Progress 10/01/19 to 09/30/20
Outputs
Target Audience:Academics in architecture, material science and civil engineering. Ultimately, professionals in the building industries. Changes/Problems:COVID shut down the lab in March 2020. What opportunities for training and professional development has the project provided?Lab training for undergraduate and graduate students. How have the results been disseminated to communities of interest?
Nothing Reported
What do you plan to do during the next reporting period to accomplish the goals?Goal 1) The technology at its current level of development is immediately applicable for low strength construction applications which is a very positive finding given the potential for high-volume utilization where strength and mechanical properties need only to be compatible with those of a compacted soil. However, if sequestration of biochar in cement-based materials is to be extended for structural applications, the strength reduction caused by the increase water demand must be prevented. Work to date suggests that the use of chemical admixtures may help in this regard but is probably not the answer by itself. Furthermore, broad application of biochar inclusion will almost certainly require tolerance to significant variability of biochar source and processing.It will therefore be necessary to find ways to reduce this variability by perhaps a combination of physical screening, presoaking, or some other chemical pretreatment. Tests scheduled the summer of 2021 will explore these options. Goals 2,3) Hopefully, now that the lab is open and staff can return to work, progress can be made on these goals. Goals 4) Work will also continue on using other types of biochar sources (rice hull ash, corn stover) as well as forms of concrete, such as geopolymer and Ultra high performance types. Again, this depends on the pandemic circumstances.
Impacts
What was accomplished under these goals?
1) Some initial testing of the use of high range water reducing admixtures (HRWRA) or "supreplasticizers". Preliminary results showthat small decreases in water content do prove the concept that the water reducing admixture is of some benefit, but at a significantly reduced effectiveness compared with use in conventional cement-based materials.This is likely due to direct interaction between the hydrocarbon molecules of water reducing admixtures and free carbon in the biochar. Given the significance of this observation the research team began to reproduce these experiments in winter of 2020 but results were inconclusive due to the early cessation of operations due to COVID-19.Reproducing key parts of this experiment is currently in progress in the laboratory with a newer batch of biochar from the same source with preliminary tests are suggesting increased effectiveness of the water reducer and compressive strengths that are edging up into the lowest acceptable range for a light-duty structural material (in the range of 2500 pounds per square inch). 2) We have not reached this stage yet due to delays brought on by the pandemic. 3)We have not reached this stage yet due to delays brought on by the pandemic. 4)We have not reached this stage yet due to delays brought on by the pandemic. 5) In progress. LCA software has been acquired and data is being collected. 6) We did use SEM (2.27kx) to investigate the morphological properties of soft-wood-derived biochar. The tubular structures confirm the observations of high levels of water absorption by the biochar. However, we have not been able to investigate charcrete samples yetdue to delays brought on by the pandemic.
Publications
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Progress 10/10/18 to 09/30/19
Outputs
Target Audience:Material science researchers, civil engineers. Changes/Problems:A. Biochar Absorption & Adsorption It was decided that before we could proceed with the outlined goals in the previous section, a better understanding fo the softwood-based biochar material was needed. Throughout the spring of 2019, a student technician was found who conducted research on the interactions between biochar and water, as follows: 1. Initial Research concentrated on quantifying biochar absorption. (The specific biochar used in this study had been commercially processed in the western US from Lodgepole Pines destroyed by the Mountain Pine Beetle and cleared from national forests to reduce fire-risk. Timber was converted to charcoal by slow pyrolysis up to 550 °C. Available oxygen during pyrolysis was limited to that released from biomass decomposition. Compositional analysis of the biochar by an independent laboratory indicated 81.7% organic carbon, 5.1% CaCO3, 1.2% total ash, with 5.6% moisture content as-sampled.) 2. Attempts were made to modify the standard ASTM method for measuring absorption of sand. The challenge is to: 1.) soak the biochar for a sufficient duration to completely fill permeable pores with water, and then 2.) dry the soaked biochar in a controlled manner to obtain particles that are internally saturated but dry on their external surfaces (this is called the "Saturated, Surface-Dry" state, or SSD). The combined measure of absorbed and adsorbed water is then determined by mass-loss between SSD and oven-dried biochar. It was observed that after a rapid initial uptake of water it may take as long as 3 to 9 days to fully saturate the biochar used, but precise measurement was hampered by the inability to reliably identify SSD state. Variations on ASTM C128 (specific gravity and absorption test) were explored from January-April, 2019 with limited success. At this point two very different approaches were initiated. 