Abstract
Abstract The objective of this study is to analyse the use of binary mixtures of pozzolanic materials and concrete demolition waste in concrete mixtures, especially the resulting mechanical properties and durability. A total of ten concrete formulations were produced distinguishing them in different types using different Portland cements, different artificial pozzolans and coarse aggregates from concrete demolition. The particular properties of each formulation were verified by testing the axial compressive strength, longitudinal modulus of elasticity and penetration of chloride under immersion. Substitutions were of 15% w.t. and 30% w.t. natural coarse aggregate substituted with concrete demolition waste and, in the case of binary mixtures, additional 25% w.t. of the binder agglomerate substituted with rice husk ash or fly ash. Results showed that the final strength to axial compression and modulus of elasticity of concrete mixtures were negatively affected by utilising demolition waste, but this effect was balanced by adding supplementary cementitious materials. Regarding the durability test, it was found that the lowest coefficients occurred in the mixtures using CP V-ARI, together with artificial pozzolans, in mixtures with 15% w.t. substitution of natural aggregate with recycled aggregate. It was concluded that using recycled aggregates in concrete is viable but conditioned to the concomitant use of pozzolanic materials.
Highlights
Using concrete in construction and engineering works is widespread and estimated at approximately 20 billion metric tons per year (WANG et al, 2017)
When natural coarse aggregate was replaced with Concrete demolition waste (CDW) in 15% w.t. and 30% w.t., average strengths were measured as 30.59 MPa with a w/b ratio of 0.55 and 30.25 MPa with w/b ratio of 0.42, respectively
These results showed that CDW substitution was detrimental to axial compressive strength, as well as longitudinal elasticity modulus
Summary
Using concrete in construction and engineering works is widespread and estimated at approximately 20 billion metric tons per year (WANG et al, 2017). This high use results in a substantial demand for cement which is its principal constituent. The global demand for cement is estimated at 4 billion metric tons per year, of which 40 million tons were the estimated demand in Brazil in 2019 (U.S GEOLOGICAL..., 2019; SINDICATO..., 2019). According to Chen et al (2017) and Huang et al (2018), the cement industry generates about 8% of global carbon dioxide (CO2) emissions. The carbon footprint of this cement demand is bound to have negative environmental effects. If there is no appropriate recycling of waste, most industrial by-products are incinerated resulting in contamination and atmospheric pollution (XUAN; POON; ZHENG, 2018)
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