Sulphate Corrosion Mechanism of Ultra-High-Performance Concrete (UHPC) Prepared with Seawater and Sea Sand.

Xin Sun,Tianyu Li,Fangying Shi,Huiwen Tian,Baorong Hou,Yingxia Zong,Xiaoyan Liu

doi:10.3390/polym14050971

Abstract

The lack of river sand is becoming increasingly serious. In this study, we consider how to use sea sand to prepare innovative construction and building materials with excellent mechanical and durability properties. Sulphate corrosion causes expansion, cracking and spalling of concrete, resulting in the reduction or even loss of concrete strength and cementation force. In this paper, artificial seawater, sea sand, industrial waste, steel fiber and polycarboxylate superplasticizer were used to prepare ultra-high-performance polymer cement mortar (SSUHPC), and the sulphate corrosion mechanism was investigated. The strength and cementation force of mortar on the SSUHPC surface decreased and flaked off with the development of sulphate erosion, and the steel fiber rusted and fell off. A 3D model was established based on X-ray computed tomography (X-CT), and the results showed that SSUHPC maintained excellent internal structural characteristics despite severe sulphate erosion on the surface. Mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques were adopted to investigate the sulphate corrosion mechanism of SSUHPC. We found a transition zone within 1–5 mm of the surface of SSUHPC. The Vickers hardness of mortar in this area was increased by 5~15%, and the porosity was reduced to 3.8489%. Obvious structural damage did not occur in this area, but a high content of gypsum appeared. UHPC prepared with seawater sea sand was found to have better sulphate resistance than that prepared with freshwater river sand, which supports the development and utilization of sea sand in concrete.

Highlights

Sulphate corrosion and chloride corrosion are the key factors of damage in concrete structures, which can result in reduced service performance and serious economic losses
Depending on the type of cement hydration products and sulphate corrosion products, sulphate corrosion can be categorized as ettringite crystallization, gypsum crystallization, or MgSO4 dissolution–crystallization, etc
We found that the thickness of mortar for each peeling on the surface of ultra-high-performance concrete (UHPC) was about 1–2 mm

Summary

Introduction

Sulphate corrosion and chloride corrosion are the key factors of damage in concrete structures, which can result in reduced service performance and serious economic losses. Sulphate corrosion is defined as the destruction of cement concrete caused by a series of chemical reactions between sulphate ions from the external environment or concrete itself and cement hydration products. These changes may cause expansion and cracking, which reduce the strength and cementation force of concrete [5]. In the early stage of sulphate erosion, mainly aluminum-phase materials react with SO42− to form ettringite. The main products formed under this type of erosion are brucite, ettringite, gypsum and hydrated magnesium silicate, etc., usually with a double-layer structure formed on the surface of the concrete. The equations for the formation of ettringite and gypsum are as follows [5]:

Methods

Results

Discussion

Conclusion