Papers by Keyword: Pozzolanic Reaction

Abstract: A concrete mixture formulation consisting of industrial wastes such as fly ash and gypsum from ceramic mold waste as partial replacements for cement was developed in this two-part study to lessen the carbon footprint from processing the conventional materials used in the construction industry. The first part aims to determine the optimum composition of the ternary binder (cement, fly ash and recycled gypsum) and the curing period (7, 28 and 90) that will provide the highest compressive strength for the casted concrete cylinders. The second part focuses on establishing the effective polypropylene fiber (PPF) dosage, utilizing the pre-optimized binder composition. The structural integrity of the concrete cylinders was evaluated through compressive strength and split tensile tests following water curing periods of 7, 28, and 90 days. Results from the initial mechanical tests revealed that the optimum ternary binder composition was C60-F37.5-G2.5 cured for 90 days. While fiber reinforcement typically has limited impact on compressive strength, the addition of 1.5% PPF yielded better long-term compressive strength development compared with other PPF dosages. For tensile strength, 0.5%-1% PPF achieved the highest values at 28 days, whereas 1.5% PPF provided the peak performance under prolonged curing at 90 days. This shift in behavior is attributed to the progressive increase in fiber-bridging effectiveness over time. Findings from these mechanical tests were supported by the results from X-Ray Diffraction (XRD) analysis and optical microscopy.

Abstract: Soil stabilization is a critical technique in the geotechnical engineering discipline, whose main purpose is to enhance the mechanical properties and long-term durability of subgrade materials used in infrastructure construction. Of the wide range of stabilization techniques, lime treatment is especially common because it can cause profound physicochemical changes in the soil matrix. Through the use of mechanisms like cation exchange, flocculation, and pozzolanic reactions, lime modifies the soil properties, thus increasing workability, reducing plasticity, and allowing the formation of cementitious compounds, namely calcium silicate hydrates (C-S-H) and calcium aluminate hydrates (C-A-H). The by-products of these chemical reactions result in enhanced compressive strength, reduced volumetric instability, and enhanced resistance to environmental factors. This study offers a systematic analysis of international design recommendations relevant to soil-lime stabilization, focusing in particular on the methods utilized in the United States, France, and the United Kingdom. The expressed recommendations reflect significant differences in soil classification systems, testing methods, optimization of lime addition, and performance assessment criteria, reflecting the unique engineering practices and environmental settings present in each nation. Through a critical analysis of these methodological differences, this study aims to enable the implementation of more consistent, performance-based stabilization methods that enhance the sustainability and effectiveness of soil treatment procedures within the field of geotechnical engineering.

Abstract: Concrete and cement pastes belong to the most used building materials in human history and represent a solidified mixture of ordinary Portland cement (OPC), water, course and fine-grained aggregates. Fly ash is used as a pozzolanic additive to improve concrete properties. The fly ash property can also be modified by various treatments such as milling or size reduction with sieving. It was suggested that a beneficial pozzolanic reaction with fly ash gives high mechanical properties. Such pozzolanic reaction results in calcium silicate hydrate (C-S-H) phase formation. In this research comparative analytical EPMA study of the paste samples prepared with the addition of the milled and non-milled fly ashes has been performed to elucidate the pozzolanic reaction of the OPC with the milled and non-milled fly ashes. A higher pozzolanic reaction with CSH phase formation was observed in milled fly ash added paste.

Abstract: The research investigated the chemical, mechanical and durability of composites developed from aluminum slag. Aluminum slag is a hazardous residue product of secondary Aluminum smelting. The objective of this research was to study the chemical and geotechnical properties of Al slag. To investigate the stabilization of Al slag with fly ash and GBFS binder to enhance the pozzolanic reaction. Lastly, to study the properties of developed composites and recommend the application. Aluminum slag can be categorized as black or white, with the black dross (slag) having low metal concentration and a granular-like appearance comparable to sand. White dross (slag) has a high metal concentration and contains small quantities of oxides and salts, forming huge blocks. Aluminum slag is a by-product of the foundry industry that is deposited in landfills, causing pollution such as soil, air, and groundwater contamination, as well as affecting human health. Aluminum slag recycling has become more popular in recent years, and it can now be used to make concrete and bricks instead of cement. When compared to properties obtained from composites produced from cement, Aluminum slag improves several properties of the material in this study. Properties such as compressive strength, workability, and durability of the material are found to be improved. At 40% binder and cured at 80°C, the mortar sample made from Al slag, GBFS binder, and fly ash had the highest unconfined compressive strength (UCS) of 24 MPa. The optimum number of days for curing was found to be 14 days. Based on the overall research, it can be concluded that Aluminum slag produced from the foundry industries can be stabilized with fly ash and GBFS binder to produce bricks and concrete

Abstract: The development of new environmentally friendly binder from calcium carbide residue and fly ash wastes were investigated in this study. The key point of this work is difference to several previous investigations in that the optimized mixture proportion of the raw materials were calculated based on their chemical composition and their reaction. The compressive strength development over the curing age was also compared with reference mortar created with OPC binder. Mortar cubes were cast from the mix containing the calcium carbide residue and fly ash, at the optimized ratio. The compressive strength of the mortar was then monitored over an extended period: at 56 days it was 10.66 MPa, which is approximately 47% of the reference mortar. The morphologies and chemical compositions of the developed mortar showed the presence of spherically shaped of unreacted fly ash powder particles embedded in a cement C–S–H gel resulting from the pozzolanic reaction of raw materials.

