Text this: Correlation between initial SiO<inf>2</inf>/Al<inf>2</inf>O<inf>3</inf>, Na<inf>2</inf>O/Al<inf>2</inf>O<inf>3</inf>, Na<inf>2</inf>O/SiO<inf>2</inf> and H<inf>2</inf>O/Na<inf>2</inf>O ratios on phase and microstructure of reaction products of metakaolin-rice husk ash geopolymer