Influence of α-Alumina on mechanical, durability and microstructural properties of high volume GGBS concrete

Utilisation of ground granulated blast furnace slag (GGBS) into conventional concrete as a replacement to the cement imparts better mechanical and durability characteristics with major drawbacks of slow early development of the compressive strength and weaker carbonation resistance at higher levels of replacement. Past research indicates that nanomaterials impart novel properties to concrete and hence become popular in the construction industry. This research work presents the investigation of advancements in the mechanical and durability properties of M40 grade GGBS concrete blended with nano-alumina (NA) (α-type) as an chemical admixture. The reference mix comprises 50% cement replaced by GGBS, and design mixes are prepared by adding different percentages of α-alumina by weight of cementitious material, viz. 0.5%, 1%, 4%, 6%, and 8%. The mechanical properties of these mixes, viz., compressive strength at 3, 7, 14, 28, and 56 days and split tensile strength at 28 days, are measured. Durability tests such as water permeability (WPT) and rapid chloride penetration tests (RCPT) are conducted at 28 days of curing period. Very little literature is available on the performance of α-Alumina as a chemical admixture in high-volume GGBS concrete. It is noticed that as the percentage of α-alumina increases beyond 1%, slump, compressive strength, and split tensile strength of concrete decrease. The design mixes with 0.5% and 1% NA performed well for early development of strength, whereas the all-other mixes showed poor results. Maximum compressive strength (51.3 MPa) and split tensile strength (3.28 MPa) at 28 days are attained at 1% addition of α-Alumina. The concrete mixes with 4%, 6%, and 8% α-Alumina showed a compressive strength lesser than that for the reference mix. The lowest rapid chloride ion penetrability (641.3 C) and lowest water permeability (14.2 mm) are observed at 1% content of α-Alumina. At the end, the relation between the compressive strength and the dosage of α-Alumina is proposed by simple regression. Similarly, an inverse proportion is perceived between the variation of RCPT values and slump of the mix. It is observed that the GGBS concrete is deficient in attaining early strength, and the addition of 1% α-Alumina eliminates completely the deficiency and also imparts better durability properties. Further SEM and XRD are employed to confirm the presence of hydrated products in the concrete. © The Author(s), under exclusive licence to Springer Nature Switzerland AG 2025.