Calcium aluminate cement (CAC) is a specialty cement with distinct advantages over ordinary portland cement (OPC).It has been successfully used in many fields for more than 100 years.However, one primary challenge in CAC concrete is to predict the "conversion" process during hydration when metastable hydrates convert to stable hydrates.In traditional OPC concrete maturity theory, it is assumed that the weights of different curing temperature are the same.This is not true for CAC due to higher temperature results in much faster conversion process and different microstructures.By assigning different weights to different curing temperature, a CAC concrete maturity theory was proposed in this paper.The key step was to determine conversion time under different isothermal temperatures.Previous research has shown that due to the hydration features of CAC,reaction rate changes reflected in chemical shrinkage test (ASTM C1608) can be used to identify conversion process of CAC at elevated temperatures (>30 ℃).This conversion process was confirmed by x-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis.After an extrapolation of conversion time under isothermal temperatures ranging from 10 ℃ to 80 ℃ was determined fiom the experimental data, a mathematical expression was given to estimate the degree of conversion given the temperature history.To verify the proposed maturity theory, CAC paste cubes was cast and cured under five conditions: 1) 10℃ water bath, 2) ambient condition (20 ℃ to 23 ℃), 3) 38 ℃ water bath, 4) 50 ℃ water bath, and 5) semi-adiabatic condition (heavily insulated box).The initial compressive strength results indicated the proposed CAC maturity theory could provide a simple and effective way to predict conversion in CAC paste system.More work needs to be done for CAC mortar or concrete system.