【摘 要】
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Returned concrete is the residual amount of fresh concrete that is not placed at the job site and returns to the ready-mix plant in the truck mixer.According to local conditions, returned concrete may
【机 构】
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R & D Department, Mapei S.p.A., Milan 20158, Italy
【出 处】
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The 14th International Congress on the Chemistry of Cement (
论文部分内容阅读
Returned concrete is the residual amount of fresh concrete that is not placed at the job site and returns to the ready-mix plant in the truck mixer.According to local conditions, returned concrete may range from 1 to 5 per cent of the overall concrete production, representing a serious burden for the ready-mix plant.Recently, a new sustainable technology, based on superabsorbent polymers and ettringite forming compounds to transform returned concrete into aggregates has been developed.The aggregates produced with the new technology consist of size-graded material, for the most part formed by a core of coarse original aggregates with a shell consisting of a finer composite of sand and hydrated cement.These aggregates can replace natural aggregates to produce new concrete for use in non-structural applications, such as pavements and slabs.In the present paper, the results of a long term investigation aimed to assess the risk of internal sulphate attack (ISA) in concrete made with the recycled aggregates are presented.Concrete specimens containing 100% of recycled aggregates were subjected to dry-wetting and freeze-thaw cycles, simulating climatic conditions experienced by concrete pavements, i.e.sunshine, day-night temperature variations, rain and frost, to verify possible deterioration induced by delayed ettringite formation (DEF).Physical tests included compressive strength, water absorption,ultrasonic pulse velocity and modulus of elasticity.X-Ray Powder Diffraction (XRPD) analysis was used to detect delayed ettringite formation and scanning electron microscope (SEM) analysis were also performed to verify the characteristics of the microstructure of cement paste during the aging process.Equivalent concrete,produced with only natural aggregates, was used as a reference.Results of long term durability tests of the present paper indicated that concrete produced with recycled aggregates behaved similarly to reference concrete made only with natural aggregates and no adverse effect due to the use of the new aggregates to produce new concrete was observed.
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