A new method for determining the cement paste, fine aggregate and coarse aggregate content of hardened concrete using micro X-ray fluorescence (μXRF) is presented. The method involves mathematical and morphological operations to extract aggregate particles from large-area (100 x 50 mm2) composite element maps acquired with μXRF. The method was tested on five concretes containing different types of aggregates including gravel, limestone, siliceous sand, and sintered lightweight aggregates. The results were compared against point count analysis and data from the actual mix design. The average errors in relation to the mix design for the measured fine aggregate, coarse aggregate, total aggregate, cement paste contents and fine/coarse aggregate ratio were 12%, 12%, 3.4%, 10%, and 27% respectively. All measured values fell within ±4% of those point-counted. An image size of > 2000 mm2 (at least five times maximum aggregate size) was found to be required to obtain representative results. The advantages and limitations of the proposed method are discussed.