Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5
poster presentation on self compaction concrete
#1

Introduction

Self-compacting concrete (SCC) is a flowing concrete mixture that is able to consolidate under its own weight. The highly fluid nature of SCC makes it suitable for placing in difficult conditions and in sections with congested reinforcement. Use of SCC can also help minimize hearing-related damages on the worksite that are induced by vibration of concrete. Another advantage of SCC is that the time required to place large sections is considerably reduced.

When the construction industry in Japan experienced a decline in the availability of skilled labour in the 1980s, a need was felt for a concrete that could overcome the problems of defective workmanship. This led to the development of self-compacting concrete, primarily through the work by Okamura1. A committee was formed to study the properties of self-compacting concrete, including a fundamental investigation on workability of concrete, which was carried out by Ozawa et al2. at the University of Tokyo. The first usable version of self-compacting concrete was completed in 1988 and was named High Performance Concrete , and later proposed as Self Compacting High Performance Concrete .

In Japan, the volume of SCC in construction has risen steadily over the years3. Data indicate that the share of application of SCC in precast concrete industry is more than three times higher than that in the ready-mixed concrete industry. This is attributable to the higher cost of SCC. The estimated average price of SCC supplied by the RMC industry in Japan was 1.5 times that of the conventional concrete in the year 2002. Research studies in Japan are also promoting new types of applications with SCC, such as in lattice type structures, casting without pump, and tunnel linings.

Since the development of SCC in Japan, many organizations across the world have carried out research on properties of SCC. The Brite-Euram SCC project4 was set up to promote the use of SCC in some of the European countries. A state-of-the-art report on SCC was compiled by Skarendahl and Petersson5 summarizing the conclusions from the research studies sponsored by the Brite-Euram project on SCC. A recent initiative in Europe is the formation of the project Testing SCC6 involving a number of institutes in research studies on various test methods for SCC. In addition, an organization with the participation from the speciality concrete product industry EFNARC7 has developed specifications and guidelines for the use of SCC that covers a number of topics, ranging from materials selection and mixture design to the significance of testing methods.

Current studies in SCC, which are being conducted in many countries, can be divided into the following categories: (i) use of rheometers to obtain data about flow behaviour of cement paste and concrete, (ii) mixture proportioning methods for SCC, (ii) characterization of SCC using laboratory test methods, (iv) durability and hardened properties of SCC and their comparison with normal concrete, and (v) construction issues related to SCC. These will be relevant to the immediate needs. In addition, the following questions also need particular attention, from a long-term perspective: (i) development of mixture design guideline tables similar to those for normal concrete, (ii) a shift to more normal powder contents in SCC, from the existing high powder mixtures, (ii) better understanding of the problems of autogenous and plastic shrinkage in SCC, and (iv) development of site quality control parameters such as in all-in-one , acceptance tests.

Materials for SCC

Mixture proportions for SCC differ from those of ordinary concrete, in that the former has more powder content and less coarse aggregate. Moreover, SCC incorporates high range water reducers (HRWR, superplasticisers) in larger amounts and frequently a viscosity modifying agent (VMA) in small doses. The questions that dominate the selection of materials for SCC are: (i) limits on the amount of marginally unsuitable aggregates, that is, those deviating from ideal shapes and sizes, (ii) choice of HRWR, (ii) choice of VMA, and (iv) interaction and compatibility between cement, HRWR, and VMA. These are discussed below.

Aggregates

Aggregates constitute the bulk of a concrete mixture, and give dimensional stability to concrete. Among the various properties of aggregate, the important ones for SCC are the shape and gradation. Many researchers have been able to produce self-compacting concrete with locally available aggregate. It is observed from these studies that self-compactability is achievable at lower cement (or fines) content when rounded aggregates are used, as compared to angular aggregates. Although there have been several studies on the effect of coarse aggregate content on the flow behaviour of SCC8,9,10, enough attention has not been paid to quantify the effect of the shape of the aggregate.

In the case of SCC, rounded aggregates would provide a better flowability and less blocking potential for a given water-to-powder ratio, compared to angular and semi-rounded aggregates. Moreover, the presence of flaky and elongated particles may give rise to blocking problems in confined areas, and also increase the minimum yield stress (rheology terms are discussed in the next section). Incorporation of aggregate shape in the mixture design would enable the selection of appropriate paste content required to overcome these difficulties. It is possible that the highly flowable nature of SCC could allow a higher proportion of flaky aggregates compared to normal concrete. However, this aspect needs to be checked.

O Flannery and O Mahony11 have devised a method for shape characterisation of coarse aggregate, which could assist in designing SCC mixtures having marginally unsuitable aggregates. The purpose of the study was to determine dimensional parameters for fingerprinting any given coarse aggregate sample. The overall idea was to overcome local deficiencies in aggregate shape and to arrive at required packing characteristics irrespective of the aggregate. Incorporation of aggregate shape in mixture design, based on the method developed by O Flannery and O Mahony, is explained in Table 1.

Another deficiency in aggregates is poor gradation. Use of fillers (either reactive or inert) has been suggested as a means of overcoming this problem12,13. At present, a trial and error approach is used to fix the type and amount of filler. Alternatively, particle packing models could be used to reduce the number of experimental trials14,15. Such models are discussed later.

In view of on increased awareness of the environmental impact of mining river sand and depleting supplies of the same, use of manufactured sand and other alternative fine aggregate has become essential in some parts of the world. In fact, river sand is simply not available in many areas. Although there are studies that have shown that quarry run could be used as a filler instead of limestone for SCC16, there has not been sufficient documentation of the use of manufactured sand, either as fine aggregate or as a filler, in SCC. Further research on this topic will be useful.
Reply

#2
hi iam manasa i want details of poster presentation on self compaction concrete

hi iam manasa. i want to give a poster presentation on self compaction concrete, so i would like to want details on poster presentation on self compaction concrete can you please guide me for doing that. thank you.
Reply



[-]
Quick Reply

Forum Jump:


Users browsing this thread:
1 Guest(s)

Powered By MyBB, © 2002-2022 iAndrew & Melroy van den Berg.