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To overcome the scarcity of river sand and dumping of construction and demolition wastes, the fine recycled aggregate (FRA) collected from C&D wastes is being utilized as a replacement to river sand. Many earlier studies reported that the higher water absorption of fine recycled aggregate and weak interfacial transition zone (ITZ) resulted in the development of the concrete with less strength and durability requirements. This study surmounts the above two factors through pre-saturation and a two-stage mixing approach (TSMA) technique. The concrete mixes prepared at 0.45 w/c ratios with 0%, 25%, 50%, and 100% of FRA were evaluated through hardened properties such as compressive strength, split tensile strength, flexural strength, and durability properties such as water absorption, sorptivity, shrinkage, rapid chloride penetration, and carbonation tests. The results indicate that the optimum level of replacement of fine recycled aggregate was 25% and the increase of fine recycled aggregate decreases the strength and durability properties. However, increased curing of concrete resulted in better strength and durability properties. The strength of the concrete was increased by 12% at 28 days and 17.46% at 90 days by two-stage mixing approach. The water absorption, porosity, shrinkage, chloride penetration, and carbonation of two-stage mixing approach was decreased by 7.45%, 15.38%, 16.57%, 18.18%, and 13.51% compared to normal mixing approach. Microstructural investigations show improvement in the interfacial transition zone with two-stage mixing approach compared to normal mixing approach.

This paper involves the study on the hardened and durability properties of the concrete at two different grades containing silica fume (SF) with various replacement percentages. Investigation on the performance of the SF was performed for M25 and M40 grades concrete with 0, 5, 10, and 15 % replacement levels at 7, 14, 28, and 90 days. The behavior of SF on the autogenous shrinkage of the concrete was studied for both the grades of concrete in the sealed (SC) and unsealed conditions (USC). The workability of the SF concrete was examined at various levels of replacement by the slump cone test. The hardened properties of the SF concrete were investigated through the estimation of compressive strength (CS) and elastic modulus (EM) at 7, 14, 28, and 90 days, respectively. Acid attack was conducted at 28 days and autogenous shrinkage of the SF concrete was investigated using length comparator at 28 day in SC and USC. Results indicate that upon increase in the percentage of SF, the hardened properties of the concrete increases at higher ages of curing and the shrinkage of the concrete tends to increase for both the grades of concrete.

Increased development in the field of construction with the use of sand, stones etc. depletes the natural resources and thus resulted in the scarcity of construction materials. Furthermore, generation of waste from several industries such as steel slag, copper slag, blast furnace slag etc. are being dumped in the nearby landfills leading to disposal problems. The scarcity of construction materials necessitated the utilization of suitable alternative materials with equivalent physical and chemical characteristics. This paper investigates the suitability of copper slag (CS) as a substitute to natural fine aggregate (NFA) in the concrete. The concrete mixes are prepared with 0%, 10%, 30%, 50%, 70% and 100% of copper slag at 0.45 w/c ratio. The behaviour of CS in the concrete was assessed by hardened properties such as compression, tension and flexure at 7, 14, 28 and 90 days and durability properties such as water absorption, porosity and chloride ion penetration at 56 days. Results indicate that the replacement of CS beyond 50% affects properties of the concrete; however increased curing improved the properties of the concrete at higher replacement levels. Characterization studies such as XRD and SEM was performed to examine the effect of CS on the properties of the concrete.