EFFECTS OF GRADING OF FINE AGGREGATE ON THE STRENGTH AND PERMEABILITY OF CONCRETE USED IN PAVEMENT CONSTRUCTION

摘要

The main objective of this research is to study the effect of grading of fine aggregate on the strength and permeability of concrete which could be used in pavement construction. It is well known that permeability is an important property in concrete pavements, where it is in contact with the ground which may contain harmful agents for the concrete. Five different gradings of fine aggregate have been chosen (in the range between 5μm up to 5 mm). A "quarry dust" from the Ewenny quarry (in South Wales) has also been employed as a very fine aggregate. Use of the quarry dust also brings the additional environmental benefit by removing an otherwise waste by-product of the quarrying process. Two different curing methods have been used: water curing and air curing (7 days water curing followed by 21 days of air curing). The BRE permeability test was used to evaluate the relative permeability of the concrete, and a torsion test for cylindrical samples was used to determine the tensile strength and Young's Modulus of the different concrete mixes. Some early and encouraging conclusions have already been drawn from this study. Although the material containing very fine grading (finer than 63μm) had a strength reduction, they are shown to have greatly improved impermeability and hence would provide a more durable concrete pavement. Furthermore, for mixes having the same water-cement (W/C) ratio and workability, mixes with the very fine grading provided the highest strength and the lowest permeability. This work provides an indication of how to improve concrete pavement impermeability (and hence its durability) as well as the environmental benefit of using waste material as a resource. The principal conclusions from the results are that, all things being equal, with the increase in amount of fine aggregate comes also lower strength and permeability (when water cement ratio is varied to retain control of workability) but conversely, higher strength when the water cement ratio is held constant (and workability is controlled by additional plasticizer). It was also found that slow water curing of concrete cube samples led to lower permeability and strength.