A method for controlling rheology of a hydratable cementitious composition in a rotatable mixer, wherein the energy required for operating said rotatable mixer containing the cementitious composition is measured and correlated with a nominal rheology value and wherein a rheology-modifying agent or combination of rheology-modifying agents is added into the cementitious composition to modify its rheology, wherein the method comprises: providing a truck having a rotatable mixer for mixing a hydratable cementitious composition and having a computer processor unit CPU for monitoring slump of the hydratable cementitious composition and for controlling dosage of chemical admixture or admixtures into said hydratable cementitious composition contained in said rotatable mixer; and (a) entering into said CPU a target rheology value TRV and load size for a hydratable cementitious composition containing or intended to contain a particular rheology-modifying agent or combination of rheology-modifying agents within said rotatable mixer; and (b) obtaining a current rheology value CRV of hydratable cementitious composition contained within said rotatable mixer; (c) comparing through use of said CPU the current rheology value obtained in step (b) against a nominal dose response NDR profile stored in CPU-accessible memory and wherein said NDR is based on at least one data set wherein various dose amounts of a particular rheology-modifying agent or combination of rheology-modifying agents and their correlative effect on rheology value, such as slump, slump flow, or yield stress, is retrievably stored, and determining the nominal dose of said particular rheology-modifying agent or combination of rheology-modifying agents required to change the obtained CRV to the TRV specified in step "(a)"; (d) dosing the hydratable cementitious composition contained in said rotatable mixer with a percentage of said particular rheology-modifying agent or combination of rheology-modifying agents that is selected or pre-selected from 5% to 99% based on the nominal dose determined in step (c) required for changing said obtained CRV to said TRV as specified in step (a); (e) obtaining a subsequent CRV of the hydratable cementitious composition contained in said rotatable mixer after the percentage of the nominal dose of the particular rheology-modifying agent or combination of rheology-modifying agents selected or preselected in step (d) is added into and uniformly mixed with said hydratable cementitious composition; comparing the dose selected or preselected in step (d) to the dose according to the NDR profile for the same change in the rheology value from step (b) to step (e), and determining the scaling factor SF by which to adjust the dose from the NDR profile, where SF is defined as the actual dose from step (d) divided by the nominal dose to achieve the same change in rheology value indicated by the NDR profile; and (f) mixing into the hydratable cementitious composition the particular rheology-modifying agent or combination of rheology-modifying agents in an amount calculated in terms of SF multiplied by the dose from the NDR profile indicated to convert the current CRV measured in step (e) to the TRV specified in step (a). (a) entering into said CPU a target rheology value TRV and load size for a hydratable cementitious composition containing or intended to contain a particular rheology-modifying agent or combination of rheology-modifying agents within said rotatable mixer; and (b) obtaining a current rheology value CRV of hydratable cementitious composition contained within said rotatable mixer; (c) comparing through use of said CPU the current rheology value obtained in step (b) against a nominal dose response NDR profile stored in CPU-accessible memory and wherein said NDR is based on at least one data set wherein various dose amounts of a particular rheology-modifying agent or combination of rheology-modifying agents and their correlative effect on rheology value, such as slump, slump flow, or yield stress, is retrievably stored, and determining the nominal dose of said particular rheology-modifying agent or combination of rheology-modifying agents required to change the obtained CRV to the TRV specified in step "(a)"; (d) dosing the hydratable cementitious composition contained in said rotatable mixer with a percentage of said particular rheology-modifying agent or combination of rheology-modifying agents that is selected or pre-selected from 5% to 99% based on the nominal dose determined in step (c) required for changing said obtained CRV to said TRV as specified in step (a); (e) obtaining a subsequent CRV of the hydratable cementitious composition contained in said rotatable mixer after the percentage of the nominal dose of the particular rheology-modifying agent or combination of rheology-modifying agents selected or preselected in step (d) is added into and uniformly mixed with said hydratable cementitious composition; comparing the dose selected or preselected in step (d) to the dose according to the NDR profile for the same change in the rheology value from step (b) to step (e), and determining the scaling factor SF by which to adjust the dose from the NDR profile, where SF is defined as the actual dose from step (d) divided by the nominal dose to achieve the same change in rheology value indicated by the NDR profile; and (f) mixing into the hydratable cementitious composition the particular rheology-modifying agent or combination of rheology-modifying agents in an amount calculated in terms of SF multiplied by the dose from the NDR profile indicated to convert the current CRV measured in step (e) to the TRV specified in step (a).