Available online at www.sciencedirect.com Procedia Engineering 00 (2011) 000–000 Procedia Engineering 28 (2012) 182 – 189 Procedia Engineering www.elsevier.com/locate/procedia 2012 International Conference on Modern Hydraulic Engineering Study on a Kind of Eco-concrete Retaining Wall’s Block with Water Purification Function SONG Wen-jiea,b, FU Hong-yuana, WANG Gui-yaoa, a* a. College of civil engineering and Architecture, Changsha University of science and technology, Changsha, 410114 , China. b. HuNan Institute of Water Resources and Hydropower Research , Changsha, 410007, China. Abstract Considering the environmental protection requirements for retaining wall and slope protection in Civil engineering and construction of water conservancy, a new type of retaining wall materials and structures with functions of slop reinforcement, slope greening and water purification was studied. In this paper, it designed a kind of Eco-concrete retaining wall’s block which has functions of slope vegetation planting and water purification, and studied functions of water purification of this kind of Eco-concrete retaining wall’s block through the water quality purification experiment. It shows that, the maximal disposable removal rates of CoDcr, TN and TP are respectively 87%, 70% and 90%, which means that functions of water purification of this kind of Eco-concrete retaining wall’s block are very good. © 2012 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of Society for Resources, © 2011 Published by Elsevier Ltd. Environment and Engineering Open access under CC BY-NC-ND license. Keywords: Eco-concrete, Retaining wall, Water purification; 1. Introduction In order to meet the demand of slope reforcement, the concrete block or mortar rubble was usually used in slope protection, but most of such kind of slope protection and retaining wall can’t be greened, causing disharmony to the environment. Considering the environmental protection requirements of retaining wall and slope protection in civil engineering and construction of water conservancy, a new kind of retaining wall material which can not only reinforce construct, but also green slope and purify water * Corresponding author. Tel.: 0731-85532664. E-mail address: [email protected] 1877-7058 © 2012 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of Society for Resources, Environment and Engineering Open access under CC BY-NC-ND license. doi:10.1016/j.proeng.2012.01.703 2 SONG Wen-jie et al. /Procedia ProcediaEngineering Engineering00 28(2011) (2012)000–000 182 – 189 SONG Wen-Jie/ should be studied. With this kind of material to build retaining wall, it can make the slope more harmony to the environment, and can improve the slope’s ecological function greatly. Based on above purposes, a new kind of retaining wall’s Eco-concrete block which has functions of water purifications was proposed (In 2010 December by the national utility model patents, PATENT NO 201020159480.3), and the water purification properties of this new kind of block was studied through the water filtration purification experiment, then a new kind of retaining wall which constructed with this Eco-concrete block was proposed. 2. Basic principle of Vegetation planting and water purification for the Eco-concrete block The front side of the block is made of Eco-concrete, and the back side of the block is made of porous permeable concrete. The cavity of the block is filled with the soil which has been added in mineral material and chronic fertilizer. All of these provide the necessary condition of plant growing. The filling of the block’s cavity is mainly composed by the natural soil, chronic fertilizer and mineral material. The filling material has certain thickness, enough nutriment and moisture, which can be used to make the bed base for the plants in Eco-concrete. Otherwise, because of the huge porosity and permeability coefficient, the nutriment in the surface soil of the slope and the ground water can get into the filling material in the cavity through the pores. And such activity make sure that there are enough moisture content and fertilizer in the filling material (bed base), which can constantly provide water and nutriment for plant growing. Fig.1 shows the construct of the block. P o ro u s c o n c re te O rd in a ry c o n c re te E c o -c o n c re te P la n ts R o o t sy stem so il an d in e ra l m a a te rial G ro u n d w ater an d n u trie n ts S o il slo p e O rd in a ry c o n c re te Fig.1 Eco-concrete block’s Vegetation principle. Eco-concrete’s functions of water purification including three aspects: the purifying effect of mineral material, the purifying effect of Eco-concrete and the purifying effect of plants. (1) The purifying effect of mineral material The mineral material can purify the water pollutant. And its basic purifying effect includes the absorption of the mineral cover, the filtration of the pore, the effect of ion exchange and the chemical activity. Such activities can all be effective during the waste water treatment. (2) The purifying effect of Eco-concrete The Eco-concrete has a continuous porous construct, so the water and air can easily transit or exit in the continuous channels. And the porous construct of