Patent Application
20240034679
The present disclosure relates to concrete substrates useful for promoting the growth of fauna and flora in an aquatic environment, eco-concrete precursors thereof, and methods of use and preparation of the same.
In contrast to natural shorelines, conventional artificial seawalls are characterized by a lack of habitat complexity (i.e., simple and homogenous granite or concrete surfaces) and unsuitable material composition (e.g., concrete with high pH of 12-13 and high carbon footprint) to sustain marine biodiversity and promote sustainable development.
Current artificial seawalls usually have simple homogenous granite or concrete surfaces, which lack the diverse microhabitats, such as crevices, holes, surface texture and water retention for both marine fauna and flora that natural seawall surfaces exhibit. An additional shortcoming of current artificial seawalls is they tend to have pH, usually in the range of 12-13, which is much higher than the pH of natural seawater (around pH 8) and can negatively impact the growth of certain organisms.
There thus exists a need to develop improved eco-tiles useful for providing artificial marine habitats capable of supporting increased biodiversity that addresses at least some of the disadvantages described above.
Provided herein is an ecologically friendly concrete mixture that incorporates waste materials to promote waste recycling and reduce carbon footprint. The composition and production method of the concrete mixture provides an eco-concrete with low pH suitable for facilitating settlement of marine organisms and sustaining their survival. The eco-concrete can be used to fabricate an ecologically engineered eco-tile that integrates ecological principles with diverse microhabitats, such as crevices, holes, surface texture and water retention for both marine fauna and flora. The eco-tile described herein has a reduced carbon footprint and low surface pH, while it comprises a variety of microhabitats for the settlement of marine species. These microhabitats effectively provide predation refuges and temperature and desiccation shelters to intertidal species compared to conventional concrete seawalls. In turn, the eco-tile can increase marine biodiversity as well as the ecosystem's functions and services.
In a first aspect, provided herein is an eco-tile comprising: at least one type of cement; aggregates comprising at least two fine aggregates and coarse aggregates; and milled incineration sewage sludge ashes (MISSA), wherein the at least two fine aggregates comprise dredged marine sediment (MSD).
In certain embodiments, a surface of the eco-tile has a pH less than 11.
In certain embodiments, a surface of the eco-tile has a pH between 9-10.5.
In certain embodiments, the eco-tile has a compressive strength 35-45 Mpa.
In certain embodiments, the at least one type of Type I Ordinary Portland Cement, Type II Modified or Blended Portland Cement, Type III Rapid Hardening Portland Cement, Type IV Low Heat Portland Cement, Type V, Sulphate-Resisting Portland Cement, or a combination thereof.
In certain embodiments, the at least two fine aggregates comprise sand.
In certain embodiments, the coarse aggregates comprise gravel.
In certain embodiments, the MISSA and the at least one type of cement are present in the eco-tile at a mass ratio of at least 1:4, respectively.
In certain embodiments, the MSD and each of the other fine aggregates present in the at least two fine aggregates are present in the eco-tile at a mass ratio of at least 1:4, respectively.
In certain embodiments, the MSD and each of the other fine aggregates present in the at least two fine aggregates are present in the eco-tile at a mass ratio of 1:4 to 2:3, respectively.
In certain embodiments, the eco-tile further comprises at least one superplasticizer selected from the group consisting of a poly(melamine sulfonate), a poly(naphthalene sulfonate), polycarboxylate, a diphosphonate terminated polyoxyethylene, and salts thereof.
In certain embodiments, at least one surface of the eco-tile is defined by a plurality of microhabitat forming features selected from the group consisting of crevices, fissures, tunnels, holes, and irregular surface features of the eco-tile surface.
