Patent Application
20220194850
This disclosure is generally directed to three-dimensional (3D) printing of building structures. More particularly, this disclosure is directed to printable unprocessed clay-based mortar for use with a 3D printing system.
Cement and other forms of concrete have played an integral role in the construction of any large-scale building structure. In a typical use case, cement can be mixed off-site and away from the construction project, and then transported by a truck to the construction site. Alternatively, cement may be mixed on-site and pumped up to a desired floor for delivery. In either instance, forming the walls of the structure involves pouring the cement at the desired location and then utilizing skilled laborers to frame and drywall the walls.
3D printing of the walls can utilize fewer skilled laborers, and can form the walls in a more cost effective and rapid fashion. In such 3D printing, specialized equipment is used to deposit a cement layer, alternatively known as an elongated “bead”, at a specific location using a degree of precision, one bead on top of the other. The inner or outer wall is therefore additively printed by applying beads on top of one another beginning with the foundation upward. Bead printing stops at the window or door locations, to leave openings for subsequently placed windows and doors. The process of additively printing elongated beads layer-by-layer on top of each other is often times referred to as the 3D additive printing process, which has been proven to reduce the overall labor, expense and cost in producing a building structure.
One problem with 3D printing of cement, or any pumping of cement for that matter, is the fluid mechanics associated with cement. Cement is typically a rather viscous fluid and difficult to pump across long distances of piping and/or through various piping structures, such as bends and nozzles of the printing assembly. Any temperature changes, or other environmental factors can further affect the viscosity of cement, making pumping and printing thereof more difficult.
Mortar and cement are used in construction of structures. Cement is a fine powder of primarily hydraulic calcium silicates that hardens with added water to form durable structures. When additively applied, cement with water forms the durable structure. Cement may also include limestone, clay, shells, and silica sand. Mortar, on the other hand, is entirely different from cement in both form and function. Mortar typically cannot form a durable structure unless it is applied to hold together solid objects, such as bricks, stones and concrete blocks. Also, mortar consist of different materials than cement, and typically includes lime and sand with cement. Portland cement is commonly used throughout the industry as a basic ingredient of concrete, mortar and grout. Portland cement can be produced by heating limestone and certain minerals in a kiln to form clinker and grinding the clinker while adding gypsum.
Like the beads of cement used to form a wall, beads of mortar can be printed across bricks, stones, and concrete blocks already present to form the wall. After the bricks are applied to the underlying bead of mortar, another layer of mortar is printed as a bead across the row of cast bricks, stones, and concrete blocks to hold those components together in the wall. Because mortar has a different form and function than cement when printed across a row of, e.g., bricks, the composition of mortar as a cementitious bead or “ink” of material must be different from cement.
A need exists for a printable cementitious ink of mortar that can be readily applied from the printing assembly onto building components with proper viscosity, strength, and slump loss utilizing readily available fine sand or clay.
To meet the needs noted above and others, the present disclosure provides a 3D printable clay-based mortar of cementitious ink (“printable mortar”) that achieves the target structural performance while reducing greenhouse emissions. The printable mortar beneficially utilizes readily available fine sands, or clay. The amount of clay being used can be much larger than that used by conventional mortar, printable or otherwise. The printable clay-based mortar includes an additive material comprising unprocessed clay and sand. As noted herein, the term “unprocessed” when referring to clay or sand is that the clay or sand does not undergo any heating above room or ordinary outside temperature, any chemical modification, or any mechanical sifting or removal of unwanted elements such as removal of excessive clay particles.
The mortar can also include a binder material comprising, according to one example, between 84 to 90 percent cement and 10 to 16 percent supplementary cementitious material (SCM). The 3D printable unprocessed clay-based mortar can further comprise an admixture selected from the group consisting of an air-entraining admixture, a water reducing admixture or plasticizer and a shrinkage reducing admixture. The water reducing admixture can comprise cations and organic molecules, and polycationic compounds configured for clay absorption and dispersion. The water-reducing admixture can reduce the required water content for the clay contained in the mortar aggregate by about 5 to 9 percent. Air-entraining admixtures can include wood-derived acid salts, or synthetic resins, or salts of sulphonated lignin, or salts of petroleum acids or proteinaceous materials or fatty or resinous acids to help increase the freeze-thaw durability of mortar and improves workability. Shrinkage reducing admixtures can be based on glycol or mono alcohol or polymeric surfactants to reduce the amount of shrinkage as the mortar dries. The supplementary cementitious material, or SCM, can comprise natural or artificial pozzolan material. A popular natural pozzolan material can include siliceous and aluminous material. A popular artificial pozzolan material can be kaolin clays of metakaolin, fly ash and silica flume. When finely divided, and in the presence of moisture, pozzolan chemically react at ordinary room or outside temperature with calcium hydroxide in the mortar to form compounds having cementitious properties, and thus are known as supplementary cementitious material.
