دانلود رایگان مقاله انگلیسی افزایش خواص مکانیکی و دوام بتن های بازیافتی - الزویر 2018

abstract

The main difference between Recycled Concrete Aggregate (RCA) and Natural Aggregate (NA) is the mortar adhered on RCA. This paper presents the effect of RCA to concrete and a treatment method utilized to improve the properties of RCA, by reducing the amount of the adhered mortar, and therefore the properties of the Recycled Aggregate Concrete (RAC). Mineral admixtures were used as partial replacement of cement. Three types of coarse RCA and two types of mineral admixtures were used (fly ash and silica fume). In addition, the RCA were employed as internal curing (IC) agents in concrete mixtures to assess their effectiveness in enhancing the properties of concrete. The mechanical properties and durability of RAC were improved using the proposed methodologies. Cost analysis showed that RAC mixtures could be less expensive than NA mixtures.

6. Conclusions

Some very useful conclusions were derived from this research aiming to dispel fears regarding the utilization of RCA into structural concrete. The key conclusion of this research is that the RAC can be enhanced in such a way to be used in some major construction activities. A simple treatment method, in the recycling process of RCA, is capable to reduce the adhered mortar at such level that diminishes the negative effects and to create a better quality RAC which is competitive to normal concrete. The main findings of the research are:

Properties of aggregates – RCA-F aggregates consisted of 24% adhered mortar. A simple treatment method though can reduce mortar to 9%, producing aggregates with less amount of mortar, slightly rounder and sounder (RCA-T aggregates). – RCA had higher water absorption values, lower density and higher LA and soundness values. Treated recycled aggregates (RCA-T) showed great improvement in all of the tests that were performed, reaching or even surpassing the properties of natural aggregates.

Replacement ratio of NA with RCA – Increasing the replacement ratio resulted in lower quality of concrete compared to normal concrete. Both mechanical and durability properties are negatively affected by the increase of the replacement ratio.

Type of aggregates – RCA-F aggregates provided good quality concrete, taking into account the low quality of aggregates. RCA-T aggregates provided good quality concrete, competitive to Control concrete. – Presoaking aggregates had some positive effect on the compressive strength, modulus of elasticity and sorptivity of concrete.