Study on the Preparation and Properties of Porous Ecological Concrete
|Course||Materials Science and Engineering|
|Keywords||porous ecological concrete mix proportion design pore structure permeability plants compatibility|
Infrastructure construction and environmental protection have become the hot issue of21st century, as well as the common concern of governments around the world. In recent years,owning to great economic development, infrastructure constructions including roads, railwaysand dams have been changing with each passing day. Consequently, the original landform andvegetation cover are cruelly destroyed; large area of soil erosion occurs, which lead to seriousdisorder of regional ecological environment. Therefore, it is a vital task for us to develop acompromising approach that allows infrastructure construction compatible with environmentalprotection.Porous ecological concrete, made from coarse aggregate wrapped by a layer of cementmortar bonding, is a “popped rice candy”-shaped porous functional building material, whoseapplication in slope protection generates noticeable benefits on ecology, self-purification, floodprotection, landscape and economy. Further researches comprising porous ecological concretepreparation and mix proportion design, pore characterization, mechanical properties anddurability, low alkalinity cementitious materials and plant compatibility are carried out in thispaper. Moreover, the mineral composition and microstructure of low alkalinity cementitiousmaterial is systematically analyzed by referring to XRD and SEM-EDS testing method. Themain conclusions are as follows:(1) Preparation technology of porous ecological concrete has a significant influence on itsmechanical property and pore structure. Research shows that the molding thickness of porousecological concrete ranges from5to10mm. The increase of molding thickness induces firstincrease and then decrease of the compressive strength. Thus, the promising porous ecologicalconcrete with required mechanical property and pore structure can be obtained by combinedmolding technology including slurry mixing, tamping, vibrating method and suppression whenthe fluidity is controlled between180and210mm.(2) As is known, adding anhydrite, limestone, slag and fly ash allows an enhancedalkalinity of sulphoaluminate cement clinker, but induces an depletion of its mechanicalproperty. The alkalinity of cementitious material reduces dramatically, by15.69%within28d,when proportion of anhydrite is40%. Meanwhile, adding limestone, slag and fly ash allows to improve the mechanical strength while maintain the alkalinity. Taking comprehensive strengthand alkalinity into account, the optimum mix proportion is determined as20%anhydrite and20%limestone, at which point, the28d compressive strength of grout is103.5MPa and28dalkalinity10.42. The porous ecological concrete made from modified sulphoaluminate cement,although slightly weaker in dry shrinkage, frost resistance and sulfate attack resistanceperformance comparing to that made from ordinary Portland cement, has higher strength andlower alkalinity in the early stage. Thus, the modified sulphoaluminate is considered as theideal cement cementitious material for preparing porous ecological concrete.(3) Porosity and strength is discrepant. With the increase of coarse aggregate size, themechanical property of porous ecological concrete reduces notably, while porosity andeffective size improve continuously. Adopting absolute volume method and mix design, theaimed porosity is26%while the optimum coarse aggregate diameter is in the range of16to19mm. At this time, it is worked out that the porosity of porous ecological concrete is26.28%,28d compressive strength15.0MPa, effective pore diameter7.0mm, the amount of inside porediameter ranging from2.0to4.5mm takes up39%.(4) Spherical wrapping mix proportion design is developed based on the stacking modularof porous ecological concrete aggregate. When the wrapping thickness of coarse aggregate is inthe range of440to690um, the porosity of porous ecological concrete is between22.17%and29.66%. The decrease of wrapping thickness leads to continuous increase of porosity andeffective diameter but degradation of mechanical performance. The3d alkalinity reduces withthe increase of wrapping thickness; however, the28d alkalinity is the opposite. It is indicatedthat the optimum wrapping thickness is590um, when the porosity is26.32%, effective porediameter4.6mm,28d alkalinity9.72and strength12.1MPa.(5) After modifying the alkalinity inside of the concrete pores using low-alkalinitycementitious material, vegetation experiment is then carried out, working on the compatibilitybetween porous ecological concrete and plants. The experiment procedures are as follows: i)mix together the natural soil, nutrition soil, compound fertilizer and seeds according to a certainproportion; ii) fill this mixture into the inside pores of the concrete; iii) Water and fertilizeregularly, the seeds sprout out of the concrete. The experiment began in September. Quality“Green scene5#” combination was chosen as the seed. It turned out that the plants grew satisfactorily well on areas covered with soil: about5cm high on the7th day and12cm high onthe28th day, thus rapidly forming a small-area ecological environment.