Shotcrete at Early Ages: Comparison of Test Results With a Thermo-Chemo-Micromechanics-Based Model for Shotcrete

Abstract

Herein, we study the evolution of both early-age stiffness and early-age compressive strength of shotcrete, in the framework of continuum micromechanics. Minimizing the number of necessary material properties, micromechanics-based modeling of shotcrete is based on nonchanging ('universal') mechanical properties of the shotcrete constituents (clinker, water, hydrates, air, and aggregates) and on hydration-dependent volume fractions of these constituents [1, 2]. We consider a two-step homogenization scheme: on the scale of cement paste, we envision polycrystal-type mutual penetration of clinker grains and hydrates, with water and air in between; and at the scale of shotcrete, we envision a matrix made of cement paste with aggregate inclusions. For establishing a micromechanical strength criterion, we assume that breakage of the most loaded hydrates on the submicron level represents the onset of macroscopic failure of shotcrete, i.e. we extend the recently developed strength model for cement paste, see [3, 4}, towards consideration of aggregates embedded into a matrix made of cement paste. To assess the perJormance of this new model, we compare model predictions with available experimental results from early-age shotcrefe testing, carried out under the realistic environmental conditions of the tunnel site of the Mina Escuela Bierzo, La Ribera de Folgoso/León, Spain. Comparison of model predictions with results from on-site shotcrete testing corroborates the micromechanical model formulation. Moreover, the micromechanical models provide valuable insight into the hydration degree-dependent evolution of both shotcrete elasticity and shotcrete strength at early shotcrete ages.