Issue 46

Y. Yanya, Frattura ed Integrità Strutturale, 46 (2018) 343-351; DOI: 10.3221/IGF-ESIS.46.31 345 To improve the mixing peaceability of recycled pervious concrete and ensure its strength, a small amount of coarse sand (natural river sand with fineness modulus of 3.3) was added (sand percentage: 10%) was added (Tab. 1). The design of mix proportion is shown in Tab. 2. Aperture size/mm 9.5 4.75 2.36 1.18 0.60 0.30 0.15 Type II grading region requirement/% 0 0-10 0-25 10-50 41- 70 70- 92 90- 100 The first accumulative sieve residue percentage/% 0 0.5 11.8 41.9 65.2 80.4 92.6 The second accumulative sieve residue percentage/% 0 0.7 13.5 43.2 67.6 83.8 91.3 Table 1: Natural sand grain grading. No. Replace ment rate/% Sand percentag e/% Material utilization amount per unit volume (kg/m 3 ) RA1 RA2 NA Natural sand Cement Water involved in cement hydration Added water RC0 0 10 0 0 1378 153 307 92 0 RC30 30 10 136 0 1240 153 307 92 3 RC50 50 10 415 0 968 153 307 92 10 RC100 100 10 1378 0 0 153 307 92 32 RC100D 100 10 826 550 0 153 307 92 28 Table 2: Mix proportion of recycled pervious concrete Note: NA: natural aggregate (5~10 mm); RA1: recycled coarse aggregate (5~10 mm); RA2: recycled coarse aggregate (10~20 mm) The forming and maintenance of test specimens All the concrete was mixed using a 50 L blender. Firstly sand and cement were mixed evenly. Then coarse aggregate and water were added. After 3 ~ 5 min of mixing, the slump degree was measured, about 35 mm~50 mm. After testing of the slump degree, the concrete mixture was poured into a steel mould and tamped; the surface was smoothed. The mould was removed after 24 hours. Then it was maintained in a curing room (20±2 °C, humidity higher than 95%). After 28 days, all the test specimens were taken out for testing. T EST METHODS Porosity and permeability coefficient he effective porosity of test specimens was calculated based on the mass variation of test specimens after being immersed in water and dried by air for 24 h. The calculation formula is: 2 1 m [1 ( )] 100% w m P v      (1) where P stands for porosity (unit: %), m 1 stands for the mass of test specimens in water (unit: g), m 2 stands for the mass of test specimens after 24 hours of air drying (unit: g), v stands for the volume of test specimens (unit: cm 3 ), and ρ w stands for the density of water at room temperature (unit: g/cm 3 ). Permeability coefficient Permeability coefficient was tested using constant water head method, and the test device is shown in Fig. 1. Pervious concrete was prepared using polyvinylchlorid pipe mould in a nominal outside diameter of 110 mm×150 mm. Then the test specimens were vertically fixed at the stent in the middle of overflow gutter. Valve for water supply was opened. After the volume of water flowing from the outflow ports of the overflow gutter and porous cylinder became stable, difference of the water levels of the porous cylinder and overflow gutter (H) was measured using a steel gauge. When the water levels were being stable for 30 s, a second chronograph was started; at the same time, water flowing from the water outlet was T