Investigation of mechanical activation effect on high-volume natural pozzolanic cements (original) (raw)
Related papers
Crystals, 2022
The aim of this study was to investigate the influence of fineness and heat-treatment on the pozzolanic and engineering properties of volcanic ash. To this end, two different fineness levels of volcanic ash, ultra-fine (VAF) and fine (VA), without and after heat treatment at different temperatures (VA550, VA650, and VA750), were partially substituted for cement. In addition to the control (100% cement), five binary mortar mixes, each containing 20% of the different types of volcanic ash (VAF and VA; heat-treated and not), were prepared. First, X-ray fluorescence (XRF), X-ray powder diffraction (XRD), particle size analysis, and modified Chappelle tests were used to characterize the material. All mortar mixes were then tested for compressive strength development, water absorption, and apparent porosity. Finally, the microstructure of each of the mixes was evaluated by performing XRD, thermogravimetric analysis (TGA), and Fourier transform infrared spectroscopy (FTIR) analyses on past...
Comparative Study of Chemically and Mechanically Activated Clay Pozzolana
Burnt clay pozzolana produced from a clay deposit at Mankranso in Ghana has been activated by mechanical means through roll milling and ball milling as well as chemically by the addition of 1% - 4% m/m Na2SO4. The pozzolana sample was chemically suitable with total SiO2 + Al2O3 + Fe2O3 content ≥70% as stipulated by the ASTM C 618 standard. The particle sizes, surface characteristics and specific surface areas obtained by the types/degrees of milling were analyzed and their effect on the strength development of Portland pozzolana cement mortar cubes prepared from the pozzolana samples was evaluated. Compressive strengths obtained showed that the activated pozzolana could be used to replace up to 40% ordinary Portland cement (OPC) and satisfy the EN 197-1 and ASTM C 595 standard requirements. Comparatively, the chemically activated pozzolana cement mortars attained higher compressive strengths than the mechanically activated pozzolana cement mortars at equal ages of tests and the same pozzolana content levels. The chemically activated pozzolana cement mortars attained higher 2 day strengths than OPC at sulphate concentrations of 3% and 4% for all pozzolana content levels between 30% - 40%. SEM image and insoluble residue in HCl of a 2 day old chemically activated pozzolana cement paste confirmed dissolution of fine pozzolana particles in the alkaline media which influenced higher early age strengths. The highest 28 day compressive strength of 54.2 MPa was obtained at 4% sulphate concentration and 30% pozzolana content for the chemically activated pozzolana. The highest 28 days compressive strength for the mechanically activated pozzolana was 35.6 MPa—obtained for the roll milled product at 30% pozzolana content. Standard consistence of the pozzolana cement pastes increased with increasing pozzolana fineness and pozzolana content. Increasing Na2SO4 concentration however had no effect on standard consistence. Setting times decreased with increase in both fineness and sulphate concentration. The EN 197-1 standard for initial setting time was satisfied by the chemically activated pozzolana cement mortars at all pozzolana content levels. Pozzolana samples activated by roll milling and 36 h ball milling had faster initial setting times than the EN 196-1 standard at all pozzolana content levels beyond 30%. The ASTM C 595 requirement for initial set was however satisfied at all pozzolana content levels.
Pozzolanic Characteristics of a Natural Raw Material for Use in Blended Cements
2009
In this study, the potential use of a natural raw material in the manufacture of blended cements was investigated. Mineralogical, petrographic and chemical analyses of the samples showed that the natural raw material was a porphyritic volcanic rock close to trachyandesite composition with a SiO 2 +Al 2 O 3 +Fe 2 O 3 content of 79.86%. Further experiments were also designed to determine the physical properties and pozzolanic activity of the raw material. The mortar samples, made with a binder of ground trachyandesite and lime, developed compressive and flexural strengths of 2.5 and 3.3 times respectively higher than those required for a natural pozzolan. Further tests revealed that when the ground trachyandesite replaced 30% w/w of Portland cement, the blended cements produced had the desired physical and chemical characteristics with compressive strengths higher than 32.9 N/mm 2 . These findings suggest that this material can be used in the production of blended cements.
Chemical activation and set acceleration of lime-natural pozzolan cement
CERAMICS SILIKATY, 2006
In order to shorten the setting time and to fasten the strength development of lime pozzolan cements, different methods including calcinations, acid treatment, prolonged grinding, elevated temperature of curing and addition of chemical activators have been tried to improve the pozzolanic reactivity of natural pozzolan. In this work, the effects of some chemical activators and set accelerators on set and strength behaviours of a lime-natural pozzolan cement containing 70% natural pozzolan of the type pumice and 30% hydrated lime (by mass) have been investigated. Results obtained show that addition of alkaline compounds and Portland cement clinker can improve the set and strength behaviours of lime-natural pozzolan cements. Sodium sulfate is the most effective chemical activator for lime-natural pozzolan cements compared to Na 2 CO 3 , NaOH, CaCl 2 ·2H 2 O, and ordinary Portland cement-clinker. The most effective set accelerator for the studied lime-natural pozzolan cement however is sodium hydroxide compared to Na 2 SO 4 , Na 2 CO 3 , NaCl, CaCl 2 ·2H 2 O and ordinary Portland cement-clinker. Addition of 6 wt.% Na 2 SO 4 could noticeably increase 90-day compressive strength and presence of 4% NaOH as a set accelerator could effectively decrease both initial and final setting times.
