Influence of recycled aggregates and high contents of fly ash on concrete fresh properties |
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| Affiliation: | 1. CERIS-ICIST, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001, Lisbon, Portugal;2. CERIS-ICIST, DECivil, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001, Lisbon, Portugal;1. Department of Civil and Chemical Engineering, College of Science, Engineering and Technology, University of South Africa, Johannesburg 1710, South Africa;2. Department of Civil Engineering Technology, Faculty of Engineering, University of Johannesburg, South Africa;3. Nanotechnology and Water Sustainability Unit, College of Science, Engineering and Technology, University of South Africa, Florida Campus, Johannesburg, South Africa;1. Geomaterials Laboratory, University Hassiba Benbouali Chlef, 02000, Algeria;2. University of Tissemsilt, 38000 Tissemsilt, Algeria;1. Department of Materials and Environment, Delft University of Technology, The Netherlands;2. Department of Building Materials Technology, AGH University of Science and Technology, Krakow, Poland;3. Strukton Civiel, Utrecht, The Netherlands |
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| Abstract: | This study presents the fresh properties of concrete with supplementary cementitious materials (SCM) and recycled concrete aggregates (RCA), with emphasis on the feasibility of using high volumes of fly ash (FA) in RCA concrete. For this purpose, two mix families (0% coarse RCA and 100% coarse RCA) were produced, both with and without superplasticizers (SP). The coarse natural aggregates (NA) were replaced with coarse RCA at 0% and 100%, respectively. For each of the mentioned families, three incorporation levels (0%, 50% and 100%) of fine RCA were used with 0%, 30% and 60% of FA, resulting in 28 compositions. Each mix was tested in the fresh state by means of slump, density and air content. The results of this study show that RCA decreased the slump of concrete mixes, but the required water content can be minimized by incorporation FA. Regardless of the water absorption of the aggregates, for a given fine RCA incorporation ratio and the same ratio of FA, no increase in water content is required to obtain the same target slump as in the reference concrete. On the other hand, for a given coarse RCA incorporation ratio, a five times lower FA ratio is enough to obtain the same target slump as in the reference concrete. Air voids in concrete mixes were more affected by the shape of the aggregates than by their water absorption. The air content of concrete mixes increased as the incorporation levels of FA and RCA increased. However, in comparison with the individual effects, the air content decreased by combining the incorporation of both FA and RCA. Moreover, the rate of reduction in fresh density by increasing the incorporation of RCA and FA was similar in concrete mixes with and without SP. |
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| Keywords: | Recycled aggregates Fly ash Concrete Fresh state Air content Fresh density FA"} {"#name":"keyword" "$":{"id":"kwrd0045"} "$$":[{"#name":"text" "_":"fly ash NA"} {"#name":"keyword" "$":{"id":"kwrd0055"} "$$":[{"#name":"text" "_":"natural aggregates OPC"} {"#name":"keyword" "$":{"id":"kwrd0065"} "$$":[{"#name":"text" "_":"Ordinary Portland cement RCA"} {"#name":"keyword" "$":{"id":"kwrd0075"} "$$":[{"#name":"text" "_":"recycled concrete aggregate SCM"} {"#name":"keyword" "$":{"id":"kwrd0085"} "$$":[{"#name":"text" "_":"supplementary cementitious materials SP"} {"#name":"keyword" "$":{"id":"kwrd0095"} "$$":[{"#name":"text" "_":"superplasticizers w/b"} {"#name":"keyword" "$":{"id":"kwrd0105"} "$$":[{"#name":"text" "_":"water to binder (ratio) w/c"} {"#name":"keyword" "$":{"id":"kwrd0115"} "$$":[{"#name":"text" "_":"water to cement (ratio) SSD"} {"#name":"keyword" "$":{"id":"kwrd0125"} "$$":[{"#name":"text" "_":"saturated surface dry |
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