Three-dimensional (3D) printing systems require a cement “fluid” that has appropriate workability and rheological properties as it is pumped through the pipe and out of the print head opening. The ensuing bead of mortar is typically only a few inches in thickness and of sufficient width to cover the print line of bricks and blocks that must be mortared together. The cementitious ink must therefore not only have the proper viscosity, but also must have the appropriate dry ingredients that, when added to the aggregate (typically sand) takes on the appropriate slump loss within the appropriate timeframe.
It is important that the binder material added to the sand aggregate not only are chosen with the correct types of materials and the correct ratios and volumes, but also that appropriate supplementary cementitious materials are utilized in the binder. Admixtures can be applied to the binder either before or after mixing of the aggregate with the binder. If the appropriate materials and percentages thereof are chosen to achieve the appropriate slump loss for 3D printing, then it is further desirable that readily available unprocessed fine sand or clay be added to that mix.
Typically, sand in the aggregate includes smaller particles or fine particles of sand along with coarse particles. The fine particles of sand are oftentimes referred to as “clay.” Clay contained in the sand aggregates is used for making mortar. However, clay often causes poor workability. This is most certainly the case when clays are used from the sand aggregate when attempting to 3D print mortar. Clays are generally considered too expansive when wetted with water, and they typically absorb or entrap too much water, making any clay-bearing mortar unworkable in 3D printing. This is primarily due to too great of slump retention, and the ensuing mortar being too wet for application as mortar beads across the printed wall. In addition, expansive clays are known to impede the performance of certain admixtures, and specifically the water-reducing admixtures known as plasticizers. While plasticizers are intended to absorb onto cement particles and to disperse within the aqueous slurry or paste, expansive clays in the aggregate will deleteriously interfere with this function.
Accordingly, when clays are used in printed mortar, they typically are removed or washed off from the more coarse sand aggregate. One way in which to remove or wash off the clays is to mechanically remove, or sift, the finer particulate matter of the clays from the sand, and discard the removed clays from the sand before the aggregate is added to the cementitious paste. Removing the fine clays that are prevalent in most all sand aggregate is both time consuming and expensive, and hereby is advantageously eliminated resulting in the ability to utilize significant amounts (or percentages) of unprocessed clay in a 3D additive printing of mortar onto a building structure.
In light of the disclosure herein, and without limitation of the scope of the invention in any way, in a first aspect of the present disclosure which may be combined with other aspects listed herein unless specified otherwise, a 3D printable clay-based mortar includes an aggregate material comprising unprocessed clay and sand. The aggregate material can be combined with a binder material comprising certain specific percentages of cement (e.g., limestone, ground calcium carbonate, and/or Type I/II Portland) and supplementary cementitious material.
In another aspect of the present disclosure, which may be combined with any other aspect listed herein unless specified otherwise, is supplementary cementitious material that comprises natural or artificial pozzolan material. Admixture also can be added, and is preferably selected from the group consisting of an air-entraining admixture, a water reducing admixture or plasticizer, and a shrinkage reducing admixture. The water reducing admixture can comprise cations and organic molecules polycationic compounds for clay absorption and dispersion.
According to another aspect of the present disclosure, which may be combined with any other aspect listed herein unless specified otherwise, the unprocessed clay is not subject to heating beyond ordinary room or outside ambient temperature, mechanical processing or separation, or chemical reaction. The unprocessed clay is a first material less than 75 microns in dimension, and the sand is a second material greater than 75 microns in dimension. The ratio of first (fine sand/clay) material to second (coarse sand) material is between 15 to 20 percent.
