Issue 46

Y. Yanya, Frattura ed Integrità Strutturale, 46 (2018) 343-351; DOI: 10.3221/IGF-ESIS.46.31 344 recycled concrete with waste concrete instead of natural aggregate has been tried in the 1950s. Many scholars in China and abroad have studied the basic properties of recycled aggregate in recent years and gained substantial research achievements. Silva et al. [5] and Akbarnezhad et al. [6] found that the performance of recycled concrete was weaker than that of natural concrete. Brito et al. [7] regarded waste concrete beams with high grade as the source of recycled aggregate and found that the mixing amount of recycled aggregate had insignificant influence on the strength of concrete. Zhang et al. [8] considered that recycled aggregate could be used for preparing high-performance concrete. Though the conclusions about the performance of recycled concrete in those studies are inconsistent, preparing concrete with recycled aggregate is extensively considered as feasible. But limited by technical and social factors, its application has not been extensively promoted [9]. Pervious concrete refers to a kind of concrete with certain strength and permeability performance which is prepared by coating and binding aggregate particles with cement paste and adding or not adding fine aggregate and whose connected pores can rapidly drain away water. The porosity depends on the grain size of aggregate [10]. America has started to study and apply pervious concrete since 1970s and 1980s. China is promoting pervious concrete currently. Low impact development construction in China greatly demands pervious concrete, which means large consumption of natural aggregate. Replacing natural aggregated rocks with waste concrete totally or partially as the aggregate source of pervious concrete can save a large number of natural resources and generate significant ecological environmental benefits [11]. Studies concerning the preparation of pervious concrete based on recycled aggregate is in the early stage. Guneyisi E et al. [12] studied the influence of different replacement rates of recycled aggregate (25%, 50%, 75% and 100%) on pervious concrete and evaluated the performance of pervious concrete using General Linear Model-Analysis of Variance (GLM-ANOVA). The results demonstrated that the strength of pervious concrete increased firstly and then decreased and permeability coefficient increased with the increase of the replacement rate of recycled aggregate; the permeability performance of pervious concrete increased with the increase of water cement ratio under the same replacement rate. But Zaetang et al. [13] considered that the compressive strength slightly increased when the replacement rate was lower than 60% and slightly decreased when the replacement ratio was 100%. Zhu found that the compressive strength of pervious concrete was the largest when the replacement rate of recycled coarse aggregate was 30% and then decreased with the increase of the replacement rate through Gaussian curve fitting. Previous studies [14,15] considered that the basic performance of pervious concrete which was prepared using recycled aggregate could satisfy requirements; however the research methods are different, and the relationship between the replacement rate and the performance of pervious concrete has not been unified. Therefore, the performance and replacement rate of recycled aggregate and the strength and permeability performance of graded recycled pervious concrete were studied by preparing graded aggregate based on waste prefabricated concrete beams through mechanical crushing and artificial screening, which provides a theoretical basis for the the application of recycled aggregate in pervious concrete and promote the recycling of waste concrete. T EST OVERVIEW Raw materials he raw materials included P·O 42.5 cement (Henan Mengdian Group, China) whose 28-day compressive strength was 53 MPa and 28-day bending strength was 8.0 MPa, natural river sand (coarse sand), natural coarse aggregate (gravel with grain size between 5 mm and 10 mm) and recycled coarse aggregate (waste road concrete blocks). Natural river sand was used as fine aggregate. The mixture of coarse sand was to ensure the strength of test specimens and improve the workability of pervious concrete and facilitate the forming of test specimens. The waste road concrete blocks were obtained by crushing with knobbling and Y132S-4 jaw crusher (Shanghai Dezhong Electric Co., Ltd., China) and screening aggregate with grain size between 5 mm and 10 mm and between 10 and 20 mm (in a small amount). Design of mix proportion Referring to relevant regulations and research achievements [16,17], water cement ratio was set as 0.30. The replacement rate of recycled aggregate was set as 0%, 30%, 50%, 100% single-sized and 100% double-sized, denoted as RC0, RC30, RC50, RC100 and RC100D. The double-sized recycled coarse aggregate included aggregate with grain size between 5 mm and 10 mm and between 10 mm and 20 mm (mass ratio: 6:4; with the maximum accumulation density). The 10-min water absorption rate of recycled aggregate usually can be 90% that of aggregate in saturation state; moreover concrete mixing can be completed within 10 min. To solve the problem of high water absorption of the recycled aggregate, added water was used in this study. The amount of added water was equal to the amount of 10-min water absorption. Influence of the water absorption of natural aggregate was not considered. T