the Eco-concrete provides a suitable environment for the microbe growing, so there are many bacterias living in the surface and the inside of the concrete, which include some aerobic bacterias such as nitrobacterium, methanebacteria and denitrifier or some anaerobic bacteria. Because many biological populations exist in the biomembrane of the Eco-concrete’s surface and inside, this concrete can give full play to the biofilm degrading water pollution matter effect, then causes water purification [1]. (3) The purifying effect of plant A variety of plants to phosphorus, nitrogen and heavy metal and cyanide, phenol, pesticides and other 183 184 SONGWen-Jie/ Wen-jie Procedia et al. / Procedia Engineering 28 (2012) 182 – 189 SONG Engineering 00 (2011) 000–000 organic compounds have absorption, accumulation and transformation abilities.For example, water hyacinth, scirpus tabernaemontani, alternanthera philoxeroides, typha latifolia, duckweed, Arc thunbergii, spirodela and pistia stratiotes can all effectively absorb, accumulate and transform the nutritive salts and many kinds of the organic pollutant in waste water. 3. The design of the concrete block’s size and construct In this paper, according to the domestic design standard, we set the size of 390mm×240mm×190mm as the main size of the Eco-concrete block, and the size of 190mm×240mm×190mm as the half block size ( Fig.2) [2~4]. The void ratio, mechanical behavior and the way of production and construction are determined by the block’s void type. So it is very important to design the block’s void type. The factors as the shape of the pore, the No. of rows of the pores, the arrangement and size of the pores should be mainly considered and these factors have different influences to the block’s void ratio and mechanical behavior. (1) The inside space of the block will be backfilled and compacted by the mix material of soil and mineral material, and the material provide effective support for the concrete on the top of the block, so a single cavity structure as the block’s construct was chosen, and there are no ribs inside the block. (2) If the round pore is used, the variation in thickness of the block’s ribbed wall is huge and hard to be controlled. Considering the thickness of the wall should be as thin as possible, prevention the stress concentration in the nook, the cylinder shape for the inside space of the block was selected. (3) When working on the masonry, a circular groove can make sure a nice quality. At present, many test data prove that the mortar will form pin keys in the circular groove after condensation and hardening, which is helpful to enhance the block’s shear performance. - - E c o -c o n c re te b lo c k O rd in a ry c o n c re te O rd in a ry c o n c re te E c o -c o n c re te - P ro file - P ro file Fig.2 Eco-concrete block’s Profile 4. The experiment of water purification Considering every component of the block, this paper uses the method of experiment, and imitates the plant-growing Eco-concrete block’s program of water purification, and evaluates the effect of disposable waste purification of the plant-growing Eco-concrete block through analyzing the results of the experiments [5]. 3 SONG Wen-jie et al. /Procedia ProcediaEngineering Engineering00 28(2011) (2012)000–000 182 – 189 SONG Wen-Jie/ 4 4.1. experimental methods Fig.3 shows the plant-growing Eco-concrete block’s program of water purification by using an experimental equipment to imitate it. The experimental water is manmade standard waste (Table.1), and the relevant indexes of the water are tested and analyzed based on the Methods of testing and analyzing water and waste. The Markov bottle should always be replenished by the standard water waste during the experiment. Under the Markov bottle, it connects with three organic glass tubes with diameter of 9cm and length of 60cm .From the top to the bottom, the tubes are filled with 10cm Eco-concrete which has been conserved by 28d, 20cm filler of soil and mineral material (bentonite) and 10cm of the Eco-concrete which has been conserved by 28d. There is a water outlet at the bottom of every organic glass tube. And we test the water quality of the experimental water outlets every 5 days to analyze the effect of disposable waste purifying of the plant-growing Eco-concrete block through analyzing the results of the experiments. No.1 test-piece’s porosity of the Eco-concrete is 20%, No.2 test-piece’s porosity of the Eco-concrete is 25% and No.3 test-piece’s porosity of the Eco-concrete is 30%. Table.1 Standard of wastewater indicators (mg/L) TP TN CODcr 0.4 2 26.7 M a rk o v b o ttle C o n tro l v a lv e V ent P la n t g ro w th sp a c e E c o -c o n c re te 1 # T e st p ie c e so il a n d in e ra l m a te ria l 2 # T e st p ie c e 3 # T e st p ie c e P o ro u s c o n c re te O u tle t Fig.3 Schematic diagram of experimental apparatus 4.2. Test result and analysis (1) The removal of chemical oxygen consumption (CoDcr) The chemical oxygen consumption is an index to measure the organic pollutant. In block processing system removal mechanism mainly has two aspects： The first one is the block’s physics and chemical action, which means the Eco-concrete mechanical retention and mineral materials chemical adsorption. 