Abstract: The research aimed to investigate the effect of calcium hydroxide content on pozzolanic reaction of calcined clays. Pozzolanic reaction of calcined clay was determined in terms of its mechanical properties, phase development and microstructures. Three clay minerals (two kaolinitic clays and kaolinite-montmorillonite clay) were chosen to produce pozzolanic materials via calcination at temperature of 700 °C to allow dehydroxylation of clay minerals. Ratios of calcium hydroxide to calcined clays were varied from 0.1 to 0.5. Mixing water contents or liquid to solid ratios (0.62, 0.75 and 0.80) and curing times (7 and 28 days) were also studied. It was found that calcium aluminosilicate hydrate (stratlingite) could be formed after pozzolanic reactions of all clay minerals. The development of stratlingite agreed with the strength development showing the highest compressive strength at 26 MPa (28 days) when kaolinite-montmorillonite clay was used as pozzolanic material and the ratio of calcium hydroxide to calcined clay was 0.5.

Abstract: The article presents the results of the evaluation of the strength of fine-grained concrete of ordinary grades on mixed cement binders with ash and slag waste of thermal power plants. To ensure the required strength, the preliminary activation of the mixed binder was envisaged, which is one of the main techniques for reducing cement consumption. Experimental-statistical models of the strength properties of fine-grained concrete was obtained, which make it possible to predict the required strength with a minimum consumption of cement and the optimal concentration of ash in the binder.

Abstract: Hydration is a chemical reaction in which the major compounds in cement form chemical bonds with water molecules and become hydration products. By the process of hydration Portland cement mixed with sand, gravel and water produces the synthetic rock we call concrete. The Therefore, the concrete properties always accompanies with the hydration degree of cement. This paper presents some experimental test results on how silica fume affects the cement hydration in cement pastes of the Reactive Powder Concrete as increasing levels of silica fume addition with the content from 0% to 30% of cement mass. The hydration process of cement/silica fume paste was followed from the estimation of heat of hydration, rate of heat evolution, of binder pastes obtained by isothermal calorimetry (TAM-Air). In addition, the portlandite content, the hydration degree of pure cement, reaction degree of binder paste as well as reaction degree of silica fume were investigated. The quantitative assessment on these characteristics are due to the simulation of the hydration of Portland cement pastes containing silica fume.

Abstract: Much of the current research on concrete engineering has been focused on including siliceous additions as supplementary cementitious materials (SCMs). Silica reacts with Calcium hydroxide release during cement hydration, and produces more C-S-H. The latter contributes to increase compactness, mechanical strengths and sustainability of concrete. This paper explores the hydration characteristics of cement paste based on various natural mineral additions, that are very abundant in Algeria and present a high silica content (ground natural pozzolana “PZ” and ground dune sand “DS”). For this purpose, several analyses were carried out on modified cement pastes and mortars. These SCMs were introduced by replacement levels of 15, 20 and 25 by weight of cement. We first, studied the effect of these SCMs on the heat of hydration and mechanical strength of mortars at different ages. The evolution of hydration of modified paste was studied, by using Thermal analysis (TG/TDA) at different ages, to analyze the Calcium Hydroxide (CH) content of the modified pastes. It is shown that the CH content of the mixes including SCMs is lower than that of the plain cement paste, indicating that silica reacts with the cement paste through a pozzolanic reaction. Increased pozzolanic activity results in higher amounts of Calcium Silicate Hydrate in the paste, which in turn results in higher compressive strength for modified cement mortars. Due to its crystalline morphology, the ground DS particles present a partial pozzolanic effect, compared to PZ which is semi-crystalline. Modified mortars by 20% DS can be the optimal composition. It presents satisfactory results: good mechanical strength and low heat of hydration. It can lead to an economic and sustainable concrete. Ground DS is very abounded in Africa and free of any impurities and can be a good alternative SCMs in cement industry.

Abstract: Application of various pozzolanic materials is the current approach to obtain suitable environmental, economic and durability parameters of composites, in which they are used. Considerable interest is focused on the possibilities of finely ground ceramic powder (CP) exhibiting pozzolanic activity. Present paper is aimed at the experimental study on the monitoring of reaction kinetics in lime-ceramic powder system (1:1). Ceramic powders with controlled grading were used. Reaction capacity was assessed in time by means of thermogravimetry. The dominant effect of the finest fractions (up to 0.030 mm) on the pozzolanic reaction was proved; coarser fractions of used CP exhibited approximately the half reaction efficiency after 28 days of curing.