Question 5 By means of Cement & Concrete Institute (South African) method, design a trial mix of concrete based on the data below and summarise quantities obtained. Cement type Sand quality Stone size Dry compacted bulk density of stone = Characteristic strength at 28 days Required slump Defective level CEM I 42.5 N (Relative density of 3.14) Average (Relative density = 2.65; FM= 2.30) 19.0 mm (Relative density = 2.70) 1540 kg/m 25 MPa 75 mm 2.5% 5.10 MPa 0.65 . Standard deviation Water: Cement ratio K value for determining stone content = 1.00 Table 5.1: Water requirements of concrete mixes for19 mm stone, 75 mm slump Sand Quality Very poor Poor Average Good Excellent Water content, litres/m Natural Crusher 240 235 225 225 210 215 195 205 180 195 Table 5.2: Adjustments to water content to compensate for stone size other than 19 mm Maximum size 9.5 13.2 19.0 26.5 37.5 of stone, mm Correction, +20 +10 0 -10 -20 1/m (20 marks)