Predicting Compressive Strength at a Specified Age Using Early Age Strength and Degree of Hydration for Concrete Mixes with OPC

In designing of concrete structures, compressive strengths at specified ages of concrete play a major role. For concretes with Ordinary Portland Cement(OPC), this is generally considered as 28-day compressive strength since the strength gain thereafter is insignificant. However, in the event of change of materials, the ready-mixed concrete suppliers find it difficult to conduct trials for a new design and verify 28-day compressive strength due to limited availability of time. Hence, developing a methodology to estimate the expected mean compressive strength of concrete at a specified age using its early age properties will be of great practical use. In this study, a model has been developed to estimate the compressive strength at specified ages of a given concrete mix with OPC, within a maximum period of 3 days. Concrete compressive strength measurements at 3 days, temperature variation of a representative mortar specimen with time under known boundary conditions, mix proportion of concrete and chemical composition of cement were used as the model inputs. Heat of hydration curve for cement was developed using a multi component finite element hydration model based on the temperature measurements of a representative mortar specimen, chemical composition of cement and mix proportion of concrete. The developed hydration model was used to estimate the degree of hydration at the respective ages of compressive strength records and at the specified age. The compressive strengths of the concrete mixes at the specified age were estimated with the use of the estimated degree of hydration and measured compressive strengths at early age. The proposed methodology was found to be satisfactory for the tested concrete mixes.