In certain embodiments, the eco-tile comprises: ordinary Portland cement; aggregates comprising MSD, sand, and gravel; MISSA; and at least one superplasticizer selected from the group consisting of a poly(melamine sulfonate), a poly(naphthalene sulfonate), polycarboxylate, a diphosphonate terminated polyoxyethylene, and salts thereof, wherein the ordinary Portland cement and the MISSA are present in the eco-tile at a mass ratio of at least 1:4, respectively; the MSD and the sand are present in the eco-tile at a mass ratio of 1:4 to 2:3, respectively; and at least one surface of the eco-tile is defined by a plurality of microhabitat forming features selected from the group consisting of crevices, fissures, tunnels, holes, and irregular surface features of the eco-tile surface.
In certain embodiments, a surface of the eco-tile has a pH between 9-10.5.
In certain embodiments, the eco-tile has a compressive strength 35-45 Mpa.
In a second aspect, provided herein is a method of promoting the growth of fauna and flora in an aquatic environment comprising placing at least one eco-tile of the first aspect in the aquatic environment.
In certain embodiments, promoting the growth of fauna and flora comprises the recruitment of 16 to 35 species per 25 cm×25 cm area of eco-tile after 12 months of deployment in the aquatic environment.
In a third aspect, provided herein is an eco-concrete mixture comprising: at least one type of cement; aggregates comprising at least two fine aggregates and coarse aggregates; at least one superplasticizer; milled incineration sewage sludge ashes (MISSA); and water, wherein the at least two fine aggregates comprise dredged marine sediment (MSD).
In certain embodiments, the at least one type of cement is ordinary Portland cement; the aggregates comprise MSD, sand, and gravel; and the at least one superplasticizer is selected from the group consisting of a poly(melamine sulfonate), a poly(naphthalene sulfonate), polycarboxylate, a diphosphonate terminated polyoxyethylene, and salts thereof.
In certain embodiments, the ordinary Portland cement, MISSA, MSD, gravel, sand, at least one superplasticizer, and water are present in the eco-concrete mixture in a 10-20 wt %, 2-7 wt %, 5-20 wt %, 30-50 wt %, 20-30 wt %, 0.01-0.5 wt %, or 5-10 wt %, respectively.
In certain embodiments, the ordinary Portland cement, MISSA, MSD, gravel, sand, at least one superplasticizer, and water are present in the eco-concrete mixture in a 12-16 wt %, 2-4 wt %, 6-14 wt %, 35-45 wt %, 20-27 wt %, 0.03-0.07 wt %, or 7-10 wt %, respectively.
The above and other objects and features of the present disclosure will become apparent from the following description of the disclosure, when taken in conjunction with the accompanying drawings.
Throughout the application, where compositions are described as having, including, or comprising specific components, or where processes are described as having, including, or comprising specific process steps, it is contemplated that compositions of the present teachings can also consist essentially of, or consist of, the recited components, and that the processes of the present teachings can also consist essentially of, or consist of, the recited process steps.
In the application, where an element or component is said to be included in and/or selected from a list of recited elements or components, it should be understood that the element or component can be any one of the recited elements or components, or the element or component can be selected from a group consisting of two or more of the recited elements or components. Further, it should be understood that elements and/or features of a composition or a method described herein can be combined in a variety of ways without departing from the spirit and scope of the present teachings, whether explicit or implicit herein.
It should be understood that the order of steps or order for performing certain actions is immaterial so long as the present teachings remain operable. Moreover, two or more steps or actions may be conducted simultaneously.
The use of the singular herein includes the plural (and vice versa) unless specifically stated otherwise. In addition, where the use of the term “about” is before a quantitative value, the present teachings also include the specific quantitative value itself, unless specifically stated otherwise. As used herein, the term “about” refers to a ±10%, ±7%, ±5%, ±3%, ±1%, or ±0% variation from the nominal value unless otherwise indicated or inferred.
The present disclosure provides an eco-tile comprising: at least one type of cement; aggregates comprising at least two fine aggregates and coarse aggregates; and milled incineration sewage sludge ashes (MISSA), wherein the at least two fine aggregates comprise dredged marine sediment (MSD).
