Engineering Properties of Marine Clay Admixed with Portland Cement and Blended Cement with Siliceous Fly Ash

Abstract

This paper presents a laboratory study on the engineering properties of marine clay admixed with siliceous fly-ash-blended cement and ordinary portland cement (OPC) through an unconfined compression test, split tensile test, bender element test, and isotropic compression test. Specimens with 20–100% of cement by weight of dry soil and 100–133% of water by weight of soil and cement solid-cured for 7–150 days were investigated for both fly-ash–cement-admixed clay and OPC-admixed clay. The results showed that the short-term strength gain of marine clay admixed with fly-ash-blended cement (FAC) is significantly lower than that of OPC-admixed clay. However, the long-term strength gains are similar, with the fly-ash–cement-admixed clay manifesting more sustained gains for curing periods beyond 28 days. The difference in the rate of strength gain between FAC-admixed clay and OPC-admixed clay is attributed to the greater prominence of the pozzolanic reaction in the fly-ash-blended cement. In order to reflect the slower initial rate of strength gain arising from the pozzolanic reaction, a generalized hyperbolic strength-gain-time function was postulated for fly ash. By superimposing the individual strength contributions of the OPC and fly ash, a semiempirical relationship for the gain in strength with time for marine clay treated by fly-ash-blended cement is obtained, which gives good agreement with the measured data. Other properties studied herein include isotropic yield strength, tensile strength, and small-strain modulus. The results show that all these properties are well-correlated to the unconfined compressive strength by linear function regardless of whether OPC or fly-ash-blended cement is used.