Development of Cementless Fly Ash Based Alkali-Activated Mortar

2009 ◽  
Vol 417-418 ◽  
pp. 721-724 ◽  
Author(s):  
Kyung Taek Koh ◽  
Su Tae Kang ◽  
Gum Sung Ryu ◽  
Hyun Jin Kang ◽  
Jang Hwa Lee
Keyword(s):  
Compressive Strength ◽  
High Temperature ◽  
Fly Ash ◽  
High Strength ◽  
Molar Ratio ◽  
Early Age ◽  
Water Curing ◽  
Curing Method ◽  
Alkali Activated Concrete ◽  
Alkali Activated

This study investigates the effects of alkaline activators and curing method on the compressive strength of mortar for the development of cementless alkali-activated concrete using 100% of fly ash as binder. Results reveal that the compressive strength improved according to the increase of the molar concentration of NaOH. In addition, molar ratio Na2O to SiO2 of 1.12 activated the reaction of fly ash with Si and Al constituents and resulted in the most remarkable development of strength. In the case of mortar requiring high strength at early age, higher curing temperatures appeared to be advantages. Curing at 60°C during 48 hours is recommended for requiring high strength at age 28days. Moreover, performing atmospheric curing after high temperature curing appeared to be more effective for the development of strength than water curing. Based on these results, it has been analyzed that alkaline activators fabricated with proportions of 1:1 of 9M NaOH and sodium silicate should be used and that atmospheric curing should be performed after curing at 60°C during 48 hours to produce high strength alkali-activated mortar exhibiting compressive strength of 70MPa at age 28 days.

scholarly journals Compressive Strength Performance of Alkali Activated Concretes under Different Curing Conditions

2021 ◽  
Author(s):  
Anıl Niş ◽  
İlhan Altındal
Keyword(s):  
Compressive Strength ◽  
Fly Ash ◽  
Strength Performance ◽  
Curing Conditions ◽  
Standardization Process ◽  
Water Curing ◽  
Curing Regimes ◽  
Alkali Activated Concrete ◽  
Alkali Activated ◽  
Ambient Curing

This study investigated the influence of different curing conditions on the compressive strength (CS) of the different alkali activated concrete (AAC) specimens at the ages of 2, 28, and 90 days for the structural utilization and standardization process of AAC instead of OPC concrete. For this aim, 100% slag (S100), 75% slag and 25% fly ash (S75FA25), and 50% slag and 50% fly ash based (S50FA50) AAC specimens were produced. Based on the oven-curing (O), water-curing (W), and ambient-curing (A) methods, the influence of 2O for 2 days, 26A2O, 2O26A, 28A, 28W, 26W2O, and 2O26W for 28 days, and 88A2O, 2O88A, 90A, 88W2O, 2O88W, 90W for 90 days on the CS of the AAC were examined in details. In addition, the influence of delayed oven-curing conditions on CS development was also investigated. The results indicated that curing conditions significantly affected on the CS and the water-curing condition could provide a better CS for those of AAC at 90 days. Although, the oven-curing enhanced CS of the S100 specimens at initial ages (first oven-curing applied), delayed oven-curing (oven-curing applied later) was found significant for S75FA25 and S50FA50 specimens. The delayed oven-curing affected more on the CS of the AAC when fly ash content increased. The most of AAC specimens with oven-curing had significantly enhanced the CS at 28 days, but S50FA50 at the age of 90 days decreased. Different curing regimes were proposed for the superior compressive strength values for each AAC specimens at the ages of 28 and 90 days.

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.

