Prepared metakaolin produced by calcination of a kaolin sample at 750°C after soaking for 5 hrs was tested as an active pozzolan for locally produced cement. Blended pastes of partially replaced ordinary Portland cement with different metakaolin amounts 5%, 10% and 15% were prepared, then they were hydrated with water for various time intervals of 1, 3, 7, 14 and 28 days. At each time interval, the hydrated paste specimens were tested for compressive strength, hydration kinetics and followed up using differential scanning calorimetry, X-ray diffractometry analyses and scanning electron microscopy techniques. Results showed that the blended pastes OPC-MK10 recorded the highest compressive strength values at all the hydration times reaching 33.10, 86.40, 101.20, 112, and 122 MPa with increasing the age of hydration as compared with the neat samples which recorded 31.70, 65.20, 72.6, 82 and 101.30 MPa respectively. Meanwhile, the OPC-MK10 blend showed a decrease in the free CaO content reaching 4.07%, 4.27%, 4.23%, 4.19%, and 4.11% CaO with increasing age of hydration compared with the neat samples which recorded 4.27%, 5.15%, 5.42%, 5.61%, and 5.96% CaO respectively. The DSC thermograms results for the hardened neat and OPC-Mk10 pastes at the 14 and 28 hydration days showed the formation of hydrated materials mainly calcium silicate hydrates, calcium sulphoaluminate hydrates and calcium aluminates hydrates. The X-ray diffractometry analyses of both hardened neat and OPC- MK10 showed that, the intensity of calcium hydroxide peaks of OPC-MK10 was lower than in case of neat OPC, while the peak of the hydration products of calcium silicate hydrates and calcium aluminates silicate hydrates of OPC- MK10 samples were of higher intensity than in case of neat OPC. Scanning electron microscopy micrographs indicated the formation of denser micro- structure for the hardened OPC-MK10 paste as compared to neat OPC pastes after the 28 days age of hydration.
展开▼
