Abstract
Recycled concrete aggregates and mixed recycled aggregates are specified as types of aggregates with lower densities, higher water absorption capacities, and lower mechanical strength than natural aggregates. In this paper, the mechanical behaviour and microstructural properties of natural aggregates, recycled concrete aggregates and mixed recycled aggregates were compared. Different specimens of unbound recycled mixtures demonstrated increased resistance properties. The formation of new cement hydrated particles was observed, and pozzolanic reactions were discovered by electronon microscopy in these novel materials. The properties of recycled concrete aggregates and mixed recycled aggregates suggest that these recycled materials can be used in unbound road layers to improve their mechanical behaviour in the long term.
Highlights
In recent years, the use of construction and demolition waste (CDW) in civil engineering has increased considerably, and recycled aggregates (RA) are widely used as subbase materials in production [1].Two types of RA can be generated from CDW: recycled concrete aggregates (RCA), which contain particles primarily originating from recycled crushed concrete [2], and mixed recycled aggregates (MRA), which are produced from recycled crushed masonry and include brick, mortar, concrete, asphalt and gypsum particles [3].Several studies have concluded that RCA exhibit lower density and higher water absorption than natural aggregates, and if this material is applied in concrete, its mechanical behaviour is reduced [4,5,6]
Poon and Chan [15] studied the possibility of using RCA and crushed clay brick as aggregates in unbound subbase materials, and the results indicated that these recycled materials (MRA) could feasibly be blended to build road subbases
CCoonnvveerrsseellyy, materials with sharp curves are very sensitive to the change in the moisture content aannddththeerereisisa naeneedetdo teonseunrseutrheathtahte tmheoimstuorisetucorentceonnttiesnctloisectloostheetoptthime oupmtivmaulume vdaulruinegducorimngpaccotmiopna[c1t5io,1n8][.15F,i1g8u].reF2igsuhroew2sshthoawt saltlhtahtealml tahtermialasteerxiahlisbietxehdibciutervdecsutrhvaetswthearte wverye vsenrysitsievnesittoivechtaoncgheasnginesthine tmheomistouirsetucreonctoenntte,ndt,edmeomnostnrsattriantgingthtehenenceecsessistyityoof feennssuurriningg tthhaatt the moisture content is close to the optimum value during compaction
Summary
The use of construction and demolition waste (CDW) in civil engineering has increased considerably, and recycled aggregates (RA) are widely used as subbase materials in production [1]. Several studies have concluded that RCA exhibit lower density and higher water absorption than natural aggregates, and if this material is applied in concrete, its mechanical behaviour is reduced [4,5,6]. Mixed recycled aggregates have been studied, especially in non-structural concrete applications [10,11] The densities of these recycled materials are lower than that of RCA, and MRA’s water absorption is higher than that of RCA. Et al [18] evaluated different types of recycled aggregates from CDW as granular materials for the construction of unbound rural path sub-bases. In both cases, the behaviour of these materials was excellent and improved in the long term. Diffraction and microscopy tests were applied to determine the underlying causes of the improvement in compressive strength or the self-cementing process observed in recycled aggregates
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