Elucidating the Fresh and Hardened Properties of Limestone Calcined Clay Cements through Data Analytics

Limestone calcined clay cements (LC3) are a broad class of blended mineral compositions that are alternatives to conventional Portland cement (PC) and are one of the most promising technologies to achieve carbon neutrality in the concrete industry. However, a mechanistic understanding of fresh and hardened properties of LC3-based pastes, mortars, and concrete, as well as empirical design approaches are lacking. This dissertation addresses these knowledge gaps by developing composition-property linkages with the purpose of facilitating the transition of LC3 from the laboratory to practice. Specifically, the influence of LC3 composition on early hydration kinetics, rheological properties, compressive strength development and durability assessed by surface resistivity test is investigated. The compositional design space considers variations in water-to-solids ratio, proportions of constituent materials (PC, calcined clay or “metakaolin” (MK), limestone (LS)), added gypsum content, limestone particle size and superplasticizing admixture dosage. The composition-property linkages are established by combining laboratory data with data analytics approaches including Machine learning (ML). A guiding hypothesis is that the sulfate balance (defined in this dissertation as time difference between the maximum of silicate peak and the sulfate depletion point measured during isothermal calorimetry), influences both the fresh (i.e., rheology) and hardened properties (e.g., compressive strength, surface resistivity) of LC3. To examine this, first, a non-parametric kernel regression technique Nadaraya-Watson (NW) estimator is applied to the heat evolution curves obtained from isothermal calorimetry, allowing quantification of the influence of compositional factors on early hydration kinetics (e.g., slope of silicate peak, sulfate depletion point) in a novel way. Thereafter, linkages between composition and sulfate balance are established first and then the hypothesis of the role of sulfate balance in influencing fresh and hardened properties of LC3 is tested in further chapters. Next, to predict the rheological behavior of LC3, domain knowledge is embedded in ML in the form of five physicochemical predictors, all based on composition. The ML modeling approach helps to elucidate the diversity of mechanisms through which the MK component dominates the rheological behavior of LC3, both directly and through its interactions with the other mineral constituents. Analytical measures (e.g., changes in portlandite and bound water contents over time) show how microstructural development translates to compressive strength and surface resistivity development. For instance, LC3 mortar strength over 28 days of hydration can be accurately predicted not only from its portlandite content over time, but also shows strong correlation with concrete surface resistivity development. Finally, a multi-objective optimization tool is developed to simultaneously predict LC3`s global warming potential and compressive strength development, which are two parameters central in the industrywide shift in cement compositions. Overall, this dissertation provides new foundational understanding of LC3`s early hydration kinetics and property evolution that supports the concrete industry`s adaptation to LC3; this work provides insights that not only rely on empirical findings but also generates models and analytical techniques that can be used to accurately predict fresh and hardened properties based on LC3 composition.Ph.D

Production of calcium sulfoaluminate cements using waste materials

The high environmental impact of ordinary portland cement (OPC) is due to its main mineral,alite (C3S), which needs elevated kiln temperatures and high lime content to form. In calciumsulfoaluminate (CS̄A) clinkers, ye’elimite (C4A3S̄ ) forms as the main clinker phase and alite doesnot. Ye’elimite can form at 200-250 °C lower temperatures and has ~40 % lower lime contentthan alite which makes CS̄A cements a promising alternative to OPC. Bauxite is typically used asa raw material to satisfy the great alumina demand of ye’elimite formation. However, bauxite isexpensive as it is not abundant and is in demand by aluminum manufacturers. Hence,incorporation of industrial wastes, particularly aluminous ones, into CS̄A cements can helpmaintain their appeal.This study used limestone, bauxite and gypsum as natural raw materials and some high-volumeindustrial wastes in Turkey, a fly ash, red mud, and desulfogypsum, to produce CS̄A cements. Flyash and red mud were incorporated in the clinker raw meal to minimize the use of bauxite.Desulfogypsum was added to the ground clinker as a source of calcium sulfate. Different CS̄Aclinkers were produced by varing calcination conditions (kiln temperature and residence time)and using various raw mixtures. CS̄A cements and mortars produced with or without variousadmixtures were investigated using strength tests, isothermal calorimetry, X-ray diffraction(XRD), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). 1-dcompressive strengths of 15 MPa and 28-d strengths exceeding 35-40 MPa could be reachedusing cements containing > 50 % industrial waste and as low as 10 % bauxite. Early strength gainis due to ye’elimite hydration, which produces ettringite. Belite hydration which ordinarilyincreases late strength can be accelerated with admixtures. XRD and TGA also indicate someettringite decomposition due to carbonation

