Millions of tonnes of aggregates are using in the production of the concrete for structures. Aggregates (natural or crushed) came from the earth, getting these quantities would have a damaging impact on the ecosystem (1). Destroying concrete buildings and discarding the debris would just make the issue worse (2). As a result, it becomes important to recycle the crushed concrete and include it into fresh concrete mixtures as coarse aggregate (3).
The fundamental component of any nation's socioeconomic progress is construction (4). Any building project needs a variety of materials, including concrete, steel material, bricks, stones, glass, clay, mud, and wood, among others (5). The primary materials used in the construction sectors is still cement concrete, though (6). Because of its tremendous compressive strength. In addition, there is a significant shortage of natural resources as a result of the high demand for new buildings (7). In India, construction sectors are thought to produce between 10 and 12 million tonnes of garbage per year. RAC is becoming more popular around the world due to environmental benefits and cost savings (8).
Every year, India generates 29.75 million tonnage of construction – waste and demolition-waste, and these numbers are expected to quadruple over the next ten to fifteen years (9). In affluent nations, C&D wastes have been viewed as a resource (10). Recycling research has underlined the need for the final product to maintain the requisite compressive strength if utilised in second generation concrete (11). Compressive strength is primarily influenced by adhering mortar, water absorption, aggregate size, original parental concrete strength, age of curing period and replacement %, interfacial transition zone, state of moisture content, impurities, and controlled environment conditions, according to a literature review (12).
The following are the important reasons for increasing the volume of demolished concrete waste:
1Many old buildings, concrete pavements in villages, bridge structures, and other structures have outlived their usefulness due to structural deterioration that is beyond repair and must be demolished.
2. Many concrete structures, even those that are fit for use, are being demolished because they no longer meet the needs of the current situation.
3. Many of the Structures are appeared into debris resulting from disasters like earthquakes, cyclones and flooding etc.
Wildlife reserves are destroyed when raw materials for making ordinary cement are quarried. Therefore, the primary goal of the responsible authorities is to either stop the widespread use of ordinary cement or switch to another environmentally friendly way of making concrete to lessen the threat that the widespread use of ordinary cement poses to the environment (13). The Romans found how to create lime by burning crushed limestone, and the Egyptians used crushed gypsum. They also discovered that adding volcanic ash or old bricks and tiles improved the setting characteristics of their cement. After Portland cement was discovered, modern concrete was created (14). Through pozzolanic activity, fly ash combines with free lime to produce the same cementitious compounds formed by the hydration of Portland cement. Due to this series of chemical reaction, rate of strength gain for fly ash concrete is relatively slower at early ages of curing (15-17). These substances could be by products from less energy-intensive industries, naturally existing substances, or industrial wastes. When combined with calcium hydroxide, these substances, known as pozzolanas, show cementitious properties. Fly ash, silica fume, metakaolin, and powdered granulated blast furnace slag are the most frequently used pozzolanas (GGBS) (18). Numerous factors contribute to these demands, but as engineers, we must consider how durable the structures made of these elements will be. We have been able to meet the requirements while putting long-term durability concerns to one side. These qualities' concrete will exhibit an odd rheological behaviour(19).In order to produce a concrete that is extremely dense, with greater compressive strengths and extremely low permeability, ultra-fine materials (GGBS AND FLY ASH) will be used to better fill the spaces between cement particles.(22).Concrete density can be increased by adding various mineral admixtures, including metakaolin, GGBS, fly ash, rice husk powder, palm oils, and silica fumes(23).Testing of the behaviour of concrete with GGBS at various drying times revealed that while its strength initially is lower, it gradually increases over time(24).Because nano-silica particles are so small, they perfectly mix and mingle with all the materials, resulting in appropriate bonding. Fly ash reacts with water to create better-order hydrated products, which increase strength and power(25).Currently, Fly ash and GGBS are used as a replacement in over 40–45 percent of the concrete that RMC firms supply in India(27-30).In accordance with IS 10262:2009 rule for practise for concrete mix design, we can save cement by substituting fly ash for it(35-39).