185 186 SONGWen-Jie/ Wen-jie Procedia et al. / Procedia Engineering 28 (2012) 182 – 189 SONG Engineering 00 (2011) 000–000 5 The second one is the microbial action, which means the microbe in the block transform the organic pollutant into inorganic matter or low molecular organic compounds which are easily absorbed by plants. Fig.4 (a) and Fig.4(b) show the test-piece’s CoDcr disposable removal ability is increased with the increase of the porous fiber concrete porosity. But as the porosity increases, the removal capacity of the increase in amplitude becomes smaller. On one hand, the experimental water’s content of dissolved oxygen and nutriment determine the limiting quantity of the microbe growing. On the other hand, when the voidage reaches 25%, it provides enough space for microbe and plant growing, so the amount of the microbe has reached the limit, and if the voidage keeps increasing, there will be a redundant of space. On the first 10 days, the No.1 test-piece’s effect of disposable CoDcr removal is better than No.2 and No.3 test-piece. In the first 20 days, the test-piece’s effect of disposable CoDcr removal was increasing. The maximum of the disposable removal rate is 74% for No.1 test-piece, 85% for No.2 test-piece and 87% for No.3 test-piece. After 20 days, each test-piece’s effect of disposable CoDcr removal begins to decrease, finally tends to be stable. This is because in the early testing the amount of plants and microbe are limited, and the mechanical interception and the mineral material’s chemical absorption are the main method to purify water, so the No.1 test-piece’s effect of disposable CoDcr removal is better than No.2 and No.3 test-piece’s. From 10d to 20d, the large amount of microbe and plant’s growth consume a large content of the dissolved oxygen in the waste. And during this period, the microbe and plant are the main materials for water purification. The small porosity of No.1 test-piece is not conducive to the growth of the microbe and plant, so the No.1 test-piece’s effect of disposable CoDcr removal is worse than No.2 and No.3 testpiece’s, but the porosity of No.3 test-piece is bigger than No.2 test-piece’s, so the No.3 test-piece’s effect of disposable CoDcr removal is better than No.2 test-piece’s. 20 days later, the amount of microbe reaches a certain limit, and the decrease of the dissolved oxygen’s content causes the decrease of the microbe’s activity, so the three test-pieces effect of disposable CoDcr removal began to decrease, and then all tend to be stable at last. 24 90 22 2# 3# 1# 20 2# 3# 1# 70 removal rate ofofCoDcr/% concentration of CoDcr(mg/L) 18 80 16 14 12 10 8 6 60 50 40 30 20 4 10 2 0 5 10 15 20 25 30 35 40 45 0 5 10 15 20 time/d 25 30 35 40 45 time/d Fig. 4. (a) Concentration of CoDcr change with time; (b) Removal rate of CoDcr change with time (2) The removal of the total nitrogen (TN) The nitrogen in the waste exists in the form of organic nitrogen and ammoniacal nitrogen. The way of removing the nitrogen includes the nitration of microbe, the absorption of the plant’s root system and the mineral material. The specific program is: first, the organic nitrogen deposit in the pore of porous concrete and filling. On one hand they can be absorbed by the plant’s root system and the mineral material of the soil. On the other hand, they can be oxidized into NH3 and then gradually hydrolyze into 187 SONG Wen-jie et al. /Procedia ProcediaEngineering Engineering00 28(2011) (2012)000–000 182 – 189 SONG Wen-Jie/ 6 ammoniumion. The ammoniumion is quite easily absorbed by the clay and other particle in the soil. Through the nitrification of the microbe in the soil, the ammoniumion can be transformed into NO3- and NO2, then the soil regain the ability of absorbing the ammoniumion. So the nitrification is vey effective. Fig.5(a) and Fig.5(b) show the test-piece’s TN disposable removal ability is increasing with the increase of the porosity of the Eco-concrete, but with the increase of the porosity, the increasing rate of the removal effect is decreasing. In the first 10 days, the No.1 test-piece’s TN diposable removal ability is better than No.2 and No.3 test-piece. In the first 20 days, the test-piece’s TN diposable removal ability is increasing. The maximum of the disposable removal rate is 40% for No.1 test-piece, 60% for No.2 testpiece and 70% for No.3 test-piece. 20 days later, each test-piece’s TN diposable removal ability begans to decrease, finally tends to be stable. This is because during the early days of the experiment, the amount of plants and microbe are limited, and the mechanical interception and the mineral material’s chemical absorption are the main factors for water purification, so the No.1 test-piece’s TN diposable removal ability is better than No.2 and No.3 test-piece’s. From 10d to 20d, the large amount of microbe and plant’s growth makes the nitration of microbe and the absorption of the plant’s root system become the main methods to remove the TN. The small porosity of No.1 test-piece is not conducive to the growth of the microbe and plant, so the No.1 test-piece’s TN diposable removal ability is worse than No.2 and No.3 test-piece’s, but the porosity of No.3 test-piece