ABSTRACT
While using shotcrete (sprayed concrete) as rock support in tunnels, rapid strength development is essential to avoid early-age damage. In particular, the ability to form a strong bond between shotcrete and rock is decisive for the quality of the rock support. Thus, cement with large cement clinker content is commonly used since supplementary cementitious materials slow down the strength development. However, decreasing the cement clinker content is important to minimize the environmental impact of shotcrete. This paper presents a methodology to evaluate the early strength development of accelerated shotcrete with low cement clinker content. With the focus on evaluating bond strength at an early age, a reverse pull-out method developed for laboratory use is adopted. Better control of shotcrete hardening will increase the quality, leading to less need for operational interruptions due to tunnel repairs and overall to a longer technical life.
