•Bio-cement can be successfully manufactured using conch shell waste as a raw material.•The physicochemical properties of bio-cement and its hydration products were similar to that of Type I ...cement.•Compressive strength of the bio-cement made with 100% conch shell was 20 MPa at 7 days.•C-S-H gel of conch shell cement had low Ca/Si and high Al/Si ratio.
This paper demonstrates a laboratory-scale synthesis and analysis of cement using conch shell waste (CS bio-cement) similar in composition to Type I ordinary portland cement (OPC) by replacing calcite raw material with ground processed conch shell waste at varying levels (0–100%). The CS bio-cements were similar to Type I OPC in phase composition, hydration behavior, strength, and microstructure development up to 60% replacement. Higher conch shell substitution (60–100%) tends to incorporate more alumina and alkali in the clinker without compromising other properties significantly. CS bio-cement with above 60% conch shell exceeded the Na2O content limit for Type I OPC or low alkali cement. Nevertheless, those cements will be qualified as high alkali cements for appropriate construction use. The results suggest that CS bio-cement has potential for applications in concrete construction. However, the durability of the concrete containing CS bio-cement should be evaluated prior to real-world applications.
Concrete is one of the most abundantly produced and commonly used construction materials in the world. The production of cement—the main binder in concrete—is energy-intensive, using roughly ten ...times the national average ratio for energy to gross output of goods and services. Given the high demand for concrete globally and the amount of energy used to produce cement, it is worthwhile to find lower embodied-energy materials to partially replace cement to improve the environmental impacts of concrete without decreasing the concrete performance. One such potential cement replacement is the panel glass found in discarded cathode-ray tubes (CRTs). It is against this backdrop that this study aimed to investigate the technical feasibility and the environmental impacts of using a novel blend of recycled glass and CRT panel glass as pozzolanic material for replacing a portion of ordinary portland cement (OPC) in concrete. Additionally, this study simultaneously looked at the concrete functional performance and environmental impact, and the study was performed at an industrial scale using existing production infrastructure, production volumes, standardized testing, and a life-cycle assessment (LCA) to support the functional testing and environmental impact quantification. Results show that the novel blend of glass met the required performance standards, and when it was blended with cement, the mixture produced concrete with similar or improved functional performance and significantly reduced environmental impacts across all examined impact categories. Future work is needed to examine the additional benefits of diverting CRTs from their current end-of-life pathways and de-risking CRT storage.
Alkali-activation of aluminosilicate materials is a significant initiative for producing a sustainable alternative binder to ordinary portland cement (OPC). Reducing OPC consumption by using the ...industrial by-products promotes the sustainability of the alkali-activated cement (AAC). Although AAC shows superior strength and durability properties compared to OPC, an economically and practically viable method to use this technology in the field has not been recognized yet. Maintaining a reasonable setting time is the most challenging issue with the AAC systems. Understanding the fundamental mechanism of hydration of alkali-activated binder is the key to address these challenges. Determining the first principles of hydration reaction using experimental investigations require complicated and time-consuming techniques which is impossible to implement for all possible mix compositions at all material ages of interest. In order to overcome the inherent difficulties related to experimental studies, a numerical study would provide the best solution, which has not been initiated yet. Thus, for the first time, this dissertation presents a new modeling framework based on the microstructural evolution to simulate the hydration kinetics of AAC systems to understand the governing mechanisms of hydration. The microstructural development of AAC is investigated using two different experimental methods. The first method involves enhancing the degree of hydration and the property evolution by using different nano/submicron seeds. Many studies have focused on the property enhancement of alkali-activated binders with different seeds, but they do not explicitly discuss or report the acceleration mechanisms in AAC system with regards to external seeds. Identifying the acceleration mechanism helps to understand the hydration reaction of AAC systems. The results show that seeds accelerate the hydration reaction in which the nucleation and growth kinetic is the phase transformation mechanisms in AAC systems. Seeds act as theiiigerm nuclei. Moreover, random volume nucleation and boundary nucleation processes could be identified in AAC system because nuclei sites are observed in between the binder particle and the boundary of the solid-liquid phase. However, seeds dissolve in the activator solution due to the high pH environment, changing the pore solution concentration and chemical composition of the reaction products. In the second method, the microstructural development mechanism is studied using the dilute suspension method. Before employing this method, a detailed experimental characterization study is performed to confirm that the dilute suspension method does not alter the reaction chemistry with several benefits. It helps to abolish the influence of the seed dissolution and germ nuclei. Additionally, this method eliminates the interaction between the grains and retards the hydration reaction by allowing the phase transformation to be captured over time. The captured morphological evolution sequence of the product phase shows the formation of the self-nuclei sites on the partially reacted surface and growth of the reaction product thereafter. This microstructural study ratifies that the nucleation and growth mechanism is the governing mechanism of hydration of AAC system. Even though experimental attempts provide a generalized view on the reaction mechanism, the basic aspects such as the nucleation type, changing the nucleation type according to the hydration stage, nucleation rate, and growth rate of the product phase remain elusive. A theoretical study on random volume nucleation and growth and boundary nucleation and growth processes is performed to identify the dominant nucleation and growth condition in each stage. The results show that random volume nucleation and growth theory can simulate the early age hydration of AAC while boundary nucleation and growth theory can simulate the later age hydration more accurately. Three different boundary nucleation and growth models, which are based on different nucleation processes, are used to mimic the hydration kinetic in AAC system. Continuous nucleation with a constant rate over time and the rapid burst ofivnucleation in a negligible time provide a better description of the deceleration period while later age growth fits for the steady stage of the hydration curve. The ultimate goal of this study is to develop a new model to simulate the AAC hydration. The model is named as the hybrid nucleation and growth (HNG) model because users can customize the model hypothesis for each hydration stage. HNG model divides the single characteristic peak hydration curves into three different kinetic stages, while it divides two characteristic peaks hydration curves into four kinetic stages. The single peak hydration curve can be divided into an initial stage (up to maximum rate), a second stage (deceleration stage), and a steady stage. The two-peak hydration curves can be divided into an initial stage (up to the maximum rate of the first peak), a decay stage (deceleration stage of the first peak), a second stage (acceleration and deceleration period of the second peak), and a steady stage. The HNG model corroborates well with the experimentally measured normalized heat flow. According to the hybrid model, the hydration of the alkali-activated system starts with the nucleation that takes place at randomly spaced locations within the volume. Subsequently, the hydration mechanism varies according to the activator solution and the binder material used in the system. Moreover, the identified hydration mechanisms for each AAC system is validated through a comprehensive microstructural analysis. Overall, the findings presented in this dissertation significantly contribute to the understanding of the hydration mechanism of AAC system by providing new insights into the phase transformation mechanism in AAC hydration. The results of this thesis work can be further extended to developing a predictive hydration kinetic model for the AAC.
