Expansive Cement Concrete for Drilled Shafts

Abstract

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 strengthening the system to carry a higher load. An expansive cement containing high-alumina cement (HAC) as the Al-bearing material was tested for expansion, strength, and setting characteristics. Although other properties were excellent, the cement showed unacceptably fast-setting behavior. To overcome the rapid slump loss of concrete using this HAC-type expansive cement, a two-stage mixing process with various admixtures is suggested. Although applicable in certain situations, this technique may not be suitable for general field application where quality control is lacking or where a delay in the expansion phase is required. An innovative solution for the problem is suggested in which the HAC is replaced with hydrated HAC (H-HAC) in the preparation of expansive cements. Concrete made with H-HAC expansive cement displayed the required properties 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 strength, free and two-dimensionally restrained expansion, expansion pressure, and friction stress obtained from especially designed test methods. Some of the expansive concretes tested during this study had compressive strength in the range of 70 MPa (10,150 psi) and developed a self-stress in excess of 8 MPa (1,160 psi).