Experimental study of the mechanical behavior of plastic concrete in triaxial compression Ahmad Mahboubi * , Ali Ajorloo Power and Water Institute of Technology, P.O. 16765-1719, Tehran, Iran Received 11 June 2003; accepted 10 September 2004 Abstract This paper is going to present the results of an extensive experimental parametric study of the mechanical responses of various types of plastic concrete in unconfined and triaxial compression tests. Plastic concrete consists of aggregates, cement, water and bentonite, mixed at a high water cement ratio, to produce a ductile material. It is used for creating an impermeable barrier (cut-off wall) for containment of contaminated sites or seepage control in highly permeable dam foundations. A plastic concrete cut-off wall acts essentially as a barrier to stop or reduce the groundwater flow. In this study the effect of specimen age, cement factor, bentonite content and confining pressure on shear strength and permeability of plastic concrete were investigated. The observed behavior is more and more ductile for increasing confining pressure. It is shown, also, that any increase in confining pressure increases the compressive strength as well as the elastic modulus and the deformability of the specimen. It is shown that an increase in cement factor increases the shear strength as well as the elastic modulus. It is obtained that increase of bentonite content, decreases the compressive strength as well as the elastic modulus. Increasing the age of the specimens causes an increase of the compressive strength as well as the elastic modulus and also the shear strength parameters are affected. Also, it is obtained that increase in confining pressure and cement factor reduces the permeability. D 2004 Elsevier Ltd. All rights reserved. Keywords: Mixture proportioning; Compressive strength; Elastic moduli; Permeability; Plastic concrete 1. Introduction Slurry walls, constructed by normal or plastic concrete, are today among the most classic geotechnical technologies and have been widely used both for structural purposes (structural walls) and for hydrogeological purposes (cut-off walls). The latter, aimed to prevent and/or modify the groundwater flow, have been extensively used in many different fields of civil engineering, such as dams, reser- voirs, tunnels, dewatering projects, and so on. Concrete cut- off walls are also used for the purpose of confining underground-contaminated sites. In dam engineering, this technology is used for the construction of the slurry cut-off wall in highly permeable dam foundations. Seepage control is critical to the safe operation of earth dams. While remedial seepage control can be achieved with a rigid concrete cut-off wall, deformation of the earth embankment and its foundation can cause the concrete wall to rupture. Therefore, materials selected for con- struction of cut-off walls must be strong and watertight and have stiffness comparable to the surrounding soil. Satisfying strain-compatibility between the wall and surrounding soil will lessen the likelihood of overstressing the wall and will allow the wall and soil to deform without separating. Plastic concrete consists of the same materials as those of normal concrete with a high water–cement ratio and the only difference is that bentonite is added to the mixture to increase its ductility. This kind of concrete shows great promise for satisfying the strength, stiffness and permeability requirements for remedial cut-off wall construction [1–4]. 0008-8846/$ - see front matter D 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.cemconres.2004.09.011 * Corresponding author. Tel.: +98 21 731 2552; fax: +98 21 731 0425. E-mail address: mahboubi@pwit.ac.ir (A. Mahboubi). Cement and Concrete Research 35 (2005) 412 – 419