In another aspect of the present disclosure, which may be combined with any other aspect listed herein unless specified otherwise, the cement can comprise Type I or II Portland cement and ground calcium carbonate. The binder material added to the unprocessed clay comprises powder material. The water to binder ratio is preferably 0.54 to 0.56. The water to powder ratio is between 0.415 to 0.417.
In yet another aspect of the present disclosure, which may be combined with any other aspect listed herein unless specified otherwise, the printable mortar includes a mixture of an aggregate comprising unprocessed clay with a binder. The binder comprises cement and supplementary cementitious material. Admixture and water is added to the aggregate and binder material to produce a slump loss of less than 3.0 cm within the first hour, and more preferably less than 2.0 cm within the first hour. The ratio of cement in the binder to unprocessed clay in the aggregate is approximately 1.02.
Additional features and advantages of the disclosed 3D printable clay-based mortar material and the devices, systems and methods for forming such material are described in, and will be apparent from, the following detailed description and the figures. The features and advantages described herein are not all inclusive and, in particular, many additional features and advantages will be apparent to one of ordinary skill in the art in view of the figures and description. Also, any particular embodiment does not have to have all of the advantages listed herein. Moreover, it should be noted that the language used in the specification has been selected for readability and instructional purposes, and not to limit the scope of the invented subject matter.
For a detailed description of various examples, reference will now be made to the accompanying drawings.
Certain embodiments described herein relate generally to the field of 3D printing systems for printing clay-based mortar cementitious ink (“printable mortar”). The printable mortar described herein has particular fluid parameters such as a certain viscosity and setting time that allow for 3D printing. Additionally, printable mortar differs from traditional cementitious ink in that the printable mortar includes unprocessed clay within the aggregate material. Thus, the aggregate material, coarse sand and fine sand/clay does not undergo any separation, removal or transformation. The aggregate material containing fine clay also does not undergo heating or calcination of the aggregate or clay at temperatures normally associated with calcination (i.e., temperatures exceeding 600° C.). The unprocessed clay is defined as the part of the sand aggregate that has sufficiently small dimension so that approximately 17 percent, within the range of 15-20 percent, of the sand aggregate will pass through 75 micron sieve. By allowing more than the normal limit of 7 percent deemed “high clay sands”, the passage of this relatively high clay content will surpass the desired aggregate specification per ASTM C33 for use in concrete or mortar. Nonetheless, instead of removing that which exceeds 7 percent, the present clay-based mortar allows use of the high clay sands in the aggregate. The present clay-based printable mortar need not be processed in any way by mechanical removal, heating or chemical alteration of the clay within the sand aggregate. The fine sands, or clay (less than 74 micron) is not washed from or discarded from the aggregate, but instead is used in its unprocessed and relatively large quantity within the mixed aggregate that forms the mortar. The unprocessed clay is unprocessed in that there is no heating of the clay to form calcined clay, nor is the unprocessed clay subject to any chemical additives or reactions to change its composition or state.
Conventional 3D printing systems may implement a pumping system, whereby the fluid is required to pass through an extended line of pipe of substantial length, and through various gate types, bends, nozzles, valves and the like. The cement mixture or printable mortar must be sufficiently fluid and have a particular viscosity to allow for adequate movement through the system. Additives, or admixtures, are used to adjust or modify the viscosity of the mortar mixture, such mixture including unprocessed fine sand or clay. Mixture that includes the clay-based sand must also have the proper slump loss so that when it is extruded from the print head nozzle as an elongated bead layer by layer to form the wall, the bead maintains its appropriate thickness and does not unduly slump. Any slump loss exceeding a certain limit or if slump loss is unduly retained, the mixture that is extruded will no longer be appropriately extruded or thereby will be improperly printed on the bricks in a 3D fashion. The printed mortar can therefor include different dry ingredients with the cement binder, and those ingredients can include Portland cement, fly ash, limestone fines, silica flume, and other fluid or liquid-based admixtures.
