Development of 3D printable stabilized earth-based construction materials using excavated soil: Evaluation of fresh and hardened properties.

Soil excavated during construction and demolition can be utilized to reduce the demand for natural sand in 3D printed constructions. This research attempts to systematically develop 3D printable stabilized earth-based materials using excavated soil (clay content of 42.5 %) as 25 % and 50 % replacement of natural sand, and examine their compressive strength, water permeable porosity, and moisture sensitivity. The effectiveness of two binder systems - Ordinary Portland Cement (OPC) and a combination of OPC and ground granulated blast furnace slag (GGBS used to replace 30 % OPC by mass), was investigated. Non-expansive clay in the soil leads to a steeper reduction in apparent viscosity, 12-15 % higher flow retention, and 50-60 % lower plastic viscosity of soil-based mixes, thus contributing to superior extrusion quality at 35-40 mm lower initial flow than OPC-sand and OPC-GGBS-sand mixes. The addition of GGBS, due to its irregular particle morphologies and interlocking effects, further enhances the shape retention of the printed layers by 8-26 % compared to OPC-soil mortars. The structural build-ups in OPC-soil and OPC-GGBS-soil mortars increase with the increase in clay content, which enabled buildability up to a height of 1.2 m compared to only 0.51-0.55 m for OPC-sand and OPC-GGBS-sand mortars. Higher water demand due to the addition of natural clay increases the porosity of 3D printed OPC-soil mortars, thereby lowering compressive strength and increasing moisture sensitivity. However, a blend of OPC and GGBS substantially reduces the moisture sensitivity of the printed mortars at 28-day age, attributed to better stabilization of clay through hydraulic and pozzolanic action of GGBS. 28-day wet compressive strength of 14-25 MPa is obtained for the printed soil-based mixes depending on the soil dosage and loading direction. In summary, the study provides a feasible solution for the 3D printing of stabilized earth structures with lower demand for natural sand and OPC.

Carbon dioxide sequestration in mortars with excavated soil: Engineering performances and environmental benefits.

Globally, substantial volume of excavated soils is generated during construction and demolition activities, which can be utilized in the manufacturing stabilized earth-based construction materials. Furthermore, increasing amount of CO2 is being released into the environment from growing industrial operations that can sequestered in earth-based materials without compromising the engineering properties. This article attempts to explore the effect of CO2 sequestration through accelerated carbonation curing on engineering properties, micro-structure and phase composition of cement-lime stabilized soil mortars. Lateritic soil (clay content of 42 %) is used to replace 25 % and 50 % of natural sand by mass. The experimental findings demonstrate an increase in CO2 uptake by 15-23 % and 33-40 % due to addition of 25 % and 50 % soil respectively compared to control (0 % soil). Precipitation of meta-stable calcium carbonates majorly contributes to the total CO2 uptake, accounting for 62-69 % and 78-87 % of the carbonates formed in 25 % soil-mortars and 50 % soil mortars. These are substantially higher compared to 40-50 % in the case of control mixes. The mentioned finding is attributed to the formation of additional calcium-silicate-hydrate and calcium-aluminate-hydrate due to clay-lime reaction, that binds CO2 and precipitate meta-stable polymorphs of calcium carbonate. Addition of lime and carbon sequestration are found to substantially enhance 1-day strength of cement-soil and cement-lime-soil mortars by 31-36 %, although no prominent effect at 7-day and 28-day marks are observed. Furthermore, capillary water absorption at 28-day age is reduced by 18-31 % in lime-added cement-soil mortars compared to the ones without lime, that reduces moisture sensitivity of the mortars. Overall, the carbon sequestered mortars demonstrate satisfactory strength (20-37 MPa) and water absorption performance of the stabilized mortars for masonry applications, which will provide a promising means to manufacture low-carbon and more durable construction products.

Carbonaceous admixtures in cementitious building materials: Effect of particle size blending on rheology, packing, early age properties and processing energy demand.

Application of biochar, produced from locally generated wastes, as admixture in cement is a strategy to upcycle biomass waste and produce durable building materials. This research explores the influence of particle size and porosity of biochar, prepared from coconut shell and wood waste, added at 2 wt% of cement, on rheology, setting time, hydration and early age strength of cement mortar. For each biochar type, three particle size gradations are explored - coarser biochar (d50 = 45-50 µm) (obtained by sieving), finer biochar (d50 = 10-18 µm) (obtained by ball milling) and combination of coarser and finer biochar (d50 = 15-25 µm). Experimental findings suggest that combination of coarser and finer biochar improves workability and rheological properties of binder pastes compared to that with (only) coarser biochar. Depending on biochar type, hydration and rate of setting are accelerated compared to control. Inclusion of finer biochar and combination of finer and coarser biochar improve packing density and degree of hydration of pastes compared to coarser biochar and control, leading to 12-19% enhancement in compressive strength at 7-day age. Micro-structural investigations show that the macro-pores of coarser biochar can be filled with dense hydration products, although some macro-pores may remain unfilled. This offsets improvement in strength that can be achieved through enhancement in packing density. The approach of blending coarser and finer biochar reduces the energy demand and cost associated with ball-milling by 23-37% and SGD 2.30-4.80 per ton respectively compared to only finer (ball-milled) biochar per cubic meter of concrete. Overall, the findings from this research demonstrate that blending of biochar of different particle size distributions can enhance physical properties of cement-based materials, while reducing associated energy consumption.

