METHOD OF BUILDING A CONCRETE ELEMENT FOR MARINE OR RIVER APPLICATIONS
A method of building marine concrete elements layer-by-layer, the method including extruding a flowable construction material through an outlet of a deposition head in order to form a layer of construction material, the construction material including a hydraulic cement and a superabsorbent polymer, wherein successive layers of construction material are placed on top of each other and allowed to cure and harden, in order to obtain the marine concrete element.
1 . A method of building marine concrete elements layer-by-layer, said method comprising:
extruding a flowable construction material through an outlet of a deposition head in order to form a layer of construction material, said construction material comprising a hydraulic cement and a superabsorbent polymer,
wherein successive layers of construction material are placed on top of each other and allowed to cure and harden, in order to obtain the marine concrete element.
2 . The method according to claim 1 , wherein the superabsorbent polymer is present in the construction material at a concentration of 0.25-5.0 wt.-%, expressed as a weight percentage of the hydraulic cement.
3 . The method according to claim 1 , wherein the superabsorbent polymer is added to the construction material before or during placing the construction material.
4 . The method according to claim 1 , further comprising immersing the marine concrete element into water and allowing the superabsorbent polymer to shrink and/or degrade, thereby creating pores in the marine concrete element.
5 . The method according to claim 1 , wherein the superabsorbent polymer is a cross-linked polymer.
6 . The method according to claim 5 , wherein the superabsorbent polymer is selected from the list of cross-linked polyacrylate/polyacrylamide copolymer, cross-linked polyglutamic acid, cross-linked polyacrylamide copolymer, cross-linked ethylene maleic anhydride copolymer, cross-linked carboxymethylcellulose, cross-linked polyvinyl alcohol copolymers, cross-linked polyethylene oxide, and cross-linked modified starch, or mixtures thereof.
7 . The method according to claim 1 , wherein the superabsorbent polymer comprises nitrogen, phosphorous, and/or potassium based compounds and their combinations.
8 . The method according to claim 1 , wherein the construction material further comprises a viscosity modifying agent.
9 . The method according to claim 1 , wherein the construction material has a pH of less than 12.
10 . The method according to claim 1 , wherein the hydraulic cement comprises at least 30 wt.-% of Portland cement, expressed as a weight percentage of the amount of hydraulic cement.
11 . The method according to claim 1 , wherein the hydraulic cement comprises less than 10 wt.-% of aluminate cement, sulphoaluminate cement, silica fume, metakaolin, or mixtures thereof, expressed as a weight percentage of the amount of hydraulic cement.
12 . The method according to claim 1 , wherein the superabsorbent polymer, before being added to the construction material, is dried at a temperature comprised between 60° C. and 95° C. so as to reach a humidity content of less than 20 wt.-%, expressed as a weight percentage of the superabsorbent polymer.
13 . The method according to claim 1 , wherein the superabsorbent polymer and optionally the viscosity modifying agent are present in an amount so as to increase the yield stress so that the first layer deposited does not collapse under the load of said at least one subsequent layer.
14 . The method according to claim 1 , wherein the superabsorbent polymer and optionally the viscosity modifying agent are added to the construction material in the deposition head, immediately before the construction material is placed.
15 . The method according to claim 14 , wherein the yield stress of the freshly placed construction material is 200-2,000 Pa measured 30-60 seconds after its placement.
16 . The method according to claim 1 , wherein construction material of the first layer is allowed to rest during a time period of not more than 2 minutes before construction material of a subsequent layer is placed onto the said construction material of the first layer.
17 . The method according to claim 1 , wherein the construction material is concrete or a cement mortar.
18 . The method according to claim 1 , wherein the hydraulic cement comprises at least 10 wt.-% of a supplementary cementing material, being one or several of any secondary constituent described in the cement standard EN 197-1 of April 2012, or concrete demolition waste.
19 . The method according to claim 1 , wherein a water reducer is added to the construction material before the conveying step of conveying the construction material to the deposition head, wherein the conveying of the construction material is performed by pumping.
20 . The method according to claim 1 , wherein the extrusion and placement of the construction material is carried out in situ, under water.
21 . A concrete element obtained from a method according to claim 1 , wherein the mineral void content is of at least 5 vol.-% expressed as a volume percentage of mineral phases in the concrete element.
22 . A method comprising providing a concrete element according to claim 21 for marine applications in contact with water to foster the development of marine life.