Early-age hydration and volume change of calcium sulfoaluminate cement-based binders

Shrinkage cracking is a predominant deterioration mechanism in structures with high surface-to-volume ratio. One way to allay shrinkage-induced stresses is to use calcium sulfoaluminate (CSA) cement whose early-age expansion in restrained condition induces compressive stress that can be utilized to counter the tensile stresses due to shrinkage. In addition to enhancing the resistance against shrinkage cracking, CSA cement also has lower carbon footprint than that of Portland cement. This dissertation aims at improving the understanding of early-age volume change of CSA cement-based binders. For the first time, interaction between mineral admixtures (Class F fly ash, Class C fly ash, and silica fume) and OPC-CSA binder was studied. Various physico-chemical factors such as the hydration of ye’elimite (main component in CSA cement), amount of ettringite (the main phase responsible for expansion in CSA cement), supersaturation with respect to ettringite in cement pore solution, total pore volume, and material stiffness were monitored to examine early-age expansion characteristics. This research validated the crystallization stress theory by showing the presence of higher supersaturation level of ettringite, and therefore, higher crystallization stress in CSA cement-based binders. Supersaturation with respect to ettringite was found to increase with CSA dosage and external supply of gypsum. Mineral admixtures (MA) altered the expansion characteristics in OPC-CSA-MA binders with fixed CSA cement. This study reports that fly ash (FA) behaves differently depending on its phase composition. The Class C FA-based binder (OPC-CSA-CFA) ceased expanding beyond two days unlike other OPC-CSA-MA binders. Three factors were found to govern expansion of CSA cement-based binders: 1) volume fraction of ettringite in given pore volume, 2) saturation level of ettringite, and 3) dynamic modulus. Various models were utilized to estimate the macroscopic tensile stress in CSA cement-based binders without taking into account the viscoelastic effects. For the first time, model based on poromechanics was used to calculate the macroscopic tensile stress that develops in CSA cement-based binders due to crystallization of ettringite. The models enabled a reasonable prediction of tensile stress due to crystallization of ettringite including the failure of an OPC-CSA binder which had high CSA cement content. Elastic strain based on crystallization stress was calculated and compared with the observed strain. A mismatch between observed and calculated elastic strain indicated the presence of early-age creep. Lastly, the application of CSA cement in concretes is discussed to link the paste and concrete behavior

Development of waterless extra-terrestrial concrete using martian regolith

Human colonization on Martian land is gaining significant attention in universal planetary exploration activities that demand in-situ resource utilization in the development of construction and building materials for human habitation. This research emphasizes the utilization of Martian regolith simulant to create extra-terrestrial concrete (ETC) with a property suitable for constructing human habitat on Mars. Mechanical, phase transition, and microstructure properties of Martian regolith basedETC under varied temperature conditions (high: 40 ºC and 50 ºC; low: 0 ºC) on Mars were investigated. The optimal mixture proportion of ETC had 70% of Martian regolith and exhibited a compressive strength of 27 MPa. The formulated ETC could retain up to 25 MPa of compressive strength under high (40 °C and 50 °C) and could reach up to 35 MPa under low (0 °C) temperature conditions. The change in compressive strength was attributed to the sulfur sublimation and pore closure brought on by freezing at high and low temperatures, respectively

Leaching characteristics of biomass ash-based binder in neutral and acidic media

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 HNO₃ 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 HNO₃ than in deionized water. Calcium silicate hydrate present in the biomass ash binder was found to be less chemically stable in 0.1M HNO₃, exhibiting complete calcium leaching at a solution-to-sample ratio of 100. Furthermore, significant leaching of calcium in 0.1M HNO₃ solution resulted in phase modification of calcium silicate hydrate, the main reaction product of the biomass ash binder

Influence of external environment on early-age expansion characteristics of calcium sulfoaluminate cement-based binders

Calcium sulfoaluminate (CSA) cements are widely being promoted as alternative low CO2 binders. CSA cements can also be expansive and designed to be shrinkage-compensating. The main phase of CSA cement is ye’elimite, which hydrates in the presence of calcium sulfate to form ettringite as the main hydration product. The availability of calcium sulfate can be used to control the hydration kinetics of ye’elimite, which affects the expansion characteristics of CSA cement. Sulfates in the form of gypsum or anhydrite are usually blended with CSA cement in the manufacturing stage. The presence of sulfates in the external environment also affects the expansion characteristics of CSA cement. This study aims to understand the effect of different exposure conditions on the expansion characteristics of CSA-based blended cement. The expansion of the specimens exposed to calcium sulfate solution was found to increase with the amount of calcium sulfate. The addition of CSA cement to Portland cement was found to have a significant influence on the early age expansion characteristics of the system, without affecting the mechanical properties such as compressive strength and dynamic modulus

Bridge Decks: Mitigation of Cracking and Increased Durability

This report discusses the application of expansive cements (Type K and Type G) and shrinkage-reducing admixtures (SRAs) in reducing the cracking due to drying shrinkage. The Type K expansive cement contained portland cement and calcium sulfoaluminate-based component whereas the Type G expansive system was made of portland cement and CaO-based component. The restrained expansion test in accordance with ASTM C 878 demonstrated that Type K and Type G concretes had minimal shrinkage at the end of 100 days. The Type K bridge deck model also exhibited a reduction in tensile strain on the order of 40-50 microstrains and reduction in excess shrinkage potential which showed its effectiveness in reducing the tensile stress due to drying shrinkage. The effect of mineral admixtures on expansion characteristics of Type K and Type G system is also discussed. The effectiveness of SRA was assessed using ASTM C 1581 that clearly showed the delay in cracking time due to addition of an SRA. The increase in SRA dosage reduced the drying shrinkage, but also resulted in reduction of compressive strength.Illinois Department of Transportation, R27-88published or submitted for publicationnot peer reviewe

Mineralogical and microstructural characterization of biomass ash binder

While the incineration of biomass residues is gaining traction as a globally available source of renewable energy, the resulting ash is often landfilled, resulting in the disposal of what could otherwise be used in value-added products. This research focuses on the beneficial use of predominantly rice husk and sugarcane bagasse-based mixed biomass ashes, obtained from two paper mills in northern India. A cementitious binder was formulated from biomass ash, clay, and hydrated lime (70:20:10 by mass, respectively) using 2M NaOH solution at a liquid-to-solid mass ratio of 0.40. Compressive strength of the biomass ash binder increased linearly with compaction pressure, indicating the role of packing density. Between the two mixed biomass ashes used in this study, the one with higher amorphous content resulted in a binder with higher strength and denser reaction product. Multi-faceted characterization of the biomass ash binder indicated the presence of aluminum-substituted calcium silicate hydrate, mainly derived from the pozzolanic reaction. Keywords: Biomass ash; Clay; Characterization; Pozzolanicity; Alkali-activation; Amorphous contentNational Science Foundation (Grant DMR-1419807

Bridge Decks: Mitigation of Cracking and Increased Durability

The application of pre-soaked lightweight aggregates (LWA) as an internal curing agent in concrete to reduce the cracking due to drying shrinkage is thoroughly studied in this report. It is determined that although LWA can significantly reduce autogenous shrinkage, its effect on drying shrinkage is minimal and in some cases it can even increase the drying shrinkage. Moreover, the combined effects of LWA and expansive cement (Type K) and LWA and shrinkage-reducing admixtures (SRAs) on drying shrinkage is also studied. It is shown that addition of Type K cement or SRA to mixtures containing LWA can significantly reduce drying shrinkage and make the mixture more volumetrically stable.Illinois Department of Transportation, R27-139Ope