Recipient Organization
ARIZONA STATE UNIVERSITY
660 S MILL AVE STE 312
TEMPE,AZ 85281-3670
Performing Department
(N/A)
Non Technical Summary
3D Printed Concrete (3DPC) is a rapidly expanding construction technology owing to its pace, material savings, and need for less labor. Despite these advantages, 3DPC suffers from volumetric shrinkage, which should be mitigated to avoid cracking. The heat produced during the exothermic hydration of higher cement content and accelerated evaporation due to the lack of formwork in 3DPC structures are the reasons for volume shrinkage. The goal is to synthesize hydrogel crystals from corn and soybeans to mitigate volume shrinkage in 3DPC. When mixed with concrete, we hypothesize that the biobased hydrogel crystals will serve as internal water reservoirs, releasing water into the cementitious matrix to compensate for the water loss due to exothermic cement hydration and evaporation. Corn starch (CS) and soy protein isolate (SPI) are chosen, considering their hydrophilicity and compatibility with concrete. The research objectives are to 1) synthesize non-toxic biobased hydrogel crystals from agricultural feedstocks, 2) determine their suitability for concrete applications, 3) evaluate the printability of biobased hydrogel infused concrete (BHIC), 4) quantify the strength and improved shrinkage characteristics of BHIC, and 5) assess the financial viability of biobased hydrogel crystals for volume shrinkage mitigation in 3DPC. The primary deliverables will be the synthesis procedures and shrinkage mitigation capacities of five CS and three SPI hydrogel crystals. Commercializing these biobased hydrogel crystals resolves the volume shrinkage issue in 3DPC, fostering a new market for corn and soybeans, which aligns with the program's goals, potentially offering new jobs and a supplementary income source for US farmers.
Animal Health Component
10%
Research Effort Categories
Basic
80%
Applied
10%
Developmental
10%
Goals / Objectives
The goal of this study is to explore an innovative solution to these challenges, specifically by employing hydrogel crystals derived from corn and soybeans.Our hypothesis posits that the corn- and soybean-derived hydrogel crystals introduced into the concrete mixture while casting/printing can act as internal curing agents (i.e., by providing a water reservoir). This will enable the controlled release of specific quantities of water during hydration and strength development, compensating for the water loss caused by the heat of hydration and evaporation. By doing so, we anticipate this approach will effectively mitigate volumetric shrinkage in 3D Printed Concrete (3DPC). The research objectives are to 1) synthesize hydrogel crystals from corn starch and soy protein isolate, 2) determine their suitability for cementitious media, 3) evaluate the printability of biobased hydrogel-infused concrete mixes, 4) characterize the strength and durability of hydrogel-infused 3DPC, and 5) assess the financial viability of employing biobased hydrogel crystals for shrinkage mitigation in 3DPC.
Project Methods
Method 1.1: Solvent-sedimentation process: For this study, we will create 10 variations of corn starch withcrystalline amylopectin ranging from 50-85% and amorphous amylose from 15-50%. These variations will serve as the raw materials for CS hydrogel crystal production. To achieve the desired amylose and amylopectin proportions, we will use a solvent sedimentation process. The resultant amylopectin and amylose will be dried and ground into fine powders with particle sizes ranging from 2-30 microns using a ball mill.Method 1.2: Synthesis of chemically crosslinked CS hydrogels: We will employ an esterification process to achieve gelation. In this method, the hydroxyl groups in amylose and amylopectin are replaced with ester bonds derived from a carboxylic acid. Citric acid thathas 3 carboxylic acid functional groups.Method 1.3: Physical crosslinking: To prepare the CS hydrogel through physical crosslinking, a specific weight percentage (design parameter) of each of the 10 custom starches from Method 1.1 will be mixed in deionized water. The mixture's temperature will then be raised to 190°F at a rate of 15°F per minute. After 20 minutes of heating, the mixture will be cooled to 135°F.Method 1.4: Photo-crosslinking: To prepare SPI-based hydrogels, a certain weight percentage (ranging between 2-10% by weight of the solution) of SPI will be dispersed in water. To this solution, we will add a 5 millimolar concentration of Tris(2,2′ bipyridyl)dichlororuthenium as a photosensitizer. The solution will be exposed to a 50W LED white light for 2 minutes, followed by an additional 30-second exposure after stirring.Method 1.5: Preparation of crystals from hydrogel lyophilization: The retrograded (aged) hydrogels will be placed into molds and then frozen at -22°F for four hours. Afterward, they will be thawed at 64°F for an equal amount of time. This freeze-thaw process will be repeated for a total of 10 cycles. On the 11th cycle, the freezing time will be extended to 12 hours. Once thawed, the hydrogel structures will be dried at 113°F for eight hours to remove any remaining moisture. Finally, these dried hydrogels will be processed to produce fine hydrogel crystals with diameters ranging between 2-30 .Method 1-6: Water swelling capacity: To assess these factors, we will place 1 gram of dry hydrogel crystals in perforated nylon bags, with perforations