Influence of metakaolin as supplementary cementing material on strength and durability of concretes

Durability of concrete is an important issue for predicting the service life of concrete structures. Recently, the properties of metakaolin as high-quality pozzolanic materials are investigated by several researchers. It is not widely produced and used due to the lack of adequate experiments on this material in the Middle East. Local kaolin with high kaolinite content was thermally treated by a special furnace at 800 °C and 60 min burning time to produce metakaolin.This study investigates the performance of concrete mixtures containing local metakaolin in terms of compressive strength, water penetration, sorptivity, salt ponding, Rapid Chloride Permeability Test (RCPT) and electrical resistivity at 7, 28, 90 and 180 days. In addition, microstructure of the cement pastes incorporating metakaolin was studied by XRD and SEM tests. The percentages of metakaolin that replace PC in this research are 0%, 10%, 12.5% and 15% by mass. The water/binder (w/b) ratios are 0.35, 0.4 and 0.5 having a constant total binder content of 400 kg/m3. Results show that concrete incorporating metakaolin had higher compressive strength and metakaolin enhanced the durability of concretes and reduced the chloride diffusion. An exponential relationship between chloride permeability and compressive strength of concrete is exhibited. A significant linear relationship was found between Rapid Chloride Permeability Test and salt ponding test results.

► Local kaolin was thermally treated at 800 °C and 60 min to produce metakaolin.
► Concrete incorporating local metakaolin had higher strength and durability.
► Exponential relationship between chloride permeability and strength is exhibited.
► A linear relationship was found between RCPT and salt ponding test results.
► The microstructure of MK cement paste is more uniform than that of the OPC paste.