Improvement in Carbonation Resistance of Portland Cement Mortar Incorporating γ-Dicalcium Silicate

Zhengxin Chen,Hyeongkyu Cho,Yunsu Lee,Hanseung Lee,Seungmin Lim

doi:10.1155/2019/9856734

Abstract

In this study, γ-dicalcium silicate (γ-C2S) was incorporated into ordinary Portland cement (OPC) to sequester CO2 to enhance the carbonation resistance of cement-based composite materials. γ-C2S can react with CO2 rapidly to form vaterite and high dense SiO2 gel which could block the pores off and then inhibit further diffusion of CO2 into the system. Cement mortar specimens containing 0%, 5%, 10%, 20%, and 40% γ-C2S as cement replacement were prepared. After water curing for 28 days followed by curing in an environmental chamber for 28 days, the specimens were then exposed to an accelerated carbonation with 5% CO2 concentration for 28 days. The carbonation depth of the cement mortar with a low replacement rate (5% and 10%) was lower than that of the OPC mortar at all ages due to the sequestration of CO2 by γ-C2S. However, the cement mortar with a high replacement rate (20% and 40%) showed less carbonation resistance due to the dilution effect of γ-C2S replacement and increase in initial porosity caused by nonhydraulic characteristic of γ-C2S.

Highlights

Carbonation is an important factor affecting the service life of reinforced concrete structures
Olivine group minerals have become a popular subject of research for CO2 storage and capture (CSC) due to their high CO2 sequestration per unit mass capabilities [12, 13]. c-C2S is considered as an insoluble substance, but it can rapidly react with CO2 [14, 15] to form calcium carbonates and highly polymerized silica gel
The carbonation resistance of cement-based composite materials incorporating 0%, 5%, 10%, 20%, and 40% of c-C2S was evaluated. e feasibility of methods incorporating c-C2S into cement mortar to capture CO2, reduce CO2 diffusion, and improve the pore structure to inhibit the carbonation reaction was verified. e main conclusions are as follows: (1) Calcite, aragonite, and vaterite were the carbonation products formed in the cement paste during the accelerated carbonation

Summary

Introduction

Carbonation is an important factor affecting the service life of reinforced concrete structures. E carbonation reaction reduces the pH value inside the concrete to a value low enough to break the protective film on the surface of steel reinforcement. In order to extend the service life of reinforced concrete buildings which can be damaged by carbonation, several factors must be considered during the design stage, such as structural aspects, material selection, concrete mix design, proper compaction, and correct curing [5]. Ese methods aim to reduce the contact of CO2 with concrete by improving pore structure to reduce channels for the diffusion of CO2 or shielding the concrete surface. The approach proposed in this study attempts to inhibit the diffusion of CO2 by introducing a highly active CO2-capturable material, c-C2S, into concrete to fix up CO2 present in the concrete, which could reduce CO2 diffusion rate. Olivine group minerals have become a popular subject of research for CO2 storage and capture (CSC) due to their high CO2 sequestration per unit mass capabilities [12, 13]. c-C2S is considered as an insoluble substance, but it can rapidly react with CO2 [14, 15] to form calcium carbonates and highly polymerized silica gel

Methods

Results

Conclusion