7-Hydroxy Frullanolide, a sesquiterpene lactone, increases intracellular calcium amounts, lowers CD4+ T cell and macrophage responses, and ameliorates DSS-induced colitis.

Sesquiterpene lactones are a class of anti-inflammatory molecules obtained from plants belonging to the Asteraceae family. In this study, the effects of 7-hydroxy frullanolide (7HF), a sesquiterpene lactone, in inhibiting CD4+ T cell and peritoneal macrophage responses were investigated. 7HF, in a dose dependent manner, lowers CD69 upregulation, IL2 production and CD4+ T cell cycling upon activation with the combination of anti-CD3 and anti-CD28. Further mechanistic studies demonstrated that 7HF, at early time points, increases intracellular Ca2+ amounts, over and above the levels induced upon activation. The functional relevance of 7HF-induced Ca2+ increase was confirmed using sub-optimal amounts of BAPTA, an intracellular Ca2+ chelator, which lowers lactate and rescues CD4+ T cell cycling. In addition, 7HF lowers T cell cycling with the combination of PMA and Ionomycin. However, 7HF increases CD4+ T cell cycling with sub-optimal activating signals: only PMA or anti-CD3. Furthermore, LPS-induced nitrite and IL6 production by peritoneal macrophages is inhibited by 7HF in a Ca2+-dependent manner. Studies with Ca2+ channel inhibitors, Ruthenium Red and 2-Aminoethoxydiphenyl borate, lowers the inhibitory effects of 7HF on CD4+ T cell and macrophage responses. In silico studies demonstrated that 7HF binds to Ca2+ channels, TRPV1, IP3R and SERCA, which is mechanistically important. Finally, intraperitoneal administration of 7HF lowers serum inflammatory cytokines, IFNγ and IL6, and reduces the effects of DSS-induced colitis with respect to colon length and colon damage. Overall, this study sheds mechanistic light on the anti-inflammatory potential of 7HF, a natural plant compound, in lowering immune responses.

Carbonaceous micro-filler for cement: Effect of particle size and dosage of biochar on fresh and hardened properties of cement mortar.

This study explores influence of biochar particle size and surface morphology on rheology, strength development and permeability of cement mortar, under moist and dry curing condition. Experimental results show that the flowability and viscosity of cement paste is more affected by macro-porous coarser (or 'normal') biochar particles of size 2-100 µm (NBC) compared to fine (or 'ground' biochar), which is in the size range of 0.10-2 µm (GBC). Addition of both GBC and NBC accelerated hydration kinetics and improved early (1-day) and 28-day strength by 20-25% compared to the control. Water permeability, measured by capillary absorption was reduced by about 50% compared to control mortar, due to the addition of 0.50-1% NBC and GBC respectively. GBC is found to be more effective in minimizing loss in strength and water tightness under dry curing condition compared to the control and mortar with NBC and quartz filler respectively. In summary, findings from the study show that finer biochar particles offer superior performance in improving early strength and water tightness compared to normal biochar (with macro-pores), while 28-day properties are similar for mortar with both GBC and NBC respectively.

Application of biochar from food and wood waste as green admixture for cement mortar.

Landfilling of food waste due to its low recycling rate is raising serious concerns because of associated soil and water contamination, and emission of methane and other greenhouse gases during the degradation process. This paper explores feasibility of using biochar derived from mixed food waste (FWBC), rice waste (RWBC) and wood waste (mixed wood saw dust, MWBC) as carbon sequestering additive in mortar. RWBC is prepared from boiled plain rice, while FWBC is prepared from combination of rice, meat, and vegetables in fixed proportion. Carbon content in FWBC, RWBC and MWBC were found to be 71%, 66% and 87% by weight respectively. Results show that addition of 1-2wt% of FWBC and RWBC in mortar results in similar mechanical strength as control mix (without biochar). 1wt% of FWBC led to 40% and 35% reduction in water penetration and sorptivity respectively, indicating higher impermeability of mortar. Biochar from mixed wood saw dust performed better in terms of mechanical and permeability properties. Increase in compressive strength and tensile strength by up to 20% was recorded, while depth of water penetration and sorptivity was reduced by about 60% and 38% respectively compared to control. Both FWBC and MWBC were found to act as reinforcement to mortar paste, which resulted in higher ductility than control at failure under flexure. This study suggests that biochar from food waste and mixed wood saw dust has the potential to be successfully deployed as additive in cement mortar, which would also promote waste recycling, and sequester high volume carbon in civil infrastructure.