High Volume of Calcareous Fly Ash for the Production of a Hydraulic Binder for Road Pavements

The construction of road pavement with concrete seems very advantageous from technical point of view especially for heavy load transportations. However, the use of concrete pavement often results in higher initial cost in comparison to asphalt one though the service life of concrete road is generally longer. The development of a commercial low cost hydraulic binder of adequate strength capacity will contribute to the reduction of the initial cost of concrete pavement. In the paper, an effort in this direction is described. Fly ashes of different compositions in terms of free lime and sulfate content are blended at laboratory with clinker and other mineral admixtures so as in the mixed systems the fly ash to be at least 50% and the clinker 20%. Limestone filler and natural local pozzolana were used as additions. A series of mixes produced at a laboratory mill were tested to find the optimum blending for required mortar 28-d strength of 40MPa. Apart from strength development the volume stability was also measured. Remarks concerning the grindability of the fly ash are made as well as comments about the relationship of fly ash composition and strength results. Although, the capacity of existing laboratory mill was limited and did not correspond to the real blended potential of the constituents, it seems that by achieving a fineness R45 value of 2-10% a 28-d strength level of 40 ± 2 MPa was obtained in mixes where 60% of clinker was replaced by calcareous fly ash. These strength values were obtained even though the water demand was greater compared to that of the control mixture. For mixed systems in which 70% clinker was replaced, this strength level was achieved at 90 days. In mixtures where 80% of clinker was replaced by calcareous fly ash a strength level of 30 ± 2 MPa was developed at 90 days. Net fly ashes mixes of R45 2-5% showed a 28-d strength of 10-20 MPa. Based on this research, the production of a high volume fly ash hydraulic binder seems feasible and a new field of exploitation of calcareous fly ash is opened.