Rheological Characteristics of Alkali Activated Fly-Ash Concrete Mixtures

2016 ◽  
Vol 677 ◽  
pp. 86-92
Author(s):  
Tomáš Váchal ◽  
Rostislav Šulc ◽  
Pavel Svoboda
Keyword(s):  
Compressive Strength ◽  
Fly Ash ◽  
Fresh Concrete ◽  
Rheological Characteristics ◽  
Fresh Mixture ◽  
Fly Ash Concrete ◽  
Concrete Mixtures ◽  
Alkali Activated Concrete ◽  
Alkali Activated

This paper describes rheological characteristics of concrete mixtures based on alkali-activated fly ash. There are shown relationships between workability of fly-ash fresh concrete mixtures and water–fly-ash ratio in fresh alkali-activated concrete. In addition, there is described relationship between workability in fresh mixture on compressive strength of alkali-activated concrete.

Effect of Specimen Size and Curing Condition on the Compressive Strength of Alkali-Activated Concrete

2017 ◽  
Vol 2629 (1) ◽  
pp. 9-14 ◽  
Author(s):  
Robert James Thomas ◽  
Sulapha Peethamparan
Keyword(s):  
Compressive Strength ◽  
Fly Ash ◽  
Specimen Size ◽  
Portland Cement Concrete ◽  
Cement Concrete ◽  
Slag Cement ◽  
Fly Ash Concrete ◽  
Activated Slag ◽  
Alkali Activated Concrete ◽  
Alkali Activated

Alkali-activated concrete is a rapidly emerging sustainable alternative to portland cement concrete. The compressive strength behavior of alkali-activated concrete has been reported by various studies to a limited extent, but these discussions have been based on minimal evidence. Furthermore, although it is known that specimen size has a distinct effect on the apparent compressive strength of concrete, this effect has yet to be modeled for alkali-activated concrete. This paper presents the results of a comprehensive study of the effects of curing condition (i.e., moist-cured at ambient temperature for 28 days or heat-cured at 50çC for 48 h) and specimen size on the compressive strength of sodium silicate–activated fly ash and slag cement concrete. The heat-cured strength of alkali-activated slag cement concrete was linearly related to the moist-cured strength; the former was about 5% greater than the latter. Heat curing also improved the strength of alkali-activated fly ash concrete, although the effect was greatly magnified for lower-strength mixtures and was much less significant at higher strengths. Existing size effect laws employed for portland cement concrete proved reasonably accurate in describing the effect of specimen size on the apparent strength of alkali-activated slag cement concrete. However, these existing models greatly underestimated the size effect in alkali-activated fly ash concrete; the authors suggest that this finding was the result of significant microcracking in the alkali-activated fly ash concrete.

Development of Non-Autoclaved Aerated Concrete by Alkali Activated Phosphorus Slag

2011 ◽  
Vol 250-253 ◽  
pp. 1147-1152 ◽  
Author(s):  
Xiao Jun Jiang ◽  
Yan Yun ◽  
Zhi Hua Hu
Keyword(s):  
Compressive Strength ◽  
Fly Ash ◽  
Bulk Density ◽  
Sodium Silicate ◽  
Setting Time ◽  
Liquid Sodium ◽  
Molar Ratio ◽  
Autoclaved Aerated Concrete ◽  
Aerated Concrete ◽  
Alkali Activated

The feasibility of manufacturing non-autoclaved aerated concrete using alkali activated phosphorus slag as a cementitious material was investigated in this paper. Liquid sodium silicate with various modules (the molar ratio between SiO2 and Na2O) was used as alkali activator and a part of phosphorus slag was replaced with fly ash which was used to control the setting time of aerated concrete. The influences of the fly ash, curing procedure, modulus of sodium silicate solution and concentration of alkalis on the compressive strength and bulk density of non-autoclaved aerated concrete have been studied. Moreover, the types of the hydration products were investigated using XRD and SEM. The results indicate that: the compressive strength of aerated concrete was influenced by concentration of alkalis obviously. The compressive strength of 11.9MPa and the bulk density of 806kg/m3 were obtained with an activator of 1.2 modulus of sodium silicate and 6% concentration of alkalis under the circumstance of 60°C curing for 28 days.

scholarly journals Frost Resistance of Alkali-Activated Concrete—An Important Pillar of Their Sustainability