The at least one cement can be any cement known in the art. Exemplary cements, include, but are not limited to, Type I Ordinary Portland Cement, Type II Modified or Blended Portland Cement, Type III Rapid Hardening Portland Cement, Type IV Low Heat Portland Cement, Type V Sulphate-Resisting Portland Cement, blast furnace slag cement, high alumina cement, white cement, colored cement, air entraining cement, expansive cement, hydrographic cement, or other types of cement, or combinations thereof. Additional exemplary cements include calcium aluminate cements, plaster materials, silicate cements, gypsum cements, phosphate cements, and cements based on magnesium oxychloride. In certain embodiments, the cement is ordinary Portland cement.
There are no particular requirements for fine aggregates. Most types of fine aggregate can be used for the preparation of the eco-tiles described herein. Exemplary fine aggregates include, but are not limited to coral sand, glass sand, immature sand, gypsum sand, ooid sand, silica sand, pit sand, river sand, sea sand, green sand, desert sand, lithic sand, mixed carbonate-silicate sand, biogenic sand, garnet sand, olivine sand, volcanic sand, heavy mineral sand, continental sand, quartz sand, clay, silt, fine sand, medium sand, coarse sand, stone dust, MSD, recycled fine aggregate derived from demolition waste or any of the materials listed for coarse aggregate that have been ground/pulverized into fine particles, and combinations thereof. In certain embodiments, fine aggregate can comprise two types of aggregates (e.g., river sand and MSD with a required proportion).
The coarse aggregate can be coarse gravel, medium gravel, fine gravel, crushed rock, pebbles, stones, recycled concrete rubbles, river gravel, sea gravel, crushed glass, slate waste, waste plastics, recycled coarse aggregate derived from demolition waste and combinations thereof.
The terms “fine aggregate” and “coarse aggregate” used herein are not intended to limit a range of sizes, but are simply used to indicate that one type of aggregate contains larger particles than the other type. For example, in a cement mixture containing two types of fine sand, the fine sand with larger particles will be called coarse aggregate.
The fine aggregates can have a particle size less than 10 mm, less than 5 mm, or less than 2 mm. In certain embodiments, fine aggregates have a particle size less than 5 mm and less than 2 mm.
The coarse aggregates can have a particle size less than 50 mm, less than 45 mm, less than 40 mm, less than 35 mm, less than 30 mm, less than 25 mm, less than 20 mm, less than 15 mm, less than 16 mm, or less than 10 mm. In certain embodiments, the coarse aggregates have a particle size between 5-10 mm or 2-8 mm.
A portion of the at least one cement can be replaced with MISSA. In certain embodiments, between 1-60% by weight, 5-60% by weight, 5-55% by weight, 5-50% by weight, 5-45% by weight, 5-50% by weight, 5-45% by weight, 5-40% by weight, 5-35% by weight, 5-30% by weight, 10-30% by weight, 10-25% by weight, 15-25% by weight, or 18-22% by weight, of the at least one cement is replaced with MISSA. In certain embodiments, about 20% by weight of the at least one cement is replaced with MISSA.
The MSD and each of the other fine aggregates present in the at least two fine aggregates can be present in the eco-tile at a ratio of at least 5:95, at least 1:9, at least 3:17, at least 1:4, at least 1:3, at least 3:7, at least 2:3, at least 1:9, at least 3:2, at least 7:3, respectively. In certain embodiments, the MSD and each of the other fine aggregates present in the at least two fine aggregates can be present in the eco-tile at a ratio of 5:95 to 7:3, 1:9 to 3:2, 1:9 to 1:1, 1:4 to 1:1, or 1:4 to 2:3, respectively. In certain embodiments, the MSD and each of the other fine aggregates present in the at least two fine aggregates can be present in the eco-tile at a ratio of about 1:4 or about 2:3, respectively.
