DOE Method of concrete Mix Design Design: Step 1: Determine the target strength from the relation. Target strength = specified characteristic strength + standard deviation x Risk factor In this case the target strength is directly given as 45 MPa at 28 days. Step 2: Find out the water/cement ratio for targeted strength 45 MPa. (a) For finding out the w/c ratio, refer to table 20.46. From this table for ordinary port-land cement and uncrushed 20 mm aggregate the 28 days strength is 42 MPa. (b) From Fig. 20.12 find the point of inter section of 42 MPa at 0.5 water/cement ratio. Through this point draw a dotted line curve parallel to the neighboring curve. Now draw a strength line from the desired strength on y-axis, where this line cuts the curve, draw a perpendicular on x-axis which will give w/c ratio for the targeted strength i.e., 45 MPa. From this curve for 45 MPa strength the water/cement ratio comes out 0.54. For uncrushed aggregate of