Referring now to
Construction system 10 effectuates the construction of the structure 5 by passing the printing assembly 150 above the foundation 4 and a wall formed layer-by-layer upward from the foundation 4. The printing assembly 150 emits extruded building material through a conduit 155 coupled to a nozzle having an outlet. Accordingly, as printing assembly 150 moves in three possible orthogonal axis, as well as angles therebetween, and the outlet emits extruded building material onto the upper surface of the structure 5 as it is being formed. The wall structure is formed layer-by-layer by laying down an elongated bead 5a of cementitious or mortar material of cement or concrete beginning with the first layer on ground or a pre-existing foundation 4. As each layer of the elongated beads 5a are laid down onto the foundation 4 or onto a previous layer or bead 5a, a plurality of stacked elongated beads 5a of an extruded building material additively, and in three-dimensions, form a building structure 5. The printing assembly 150 may shut off delivery of extruded material in order to switch cementitious or mortar ink and/or nozzles printing different cementitious or mortar inks. In addition the printing assembly 150 moves along a truss structure 110 between vertical assemblies 60, 62, 64 and 66 that move along rail assemblies 20 affixed 20a onto the outer sidewall perimeter of the preexisting foundation 4. The vertical assemblies, and thus the truss 70, 110 width, can adapt to varying widths of foundation 4 via adjustable rail assemblies affixed to the side surfaces of a varying width foundation 4, to adjust the width of the gantry 50 as illustrated by W50.
The presently disclosed 3D printable clay-based mortar includes a blend of commercially available cement within the binder (i.e., Type I or II Portland cement) with sand. The sand, which is the aggregate, is bound together when mixed with the binder. When also mixed with water, the above-noted dry components of binder and aggregate, when mixed at a specific ratio, form the printable mortar suitable for pumping, extrusion, and stacking the multiple layers using 3D printing.
The printable mortar differs from traditional cementitious ink in that the mortar includes approximately 13 percent less, or between 10 and 16 percent less cement. In one embodiment, the printable mortar includes supplementary cementitious material, SCM, of natural and artificial pozzolans. The pozzolans of the SCM can include siliceous and aluminous material. The pozzolans can react with the calcium hydroxide or crushed limestone or lime that can be added to the Portland cement to form calcium silicate hydrate, similar to the production by hydration of Portland cement. This adds to the strength, impermeability and sulphate resistance, while reducing expansion from the alkali-silica reaction that might otherwise take place. Use of pozzolans can also modify the water demand within the mixture to achieve the appropriate slump retention or loss rate.
SCM, such as pozzolans, thereby provide a number of advantages to the printable mortar. Improvement in shape retention and stacking of layers can occur at relative shorter times. The printable mortar has a relatively high “green strength,” referring to the ability to extrude while coming out of the nozzle and the ability to stack layers while the printable mortar is relatively plastic. A high green strength corresponds to better inner layer adhesion. The printable mortar can accommodate shorter lift times with high initial fluidity, allowing for the structure to be built more quickly.
SCM in the binder at the appropriate percentage relative to Portland cement, in addition to fine sized clay in the aggregate, when mixed with water reacts with water and therefor contributes to the strength and impermeability of the final structure. The dry components, such as cement and SCM constitute the binder material of the printable mortar. The binder material reacts with the aggregate, which comprises both coarse and fine sized sand to form printable mortar if relative percentages of cement to SCM in the binder and fine and coarse sand in the aggregate are followed.
Most natural or artificial sand contains fine silica particles. While natural sand often contains less than 5 percent of material finer than 75 micron sieves, manufactured sand usually has 10 percent to 20 percent material finer than 75 microns. Whether manufactured or in their natural state, sands therefore contain deleterious clay minerals. Those clays are present as hydrous aluminum phyllosilicates and contain tetrahedral or octahedral sheets. Clays can exhibit surface chain charges and have very fine particle size, some of which are less than 2 microns. Expansive and non-expansive clays can negatively impact concrete behavior by increasing the amount of water needed for achieving the desired concrete rheology. Expansive clays generally have a greater influence on concrete rheology than non-expansive clays because they can expand and consume free water from the concrete mixture. Thus, conventional processing techniques are used to remove the fine sands or clays that would normally expand and consume free water from the mixture. However, according to one embodiment herein, the fine sands or clay within the sand aggregate are maintained and kept in the mixture. Any deleterious effects of that fine sand or clay are offset using an appropriate SCM within the binder. Moreover, liquid or fluid admixtures can also be inserted into the mixture.