Influence of production parameters on calcium sulfoaluminate cements

The main appeal of calcium sulfoaluminate (C (S) over barA) cements is the possibility of reducing CO2 emissions. C (S) over barA clinkers can generally be produced at lower kiln temperatures and with lower limestone contents than required for portland cement clinker. However, it is important to assess the effects of various production parameters on the properties of C (S) over barA clinkers and cements. The influence of kiln maximum temperature, kiln retention time, and raw mixture proportioning on clinker properties, and those of water-to-cement ratio (W/C) and gypsum addition on cement hydration, were investigated. C (S) over barA clinkers were prepared in a laboratory furnace, with limestone, bauxite, and gypsum. Clinker and cement properties were explored with X-ray diffraction, isothermal calorimetry, thermogravimetric analysis, and scanning electron microscopy. Kiln temperatures as low as 1250 degrees C and retention times as low as 90 min. yielded satisfactory clinkers. Raw meal composition and calcination temperature have a greater effect on clinker phases than retention time. Hydration heat is affected mostly by raw meal composition. Hydration and strength gain were rapid until 3 d, after which they slowed down due to ettringite and AH(3) coating the clinkers particles. Mortars with W/C = 0.6, achieved using citric acid as a retarder, gained similar to 50 MPa strength at 28 d, 50-60% higher than mortars with W/C = 0.7

Laboratory production of calcium sulfoaluminate cements with high industrial waste content

A drawback of conventional calcium sulfoaluminate (CSA) cement production is the use of the costly raw material bauxite as a source of alumina to form the main clinker phase ye'elimite. Replacement of bauxite with industrial wastes can benefit CSA cements economically and environmentally. This study demonstrates the use of high amounts of red mud, a sulfate-rich/high-lime fly ash, and desulfogypsum as raw materials in producing CSA clinkers and cements with better mechanical performances than an all-natural raw material CSA reference cement. Mineralogical compositions of the clinkers and hydrated cement pastes were investigated using x-ray diffraction, isothermal calorimetry, thermogravimetric analysis and scanning electron microscopy. Compressive strength development of mortars, made with citric acid, were studied up to 28 d. It was found that increasing fly ash increases the belitic nature, and increasing red mud increases the terrific nature of the clinkers. Mortars with 28-d strengths exceeding 40 MPa could be made with cements containing similar to 38% waste and only half the bauxite in the reference. Medium early and ultimate strength mortars could be made with a similar to 55% waste cement when bauxite was reduced to a quarter of the reference, with small additions of Ca(NO3)(2)center dot 4H(2)O or Li2CO3. Desulfogypsum, as a source of sulfates, was more beneficial to strength development than natural gypsum. Ye'elimite reactivity was enhanced in red-mud containing cements. Cements with both fly ash and red mud experienced lower carbonation than those made with only one of the two wastes

Activation of Blast Furnace Slag with Soda Production Waste

Although the absence of portland cement (PC) in alkali-activated slag (AAS) lowers its carbon footprint, conventional alkaline activators like sodium silicate are expensive and have large environmental impacts. Soda solid waste (SSW) is an alkaline waste of the glass industry, and its disposal poses environmental problems. This study investigated the use of SSW to activate ground slag at 60 degrees C-120 degrees C. Strength development of mortars and heat evolution of pastes were evaluated. Hydration products were studied using X-ray diffraction and thermal analysis. Strength gain, rapid in the first 3-7 days, is attributed to formation of amorphous phases and partly crystalline calcium silicate hydrate (C-S-H). Increasing SSW content causes a weaker and broader rate of heat evolution peak in the first few hours and evolves greater total heat in the first day. SSW-activated slag pastes evolve significantly less heat up to 7 days than a typical room-temperature-cured PC paste but similar when heat is normalized by compressive strength. Mortars containing 40% slag and 60% SSW reach similar to 20 MPa after 7 days of curing at 120 degrees C. (c) 2019 American Society of Civil Engineers