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This study analysed the fine particle (<5 mm) waste generated during siliceous or calcareous (depending on the composition of the original aggregate) concrete waste crushing. In the absence of industrial applications, such waste is amassed in open-air stockpiles on construction and demolition wastes (CDW) management plant grounds. The aim pursued was to find an outlet for that material in the cement industry. The starting waste, sourced from six Spanish management facilities, was characterised for its chemical and mineralogical composition, physical properties and pozzolanicity. The mineralogical phases in the CDW/lime system and their variations during the pozzolanic reaction were likewise identified. The findings showed that the fine waste consisted primarily in quartz, calcite, micas and feldspars, with smaller fractions of kaolinite and cement anhydrous phases. No portland cement hydration phases were identified. All six types analysed exhibited medium to low pozzolanicity, with the highest values recorded for the siliceous waste. Ettringite, C–S–H gels and calcium aluminate hydrates (C4AH13, C4AcH12) were identified during the pozzolanic reaction in CDW/lime system. Therefore, this type of waste can be reused as supplementary cementitious material with low-medium pozzolanic activity.

Silica fume is the most performing siliceous product among the pozzolanic materials. This is mainly related to his high content (around of 90%) of amorphous silica. However, this residue has a high cost and the quantities available are limited. This limits its use in the modern construction industry, particularly in developing countries. For this reason it is motivating to look for an alternative to replace it with other waste materials with similar behavior, especially in these countries. It is known that bamboo leaf ash (BLAsh) is a pozzolan with high reactivity, possessing a high amount of amorphous silica. The paper presents a qualitative and quantitative characterization of the pozzolanic reactivity of bamboo leaf ash (BLAsh) and silica fume (SF). The pozzolanic activity is evaluated by using a conductometric method. In this method the electrical conductivity in a BLAsh/Ca(OH)2 and SF/Ca(OH)2 solution is measured with the reaction time. Latter, a kinetic-diffusive model is applied which allows computing the kinetic parameters of the pozzolanic reaction. The values of these parameters, specifically the reaction rate constant, characterize the reacting process and allow evaluating quantitatively the pozzolanic activity of these materials. The application of other experimental techniques employed in this research [X-ray diffraction (XRD) and scanning electron microscopy (SEM)], support the results coming from the conductometric method. The results show that BLAsh and SF are formed fundamentally by amorphous silica with a high pozzolanic activity. The comparison of BLAsh with SF allows concluding that both have a similar reactivity with reaction rate constant of 4.78 × 10−1 and 5.11 × 10−1 h−1 respectively. This fact reveals the importance of this agricultural residue for their use in the manufacture of blended cements.

The paper presents a study of the pozzolanic activity of Cuban bamboo leaf ash. To evaluate the pozzolanic activity a conductometric method was used, which is based on the measurement of variation in electrical conductivity of a bamboo leaf ash (BLAsh)/lime solution with reaction time. Later, the kinetic parameters (in particular, the reaction rate constant and free energy of activation) are quantified by applying a kinetic-diffusive model. The pozzolanic activity is quantitatively evaluated according to the values obtained of the kinetic parameters. Other experimental techniques, such as X-ray diffraction and scanning electron microscopy, which complement the results coming from the conductometric method, were applied. Also, the paper reports on the influence of calcining temperature (500, 600 and 700 C) on the pozzolanic activation of the bamboo leaves. The results show good pozzolanic properties of bamboo leaf ashes for temperatures between 500 and 700 C, and only a little difference on the activation of bamboo leaf ash as a function of the calcining temperature applied. The BLAsh calcined at 500 C showed the highest pozzolanic activity.

In the context of cement industry sustainability and socio-economic development, one of the primary objectives of the circular economy is the use of industrial waste as a supplementary cementitious material in the manufacture of future eco-efficient binders. This paper reports a first-time study of the effect of large proportions of the activated carbon (AC) waste used in low clinker cements on the properties and structure of the new binders. The behaviour of blended cement matrices prepared with 20%–50% AC as a pozzolan was analysed in terms of their chemical, mechanical and physical (rheology, heat of hydration, drying shrinkage, microporosity) properties. Macroporosity was also assessed with computed tomography (CT). The findings showed that these blended cements meet standard chemical and rheological requirements and that the 50% AC binder qualifies as a low heat cement. Drying shrinkage was observed to intensify with higher percentages of AC. A rise in total porosity was attendant upon pore size refinement, with an increase in the <100 nm fraction. Compressive strength declined with rising replacement ratios. Further to the CT findings, macroporosity (0.001–0.09 mm3) also increased with AC content, especially in the binders bearing 50% of the addition.

