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.

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.

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.

HYDRATION KINETICS OF CEMENT PASTE WITH SILICA FUME AND FLY ASH

2016 ◽  
Vol 3 (1) ◽  
Author(s):  
Miguel Picornell ◽  
Sameer Hamoush ◽  
Taher Abu-Lebdeh
Keyword(s):  
Compressive Strength ◽  
Fly Ash ◽  
Silica Fume ◽  
Cement Paste ◽  
Regional Analysis ◽  
Testing Machine ◽  
Testing System ◽  
Hydration Kinetics ◽  
Curing Conditions ◽  
Water Curing

This research study investigates the effect of fly ash and silica fume on the cement paste hydration. A total of 350 samples of different percentages of each additive were tested and compared with the controlled cement paste without additives. Testing method includes water curing and vacuum curing conditions and involves the use of Forney Universal Testing Machine and MTS Landmark Servohydraulic Testing System (MTS) for compressive strength; Fourier Transfer Infrared Spectroscopy (FTIR) monitored the hydration with spectra; and Scanning Electron Microscope (SEM) generated images for regional analysis. Compressive strength testing demonstrated that silica fume replacement had the highest overall strength under water curing. Replacement of fly ash exhibited the highest overall strength under vacuum curing. The hydration process was monitored with the use of FTIR and SEM. Signatures of CSH which produce most of the concretes’ strength, has been determined and examined from 3 to 56 days. FTIR and SEM testing showed an increase in the change of CSH area with age. SEM testing revealed the formation of pores, CSH, and CH in images at all ages. The area of CSH grows most in early ages and diminishes over time. It is clear that the method of curing makes a difference in hydration. Results indicated that the area at which the possible formation of CSH was determined from each sample, has increased with respect to time; signifying the increase in strength over the course of testing days.

Relationship between Microscopic Structures and Compressive Strength of Alkali-Activated Fly Ash Mortar

2010 ◽  
Vol 452-453 ◽  
pp. 737-740
Author(s):  
Hyun Jin Kang ◽  
Gum Sung Ryu ◽  
Gyung Taek Koh ◽  
Su Tae Kang ◽  
Jung Jun Park
Keyword(s):  
Compressive Strength ◽  
Fly Ash ◽  
Curing Temperature ◽  
Microscopic Structure ◽  
Curing Conditions ◽  
The Relationship ◽  
Alkali Activated

This paper evaluates the relationship between the compressive strength and microscopic structure of geopolymer mortar using 100% of fly ash instead of cement. The experimental variable is the curing temperature, which may influence the compressive strength of the geopolymer. The compressive strength, porosity, XRD, SEM and EDS are examined after 48 hours of curing at 30, 60 and 90°C. The resulting compressive strength at 60°C appeared to be the largest. In order to evaluate the voids produced during the polymerization, the porosity was measured and showed also the largest value after curing at 60°C during 48 hours. Furthermore, SEM and EDS analyses verified clear improvement of the microstructure after 48 hours of curing at 60°C. Such result can be explained by the variation of the Si-Al ratio according to the curing conditions, which revealed to be lower for curing at 30 and 90°C than at 60°C and demonstrated that the curing temperature has significantly effect on the compressive strength of the geopolymer.

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.

scholarly journals Optimizing Precursors and Reagents for the Development of Alkali-Activated Binders in Ambient Curing Conditions

2021 ◽  
Vol 5 (2) ◽  
pp. 59
Author(s):  
Dhruv Sood ◽  
Khandaker M. Anwar Hossain
Keyword(s):  
Blast Furnace ◽  
Fly Ash ◽  
Blast Furnace Slag ◽  
Curing Conditions ◽  
Granulated Blast Furnace Slag ◽  
Hardened State ◽  
Alkali Activated Binders ◽  
Furnace Slag ◽  
Alkali Activated ◽  
Ambient Curing

