Philosophy of rational mixture proportioning of alkali-activated materials validated by the hydration kinetics of alkali-activated slag and its microstructure
“…11 , 12 , and 13 . This can be explained through the following: (i) Increasing the solution modulus (Ms) results in increasing the Si ions; (ii) The Si ions lower the alkalinity of the activator which results in prolonged time for the process of activation and sequentially lower slump loss rate, this finding agrees with the previous literature 24 – 27 . Figure 7 The slump values versus time for the different HF levels at Ms = 0.…”
Section: Test Results and Discussionsupporting
confidence: 90%
“…From Fig. 26 it can be concluded that the silicate-based (Ms > 0) activators achieve better compressive strength whatever the HF level, this can be attributed to the better microstructure and denser matrix of the formed matrix 27 , 28 . Figure 16 The compressive strength values versus time for the different Ms levels at HF = 0.60.…”
Alkali Activated Slag Concrete (AASC) has been a sustained research activity over the past two decades. Its promising characteristics and being environmentally friendly compared to Ordinary Portland Cement made AASC of exceptional interest. However, there is still no firm mix design, for the AASC, that can provide desirable fresh and hardened properties based on the composition of the binder and activator. This research specifically aims to investigate the affecting parameters on the slump and compressive strength of alkali-activated slag/lime-based concrete and provide a better understanding of the potential reasons for these characteristics. The experimental program consisted of two stages; the first stage studied the effect of different binder and activator compositions, and the second stage studied the water-to-binder ratio and binder content effects on the slump and compressive strength of alkali-activated slag/lime-based concrete. The binder and activator compositions were defined through two main parameters, the hybrid factor (HF = CaO/Si2O + Al2O3) and the solution modulus (Ms = SiO2/Na2O). The compressive strength, initial slump, and slump loss were measured to evaluate the different mixes and specify the optimum range of compositions. Based on the studied parameters, the effective range to achieve desirable slump and concrete compressive strength is from HF 0.6 up to 0.8 at Ms 1.5, this would achieve a compressive strength of more than 30 MPa and a slump of 100 mm after 90 min.
“…11 , 12 , and 13 . This can be explained through the following: (i) Increasing the solution modulus (Ms) results in increasing the Si ions; (ii) The Si ions lower the alkalinity of the activator which results in prolonged time for the process of activation and sequentially lower slump loss rate, this finding agrees with the previous literature 24 – 27 . Figure 7 The slump values versus time for the different HF levels at Ms = 0.…”
Section: Test Results and Discussionsupporting
confidence: 90%
“…From Fig. 26 it can be concluded that the silicate-based (Ms > 0) activators achieve better compressive strength whatever the HF level, this can be attributed to the better microstructure and denser matrix of the formed matrix 27 , 28 . Figure 16 The compressive strength values versus time for the different Ms levels at HF = 0.60.…”
Alkali Activated Slag Concrete (AASC) has been a sustained research activity over the past two decades. Its promising characteristics and being environmentally friendly compared to Ordinary Portland Cement made AASC of exceptional interest. However, there is still no firm mix design, for the AASC, that can provide desirable fresh and hardened properties based on the composition of the binder and activator. This research specifically aims to investigate the affecting parameters on the slump and compressive strength of alkali-activated slag/lime-based concrete and provide a better understanding of the potential reasons for these characteristics. The experimental program consisted of two stages; the first stage studied the effect of different binder and activator compositions, and the second stage studied the water-to-binder ratio and binder content effects on the slump and compressive strength of alkali-activated slag/lime-based concrete. The binder and activator compositions were defined through two main parameters, the hybrid factor (HF = CaO/Si2O + Al2O3) and the solution modulus (Ms = SiO2/Na2O). The compressive strength, initial slump, and slump loss were measured to evaluate the different mixes and specify the optimum range of compositions. Based on the studied parameters, the effective range to achieve desirable slump and concrete compressive strength is from HF 0.6 up to 0.8 at Ms 1.5, this would achieve a compressive strength of more than 30 MPa and a slump of 100 mm after 90 min.
“…The late strength of the samples is significantly higher when N e is 4.0% compared to 6.0% and 8.0% N e samples. Its average compressive strength at 28 days is 55.4% higher than that at 7 days, which is related to the slow reaction process of the paste due to the activation of low alkali concentration [ 32 ].…”
To improve solid waste resource utilization and environmental sustainability, an alkali-activated material (AAM) was prepared using steel slag (SS), fly ash, blast furnace slag and alkali activators in this work. The evolutions of SS content (10–50%) and alkali equivalent (4.0–8.0%) on workability, mechanical strength and environmental indicators of the AAM were investigated. Furthermore, scanning electron microscopy, X-ray diffraction and nuclear magnetic resonance techniques were adopted to characterize micromorphology, reaction products and pore structure, and the reaction mechanism was summarized. Results showed that the paste fluidity and setting time gradually increased with the increase in SS content. The highest compressive strength was obtained for the paste at 8.0% alkali equivalent due to the improved reaction rate and process, but it also increased the risk of cracking. However, SS was able to exert a microaggregate filling effect, where SS particles filling the pores increased the structural compactness and hindered crack development. Based on the optimal compressive strength, global warming, abiotic resource depletion, acidification and eutrophication potential of the paste are reduced by 76.7%, 53.0%, 51.6%, and 48.9%, respectively, compared with cement. This work is beneficial to further improve the utilization of solid waste resources and expand the application of environmentally friendly AAMs in the field of construction engineering.
“…Based on the above, this work pioneers the transition of AAS pastes to mortars with different activators (sodium waterglass -SWG, sodium carbonate -SC, and sodium hydroxide -SH) by means of mechanical properties and shrinkage. The mix proportioning followed our approach very recently published in [14] and was based on the same molarity of all activators and various paste volume fractions in the resulting mortars. The results were compared to those obtained on pastes, which were already published in our previous study, but in a limited timescale [12].…”
One of the critical factors affecting the performance of alkali-activated slag (AAS) is the nature and dose of alkali activator. The activator type can play a significant role during the transition from pastes to mortars or concretes. Therefore, three basic sodium activators (water glass, carbonate, and hydroxide) of the same molarity of 4M Na+ were used to prepare AAS-based mortars with different volume fractions of siliceous sand. These were compared by means of workability, mechanical strength, and long-term shrinkage under autogenous conditions. The results were compared to those obtained on pastes with similar workability. Increasing the content of the sand tended rather to decrease the mechanical properties, while greatly decreased autogenous shrinkage. Nevertheless, the most remarkable differences for different activators were observed when comparing the mortars with pastes. The transition from pastes to mortars resulted in the highest reduction in both compressive and flexural strength for sodium hydroxide. The flexural strength of the mortars with sodium water glass and sodium carbonate even increased considerably in presence of sand.
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