1.1 RECYCLED (RA) TYPES
RA is often divided into groups based on grain size. Usually, fine RA (4 mm) is significantly more difficult to use in the manufacturing of concrete than coarse RA (>4 mm). This is due to the proportion of high-quality natural aggregates being substantially larger in the coarse than in the fine portions of the concrete following standard crushing and screening operations. After using cutting-edge production techniques, coarse RA can primarily be made of natural aggregate. Additionally, RA can be utilised to create filler materials with low strength, ecological ingredients, and low or no cement content at all.
1.2 RECYCLED CONCRETE AGGREGATE'S BASIC PROPERTIES FOR CONCRETE
When old concrete is crushed, some of the mortar and cement particles of paste are left bonded to the stone-Aggregate particles in the recycled-aggregate. The fundamental cause of RCA's inferior quality compared to natural aggregate is its attached mortar (NA). When compared to NA, RCA has the following qualities:
1. A greater absorption of water.
2. A reduction in bulk density
3. Reduced specific gravity
4. Abrasion loss that is worse.
1.3 INCORPARATION OF GGBS IN CONCRETE
For years, the construction industry has substituted GGBS for OP cement. The main components of GGBS by-product of the iron-production process, are calcium and alumina silicates. These run at a temperature of roughly FIFTEEN HUNDED °C and are provided with a precisely measured combination of coke, and limestone, iron ore. The residual component from a slag is floating on top of the iron are all that remain after the iron ore is converted to iron. This slag is regularly tapped out as a molten liquid and must be quickly cooled in a lot of water if it is to be employed in the production of GGBS.
G.Mallikarjun rao et al. (2017) (1) To process fly ash and GGBS, alkaline activator solution of soluble glass and caustic soda was used. With an 8 ML concentration of NaOH solution, the Na2SiO3/NaOH ratio was set at 2.5. The primary variables in the study for various mixtures of fly ash and GGBS were binder content and alkaline solution/binder ratio. Curing conditions both in outdoor conditions and oven curing also. The alkaline solution to the binder ratio, GGBS content, and curing condition were found to have the greatest effects on the Concrete-compressive strength and workability of geopolymer -concrete.
D.SURESH et.al (2015) (2) Resulting in the use of large amounts of concrete. Contrarily, the high cost of concrete is a result of the expensive and limited nature of its constituent parts, which forces the use of more affordable materials in its manufacture. This need has prompted researchers to look for novel alternatives for the ingredients in concrete. The current technical paper's goal is to look into the properties of concrete that uses some of the cement (GGBS).The topic discusses the use of GGBS and its benefits and drawbacks. Since GGBS is a byproduct, this method of using it is eco-friendly because it avoids dumping the product on the ground and replaces conventional building materials that are already running out.
In a study by A. Oner and S. Akyuz [3], GGBS was used in place of cement in different % ranging from 15% to 100%. compressive strength of test specimens that were cured for 7, 14, 28, 63, 180, and 365 days was tested, and it is discovered that the strength values of the GGBS concrete mix are lower at the early age than they are as time passes. This is because GGBS concrete takes longer to build strength because the pozzolanic reaction is sluggish and dependent on the availability of calcium hydroxide. Additionally, it was found that the strength gain improves as the percentage of GGBS rises. For maximum strength, GGBS content should range between 55% and 59%.
1.4 FLY ASH IN CONCRETE
When pulverised coal is burned in a thermal power plant, a charred and powdery by-product of inorganic mineral matter is produced. The main chemical components of the coal's burnt ash are silica, alumina, calcium, and iron. The mineral phases of quartz (SiO2), mullite (3Al2O3.2H2O), hematite (FeO3), magnetite (Fe3O4), wustite (FeO), metallic iron, orthoclase (KO ALO, 6SiO2), and fused silicates typically occur in crystalline to non-crystalline patterns depending on the coal's burning temperature. In the classification of thermal plants, silica and alumina make up roughly 75 to 95% of the material. Based on reactive calcium oxide content, fly ash is classified as class-F (less than 10%) and class-C (greater than 10%).
