EXPANSIVE CEMENT CONCRETE FOR DRILLED SHAFTS

This research is aimed at developing techniques for the use of highly expansive cement concrete in drilled shafts to produce a stronger bond between the shaft concrete and the surrounding soil, thus strengtheni ng the system to carry a higher load. An expansive cement containing h igh-alumina cement (HAC) as the Al-bearing material was tested for exp ansion, strength, and setting characteristics. Although other properti es were excellent, the cement showed unacceptably fast-setting behavio r To overcome the rapid slump loss of concrete using this HAC-type exp ansive cement, a two-stage mixing process with various admixtures is s uggested. Although applicable in certain situations, this technique ma y not be suitable for general field application where quality control is lacking or where a delay in the expansion phase is required. An inn ovative solution for the problem is suggested in which the HAC is repl aced with hydrated HAC (H-HAC) in the preparation of expansive cements . Concrete made with H-HAC expansive cement displayed the required pro perties before and after setting. This paper reports the properties of a select group of cement pastes and concretes made from HAC-type and H-HAC-type expansive cements that include slump loss, compressive stre ngth, free and two-dimensionally restrained expansion, expansion press ure, and friction stress obtained from especially designed test method s. Some of the expansive concretes tested during this study had compre ssive strength in the range of 70 MPa (10, 150 psi) and developed a se lf-stress in excess of 8 MPa (1160 psi).