دانلود رایگان مقاله انگلیسی ارزیابی استحکام بتنی بازیافتی خودمتراکم با استفاده از روش آماری - الزویر 2018

abstract

The use of self-compacting recycled concrete appears as to be a very interesting technology for the sustainable construction future. However, one of the major obstacles to a more widespread use of selfcompacting concrete is to obtain a robust material. Therefore, the emphasis of this work is placed on analysing both practice and theory to understand the properties that control and assess self-compacting recycled concrete robustness. Hence, forty-nine different mixes were produced with several replacement percentages of recycled concrete coarse aggregate (0, 20, 50 or 100%) and with two different mixing procedures (all aggregates in dry-state conditions or recycled aggregate with a 3% of natural moisture). The experimental program consisted of making, in the fresh state, rheological tests (a stress growth test and a flow curve test) and empirical characterization tests (slump flow, V-funnel, L-box, J-Ring and sieve segregation) at 15, 45 and 90 min from cement-water contact. In the hardened state, compressive strength was measured at 3, 7 and 28 days. All results were analysed using a statistical approach based on Kendall’s coefficient of concordance and Spearman’s rank correlation. This approach allowed us to successfully identify six key properties that can be measured to evaluate SCRC robustness (capacity of the material to tolerate certain variations in material characteristics and mixture parameters). For each mix, a ranking that defines its robustness category was obtained by considering all properties. Also, it showed that water control is the key factor that affects SCRC robustness.

4. Conclusions

The robustness of self-compacting recycled concrete (SCRC) was deeply analysed. Based on the results obtained, the following conclusions can be drawn:

The key materials that have to be controlled when SCRC robustness is taken into account in an industrial production are the recycled aggregate percentage and the water variations (especially those due to aggregate moisture). When low replacement percentages of recycled coarse aggregate are used, SCRC shows a higher level of robustness. Moreover, when aggregates are used with a moisture content, the control of water is more difficult and this affects SCRC robustness negatively. Therefore, in a real production process, previous moisture of recycled aggregate has to be thoroughly controlled.

In general, the 20% replacement concretes show a medium-high level of robustness and SCRCs with a 100% of recycled aggregate display low robustness. Regarding the 50% replacement concretes, the level of robustness depends largely on the mixing procedure in terms of water control and previous moisture of recycled aggregates.