Study On Preparation And Properties Of Ecological Porous Concrete With Recycled Aggregate

At present,there is ecological imbalance in most regions.How to protect the environment and restore ecology in the process of pursuing economic development is an important task in the21 st century,and it is also the focus problem that we all pay close attention to and try our best to solve.In order to reduce the environmental load and improve the ecological environment,the experimental study on porous concrete has been carried out at home and abroad for some decades.Porous concrete is an ecological concrete with special pore structure and surface characteristics prepared by special process.In the paper,the porous ecological concrete prepared with recycled coarse aggregate not only has high compressive strength and good permeability,but also can alleviate the pressure that construction waste occupies a large number of land resources,which has good ecological and economic benefits.In addition,the porous vegetation concrete can be used in construction for slope protection,pavement,roof garden and so on,which has produced a good effect of scour prevention,flood control and ecological restoration.It has the advantages of purifying water quality and improving landscape as well.Considering the practical application of porous ecological concrete,the voidage of porous concrete prepared in this paper is controlled at 20%,25% and 30% respectively.And the effects of water-cement ratio,designed voidage,fly ash substitution rate and admixture on the properties of porous concrete are studied in the experiment.Moreover,the mix proportion design,preparation technology,basic mechanical properties,durability and plant compatibility of porous concrete are studied.The results shows that:(1)Based on the designed voidage as the control parameter and the unit volume method for the mix proportion design,the voidage of porous concrete prepared by special feeding order,mixing process,molding process has good pore structure and surface characteristics,which meets the practiceal requirements.(2)With the increase of the water-cement ratio(0.28-0.42),the 7-day compressive strength and the 28-day compressive strength of the recycled aggregate porous concrete increase at first and then decrease.And when the water-cement ratio is 0.38,the 7-day strength and the 28-day strength of the porous ecological concrete reached at a peak value.The water-cement ratio of0.38 can be used as the most suitable water-cement ratio for studying the porous concrete in this experiment.(3)With the increase of designed porosity,the strength of porous concrete decreases obviously.The suitable content of fly ash can improve the strength of porous ecological concrete.When the replacement rate of fly ash is 20%,the compressive strength of porous concrete reaches the peak at 7 days and 28 days,which is beneficial to the improvement of strength.But when the substitution rate of fly ash is 30%-40%,the strength of fly ash does not increase obviously.(4)The dry shrinkage and freezing resistance of porous ecological concrete are of great significance to guide practical engineering application.Within 28 days,the shrinkage of porous ecological concrete changes rapidly,which can basically reach about 60% of the shrinkage value of 180 days.After 28 days,the shrinkage trend of porous concrete gradually slows down,and after 90 days,the shrinkage is basically stable and almost no longer increases.Undergoing rapid freeze-thaw cycle,the anti-freezing property of the porous ecological concrete is very poor.After freeze-thaw cycles for 30 times,the mass loss of the specimen is smaller,but the strength decreases very rapidly,and the strength loss rate reaches the upper limit of the code.(5)It showed that Tall Fescue grows in good condition based on the experiment of planting Tall fescue seeds on recycled porous concrete after alkali reduction.The plant as Tall Fescue has strong adaptability and strong resistance.Its roots are luxuriant with strong penetration ability.And finally,the root system of Tall Fescue penetrates through the porous concrete with the thickness of 6 cm,which can enhance the anchoring force between porous concrete and natural foundation.It will produce good landscape benefit and environmental benefit in the future.