The MISSA and the at least one type of cement can be present in the eco-tile at a mass ratio of at least 5:95, at least 1:9, at least 3:17, at least 1:4, at least 1:3, at least 3:7, at least 2:3, at least 1:9, at least 3:2, at least 7:3, respectively. In certain embodiments, the MISSA and the at least one type of cement can be present in the eco-tile at a mass ratio of 5:95 to 7:3, 1:9 to 3:2, 1:9 to 1:1, 1:4 to 1:1, or 1:4 to 2:3, respectively. In certain embodiments, the MISSA and the at least one type of cement can be present in the eco-tile at a mass ratio of about 1:4, respectively.
A portion of the at least two fine aggregates can comprise MSD. In certain embodiments, between 1-60% by weight, 5-60% by weight, 10-60% by weight, 10-55% by weight, 10-50% by weight, 15-50% by weight, 15-45% by weight, 20-45% by weight, or 20-40% by weight of the at least two fine aggregates comprise MSD. In certain embodiments, about 20% by weight or about 40% by weight of the at least one cement comprises MSD.
The eco-tile can comprise one or more superplasticizers. A superplasticizer can improve dispersion of the eco-concrete, so that less water is needed for good rheological properties, i.e. the ability to spread the coating in a thin, even layer prior to curing. In certain embodiments, the cementitious coating composition comprises one or more superplasticizer selected from a poly(melamine sulfonate), a poly(naphthalene sulfonate), a polycarboxylate, a diphosphonate terminated polyoxyethylene, salts thereof and derivatives thereof, and combinations of the foregoing. Exemplary superplasticizers include, but are not limited to, poly(ethyleneoxide)-grafted polyacid species, sodium salts of poly(melamine sulfonate), poly(naphthalene sulfonate), and polycarboxylates and sodium naphthalene sulfonate formaldehyde. In certain embodiments, the superplasticizer is a polycarboxylate sold by BASF™ under the trademark ADVA® 109.
The one or more superplasticizers can be present in the eco-tile at 0<1 wt %. In certain embodiments, the one or more superplasticizers is present in the eco-tile at 0.01-1 wt %, 0.01-0.9 wt %, 0.01-0.8 wt %, 0.01-0.7 wt %, 0.01-0.6 wt %, 0.01-0.5 wt %, 0.01-0.4 wt %, 0.01-0.3 wt %, 0.01-0.2 wt %, 0.01-0.1 wt %, 0.01-0.09 wt %, 0.02-0.09 wt %, 0.03-0.09 wt %, 0.04-0.09 wt %, 0.04-0.08 wt %, 0.05-0.08 wt %, 0.05-0.07 wt %, or 0.055-0.07 wt %. In certain embodiments, the about 0.057 wt % or about 0.066 wt %.
One or more surfaces of the eco-tile can be defined by a plurality of microhabitat forming features selected from the group consisting of crevices, fissures, tunnels, holes, and irregular surface features of the eco-tile surface.
The surface of the eco-tile descripted herein can have a pH which promotes the recruitment and growth of fauna and flora on the eco-tile surface. In certain embodiments, a surface of the eco-tile can have a pH below 11, below 10, below 9, below 8, or about 7. In certain embodiments, the pH of the eco-tile can range from about 9 to about 10.5.
The eco-tiles described herein can exhibit high compressive strength, which can increase their lifetime in aquatic conditions. In certain embodiments, the compressive strength of the eco-tile is between about 35 to about 45 Mpa or about 33 to about 43.5 Mpa.
The present disclosure also provides a method of promoting the growth of fauna and flora in an aquatic environment comprising placing at least one eco-tile described herein in the aquatic environment.
Promoting the growth of fauna and flora can comprise the recruitment of at least 1 species, at least 5 species, at least 10 species, at least 15 species, at least 20 species, at least 25 species, at least 30 species, at least 35 species, at least 40 species, at least 45 species, or at least 50 species per 25 cm×25 cm area of eco-tile (calculated by multiplying length (Y) and width (X) as shown in
Also provided herein is an eco-concrete mixture useful for preparing the eco-tiles described herein. In certain embodiments, the eco-concrete comprises at least one type of cement; aggregates comprising at least two fine aggregates and coarse aggregates; at least one superplasticizer; MISSA; and water, wherein the at least two fine aggregates comprise MSD.
