Editor: Moncef L. Nehdi

With increasing world population and urbanization, the depletion of natural resources and generation of waste materials is becoming a considerable challenge. As the number of humans has exceeded 7 billion people, there are about 1.1 billion vehicles on the road, with 1.7 billion new tires produced and over 1 billion waste tires generated each year. In the USA, it was estimated in 2011 that 10% of scrap tires was being recycled into new products, and over 50% is being used for energy recovery, while the rest is being discarded into landfills or disposed. The proportion of tires disposed worldwide into landfills was estimated at 25% of the total number of waste tires. Likewise, in 2013, Americans generated about 254 million tons of trash. They only recycled and composted about 87 million tons (34.3%) of this material. On average, Americans recycled and composted 1.51 pounds of individual waste generation of around 4.4 pounds per person per day. In 2011, glass accounted for 5.1 percent of total discarded municipal solid waste in the USA. Moreover, energy production and other sectors are generating substantial amounts of sludge, plastics and other post-consumer and industrial by-products. In the pursuit of its sustainability goals, the construction industry has a potential of beneficiating many such byproducts in applications that could, in some cases, outperform the conventional materials using virgin ingredients. This Special Publication led by the American Concrete Institute’s Committee 555 on recycling is a contribution towards greening concrete through increased use of recycled materials, such as scrap tire rubber, post-consumer glass, reclaimed asphalt pavements, incinerated sludge ash, 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 long-term behavior of concrete civil infrastructure.

Note: The individual papers are also available. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP-314

There are significant environmental benefits of recycling and reusing waste concrete as aggregate for structural concrete. The use of recycled aggregate concrete (RAC), however, is currently limited to non-structural applications such as road base and erosion control. Widespread application of RAC, such as seismic applications, therefore requires an improved knowledge of the behavior under multi-axial state of stresses and development of behavioral models to describe the behavior under compression is essential. This paper presents part of the results of an extensive experimental investigation on mechanical properties of unreinforced RAC where the behavior under quasi-static axial loading was investigated and a one-of-a-kind stress-strain model was developed. It was observed that, quite similar to normal concrete, the stress-strain can be defined by a hyperbolic ascending-descending curve that is primarily a function of compressive strength, a straight descending branch which slope is a linear function of compressive strength followed by a sustaining branch.

Green construction has been a very important aspect in the concrete production field in the last decade. One of the most problematic waste materials is scrap tires. The use of scrap tires in civil engineering is increasing. This article investigates the dynamic properties of concrete with replacement of fine aggregate with scrap tire. Two different rubberized concrete mixtures were designed. The first set; variable slump (VS) was designed to keep the mix proportions constant with rubber replacement as the only variable. The other set; constant slump (CS) was designed to keep the workability the same using superplasticizer. The compressive strength of the concrete was reduced by the use of rubber. The viscous damping ratio was investigated using free vibration tests with impact hammer on simply supported beams and drop weight tests. The replacement of up to 20% of sand with rubber resulted in an increase in damping with the increase being more in the CS beams as well. Beyond 20%, the effect on damping was insignificant. The average hysteresis damping was found to increase with the increase of rubber content. The fracture energy was found to increase with the increase of rubber content up to 20%. Microstructure investigation was also performed on the two mixes. It is concluded that the choice of the rubber content and the mixing process can have a significant effect on the dynamic properties of rubberized concrete. Recommendations for these two aspects were provided.

The aim of this study is to investigate the physical and mechanical properties of cement mortar by replacing a portion of cement with incinerated sludge ash (SA) and silica fume (SF) at different proportions. The experimental program consists of four series. In series-A, the substitution amounts include 0%, 5%, 7.5%, 10%, 12.5% and 15% of SA. In addition, in series A, B, C and D of the experimental program, 0%, 10% 15% and 20% of SF were added, respectively. The tests performed include consistency, setting time, flow table spread value, flexural strength (Rf), compressive strength (Sc), apparent bulk density, water absorption and sorptivity. The results show that the initial and the final setting times and workability increased, when the percentage of SA was higher. Due to little pozzolanic reaction, the strength activity index (SAI), and the initial compressive and flexural strengths of SA mortar decreased. However, addition of SF to SA mortar could improve its mechanical properties. Statistical analysis is also conducted to forecast the flexural and compressive strengths of mortar, and an equation is proposed by performing regression analysis.

The continuous consumption of natural aggregate in concrete production is steadily straining such natural resources. The need for a more sustainable solution has led to a serious consideration of using recycled concrete aggregate as a replacement to natural aggregate. Studies in the literature were conducted to determine the properties of recycled aggregate concrete. For non-structural applications, recycled aggregate concrete has been widely accepted in several countries mostly in Japan. However, further studies on its durability are still required. The lack of comprehensive standard guidelines for mixture proportion as well as the limited studies on its durability has hindered its wider implementation especially in structural applications. The studies performed on the durability of recycled aggregate concrete has been surveyed and compiled in this paper. The paper addresses issues pertaining to durability including the mixture design, permeability and water absorption, the resistance to alkali-silica reactions, reinforcement corrosion, abrasion, freeze-thaw resistance, and sulfate attack. Generally, a coarse aggregate replacement ratio of 20% to 50% did not negatively affect the performance of recycled aggregate concrete in many cases. The literature overview showed that recycled aggregate concrete performs satisfactorily under various conditions and has a comparable durability to natural aggregate concrete if designed properly.