Concrete cracking can be classified into many categories. When a tensile stress is applied to concrete that exceeds its tensile capacity then cracking can often occur. This is particularly true for early age concrete which is very vulnerable to cracking due to its low tensile strength. The cracks can be caused by thermal stress, restrained shrinkage and stress induced by movement. Currently knowledge of the properties of early age concrete is limited and further research in this area is required.
With a better understanding of early age concrete, industrial practices could be improved and the economic in general may improves as less revenue is pump back to the industry for rehabilitation of structures and infrastructures suffering from concrete deterioration due cracking. In everyday application, this would also allow a better understanding of when saw-cuts could be made to minimise cracks on huge slab pavement..
The research undertaken in this Undergraduate Project Thesis investigates the early age tensile strength of concrete from as early as two hours to eight hours after casting, under the guidance of Associate Professor P. Dux, Dr P. Morris and Mr. Dao Ngoc The Vinh. This study will produce an empirical comparison of antecedent data and their discussion; investigate on factors which can influence early age concrete cracking. The study will also empirically show how relatively linked is certain factor for two very different materials.
Fly ash saturated two solutions, distilled water and saturated NaCl solution of different moisture content were tested and correlate to concrete specimens of two slumps; 25mm and 80 mm. direct tensile tests were carried out on a frictionless air bearing bed, under various ambient temperatures and relative humidity. The results that were achieved will hopefully help to shed light on basic mechanism of plastic cracking of early age concrete within several hours after casting.