In certain embodiments, the eco-concrete mixture comprises ordinary Portland cement, MSD, sand, gravel, water, and the at least one superplasticizer selected from the group consisting of a poly(melamine sulfonate), a poly(naphthalene sulfonate), polycarboxylate, and a diphosphonate terminated polyoxyethylene.
The eco-concrete mixture can comprise the at least one cement at a concentration of 5-50 wt %, 10-50 wt %, 10-40 wt %, 10-35 wt %, 10-30 wt %, 10-25 wt %, 10-20 wt %, 11-19 wt %, 12-18 wt %, 12-17 wt %, 12-16 wt %, 13-16 wt %, or 13-15 wt %. In certain embodiments, the eco-concrete mixture can comprise the at least one cement at a concentration of about 14 wt %.
The eco-concrete mixture can comprise MISSA at a concentration of 1-10 wt %, 2-10 wt %, 1-9 wt %, 2-9 wt %, 1-8 wt %, 2-8 wt %, 1-7 wt %, 2-7 wt %, 1-6 wt %, 2-6 wt %, 1-5 wt %, 2-5 wt %, 1-4 wt %, 2-4 wt %, 1-3.5 wt %, 2-3.5 wt %, 1.5-3.5 wt %, 2.5-3.5 wt %, or 3.0-3.5 wt %. In certain embodiments, the eco-concrete mixture can comprise MISSA at a concentration of about 3.3 wt %.
The eco-concrete mixture can comprise the coarse aggregate at a concentration of 20-60 wt %, 25-60 wt %, 30-60 wt %, 30-55 wt %, 30-50 wt %, 30-45 wt %, or 35-45 wt %. In certain embodiments, the eco-concrete mixture can comprise the coarse aggregate at a concentration of about 40%.
The eco-concrete mixture can comprise the at least two fine aggregates excluding the weight of the MSD at a concentration of 15-40 wt %, 20-40 wt %, 20-35 wt %, 20-30 wt %, 25-30 wt %, 15-35 wt %, 15-30 wt %, or 15-25 wt %. In certain embodiments, the eco-concrete mixture can comprise the at least two fine aggregates excluding the weight of the MSD at a concentration of about 20 wt % to about 27.4 wt %.
The eco-concrete mixture can comprise the MSD at a concentration of 1-30 wt %, 1-25 wt %, 1-20 wt %, 5-20 wt %, or 5-15 wt %. In certain embodiments, the eco-concrete mixture can comprise the MSD at a concentration of about 6.9 wt % to about 13.7 wt %.
The eco-concrete mixture can comprise the at least one superplasticizer at a concentration of about 0.01-1.0 wt %, 0.01-0.9 wt %, 0.01-0.8 wt %, 0.01-0.7 wt %, 0.01-0.6 wt %, 0.01-0.5 wt %, 0.01-0.4 wt %, 0.01-0.3 wt %, 0.01-0.2 wt %, 0.01-0.1 wt %, 0.01-0.09 wt %, 0.01-0.08 wt %, 0.02-0.08 wt %, 0.03-0.08 wt %, 0.03-0.07 wt %, 0.04-0.07 wt %, or 0.05-0.07 wt %. In certain embodiments, the eco-concrete mixture can comprise the at least one superplasticizer at a concentration of about 0.052 wt % to about 0.061 wt %.
The eco-concrete mixture can comprise water at a concentration of 5-20 wt %, 5-15 wt %, 5-10 wt %, 6-9 wt %, or 8-9 wt %. In certain embodiments, the eco-concrete mixture can comprise water at a concentration of about 8.5 wt %.