smaller than 2 μm to ensure no crystals escape. These bags will be submerged in a beaker of deionized water for 30 minutes.Method 2.1: Porosity and particle size distribution: We will employ both scanning electron microscopy (SEM) and microcomputed tomography to evaluate the surface morphology and porosity.Method 2.2: Rheological properties of hydrogels: Swollen hydrogel samples will be prepared by adding 20 grams of water to a gram of each qualified biobased hydrogel crystals. The prepared hydrogel will be left to mature under room temperature and at a 40% relative humidity for 30 minutes before transferring them onto rotational rheometer that applies a small amplitude shear strain in a sinusoidal manner. The storage modulus, and loss modulus, will be measured with respect to the total strain.Method 2.3: Swollen hydrogel water kinetics in a cementitious matrix: The water absorption capacity of the synthesized hydrogel crystals will be evaluated in the cement pore solution. The cement pore solution will be obtained by mixing 100 grams of cement in 1000 grams of water. One gram of biobased hydrogel crystals will be poured in a perforated nylon bag with holes smaller than the smallest hydrogel particles. This bag will be immersed in the prepared pore solution, which is constantly stirred for 30 minutes. At 30 minutes, the bag with the swollen hydrogel particles will be weighed to measure the water absorption capacity.Method 3.1: Concrete 3D Printing: In this study, we will utilize a gantry-based 3D printer with a screw extrusion system for our concrete printing. The control concrete mix will consist of Type I/II OPC (35% by mass), limestone powder or fly ash (15% by mass), and commercial sand (50% by mass). For hydrogel-infused mixes, we will maintain a weight fraction of 0.2%-0.4% for the dry hydrogel crystals in relation to the binder.Method 3.2: Rheology of hydrogel-infused concrete: A rotational rheometer available in PD-our lab that offers a range of speeds between 0.3 to 1500 rpm will be used to evaluate the rheological properties. The point on the stress-versus-time curve where the material's response deviates from its elastic behavior will be recorded as the corresponding static yield stress.Method 3.3: Extrudability of the hydrogel-infused 3DPC: We will mount a stereographic hawk camera parallel to the nozzle, which obtains 120 frames per second to monitor the depth defects in each printed layer and deviation from the in-plane deposition as the concrete is deposited. To this end, the 3D printed layers in the images will be segmented automatically using MaskR-CNN, followed by evaluation of the area of each layer over which the depth defects are more than 5% the depth or width of the layer, whichever is smaller.Method 3.4: Buildability of hydrogel-infused 3DPC: Compression tests will be performed on cylinders extracted from freshly printed prisms at various times (0.5 h, 1 h, 1.5 h and 2 h) after mixing to obtain the stress-strain behaviors. Elastic and plastic yield stresses and moduli will be evaluated from these stress-strain curves. This information along with the geometry of each layer, will be used to determine the critical height to failure for all the hydrogel-infused concrete mixes.Method 4.1: Evaluation of compressive strength and concrete porosity: After printing, the specimens will undergo moist curing for 28 days. For compressive strength tests, we will extract cylinders from the cubes, measuring 100 mm in diameter and 200 mm in depth, from all three directions. For porosity tests, we will extract 50 mm thick circular disks with a diameter of 100 mm. To quantify the porosity of the hydrogel-infused 3DPCs, we will employ vacuum saturation method described in a recent work.Method 4.2: Autogenous shrinkage test: Our procedure involves printing six layers, each 45 cm long and 20 mm thick. Temperature FBG sensors will be embedded on the layer after the 2nd and 4th layers, and the temperature sensor will be embedded after the 3rd layer to monitor strain and temperature changes in real-time. We will apply this process to both the control mix and the mixes containing qualified hydrogel crystals. After printing, a rigid cracking inducer will be inserted on the top of the printed specimen that restricts shrinkage, leading to discernable cracks. We will then gather data on shrinkage strains and temperature changes.Method 4.3: Drying shrinkage test: In our study, we will print prismatic specimens of 60×60×300 mm dimensions using both the control mortar and the approved hydrogel-infused mortars. We will employ three distinct printing patterns - longitudinal, transverse, and diagonal - to thoroughly gauge drying shrinkage across different printing techniques. After printing, they will be moist-cured for seven days. During this 7-day period, the majority of the chemical and autogenous shrinkage will take place. To monitor this, two metal anchors will be embedded into the prisms, 250 mm apart, during printing. A linear potentiometer will be attached to these anchors to continuously track length changes after the 7-day curing period.Method 5: Techno-economic Analysis: The finalist CS and SPI hydrogel crystals will have 1) a milder lifecycle impact, 2) with a payback period of less than 2 years, considering everything, including the initial capital investment and workforce training costs, 3) a positive Net Present Value; & 4) an Internal Rate of Return of less than 1 year.