ABSTRACT

The reduction of variability in quality, particularly the concrete compressive strength, is an important aim in construction quality control (BSI 1992,ACI 1973, BSI 1985). 28 day strength variations (Kong & Evans 1975) by standard deviations, of 4-5 N/mm2 signify good control, 5-7 N/mm2 show fair control and 7-8 N/mm2

indicates poor control. Variability is influenced by properties. Permeability has largest scatter and density, the least variability. Scatter is usually due to inadequate equipment and site production practice. However, the scatters, now deduced, arise from unstable design of fresh mixes.