The eco-tiles described herein can be fabricated from the eco-concrete described herein using conventional methods well known to those of ordinary skill in the art. In certain embodiments, the eco-concrete is added to a mould and cured. The mould can optionally comprise one or more surfaces comprising crevices, fissures, tunnels, holes, irregular surface features, or a combination thereof. Curing can comprise allowing the eco-concrete to set at room temperature. Curing can also comprise the application of heat and/or reduced pressure to the eco-concrete. In certain embodiments, curing comprises allowing the eco-concrete. Curing can optionally be conducted in the presence of CO2, which can result in a decrease in the pH of the surface of the thus formed eco-tile and/or the compressive strength of the eco-tile.
In certain embodiments, curing comprises exposing the eco-concrete to air for 1-21, 1-14, 7-14, or 5-10 days. In certain embodiments, curing can further comprise exposing the eco-concrete to an atmosphere comprising CO2 for 1-5 days, 1-4 days, or 1-3 days.
The eco-concrete mixture can be made with milled incineration sewage sludge ashes (MISSA) to partially replace ordinary Portland cement (OPC) and combined with fine aggregates (river sand) (≤5 mm), coarse aggregate (crushed natural granite) (5-10 mm), and dredged marine sediment (MSD). Marine sediment can be used to partially substitute fine aggregates (Table 1). At least 20% of the OPC can be replaced with MISSA, and 20-40% of the fine aggregates are replaced with dredged marine sediment (Table 1). The amount of MISSA and MSD can vary according to the engineering requirements.
The eco-concrete mixture with MISSA and MSD can be cured under different combinations of air, steam, and CO2 to increase the compressive strength and reduce the surface pH. CO2 curing is conducted in a carbonation chamber at 1 bar to further reduce surface pH below 10.5 (Table 2).
The design of a eco-tile that has been tested for enhancing marine biodiversity on vertical concrete seawalls is described herein. The eco-tile comprising the eco-concrete described herein provides an appropriate substratum for the recruitment and growth of marine species, such as. The eco-concrete mixture is suitable for casting using various metal, plywood, plastic and silicone moulds. Thus, the eco-concrete can also be used to fabricate various concrete structures to enhance the biodiversity of different aquatic ecosystems. These concrete structures can take the form of tiles and panels to retrofit vertical seawalls, or blocks, armours and tidal pools (i.e., basins) to enhance sloping seawalls. The eco-concrete can also be used to build artificial subtidal reefs and to enhance artificial freshwater habitats.
The eco-tiles can be easily fixed onto existing and future seawalls and breakwaters. The eco-tiles can be fabricated using silicone moulds with a variety of features that include surface texture, tilted ridges, flat cool surfaces, crevices and holes (
In accordance with Table 1, all constituents of the concrete were first mixed in a pan mixer. Workable fresh concrete mixtures were then obtained and cast in the designed silicone moulds with specific features.
The finish of the cast Eco-concrete tiles is shown in
After air curing for one day r, all eco-concrete tiles were demoulded and continually cured according to the curing conditions in Table 2.
The final eco-concrete tiles are shown in
In accordance with the preparing procedures described above, the compressive strength and surface pH of the concrete mixtures are listed in Table 2.
Preliminary engineering analyses were conducted on Sai Kung's eco-tiles after 12 months of deployment. Such analyses were conducted at the Department of Civil and Environmental Engineering at The Hong Kong Polytechnic University.
Scanning electron microscope (SEM) analysis was conducted on the eco-tiles with a Tescan VEGA 3 apparatus. The morphologies of the concrete samples (
At the Sai Kung trial site, temperatures of the different types of eco-tiles were significantly lower than the temperature of the seawall control plot (F4,15=8.708, P<0.001,
At the Lung Kwu Tan trial site, temperatures of the eco-tiles and the control plot were not significantly different (F4,15=8.708, P<0.001,
At the Ma Liu Shui trial site, temperatures of the eco-tiles and the control plot were not significantly different (F4,15=1.933.708, P<0.001,
The lack of difference between eco-tiles and the control plots at Lung Kwu Tan and Ma Liu Shui might be due to the season and the time at which the surveys were conducted (i.e., May). Due to the orientation of the seawall and surveying time, the eco-tiles and the control plots were mostly shaded when the temperature was measured. At Lung Kwu Tan, also large waves and splashes (mainly caused by marine traffic) could have lowered the surface temperature of the eco-tile and the control plot, affecting the thermo images recording. Marked differences should be therefore found when the eco-tiles were exposed directly to the sun in extended low tides.
