Using Modified ASTM C403 Test Procedure to Evaluate Set Time and Admixture Compatibility of Shotcrete Mortar

Abstract Set time of shotcrete is mainly driven by the use of a highly reactive set accelerator. The control of set time is very important for providing successful application of shotcrete in the construction site, because it determines key parameters such as capability to increase layer thickness and loss of the material caused by rebound of shotcrete. However, there is no standard test procedure available to determine the set and stiffening process of shotcrete. In this research, the stiffening process of shotcrete mortar was measured using the penetration resistance test in the American Society for Testing and Materials (ASTM) C403, Standard Test Method for Time of Setting of Concrete Mixtures by Penetration Resistance. Various types of shotcrete accelerators and three different sources of portland cement have been used to investigate the set and stiffening process of shotcrete mortar. According to the experimental results, calcium aluminate type accelerators worked most effectively in controlling set and stiffening of shotcrete mortar. It was found that the penetration resistance test can be used to evaluate compatibility issues between the cement and the shotcrete accelerator. The set time of shotcrete can be determined using best fitted function using current set time criteria of 3.5 and 27.6 MPa for initial and final set.