Due to economical and sustainable issues there is growing interest in investigating agro-industrial wastes as alternative route for future eco-efficient and sustainable pozzolans. The generation of ashes from cogeneration processes in which sugar cane wastes are used as biomass, involves significant environmental, social and health problems when they are accumulated in dumps. This paper explores the scientific and technical aspects of two Brazilian sugar cane ashes from different processes of production: one from an industrial cogeneration process and another from laboratory scale, maintaining the same proportions of mixture (50% mixture of bagasse and leaf). Subsequently, their behavior in ordinary Portland cement matrices made with 20% ashes substitution was analyzed. The results show that the industrial ashes presented variations on the chemical and mineralogical compositions, pozzolanic reaction rate and different formation of hydrated phases with respect to the laboratory ashes. The 20% blended cements complied with the chemical, physical and mechanical requirements set out in the existing Standards, maintaining the mechanical performance with respect to the control mortar at 60 days of curing.

This paper presents for the first time the influence of mixing different thermally activated paper sludges (APS) and fly ash (FA) on the pozzolanic reaction kinetics in APS–FA–Ca(OH)2 systems as a previous step to manufacture the future commercial ternary blended cements. In this study, two paper sludge wastes from different origins and activation conditions (laboratory (LS) and industrial (IS) scale) have been investigated, once mixed with fly ash at a ratio of 1:1 by weight. The results indicated that binary blends of pozzolans exhibited a high pozzolanic activity, showing that the hydrated phases produced during the pozzolanic reaction depend on the origin and activation conditions of clay wastes. At all times of reaction, the predominant phase turn out to be the LDH structures when LS pozzolan was used; meanwhile for the IS pozzolan the C4ACH12 along with the LDH were the main phases during the first 28 days.

Zeolites generally show pozzolanic activity due to their structural characteristics. The utilisation of pozzolans as additions to cements results in added technical advantages of the construction materials. In this study, the pozzolanic activity of a thermally treated natural mordenite- type zeolite from the Palmarito open-air deposit (Cuba) was evaluated with respect to a non-treated zeolite. Initially, a thermal treatment of the zeolite was performed at different temperatures within the range 300–1000 C for 5 h in order to evaluate the better temperature of treatment. Afterwards, the pozzolanic activity was determined for each temperature after 7 days of reaction with a saturated Ca(OH)2 solution that simulates the release of lime from ordinary Portland cement during the hydration reaction. The higher pozzolanic activity was achieved with the thermal treatment performed at 300 C. Therefore, a further study studied the evolution of the mineralogical phases produced during pozzolanic reaction up to 90 days, carried out with the zeolite treated at that temperature. Consumption of Ca2? in solution and formation of C–S–H-like phases with low Ca/Si ratio were experimentally observed as the main pozzolanic products. The thermodynamic study confirms high reactivity of the zeolite at short-term and chemical stability of the reaction products after 28 days. The zeolite thermally treated at 300 C confirmed an increase in the pozzolanic activity with respect to the nontreated zeolite.

The worldwide production of bamboo generates large volumes of leaf wastes, which are deposited in landfills or burned in an uncontrolled manner, with negative effects in the environment. The ash obtained by calcining of the bamboo leaf waste, shows good qualities as supplementary cementing material for the production of blended cements. The current paper shows a detailed scientific study of a Brazilian bamboo leaf ash (BLA) calcined at 600 °C in small scale condition, by using different techniques (XRF, XRD, SEM/EDX, FT–IR, TG/DTG) and technical study in order to analyse the behaviour of this ash in blended cements elaborated with 10% and 20% by mass of BLA. The results stated that this ash shows a very high pozzolanic activity, with a reaction rate constant K of the order of 10−1/h and type I CSH gel was the main hydrated phase obtained from pozzolanic reaction. The BLA blended cements (10% and 20%) complied with the physical and mechanical requirements of the existing European standards.

[EN] For proper management of wastes and their possible recycling as raw materials, complete characterization of the materials is necessary to evaluate the main scientific aspects and potential applications. The current paper presents a detailed scientific study of different Brazilian sugar cane bagasse ashes from the cogeneration industry as alternative cementing materials (active addition) for cement manufacture. The results show that the ashes from the industrial process (filter and bottom ones) present different chemical and mineralogical compositions and pozzolanic properties as well. As a consequence of its nature, the kinetic rate constant (K) states that the pozzolanic activity is null for the bottom ash and very low for the filter ash with respect to a sugar cane bagasse ash obtained in the laboratory under controlled burning conditions (reference). The scarce pozzolanic activity showed by ashes could be related to a possible contamination of bagasse wastes (with soils) before their use as alternative combustibles. For this reason, an optimization process for these wastes is advisable, if the ashes are to be used as pozzolans.

