Monitoring the reactivity of pozzolans by thermogravimetric method

This work fits within the framework of sustainable management of sludge generated from wastewater treatment in industrial network. The studied sludge comes from an industry manufacturing sanitary ware products.Physico-chemical and mineralogical characterization was performed to give an identity card to the sludge. We noted the absence of metal pollution.The industrial sludge has been subjected to thermal activation at various temperatures (650°C to 850°C). The pozzolanic activity was evaluated by physico- chemical and mechanical methods [1]. Pozzolanicity measurement was carried out based on Chapelle test and conductivity revealed the existence of pozzolanic properties of the calcined samples. The best pozzolanic reactivity was obtained for the sample calcined at 800°C. We noticed a decrease in the reactivity of the sample calcined at 850°C. In addition, analysis by means of X-ray diffraction and Fourier transform infrared spectroscopy showed that sludge recrystallization begins at a temperature of 850°C. Pozzolanicity index of the thermally treated samples was determined by measuring the mechanical resistance of mortar specimens previously kept in a saturated lime solution for 28 days (ASTM C618 [2]). The best pozzolanic activity index was obtained for the sample calcined at 800°C (109.1%).This work is a contribution to the research for new supplying sources of raw materials and additives in the field of construction. It presents a proposition of a promising solution for the valorization of waste material as an additive instead of being discharged into open air dumps causing a major environmental problem.

Reactivity of raw, pyroprocessed and GGBS-blended alum sludge (AS) waste for sustainable cement production

Part 1 of the current paper demonstrated the lack of agreement between the results obtained from different standard pozzolanic activity tests. This can be explained by the significant differences observed in the recommended test procedures that, in some cases, allow variations in parameters which have a remarkable influence on the pozzolanic reaction. Given this fact, the part of the research programme presented here was conducted to verify the actual influence of several different parameters on the consistency and compressive strength of mortar specimens. These parameters included water/cementitious materials ratio, pozzolan type and content, type of cement, age and presence of water-reducing admixtures. It was found that the performance exhibited by pozzolans in these tests did not correlate with that obtained in standard pozzolanic activity index tests shown in the first part of this research.

Studies of the use of agricultural wastes or natural resources as cement replacements have increased in recent years. The evaluation of their pozzolanic activity is essential to predict the behavior of modified cementitious materials elaborated with these resources. This work presents a study of the pozzolanic activity of bamboo stem ashes, which were obtained by calcining bamboo stem at 600 °C for 3 h in a calcination furnace. Several methods such as Chapelle test, saturated lime method, thermogravimetric analysis and strength activity index were proposed to evaluate the pozzolanic activity. The results of X-ray fluorescence and X-ray diffraction indicate that bamboo stem ashes are mainly composed of Silica (SiO2) with an amorphous phase. The Chapelle test and the saturated lime method showed the pozzolanic activity of bamboo stem ashes. Finally, at 7 and 28 days, mortars containing 10 % by weight of bamboo stem ashes show a strength activity index greater than 75 % as recommended by ASTM C618.

The aim of this study is to compare sinking beads (SB) with fly ash (FA) and metakaolin (MK) with regard to their ability to improve the performance of concretes. The workability, compressive strength, free shrinkage and chloride resistance of concretes with and without the above mineral admixtures are investigated. To explicate the differences of above results, the pore structure and pore solution chemistry were also studied. Besides, the Chapelle test was adopted to compare the pozzolanic activity of the mineral admixtures. The water-to-binder ratio of concretes and pastes was 0.35 by mass. The incorporation level of MK was 5 and 10 wt%, while that of FA and SB was 10, 20 and 30 wt%. A systematic improvement in flowability, compressive strength, chloride resistance, free shrinkage is observed for SB concretes compared with FA concretes due to the smaller particle size, more round particle shape and higher pozzolanic activity of SB. MK shows the overwhelming ability to improve compressive strength and chloride resistance ability of concretes compared with SB and FA for the same replacement level, but comparable compressive strength and chloride resistance for SB concretes can be obtained by increasing the content of SB. In addition, inclusion of 20 wt% SB demonstrates remarkable potential to reduce free shrinkage to 25% less than concretes with 10 wt% MK. It may be ascribed to the dense structure of SB, which brings less volume reduction or even some increase during pozzolanic reaction.

