Effects of Environment in the Microstructure and Properties of Sustainable Mortars with Fly Ash and Slag after a 5-Year Exposure Period

José Ortega,Miguel Climent,Isidro Sánchez,Rosa Tremiño

doi:10.3390/su10030663

Abstract

Nowadays, getting a more environmentally sustainable cement production is one of the main goals of the cement industry. In this regard, the use of active additions, like fly ash and ground granulated blast-furnace slag, has become very popular. The behaviour, in the short-term, of cement-based materials with those additions is well-known when their hardening is produced under optimum conditions. However, real structures are exposed to different environments during long periods, which could affect the development of microstructures and the service properties of cementitious materials. The objective of this work is to analyse the effects in the long-term (up to 5 years approximately) produced by the exposure to different non-optimum laboratory conditions in the microstructure, mechanical and durability properties of mortars made with slag and fly ash commercial cements. Their performance was compared to that observed for ordinary Portland cement (OPC) mortars. The microstructure has been analysed using mercury intrusion porosimetry. The effective porosity, the capillary suction coefficient, the chloride migration coefficient and mechanical strengths were analysed too. According to the results, mortars prepared using slag and fly ash sustainable commercial cements, exposed to non-optimum conditions, show a good performance after 5-years hardening period, similar or even better than OPC mortars.

Highlights

Nowadays, getting a more environmentally sustainable cement production is one of the main goals of the cement industry
This result could be related to the high relative humidity (100%) combined with a high enough temperature (20 ◦C) of this optimum environment, which allows an adequate development of clinker and slag hydration [30,44] and fly ash pozzolanic reactions [44,48], whose products would entail a rise of samples solid fraction and a porosity reduction
The slightly higher total porosities and their slower decrease observed for environment B could be due to its lower temperature (15 ◦C), which would slow down the development of clinker and slag hydration [29,30], as well as the fly ash pozzolanic reactions [36,49], producing a slower formation of new solid phases

Summary

Introduction

Nowadays, getting a more environmentally sustainable cement production is one of the main goals of the cement industry. The most popular active additions are ground granulated blast-furnace slag and fly ash and their effects on the pore structure and cementitious materials properties have been well-studied, mainly when their hardening was produced in optimum laboratory conditions [7,8,9]. Under those conditions, they showed a better behaviour compared to cement-based materials prepared using ordinary Portland cement (OPC) without any addition [7]. The abovementioned pore refinement produced by both additions improves the performance of cementitious materials, for example their chloride ingress resistance [12,13,14,15,16,17] and their permeability [18]

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Conclusion