Effect of GGBFS and Micro-Silica on Mechanical Properties, Shrinkage and Microstructure of Alkali-Activated Fly Ash Mortar

Abstract

Performance of drying shrinkage, flow rate, mechanical properties, and microstructure of three materials -alkali-activated fly ash (FA); ground granulated blast-furnaced slag (GGBFS); and un-densified micro-silica (M) are investigated. Mixtures used herein are referred to as AAM -alkali activated materialsof four types according to composition: AAM-IV, AAM-V, AAM-VI and AAM-VII (note: types 1 through 3 were investigated in previous research) with corresponding mixture FA, GGBFS and M ratios of 47.5/47.5/5, 45/45/10, 42.5/42.5/15, 40/40/20 by weight percentage. The AAM samples were air-cured under a sealed condition for 6 days followed by unsealed curing up to the test at 18-20° C and a low relative humidity of 30-50%. The samples AAM-IV through VII were composed of a progressive decrease of fly ash and GGBFS and an increase in M content. Results show that flow rate and compressive strength increased from AAM-IV to AAM-VI; contrarily, it decreased in AAM-VII. Both flexural strength -a positive aspect -and drying shrinkage -negative as it leads to cracking -increased in all samples. Incorporation of both GGBFS and M in alkaliactivated fly ash mortar was found to improve performance compared to that incorporated solely of GGBFS in alkali-activated fly ash. The incorporation of M of certain values improves strength and flowability of AAM; conversely, it results in a higher drying shrinkage value, which leads to increased cracking. SEM and XRD results confirm these results. Unreacted particles of AAM-VI and AAM-VII appear to act as a 'microaggregate,' resulting in increased compressive and flexural strength.

Characterization Alkali-Activated Mortar Made From Fly Ash and Sandblasting

“…The GGBFS substitution on AAM4 can increase compressive strength. Substitution of reactive Si from micro-silica and Ca from GGBFS on AAM5 causes higher compressive strength than that of AAM3 at the 14-day age [17]. Class C fly ash mortar (AAM1) has a higher compressive strength than that of class F fly ash mortar (AAM3).…”

Impact of Pva Fiber as Fine Aggregate Replacement in Alkali-Activated Fly Ash on Flow Rate, Mechanical Properties and Drying Shrinkage

“…Total 2% of solid precursor mass was used as the mass of air entrained-agent. The ratios of liquid and alkaline solution per solid precursor were fixed at 0.558 and 0.538 by weight for all AAM mixtures respectively [24].…”

“…7 illustrates the average compressive strength of all specimens. The AAM-VI is plain geopolymer mortar as a reference to control fiber mortar AAM-F [24]. Fig.…”

Reliability of Alkali-Activated and Portland Cement Mortar Under Compressive Test by Acoustic Emission

“…AAM mortars are mixtures made from precursor materials (fly ash/GGBFS/micro-silica), mixed with a fixed alkaline solution (Na2SiO3+NaOH), and standardized sand. All of these materials are then compacted, demolded, cured as previous papers [10][11][12][13]. Fixed alkali solution ratio of Na2SiO3 to 8 M NaOH of 1.5 is used.…”

“…In previous work [10][11], the researcher investigated the utilization of low calcium fly ash for alkali-activated (geopolymer) matrices. Researchers developed low calcium fly ash, ground granulated blast furnace slag (GGBFS), and microsilica as binding materials for alkali-activated mortar [12][13]. There has been no paper discussing the reliability of strength of alkali-activated (geopolymer) mortars by using Acoustic Emission.…”