: Chemical, physical, and mechanical tests were conducted to assess the feasibility of using naturally occurring pozzolan as a ce-ment mortar additive. One test series assessed the feasibility of substituting pozzolan for a portion of cement in concrete mortar mixtures. The chemical composition of five natural pozzolans was determined. Compressive testing was conducted on specimens with varying amounts and types of pozzolan. One pozzolan was found suitable for cement replacement in Type M mortars, and one was suitable for cement replacement in Type N mortars at a different proportion. The results indicate that, within certain mixture percentage limits, partial replacement of cement with pozzolan does not compromise mortar compressive strength. A second test series evaluated four mixes prepared using three types of natural pozzolan as well as Class F fly ash. The effective-ness of each cement replacement material in controlling alkali-silica reactions was studied. Correlations were made between the mechanical properties of the proposed mixes and a Portland cement control mix. The results were also compared with industry standards for mortars made with fly ash and silica fume. Results indicate that one type of pozzolan may be used as a substitute for fly ash, but not for silica fume.

Comparing pozzolanic activity from thermal-activated water-washed and coal-series kaolin in Portland cement mortar

Hollow glass microspheres (HGMS) have been widely used in the hydrocarbon industry for cementing wells with low-density slurries. These consist of amorphous siliceous hollow spheres filled with gas, providing a low-density material with high compressive strength. The present study aims to characterize the interaction between HGMS and the cement paste, focusing mainly on the development of the pozzolanic activity, given the nature of amorphous silica. Thus, two HGMS of different crush strength were studied. HGMS were used as a replacement of total cementitious binder at 10% by weight of cement. The pozzolanic activity was measured with the modified Chapelle test, the portlandite quantification with thermogravimetric analysis, and the strength activity index comparing the compressive strength of hardened cement paste samples. Additionally, isothermal calorimetry analysis, X-ray diffraction patterns and scanning electron microscopy images were obtained. Results demonstrated that HGMS interact with the cement paste initially as nucleation agents and later with a pozzolanic reaction, presenting an activity comparable to that of metakaolin or fly ash.

Kaolin is an industrial mineral used in a wide variety of applications due to its crystalline structure, mineral and elemental composition. After kaolin undergoes heat treatment in a specific temperature range, metakaolin, which exhibits a strong pozzolanic reaction, is formed. This paper examines the effects of different kaolin qualities on the thermal activation process of metakaolin production. The qualities of kaolin depend on the impurities they contain, such as mica, feldspar and quartz. In this study, four different samples of kaolin are investigated. Each sample was heat treated in a lab-scale rotary kiln in order to study the chemical, structural and morphological changes that occurred and their influence on pozzolanic activity. The parameters being considered in the experimental process were the temperature and the duration of the treatment. Thus, the calcination process for each of the four kaolin types was carried out at 600, 650 and 700 °C for 3 h. The occurred changes were monitored using XRD, FTIR and DTA analysis. Additionally, the reactivity of all thermally treated samples was evaluated based on the Chapelle test. The results showed that the fewer the impurities, the easier the transformation of the material to metakaolin. The optimum result was the metakaolin, which originated from the purest quality of kaolin and was comparable to the commercial product. Finally, the pozzolanic activity of the thermally activated samples also depended on the purity of the kaolin.

Rice husk, an abundant agricultural waste rich in silica (SiO2), is a promising material for use in cement-based composites. When thermally treated, rice husk is converted into rice husk ash (RHA) and rice husk biochar (RHB), both containing silica in different forms (amorphous and crystalline) and ratios that may affect pozzolanic reactivity. This study evaluated the pozzolanic activity of rice husk biochar (RHB) produced at 450°C and 650°C, and rice husk ash (RHA) as well as the effect of ball milling activation, for use in cement-based composites. The X-ray diffraction (XRD) analysis of the samples showed that RHA had a high degree of crystallinity, indicated by the sharp peak at 2θ ≈ 22° representing crystalline silica. This suggested that RHA, although rich in SiO2 (79.67%), may have limited pozzolanic reactivity due to its crystalline structure. In contrast, both RHB 450°C and RHB 650°C were predominantly amorphous, with broad, low-intensity humps around 2θ ≈ 22°. The amorphous nature of these structures, along with the SiO2 content in RHB at 450°C (33.50%) and 650°C (41.30%), suggested a higher potential for pozzolanic reactivity compared to crystalline silica, confirming the presence of silica in a more reactive form conducive to pozzolanic activity. Furthermore, the ball mill activation could enhance the active surface area of RHA and RHB, resulting in enhancement of the pozzolanic reactivity. Such results could improve the hydration reaction by forming additional calcium silicate hydrate (C-S-H), a crucial component for early strength development where it could effectively fill voids within the cement matrix. This contributes to increased compressive strength, reduced porosity, and enhanced durability of the composite. This research provides insights into the use and preparation of RHB in low-carbon concrete composites, offering an innovative approach to enhancing material properties and reducing cement demand in construction.

