Effects of acid attack and cassava flour dosage on the interfacial transition zone thickness, durability and mechanical characteristics of high-strength (HS) concrete

Due to its higher porosity, the interfacial transition zone (ITZ), that is, the zone between the hardened cement paste (HCP) and the aggregate, is the weakest point in concrete. It is less resistant to cracking than both HCP and aggregate, and microcracks begin in this zone when the load is applied and propagates into the mass of concrete. The goal of this research is to investigate how various dosages of cassava flour (CF) addition affect the ITZ and how this is related to the mechanical properties of concrete, including its resistance to sulfuric acid. CF is added as a percentage of Portland pozzolanic cement (PPC) used as a binder, with dosages of 1, 2, 3, 4, and 5%. The morphology of CF and PPC was studied using x-ray diffraction (XRD) and x-ray fluorescent (XRF) techniques. Changes in the thickness of the ITZ were observed using a scanning electron microscope (SEM). The effect of sulfuric acid was observed by immersing samples of concrete in a 2% sulfuric acid solution. The results show that adding CF up to 3% progressively reduced the thickness of ITZ and improved the densification of concrete. As more CF was added, the ITZ began to widen again, but even at 5% CF addition, the thickness of the ITZ remained well below that of the control. The workability of fresh concrete decreased with an increase in CF dosage, but CF addition increased the compressive, tensile, and flexural strengths of hardened concrete. The greatest compression resistance was achieved at a 3% cassava flour addition level, which was 83.8 MPa after 180 days of curing and 8.9 MPa, 4.7 MPa for flexural and splitting strengths, respectively, after 90 days of curing. All the concrete samples containing CF had lower strengths than the control after immersion in sulfuric acid, with the concrete with 3% CF performing better than the others. The research concludes that CF used as an additive to concrete in dosages up to 5% improves the ITZ zone, leading to improved mechanical properties. However, resistance to sulfuric acid attacks is reduced. In all tests, it has been shown that a CF dosage of 3% gives the best results.