Mortars with CDW Recycled Aggregates Submitted to High Levels of CO2

Ricardo Infante Gomes,Paulina Faria,Cinthia Maia Pederneiras,Rosário Veiga,António Santos Silva,Catarina Brazão Farinha,David Bastos,Jorge De Brito

doi:10.3390/infrastructures6110159

Abstract

Construction and demolition wastes (CDW) are generated at a large scale and have a diversified potential in the construction sector. The replacement of natural aggregates (NA) with CDW recycled aggregates (RA) in construction materials, such as mortars, has several environmental benefits, such as the reduction in the natural resources used in these products and simultaneous prevention of waste landfill. Complementarily, CDW have the potential to capture CO2 since some of their components may carbonate, which also contributes to a decrease in global warming potential. The main objective of this research is to evaluate the influence of the exposure of CDW RA to CO2 produced in cement factories and its effect on mortars. Several mortars were developed with a volumetric ratio of 1:4 (cement: aggregate), with NA (reference mortar), CDW RA and CDW RA exposed to high levels of CO2 (CRA). The two types of waste aggregate were incorporated, replacing NA at 50% and 100% (in volume). The mortars with NA and non-carbonated RA and CRA from CDW were analysed, accounting for their performance in the fresh and hardened states in terms of workability, mechanical behaviour and water absorption by capillarity. It was concluded that mortars with CDW (both CRA and non-carbonated RA) generally present a good performance for non-structural purposes, although they suffer a moderate decrease in mechanical performance when NA is replaced with RA. Additionally, small improvements were found in the performance of the aggregates and mortars with CRA subjected to a CO2 curing for a short period (5 h), while a long carbonation period (5 d) led to a decrease in performance, contrary to the results obtained in the literature that indicate a significant increase in such characteristics. This difference could be because the literature focused on made-in-laboratory CDW aggregates, while, in this research, the wastes came from real demolition activities, and were thus older and more heterogeneous.

Highlights

This paper presents the results of the evaluation of the performance of mortars formulated with an recycled aggregates (RA) of Construction and demolition wastes (CDW) subjected to forced and accelerated carbonation over both a short and a long period of time: 5 h (CRA-5h) and 5 days (CRA-5d)
A CDW commercialised by a Portuguese recycling plant was incorporated in cementiA CDW commercialised by a Portuguese recycling plant was incorporated tious non-structural mortars, replacing sand at 50% and 100%
Submitted to forced and accelerate carbonation for a short and a long period of 5 h and 5 days, respectively, were analysed bonation for a short and a long period of h and days, respectively, were analy in terms of the needs of mixing water to achieve a fixed consistency according to flow terms of the needs of mixing water to achieve a fixed consistency according to table, and bulk density in the fresh state, as well as being analysed in terms of their bulkflow tabl bulk behaviour density in the state, as well asbybeing analysed of their bulk density density, mechanical andfresh water absorption capillarity in in theterms hardened state

Summary

Introduction

The concentration of carbon dioxide (CO2 ) in the atmosphere has exponentially increased. It is estimated that 40% of this increase is due to human activities [1]. The high concentration of this gas, as well as the other greenhouse gases, is responsible for the phenomenon known as global warming. This is one of the main global threats and measures to combat it are urgently required

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Methods

Discussion

Conclusion