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  American University of Beirut    Dept. of Civil and Environmental Engineering   Faculty of  Engineering and Architecture
                                  Portland Cement Concrete
              •       Concrete Quality Requirement: 
                    –      Acceptable workability of freshly mixed concrete.
                    –      Durability, strength, and uniform appearance of 
                           hardened concrete.
                    –      Economy (Cost effective).
              •       Basic Steps for Weight and Absolute Volume 
                      Methods:
                    1.     Evaluate Strength requirement.
                    2.     Determine the water-Cement ratio required.
                    3.     Evaluate coarse aggregate requirements:
                          •     Maximum aggregate size.
                          •     Quantity of the coarse aggregate.
  American University of Beirut    Dept. of Civil and Environmental Engineering   Faculty of  Engineering and Architecture
                                 Portland Cement Concrete
           •       Basic Steps for Weight and Absolute Volume 
                   Methods:
                 4.     Determine  air entrainment requirements.
                 5.     Evaluate workability requirements of the plastic 
                        concrete.
                 6.     Estimate the water content requirements of the mix.
                 7.     Determine cement content and type needed.
                 8.     Evaluate the need and application rate of admixtures.
                 9.     Evaluate the fine aggregate requirement.
                 10.    Determine moisture corrections
                 11.    Make and test trial mixes.
  American University of Beirut    Dept. of Civil and Environmental Engineering   Faculty of  Engineering and Architecture
                                 Portland Cement Concrete
           • Evaluate Strength requirements:
                 – Specified compressive strength, f’c
                 – Variability or standard deviation s, and
                 – Allowable risk of making concrete with unacceptable 
                     strength.
                 The standard deviation s for a plant. Allowable risk by the American Concrete 
                     Institute (ACI) states that there should be less than 10% chance that the 
                     strength of concrete mix is less than the specified strength.  
                     f’ = f’ + 1.34s      (1)
                        cr      c 
                     f’ = required average compressive strength, MPa or psi
                        cr 
                     f’ = specified compressive strength, MPa or psi
                        c 
                     s = standard deviation, MPa or psi
  American University of Beirut    Dept. of Civil and Environmental Engineering   Faculty of  Engineering and Architecture
                                 Portland Cement Concrete
           • Evaluate Strength requirements (cont’d):
                 For mixes with a large standard deviation in strength, ACI 
                     has another risk criterion: 
                        f’ = f’ + 2.33s – 3.45   (units in MPa)      (2)
                           cr      c 
                 Or   f’cr= f’c + 2.33s – 500    (units in psi) 
                 The standard deviation is determined from at least 30 
                     strength tests. If computed from 15 to 30: then s must 
                     be multiplied by a  modification factor F.
                                            No. of Tests               F
                                                   15                1.16
                                                   20                1.08
                                                   25                1.03
                                             30 or more              1.00
  American University of Beirut    Dept. of Civil and Environmental Engineering   Faculty of  Engineering and Architecture