Ash's calcium-bearing silica and silicate minerals easily react with water and develop pozzolanic properties. However, the crystalline mineral phases of quartz and Mullite present in the ash are non-hydraulic silica and silicate structures. These two mineral phases are typically the major constituents of fly ash. As a result, the use of fly ash in building materials such as fibre cement sheets is heavily influenced by the mineral structure and pozzolanic property.
Fly ash is classified into two types: Class F & C.
As per ASTM C618, fly ash is classified as Class F if the (SiO+AbO+Fe2O) content is greater than 70% and Class C if the (SiO: +Al2O+Fe2Os) content is greater than 50 percent.
Subramaniam, Gromotka, Shah, Obla, and Hill (2005) (1) Investigated the effect of ultra-fine fly ash on the early stage(age) property development, shrinkage, and shrinkage cracking potential of concrete (1). Furthermore, the performance of silica fume and ultrafine fly ash as cement substitutes was compared. To determine the mechanisms causing an increase in early age stress due to constrained shrinkage, free shrinkage and elastic modulus were measured at an early age.
Age was also considered when determining the material's resistance to tensile fracture and strength growth.
By comparing the outcomes of all the tests, the authors concluded that employing ultrafine fly ash would reduce shrinkage strains and the likelihood of restrained shrinkage cracking.
Early phases of the project is to investigate the usage of significant amounts of High lime- fly ash in concrete were described by Namagg & Atadero (2009)(2). The authors replaced some of the fine aggregates and cement with fly ash. In their investigation, replacement percentages between 0% and 50% were explored. According to their findings, concrete consists of 25% to 35% fly ash produced the best results for its characteristic -compressive strength. They came to the conclusion that high lime fly ash's pozzolanic activity was to blame. (Jones & McCarthy, 2005) conducted a thorough lab-based examination into the use of low-lime fly ash that has not been treated as a sand substitute in foamed concrete. The spread seen in fly ash concretes was up to 2.5 times larger than that found in sand mixes for a given plastic density. Both sand and fly ash concrete were found to have similar early age strengths, however the 28-day values have great variation with density. Concrete made with fly ash had a resilience that was more than three times that of concrete made with sand. The strength of fly ash foamed concrete was up to 1.7 to 2.5 times stronger at 56 and 180 days compared to 28 days values, but the strength of sand mixtures stayed largely constant after 28 days.
Rebeiz, Serhal, and Craft (2004) (3) Research on substitution of fly ash for sand in polymer concrete was reported. Fly ash replaced 15% of the sand in the weight mix design. The compressive strength was increased by around 30% by replacing 15% of the sand with fly ash. Furthermore, the stress-strain curve improved. They also noticed a good surface finish as a result of replacing sand with fly ash, which reduces permeability and has an appealing dark colour. Steel-reinforced polymer concrete beams now have a 15% higher flexural strength. After 80 thermal cycles, polymer concrete with fly ash has a 7% improvement in thermal cycling resistance when compared to polymer concrete without fly ash.
(Pofale, &Deo, 2010) (4) found that substituting low-lime fly ash for 27% of the sand increased concrete's compressive strength by around 20% and flexural strength by about 15% compared to control concrete. In the investigation, Portland pozzolana cement with a fly ash basis was used. Additionally, the author found fly ash-based concrete was roughly 25% more workable than control concrete. Only the papers that were judged to be extremely important from the enormous number of publications researched were included for outlining current goals. According to the literature reviewed, concrete that had fly ash partially replace some of the scarce sand had stronger results after three days than control concrete. When compared to the control concrete, long-term strength was around 20% higher.
Scope of Work
In this project, recycled coarse aggregate (RCA), fly ash (FA), and granulated blast furnace slag (GBFS) are used as limited substitutes for natural coarse aggregate, cement, and water, respectively, In order to explore the characteristic properties of concrete. In the study, concrete specimens with different ratios of RCA, FA, and GBFS are cast, and their compressive strength, flexural strength, water absorption, and density are assessed. Analysis and comparison of the outcomes with the reference concrete mixture are performed. Based on the findings, suggestions are made for more study and optimization of concrete mix design using RCA, FA, and GBFS.