5 LITERATURE REVIEW
5.1 History of Self-Compacting Concrete (SCC)
Self- compacting concrete (SCC) was developed by Professor Hajime Okamura in Japan in the year 1986 but was industrialised in 1988 utilizing constituents present in the market. The prototype performed satisfactorily with regards to drying and hardening shrinkage, heat of hydration, denseness after hardening, and other properties. The basis of this prototype was rooted on technologies utilized in underwater concrete casting, to eradicate poor durability performance in concrete in structures caused by poor workmanship of inadequately compacting the concrete during casting operations.
5.2 constituent materials and selection criteria of (SCC)
Cement is a binder, a powder product manufactured from limestone that sets and hardens independently, and can bind other materials together, the most important use of cement is the production of mortar and concrete for bonding of natural artificial aggregates to form a strong building material that is durable in the face of normal environmental effects. They are different types of cements that are used in the industry.
Ordinary Portland Cement (OPC)- is the most common type of cement in general usage. It is a basic ingredient of concrete, mortar and plaster. It is a mixture of oxides of calcium, silicon and aluminum.
Fly Ash as SCM- most used by-product materials in the construction field resembling Portland cement. It is an inorganic, non-combustible, finely divided residue collected or precipitated from the exhaust gases of any industrial furnace. Fly ash is much cheaper than cement), the addition of fly ash has many technical benefits. dosage of fly ash varies with the reactivity of the ash and the desired effects on the concrete Fly ash has a high amount of silica and alumina in a reactive form. These reactive elements complement hydration chemistry of cement.
Aggregates occupy 70% to 80% of the volume of concrete, they are granular materials, derived for the most part from natural rock, In addition to their use as economical filler, aggregates generally provide concrete with better dimensional stability and wear resistance, In order to obtain a good concrete quality, aggregates should be hard and strong, free of undesirable impurities, and chemically stable. Aggregates should also be free of impurities like silt, clay, dirt, or organic matter. The maximum course aggregate size needs to be chosen according to rebar diameter and spacing, so that blocking is avoided the properties of fine aggregates have a significantly greater influence on fresh properties of SCC than those of coarse
aggregates. Depending on material properties such as grainsize and grading, different types of available fine aggregate may need to be mixed for optimum performance. The aggregate fraction finer than 0,125 mm is assumed to contribute to the powder content of the mix and needs to be taken into account when calculating the water powder ratio.
Types of Aggregates — Aggregates for concrete are divided into two types as follows
• Type of Aggregates
Fine Aggregates (Sand)
Sand is a naturally occurring granular material composed of finely divided rock and mineral particles, most common constituent of sand is silica (silicon dioxide, or SiO2), usually in the form of quartz.
Aggregates are the most mined material in the world. Aggregates are a component of composite materials such as concrete and asphalt concrete; the aggregate serves as reinforcement to add strength to the overall composite material
Coarse aggregate (Grit)
Grit is granular material which can be between coarse sand and pebbles. Generally, 4.75mm-12.5mm in size, grit has limited uses in the construction industry on its own, other than as a surface dressing
Coarse aggregate (Gravel)
Granular material which can be of almost any rock types, it is usually between 60mm and 4.75 mm in size which may be rounded, if from a marine or fluvial source, or angular if a quarried and crushed product. Gravels are sold in mixed sizes.
Water is an important ingredient of concrete as it actively participates in the chemical reaction with cement, In practice normally if water is fit for drinking it is considered suitable for making concrete, Water with pH value between 6 to 8 is acceptable but the best coarse to find out whether a particular source of water is suitable for concrete or not, If the compressive strength is up to 90 percent, the source is acceptable.
Admixture is defined as a material, other than cement, water and aggregates, which is used as an ingredient of concrete and is added immediately cement factory. Various admixtures are categorized based on their function in the concrete namely Plasticizers, Superplasticizers, retarders and retarding plasticizers, accelerators and accelerating plasticizer, Air-entraining Admixtures, Damp-proofing and Waterproofing Admixtures, Gas forming Admixtures, workability admixtures, grouting admixtures, bonding admixtures, colouring admixtures. Fore or during mixing, it is a material which is added at the time of grinding cement clinker Superplasticisers are an essential component in limiting the water content and at the same time achieving the required fluidity of SCC.