Experimental Investigation on Properties of Reactive Powder Concrete

INTRODUCTION

To obtain ultra-high strength with very low water/cement ratios, RPC cement dosage is often as high as 800–1000 kg/m3. A large amount of cement not only increases production costs, but it also increases hydration heat and can cause shrinkage problems. Mineral admixtures may be a viable option for resolving these issues in RPC. The primary goal of this study is to see how mineral admixtures affect the mechanical properties of the RPC. Furthermore, the goal of this study was to reduce cement and silica fume use in order to reduce material prices and negative impacts (heat of hydration, shrinkage and environmental problems).

1) Composition of Reactive Powder Concrete- Steel fibres, super plasticizers, and very fine powders (cement, sand, quartz powder, and silica fume) make up RPC. When applied at its recommended dosage, the super plasticizer reduces the water to cement ratio (W/C) while enhancing concrete workability. The granular packing of dry fine powders is optimised to create a dense matrix. The compressive strength of these reactive powder concretes ranges from 200 to 800 MPa. 2) Basic Principles for the Composition of RPC: a) The removal of coarse particles in order to improve homogeneity. b) Granular mixture optimization for increased compaction density. c) Making use of silica fume's pozzolanic characteristics. d) The use of a superplasticizer as an alternative to minimise the W/C ratio and improve compaction. e) Microstructure improvement via post–set heat treatment. f) Small steel fibres are added to increase ductility.

1) Sand: The desired maximum and minimum particle sizes establish the particle size range indirectly. To avoid interference with the largest cement particles (80-100µm) and silt content in natural sand, the maximum particle size is limited to 600 µm, while particle sizes below 150 µm are avoided for the minimum value. Crushed sand with extremely angular grains or natural quarry sand with more spherical grains are screened to produce fine sand. RPC can be done with either sort of sand. 2) Cement: Because of the high cement factor, the type of cement used can have a significant impact on RPC performance. The optimum cement, according to published practise, contains a high percentage of C3S and C2S (di- and tricalcium silicates) and very little C3A (tricalcium aluminate). This is understandable given that C3A has minimal inherent value as a binding agent and is mostly used in cement as a flux during the calcination process. In this 3) Silica Fume: The absence of aggregates is the major characteristic of silica fume. As a result, non-compacted silica fumes are used. The quality of water in slurry surpasses the total amount of water required for the mixture, so it can't be used. Carbon and alkalis are the most harmful pollutants. The particle size is a secondary consideration. The best results are obtained with Elkem India (P) Ltd.'s silica fume, which is devoid of contaminants and completely disaggregated. RPC typically uses a fume/cement ratio of 0.27 to 0.3. This ratio corresponds to the best filling performance and is near to the dosage required for complete lime consumption as a result of total cement hydration. However, with RPC concrete, cement hydration is incomplete, and the amount of silica fume accessible exceeds the pozzolanic reaction's requirements. Elkem India (P) Ltd. provided silica fume under the brand name "Elkem Micro Silica Grade 920-D."The properties are given in table 1.

4) Quartz Sand: Additional silica is required to change the CaO/SiO2 ratio in RPC mixes designed to be cured at temperatures above 90°C, including autoclaving at high pressures. Powdered quartz flour with a mean particle size of 10 - 15 mm was used in these circumstances. 20 Microns Ltd provided the quartz sand under the brand name "Micron Silica 2080." The properties are given in table 2.

5) Steel Fibers: The nature of plain concrete is that it is brittle. It has a low tensile strength constrained. To improve RPC ductility, micro-fibers of corrugated carbon steel wire, 12.5 mm in length and 0.45 mm in diameter, with a minimum wire tensile strength of 2000 MPa, were included in various mixtures. Steel fibres material has a specific gravity of 7.1. 6) Super plasticizer: The fluidizing power of high-quality third generation super-plasticizing chemicals allows RPC to achieve such low w/b (cement + silica fume) ratios. To ensure adequate workability of the RPC mix, a polycarboxylate-based new generation plasticizer was utilised. Polycarboxylitic Ether (PCE) superplasticizers are a big development in concrete technology since they can save up to 40% on water and provide incredible workability without the negative consequences of retardation and segregation. As a result of PCE super plasticizers, there is less need for redusing with extra admixtures or retempering with water, especially with low w/c ratio mixes, lengthy haulages, and hot weather conditions. BASF Chemicals (India) Pvt. Ltd. has supplied the super plasticizer. Table 3 lists the characteristics of Glenium-51 (Polycarboxylic ether base)

There were two fundamental types of RPC produced: a low temperature mix designed to be cured in ambient settings, as is standard site practice, and a high temperature mix suitable for production activities such as pre-cast plants with steam curing facilities. In the experimental technique, the optimization of granular mix is performed by a series of experiments for various mixtures.

The water demand of the combination is the most important factor that determines its quality (quantity of water for minimum flow of concrete). In reality, the mixture's voids index is proportional to the total of water demand and imprisoned air. Cubes were cast and compressive strength was assessed at 7 and 28 days after selecting a mixture design based on minimum water consumption. On the basis of the foregoing compositions, a number of trials for various mixes for various compositions are conducted to optimise the granular mixture. Initially, studies to achieve an acceptable RPC flow were carried out with the lowest water-cement ratio and the highest superplasticizer doses.

flask and all ingredients were carefully weighed with a weighing machine. The liquid-to-cement ratio was set at 0.019. According to Euro code, the initial batch of concrete had a W/C ratio of 0.3 with 0% fibres. Steel fibres were used as 1% of the volume in the second batch of concrete mix. Steel fibre accounted for 2% of the cement volume in the third batch of concrete Fibers and water in the proper quantities were mixed separately for each batch and added to the dry mix. Each batch of concrete was crushed evenly with a tamping rod until no bubbles were visible at the surface. The corner zone received special attention in order to achieve optimum compaction at the corners. After 24 hours of casting, all of the specimens were demoulded.

The specimens are held in the mould for 24 hours after casting and polishing the surface. The specimens are numbered when they have been removed from the mould. The specimens are then placed in the curing tank for a usual curing period of 28 days. For hot water curing, the specimen is placed in a hot water curing tank for the first 48 hours and then placed in a standard water curing tank for the remainder duration up to 28 days. The specimens are taken from the curing tank after 28 days and white washed before being tested.

► TESTING OF SPECIMENS:

The compressive strength of a cubical specimen of 50 mm x 50 mm x 50 mm was cast and tested according to the IS 516-1959 specification. Compressive strength was measured on 50 mm cubes that were cured in a water tank totally immersed at constant temperature 27o C for 7 and 28 days, with 3 specimens in each case.The test is conducted on CTM.

When the test findings were compared to the results of normal concrete, it was discovered that the Reactive Powder Concrete had a higher strength than the usual concrete. However, Reactive Powder Concrete is more expensive, it can be employed in situations when high strength is necessary. RPC has a great strength, frost resistance, and impermeability. RPC is a material with a lot of potential that has yet to be discovered. As a result, it

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PG Student-Civil Engineering Department, SVERI‘S College of Engineering, Pandharpur, Maharashtra