Avocado peel ash as a supplementary cementitious material: study of a new binder

In this research, avocado peel ash was tested as a supplementary cementitious material to Portland cement in mortars. The characterization of the material showed high potassium and iron content, implying that the material is not a pozzolan, but has potential for application as a cementitious material due to its amorphous structure and granulometry compatible with cement. Tests of mass density in the fresh state, incorporated air, calorimetry, water absorption, mass density in the hardened state and compressive strength at 7 and 28 days were tested, using compositions 1:3:0.60 (cement: sand: water), with replacement of 0, 5 and 10% of cement by avocado peel ash. The results of the consistency and incorporated air test showed that avocado peel ash reduces workability when compared to the reference composition but causes a reduction in water absorption and an increase in compressive strength, when used in 5% replacement. Furthermore, avocado peel ash causes a delay in cement hydration, increasing the dormancy in calorimetry tests, although this does not imply a reduction in strength at 7 and 28 days for 5% composition. This occurs because the use of avocado peel ash promotes the formation of a hydrated potassium-calcium fayalite phase as a complement to the formation of C–S–H, as demonstrated in the XRD, DTA/TGA and SEM results. However, the use of 10% avocado peel ash promotes the delay in cement setting, reducing compressive strength at 7 and 28 days because of the high content of K₂O and Al₂O₃ present in the material. It is concluded that the use of avocado peel ash is viable as a supplementary cementitious material, if it is limited to contents of 5%.