2021 ◽  
Vol 13 (2) ◽  
pp. 473
Author(s):  
Vlastimil Bilek ◽  
Oldrich Sucharda ◽  
David Bujdos
Keyword(s):  
Frost Resistance ◽  
Potassium Hydroxide ◽  
Water To Cement Ratio ◽  
Water Curing ◽  
Sustainable Materials ◽  
Wide Group ◽  
Curing Method ◽  
Alkali Activated Concrete ◽  
Alkali Activated

Sustainable development of concrete construction requires sustainable materials or sustainable binders. Specifically, alkali-activated materials (AAMs) are an interesting and wide group of materials. They have good strengths and are considered environmentally friendly materials because secondary materials are consumed during the preparation of AAMs. The durability of AAMs is also excellent. One of the most important parts of durability is frost resistance. The frost resistance of alkali-activated materials is usually very good. However, some studies showed opposite properties and poor frost resistance. The reason for this may be a different composition of the activator. The content of alkalis is often considered the main characteristic of alkali-activated materials. However, SiO2 content can play an important role too. This paper discusses the different results for the mechanical properties and frost resistance of different compositions of alkali activators made of sodium water glass with a silicate modulus modified with potassium hydroxide. The role of the activator content and the water-to-cement ratio in this phenomenon is discussed. The results of this article show that the strengths of AAMs are significantly affected by the curing method. Water curing reduced some of the strength of the specimens compared to foil-covered specimens. Frost resistance depends on the method of curing and on the composition of the activator; some concretes with high strengths showed very low frost resistance.

scholarly journals Effect of Mix Constituents and Curing Conditions on Compressive Strength of Sustainable Self-Consolidating Concrete

2019 ◽  
Vol 11 (7) ◽  
pp. 2094 ◽  
Author(s):  
Osama Ahmed Mohamed
Keyword(s):  
Compressive Strength ◽  
Fly Ash ◽  
Silica Fume ◽  
Stability Index ◽  
Strength Development ◽  
Self Consolidating Concrete ◽  
Curing Conditions ◽  
Practical Applications ◽  
Water Curing ◽  
Curing Method

The production of cement requires significant energy and is responsible for more than 5% of global CO2 emissions; therefore it is imperative to reduce the production and use of ordinary portland cement (OPC). This paper examines the compressive strength development of low water-to-binder (w/b) ratio self-consolidating concrete (SCC) in which 90% of the cement is replaced with industrial by-products including ground granulated blast furnace slag (GGBS), fly ash, and silica fume. The emphasis in this paper is on replacing a large volume of cement with GGBS, which represented 10% to 77.5% of the cement replaced. Fresh properties at w/b ratio of 0.27 were examined by estimating the visual stability index (VSI) and t50 time. The compressive strength was determined after 3, 7, 28, and 56 days of curing. The control mix made with 100% OPC developed compressive strength ranging from 55 MPa after three days of curing to 76.75 MPa after 56 days of curing. On average, sustainable SCC containing 10% OPC developed strength ranging from 31 MPa after three days of curing to 56.4 MPa after 56 days of curing. However, the relative percentages of fly ash, silica fume, and GGBS in the 90% binder affect the strength developed as well. In addition, this paper reports the effect of the curing method on the 28 day compressive strength of environmentally friendly SCC in which 90% of the cement is replaced by GGBS, silica fume, and fly ash. The highest compressive strength was achieved in samples that were cured for three days under water, then left to air-dry for 25 days, compared to samples cured using chemical compounds or samples continuously cured under water for 28 days. The study confirms that SCC with 10% OPC and 90% supplementary cementitious composites (GGBS, silica fume, fly ash) can achieve compressive strength sufficient for many practical applications by incorporating high amounts of GGBS. In addition, air-curing of samples in a relatively high temperature (after three days of water curing) produce a higher 28 day compressive strength compared to water curing for 28 days, or membrane curing.

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