The hydration of cement generates heat due to the exothermic nature of the hydration process. Poor heat dissipation in mass concrete results in a temperature gradient between the inner core and the outer surface of the element. High temperature gradients generate tensile stresses that may exceed the tensile strength of concrete thus leading to thermal cracking. The present paper is an attempt to understand the thermal (heat sink property) and microstructural changes in the hydrated graphene-Portland cement composites. Thermal diffusivity and electrical conductivity of the hydrated graphene-cement composite were measured at various graphene to cement ratios. The mass-volume method was implemented to measure the density of the hydrated graphene-cement composite. Particle size distribution of Portland cement was measured by using a laser scattering particle size analyzer. Heat of hydration of Portland cement was assessed by using a TAMAIR isothermal conduction calorimeter. Scanning electron microscopy (SEM) was implemented to study microstructural changes of the hydrated graphene-cement composites. The mineralogy of graphene-cement and the hydrated graphene-cement composites was investigated by using X-ray diffraction. The findings indicate that incorporation of graphene enhances the thermal properties of the hydrated cement indicating a potential for reduction in early age thermal cracking and durability improvement of the concrete structures.

Two industrial ASTM Portland cements were carefully tested for heat of hydration (HOH) continuously up to 7 days at 23º C using isothermal conduction calorimetry in accordance to ASTM C1702. Internal and external mixing procedures were implemented. The results for HOH measurements at 7 days using isothermal calorimetry were compared to those obtained through heat of solution method (ASTM C186). The results indicate that for a given Portland cement, the shape of the HOH curve can be predicted with sufficient accuracy by measuring the heat of hydration to an age corresponding to an approximately ten times the age at maximum heat flow or main hydration peak. The heat of hydration at ages up to 7 days can be predicted by fitting an analytical function similar to functions used in Maturity calculations. The suggested approach would eliminate the need for measuring data at ages when the heat flow has decreased substantially well past its maximum where the signal to noise ratio is low. This approach effectively proposes a method for predicting accurately the total heat generated at 7 days by Portland cement based on 3 days heat flow measurements.

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