Expansive concrete for use in drilled shafts.

摘要

This research is aimed at developing techniques for the use of highly expansive cement concrete in drilled shafts, in order to produce a stronger bond between the shaft concrete and the surrounding soil, thus strengthening it to be able to carry a high load. Two types of such materials are suggested: (1) High alumina cement (HAC) type expansive concrete made from commercial raw materials which, by a two-stage mixing process, is currently available for use in construction under proper supervision; (2) Hydrated high alumina cement (H-HAC) type expansive concrete which has normal setting characteristics and more satisfactory expansion properties. This second type, developed in this work, is an innovative material that can be used with normal concreting practices, if H-HAC is available or prepared before mixing concrete.;This thesis reports the properties of cement pastes and concretes made from these materials including: slump loss, compressive strength, free and two-dimensionally restrained expansion, expansion pressure, and friction stress obtained from specially designed test methods. An investigation at the microstructural level was also carried out to interpret the mechanisms of hydration processes and the properties of expansive cement paste before and after set. This investigation included analyses such as X-ray diffraction (XRD), mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM).;A field test involving the application of the HAC type expansive concrete in drilled shaft performed in Dallas, Texas is also reported, from which some aspects of construction management and quality control are studied.