Effect of Nano-Silica on the Autogenous Shrinkage, Strength, and Hydration Heat of Ultra-High Strength Concrete

Guang-Zhu Zhang,Xiao-Yong Wang,Hyeong-Kyu Cho

doi:10.3390/app10155202

Abstract

In this paper, the effect of nano-silica on the autogenous shrinkage, hydration heat, compressive strength hydration products of Ultra-High Strength Concrete (UHSC) is studied. The water/binder ratio (w/b) of UHSC is 0.2. The nano-silica replaces 2% and 4% of the mass fraction of the cement in UHSCs, respectively. A new instrument was developed to simultaneously measure the autogenous shrinkage, internal relative humidity, and internal temperature of UHSC. The following results were obtained from the analysis of the experimental data: (1) The trends in the autogenous shrinking of UHSC can be divided into two stages, which are the variable temperature stage and the room temperature stage. The dividing point between the two stages occurs at the age of approximately 2 days. During the room temperature stage, the internal relative humidity and autogenous shrinkage showed a good linear relationship. (2) The compressive strength of UHSC increased significantly with the increase of nano-silica content at 3 days, 7 days, and 28 days. (3) The total accumulated heat of UHSC increased during the 72 h, with the increasing of nano-silica content. (4) The XRD data at the age of 28 days showed that the Ca(OH)2 peaks of nS2 and nS4 have a tendency to weaken due to the pozzolanic reaction, compared with the peak of nS0.

Highlights

Concrete is widely used in the construction industry because of its many advantages, such as its low-cost [1], high strength, good plasticity [2], and good durability
The PCE used in this study delayed the binder hydration kinetics in all ultra-high strength concrete (UHSC) systems with its dosage
The surface dissolution and product nucleation sites were inhibited by this adsorption of PCE molecules, resulting in suppression of the hydration kinetics in the induction period [27]

Summary

Introduction

Concrete is widely used in the construction industry because of its many advantages, such as its low-cost [1], high strength, good plasticity [2], and good durability. With the development of the construction industry, ordinary strength concrete cannot meet the needs of actual projects. Ultra-high strength concrete (UHSC), with its superior mechanical properties and durability, has been studied and produced [3]. UHSC is a type of concrete with a low water/binder ratio and various additives. With nanotechnology’s continuous development, more and more nano-mineral materials are being applied in the construction industry, such as nano-calcium carbonate (nano-CaCO3 ) [4,5], nano-titanium dioxide (nano-TiO2 ) [6,7], nano-silica (nano-SiO2 ) [8,9], and so on. Due to its high level of activity and very high specific surface area, nano-SiO2 (nS) is often integrated into the construction of cement-based materials to obtain a superior performance, compared with traditional materials [10,11]

Methods

Results

Conclusion