[EN] It is well known that the transformation of some clay minerals into pozzolanic materials for the manufacture of Portland cements depends on the activation conditions. In the current paper, a study was carried out to evaluate the effect of activation temperature in the range of 500–700°C on the characteristics of thermally activated clay wastes (ACWs). Different chemical, morphological, mineralogical and pozzolanic characteristics as well as kinetic parameter determinations were analysed in order to provide a complete study of the activated products and the viability of their use in the manufacture of blended cements. The results obtained showed that activation temperature plays a special role in the mineralogy of ACWs as well as their pozzolanic behaviour. Mineralogically, the ACWs were essentially formed from calcite and talc; kaolinite and chlorite were also identified depending on activation conditions. The values of the kinetic parameters indicated different pozzolanic activity of the ACWs, mainly over the short term.

[EN] A natural mordenite-type zeolite from Palmarito ore deposit (Cuba) was studied along the reaction with a saturated lime solution at 40 °C in order to determine its pozzolanic activity. Ca(OH)2 is an alkali activating agent that simulates the release of lime from ordinary portland cement during the hydration reaction. Formation of C–S–H-like phases with very low Ca/Si ratio (below 0.8) was observed in agreement with previous studies, however, the transformation of the original mordenite into a heulandite–clinoptilolite-type secondary zeolite was also detected. A thermodynamic approach was used to evaluate the stability of the zeolite minerals and showed that clinoptilolite is the most stable zeolite that forms under the experimental alkaline conditions. The results indicate that not all Ca2+ consumed from solution is used in the pozzolanic reaction. Calcium aluminates hydrates were not detected as products of the alkali-activated reaction.

[EN]The present paper describes a study of the influence of calcining temperature (800 and 1000°C) on the activation of sugar-cane bagasse. The reaction kinetics in a bagasse ash–lime system were investigated by means of X-ray diffraction patterns and thermogravimetric curves. The kinetic parameters were calculated by applying a kinetic– diffusive model. The results obtained in this study show, on one hand, that the bagasse ash calcined at 800 and 1000°C has a similar pozzolanic activity after 28–90 days of reaction. There were, however, important differences with regard to its activation rate. On the other hand, no crystalline compounds from a pozzolanic reaction were detected. The values of the kinetic parameters confirmed the different activation of bagasse ash as a function of the calcining temperature applied.

[EN] This paper presents a study of the pozzolanic reaction kinetics between calcium hydroxide and a mixture of sugar cane bagasse with 20 and 30% of clay, burned at 800 and 1000°C (SCBCA) by electrical conductivity measurements. A kinetic–diffusive model produced in previous studies by some of the authors was used. The model was fitted to the experimental data, which allowed the computation of the kinetic parameters of the pozzolanic reaction (reaction rate constant and free energy of activation) that rigorously characterised the pozzolanic activity of the materials. The results show that SCBCA demonstrated reactivity and good pozzolanic qualities in the range 800–1000°C.

[EN] The paper presents a comparative study in which different kinetic models were applied to describe the reaction kinetics of a mixture of sugar cane straw with 20 and 30% of clay, burned at 800 and 1000°C (SCSCA), and hydrated lime [calcium hydroxide (CH)]. Classical models, such as the Jander, Jander Modified and Zuravlev models were applied. These models were compared with a kinetic-diffusive model previously published by some of the present authors. The models were fitted to the experimental data by computerised methods, which allowed the computation of the kinetic parameters that rigorously characterise the pozzolanic activity of the materials. The results showed that Jander, Jander Modified and Zuravlev models did not describe the pozzolanic reaction kinetics in this system correctly, whereas the model proposed by the authors gave the best results with respect to fitting to the experimental data. This demonstrated that the model proposed by the authors was the most adequate for describing the reaction kinetics in the SCSCA system.

[EN] The reaction kinetics of a mixture of sugar cane straw with 20% and 30% of clay burned at 800 and 1000 °C and lime (calcium hydroxide) is studied. A direct method (accelerated chemical method) based on the measurement of the amount of lime reacted as the reaction proceeds is applied. A kinetic–diffusive model published in a previous paper by some authors of this research is used. The fitting of the model by computerized methods allows determining the kinetic coefficients that characterize the process: in particular, the reaction rate constant. The index of pozzolanic activity evaluated according to the obtained values of the reaction rate constant permits to characterize the pozzolanic activity of these materials in a rigorous way. The results are compared with the results obtained applying an indirect method (conductometric method). The kinetic results obtained in the current paper allow affirming that the kinetic–diffuse model used in order to evaluate the pozzolanic reaction is valid, independently of the method used for the evaluation of the pozzolanic activity.