The Effect of Crystalline Waterproofing Admixtures on the Self-Healing and Permeability of Concrete.

Anita Gojević,Ivanka Netinger Grubeša,Ana Baričević,Ivana Banjad Pečur,Vilma Ducman

doi:10.3390/ma14081860

Abstract

This paper investigates the effectiveness of a specific crystalline waterproofing admixture (CWA) in concrete as a function of a water–binder ratio. Four concrete mixes with and without CWA were prepared; two of them with a water–binder ratio of 0.45 and two of them with a water–binder ratio of 0.55. Water permeability and compressive strength were tested on hardened concrete specimens and self-healing of cracks over time was observed. Cement paste and CWA paste were prepared to clarify the results obtained on the concrete specimens. SEM and EDS and XRD and FTIR were performed on the hardened pastes to explain the mechanism of CWA working. The results show that the addition of CWA had no significant effect on the compressive strength of the concrete, but reduced the water penetration depth in the concrete, and the reduction was more effective for mixes with lower water–binder ratio. Regarding the self-healing effect, it can be concluded that the addition of CWA improves the crack healing in concrete, but the efficiency of self-healing is highly dependent on the initial crack width. The mechanisms involved in the reduction of water penetration depth and crack healing in concrete can be explained by different mechanisms; one is creation of the CSH gel from unreacted clinker grains, then formation carbonate, and additional mechanism is gel formation (highly expansive Mg-rich hydro-carbonate) from magnesium based additives. The presence of sodium silicate, which would transform into carbonate/bicarbonate, also cannot be excluded.

Highlights

A well-known and widely accepted method to reduce the permeability of concrete mixtures and increase their durability is the addition of supplementary cementitious materials (SCMs) to concrete mixtures [4,5]
The effectiveness of crystalline waterproofing admixture (CWA) in concrete mixes was studied as a function of the water–binder ratio
The methods scanning electron microscope reduction (SEM) and EDS and X-ray the diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) were used to explain the effect of self-healing

Summary

Introduction

The durability of concrete largely depends on the properties of its microstructure, such as porosity and pore size distribution, since gases (e.g., CO2 from the atmosphere) and liquids (e.g., water in which aggressive ions are dissolved) can penetrate into the material through the pores [1]. A well-known and widely accepted method to reduce the permeability of concrete mixtures and increase their durability is the addition of supplementary cementitious materials (SCMs) to concrete mixtures [4,5]. Due to the pozzolanic activity and the filling effect, the use of SCMs can result in high performance concrete that has both improved mechanical properties and reduced permeability, leading to improved durability [6,7,8]

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