A new matrix method was developed for estimating the strength of in situ concrete exposed to unisothermal curing conditions. The model considers effect of various curing temperatures occurred at different ages of concrete on strength development of concrete. The cross-over effects on later age concrete strength due to hot or cold weather conditions in early-ages of concrete were also considered. The model ensures precise strength estimations with error percentages below 7%. The time required for form removal of concrete can be determined by the method. (C) 2010 Elsevier Ltd. All rights reserved.