در شمال محور آبیک- قزوین واحدهای آتشفشانی متنوعی شامل اولیوین‌بازالت، بازالت، آندزی‌بازالت، داسیت، تراکی‌آندزیت و توف­های همراه، با سن ائوسن تا پلیوکواترنر رخنمون دارند. به منظور یافتن ویژگی‌های ژئوشیمیایی و سنگ‌نگاری تأثیرگذار در کیفیت پوزولان، فعالیت پوزلانی 5 نمونه از سنگ­های مختلف منطقه در آزمایشگاه مرکز تحقیقات ساختمان و مسکن مطالعه شد. این نمونه­ها در این آزمایشگاه خردایش و بر روی آنها آزمایش­های تعیین فعالیت پوزولانی با استفاده از روش ترموگراویمتری انجام شد. واحدهای توفی با بافت شیشه‌ای کم و بیش سالم با فعالیت پوزولانی 83/26 درصد مناسب­ترین نتیجه، واحدهای توفی به نسبت دگرسان و واحد داسیتی با فعالیت پوزولانی 21 تا 24 درصد و در رده متوسط تا خوب قرار می­گیرند. توف­های لیتیک‌دار فعالیت پوزولانی 70/19 درصد دارند و در رده ضعیف قرار می‌گیرند. بنابراین در منطقه به طور کلی واحدهای توفی شیشه­ای بدون دگرسانی و داسیت­ها، برای استفاده به عنوان پوزولان مناسب و واحدهای با دگرسانی بالا و لیتیک­دار بدون کیفیت پوزولانی هستند.

Construction and demolition waste accounts for a significant amount of the total solid waste produced worldwide, and its recycling is challenging. Although some demolition waste is processed into recycled sand and rubble, the finer fractions resulting from screening and washing of recycled aggregates are not used. This research investigates the potential of use of real demolition wastes, namely concrete screening fines (CS), mixed concrete-ceramic screening fines (MS), and mud from recycled aggregates washing (WM), as supplementary cementitious materials (SCMs) in eco-efficient blended cement. The study employed various experimental methods, such as isothermal calorimetry, thermogravimetric analysis (TGA), and setting time tests, to evaluate the hydraulic activity of waste materials and the Chapelle test and TGA to assess their pozzolanic activity. The mechanical properties and microstructure of mortars containing 20% of waste powders were evaluated using compressive strength tests and scanning electron microscopy (SEM). The results showed that thermal treatment of waste materials at 500 °C improved the mechanical properties of mortars, increasing Strength Activity Index (SAI) by 10% for CS and MS and by 6% for WM after 90 days of curing. All three waste types achieved similar mechanical properties, with compressive strengths of at least 37.93 MPa, 46.25 MPa, and 51.33 MPa after 7, 28, and 90 days of curing, respectively. The contribution of waste powders to mortar strength was due to filler effect and partially dehydrated C-S-H products. However, pozzolanic ceramic inclusions in waste powders did not affect mortar strength at a 20% substitution rate. Therefore, the research findings indicate that waste materials derived from demolition can potentially be used as environmentally friendly materials in construction. Their use as SCMs with a substitution rate of 20% can reduce the CO2 emissions of cement production by at least 10.7%.

The current methodologies used for the selection and classification of pozzolans present certain chemical and physical requirements that may restrict their use. A good example of this is the use of the pozzolanic activity index as the main parameter in the selection and classification of pozzolans. This is determined by several different methodologies that do not take into account a number of factors that influence pozzolanic reaction. The current paper presents a comparison of the pozzolanic activity index results obtained from several test procedures prescripted by Brazilian, American and British Standards to evaluate three types of pozzolan: fly ash, silica fume and rice-husk ash. Two ordinary Portland cements of different brands were used in the tests. It was noted that in most cases the current standard test procedures led to some distinct and sometimes conflicting results. It is suggested that a complementary investigation is needed to determine which methodologies are most suitable for the selection of pozzolans to be used in mortar and concrete; this is presented in Part 2 of the current paper.

Assessment of pozzolanic activity of calcined coal-series kaolin

Five local clays were characterised by several physicochemical methods to predict their pozzolanic reactivity. The studied samples were treated thermally at 600, 700 and 800°C. The heat-treated samples were characterised by X-ray diffraction. The pozzolanic activity was assessed by chemical (Chappelle test), mechanical (compressive strength at 28 days) and physical (differential thermal analysis/thermogravimetry) methods. It was found that under the chosen conditions, the kaolinitic clay fraction was transformed to an amorphous phase that was reactive with lime, whereas the illitic phase remained in a crystalline form and was consequently unable to produce pozzolans. The montmorillonitic fraction started to gain pozzolanic activity above a calcination temperature of 700°C. It was also demonstrated that the pozzolanic activity of the clays calcined at 700°C was directly related to the percentage of kaolinite in the crude samples. The hydration products were C–S–H and C4AH13, and C3AH6 and C2ASH8 were also detected in samples that were rich in alumina.