The Influence of Crystalline Admixtures on the Properties and Microstructure of Mortar Containing By-Products

Jakub Hodul,Nikol Žižková,Ruben Paul Borg

doi:10.3390/buildings10090146

Abstract

Crystalline admixtures and industrial by-products can be used in cement-based materials in order to improve their mechanical properties. The research examined long-term curing and the exposure to environmental actions of polymer–cement mortars with crystalline admixture (CA) and different by-products, including Bengħisa fly ash and Globigerina limestone waste filler. The by-products were introduced as a percentage replacement of the cement. A crystallization additive was also added to the mixtures in order to monitor the improvement in durability properties. The mechanical properties of the mortar were assessed, with 20% replacement of cement with fly ash resulting in the highest compressive strength after 540 days. The performance was analyzed with respect to various properties including permeable porosity, capillary suction, rapid chloride ion penetration and chloride migration coefficient. It was noted that the addition of fly ash and crystalline admixture significantly reduced the chloride ion penetration into the structure of the polymer cement mortar, resulting in improved durability. A microstructure investigation was conducted on the samples through Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy (SEM-EDS). Crystals forming through the crystalline admixture in the porous structure of the material were clearly observed, contributing to the improved properties of the cement-based polymer mortar.

Highlights

The constituent materials of cement-based materials usually include cement, water, aggregates, admixtures and additives
Crystalline admixtures can increase the durability of cement-based materials, especially in the case when these materials are exposed to aggressive environments
The mechanical and durability properties based on different test methods, are presented for all test variables considered, including the addition of crystalline admixture and the substitution of cement with waste limestone and fly ash

Summary

Introduction

The constituent materials of cement-based materials usually include cement, water, aggregates, admixtures and additives. Materials which are designed to perform in aggressive chemical conditions must be of sufficient durability and should have the capacity to withstand the physical and chemical conditions to which they are exposed, throughout their service life [2]. Cracks have a negative impact on concrete structures, and affect their performance in different ways, including weakening the structure as a result of reduced mechanical properties, or lowering the durability as a result of the penetration of harmful agents into the structure resulting in degradation of reinforcing steel or concrete [3]. Crystalline admixtures can increase the durability of cement-based materials, especially in the case when these materials are exposed to aggressive environments. The catalytic reaction of the chemicals in the crystalline admixture, occurs as long as there is moisture in the cement-based materials. The crystalline admixtures react with calcium hydroxide and other products resulting from the hydration

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Conclusion