Piyush Chaunsali

Human colonization on Martian land is gaining significant attention in space exploration activities that demand in-situ resource utilization in the development of construction and building materials for human habitation. This research explores the utilization of Martian regolith simulant and sulfur to create extra-terrestrial concrete (ETC) with a property suitable for constructing human habitat on Mars. The primary objective of the study is to maximize the utilization of Martian regolith simulant to achieve the desired compressive strength of 25 MPa (average compressive strength specified for concrete used in residential buildings on Earth). Mechanical properties, phase transition, and microstructural characteristics of Martian regolith based-ETC under varied temperature conditions (0 °C, 40 °C, and 50 °C) on Mars were investigated. The optimal mixture proportion of ETC had 70% (by wt.) of Martian regolith and exhibited an average compressive strength of 27 MPa. The formulated ETC could retain up to 25 MPa of compressive strength at 40 ℃ and 50 ℃, and could reach up to 35 MPa at 0 ℃ temperature conditions. The change in compressive strength was attributed to the sulfur sublimation and pore closure brought about by freezing at extreme temperatures, respectively.

Slags with varied amorphous and crystalline content, typical of iron and steel production, are generally underutilized. One promising reuse pathway for these wastes is chemical activation, producing alternatives to conventional building materials with lower embodied energy. The formation of a hardened binder is dependent on the slag mineralogy and, specifically, the reactivity of relevant phases. Reactivity can be understood by monitoring elemental dissolution rates through inductively coupled plasma (ICP-OES) analysis. Post-dissolution ICP analysis of activating solution and spectroscopic analysis of remaining solids was performed on several highly crystalline slags and on relevant synthetic minerals to track changes in chemical and phase composition. Amorphous and ionic phases have been observed as more reactive than other crystalline phases. This work aims to inform future studies on waste blending in alkali-activated systems, a promising avenue for valorization of industrial wastes with varied physicochemical properties. To this end, dissolution tests with varied initial Si, Al, and Ca concentrations in activating solution were also performed.

Cementitious materials are alkaline in nature. As a result, they are prone to neutralisation reaction by acids and possible deterioration. Among the existing binders, the acid resistance of calcium sulfoaluminate (CSA) cement is not well explored. Moreover, the phase composition of CSA cement varies significantly to reflect its expansive and non-expansive characteristics. In this article, the effect of chemical composition on acid resistance is evaluated in terms of acid neutralisation capacity (ANC) or acid consumption, providing a novel approach to evaluate the durability of CSA cements in low pH environment. This research focuses on evaluating citric acid and sulfuric acid resistance of Portland cement (PC), high ye'elimite CSA cement (CSA (HY)), and calcium aluminate cement (CAC). The tests were performed on monolithic specimens as well as powdered hydrated samples using an autotitrator. The acid resistance of three binders could be evaluated from total acid consumption and predicted based on early period of test depending on a binder's acid - pH interaction curve. Furthermore, a procedure was developed to correlate powder and monolithic tests.

Calcium sulfoaluminate (CSA) cement-based binders are low CO2 binders which exhibit rapid hardening or shrinkage compensating characteristics. Due to their unique properties, they have potential to be used in concrete elements exposed to acidic environment such as sewage system. In this paper, the performance of CSA-based binders in acidic environment is examined and compared against Portland cement (PC). Attack of sulfuric acid and citric acid on PC and CSA-based binders was evaluated with respect to mass loss, dimensional change, cumulative H+ ion neutralisation, strength loss, and changes in mineralogical and microstructural characteristics. CSA-based binder exhibited higher resistance than PC-dominated binder in citric acid attack (pH ∼ 2–3), whereas PC-dominated binder outperformed CSA-based binder in case of sulfuric acid attack (pH ∼ 1.5–2). The mechanism of acid attack was found to be dependent on acid type. A calcium citrate salt was identified as the major product in case of citric acid attack of PC-dominated binders.

An untapped source of amorphous SiO2, industrially generated Indian biomass ash (SA)—90% amorphous, with composition of ~60% SiO2 and ~20% unburnt carbon—can be used to produce cementitious and alkali-activated binders. This study reports dissolution of amorphous Si from SA in 0.5 mol/L and 1 mol/L aqueous NaOH, with and without added Ca(OH)2, at SA:Ca(OH)2 wt% ratios of 100:0, 87.5:12.5, and 82.5:17.5. Monitoring of elemental dissolution and subsequent/simultaneous product uptake by ICP-OES offers an effective process for evaluating utility of industrial wastes in binder-based systems. After 28 days in solution, up to 68% of total Si is dissolved from SA in 1 mol/L NaOH, with values as much as 38% lower in the presence of Ca(OH)2, due to the formation of tobermorite-like C-S-H. FTIR, 29Si MAS-NMR, and XRD are used to characterize solid reaction products and observe reaction progress. Product chemistries calculated from ICP-OES results and verified by selective dissolution in EDTA/NaOH—namely, Ca/Si of 0.6-1 and Na adsorption of 1-2 mmol/g—are found to be consistent with those indicated by aforementioned techniques. This indicates the efficacy of ICP-OES in estimating product chemistry via such a methodology.

