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Abstract
In the last several decades, the growth of Construction and Demolition Waste (CDW) production and the increased consumption of natural resources have led to promoting the use of secondary raw materials for a more sustainable construction. Specifically, the use of Recycled Concrete Aggregate (RCA), derived from waste concrete, for the production of Recycled Aggregate Concrete (RAC) has attracted a significant interest both in industry and in academia. However, the use of RAC in field applications still finds some barriers. In this context, the present study investigates experimentally the effects of freeze-thaw and wet-dry cycles on the stress transfer mechanisms of reinforced RAC elements through tension stiffening tests. First of all, the paper presents a detailed analysis of the degradation due to the aging process of RAC with RCAs obtained from different sources. Particularly, the results of tension stiffening tests are analyzed in terms of crack formation and propagation, matrix tensile strength contribution and steel-to-concrete bond. The results highlight that the pre-cracking elastic modulus, the first crack strength as well as the maximum concrete strength are strongly influenced by the presence of the Attached Mortar (AM) in RCA, as the former affects the concrete’s open porosity. Therefore, the amount of AM is identified as the key parameter for the evaluation of durability of reinforced RAC members: a degradation-law is also proposed which correlates the initial concrete open porosity with the damage observed in reinforced RAC elements.
Highlights
The continuous development of the construction and infrastructure sectors has become a global concern in regards to sustainability issues, due to the high consumption of nonrenewable natural resources as raw materials and the massive production of Construction and Demolition Waste (CDW)
The reinforced concrete elements subjected to tension stiffening tests behave in accordance with the well-known ACK model [44], characterized by the following four phases: (i) Pre-cracking elastic phase; (ii) Multiple crack formation; (iii) Stabilized crack phase; and (iv) Yielding of reinforcement
Until the appearance of the first crack, since the composite is in the elastic phase, the load-strain curve slope is governed by the pre-cracking elastic modulus of the composite (Epre ): the results show that for unconditioned elements, the presence of Recycled Concrete Aggregate (RCA) did not significantly influence this property
Summary
The continuous development of the construction and infrastructure sectors has become a global concern in regards to sustainability issues, due to the high consumption of nonrenewable natural resources as raw materials and the massive production of Construction and Demolition Waste (CDW). The use of CDW to produce Recycled Concrete Aggregate (i.e., RCA identifying recycled aggregate obtained from concrete debris) can be an effective way to mitigate these negative environmental impacts [1,2,3]. The main difference between Recycled Concrete Aggregate (RCA) and Natural Aggregate (NA) relies on the presence of the existing Attached Mortar (AM) layer on the recycled aggregate surface, and, the presence of an Interfacial Transition Zone (ITZ). RCA presents lower value of specific gravity and higher water absorption capacity, apart from typically higher value of L.A. abrasion wear [4,6]. Amario et al [7]
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