium Sulphate ◽

Unburned Carbon ◽

Chloride Permeability ◽

Chemical Attack ◽

Concrete Production ◽

Alkali Activated

The environmental impacts related to Portland cement production in terms of energy consumption, the massive use of natural resources and CO2 emissions have led to the search for alternative cementitious materials. Among these materials, alkali-activated cements based on fly ash (FA) have been considered for concrete production with greater sustainability. In the present article, the chemical durability properties (resistance to sulphates, chloride permeability, and resistance to carbonation) of a hybrid alkali-activated concrete based on fly ash–ordinary Portland cement (FA/OPC) with proportions of 80%/20% were evaluated. It is noted that the FA was a low-quality pozzolan with a high unburned carbon content (20.67%). The results indicated that FA/OPC concrete had good durability with respect to the OPC concrete, with 95% less expansion in the presence of sodium sulphate and a 2% strength loss at 1100 days, compared with the 56% strength loss of the OPC concrete. In addition, FA/OPC showed lower chloride permeability. On the contrary, the FA/OPC was more susceptible to carbonation. However, the residual compressive strength was 23 MPa at 360 days of CO2 exposure. Based on the results, FA/OPC, using this type of FA, can be used as a replacement for OPC in the presence of these aggressive agents in the service environment.

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Application on cementitious materials to promote durability of alkali-activated concrete containing co-fired fly ash and water-quenched slag

Monatshefte für Chemie - Chemical Monthly ◽

10.1007/s00706-017-1951-7 ◽

2017 ◽

Vol 148 (7) ◽

pp. 1349-1354 ◽

Cited By ~ 4

Author(s):

Che-Hung Sung ◽

Ran Huang ◽

Chia-Jung Tsai ◽

Yann-Hwang Wu ◽

Wei-Ting Lin ◽

...

Keyword(s):

Fly Ash ◽

Cementitious Materials ◽

Alkali Activated Concrete ◽

Alkali Activated

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Understanding the effect of recycled concrete aggregate and cementitious materials on concrete's fire resistance

Journal of Structural Fire Engineering ◽

10.1108/jsfe-09-2021-0056 ◽

2021 ◽

Vol ahead-of-print (ahead-of-print) ◽

Author(s):

Mohammed Ahmed Abed ◽

Eva Lubloy

Keyword(s):

Fly Ash ◽

High Temperatures ◽

Fire Resistance ◽

Blended Cement ◽

Cementitious Materials ◽

Recycled Concrete ◽

Supplementary Cementitious Materials ◽

Concrete Aggregate ◽

Recycled Concrete Aggregate ◽

Content Type

PurposeFire can severely affect concrete structures and with knowledge of the properties of materials, the damage can be assessed. Aggregate, cement matrix and their interaction are the most important components that affect concrete behaviour at high temperatures. The effect of incorporating recycled concrete aggregate or cementitious materials, namely, cement type and pulverized fly ash, are reviewed to provide a better understanding of their involvement in fire resistance.Design/methodology/approachMore investigation research is needed to understand the fire resistance of such sustainable concrete that was already constructed. The present study illustrates the effect of using recycled concrete aggregate and cementitious materials on the fire resistance of concrete. To do so, a literature review was conducted and relevant data were collected and presented in a simple form. The author's selected research findings, which are related to the presents study, are also presented and discussed.FindingsRecycled concrete aggregate enhances the concrete behaviour at high temperatures when it substitutes the natural aggregate by reasonable substitution (more than 25–30%). It also almost eliminates the possibility of spalling. Moreover, utilizing both supplementary cementitious materials with recycled concrete aggregate can improve the fire resistance of concrete. The incorporation of pulverized fly ash and slag in Portland cement or blended cement can generally keep the mechanical properties of concrete at a higher level after heating to a high temperature.Originality/valueRecycled concrete aggregate enhances the concrete behaviour at high temperatures when it substitutes the natural aggregate by reasonable substitution (more than 25–30%). It also almost eliminates the possibility of spalling. Moreover, utilizing both supplementary cementitious materials with recycled concrete aggregate can improve the fire resistance of concrete. The incorporation of pulverized fly ash and slag in Portland cement or blended cement can generally keep the mechanical properties of concrete at a higher level after heating to a high temperature.

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Effects of Combined Usage of Supplementary Cementitious Materials on the Thermal Properties and Microstructure of High-Performance Concrete at High Temperatures

Materials ◽

10.3390/ma13081833 ◽

2020 ◽

Vol 13 (8) ◽

pp. 1833 ◽

Cited By ~ 4

Author(s):

Dong Lu ◽

Zhuo Tang ◽

Liang Zhang ◽

Jianwei Zhou ◽

Yue Gong ◽

...

Keyword(s):

Thermal Conductivity ◽

High Temperature ◽

Fly Ash ◽

High Temperatures ◽

High Performance ◽

High Performance Concrete ◽

Cementitious Materials ◽

Supplementary Cementitious Materials ◽

Amorphous Phases ◽

Micro Cracks

Concrete has low porosity and compact microstructure, and thus can be vulnerable to high temperature, and the increasing application of various types of supplementary cementitious materials (SCMs) in concrete makes its high-temperature resistant behavior more complex. In this study, we investigate the effects of four formulations with typical SCMs combinations of fly ash (FA), ultra-fine fly ash (UFFA) and metakaolin (MK), and study the effects of SCMs combinations on the thermal performance, microstructure, and the crystalline and amorphous phases evolution of concrete subjected to high temperatures. The experimental results showed that at 400 °C, with the addition of 20% FA (wt %), the thermal conductivity of the sample slightly increased to 1.5 W/(m·K). Replacing FA with UFFA can further increase the thermal conductivity to 1.7 W/(m·K). Thermal conductivity of concrete slightly increased at 400 °C and significantly reduced at 800 °C. Further, combined usage of SCMs delayed and reduced micro-cracks of concrete subjected to high temperatures. This study demonstrates the potential of combining the usage of SCMs to promote the high-temperature performance of concrete and explains the micro-mechanism of concrete containing SCMs at high temperatures.

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Durability of alkali-activated fly ash cementitious materials

Journal of Materials Science ◽

10.1007/s10853-006-0584-8 ◽

2006 ◽

Vol 42 (9) ◽

pp. 3055-3065 ◽

Cited By ~ 283

Author(s):

A. Fernandez-Jimenez ◽

I. García-Lodeiro ◽

A. Palomo

Keyword(s):

Fly Ash ◽

Cementitious Materials ◽

Alkali Activated

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Preparation and Properties of Pressed Metakaolin and Fly Ash Based Alkali-Activated Binders

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.897.65 ◽

2014 ◽

Vol 897 ◽

pp. 65-68 ◽

Cited By ~ 5

Author(s):

Jana Boháčová ◽

Stanislav Staněk ◽

Pavel Mec

Keyword(s):

Tensile Strength ◽

Fly Ash ◽

High Temperatures ◽

Frost Resistance ◽

Raw Materials ◽

Fly Ashes ◽

Secondary Raw Materials ◽

Alkali Activated Binders ◽

Alkali Activated

Metakaolin, fly ashes and other secondary raw materials serves as suitable input in preparation of alkali-activated binders. This work deals with preparation of alkali-activated materials based on metakaoline and fly ash. Mixtures were prepared with a minimum of mixture water, ready for pressing. Prepared specimens were tested for tensile strength and pressure strength, resistance to high temperatures, frost resistance and resistance to water and salt.

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