In the context of world concern with the environment, this study aims to characterize an auto-combustion produced bamboo leaf ash (BLA) by its pozzolanic behaviour, reactivity and its influence in the total porosity, pore size distribution, tortuosity and mechanical behaviour of cementitious matrices. The chemical and physical characterization of the BLA was carried using X-ray fluorescence, determination of amorphous silica content, X-ray diffraction, Fourier Transform Infrared Spectrophotometry (FTIR), laser granulometry and field emission scanning electron microscopy (FESEM). The assessed BLA is a siliceous material (74.23%) with an amorphous nature due to the amorphous silica content, which represents 92.33% of the total silica. The BLA was classified as highly reactive by assessing its pH and conductivity in a saturated calcium hydroxide (CH) medium for different proportions and temperatures. Frattini analysis, the study of CH:BLA pastes (Thermogravimetric analysis and FTIR) and Portland cement (OPC) /pozzolan pastes (Thermogravimetric analysis and FESEM) are in agreement with this classification. The replacement of OPC by BLA improved the mechanical behaviour of the cementitious matrices, as well their durability. All the mortars containing BLA presented very similar compressive strength to a control mortar (100% OPC) after only 3 days of curing and at the following tested curing ages: 7, 28 and 90 days. In the mercury intrusion porosimetry analysis, the pastes with 20 and 30% BLA content presented higher tortuosity or fewer connected pores than the control paste. Thus, the auto-combustion method proved to be successful and BLA is a suitable alternative for sustainable highperformance matrices.
h i g h l i g h t s Sugar cane straw ash (SCSA) was successfully used in alkali activated binders. New alkali-activated mixtures of SCSA and blastfurnace slag (BFS) were characterized. Total replacement of sodium silicate (SS) solution by SCSA enhanced sustainability. Good compressive mortar strength (37-48 MPa) was achieved without the use of SS. Replacement of 50% of BFS by SCSA showed an excellent mechanical behavior.
11In recent years, geopolymers have become a widely researched binding material. There are technological 12 and environmental advantages to using this type of binder instead of Portland cement. In this study,
13binary systems of geopolymers were produced by using mixtures of metakaolin (MK), a well-known 14 aluminosilicate raw material, and a residue from sewage sludge incineration: sewage sludge ash (SSA).
15This ash was used to partially replace the metakaolin in proportions of 0-20%. The mixtures were 16 activated with alkaline solutions and they were cured by using two different conditions: at room 17 temperature (25 ºC) and in a thermal bath (65 ºC). The samples were assessed by X-ray diffraction,
Due environmental problems related to Portland cement consumption, many studies have been performed to diminish its use. One solution is the development of alkali-activated binders, which can decrease CO 2 emissions and energy consumption by 70% when compared to Portland cement production. In addition, an alkali-activated binder presents mechanical properties similar to Portland cement mixtures, which turns into an interesting material in civil construction. Aluminosilicate-based materials are important raw materials to produce the alkali-activated binders. Therefore, two residues are presented as an aluminosilicate source in this study: fly ash (FA) and sugarcane bagasse ash (SCBA). Both residues were obtained from a combustion process to generate energy, the former from coal and the latter from the bagasse of the sugarcane industry. In addition, the alkaline activating solution is an important factor to achieve improved mechanical properties. In this context, this study investigated the influence of four different SiO 2 /K 2 O molar ratios (0, 0.36, 0.75 and 1.22) in the activating solution with a constant water content, and three FA/SCBA binder proportions (75/25, 50/50 and 25/75). Microstructural characterization was carried out by X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy, mercury intrusion porosimetry, pH and electrical conductivity measurements to study the evolution of the reaction process. The compressive strength of mortars was assessed in order to determine the optimum SiO 2 /K 2 O molar ratio and FA/SCBA ratio. The tests showed that a SiO 2 /K 2 O molar ratio of 0.75 and FA/SCBA proportion of 75/25 provided the best mechanical properties.
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