Steel fibre reinforced self-stressing concrete (SFRSSC) has been developing steadily over the last decades with applications of the material now including ground and pile supported slabs as well as raft foundations. Such building elements commonly come into contact with groundwater and are therefore typically covered on their exterior surface by a waterproofing membrane system in an attempt to prevent water seepage into the structure. The final performance of a waterproofing membrane system is heavily influenced by the quality, skill, and attention to detail both in the installation of the membrane and during subsequent works carried out (e.g., reinforcement placement, concrete pouring, etc.) over top of the membrane. Concrete slabs and foundations constructed using SFRSSC, which is typically less prone to cracking than ordinary concrete, may potentially have improved resistance to water ingress than ordinary concrete. In this paper, water penetration testing per EN 12390-8 and mercury intrusion porosimetry testing are completed on various SFRSSC mixtures and compared to reference concrete mixtures to assess changes in the material pore size distribution and its ability to resist water penetration. The presented test results indicate that SFRSSC can have a more refined pore network with improved resistance to water penetration compared to reference concrete mixes with the same water-to-cement ratio. As discussed in the paper, the SFRSSC additional characteristic of reduced shrinkage (and subsequent reduced potential for cracking) indicates that the material may be able to provide improved watertightness, with a potential to reduce demands for external waterproofing membranes under certain circumstances.

Ordinary portland cement (OPC) manufacturing contributes to about 5–8% of the CO2 emissions globally and its consumption is expected to increase. Finding alternative to OPC is a global issue in the recent times. Calcium sulfoaluminate (CSA)-based binder is gaining attention due to the lower requirement of limestone and temperature requirement during its production. There are several lab-scale studies where CSA has been produced using different alternative raw materials. In this study, earlier research works were reviewed to understand the different types of raw materials used to produce CSA. The data for cement production was collected from a cement plant in India to conduct a life cycle assessment (LCA). Two hypothetical cases of CSA production were assumed in the same cement plant, and environmental impacts were calculated in terms of CO2 emissions and energy consumed. It was found that with the change in alternative raw materials, the impact could vary from 460 to 590 kg CO2 per tonne of CSA. Generally, 30–45% of CO2 emissions reduction was observed when compared to Portland cement, whereas the substantial change in energy consumption was not evident. Transportation distance of raw materials seemed to be critical with respect to energy consumed.

Expansive characteristics of calcium sulfoaluminate-belite (CSAB) cement can be harnessed for making shrinkage-compensating concrete. The level of expansion is dependent on several factors, such as the amounts of ye'elimite and calcium sulfate available in CSAB cement. Moreover, calcium sulfate from an external source can also influence the expansion characteristics by increasing the supersaturation with respect to ettringite. In this study, the influence of externally available calcium sulfate was investigated by curing a blend of Portland cement (PC) and CSAB cement to different concentrations (1 g/l and 5 g/l) of gypsum solutions. Expansion of the PC-CSAB blended cement was found to be directly affected by the ye'elimite content (CSAB dosage) and the gypsum concentration in exposure solution. The presence of external calcium sulfate during the hydration of ye'elimite was found to affect the hydrate phase assemblage, the pore structure, and the morphology of ettringite. Furthermore, the level of expansion depended on the age at which the specimens were exposed to the gypsum solution, indicating the influence of matrix stiffness on resultant expansion.

Biomass ash results from the combustion of agricultural residues, which, in many developing countries, are a primary source of power generation for small and medium size industries. This study focuses on the performance of a binder synthesized from an Indian biomass ash, Indo-Gangetic clay, hydrated lime, and aqueous 1M NaOH solution. To measure the extent of leaching and its impact on physicochemical properties, the biomass ash binder in powder form (<45 μm size) was exposed to two different leaching media: deionized water and 0.1M HNO 3 at two different solution-to-sample ratios (by wt.) of 10 and 100. Sodium leaching was found to be prominent in the biomass ash binder irrespective of leaching medium and solution-to-sample ratio. However, calcium leaching was significantly higher in 0.1M HNO 3 than in deionized water. Calcium silicate hydrate present in the biomass ash binder was found to be less chemically stable in 0.1M HNO 3 , exhibiting complete calcium leaching at a solution-to-sample ratio of 100. Furthermore, significant leaching of calcium in 0.1M HNO 3 solution resulted in phase modification of calcium silicate hydrate, the main reaction product of the biomass ash binder.

There has been a significant push in the direction of reducing carbon footprint of concrete through the development of alternative binders. To that end, calcium sulfoaluminate-belite (CSAB) cement is a promising alternative due to its lower carbon footprint and higher resistance against shrinkage cracking. Lower burning temperature and lesser amount of limestone requirement for CSAB cement manufacturing can provide up to 30% reduction in carbon footprint of concrete. Moreover, the porous nature of CSAB cement clinker lowers the grinding energy requirement. The main constituents of CSAB cement are ye’elimite, belite, ferrite, and calcium sulfate. Hydration of ye’elimite in presence of calcium sulfate results in the formation of ettringite, leading to early-age expansion. For shrinkage-compensating property, CSAB cement can be formulated as an expansive cement system. Nonetheless, the use of CSAB cement in concrete has been limited to niche applications. This paper reviews the manufacturing, composition, mechanical properties and durability characteristics of CSAB cement. The current challenges with respect to its wider application in concrete are also discussed.