ABSTRACT
ABSTRACT. This paper looks at the effect of different concrete mix proportions on the crack formation in in-situ concrete tunnel linings. Seven mix combinations, using OPC and blends of OPC/FIy Ash as well as OPC/GGBS at different total binder contents were used during the construction on an experimental lining section in a water transfer tunnel. One OPC/FIy Ash section also contained steel fibre. Each of the nine test blocks was six meters long. In-situ temperature and strength development as well as crack formation were monitored for up to five years. The field trials were followed by a three year laboratory investigation. Three curing regimes were used, with TMC (temperature-matched-curing) being the most important, because it was based on actual in-situ temp, measurements from the nine different tunnel segments. Parameters evaluated included compressive, tensile, tensile splitting and flexural strength, water permeability, E-Modul under compression and tension, drying shrinkage, short term and long term creep and creep under tension. Results from all these tests help to explain the large variations in crack formation found during the field-trials and thereafter. The early findings from this study were also used to design and construct a crack free tunnel lining at the Lesotho Highlands Water Project.
