Plastic concrete is used in the manufacture of cut off wall and its mechanical properties is important for performance of dam. In this paper, in order to investigate the durability and mechanical properties of plastic concrete, uniaxial and triaxial compressive strength tests were performed on plastic concrete specimens in different ages (7, 14, 28, 56 and 90 days) and different percentage of replacement cement by nano silica (0, 1.5, 3, 4.5 and 6%) and compressive strength, the stress–strain behavior, elastic modulus, shear strength parameters of plastic concrete have been evaluated. According to the result, as the age of the specimen increases, elastic modulus, compressive strength and triaxial strength of the plastic concrete enhances. Furthermore, although by increasing the amount of nano silica the strength parameters of plastic concrete are improved and workability of concrete is reduced and the amount of elastic modulus of the specimen is almost constant. The results of shear strength parameters also show that the addition of up to 3% of nano silica increases the cohesion and internal friction angle decreases and with over 3% nano silica this trend is reversed and cohesion decreases and friction angle increases.

Introduction

The rheology and permeability of various concrete and advantage of nano material as a partial replacement for cement is well established in previous papers [1–۱۱]. Besides, plastic concrete of cut-off wall is buried inside the soil in geotechnical project [12–۱۴]. Two main attributes are necessary. Firstly, they should have enough strength to bear the weight of the dam body and secondly, a low elastic modulus that works seamlessly integrated with the surrounding environment soil [15–۱۹]. If the elastic modulus is much higher than the surrounding soil of cut-off wall, soil and wall do not have load bearing capacity for unified action and cut-off wall will be cracked and its performance will be lost. The high elastic modulus of normal concrete is the reason for not using normal concrete in making the cut-off wall. As a result, plastic concrete satisfies both of the above conditions, and so is used to construct a cut-off wall. The water to cement ratio of plastic concretes is usually considered in the range of 1.5–۴ to achieve the low elastic modulus; however, in normal concretes, this range varies between 0.35 and 0.65 [16,20–۲۴]. In the previous researches [25,26], the compressive strength parameters of plastic concrete are investigated by performing uniaxial compressive strength. They showed that the compressive strength of concrete specimens depends on various parameters such as cement and bentonite content, aggregate size and specimen age.