Q2. How was the sodium hydroxide solution prepared?
The sodium hydroxide solution was prepared at 30% w/w by the dissolution of solid commercial grade (99% purity) sodium hydroxide and was allowed to cool to room temperature prior to sample preparation.
Q3. What is the reason for the mass loss in the PC mixes?
These mass losses are also due to the dissolution of ettringite and AFm phases, such as semicarbonate, which was also observed in the PC mixes by XRD, TGA and FTIR after acid attack.
Q4. What is the cause of the cracks around the edge of the sample?
Following exposure to 5% sulfuric acid GP4 has cracks around the edge of the sample which may be related to expansion caused by the formation of additional products during the acid attack.
Q5. What tests were used to study the acid resistance of GP mortars and pastes?
Paste mixes were used to study the leaching behaviour by pH and inductively coupled plasma mass spectrometry (ICP) analysis of the acid solutions.
Q6. What is the main loss due to moisture within GP and PC mixes?
The main weight loss due to moisture within C-S-H type gel (GP and PC mixes) occurs between 50 and 200 °C [74] and the loss of water within N-A-S-H gel (GP mixes) is reported to occur at around 100 °C [75].
Q7. Why was the majority of the region removed from the GP mixes?
the majority of the region which was considered to have lost alkalinity was removed due to the acid attack in the PC mixes.
Q8. Why did a small mass gain occur in the PC mixes?
A small mass gain was reported for the PC mixes likely due to the formation of additional compounds during sulfuric acid exposure.
Q9. What is the concentration of aluminium in the GP mixes?
As the slag content increases, the aluminium concentrations decrease to 4100, 2800 and 2100 ppm for GP2, GP3 and GP4, respectively.
Q10. What is the cumulative concentration of sodium due to the GP mixes?
The cumulative concentration of sodium due to the GP mixes is graduallydecelerating with time suggesting that less sodium is released during each exposure period.
Q11. What is the effect of the larger depth of acid penetration on the fly ash GP materials?
the larger depth of acid penetration appears to have little effect on the fly ash GP materials overall as the corroded zone remained attached to the undamaged core because the reaction products have more resistance to sulfuric acid attack than those produced as the slag content increases.
Q12. What is the main mass loss for GP pastes after exposure to acid?
It is worth noting that the GP pastes have no significant mass losses after approximately 200 °C which suggests that they mainly consist of amorphous gels with physically and chemically bound water [72].
Q13. What is the advantage of the main binding gel in GP mixes?
the nature of the main binding gel in GP mixes and the absence of calcium hydroxide, ettringite and AFm phases is a significant advantage for the sulfuric acid resistance of GP materials.
Q14. What is the effect of increasing the slag content on the GP mix?
On the other hand, fly ash GP mixes have a higher porosity which is reduced as the slag content increases due to the formation of space filling C-A-S-H gel.
Q15. What is the advantage of a reduced alkalinity loss?
The only advantage is the reduced alkalinity loss which may be beneficial in structural applications when steel reinforcement is required.
Q16. How much slag content is in GP mortars?
The effect of the slag content on the acid resistance of fly ash GPs has been assessed byincreasing the slag content in both mortar and paste mixes, i.e. 0%, 20%, 40% and 70% for mixes GP1, GP2, GP3 and GP4, respectively.
Q17. How did the pH of the GP and PC mixes change after exposure to 5% sulfuric?
The alkalinity loss was determined by investigating the depth of the GP and PC mixes to which the pH has reduced below 9.0 including the depth of any material removed due to acid attack.
Q18. What is the sodium content of the GP mixes?
The GP mixes have much larger initial sodium content due to the sodium hydroxide and sodium silicate solutions used as alkaline activators.
Q19. How was the paste content kept constant?
The paste content was kept constant at 50% for all mortars, so that a fair comparison could be carried out between different mixes.