再生骨料透水混凝土强度及透水性能试验

Experiment on strength and permeability of recycled aggregate pervious concrete

利用再生废弃混凝土骨料制备透水混凝土是目前研究的热点和趋势,其中强度和透水性是其关注及目前亟待突破的关键性能。以废弃的预制混凝土梁构件为再生骨料来源制备透水混凝土,并以水胶比0.3,砂率10%为基准,设计6组配合比,并通过标准养护下的立方体试块试验,研究了单一因素下再生骨料透水混凝土的孔隙率、透水性及其强度性能,其范围分别为孔隙率17.8%~23.8%,渗透系数0.27~0.57 cm/s以及抗压强度4.0~9.63 MPa。结果表明,再生骨料透水混凝土基本性能够满足要求,其中内掺粉煤灰能大幅提高其抗压强度,提高约44%,外掺钢纤维提高透水性,掺入萘系高效减水剂及硅粉的效果不明显。此外,再生骨料透水混凝土的毛细吸水过程与普通混凝土类似,即前期吸水快,后期趋于平缓。

To prepare pervious concrete with recycled concrete aggregate is a hot point and the trend of the current research,while strength and water permeability are the key performance highlighted and to be broken through at present. With waste prefabricated concrete beam members as the source of recycled aggregate, pervious concrete was prepared, and 6 groups of mixture ratios were designed with water cement ratio of 0.3 and sand ratio of 10% as the benchmark. Besides, through the experiment on test cubes under standard maintenance, the porosity, water permeability and strength performance of recycled aggregate pervious concrete（RPC） under a single factor were studied. The grain size of coarse aggregate was 4.75-9.5 mm and the natural coarse aggregate（NCA） came from gravels. With the pervious concrete prepared with 100% recycled coarse aggregate as the benchmark, 5 kinds of pervious concretes were designed on the premise of not changing the water-binder ratio and sand ratio： 1） ordinary pervious concrete（wholly made of natural aggregate）; 2） equivalent replacement of 20% cement with fly ash; 3） equivalent replacement of 6% cement with silica fume; 4） adding naphthalene superplasticizer equivalent to1% of the mass of the cement; 5） external addition of steel fiber equivalent to 3% of the mass of the cement. To reduce the influence of the high water absorption of the recycled coarse aggregate, the method of increasing additional water compensation was adopted and the amount of additional water was determined as the amount of water absorbed in 10 min by the recycled coarse aggregate. On the basis of the test and research of the capillary water absorption of concrete by predecessors, a capillary water absorption device for pervious concrete was self-made. It was measured in the experiment that the range of porosity, permeability coefficient and compressive strength was 17.8%-23.8%, 0.27-0.57 cm/s and 4.0-9.63 MPa respectively. According to these results, the basic performance of pervious concrete made of recycled aggregate could satisfy the requirements. Compared with RPC, adding fly ash could realize effective improvement of the compressive strength of the pervious concrete to 9.63 MPa, an increase of about 44%, the external addition of steel fiber could improve the water permeability, and the mixing of naphthalene super plasticizer and silica fume didn＇t have obvious effect. Admixtures and additives would both exert adverse effect on the splitting tensile strength, and their affecting degree was super plasticizer, fly ash silica fume steel fiber. The ratio of the measured splitting tensile strength to the compressive strength（ratio of tension to compression） was 9.5%-16.9%, with the average value being 13.5%. The water permeability increased with the increase of the porosity, and the two presented an exponential relationship, which was basically consistent with the description of ordinary pervious concrete. In addition, it was figured out in the experiment that the maximum capillary water absorption height was19.4 mm, and the maximum immersion amount in capillary water absorption was 0.01 g/cm3; the water absorption height of RPC internally doped with 20% fly ash was about 13.5 mm, while the amount of water absorbed was about 28 g, both values being consistent with the test results of capillary water absorption of existing ordinary concrete in terms of the order of magnitude. In nondestructive condition, the capillary water absorption process of previous concrete made of recycled aggregate was similar with that of ordinary concrete, namely, fast absorption in the early stage and steady absorption in the late stage.