is bigger than No.2 test-piece’s, so the No.3 test-piece’s TN diposable removal ability is better than No.2 test-piece’s. 20 days later, the amount of microbe reaches a certain limit, and the decrease of the dissolved oxygen’s content causes the decrease of the microbe’s activity, so the three test-pieces TN diposable removal ability began to decrease, and then all tend to be stable at last. 70 1.8 2# 3# 1# 2# 3# 1# 60 1.4 removal rate ofof TN/% concentration of TN(mg/L) 1.6 1.2 1.0 0.8 50 40 30 20 10 0.6 0 5 10 15 20 25 30 35 40 45 0 5 10 time/d 15 20 25 30 35 40 45 time/d Fig. 5. (a) Concentration of TN change with time; (b) Removal rate of TN change with time (3) The removal of the total phosphorus (TP) Fig.6 (a) and Fig.6 (b) show the test-piece’s TP diposable removal ability is increasing with the increase of the porosity of the Eco-concrete, but with the increase of the porosity, the increasing rate of the removal effect is decreasing. In the first 10 days, the No.1 test-piece’s TP diposable removal ability is better than No.2 and No.3 test-piece. In the first 20 days, the test-piece’s TP diposable removal ability is increasing. The maximum of the disposable removal rate is 72.5% for No.1 test-piece, 87.5% for No.2 test-piece and 90% for No.3 test-piece. 20 days later, each test-piece’s TP diposable removal ability begans to decrease, finally tends to be stable. This is because in the early testing, the amount of plants and microbe are limited, and the mechanical interception and the mineral material’s chemical absorption are 188 SONGWen-Jie/ Wen-jie Procedia et al. / Procedia Engineering 28 (2012) 182 – 189 SONG Engineering 00 (2011) 000–000 7 the main factors for water purification, so the No.1 test-piece’s TP diposable removal ability is better than No.2 and No.3 test-piece’s. From 10d to 20d, the large amount of microbe and plant’s growth consume a large content of the dissolved oxygen in the waste. And during this period, the microbe and plant are the main material for water purification. The small porosity of No.1 test-piece is not conducive to the growth of the microbe and plant, so the No.1 test-piece’s TP diposable removal ability is worse than No.2 and No.3 test-piece’s, but the porosity of No.3 test-piece is bigger than No.2 test-piece’s, so the No.3 testpiece’s TP diposable removal ability is better than No.2 test-piece’s. 20 days later, the amount of microbe reaches a certain limit, and the decrease of the dissolved oxygen’s content causes the decrease of the microbe’s activity, so the three test-pieces TP diposable removal ability began to decrease, and then all tend to be stable at last. 100 0.35 2# 3# 1# 0.30 90 80 70 removal rate ofof TP/% concentration of TP(mg/L) 0.25 0.20 0.15 0.10 2# 3# 1# 60 50 40 30 0.05 20 0.00 0 5 10 15 20 25 30 35 40 45 0 5 10 time/d 15 20 25 30 35 40 45 time/d Fig. 6. (a) Concentration of TP change with time; (b) Removal rate of TP change with time Based on analysis above, it can be seen that with the passage of the time, the Eco-concrete block’s diposable removal ability in wastewater disposal firstly increases, then decreases, and finally tends to be stable. In the early period of the test, the effect of the Eco-concrete block’s purification mainly depends on the pore mechanical interception and adsorption of mineral materials. And finally, the effect of the Eco-concrete block’s purification mainly depends on the microbe action and the absorption of the plant’s root system. TP diposable removal ability of the Eco-concrete block is increasing with the increase of the porosity of the Eco-concrete, but with the increase of the porosity, the increasing rate of the removal effect is decreasing. The maximal disposable removal rates of CoDcr, TN and TP are respectively 87%, 70% and 90%, which means that fuctions of water purification of this kind of Eco-concrete retaining wall’s block are very good. 5. Conclusion Through the analysis above, we can draw the following conclusions: (1) This new kind of Eco-concrete retaining wall block is suitable for water purification and grass planting, which also has enough block strength. (2) The main size of the Eco-concrete block is 390mm×240mm×190mm, and the half block size is 190mm×240mm×190mm. (3) The mortar will form the pin keys in the circular grooves around the surfaces after condensation and hardening, which is helpful to enhance the masonry structure’s shear performance. 8 SONG Wen-jie et al. /Procedia ProcediaEngineering Engineering00 28(2011) (2012)000–000 182 – 189 SONG Wen-Jie/ (4) With the passing of time, the Eco-concrete block’s diposable removal ability in wastewater disposal firstly increases, then decreases, and finally tends to be stable. The maximal disposable removal rates of CoDcr, TN and TP are respectively 87%, 70% and 90%, which means that functions of water purification of this kind of Eco-concrete retaining wall’s block are very good. Acknowledgements It is funded by Key Science and technology projects of Changsha City(contract number: K0904029-11) and science and technology projects of The Western Traffic Construction(contract number: 20113188241320) . References [1] Chen Zhishan, Liu xuanju. 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