In a preferred embodiment, the percentage of Portland cement to SCM is approximately 87 percent Portland Cement and 13 percent SCM. This type of binder system can also produce a dense microstructure that has a lower environmental impact in that no calcined clay is needed, and thus no heating or processing of the clay is needed. The dense microstructure results from the addition from possibly calcium carbonate, if needed, in hydration of the unprocessed clay. In place of typical limestone, the printable mortar may also include a blend of limestone and marble dust. The combination of unprocessed clay and fine limestone (if applied and mixed therein) also improves the green strength, and improves stacking of layers during the plastic stage. Action of the binder system is controlled by the addition of further chemical admixtures, if needed. The chemical admixtures, such as plasticizers or water-reducers help delay the initial setting of the mix, increasing the open time where more layers can be added without cold joints despite the elevated ambient temperatures.
The printable mortar includes a ratio of Portland cement to fine sand, or clay, of approximately 1.02. The components also have a ratio of water to binder of approximately 0.55 and water to powder of approximately 0.416. Binder is defined as Portland cement and SCM, whereas powder is defined as binder plus fine sand or clay smaller than 75 microns, where preferably more than 17% of the sand will pass through a 75 micron opening within a sieve as find sand or clay. In a preferred embodiment, the 3D printable mortar includes liquid admixtures, such as high range water reducers, a slump retention admixture, a shrinkage reducing admixture, a hydration stabilizer, and an air-entraining agent.
As shown in
The control sample 34 uses the unprocessed fine clay within the aggregate, and modified the binder ratio between cement and SCM so that approximately 87 percent Portland cement is used relative to 13 percent SCM. The powder increased since fine sand is utilized in control sample 34. Unfortunately, there is too much slump retention due to the slump values staying around 13 cm for almost an hour, which makes the material too wet as printable mortar since the printable mortar would not retain its shape and thus hinder the stack ability of the beads.
The target slump is approximately one inch slump loss between 10 and 12 cm during a first hour for suitability of 3D printing. Thus, several iterations were performed by adjusting the high range water reducer and water-to-powder (W/P) ratio as shown the control sample 36 and control sample 38. The water-to-powder ratio is reduced to approximately 0.416 in the control sample 36 by using fine clay sand and including approximately 13 percent SCM into the binder. “X” is shown in
According to one example, a water reducing admixture is applied to the binder for retaining slump, while fine clays are maintained and unprocessed within the sand aggregate. The admixture clay-activity-modifying agents include cations that help increase use of clay-containing sands to offset the decline in high quality natural or artificial sands. A popular water reducing admixture includes chemical and mineral admixtures available in the industry from various vendors.
The aggregate of sand containing fine sand or fine clay can be processed. Specifically, the fine clay 44 can be processed 54 either mechanically, chemically or heated 53, 55 and 57. If heated 57, or calcined, the clay is converted to calcined clay. Alternatively, the clay can be removed by a mechanical sieve 53. Further alternative would include adding a chemical 55 to the clay to change its properties. Alternatively, and preferably, the fine clay is not processed, and therefore is unprocessed 61. The aggregate in its entirety is passed unprocessed 61 to a mixing unit where the binder, water and chemical or admixture is added. Unprocessed fine clay with the aggregate, and also containing the admixture 52 and water 51 added thereto in
As used in this specification, including the claims, the term “and/or” is a conjunction that is either inclusive or exclusive. Accordingly, the term “and/or” either signifies the presence of two or more things in a group, or signifies that one selection may be made from a group or alternatives.
Without further elaboration it is believed one skilled in the art can use the proceeding description to utilize the claimed inventions to their fullest extent. The examples and embodiments disclosed herein are to be construed as merely illustrative and not a limitation on the scope of the present disclosure in any way. It will be apparent to those skilled in the art that changes may be made to the details of the above-described embodiments without departing from the underlying principles discussed. In other words, various modifications and improvements of the embodiments specifically disclosed in the description above are within the scope of the appended claims. For example, any suitable combination of features of the various embodiments described is contemplative.
This application incorporates by reference and claims the benefit of priority to U.S. Provisional Application No. 63/126,761, filed on Dec. 17, 2020.
| Number | Date | Country | |
|---|---|---|---|
| 63126761 | Dec 2020 | US |