At Sai Kung, a total of 31 species were recorded on the eco-tiles, control and reference plots (
In Lung Kwu Tan, 33 species were recorded on the eco-tiles, control plots and reference site (
In Ma Liu Shui, 30 species were recorded on the eco-tiles, control plots and reference site (
In Sai Kung the mean species richness on eco-tiles was significantly higher than that on seawall control plots (F4,15=16.993, P<0.001,
In Lung Kwu Tan the mean species richness on eco-tiles was significantly higher than that on seawall control plots (F4,15=21.355, P<0.001,
In Ma Liu Shui the mean species richness on eco-tiles and control plots was not significantly different (F4,15=1.985, P=0.149,
In Sai Kung, most of the eco-tiles had significantly higher mean number of mobile species than the seawall control plot (F4,15=5.385, P=0.007,
In Lung Kwu Tan, eco-tiles had higher mean number of mobile species than the control plots (F4,15=3.724, P=0.027), but this difference was only significant for eco-tile M1 (
In Ma Liu Shui, there was a trend of higher mean number of mobile species on the eco-tiles in comparison to the seawall control plot, however, this difference was not statistically significant (F4,15=0.610, P=0.662). The most common mobile species across the eco-tiles and control plots were the herbivore limpet Patelloida ryukyuensis, followed by the scavenger crab Nanosersarma minutum and isopod Ligia exotica (
In general, all eco-tiles tended to have higher abundance of mobile species than the control and reference plots in all three sites (
Overall percentage coverages of epibiota on the eco-tiles, control plots and reference plots were close to 100% at all three sites. Part of the coverage was represented by algae (including biofilm), which are common on seawalls (
In Sai Kung the coverage of sessile invertebrates was significantly higher on eco-tiles than on control plots (F4,15=14.991, P<0.001,
In Lung Kwu Tan, the percentage coverage of sessile invertebrates on the eco-tiles and control plots was not significantly different (F4,15=1.178, P=0.360). Overall, the coverage ranged between 51% and 64% with a slightly higher coverage on the control plot (
In Ma Liu Shui, the percentage coverage of sessile invertebrates on the eco -tiles was significantly higher than the coverage on the control plots (F4,15=5.420, P=0.007,
The percentage coverage showed that the eco-tiles promoted the recruitment and survival of sessile invertebrates like bivalve, barnacles and polychaetes in Sai Kung and Ma Liu Shui. Overall, differences among eco-tiles with different concrete mixtures and pH were not consistent, indicating that the design and microhabitats of the eco-tiles may be more relevant in enhancing sessile communities than the composition of the concrete mixture. The increase of sessile species like bivalves and barnacles may further contribute to an increase of biodiversity (Bradford et. al., 2020).
In general, the eco-tiles tended to have higher mean species richness, abundance of mobile species and coverage of sessile invertebrates when compared with that of the control plots (
Based on the results, there were no apparent differences between M1 and M1+C with low pH, or between OPC and OPC+C with low pH. As observed in the engineering analysis, the pH of all eco-tiles decreased to below 9.0 after one year of deployment. This suggests that there was natural neutralisation of surface pH of the eco-features, and pH might not be an important controlling factor for the development of intertidal communities on concrete surfaces in sub-tropical Hong Kong. Similarly, the use of recycled MISSA and dredged marine sediment in eco-tiles showed to be suitable for the recruitment and growth of marine organisms. Thus, the use of recycled waste material in concrete mixture with normal pH can become a feasible alternative to produce eco-shoreline features with a lower carbon footprint.
