International Concrete Abstracts Portal

To improve the eco-efficiency and sustainability of concrete, the cement and concrete industry can exploit many byproducts in applications that could, in some cases, outperform conventional materials made with traditional ingredients. This Special Publication of the American Concrete Institute Committee 555 (Concrete with Recycled Materials) is a contribution towards improving the sustainability of concrete via using recycled materials, such as scrap tire rubber and tire steel wire fiber, GFRP waste, fluff, reclaimed asphalt pavements, recycled latex paint, and recycled concrete aggregate. Advancing knowledge in this area should introduce the use of recycled materials in concrete for applications never considered before, while achieving desirable performance criteria economically, without compromising the quality and long-term performance of the concrete civil infrastructure.

There is a growing need for alternative binders with smaller carbon footprint. The cement manufacture is an energy intensive process that is one of the major global contributors to carbon dioxide emission. Fly ash-based geopolymer binders represent one of these potential alternatives. Beside consuming a largely produced byproduct, fly ash-based geopolymers generally have better mechanical performance when exposed to elevated temperatures. This study evaluates the effect of the initial curing temperature and the alkaline activation solution proportions on the strength, pores structure and crystal structure of fly ash-based geopolymer mortars. The geopolymer was synthesized using Class F fly ash, potassium hydroxide solution and sodium silicate solution. The specimens were made using various ratios of sodium silicate to potassium hydroxide and were initially cured at different temperatures and their properties were studied in terms of mechanical and microstructural properties.

Various studies on the use of recycled concrete aggregate (RCA) were developed in the past decades. Yet, very often direct replacement techniques are adopted to proportion RCA concrete, which leads to inferior performance of the recycled material when compared to conventional concrete. RCA is a multi-phase material comprised of original virgin aggregate and residual mortar (RM) and thus these distinct phases should be considered during the RCA mix-design process. The Equivalent Mortar Volume (EMV) mix-design method accounts for the RM to proportion RCA concrete. Although great results are normally achieved in the hardened state, EMV-designed mixtures may present important challenges in the fresh state. Modifications of the original EMV such as the modified-EMV and the Equivalent Volume method were recently proposed to tackle issues related to the fresh state and binder efficiency of recycled mixtures. This paper discusses the differences among the recent mix-design procedures developed to proportion RCA concrete.

Detailed experimental and analytical studies were carried to investigate the effect of recycled tire-derived aggregates (TDA) on ductility and toughness of lightweight aggregate (LWA) concrete specimens containing coarse expanded shale aggregates and fine mineral aggregates. Investigations covered six different concrete mix with various portions of LWA replaced by TDA. Mechanical properties of each mix, including compressive strength, splitting tensile strength, flexural strength, and modulus of elasticity were measured to obtain the optimum range of TDA to LWA ratio. Further, dynamic destructive tests were carried to highlight the performance of tire-derived lightweight aggregate concrete (TDLWAC) subjected to impact loads. Moreover, the post-peak behavior of these specimens was modeled using a linear elastic fracture mechanics relationship. The model successfully demonstrated the effect of TDA in the enhancement of cracking behavior of TDLWAC.

A detailed investigation on the use of automotive shredder residues, the so-called fluff, as an alternative aggregate of structural lightweight concrete, is the subject of the present paper. Specifically, a new granulated fluff, obtained through a granulation process already used to treat returned concrete, substitutes the traditional gravel made with expanded clay. Slump values are measured with the slump cone test on fresh concrete, whereas the depth of penetration of water under pressure, and the uniaxial compressive tests as well, are performed on hardened concrete cylinders. As a result, a new parameter, herein called “inconsistency parameter”, is introduced and used to define both the mechanical properties (i.e., the strength and ductility) and the workability of the lightweight concretes made with virgin or plastic waste aggregates. According to the required structural performances in service, the optimal value of the inconsistency parameter can be defined as a function of both the water/cement ratio and the content of the granulated fluff.