Experimental Study On Performance Of Marine Ecological Concrete With Oyster Shell Sand

The induced oyster marine concrete can recruit oyster settle on the concrete engineering to restore the oyster reefs.The oyster reefs,named ecosystem engineers,can provide the ecosystem services such as water filtration and so on.Thus,the induced oyster concrete can maintain a balance between marine engineering construction and marine ecological protection to promote sustainable development.Previous studies have found that the settlement of oyster on the concrete was improved by the inducer like oyster shells and calcium carbonate.In addition,the oyster shells as the substitute for river sand can not only attract oyster to settle on the concrete,but also realize the secondary utilization of agriculture wastes.To explore the influence of oyster shells or/and inducers on the properties of ecological marine concrete,a series of experimental studies were carried out.Oyster shells with modulus of 2.52 were selected to replace river sand.To study the influence of oyster shells on the mechanical property and permeability of concrete,the replacement levels include six gradients of 0%,30%,40%,50%,60%and 100%.Then,the influence of oyster shells,slag,fly ash and dark pigments,which were compound mixed into concrete with three levels,on the mechanical properties and permeability were considered.Finally,according to the best proportion in the orthogonal test,the coupling effects of oyster shells with 30%,60%and 100%gradients and some oyster inducer X/Y/Z on the properties of concrete were studied.For the mechanical properties of concrete,oyster shells reduce the compressive strength with some fine aggregates replaced.And the increase of replacement ratio leads to the worse compressive strength.Then,Main factors,including oyster shells,mineral admixtures and dark pigments,were analyzed.And the important ranking of them is the proportion of oyster shells replacing river sand(A),fly ash(B),T powder(D),slag(C).And the best mix proportion is A₁B₃C₃D₁.In addition,the combination between X/Y inducer and the four factors enhances the compressive strength,while Z inducer reduces the compressive strength.For the impermeability of concrete,oyster shells replacing some fine aggregate decline the resistance to chloride ion penetration.And the higher the replacement ratio,the worse the chloride ion impermeability.With the increase of oyster shells,the capillary adsorption coefficient K of concrete firstly decreases and then increases.Furthermore,according to the orthogonal test,the most significant matter on chloride ion impermeability is C,A,D,B.As for the capillary adsorption coefficient K,the most significant factor is A,C,B,D.And the best mix proportion on the impermeability is A₁B₃C₃D₁.Additionally,the combination between X/Y/Z inducer and the four factors reduces the chloride ion impermeability.For the volume stability of concrete,the autogenous shrinkage stability value?when some fine aggregates were replaced by oyster shells shows a trend of first decreasing and then increasing with the increase of oyster shells.When all oyster shells,mineral admixtures and dark pigments were mixed into the concrete,the important ranking of the four factors is A,B,C,D.And the best mix proportion is A₁B₂C₃D₃.In summary,considering all the mechanical properties,impermeability and volume stability of concrete,the best mix proportion is to replace 30%of fine aggregates with oyster shells and add a few mineral admixtures,dark pigments and a certain amount of X inducer into the induced oyster concrete.