17-12-2012, 01:59 PM
Production of Self–compacting Concrete Using Crusher Rock and Marble Sludge Dusts
ABSTRACT
Owing to all its properties, use of SCC is constantly increasing all over the world. But the adoption has not been as fast as it should have been due to its higher cost of production. In India, SCC is used in limited owing to lack of awareness and the higher costs associated with its production. SCC is defined by two primary properties: Deformability and Segregation resistance. Deformability or flowability is the ability of SCC to flow or deform under its own weight (with or without obstructions). Segregation resistance or stability is the ability to remain homogeneous while doing so. High range water reducing admixtures are utilized to develop sufficient deformability. At the same time, segregation resistance is ensured, which is accomplished either by introducing a chemical VMA or by increasing the amount of fines in the concrete. These viscosity modifying admixtures are very expensive and the main cause of increase in the cost of SCC. Self-compacting Concrete is considered to be the most promising building material for the expected revolutionary changes at the job sites as well as on the desk of designers and civil engineers. However, the basic principles of this material are substantially based on those of flowing, cohesive, and superplasticized concretes developed in the mid of 1970's. The necessary ingredients for manufacturing SCC are superplasticizers and powder materials (including cement, fly ash, ground fillers or other mineral additions even in the form of fine recycled aggregate) at an adequate content (> 400 kg/m3 of cement and filler), with some limits in the maximum size of the coarse aggregate (< 25 mm).
The self-compacting concrete differs from conventional concrete in the following three characteristic features, namely, (i) appropriate flowability, (ii) non-segregation, and (iii) no blocking tendency. An increase in the flowability of concrete is known to increase the risk of segregation. Therefore, it is essential to have a proper mix design. This paper reports the results of an investigation into the development of low-bleeding self-compacting concrete. V-Funnel test is used to assess the flowability and segregation resistance of the self-compacted concrete.
Self-compacting High Performance Concrete
The prototype of SCC was first completed in 1988 using materials already on the market. The prototype performed satisfactorily with regard to drying and hardening shrinkage, heat of hydration, denseness after hardening, and other properties and was named "High Performance Concrete." Since then, the term high performance concrete has been used around the world to refer to high durability concrete. Therefore, Okamura [1] has changed the term for the proposed concrete to "Self-compacting High Performance Concrete" (SCHPC) and this was defined as follows at the three stages of concrete:
1. Fresh : Self–compactable.
2. Early age : avoidance of initial defects.
3. After hardening : Protection against external factors.
SCHPC can be described as a high performance material which flows under its own weight without requiring vibrators to achieve consolidation by complete filling of formworks even when access is hindered by narrow gaps between reinforcement bars [2]. With the advancement of concrete technology, high performance concrete is getting popular in prestressed applications. The attributes of high performance concrete are as follows:
• High strength
• Minimum shrinkage and creep
• High durability
• Easy to cast
• Cost effective.
The Role of Superplasticizers and Powder Materials
With the advent of superplasticizers, flowing concretes with slump level up to 250 mm were manufactured with no or negligible bleeding, provided that an adequate cement factor was used [3]. The slump was increased by increasing the amount of mixing water. When the slump is over 175 mm the bleeding increases too much and this was the reason why ACI in 1973 did not recommend slump higher than 175 mm [4]. The most important basic principle for flowing and cohesive concretes including SCCs is the use of superplasticizer combined with a relatively high content of powder materials in terms of portland cement, mineral additions, ground filler and/or very fine sand.