Properties and microstructure of alkali-activated red clay brick waste

Sintered red clay ceramic is used to produce hollow bricks which are manufactured in enormous quantities in Spain. They also constitute a major fraction of construction and demolition waste. The aim of this research was to investigate the properties and microstructure of alkali-activated cement 21 pastes and mortars produced using red clay brick waste. The work shows that the type and concentration of alkali activator can be optimised to produce mortar samples with compressive strengths up to 50 MPa after curing for 7 days at 65 °C. This demonstrates a new potential added value reuse application for this important waste material.

14 Different alternatives have been proposed to reduce the environmental impact of cement and these 15 include reusing waste materials to produce low-CO 2 cement binders. In the study by Puertas et al.

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This research aimed to optimise alkali-activation of RCBW and understand the influence of the type 6 and concentration of alkali activator used on the mechanical strength and microstructure of the binders 7 formed. As-received RCBW was crushed to give a granular material with particles less than 4 mm in diameter.

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The microstructure of RCBW paste samples was examined using SEM-EDX (JEOL JSM-6300). X-ray 8 diffraction (XRD) was used to identify mineralogical phases (Philips diffractometer PW1710 with Cu K 9 radiation, 40 kv and 20 mA, 2 from 5-55º). Fourier transformed infrared spectroscopy (FTIR) analysis 10 of the nanostructure of the materials obtained was conducted with a Mattson Genesis II spectrometer.

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According to Duxson et al. [13], this is because zeolitic-like phases are less likely to form in highly 5 concentrated solutions due to increased difficulties in phase transport and reorganization. found to be largely unreactive [12], and remained in the sample after the alkali-activation process.

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Paste showed a peak that did not appear in the raw material, denoting the formation of  Fracture surfaces of alkali-activated RCBW pastes are shown in Fig. 11. RCBR particles can be  1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25  26  27  28  29  30  31  32  33  34  35  36  37  38  39  40  41  42  43  44  45  46  47  48  49  50  51  52  53  54  55  56  57  58  59  60  61  62  63  64  65 11 complete reaction depends on the particle size. This has led to the development of different 1 morphologies, giving rise to a heterogeneous microstructure containing unreacted ceramic waste 2 particles surrounded by alkali-activation reaction products. It seems that smaller particles were 3 completely dissolved by the alkali solution, while the larger ones are only partially reacted. The 4 strengthening or weakening effect will depend on whether the particles themselves are strong or 5 weak, and also whether they are bonded on the surfaces to the matrix. Studies performed by Yungsen 6 et al. [38] showed that the unreacted particles reduced the compressive strength while Kourti et al.