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.

Due to their unique mechanical characteristics, glass fiber reinforced polymer (GFRP) composite materials are difficult to recycle at the end of their service lives. In the present work, a specific approach of recycling GFRP waste for use in concrete is investigated. Scrap from GFRP rebar and waste from a GFRP wind turbine blade shell were processed into slender elements, referred to as “needles,” with a length of 100 mm and used in concrete to replace 5% and 10% of natural coarse aggregate. The results of testing various concrete specimens revealed that the incorporation of needles with longitudinally aligned glass fibers increased the splitting tensile strength of concrete significantly. Both types of recycled needles, regardless of the source of waste and orientation of glass fibers, increased the tensile toughness of concrete significantly. In addition, it was observed that incorporating needles did not reduce concrete’s slump, due to the relatively high specific surface area of the needles. The findings suggest that recycling GFRP waste into needles as concrete reinforcement may be a viable GFRP waste management strategy and deserves further research.

Potential issues associated with depletion of good aggregate sources and management of excess RAP stockpiles increasingly motivate use of RAP in PCC as a coarse aggregate replacement. Texas has shown great interest in disposing excess RAP stockpiles and a systematic study on using RAP in PCC for Texas pavement applications was conducted by the authors recently. This paper provides a concise summary of the findings from this study. The major conclusions are (1) PCC mixture with dense aggregate gradation can be achieved by adding coarse RAP with adequate intermediate sized particles, which offers better overall performance in terms of workability and mechanical properties, (2) RAP-PCC with coarse RAP replacement up to 40% showed considerable reduction for modulus of rupture. Asphalt cohesive failure (crack passing through the asphalt layer) was found to be the main mechanism responsible for the strength reductions, (3) the addition of allowable amounts of RAP into PCC provides equivalent durability performance relative to plain PCC, and (4) constructing pavements with RAP-PCC yields economic, environmental and social benefits.

High strength concrete (HSC) is considered a material which have been implemented in many construction applications. The effect of Metakaolin (MK) and steel fiber (SF) combinations on the mechanical properties of HSC was investigated in this paper. Concrete mixtures’ compressive strength split tensile strength and bond strength were evaluated. All mixtures were designed as a grade M60 with various levels of cement replacement with high percentages of MK (10%, 15%, 20%, 30%, 40%, and 50% by weight of cement) and steel fibers (0.25% and 0.50% by volume fraction). The results of this study were compared to the recent similar studies conducted, and it showed consistence conclusions. Test results revealed that a 15% of MK as replacement of cement showed the highest compressive and tensile strengths. Even with 50% of cement replacement with MK and SF, the mixtures showed good mechanical properties compared to the 100% cement concrete.

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.