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Concrete In Australia : December 2013
Challenges in producing low fines self-consolidating concrete in Asia Pacific Nilotpol Kar, Business Manager – Admixture Systems, BASF Australia Hironobu Yamamiya, Marketing Manager – Admixture Systems, BASF Pozzolith Takumi Sugamata, Deputy Manager, Admixture Systems, Technical Services, Construction Chemicals, BASF Australia Minoru Yaguchi, Manager, Technical and Marketing Technical Center AS, BASF Pozzolith Numerous attempts have been made to produce low fines self-consolidating concrete (LF-SCC) at a commercial level. Initial commercial success for producing LF-SCC (less than 380 kg/m3 cementitious) was possibly recorded first in Europe around 2007. Diversity in concrete constituents, codes of practice and environmental conditions across the Asia Pacific, offers challenges in the production of LF-SCC. In Japan, LF-SCC has been produced commercially using less than 380 kg/m3 cementitious content, while in New Zealand the use of a cement content as low as 300 kg/m3 has been recorded at the laboratory level using local aggregates and cement without special fillers. “Robustness” is the main challenge addressed with advanced polymer technology combined with a state-of-art synthetic viscosity modifier for production of LF-SCC. Given the variations, a “forgiving” balance between plastic viscosity and yield is achieved. Concrete strength classes between 20–35 MPa still constitute 70–80% of concrete consumed. The key benefits of LF-SCC are higher productivity, use of lower fines, utilisation of less manpower, use of manufactured sands and lower energy costs. These are the key value gains bringing benefits to multiple stake holders. This paper highlights adoption of LF-SCC in lieu of traditional vibratable concrete or high/super workable concrete with some background developmental work to implement the concept on a practical level. Examples are highlighted from Japan, China and Singapore. The key properties are discussed emphasising that there is no difference to the concrete properties between a traditional vibratable concrete versus LF-SCC . 1.0 INTRODUCTION Concrete has always been an enigma. Among the various types, Self Consolidating Concrete (SCC) was one of the most novel types evolving in Japan during the 1980s.1 The main feature of this type of concrete was a non segregated high flowabilty concrete with a high binder content and the mix design. Almost 25 years after the evolution of the first SCC in Japan, another innovation in SCC with low cementitious fines was found to be more practical and affordable. Low fines self-consolidating concrete (LF-SCC) had its first success in Europe in 2007. Capitalising on this success, an attempt was made to establish the feasibility of LF-SCC in the Asia Pacific. In developing countries, owners, specifiers and concrete producers are challenged to complete projects in time, given the constraints normally associated with traffic, space and labour. In those countries, the challenge is about improving existing standards and productivity. In attempting to make the dream of LF-SCC in the Asia Pacific a reality, where more than 70% of the ready mix concrete volume consists of 25–35 MPa concrete, the focus has been in formulating admixtures through chemistry with use of low cementitious fines and, in most cases, without fillers like limestone. Hence, if we were to focus on innovations in SCC, the Asia Pacific sector is where this novel concrete is most attractive on a practical and commercial scale. The European guidelines for traditional Self Compacting Concrete (Specification, Production and Use)2 has been a good reference document as well as the ACI Committee 237 report3 on SCC. In the fresh state, the filling ability and stability of SCC can be defined by four key characteristics: flowability, viscosity (assessed by rate of flow), passing ability and segregation resistance. The composition of traditional SCC can vary between regions within the Asia Pacific, even if the fresh and hardened properties are same, in terms of flow (or rate of flow, which forms a very important aspect in pumpability) and passing ability. As cement and the pozzolanic content could vary in their composition including the crushed or natural fines, the unit water content can also vary appreciably based on normal consistency of cementitious material and the water absorption characteristic of the aggregates. The benefits of traditional SCC accruing to the pre-cast industry in terms of tangible (materials cost saving, production increase, superior quality, reduction of patching work) and intangible (processes made simpler, noise reduction and safe environment) is different from the ready mix concrete producer who does not derive any benefit instantly as his product (in the form of SCC) has to be delivered to his customer in the fresh state. The strengths delivered are much greater owing to the nature of traditional SCC with its high cementitious FEATURE: RHEOLOGY 29-35 Kar.indd 29 29-35 Kar.indd 29 25/11/13 2:56 PM 25/11/13 2:56 PM