Alkali-activated binders (AABs) are developed through the activation of aluminosilicate-rich materials using alkaline reagents. The characteristics of AABs developed using a novel dry-mixing technique incorporating powder-based reagents/activators are extensively explored. A total of forty-four binder mixes are assessed in terms of their fresh and hardened state properties. The influence of mono/binary/ternary combinations of supplementary cementitious materials (SCMs)/precursors and different types/combinations/dosages of powder-based reagents on the strength and workability properties of different binder mixes are assessed to determine the optimum composition of precursors and the reagents. The binary (55% fly ash class C and 45% ground granulated blast furnace slag) and ternary (25% fly ash class C, 35% fly ash class F and 40% ground granulated blast furnace slag) binders with reagent-2 (calcium hydroxide and sodium sulfate = 2.5:1) exhibited desired workability and 28-day compressive strengths of 56 and 52 MPa, respectively. Microstructural analyses (in terms of SEM/EDS and XRD) revealed the formation of additional calcium aluminosilicate hydrate with sodium or mixed Ca/Na compounds in binary and ternary binders incorporating reagent-2, resulting in higher compressive strength. This research confirms the potential of producing powder-based cement-free green AABs incorporating binary/ternary combinations of SCMs having the desired fresh and hardened state properties under ambient curing conditions.

Influence of water, alkali activators, and curing regime on the workability and compressive strength of the alkali activated mortar

2019 ◽  
Author(s):  
Eslam Gomaa ◽  
Simon Sargon ◽  
Cedric Kashosi ◽  
Ahmed Gheni ◽  
Mohamed ElGawady
Keyword(s):  
Compressive Strength ◽  
Fly Ash ◽  
Calcium Content ◽  
Chemical Compositions ◽  
Heat Curing ◽  
High Calcium ◽  
Influence Of Water ◽  
Curing Regime ◽  
Curing Regimes ◽  
Alkali Activated

<p>The effect of the water to fly ash (W/FA), alkali activators to fly ash (Alk/FA), and curing regimes on the workability and compressive strength of the alkali-activated mortar (AAM) was studied. Three high calcium fly ashes (FAs) having different chemical compositions were used. Sodium hydroxide (SH) and sodium silicate (SS) were used as the alkali activators. The two alkali activators were mixed together at ratio of 1.0. Two curing regimes, elevated heat curing in an electric oven at 70°C for 24 hr and ambient curing at 23 ± 2°C, were applied. The water to fly ash (W/FA) ratios were 0.350, 0.375, and 0.400. However, the alkali activators to fly ash (Alk/FA) ratios were 0.250, 0.275 and 0.300. The results revealed that the workability and the compressive strength of the oven cured specimens were decreased with increasing the calcium content of FA in the mixture. However, the compressive strength of the specimens that cured under the ambient temperature increased with increasing the calcium content. The workability increased with increasing the W/FA and decreasing the Alk/FA. The compressive strength based on both curing regimes decreased with increasing the W/FA. The optimum Alk/FA was 0.275 with W/FA of 0.400.</p>

scholarly journals Geopolymer Concrete under Ambient Curing

2021 ◽  
Author(s):  
M. Indhumathi Anbarasan ◽  
S.R. Sanjaiyan ◽  
S. Nagan Soundarapandiyan
Keyword(s):  
Tensile Strength ◽  
Compressive Strength ◽  
Fly Ash ◽  
Flexural Strength ◽  
Setting Time ◽  
Geopolymer Concrete ◽  
Split Tensile Strength ◽  
Carbon Footprints ◽  
Curing Conditions ◽  
Ambient Curing

Geopolymer concrete (GPC) has significant potential as a more sustainable alternative for ordinary Portland cement concrete. GPC had been introduced to reduce carbon footprints and thereby safeguarding environment. This emerging eco friendly construction product finds majority of its application in precast and prefabricated structures due to the special curing conditions required. Sustained research efforts are being taken to make the product suitable for in situ applications. The developed technology will certainly address the issues of huge energy consumption as well reduce water use which is becoming scarce nowadays. Ground Granulated Blast Furnace Slag (GGBS) a by-product of iron industries in combination with fly ash has proved to give enhanced strength, durability as well reduced setting time. This study investigates the effect of GGBS as partial replacement of fly ash in the manufacture of GPC. Cube and cylindrical specimens were cast and subjected to ambient curing as well to alternate wetting-drying cycles. The 28 day compressive strength, split tensile strength, flexural strength and density of GPC specimens were found. The study revealed increase in compressive strength, split tensile strength, density as well flexural strength up to 40 percent replacement of fly ash by GGBS.

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