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

Molecules ◽  
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.

Effect of ground granulated blast funrnace slag and fly ash on strength, permeability, and under-water abrasion of fine-grained concrete

2020 ◽  
Vol 71 (7) ◽  
pp. 775-788
Author(s):  
Quyet Truong Van ◽  
Sang Nguyen Thanh
Keyword(s):  
Fly Ash ◽  
Concrete Strength ◽  
Cementitious Materials ◽  
Supplementary Cementitious Materials ◽  
Chloride Permeability ◽  
Cement Replacement ◽  
Fine Grained ◽  
Granulated Blast Furnace Slag ◽  
Compressive Strength Test ◽  
Economic Ground

The utilisation of supplementary cementitious materials (SCMs) is widespread in the concrete industry because of the performance benefits and economic. Ground granulated blast furnace slag (GGBFS) and fly ash (FA) have been used as the SCMs in concrete for reducing the weight of cement and improving durability properties. In this study, GGBFS at different cement replacement ratios of 0%, 20%, 40% and 60% by weight were used in fine-grained concrete. The ternary binders containing GGBFS and FA at cement replacement ratio of 60% by weight have also evaluated. Flexural and compressive strength test, rapid chloride permeability test and under-water abrasion test were performed. Experimental results show that the increase in concrete strength with GGBFS contents from 20% to 40% but at a higher period of maturity (56 days and more). The chloride permeability the under-water abrasion reduced with the increasing cement replacement by GGBFS or a combination of GGBFS and FA

scholarly journals A Review of the Mechanical Properties and Durability of Ecological Concretes in a Cold Climate in Comparison to Standard Ordinary Portland Cement-Based Concrete

Materials ◽  
2020 ◽  
Vol 13 (16) ◽  
pp. 3467
Author(s):  
Ankit Kothari ◽  
Karin Habermehl-Cwirzen ◽  
Hans Hedlund ◽  
Andrzej Cwirzen
Keyword(s):  
Carbon Dioxide ◽  
Portland Cement ◽  
Ordinary Portland Cement ◽  
Cementitious Materials ◽  
Cold Climate ◽  
Supplementary Cementitious Materials ◽  
Short Exposure ◽  
Chemical Admixtures ◽  
Composite Cements ◽  
Alkali Activated

Most of the currently used concretes are based on ordinary Portland cement (OPC) which results in a high carbon dioxide footprint and thus has a negative environmental impact. Replacing OPCs, partially or fully by ecological binders, i.e., supplementary cementitious materials (SCMs) or alternative binders, aims to decrease the carbon dioxide footprint. Both solutions introduced a number of technological problems, including their performance, when exposed to low, subfreezing temperatures during casting operations and the hardening stage. This review indicates that the present knowledge enables the production of OPC-based concretes at temperatures as low as −10 °C, without the need of any additional measures such as, e.g., heating. Conversely, composite cements containing SCMs or alkali-activated binders (AACs) showed mixed performances, ranging from inferior to superior in comparison with OPC. Most concretes based on composite cements require pre/post heat curing or only a short exposure to sub-zero temperatures. At the same time, certain alkali-activated systems performed very well even at −20 °C without the need for additional curing. Chemical admixtures developed for OPC do not always perform well in other binder systems. This review showed that there is only a limited knowledge on how chemical admixtures work in ecological concretes at low temperatures and how to accelerate the hydration rate of composite cements containing high amounts of SCMs or AACs, when these are cured at subfreezing temperatures.

Application of Zeolite as a Partial Replacement of Cement in Concrete Production

2014 ◽  
Vol 621 ◽  
pp. 30-34
Author(s):  
Eva Vejmelková ◽  
Dana Koňáková ◽  
Monika Čáchová ◽  
Martin Keppert ◽  
Adam Hubáček ◽  
...  
Keyword(s):  
Portland Cement ◽  
Natural Zeolite ◽  
General Rule ◽  
Cementitious Materials ◽  
Supplementary Cementitious Materials ◽  
Partial Replacement ◽  
Large Variability ◽  
Substitution Level ◽  
Concrete Production ◽  
Zeolite Rock

Natural zeolite rocks are known to be able to act as Supplementary Cementitious Materials (SCM) in Portland cement based concrete. Generally SCMs are reacting with portlandite and providing binding hydration products just as Portland cement does. In this way an SCM can substitute certain amount of Portland cement in concrete and thus reduce the related energy consumption and CO2 generation. Due to a large variability of SCMs composition and properties there is not any general rule for an optimum Portland cement substitution level. In this paper, the influence of natural zeolite rock on selected mechanical, hygric and thermal properties of concrete is studied. Experimental results show that the analyzed zeolite is acting as a pozzolan but for higher amounts its application leads to an increase in concrete porosity which affects its properties in a significant way.

Mechanical Characteristics Analysis of Alkali-Activated Fly Ash Cementitious Materials

2010 ◽  
Vol 452-453 ◽  
pp. 721-724
Author(s):  
Gum Sung Ryu ◽  
Hyun Jin Kang ◽  
Su Tae Kang ◽  
Gyung Taek Koh ◽  
Jang Hwa Lee
Keyword(s):  
Fly Ash ◽  
Mechanical Characteristics ◽  
High Strength ◽  
Cementitious Materials ◽  
Molar Concentration ◽  
Basic Study ◽  
Co2 Gas ◽  
Characteristics Analysis ◽  
Alkali Activated Concrete ◽  
Alkali Activated

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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