I would like to ask if there are any articles, references, etc, which reference procedures to determine the maturity of the concrete applied via shotcrete? Basically, how to generate the validation curves?

Shotcrete is a placement method for concrete. Thus, generating the maturity curves would be based on the concrete mixtures. There are several online resources about the maturity method. One that discusses production of the curves is from the Minnesota DOT and available in PDF format at www.dot.state.mn.us/materials/concretedocs/MaturityMethodProcedure.pdf.