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.

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.

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.

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.

This study discusses the results of an experimental program conducted to study the fresh, hardened and unrestrained shrinkage characteristics of self-consolidating concrete (SCC) using fine recycled asphalt pavement (FRAP) and high volume of supplementary cementitious materials (SCMs) including class C fly-ash (FA) and slag (S). Sixteen mixtures were prepared with different percentages of FA, S, and FRAP. SCC mixtures were divided into four groups where each group had a different percentage of FRAP replacing fine aggregate (10%, 20%, 30%, 40%) and Portland cement being replaced by different percentages of SCMs. The water to cementitious material (w/cm) ratio of 0.4 was used for SCC mixtures with a target slump flow higher than 500 mm. The flowability, deformability, filling capacity and resistance to segregation were measured to determine the fresh properties of the mixtures. Moreover, the compressive strength at 14, 28, and 90 days and split tensile strength at 28 days were determined and durability characteristics including unrestrained shrinkage up to 90 days were tested. Analysis of experimental data showed that most of the mixtures satisfied the SCC fresh properties requirements. The addition of FRAP had an adverse effect on the compressive, tensile strength and unrestrained free shrinkage of SCC mixtures.