Crimson Publishers LLC, 2020
In this research work a synthetic review of the quantitative characterization of various materials (sugar cane waste ashes, bamboo leaf ash, calcined paper sludge, loessic soils, zeolite, fly ash and silica fume) based on the computing of the kinetic parameters of the pozzolanic reaction in pozzolan/calcium hydroxide(CH) systems is offered. The paper presents of more relevant results in the quantitative characterization (computing of the kinetic parameters) of the pozzolanic reaction of different materials originated from agriculture, mining or industry activities carried out by the authors.Two pozzolanic activity tests (conductometric method and accelerated chemical method) are employed. A kinetic-diffusive model (published by the authors in previous works) is used to describe the pozzolanic reaction. The kinetic parameters that characterize the process (in particular, the reaction rate constant and free energy of activation) are determined with relative accuracy in the fitting process of the model. The pozzolanic activity is quantitatively evaluated according to the results obtained for the kinetic parameters. This allows the comparison in a direct way of the pozzolanic reactivity of the materials, which is very useful for the employment of these materials for envisaged applications. The values of the reaction rate constant jointly with the free energy of activation give a precise index of the reactivity or pozzolanic activity of the materials. Complementary experimental techniques, such as X-ray diffraction (XRD) and scanning electron microscope (SEM), were also employed, but not shown in the paper for space reason since that would necessitate a much larger paper.
Revista IBRACON de Estruturas e Materiais, 2022
resumo: Portland cement remains the main material of choice in construction due to its thermal, mechanical and durability properties. However, there is growing concern about the large amount of energy consumed and the environmental pollution generated during its production. The objective of this study, therefore, was to evaluate the potential of the fine residual material produced by crushing basalt rocks to form a supplementary cementitious matrix through alkaline activation. Basalt powder with a particle size of less than 53µm was prepared and activated with a sodium hydroxide solution, with a sodium silicate solution as an adjuvant. The curing process of the material was also carried out at 5 temperature levels, 75, 85, 100, 115, 125°C, according to the experimental design. The paste was dry curing at a standard digital laboratory oven for 24 hours. After curing, the compressive strength of the material was evaluated, reaching a mean value of 10.21 MPa for the H5S15T125 mixture a...
On the Utilization of Pozzolanic Wastes as an Alternative Resource of Cement
Materials, 2014
Recently, as a supplement of cement, the utilization of pozzolanic materials in cement and concrete manufacturing has increased significantly. This study investigates the scope to use pozzolanic wastes (slag, palm oil fuel ash and rice husk ash) as an alkali activated binder (AAB) that can be used as an alternative to cement. To activate these materials, sodium hydroxide solution was used at 1.0, 2.5 and 5.0 molar concentration added into the mortar, separately. The required solution was used to maintain the flow of mortar at 110% ± 5%. The consistency and setting time of the AAB-paste were determined. Mortar was tested for its flow, compressive strength, porosity, water absorption and thermal resistance (heating at 700 °C) and investigated by scanning electron microscopy. The experimental results reveal that AAB-mortar exhibits less flow than that of ordinary Portland cement (OPC). Surprisingly, AAB-mortars (with 2.5 molar solution) achieved a compressive strength of 34.3 MPa at 28 days, while OPC shows that of 43.9 MPa under the same conditions. Although water absorption and porosity of the AAB-mortar are slightly
Use of coal mining waste as pozzolanic material in new blended cement matrixes
2014
Research and eco-innovation geared to obtain alternative sources of raw materials from waste constitute pathways for enhancing the competitiveness of resource-intensive industries. Cement and concrete manufacture calls for new sources of new, highly pozzolanic products to improve the mechanical properties and durability of the resulting matrices, while at the same time reducing production costs and environmental impact. Spanish coal mining wastes generated in the extraction and washing steps from a mine in the Castilla-Leon region were investigated. Mineralogically, these wastes are composed by kaolinite (20-30%), illite (45-70%) and quartz (5-15). This composition is very interesting in order to activate, by controlled thermal activation, the present kaolinite that generates metakaolin, a highly pozzolanic product. Morphological, textural and microstructural changes affect the activity and reactivity of activated wastes. These first studies open up a new research line, practically ...
Cement and Concrete Research, 1999
A portland cement clinker, a natural pozzolan, and a granulated blast furnace slag (GBFS) were used to obtain blended cements that contain 25% mineral additives. The natural pozzolan, which was softer, was more grindable and granulated blast furnace slag, which was harder, was less grindable than the clinker. Two of the cements produced were obtained by intergrinding and the other two were obtained by separate grinding and then blending. All of the blended cements and the control cement without any additive had the same fineness as 3500 Ϯ 100 cm 2 /g Blaine fineness. During grinding, energy consumption of the mill was recorded and a sample corresponding to each energy level as taken from the mill at regular intervals and particle size distribution was determined. Cements produced were compared for change in particle size distribution during grinding and 1-, 2-, 7-, 28-, and 90-day compressive strengths points of view. Also, interactions between clinker and mineral additive portions of blended cements during intergrinding is highlighted.