3. At the macro level, and following a lead from study of highly porous and absorbent aggregates, use of a centrifuge to spin-dry saturated biochar to SSD conditions was explored. Multiple state-of-the-art centrifuges were tried with little success, but progress was made when we obtained an older "bowl-style" centrifuge from the Biological Engineering department in Cornell's College of Agriculture. (The right type of centrifuge was not acquired until mid-May, 2019, leaving experimental follow-up until July-August.) The strategy was to soak biochar in water for various time periods, and then spin it to SSD conditions. This technique is quite promising, but variables that influence results include: soak-time, mass of biochar, method of placement in the centrifuge bowl, rpm, spin-time, and post-spin sampling. Earlier work points to an approximate absorption of at least 125% of oven-dry mass, suggesting that the centrifuge has the capacity to over-dry the biochar. Results are masked, however, by variations of moisture content within the mass of centrifuged biochar. Nevertheless, an optimum combination of pre-soak duration, sample mass, rpm, and spin-time may either produce an approximately SSD condition, or may consistently produce a slightly wetter condition that could be manipulated to SSD by normal methods. 4. A "micro" or materials-science approach was briefly explored in April-May, 2019, where the water-uptake problem was first addressed via "Adsorption Isotherms" whereby oven-dry biochar was exposed to air with successively increasing water-vapor pressures to observe fundamental behavior. The inverse problem was explored via "Thermo-gravimetric Analysis" (TGA) whereby small samples of pre-soaked biochar were dried at increasing temperature while mass was continuously monitored. This process continued all the way to combustion of the carbon, verified at about 80% of total dry mass. One intriguing observation, however, was that while a specific biochar may absorb or adsorb water, another biochar, or portions of any given biochar, may in fact be hydrophobic as was suggested by a few samples. This also suggests that some sort of pre-treatment to render 100% of the biochar hydrophobic may solve the water-uptake problem. Personnel involved in this line of inquiry were not available in the summer or fall of 2019, but follow-up is planned for Spring 2020. What opportunities for training and professional development has the project provided?The student who did the research was an undergraduate in Civil Engineering and was given first-hand opportunities to conduct rigorous material science research in a lab setting. How have the results been disseminated to communities of interest?
Nothing Reported
What do you plan to do during the next reporting period to accomplish the goals?1. Change type of High Range Water Reducer (HRWRA) and repeat key flow tests to find out if there is a simple solution. 2. Follow-up on centrifuge study of biochar, adsorption isotherms, and TGA to characterize absorption, adsorption, and hydrophobicity of this biochar and how that may vary with another source. 3. Follow-up on alternative methods of pre-soaking (pressure, radiation) and on a pre-treatment to make the biochar hydrophobic and thus by-pass the absorption problem.
Impacts
What was accomplished under these goals?
It was decided that before we could proceed with these research goals, a better understanding fo the softwood-based biochar material was needed. Throughout the spring of 2019, a student technician was found who conducted research on the interactions between biochar and water. This work is explained in the following section on "Changes/Problems". However, in the summer of 2019, a new line of research was initiated that addresses the first objective, of testing the workability of Charcrete with the use of plasticizers. The results are as follows: B. Flowability and use of Surfactant (Plasticizer) This aspect of the research addresses the first objective, to test the affect that plasticizers have on the Charcrete mix. The research thus far has been on the flowability of the mortar mix, not on the strength impacts. 1. The primary research goal for summer, 2019, was to investigate whether the use of a surface active agent could be used to establish flowability of biochar mortars without addition of water. The approach was to replicate the baseline mortars from the earlier research, with and without the chemical admixture. Within the cement, mortar, and concrete industry, such admixtures are typically known as "Water-Reducing Admixtures," and these chemicals are available in 3 grades of effectiveness (and cost). We used the most powerful type, officially classified as a "High Range Water Reducer," (HRWRA) but known in the field as a "Superplasticizer." A fundamental complication, however, is that these chemicals are organic and hence are preferentially adsorbed to carbon surfaces. It would therefore be expected that higher doses than usual would be required. (A normal high-dose would be in the range of surfactant mass »1/2% of mass of cement.) This increase in dose is not unusual, and is often needed when concrete or mortar mixtures incorporate carbon such as carbon-based pigments or coal fly ash. Mortars were prepared with multiple stages of water addition and measurement of flow via the ASTM C1437 test for flow of hydraulic cement mortars. (This was a slow and painful process.) The capacity of the HRWRA to dramatically increase flowability is clear in the first two curves on the left. Equally clear is how the inclusion of biochar dramatically increases water-demand (and subsequently decreases strength). Double the normal dose of HRWRA has essentially no effect on flow at 12.5% biochar (ref to sand weight), with significant improvements in flow (i.e., reductions in water-demand) only at 4 to 8 times the normal dose. Even if the high cost impact of HRWRA were not an issue, this chemical also significantly slows the hydration and setting of portland cement to the point of making it unusable for some applications. Pre-soaking the biochar was not as effective as expected, but the pre-soaked material may not have been fully saturated.
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2019
Citation:
Cheng, W., Elliott J., Hover, K., High-Volume Carbon Sequestration for
Controlled Low- Strength Materials , Materials Journal of the American
Concrete Institute. vol.116, no. 4, 18-343.
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